Nitride-based semiconductor light-emitting element

Abstract

A nitride-based semiconductor light-emitting element (100) is provided with a semiconductor laminate (100S) and a P-side electrode (113). The semiconductor laminate (100S) has: an N-type first cladding layer (102); an N-side guide layer (104) disposed above the N-type first cladding layer (102); an active layer (105) disposed above the N-side guide layer (104) and having a quantum well structure; a P-side first guide layer (106) disposed above the active layer (105); a P-side second guide layer (107) disposed above the P-side first guide layer (106); and a P-type cladding layer (110) disposed above the P-side second guide layer (107). The band gap energy of the P-side second guide layer (107) is greater than the band gap energy of the N-side guide layer (104), the band gap energy of the N-side guide layer (104) is greater than or equal to the band gap energy of the P-side first guide layer (106), and the P-side electrode (113) includes Ag.

Description

Nitride-based semiconductor light-emitting device

[0001] The present disclosure relates to a nitride-based semiconductor light-emitting device.

[0002] Conventionally, nitride-based semiconductor light-emitting elements have been used as light sources for processing equipment and the like. Light sources for processing equipment are required to have ever higher output and efficiency. To improve the efficiency of nitride-based semiconductor light-emitting elements, for example, techniques for reducing the operating voltage are known (see, for example, Patent Documents 1 to 3). The invention described in Patent Document 1 aims to increase the optical confinement coefficient in the active layer while reducing the operating voltage.

[0003] International Publication No. WO 2022 / 172797 International Publication No. WO 2023 / 281902 International Publication No. WO 2023 / 026858

[0004] There is a demand for even higher efficiency in nitride-based semiconductor light-emitting devices.

[0005] The present disclosure is intended to solve such problems, and has an object to provide a highly efficient nitride-based semiconductor light-emitting device.

[0006] In order to solve the above problems, one aspect of the nitride-based semiconductor light-emitting device according to the present disclosure is a nitride-based semiconductor light-emitting device comprising: a semiconductor laminate; and a P-side electrode disposed above the semiconductor laminate; and emitting light from an end face perpendicular to a stacking direction of the semiconductor laminate, wherein the semiconductor laminate comprises: an N-type first cladding layer; an N-side guide layer disposed above the N-type first cladding layer; an active layer disposed above the N-side guide layer, the active layer including a well layer and a barrier layer and having a quantum well structure; a P-side first guide layer disposed above the active layer; a P-side second guide layer disposed above the P-side first guide layer; and a P-type cladding layer disposed above the P-side second guide layer, wherein the band gap energy of the P-side second guide layer is larger than the band gap energy of the N-side guide layer and the band gap energy of the N-side guide layer is equal to or greater than the band gap energy of the P-side first guide layer; and the P-side electrode contains Ag.

[0007] In order to solve the above problems, another aspect of the nitride-based semiconductor light-emitting device according to the present disclosure is a nitride-based semiconductor light-emitting device comprising: a semiconductor laminate; and a P-side electrode disposed above the semiconductor laminate; and emitting light from an end face in a direction perpendicular to the lamination direction of the semiconductor laminate; the semiconductor laminate comprising: an N-type first cladding layer; an N-side guide layer disposed above the N-type first cladding layer; an active layer disposed above the N-side guide layer and including a well layer and a barrier layer, the active layer having a quantum well structure; a P-side guide layer disposed above the active layer; and a P-side electrode disposed above the P-side guide layer. and a P-type cladding layer positioned thereon, wherein the band gap energy of the P-side guide layer monotonically increases with increasing distance from the active layer, the P-side guide layer includes a portion whose band gap energy continuously increases with increasing distance from the active layer, the average band gap energy of the P-side guide layer is equal to or greater than the average band gap energy of the N-side guide layer, the band gap energy of the barrier layer is equal to or less than the minimum value of the band gap energies of the N-side guide layer and the P-side guide layer, and the P-side electrode contains Ag.

[0008] In order to solve the above-described problems, yet another aspect of the nitride-based semiconductor light-emitting element according to the present disclosure is a nitride-based semiconductor light-emitting element including a semiconductor laminate and a P-side electrode disposed above the semiconductor laminate, and emitting light from an end face perpendicular to a stacking direction of the semiconductor laminate, wherein the semiconductor laminate includes an N-type first cladding layer, an N-side guide layer disposed above the N-type first cladding layer, an active layer disposed above the N-side guide layer and including a well layer and a barrier layer and having a quantum well structure, a P-side guide layer disposed above the active layer, and a P-type cladding layer disposed above the P-side guide layer, wherein the bandgap energy of the N-side guide layer monotonically increases with increasing distance from the active layer, the N-side guide layer includes a portion where the bandgap energy continuously increases with increasing distance from the active layer, the average bandgap energy of the P-side guide layer is equal to or greater than the average bandgap energy of the N-side guide layer, and the P-side electrode contains Ag.

[0009] According to the present disclosure, a highly efficient nitride-based semiconductor light-emitting device can be provided.

[0010] 1 is a schematic plan view showing the overall configuration of a nitride-based semiconductor light-emitting device according to a first embodiment. FIG. 2 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to a first embodiment. FIG. 3 is a schematic cross-sectional view showing the configuration of an active layer included in the nitride-based semiconductor light-emitting device according to a first embodiment. FIG. 4 is a schematic view showing an outline of the light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting device according to the first embodiment. FIG. 5 is a graph showing coordinates of positions in the stacking direction of the nitride-based semiconductor light-emitting device according to the first embodiment. FIG. 6 is a diagram showing element structures used in simulations of the nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 5 and the nitride-based semiconductor light-emitting device according to the first embodiment. FIG. 7 is a graph showing simulation results of the light intensity distribution and refractive index distribution in a portion below the ridge of the nitride-based semiconductor light-emitting device of Comparative Example 1. FIG. 8 is a graph showing simulation results of the light intensity distribution and refractive index distribution in a portion below the ridge of the nitride-based semiconductor light-emitting device according to Comparative Example 3. FIG. 9 is a graph showing simulation results of the light intensity distribution and refractive index distribution in a portion below the ridge of the nitride-based semiconductor light-emitting device according to the first embodiment. FIG. 10 is a diagram showing numerical values ​​obtained in simulations of the nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 5 and the nitride-based semiconductor light-emitting device according to the first embodiment. 1 is a graph showing the relationship between the position in the width direction of the ridge according to the first embodiment and the amount of spontaneous emission light reabsorbed by the active layer by the P-side electrode. FIG. 2 is a first graph showing the relationship between the position in the width direction of the ridge according to the first embodiment and the amount of spontaneous emission light reabsorbed by the active layer. FIG. 3 is a second graph showing the relationship between the position in the width direction of the ridge according to the first embodiment and the amount of spontaneous emission light reabsorbed by the active layer. FIG. 4 is a graph showing the relationship between the ridge width and the amount of spontaneous emission light reabsorbed by the active layer according to the first embodiment. FIG. 5 is a graph showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element of Comparative Example 5 and each numerical value obtained by simulation. FIG. 6 is a graph showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element according to the first embodiment and each numerical value obtained by simulation. FIG. 7 is a graph showing the simulation results of the relationship between the radiation angle and light intensity of the nitride-based semiconductor light-emitting element according to the first embodiment.1 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to a second embodiment. 2 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to a third embodiment. 3 is a cross-sectional view showing the configuration of an active layer included in the nitride-based semiconductor light-emitting device according to the third embodiment. 4 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to a fourth embodiment. 5 is a cross-sectional view showing the configuration of an active layer included in the nitride-based semiconductor light-emitting device according to the fourth embodiment. 6 is a schematic graph showing the distribution of band gap energy of the active layer and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device according to the fourth embodiment. 7 is a graph showing the refractive index distribution and the light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9 and the nitride-based semiconductor light-emitting device according to the fourth embodiment. 8 is a graph showing the simulation results of the distribution of valence electron charge potential and hole Fermi level in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9 and the nitride-based semiconductor light-emitting device according to the fourth embodiment. 10 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element of Comparative Example 11 and each numerical value obtained by simulation. FIG. 11 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element according to Embodiment 4 and each numerical value obtained by simulation. FIG. 12 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 5. FIG. 13 is a schematic graph showing the distribution of band gap energy of the active layer and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting element according to Embodiment 5. FIG. 14 is a graph showing the simulation results of the distribution of valence electron charge potential and hole Fermi level in the stacking direction of the nitride-based semiconductor light-emitting element according to Embodiment 5. FIG. 15 is a graph showing the simulation results of the distribution of carrier concentration in the stacking direction of the nitride-based semiconductor light-emitting element according to Embodiment 5. FIG. 16 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 6. FIG. 17 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 7.13 is a graph showing the distribution of Al composition ratio in the stacking direction of an electron barrier layer according to an eighth embodiment. It is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to a ninth embodiment. It is a schematic cross-sectional view showing the configuration of an active layer included in the nitride-based semiconductor light-emitting device according to the ninth embodiment. It is a schematic graph showing the distribution of band gap energy of the active layer of the nitride-based semiconductor light-emitting device according to the ninth embodiment and each layer in the vicinity thereof. It is a graph showing the refractive index distribution and the light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14 and the nitride-based semiconductor light-emitting device according to the ninth embodiment. It is a graph showing the simulation results of the distribution of valence electron charge potential and hole Fermi level in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14 and the nitride-based semiconductor light-emitting device according to the ninth embodiment. It is a graph showing the simulation results of the distribution of carrier concentration in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14 and the nitride-based semiconductor light-emitting device according to the ninth embodiment. 10 is a graph showing the relationship between the position in the stacking direction of the nitride-based semiconductor light-emitting element of Comparative Example 14 and the piezoelectric polarization charge density, piezoelectric polarization electric field, and conduction field potential. FIG. 11 is a graph showing the relationship between the position in the stacking direction of the nitride-based semiconductor light-emitting element of Comparative Example 14 and the piezoelectric polarization charge density, piezoelectric polarization electric field, and conduction field potential. FIG. 12 is a graph showing the relationship between the position in the stacking direction of the nitride-based semiconductor light-emitting element of Comparative Example 14 and the piezoelectric polarization charge density, piezoelectric polarization electric field, and conduction field potential. FIG. 13 is a graph showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element of Comparative Example 15 and each numerical value obtained by simulation. FIG. 14 is a graph showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element 900 of the ninth embodiment and each numerical value obtained by simulation. FIG. 15 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element of Embodiment 10. FIG. 16 is a schematic graph showing the distribution of band gap energy in the active layer and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting element of the tenth embodiment. FIG. 17 is a graph showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element of Comparative Example 16 and each numerical value obtained by simulation. 13 is a diagram showing the relationship between the film thickness of a P-type cladding layer 910 of a nitride-based semiconductor light-emitting element according to an embodiment 10 and each numerical value obtained by simulation. FIG. 14 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to an embodiment 11.16 is a schematic graph showing the distribution of band gap energy of the active layer and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device according to embodiment 11. FIG. 17 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting device of comparative example 17 and each numerical value obtained by simulation. FIG. 18 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting device according to embodiment 11 and each numerical value obtained by simulation. FIG. 19 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to embodiment 12. FIG. 19 is a schematic graph showing the distribution of band gap energy of the active layer and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device according to embodiment 12. FIG. 19 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to embodiment 13. FIG. 19 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to embodiment 14. FIG. 19 is a schematic graph showing the distribution of band gap energy of the active layer and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device according to embodiment 14. Fig. 20 is a schematic graph showing the distribution of band gap energy in the active layer and each layer in the vicinity thereof of a nitride-based semiconductor light-emitting device according to embodiment 15. Fig. 21 is a schematic graph showing the distribution of band gap energy in the active layer and each layer in the vicinity thereof of a nitride-based semiconductor light-emitting device according to modification 1 of embodiment 15. Fig. 22 is a schematic graph showing the distribution of band gap energy in the active layer and each layer in the vicinity thereof of a nitride-based semiconductor light-emitting device according to modification 2 of embodiment 15. Fig. 23 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to modification 1. Fig. 24 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device according to modification 2.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, and the arrangement and connection of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0012] Furthermore, each figure is a schematic diagram and is not necessarily an exact representation. Therefore, the scales and the like do not necessarily match in each figure. In each figure, the same reference numerals are used to denote substantially the same components, and redundant explanations will be omitted or simplified.

[0013] In this specification, the terms "above" and "below" do not refer to vertically above and below in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. The terms "above" and "below" are used not only when two components are arranged with a gap between them and another component is present between them, but also when two components are arranged in contact with each other.

[0014] First Embodiment A nitride-based semiconductor light-emitting device according to a first embodiment will be described.

[0015] [1-1. Overall Configuration] First, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described with reference to FIGS. 1, 2A, and 2B. FIGS. 1 and 2A are a schematic plan view and a cross-sectional view, respectively, showing the overall configuration of nitride-based semiconductor light-emitting device 100 according to this embodiment. FIG. 2A shows a cross section taken along line IIA-IIA in FIG. 1. FIG. 2B is a schematic cross-sectional view showing the configuration of active layer 105 included in nitride-based semiconductor light-emitting device 100 according to this embodiment. Note that each figure shows an X-axis, a Y-axis, and a Z-axis, which are orthogonal to each other. The X-axis, the Y-axis, and the Z-axis are in a right-handed Cartesian coordinate system. The stacking direction of nitride-based semiconductor light-emitting device 100 is parallel to the Z-axis direction, and the main emission direction of light (laser light) is parallel to the Y-axis direction.

[0016] As shown in FIG. 2A , the nitride-based semiconductor light-emitting element 100 includes a semiconductor stack 100S including nitride-based semiconductor layers, and emits light from a facet 100F (see FIG. 1 ) perpendicular to the stacking direction (i.e., the Z-axis direction) of the semiconductor stack 100S. In this embodiment, the nitride-based semiconductor light-emitting element 100 emits light in the 445 nm wavelength band. In this embodiment, the nitride-based semiconductor light-emitting element 100 is a semiconductor laser element having two facets 100F and 100R that form a cavity. The facet 100F is a front facet from which laser light is emitted, and the facet 100R is a rear facet having a higher reflectivity than the facet 100F. In this embodiment, the reflectivities of the facets 100F and 100R are 16% and 95%, respectively. The cavity length of the nitride-based semiconductor light-emitting element 100 according to this embodiment (that is, the distance between the end face 100F and the end face 100R) is about 1200 μm.

[0017] 2A , the nitride-based semiconductor light-emitting element 100 includes a semiconductor stack 100S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor stack 100S includes a substrate 101, an N-type first cladding layer 102, an N-type second cladding layer 103, an N-side guide layer 104, an active layer 105, a P-side first guide layer 106, a P-side second guide layer 107, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 110, and a contact layer 111.

[0018] The substrate 101 is a plate-like member that serves as a base for the nitride-based semiconductor light-emitting device 100. In this embodiment, the substrate 101 is an N-type GaN substrate.

[0019] The N-type first cladding layer 102 is an example of an N-type cladding layer disposed above the substrate 101. The N-type first cladding layer 102 has a smaller refractive index than the active layer 105 and a larger band gap energy. In this embodiment, the N-type first cladding layer 102 is a 1200 nm thick N-type Al ０．０３５ Ga ０．９６５ The N-type first cladding layer 102 contains an impurity with a concentration of 1×10 １８ cm －３ is doped with Si.

[0020] The N-type second cladding layer 103 is an example of an N-type cladding layer disposed above the substrate 101. In this embodiment, the N-type second cladding layer 103 is disposed above the N-type first cladding layer 102. The N-type second cladding layer 103 is a layer having a smaller refractive index than the active layer 105 and a larger band gap energy. In this embodiment, the N-type second cladding layer 103 is an N-type GaN layer having a film thickness of 100 nm. The N-type second cladding layer 103 contains impurities at a concentration of 1×10 １８ cm －３ is doped with Si.

[0021] The N-side guide layer 104 is an optical guide layer disposed above the N-type second cladding layer 103. The N-side guide layer 104 has a higher refractive index and a smaller band gap energy than the N-type first cladding layer 102 and the N-type second cladding layer 103. In this embodiment, the N-side guide layer 104 is an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ This is the N layer.

[0022] The active layer 105 is a light-emitting layer having a quantum well structure and is disposed above the N-side guide layer 104. In this embodiment, the active layer 105 includes well layers 105b and 105d and barrier layers 105a, 105c, and 105e, as shown in FIG.

[0023] The barrier layer 105a is disposed above the N-side guide layer 104 and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 105a is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0024] The well layer 105b is disposed above the barrier layer 105a and functions as a well of the quantum well structure. The well layer 105b is disposed between the barrier layer 105a and the barrier layer 105c. In this embodiment, the well layer 105b is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0025] The barrier layer 105c is disposed above the well layer 105b and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 105c is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0026] The well layer 105d is disposed above the barrier layer 105c and functions as a well of the quantum well structure. The well layer 105d is disposed between the barrier layer 105c and the barrier layer 105e. In this embodiment, the well layer 105d is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0027] The barrier layer 105e is disposed above the well layer 105d and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 105e is an undoped In layer having a thickness of 5 nm. ０．０５ Ga ０．９５ This is the N layer.

[0028] The P-side first guide layer 106 is an optical guide layer disposed above the active layer 105. The P-side first guide layer 106 has a refractive index higher than that of the P-type cladding layer 110 and a band gap energy smaller than that of the P-type cladding layer 110. In this embodiment, the P-side first guide layer 106 is an undoped InP layer having a thickness of 80 nm. ０．０４５ Ga ０．９５５ This is the N layer.

[0029] The P-side second guide layer 107 is an optical guide layer disposed above the P-side first guide layer 106. The P-side second guide layer 107 has a higher refractive index and a smaller band gap energy than the P-type cladding layer 110. In this embodiment, the P-side second guide layer 107 is an undoped InP layer having a thickness of 195 nm. ０．０１ Ga ０．９９ This is the N layer.

[0030] The intermediate layer 108 is a layer disposed above the active layer 105. In this embodiment, the intermediate layer 108 is disposed between the P-side second guide layer 107 and the electron barrier layer 109, and reduces stress caused by the difference in lattice constant between the P-side second guide layer 107 and the electron barrier layer 109. This makes it possible to suppress the occurrence of crystal defects in the nitride-based semiconductor light-emitting element 100. In this embodiment, the intermediate layer 108 is an undoped GaN layer with a thickness of 20 nm.

[0031] The electron barrier layer 109 is disposed above the active layer 105 and is a nitride-based semiconductor layer containing at least Al. In this embodiment, the electron barrier layer 109 is disposed between the intermediate layer 108 and the P-type cladding layer 110. The electron barrier layer 109 is a P-type AlGaN layer with a thickness of 5 nm. The electron barrier layer 109 also has an Al composition ratio gradient region in which the Al composition ratio monotonically increases toward the P-type cladding layer 110. Here, the configuration in which the Al composition ratio monotonically increases also includes a configuration including a region in which the Al composition ratio is constant in the stacking direction. For example, the configuration in which the Al composition ratio monotonically increases also includes a configuration in which the Al composition ratio increases stepwise. In the electron barrier layer 109 according to this embodiment, the entire electron barrier layer 109 is an Al composition ratio increasing region, and the Al composition ratio increases at a constant rate in the stacking direction. Specifically, the electron barrier layer 109 has an Al composition ratio gradient region near the interface with the intermediate layer 108. ０．０２ Ga ０．９８ The Al composition ratio monotonically increases as the layer approaches the P-type cladding layer 110, and the Al composition ratio is ０．３６ Ga ０．６４ The electron barrier layer 109 contains impurities at a concentration of 1×10 １９ cm －３ It is doped with Mg.

[0032] The electron barrier layer 109 can prevent electrons from leaking from the active layer 105 to the P-type cladding layer 110. Furthermore, since the electron barrier layer 109 has an Al composition ratio increasing region where the Al composition ratio increases monotonically, the potential barrier of the valence band of the electron barrier layer 109 can be reduced compared to when the Al composition ratio is uniform. Therefore, holes can flow more easily from the P-type cladding layer 110 to the active layer 105. Therefore, even when the combined thickness of the P-side first guide layer 106 and the P-side second guide layer 107, which are undoped layers, is large, as in this embodiment, an increase in the electrical resistance of the nitride-based semiconductor light-emitting element 100 can be suppressed. This allows the operating voltage of the nitride-based semiconductor light-emitting element 100 to be reduced. Furthermore, self-heating of the nitride-based semiconductor light-emitting element 100 during operation can be reduced, thereby improving the temperature characteristics of the nitride-based semiconductor light-emitting element 100. Therefore, high-power operation of the nitride-based semiconductor light-emitting element 100 is possible.

[0033] The P-type cladding layer 110 is a P-type cladding layer disposed above the active layer 105. In this embodiment, the P-type cladding layer 110 is disposed between the electron barrier layer 109 and the contact layer 111. The P-type cladding layer 110 has a lower refractive index and a higher band gap energy than the active layer 105. The thickness of the P-type cladding layer 110 may be 460 nm or less. This reduces the electrical resistance of the nitride-based semiconductor light-emitting device 100. Therefore, the operating voltage of the nitride-based semiconductor light-emitting device 100 can be reduced. Furthermore, self-heating during operation of the nitride-based semiconductor light-emitting device 100 can be reduced, thereby improving the temperature characteristics of the nitride-based semiconductor light-emitting device 100. Therefore, high-power operation of the nitride-based semiconductor light-emitting device 100 is possible. In the nitride-based semiconductor light-emitting device 100 according to this embodiment, the thickness of the P-type cladding layer 110 may be 200 nm or more in order for the P-type cladding layer 110 to fully function as a cladding layer. The thickness of the P-type cladding layer 110 may be 250 nm or more. In this embodiment, the P-type cladding layer 110 is a P-type Al 1N 2 O 3 layer having a thickness of 450 nm. ０．０３５ Ga ０．９６５The P-type cladding layer 110 is an N layer. The P-type cladding layer 110 is doped with Mg as an impurity. The impurity concentration at the end of the P-type cladding layer 110 closer to the active layer 105 is lower than the impurity concentration at the end farther from the active layer 105. Specifically, the P-type cladding layer 110 has a concentration of 2×10 １８ cm －３ P-type Al doped with Mg having a thickness of 150 nm ０．０３５ Ga ０．９６５ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 300 nm ０．０３５ Ga ０．９６５ N layers.

[0034] A ridge 110R is formed in the P-type cladding layer 110 of the nitride-based semiconductor light-emitting device 100. Two grooves 110T are formed in the P-type cladding layer 110, arranged along the ridge 110R and extending in the Y-axis direction. In this embodiment, the ridge width W is approximately 30 μm. As shown in FIG. 2A , the distance between the lower end of the ridge 110R (i.e., the bottom of the groove 110T) and the active layer 105 is defined as dp. The film thickness of the P-type cladding layer 110 at the lower end of the ridge 110R (i.e., the distance between the lower end of the ridge 110R and the interface between the P-type cladding layer 110 and the electron barrier layer 109) is defined as dc.

[0035] The contact layer 111 is disposed above the P-type cladding layer 110 and is in ohmic contact with the P-side electrode 113. In this embodiment, the contact layer 111 is a P-type GaN layer with a film thickness of 100 nm. The contact layer 111 contains impurities with a concentration of 1×10 ２０ cm －３ It is doped with Mg.

[0036] The current blocking layer 112 is disposed above the P-type cladding layer 110 and is an insulating layer that is transparent to light from the active layer 105. The current blocking layer 112 is disposed on the upper surface of the P-type cladding layer 110 in a region other than the upper surface of the ridge 110R. In this embodiment, the current blocking layer 112 is made of SiO ２It is a layer.

[0037] The P-side electrode 113 is a conductive layer disposed above the semiconductor stack 100S. In the present embodiment, the P-side electrode 113 is disposed above the contact layer 111 and the current blocking layer 112, and is in contact with the contact layer 111. The P-side electrode 113 contains Ag.

[0038] By using Ag, which has a low refractive index for light in the 445 nm wavelength band, for at least a portion of the p-side electrode 113 on the contact layer 111, it is possible to reduce the leakage of light propagating through the waveguide into the p-side electrode 113, thereby reducing the waveguide loss generated in the p-side electrode 113. Ag has a refractive index of 0.5 or less in the wavelength range of 325 nm to 1500 nm and a refractive index of 0.2 or less in the wavelength range of 360 nm to 950 nm. Therefore, it is possible to reduce the leakage of light propagating through the waveguide into the Ag-containing p-side electrode 113 over a wide wavelength range of 325 nm to 1500 nm, thereby reducing the waveguide loss generated in the p-side electrode 113. This effect is even greater in the wavelength range of 360 nm to 950 nm. In this case, even if the thickness of the P-type cladding layer 110 is 0.4 μm or less, it is possible to reduce the leakage of light propagating through the waveguide to the P-side electrode 113, thereby suppressing an increase in waveguide loss while reducing the series resistance of the nitride-based semiconductor light-emitting element 100. As a result, it is possible to reduce the operating voltage and operating current.

[0039] Furthermore, since Ag has an extremely small refractive index, when Ag is used for the p-side electrode 113, spontaneously emitted light emitted from the active layer 105 can be reflected by the p-side electrode 113 with high reflectivity and fed back to the active layer 105. Of the spontaneously emitted light components fed back to the active layer 105, components with wavelengths shorter than the laser oscillation wavelength are reabsorbed in the active layer 105 to generate electron-hole pairs, which can be used again as electron-hole pairs for laser oscillation. As a result, the quantum efficiency of the electrons and holes injected into the active layer 105 contributing to laser oscillation is improved, the oscillation threshold is reduced, and the slope efficiency is improved.

[0040] Furthermore, using Ag for the P-side electrode 113 allows the thickness of the P-type cladding layer 110 to be thinned without significantly increasing waveguide loss. As a result, the optical path length of spontaneously emitted light that is emitted in the active layer 105, reflected by the P-side electrode 113, and returned to the active layer 105, passing through the P-type cladding layer 110, which has high free carrier absorption, is shortened, reducing the amount of attenuation of the spontaneously emitted light in the P-type cladding layer 110 and increasing the amount of feedback of the spontaneously emitted light to the active layer 105. As a result, quantum efficiency and slope efficiency can be further improved. To obtain high reflectivity with the Ag-containing P-side electrode 113, the thickness of the P-side electrode 113 should be 100 nm or more. Furthermore, to ensure ease of the resist lift-off process during electrode formation, the P-side electrode 113 should be formed to a thickness of 500 nm or less.

[0041] Furthermore, to obtain high reflectance of spontaneously emitted light from the Ag-containing p-side electrode 113, it is preferable that the Ag film contained in the p-side electrode 113 is formed in contact with the contact layer 111. However, the p-side electrode 113 may contain other metals (hereinafter also referred to as interface region metals) with a thickness of 5 nm or less in the interface region with the contact layer 111, such as Cr, Ti, Ni, Pd, Pt, and Au. Within this film thickness range, a decrease in the reflectance of the Ag film due to the interface region metal can be suppressed. If the film thickness of the interface region metal is set to 3 nm or less, a decrease in the reflectance of the Ag film can be further suppressed.

[0042] Furthermore, by using Pd as the interface region metal, it is possible to obtain low-resistance ohmic contact between the p-side electrode 113 and the contact layer 111 while maintaining the high reflectance of the Ag film.

[0043] The N-side electrode 114 is a conductive layer disposed below the substrate 101 (i.e., on the principal surface of the substrate 101 opposite to the principal surface on which the components of the semiconductor stack 100S other than the substrate 101 are disposed). The N-side electrode 114 is a single-layer film or a multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au, for example.

[0044] 2A , the nitride-based semiconductor light-emitting element 100 has the above-described configuration, and therefore an effective refractive index difference ΔN occurs between the portion below the ridge 110R and the portion below the groove 110T, which allows light generated in the portion of the active layer 105 below the ridge 110R to be confined in the horizontal direction (i.e., the X-axis direction).

[0045] [1-2. Light Intensity Distribution and Light Output Stability] Next, the light intensity distribution and light output stability of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be described.

[0046] First, the light intensity distribution in the stacking direction (Z-axis direction in each drawing) of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing an outline of the light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting element 100 according to this embodiment. Fig. 3 shows a schematic cross-sectional view of the nitride-based semiconductor light-emitting element 100 and a graph showing an outline of the light intensity distribution in the stacking direction at positions corresponding to the ridge 110R and the groove 110T.

[0047] In general, in nitride-based semiconductor light-emitting devices, light is generated in the active layer, but the light intensity distribution in the stacking direction depends on the stacking structure, and the peak of the light intensity distribution does not necessarily lie in the active layer. Furthermore, since the stacking structure of the nitride-based semiconductor light-emitting device 100 according to this embodiment differs between the portion below the ridge 110R and the portion below the groove 110T, the light intensity distribution also differs between the portion below the ridge 110R and the portion below the groove 110T. As shown in FIG. 3 , the peak position of the light intensity distribution in the stacking direction at the center in the horizontal direction (i.e., the X-axis direction) below the ridge 110R is designated PS1. Furthermore, the peak position of the light intensity distribution in the stacking direction below the groove 110T is designated PS2. Positions PS1 and PS2 will now be described with reference to FIG. 4 . FIG. 4 is a graph showing coordinates of positions in the stacking direction of the nitride-based semiconductor light-emitting device 100 according to this embodiment. 4, of the well layers 105b and 105d included in the active layer 105, the coordinate of the N-side end face of the well layer 105b that is closest to the N-side guide layer 104, that is, the end face of the well layer 105b closer to the N-side guide layer 104, in the stacking direction is defined as zero, the downward direction (the direction toward the N-side guide layer 104) is defined as the negative direction of the coordinate, and the upward direction (the direction toward the P-side first guide layer 106) is defined as the positive direction of the coordinate. The absolute value of the difference between positions PS1 and PS2 is defined as the peak position difference ΔP.

[0048] In the nitride-based semiconductor light-emitting device 100 according to this embodiment, the thickness of the P-type cladding layer 110 is set to be relatively thin in order to reduce the operating voltage. Accordingly, the height of the ridge 110R (i.e., the height of the ridge 110R from the bottom surface of the groove 110T) is also set to be relatively low. In a semiconductor light-emitting device having such a configuration, the peak position of the light intensity distribution in the stacking direction generally shifts from the active layer toward the N-type cladding layer. This reduces the optical confinement factor in the active layer, and accordingly reduces the thermal saturation level of the optical output. This makes it difficult for the semiconductor light-emitting device to operate at high output. In this embodiment, the bandgap energy of the P-side second guide layer 107 is greater than the bandgap energy of the N-side guide layer 104, and the bandgap energy of the N-side guide layer 104 is equal to or greater than the bandgap energy of the P-side first guide layer 106. Furthermore, when the thickness of the P-side first guide layer 106 is Tp1, the thickness of the P-side second guide layer 107 is Tp2, and the thickness of the N-side guide layer 104 is Tn1, the relationship Tn1<Tp1+Tp2 (1) is satisfied.

[0049] Thus, in the nitride-based semiconductor light-emitting device 100, the band gap energy of the N-side guide layer 104 is equal to or greater than the band gap energy of the P-side first guide layer 106. Specifically, the P-side first guide layer 106 is made of In Ｘｐ１ Ga １－Ｘｐ１ The N-side guide layer 104 is made of In. Ｘｎ１ Ga １－Ｘｎ１ N, satisfying the relationship Xn1≦Xp1 (2). Therefore, the refractive index of the N-side guide layer 104 is equal to or less than the refractive index of the P-side first guide layer 106. This allows the light intensity distribution to move from the active layer 105 toward the P-side first guide layer 106, as compared to when the refractive index of the N-side guide layer 104 is higher than the refractive index of the P-side first guide layer 106, for example.

[0050] In this embodiment, the In composition ratios Xn1 and Xp1 of the N-side guide layer 104 and the P-side first guide layer 106 described above satisfy the relationship: Xn1<Xp1 (3). More specifically, the N-side guide layer 104 contains In ０．０４ Ga ０．９６ The P-side first guide layer 106 is an In ０．０４５ Ga ０．９５５ The N-side guide layer 104 is an N-layer. Here, in an InGaN layer, as the In composition ratio increases, the bandgap energy decreases and the refractive index increases. Therefore, the bandgap energy of the N-side guide layer 104 is greater than the bandgap energy of the P-side first guide layer 106. In other words, the refractive index of the N-side guide layer 104 is smaller than the refractive index of the P-side first guide layer 106. This allows the light intensity distribution to shift from the active layer 105 toward the P-side first guide layer 106, compared to when the refractive index of the N-side guide layer 104 is equal to or greater than the refractive index of the P-side first guide layer 106.

[0051] As described above, the sum of the thickness Tp1 of the P-side first guide layer 106 and the thickness Tp2 of the P-side second guide layer 107 is greater than the thickness Tn1 of the N-side guide layer 104. By making the sum of the thicknesses of the P-side first guide layer 106 and the P-side second guide layer 107, which have relatively high refractive indices, greater than the thickness Tn1 of the N-side guide layer 104, the light intensity distribution can be shifted from the active layer 105 toward the P-side first guide layer 106, compared to when the sum of the thicknesses of the P-side first guide layer 106 and the P-side second guide layer 107 is equal to or less than the thickness Tn1 of the N-side guide layer 104. Therefore, the peak of the light intensity distribution in the stacking direction can be prevented from shifting in the direction from the active layer 105 toward the N-type second cladding layer 103. Here, the band gap energy of the P-side second guide layer 107 is greater than the band gap energy of the N-side guide layer 104. That is, the refractive index of the P-side second guide layer 107 is smaller than the refractive index of the N-side guide layer 104. This makes it possible to prevent the light intensity distribution from moving too far in the direction approaching the P-type cladding layer 110 from the active layer 105.

[0052] As described above, the band gap energy of the P-side second guide layer 107 is larger than the band gap energy of the N-side guide layer 104. Specifically, the P-side second guide layer 107 is made of In Ｘｐ２ Ga １－Ｘｐ２ The In composition ratio Xp2 of the P-side second guide layer 107 and the In composition ratio Xn1 of the N-side guide layer 104 satisfy the relationship: Xp2<Xn1 (4). More specifically, the N-side guide layer 104 is made of In. ０．０４ Ga ０．９６ The P-side second guide layer 107 is an In layer. ０．０１ Ga ０．９９ Therefore, the refractive index of the N-side guide layer 104 is greater than the refractive index of the P-side second guide layer 107. This makes it possible to prevent the light intensity distribution from moving too far in the direction approaching the P-type cladding layer 110 from the active layer 105.

[0053] In this embodiment, the barrier layers 105a, 105c, and 105e of the active layer 105 are made of In. Ｘｂ Ga １－Ｘｂ The In composition ratios Xb and Xp1 of each barrier layer and the P-side first guide layer 106 satisfy the relationship Xp1<Xb (5). This allows the refractive index of each barrier layer to be greater than those of the P-side first guide layer 106 and the N-side guide layer 104. This allows the peak of the light intensity distribution in the stacking direction to be positioned in the active layer 105. Furthermore, it is possible to prevent the light intensity distribution from moving too far in a direction approaching the P-type cladding layer 110 from the active layer 105.

[0054] In this embodiment, the average refractive index of the P-side first guide layer 106 and the P-side second guide layer 107 is smaller than the average refractive index of the N-side guide layer 104. This makes it possible to prevent the light intensity distribution from moving too far in the direction approaching the P-type cladding layer 110 from the active layer 105.

[0055] Furthermore, in this embodiment, the film thicknesses Tp1 and Tp2 of the P-side first guide layer 106 and the P-side second guide layer 107 satisfy the relationship Tp1<Tp2 (6). Thus, by making the film thickness of the P-side first guide layer 106, which has a small band gap energy, i.e., a large refractive index, relatively small, it is possible to prevent the light intensity distribution from moving too far in the direction approaching the P-type cladding layer 110 from the active layer 105. Furthermore, by making the film thickness of the P-side first guide layer 106, which has a small In composition ratio, relatively small, it is possible to avoid disposing the P-side first guide layer 106, which has a small In composition ratio and a large film thickness, above and in the vicinity of the well layers 105b and 105d, which have the highest In composition ratio in the semiconductor laminate 100S. Therefore, it is possible to suppress the occurrence of lattice defects.

[0056] Furthermore, in this embodiment, the film thicknesses Tp1 and Tn1 of the P-side first guide layer 106 and the N-side guide layer 104 satisfy the relationship Tp1<Tn1 (7). In this way, by making the film thickness of the P-side first guide layer 106, which has a small band gap energy, i.e., a large refractive index, smaller than the film thickness of the N-side guide layer 104, it is possible to prevent the light intensity distribution from moving too far in the direction approaching the P-type cladding layer 110 from the active layer 105.

[0057] In this embodiment, the band gap energy of the N-type second cladding layer 103 is smaller than that of the N-type first cladding layer 102 and larger than that of the P-side second guide layer 107. In this way, by disposing the N-type second cladding layer 103, which has a smaller band gap energy than the N-type first cladding layer 102, i.e., a larger refractive index, between the N-type first cladding layer 102 and the N-side guide layer 104, it is possible to prevent the light intensity distribution from moving too far in a direction from the active layer 105 toward the P-type cladding layer 110. Furthermore, by making the band gap energy of the N-type second cladding layer 103 larger than that of the P-side second guide layer 107, it is possible to prevent the light intensity distribution from moving too far from the active layer 105 toward the N-type second cladding layer 103.

[0058] With the above-described configuration, in this embodiment, the position PS1 of the peak of the light intensity distribution in the stacking direction below the ridge 110R can be set to 9.8 nm. In other words, the peak of the light intensity distribution can be positioned in the active layer 105. Furthermore, ΔP can be suppressed to 9.0 nm. This allows the light confinement factor in the active layer 105 to be increased to approximately 1.36%.

[0059] As described above, according to the nitride-based semiconductor light-emitting element 100 of this embodiment, the peak of the light intensity distribution in the stacking direction can be positioned in the active layer 105. Note that "the peak of the light intensity distribution in the stacking direction is positioned in the active layer 105" means that the peak of the light intensity distribution in the stacking direction is positioned in the active layer 105 at least one position in the horizontal direction of the nitride-based semiconductor light-emitting element 100, and is not limited to a state in which the peak of the light intensity distribution in the stacking direction is positioned in the active layer 105 at all positions in the horizontal direction.

[0060] When the peak of the light intensity distribution in the stacking direction is positioned in the active layer 105 as in this embodiment, the proportion of the light located in the P-type cladding layer 110 can be increased compared to when the peak of the light intensity distribution is positioned in the N-side guide layer 104. Here, since the P-type cladding layer 110 has a higher impurity concentration than the N-type first cladding layer 102 and the N-type second cladding layer 103, an increase in the proportion of the light located in the P-type cladding layer 110 raises concerns about an increase in free carrier loss in the P-type cladding layer 110. However, in this embodiment, the P-side first guide layer 106 and the P-side second guide layer 107 are undoped layers, and the sum of the thickness Tp1 of the P-side first guide layer 106 and the thickness Tp2 of the P-side second guide layer 107 is relatively large, thereby increasing the proportion of the light intensity distribution located in the undoped layers. Therefore, an increase in free carrier loss can be suppressed. Specifically, in this embodiment, the waveguide loss is reduced to 1.6 cm. －１ It can be suppressed to a certain extent.

[0061] Furthermore, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the effective refractive index difference ΔN between the portion below the ridge 110R and the portion below the groove 110T is set to be relatively small in order to reduce the divergence angle of the emitted light in the horizontal direction (i.e., the X-axis direction). Specifically, the effective refractive index difference ΔN is set by adjusting the distance dp (see FIG. 2A ) between the current blocking layer 112 and the active layer 105. Here, the greater the distance dp, the smaller the effective refractive index difference ΔN. In this embodiment, the effective refractive index difference ΔN is 2.4×10 －３ Therefore, in this embodiment, the effective refractive index difference ΔN is about 2.4×10 －３ When the ridge 110R is larger than the ridge 110R, the number of higher-order modes (i.e., higher-order transverse modes) that can propagate through the waveguide formed by the ridge 110R is smaller. Therefore, the proportion of each higher-order mode among all transverse modes included in the emitted light from the nitride-based semiconductor light-emitting element 100 is relatively large. Therefore, the increase or decrease in the number of modes and the change in the optical confinement factor in the active layer 105 due to inter-mode coupling are relatively large. Therefore, when the increase or decrease in the number of modes and inter-mode coupling occur in the nitride-based semiconductor light-emitting element 100, the linearity of the optical output characteristic with respect to the supplied current (the so-called IL characteristic) is reduced. In other words, a non-linear portion (a so-called kink) appears in the graph showing the IL characteristic. This may result in a reduction in the stability of the optical output of the nitride-based semiconductor light-emitting element 100.

[0062] The above-described decrease in the stability of the optical output will be explained below. In the nitride-based semiconductor light-emitting element 100, the optical intensity distribution in the portion below the ridge 110R is dominated by the fundamental mode (i.e., the zeroth-order mode), while the optical intensity distribution in the portion below the groove 110T is dominated by a higher-order mode. Therefore, when the difference ΔP between the peak position PS1 of the optical intensity distribution in the stacking direction in the portion below the ridge 110R of the nitride-based semiconductor light-emitting element 100 and the peak position PS2 of the optical intensity distribution in the stacking direction in the portion below the groove 110T is large, an increase or decrease in the number of modes and inter-mode coupling occur, which fluctuates the optical confinement factor in the active layer 105, thereby decreasing the stability of the optical output.

[0063] For example, if the number of higher-order modes decreases, the peak of the light intensity distribution obtained by adding together the light intensity distributions below both the ridge 110R and the groove 110T moves to a position closer to position PS1. Therefore, the larger the difference ΔP between positions PS1 and PS2, the greater the fluctuation in the light confinement factor in the active layer 105 when the number of modes changes. Therefore, the stability of the light output decreases.

[0064] The nitride-based semiconductor light-emitting device 100 according to this embodiment includes the N-side guide layer 104, the P-side first guide layer 106, and the P-side second guide layer 107 having the above-described configuration, and therefore the peak of the light intensity distribution can be positioned in the active layer 105 both below the ridge 110R and below the trench 110T. That is, the difference ΔP between the positions PS1 and PS2 of the light intensity distribution peaks can be reduced. As a result, even if the number of modes increases or decreases and inter-mode coupling occurs, fluctuations in the position in the stacking direction of the peak of the light intensity distribution obtained by adding the light intensity distributions below both the ridge 110R and the trench 110T can be suppressed. Therefore, the stability of the light output can be improved.

[0065] As described above, the distance dp is set to a relatively large value in order to set the effective refractive index difference ΔN to a relatively small value. When the distance dp is set, if the lower end of the ridge 110R (i.e., the bottom of the groove 110T) is set to be lower than the electron barrier layer 109, the electron barrier layer 109 has a large band gap energy, so holes injected from the contact layer 111 tend to leak from the sidewall of the ridge 110R to the outside of the ridge 110R when passing through the electron barrier layer 109. As a result, the holes flow downward into the groove 110T. Accordingly, the light distribution intensity is low in the active layer 105 below the groove 110T, reducing the probability of radiative recombination between electrons and holes injected into the active layer 105 and increasing non-radiative recombination. This makes the nitride-based semiconductor light-emitting element 100 more susceptible to degradation. Therefore, the lower end of the ridge 110R is set to be higher than the electron barrier layer 109. Furthermore, if the distance dc (see FIG. 2A) from the bottom end of the ridge 110R to the electron barrier layer 109 becomes too large, holes will flow from the ridge 110R into between the groove 110T and the electron barrier layer 109, resulting in leakage current. To prevent this leakage current from increasing, the distance dc is set to as small a value as possible.

[0066] [1-3. Effects] The effects of the nitride-based semiconductor light-emitting element 100 according to the present embodiment will be described with reference to FIGS. 5 to 9 , comparing it with nitride-based semiconductor light-emitting elements of comparative examples. FIG. 5 is a diagram showing the device structures used in simulations of the nitride-based semiconductor light-emitting elements of Comparative Examples 1 to 5 and the nitride-based semiconductor light-emitting element 100 according to the present embodiment. FIGS. 6, 7, and 8 are graphs showing simulation results of the light intensity distribution and refractive index distribution in the portion below the ridge 110R of the nitride-based semiconductor light-emitting element of Comparative Example 1, Comparative Example 3, and the nitride-based semiconductor light-emitting element according to the present embodiment, respectively. The horizontal axis in FIGS. 6 to 8 indicates the position in the stacking direction, and the left and right vertical axes indicate the light intensity and the refractive index, respectively. In FIGS. 6 to 8 , the light intensity distribution in the stacking direction in the portion below the trench 110T is also shown by a dotted line.

[0067] 9 is a diagram showing numerical values ​​obtained by simulation of the nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 5, and the nitride-based semiconductor light-emitting device 100 according to this embodiment. Fig. 9 shows the distance dc from the lower end of the ridge 110R to the electron barrier layer 109, the optical confinement factor, the waveguide loss, the effective refractive index difference ΔN, the peak position PS1 of the light intensity distribution in the stacking direction at the horizontal center of the lower portion of the ridge 110R, and the absolute value ΔP of the difference between the peak position PS1 and the peak position PS2 in the stacking direction of the limit mode for wave-guiding. The distance dc is set when the effective refractive index difference is 2.8×10 －３ The distance is set to be such that the following can be achieved. The limiting mode of waveguide refers to the highest-order mode that can propagate in each nitride-based semiconductor light-emitting element. The peak position of the limiting mode of waveguide in the stacking direction is a value corresponding to the peak position of the light intensity distribution in the portion below groove 110T where higher-order modes are dominant.

[0068] The nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 5 shown in FIG. 5 differ from the nitride-based semiconductor light-emitting device 100 according to the present embodiment in at least one of the configurations of the N-side guide layer and the P-side guide layer and the configuration of the P-side electrode. The nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 4 differ from the nitride-based semiconductor light-emitting device 100 according to the present embodiment in the configurations of the N-side guide layer and the P-side guide layer. The nitride-based semiconductor light-emitting device of Comparative Example 5 has the same configuration of the N-side guide layer and the P-side guide layer as the nitride-based semiconductor light-emitting device 100 according to the present embodiment. Furthermore, the nitride-based semiconductor light-emitting devices of Comparative Examples 1, 3, and 5 differ from the nitride-based semiconductor light-emitting device 100 according to the present embodiment in the configuration of the P-side electrode. Specifically, the P-side electrodes of the nitride-based semiconductor light-emitting devices of Comparative Examples 1, 3, and 5 are made of Pd. On the other hand, the P-side electrodes of the nitride-based semiconductor light-emitting devices of Comparative Examples 2 and 4 contain Ag, like the P-side electrode according to the present embodiment.

[0069] 5, in the nitride-based semiconductor light-emitting devices of Comparative Examples 1 and 2, the thickness Tn0 of the N-side guide layer is equal to the thickness Tp0 of the P-side guide layer. Specifically, both the N-side guide layer and the P-side guide layer are made of InP with a thickness of 220 nm. ０．０３Ga ０．９７ This is the N layer.

[0070] The nitride-based semiconductor light-emitting devices of Comparative Examples 3 and 4 have an N-side guide layer, a P-side first guide layer, and a P-side second guide layer, similar to the nitride-based semiconductor light-emitting device 100 according to the present embodiment. In the nitride-based semiconductor light-emitting devices of Comparative Examples 3 and 4, the band gap energy of the P-side second guide layer is larger than the band gap energy of the N-side first guide layer, and the band gap energy of the N-side first guide layer is equal to the band gap energy of the P-side first guide layer, and the following relationships hold for the thickness Tp1 of the P-side first guide layer, the thickness Tp2 of the P-side second guide layer, and the thickness Tn1 of the N-side first guide layer: Tn1=Tp1+Tp2, (8) and Tp1=Tp2 (9) Specifically, the N-side guide layer is an InN-type GaN layer having a thickness of 220 nm. ０．０３ Ga ０．９７ The P-side first guide layer is an In layer with a thickness of 110 nm. ０．０３ Ga ０．９７ The P-side second guide layer is an In layer with a thickness of 110 nm. ０．０１ Ga ０．９９ This is the N layer.

[0071] In the simulation, the Al composition ratios of the electron barrier layers of Comparative Examples 1 to 5 and the electron barrier layer 109 according to this embodiment are uniform. In other words, the Al composition ratios of the electron barrier layers are not graded in the stacking direction.

[0072] The results of simulations of the nitride-based semiconductor light-emitting devices according to Comparative Examples 1 to 5 and the present embodiment will be described below.

[0073] In the nitride-based semiconductor light-emitting device of Comparative Example 1, as shown in FIG. 6 , the film thickness of the N-side guide layer is equal to the film thickness of the P-side guide layer, so the peak of the light intensity distribution is located within the active layer 105 below the ridge 110R. Therefore, the light confinement factor for the active layer 105 is high below the ridge 110R. However, in the nitride-based semiconductor light-emitting device of Comparative Example 1, the film thickness of the P-side guide layer is not large, so it is affected by the light intensity distribution of the current blocking layer 112 disposed in the groove 110T. Because the peak of the light intensity distribution in the stacking direction below the groove 110T is located in the N-side guide layer, the light confinement factor is low below the groove 110T. Furthermore, the difference ΔP between the peak position of the light intensity distribution in the stacking direction below the ridge 110R and the peak position of the light intensity distribution in the stacking direction below the groove 110T is relatively large. Therefore, the linearity of the IL characteristics of the nitride-based semiconductor light-emitting device of Comparative Example 1 is low.

[0074] In the nitride-based semiconductor light-emitting device of Comparative Example 3, the film thickness of the P-side second guide layer is smaller than that of the nitride-based semiconductor light-emitting device 100 according to the present embodiment, and therefore the influence of the current blocking layer 112 on the light intensity distribution is relatively large, as shown in Fig. 7. For this reason, the difference ΔP between the peak position of the light intensity distribution in the stacking direction below the ridge 110R and the peak position of the light intensity distribution in the stacking direction below the groove 110T is relatively large. Therefore, the linearity of the IL characteristics of the nitride-based semiconductor light-emitting device of Comparative Example 3 is low.

[0075] In contrast to the above comparative examples, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the sum of the thickness Tp1 of the P-side first guide layer 106 and the thickness Tp2 of the P-side second guide layer 107 is larger than the thickness Tn1 of the N-side guide layer 104, so the effective refractive index difference ΔN can be reduced. Therefore, the horizontal divergence angle of the emitted light can be reduced. Furthermore, the distance dc from the bottom end of the ridge 110R to the electron barrier layer 109 can be set to 40 nm, which is significantly smaller than the distance dc in the comparative examples. Therefore, the leakage current flowing between the bottom end of the ridge 110R and the electron barrier layer 109 can be suppressed, and the oscillation threshold current can be reduced.

[0076] 8, in this embodiment, the peak of the light intensity distribution in the stacking direction can be positioned in the active layer 105 in both the portion below the ridge 110R and the portion below the groove 110T. Therefore, the optical confinement factor can be increased compared to the comparative examples. Furthermore, since the difference ΔP in the peak positions can be reduced, the linearity of the IL characteristics can be improved.

[0077] Furthermore, in the nitride-based semiconductor light-emitting device 100 according to this embodiment, the peak of the light intensity distribution in the stacking direction is located in the active layer 105, and therefore the light intensity in the P-type cladding layer 110 is higher than when the peak of the light intensity distribution is located in the N-side guide layer as in Comparative Example 3. This raises concerns about increased free carrier loss in the P-type cladding layer 110, which has a higher impurity concentration than the N-type first cladding layer 102 and the N-type second cladding layer 103. However, in this embodiment, the P-side first guide layer 106 and the P-side second guide layer 107 are undoped layers, and the sum of the film thickness Tp1 of the P-side first guide layer 106 and the film thickness Tp2 of the P-side second guide layer 107 is relatively large, thereby increasing the proportion of the portion of the light intensity distribution located in the undoped layers. Therefore, an increase in free carrier loss can be suppressed. Furthermore, in this embodiment, the impurity concentration at the end of the P-type cladding layer 110 closer to the active layer 105 is lower than the impurity concentration at the end farther from the active layer 105, and therefore, free carrier loss at the end of the P-type cladding layer 110 closer to the active layer 105, where the light intensity is relatively high, can be suppressed.

[0078] Furthermore, in this embodiment, since the p-side electrode 113 contains Ag, it is possible to reduce the refractive index of the p-side electrode 113 and increase the reflectance thereof, thereby suppressing light leakage into the p-side electrode 113 and reducing optical loss in the p-side electrode 113.

[0079] Furthermore, because the reflectivity of the P-side electrode 113 is high, a portion of the spontaneously emitted light generated in the active layer 105 and incident on the P-side electrode 113 is reflected by the P-side electrode 113 and returns to the active layer 105 (i.e., is fed back). This enables optical excitation of the active layer 105, thereby increasing the ratio of optical output to input power of the nitride-based semiconductor light-emitting element 100. In other words, the efficiency of the nitride-based semiconductor light-emitting element 100 can be improved. The effect of the P-side electrode 113 on spontaneously emitted light will be described with reference to FIGS. 10 to 13.

[0080] FIG. 10 is a graph showing the relationship between the position in the width direction (i.e., the X-axis direction) of the ridge 110R according to this embodiment and the amount of feedback of spontaneously emitted light by the P-side electrode 113 to the active layer 105. FIG. 10 also shows a graph (dashed line) showing the amount of feedback when the P-side electrode is made of Pd, and a graph (dotted line) showing the amount of feedback by the N-side electrode 114 made of Ti. FIG. 11 is a first graph showing the relationship between the position in the width direction of the ridge 110R according to this embodiment and the amount of reabsorption of spontaneously emitted light by the active layer 105. FIG. 11 also shows the amount of reabsorption when the P-type cladding layer 110 has a thickness Tpc of 0.15 μm, 0.25 μm, 0.35 μm, and 0.45 μm. FIG. 11 also shows a graph when the P-side electrode is made of Pd and the thickness Tpc of the P-type cladding layer 110 is 0.45 μm. 12 is a second graph showing the relationship between the position in the width direction of the ridge 110R according to this embodiment and the amount of re-absorption of spontaneously emitted light by the active layer 105. FIG. 12 shows the amount of re-absorption when the ridge width W is 3 μm, 15 μm, 30 μm, 45 μm, 60 μm, 90 μm, 120 μm, 200 μm, and 300 μm. The position where the horizontal axis in FIGS. 10 to 12 is 0 μm indicates one end of the ridge 110R in the width direction. The position where the horizontal axis in FIGS. 10 and 11 is 45 μm indicates the other end of the ridge 110R in the width direction. 12 indicates the other end in the width direction of ridge 110R when the ridge width W is 3 μm, 15 μm, 30 μm, 45 μm, 60 μm, 90 μm, 120 μm, 200 μm, and 300 μm, respectively. Fig. 13 is a graph showing the relationship between the ridge width W and the amount of spontaneous emission light re-absorption by active layer 105 according to this embodiment.

[0081] 10 , when the p-side electrode 113 contains Ag, the amount of feedback of spontaneously emitted light can be significantly increased compared to when the p-side electrode is made of Pd. Also, as shown in FIG. 10 , the proportion of the feedback amount of spontaneously emitted light from the p-side electrode 113 is overwhelmingly greater than the proportion from the n-side electrode 114. Therefore, in order to increase the amount of feedback of spontaneously emitted light, it is effective to increase the reflectance of spontaneously emitted light at the p-side electrode 113, as in this embodiment.

[0082] As shown in FIG. 11, by reducing the thickness Tpc of the P-type cladding layer 110, the re-absorption of spontaneously emitted light by the active layer 105 can be further increased.

[0083] 12 and 13, as the ridge width W increases, the amount of re-absorption of spontaneously emitted light increases. For this reason, the ridge width W may be 30 μm or more. Furthermore, to further increase the amount of re-absorption of spontaneously emitted light, the ridge width W may be 40 μm or more. However, if the ridge width W becomes too large, the adverse effects of heat generation become significant, so the ridge width W may be 200 μm or less.

[0084] In the nitride-based semiconductor light-emitting devices of Comparative Examples 2 and 4 described above, the use of the Ag-containing P-side electrode 113 provides the same effects as those provided by the P-side electrode 113 in the nitride-based semiconductor light-emitting device 100 according to this embodiment. However, in Comparative Examples 2 and 4, the configurations of the N-side guide layer and P-side guide layer are different from those in this embodiment, and therefore the waveguide loss is larger than that in this embodiment.

[0085] The effect of the P-side electrode 113 will be further described with reference to Figs. 14 and 15. Fig. 14 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting element of Comparative Example 5 and each numerical value obtained by simulation. Fig. 15 is a diagram showing the relationship between the film thickness of the P-type cladding layer 110 of the nitride-based semiconductor light-emitting element 100 according to this embodiment and each numerical value obtained by simulation. In this simulation, the P-type cladding layer 110 having a concentration of 1 x 10 １９cm －３ Mg-doped P-type Al ０．０３５ Ga ０．９６５ By changing the thickness of the N layer, the thickness of the entire P-type cladding layer 110 was changed to 0.45 μm, 0.35 μm, 0.25 μm, and 0.20 μm.

[0086] 14 and 15 , there is no significant difference between Comparative Example 5 and the present embodiment in terms of the values ​​other than the waveguide loss, but the waveguide loss is significantly different between Comparative Example 5 and the present embodiment. Specifically, as the thickness of the P-type cladding layer 110 decreases, the waveguide loss increases in Comparative Example 5. This is because as the thickness of the P-type cladding layer 110 decreases, light seeps into the P-side electrode made of Pd, causing light loss. On the other hand, in the present embodiment, even if the thickness of the P-type cladding layer 110 decreases, light seeps into the P-side electrode 113 containing Ag can be suppressed, so the waveguide loss hardly increases.

[0087] In this way, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, by providing the P-side electrode 113 containing Ag, it is possible to suppress an increase in waveguide loss even when the P-type cladding layer 110 is thinned to about 200 nm.

[0088] Here, the output characteristics of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be described with reference to Figs. 16 and 17. Fig. 16 is a graph showing the results of a simulation of the relationship between the radiation angle and light intensity of the nitride-based semiconductor light-emitting element 100 according to this embodiment. Fig. 16 shows a comparative example 6 in which the effective refractive index difference ΔN is 7×10 －３ 17 is a graph showing the simulation results of the IL characteristics of nitride-based semiconductor light-emitting element 100 according to the present embodiment. Also shown in FIG. 17 are the IL characteristics of nitride-based semiconductor light-emitting elements of Comparative Examples 1 and 5.

[0089] As shown in FIG. 16, in the nitride-based semiconductor light-emitting device 100 according to this embodiment, the effective refractive index difference ΔN is 2.7×10 －３Therefore, the beam divergence angle in the horizontal direction can be reduced compared to the nitride-based semiconductor light-emitting device of Comparative Example 6.

[0090] 17, the nitride-based semiconductor light-emitting device 100 according to this embodiment can obtain IL characteristics with higher linearity than the nitride-based semiconductor light-emitting devices of the respective comparative examples, and can also obtain higher slope efficiency than the respective comparative examples.

[0091] Next, the relationship between the configuration and effects of the p-side second guide layer 107 according to this embodiment will be described.

[0092] The above-described simulations have revealed that by setting the thickness Tp2 of the P-side second guide layer 107 to 100 nm or more, it is possible to simultaneously achieve a reduction in waveguide loss, an increase in the optical confinement factor Γv, and a reduction in the effective refractive index difference ΔN. Furthermore, to further increase the optical confinement factor Γv, the thickness Tp2 may be 250 nm or less. Furthermore, to position the positions PS1 and PS2 near the well layers 105b and 105d of the active layer 105, the In composition ratio Xp2 of the P-side second guide layer 107 may be 0.5% or more.

[0093] (Embodiment 2) A nitride-based semiconductor light-emitting device according to embodiment 2 will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from nitride-based semiconductor light-emitting device 100 according to embodiment 1 in the relationship between the Al composition ratios of the N-type first cladding layer and the P-type cladding layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below with reference to FIG. 18 , focusing on the differences from nitride-based semiconductor light-emitting device 100 according to embodiment 1.

[0094] 18 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 200 according to this embodiment. As shown in FIG. 18 , the nitride-based semiconductor light-emitting device 200 according to this embodiment includes a semiconductor stack 200S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor stack 200S includes a substrate 101, an N-type first cladding layer 202, an N-type second cladding layer 103, an N-side guide layer 104, an active layer 105, a P-side first guide layer 106, a P-side second guide layer 107, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 210, and a contact layer 111.

[0095] The N-type first cladding layer 202 according to this embodiment is an N-type Al 1N 2 O 3 layer having a thickness of 1200 nm. ０．０３６ Ga ０．９６４ The N-type first cladding layer 202 contains an impurity with a concentration of 1×10 １８ cm －３ is doped with Si.

[0096] The P-type cladding layer 210 according to this embodiment is a P-type Al layer having a thickness of 450 nm. ０．０２６ Ga ０．９７４ The P-type cladding layer 210 is an N layer. The P-type cladding layer 210 is doped with Mg as an impurity. The impurity concentration at the end of the P-type cladding layer 210 closer to the active layer 105 is lower than the impurity concentration at the end farther from the active layer 105. Specifically, the P-type cladding layer 210 has a concentration of 2×10 １８ cm －３ P-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 300 nm ０．０２６ Ga ０．９７４ N layers.

[0097] The P-type cladding layer 210 also has a ridge 210R formed therein, similar to the P-type cladding layer 110 according to embodiment 1. The P-type cladding layer 210 also has two grooves 210T formed therein, which are arranged along the ridge 210R and extend in the Y-axis direction.

[0098] The nitride-based semiconductor light-emitting device 200 according to this embodiment also provides the same effects as those of the nitride-based semiconductor light-emitting device 100 according to the first embodiment.

[0099] Furthermore, in this embodiment, the N-type first cladding layer 202 and the P-type cladding layer 210 contain Al, and when the Al composition ratios of the N-type first cladding layer 202 and the P-type cladding layer 210 are Ync and Ypc, respectively, the relationship Ync>Ypc (10) is satisfied.

[0100] Here, when at least one of the N-type first cladding layer 202 and the P-type cladding layer 210 has a superlattice structure, the composition ratios Ync and Ypc indicate average Al composition ratios. For example, when the N-type first cladding layer 202 includes multiple 2-nm-thick GaN layers and multiple 2-nm-thick AlGaN layers with an Al composition ratio of 0.07, and the multiple GaN layers and the multiple AlGaN layers are alternately stacked, Ync is 0.035, which is the average Al composition ratio of the entire N-type first cladding layer 202. When the P-type cladding layer 210 includes multiple 2-nm-thick GaN layers and multiple 2-nm-thick AlGaN layers with an Al composition ratio of 0.07, and the multiple GaN layers and the multiple AlGaN layers are alternately stacked, Ypc is 0.035, which is the average Al composition ratio of the entire P-type cladding layer 210.

[0101] This allows the refractive index of the N-type first cladding layer 202 to be lower than the refractive index of the P-type cladding layer 210. Therefore, even if the film thickness of the P-type cladding layer 210 is reduced in order to reduce the operating voltage of the nitride-based semiconductor light-emitting device 200, the refractive index of the N-type first cladding layer 202 is lower than the refractive index of the P-type cladding layer 210, and therefore it is possible to prevent the peak of the light intensity distribution in the stacking direction from shifting in a direction approaching the N-type first cladding layer 202 from the active layer 105.

[0102] (Embodiment 3) A nitride-based semiconductor light-emitting device according to embodiment 3 will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from nitride-based semiconductor light-emitting device 200 according to embodiment 2 in the configuration of the active layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below with reference to Figures 19A and 19B, focusing on the differences from nitride-based semiconductor light-emitting device 200 according to embodiment 2.

[0103] Fig. 19A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 300 according to this embodiment. Fig. 19B is a cross-sectional view showing the configuration of an active layer 305 included in the nitride-based semiconductor light-emitting device 300 according to this embodiment.

[0104] 19A , a nitride-based semiconductor light-emitting element 300 according to this embodiment includes a semiconductor stack 300S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor stack 300S includes a substrate 101, an N-type first cladding layer 202, an N-type second cladding layer 103, an N-side guide layer 104, an active layer 305, a P-side first guide layer 106, a P-side second guide layer 107, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 210, and a contact layer 111.

[0105] 19B , the active layer 305 according to the present embodiment has a single quantum well structure, including a single well layer 105 b and barrier layers 105 a and 105 c sandwiching the well layer 105 b. The well layer 105 b has a structure similar to that of the well layer 105 b according to the first embodiment, and the barrier layers 105 a and 105 c have a structure similar to that of the barrier layers 105 a and 105 c according to the first embodiment.

[0106] The nitride-based semiconductor light-emitting device 300 according to this embodiment achieves the same effects as the nitride-based semiconductor light-emitting device 200 according to the second embodiment. In particular, in the nitride-based semiconductor light-emitting device 300 having the single quantum well structure as described above, the active layer 305 has a single well layer 105b. Thus, even in the nitride-based semiconductor light-emitting device 300 having a small number of well layers 105b with a high refractive index, the peak of the light intensity distribution in the stacking direction can be positioned in or near the active layer 305 by the configuration of the N-side guide layer 104, the P-side first guide layer 106, the P-side second guide layer 107, etc. Therefore, the optical confinement factor can be increased.

[0107] (Fourth Embodiment) A nitride-based semiconductor light-emitting device according to the fourth embodiment will be described. The nitride-based semiconductor light-emitting device according to the present embodiment differs from the nitride-based semiconductor light-emitting device 100 according to the first embodiment mainly in the configuration of the P-side guide layer. The nitride-based semiconductor light-emitting device according to the present embodiment will be described below with reference to FIGS. 20A to 27.

[0108] [4-1. Overall Configuration] First, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described with reference to Figures 20A and 20B. Figure 20A is a schematic cross-sectional view showing the overall configuration of nitride-based semiconductor light-emitting device 400 according to this embodiment. Figure 20B is a schematic cross-sectional view showing the configuration of active layer 405 included in nitride-based semiconductor light-emitting device 400 according to this embodiment.

[0109] 20A , the nitride-based semiconductor light-emitting element 400 includes a semiconductor stack 400S, a current blocking layer 412, a P-side electrode 413, and an N-side electrode 414. The semiconductor stack 400S includes a substrate 401, an N-type first cladding layer 402, an N-type second cladding layer 403, an N-side guide layer 404, an active layer 405, a P-side guide layer 406, an intermediate layer 408, an electron barrier layer 409, a P-type cladding layer 410, and a contact layer 411.

[0110] The substrate 401 is a plate-like member that serves as a base for the nitride-based semiconductor light-emitting device 400. In this embodiment, the substrate 401 is an N-type GaN substrate.

[0111] The N-type first cladding layer 402 is an example of an N-type cladding layer disposed above the substrate 401. The N-type first cladding layer 402 has a smaller refractive index than the active layer 405 and a larger band gap energy. In this embodiment, the N-type first cladding layer 402 is a 1200 nm thick N-type Al ０．０２６ Ga ０．９７４ The N-type first cladding layer 402 contains an impurity with a concentration of 1×10 １８ cm －３ is doped with Si.

[0112] The N-type second cladding layer 403 is an example of an N-type cladding layer disposed above the substrate 401. In this embodiment, the N-type second cladding layer 403 is disposed above the N-type first cladding layer 402. The N-type second cladding layer 403 is a layer having a smaller refractive index than the active layer 405 and a larger band gap energy. In this embodiment, the N-type second cladding layer 403 is an N-type GaN layer having a film thickness of 100 nm. The N-type second cladding layer 403 contains impurities at a concentration of 1×10 １８ cm －３ The band gap energy of the N-type second cladding layer 403 is smaller than the band gap energy of the N-type first cladding layer 402 and is equal to or larger than the maximum value of the band gap energy of the P-side guide layer 406.

[0113] The N-side guide layer 404 is an optical guide layer disposed above the N-type second cladding layer 403. The N-side guide layer 404 has a higher refractive index and a smaller band gap energy than the N-type first cladding layer 402 and the N-type second cladding layer 403. In this embodiment, the N-side guide layer 404 is an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ This is the N layer.

[0114] The active layer 405 is a light-emitting layer having a quantum well structure and is disposed above the N-side guide layer 404. In this embodiment, the active layer 405 includes well layers 405b and 405d and barrier layers 405a, 405c, and 405e, as shown in FIG.

[0115] The barrier layer 405a is disposed above the N-side guide layer 404 and functions as a barrier of the quantum well structure. In this embodiment, the barrier layer 405a is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0116] The well layer 405b is disposed above the barrier layer 405a and functions as a well of the quantum well structure. The well layer 405b is disposed between the barrier layer 405a and the barrier layer 405c. In this embodiment, the well layer 405b is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0117] The barrier layer 405c is disposed above the well layer 405b and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 405c is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0118] The well layer 405d is disposed above the barrier layer 405c and functions as a well of the quantum well structure. The well layer 405d is disposed between the barrier layer 405c and the barrier layer 405e. In this embodiment, the well layer 405d is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0119] The barrier layer 405e is disposed above the well layer 405d and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 405e is an undoped In layer having a thickness of 5 nm. ０．０５ Ga ０．９５ This is the N layer.

[0120] In this embodiment, the bandgap energy of each barrier layer is equal to or less than the minimum value of the bandgap energy of the N-side guide layer 404 and the P-side guide layer 406. In other words, the refractive index of each barrier layer is greater than the refractive index of the N-side guide layer 404 and the P-side guide layer 406. Therefore, the optical confinement factor in the active layer 405 can be increased.

[0121] The P-side guide layer 406 is an optical guide layer disposed above the active layer 405. The P-side guide layer 406 has a higher refractive index and a smaller bandgap energy than the P-type cladding layer 410. The bandgap energy of the P-side guide layer 406 increases monotonically with increasing distance from the active layer 405. A configuration in which the bandgap energy increases monotonically also includes a configuration in which a region in which the bandgap energy is constant in the stacking direction exists. The P-side guide layer 406 includes a portion in which the bandgap energy increases continuously with increasing distance from the active layer 405. A configuration in which the bandgap energy increases continuously does not include a configuration in which the bandgap energy changes discontinuously in the stacking direction. In the present disclosure, a configuration in which the bandgap energy increases continuously and monotonically means a configuration in which the discontinuous increase in the bandgap energy at a certain position in the stacking direction is less than 2% of the magnitude of the bandgap energy at that position. For example, a configuration in which the bandgap energy increases continuously does not include a configuration in which the bandgap energy increases stepwise by 2% or more in the stacking direction, but does include a configuration in which the bandgap energy increases stepwise by less than 2% in the stacking direction. In this embodiment, the bandgap energy increases continuously throughout the entire P-side guide layer 406 with increasing distance from the active layer 405, but the configuration of the P-side guide layer 406 is not limited to this. For example, the ratio of the film thickness of the portion in which the bandgap energy increases continuously with increasing distance from the active layer 405 to the entire film thickness of the P-side guide layer 406 may be 50% or more. Alternatively, this ratio may be 70% or more, or 90% or more.

[0122] The increase in the bandgap energy of the P-side guide layer 406 in the stacking direction (ΔEgp) is preferably 100 meV or more. Here, the increase in the bandgap energy of the P-side guide layer 406 in the stacking direction is defined, for example, as the difference between the bandgap energy near the end face of the P-side guide layer 406 closer to the active layer 405 and the bandgap energy near the end face closer to the P-type cladding layer 410. The magnitude of the continuously increasing bandgap energy in ΔEgp may be 70% or more. This proportion may also be 80% or more, or 90% or more.

[0123] The P-side guide layer 406 is In Ｘｐ Ga １－Ｘｐ When the p-side guide layer 406 is made of N, the In composition ratio Xp of the p-side guide layer 406 monotonically decreases with increasing distance from the active layer 405. As a result, the bandgap energy of the p-side guide layer 406 monotonically increases with increasing distance from the active layer 405. Here, a configuration in which the In composition ratio Xp decreases continuously and monotonically includes a configuration in which there is a region in which the In composition ratio Xp is constant in the stacking direction. The p-side guide layer 406 includes a portion in which the In composition ratio Xp decreases continuously with increasing distance from the active layer 405. Here, a configuration in which the In composition ratio Xp decreases continuously does not include a configuration in which the In composition ratio Xp changes discontinuously in the stacking direction. In the present disclosure, a configuration in which the In composition ratio Xp decreases continuously means a configuration in which the discontinuous decrease in the In composition ratio Xp at a certain position in the p-side guide layer 406 in the stacking direction is less than 20% of the In composition ratio Xp at that position.

[0124] The average band gap energy of the P-side guide layer 406 is equal to or greater than the average band gap energy of the N-side guide layer 404. In other words, the average value of the In composition ratio of the N-side guide layer 404 is equal to or greater than the average value of the In composition ratio of the P-side guide layer 406. In this embodiment, the average value of the In composition ratio of the N-side guide layer 404 is greater than the average value of the In composition ratio of the P-side guide layer 406. Furthermore, when the thickness of the P-side guide layer 406 is Tp and the thickness of the N-side guide layer 404 is Tn, the following relationship is satisfied: Tn<Tp (21)

[0125] The maximum value of the In composition ratio in the p-side guide layer 406 is equal to or less than the In composition ratio of each barrier layer.

[0126] In this embodiment, the p-side guide layer 406 is an undoped In layer having a thickness of 280 nm. Ｘｐ Ga １－Ｘｐ More specifically, the P-side guide layer 406 has an In layer near the interface on the side closer to the active layer 405. ０．０４ Ga ０．９６ The p-side guide layer 406 has a composition represented by N, and a composition represented by GaN near the interface far from the active layer 405. The In composition ratio Xp of the p-side guide layer 406 decreases at a constant rate as it becomes farther from the active layer 405.

[0127] The intermediate layer 408 is a layer disposed above the active layer 405. In this embodiment, the intermediate layer 408 is disposed between the P-side guide layer 406 and the electron barrier layer 409, and reduces stress caused by the difference in lattice constant between the P-side guide layer 406 and the electron barrier layer 409. This makes it possible to suppress the occurrence of crystal defects in the nitride-based semiconductor light-emitting element 400. In this embodiment, the intermediate layer 408 is an undoped GaN layer with a thickness of 20 nm.

[0128] The electron barrier layer 409 is a nitride-based semiconductor layer that is disposed above the active layer 405 and contains at least Al. In this embodiment, the electron barrier layer 409 is disposed between the intermediate layer 408 and the P-type cladding layer 410. The electron barrier layer 409 is a 5-nm-thick P-type Al ０．３６ Ga ０．６４ The electron barrier layer 409 contains an impurity of 1×10 １９ cm －３ The electron barrier layer 409 can prevent electrons from leaking from the active layer 405 to the P-type cladding layer 410.

[0129] The P-type cladding layer 410 is a P-type cladding layer disposed above the active layer 405. In this embodiment, the P-type cladding layer 410 is disposed between the electron barrier layer 409 and the contact layer 411. The P-type cladding layer 410 has a lower refractive index and a higher bandgap energy than the active layer 405. The thickness of the P-type cladding layer 410 may be 460 nm or less. This reduces the electrical resistance of the nitride-based semiconductor light-emitting device 400. Therefore, the operating voltage of the nitride-based semiconductor light-emitting device 400 can be reduced. Furthermore, self-heating during operation of the nitride-based semiconductor light-emitting device 400 can be reduced, thereby improving the temperature characteristics of the nitride-based semiconductor light-emitting device 400. Therefore, high-power operation of the nitride-based semiconductor light-emitting device 400 is possible. In the nitride-based semiconductor light-emitting device 400 according to this embodiment, the thickness of the P-type cladding layer 410 may be 200 nm or more in order for the P-type cladding layer 410 to fully function as a cladding layer. The thickness of the P-type cladding layer 410 may be 250 nm or more. In this embodiment, the P-type cladding layer 410 is a P-type Al 1N 2 O 3 layer having a thickness of 450 nm. ０．０２６ Ga ０．９７４ The P-type cladding layer 410 is an N layer. The P-type cladding layer 410 is doped with Mg as an impurity. The impurity concentration at the end of the P-type cladding layer 410 closer to the active layer 405 is lower than the impurity concentration at the end farther from the active layer 405. Specifically, the P-type cladding layer 410 has an impurity concentration of 2×10 １８ cm －３ P-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 300 nm ０．０２６ Ga ０．９７４ N layers.

[0130] A ridge 410R is formed in the P-type cladding layer 410 of the nitride-based semiconductor light-emitting device 400. Two grooves 410T are formed in the P-type cladding layer 410, arranged along the ridge 410R and extending in the Y-axis direction. In this embodiment, the ridge width W is approximately 30 μm. As shown in FIG. 20A , the distance between the lower end of the ridge 410R (i.e., the bottom of the groove 410T) and the active layer 405 is defined as dp. The film thickness of the P-type cladding layer 410 at the lower end of the ridge 410R (i.e., the distance between the lower end of the ridge 410R and the interface between the P-type cladding layer 410 and the electron barrier layer 409) is defined as dc.

[0131] The contact layer 411 is disposed above the P-type cladding layer 410 and is in ohmic contact with the P-side electrode 413. In this embodiment, the contact layer 411 is a P-type GaN layer with a film thickness of 60 nm. The contact layer 411 contains impurities with a concentration of 1×10 ２０ cm －３ It is doped with Mg.

[0132] The current blocking layer 412 is disposed above the P-type cladding layer 410 and is an insulating layer that is transparent to light from the active layer 405. The current blocking layer 412 is disposed on the upper surface of the P-type cladding layer 410 in a region other than the upper surface of the ridge 410R. In this embodiment, the current blocking layer 412 is made of SiO ２ It is a layer.

[0133] The P-side electrode 413 is a conductive layer disposed above the semiconductor stack 400S. In the present embodiment, the P-side electrode 413 is disposed above the contact layer 411 and the current blocking layer 412, and is in contact with the contact layer 411. In the present embodiment, the P-side electrode 413 contains Ag.

[0134] The N-side electrode 414 is a conductive layer disposed below the substrate 401. The N-side electrode 414 is, for example, a single-layer film or a multi-layer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au.

[0135] 20A , the nitride-based semiconductor light-emitting element 400 has the above-described configuration, and therefore an effective refractive index difference ΔN occurs between the portion below the ridge 410R and the portion below the groove 410T, which allows light generated in the portion of the active layer 405 below the ridge 410R to be confined in the horizontal direction (i.e., the X-axis direction).

[0136] 4-2. Stability of Light Intensity Distribution and Light Output Next, the stability of light intensity distribution and light output of the nitride-based semiconductor light-emitting element 400 according to this embodiment will be described.

[0137] The light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting element 400 according to this embodiment will be described below with reference to Fig. 21. Fig. 21 is a schematic graph showing the distribution of band gap energy in the active layer 405 and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting element 400 according to this embodiment.

[0138] In the nitride-based semiconductor light-emitting device 400 according to this embodiment, the thickness of the P-type cladding layer 410 is set to be relatively thin in order to reduce the operating voltage. Accordingly, the height of the ridge 410R (i.e., the height of the ridge 410R from the bottom surface of the groove 410T) is also set to be relatively low. In general, in a semiconductor light-emitting device having such a configuration, the peak position of the light intensity distribution in the stacking direction shifts from the active layer 405 toward the N-type second cladding layer 403. This reduces the optical confinement factor in the active layer, and therefore reduces the thermal saturation level of the optical output. This makes it difficult for the semiconductor light-emitting device to operate at high output. In this embodiment, as shown in FIG. 21 , the average bandgap energy of the P-side guide layer 406 is equal to or greater than the average bandgap energy of the N-side guide layer 404. Meanwhile, the thickness Tp of the P-side guide layer 406 is greater than the thickness Tn of the N-side guide layer 404 (see the above inequality (21)). In this way, by increasing the film thickness of the P-side guide layer 406, which has a refractive index higher than that of each cladding layer, it is possible to shift the light intensity distribution in a direction from the active layer 405 toward the P-side guide layer 406. Therefore, with the nitride-based semiconductor light-emitting element 400 according to this embodiment, it is possible to control the peak of the light intensity distribution in the stacking direction so that it is located in the active layer 405.

[0139] Furthermore, in this embodiment, the P-side guide layer 406 has a portion in which the band gap energy increases continuously and monotonically with increasing distance from the active layer 405. In other words, the P-side guide layer 406 has a portion in which the refractive index increases continuously and monotonically with increasing distance from the active layer 405. Since the refractive index of the P-side guide layer 406 increases with increasing distance from the active layer 405, the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 405.

[0140] In this embodiment, the barrier layers 405a, 405c, and 405e of the active layer 405 are made of In. Ｘｂ Ga １－ＸｂThe In composition ratios Xb, Xn, and Xp of each barrier layer, the N-side guide layer 404, and the P-side guide layer 406 satisfy the following relationships: Xp≦Xb (22) Xn≦Xb (23). As a result, the bandgap energy of each barrier layer is equal to or less than the minimum value of the bandgap energy of the N-side guide layer 404 and the P-side guide layer 406. That is, the refractive index of each barrier layer can be equal to or greater than the maximum value of the P-side guide layer 406 and the N-side guide layer 404. As a result, the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 405. Furthermore, excessive movement of the light intensity distribution from the active layer 405 toward the P-type cladding layer 410 can be suppressed. This effect can be further enhanced by making the refractive index of each barrier layer greater than the maximum value of the P-side guide layer 406 and the N-side guide layer 404.

[0141] With the above-described configuration, in this embodiment, the position PS1 of the peak of the light intensity distribution in the stacking direction below the ridge 410R can be set to 1.3 nm. In other words, the peak of the light intensity distribution can be positioned in the well layer 405b of the active layer 405. Furthermore, ΔP can be suppressed to 5.6 nm. This allows the light confinement factor in the active layer 405 to be increased to approximately 1.49%.

[0142] As described above, according to the nitride-based semiconductor light-emitting element 400 of this embodiment, the peak of the light intensity distribution in the stacking direction can be positioned in the active layer 405. Note that, "the peak of the light intensity distribution in the stacking direction is positioned in the active layer 405" means that the peak of the light intensity distribution in the stacking direction is positioned in the active layer 405 at least one position in the horizontal direction of the nitride-based semiconductor light-emitting element 400, and is not limited to a state in which the peak of the light intensity distribution in the stacking direction is positioned in the active layer 405 at all positions in the horizontal direction.

[0143] When the peak of the light intensity distribution in the stacking direction is positioned in the active layer 405 as in this embodiment, the proportion of the light located in the P-type cladding layer 410 can be increased compared to when the peak of the light intensity distribution is positioned in the N-side guide layer 404. Here, since the P-type cladding layer 410 has a higher impurity concentration than the N-type first cladding layer 402 and the N-type second cladding layer 403, the proportion of the light located in the P-type cladding layer 410 increases, which raises concerns about an increase in free carrier loss in the P-type cladding layer 410. However, in this embodiment, the P-side guide layer 406 is an undoped layer, and the thickness Tp of the P-side guide layer 406 is relatively large, thereby increasing the proportion of the light intensity distribution located in the undoped layer. Therefore, an increase in free carrier loss can be suppressed. Specifically, in this embodiment, the waveguide loss is reduced to 3.2 cm －１ It can be suppressed to a certain extent.

[0144] Furthermore, in the nitride-based semiconductor light-emitting device 400 according to this embodiment, in order to reduce the spread angle of the emitted light in the horizontal direction (i.e., the X-axis direction), the effective refractive index difference ΔN between the portion below the ridge 410R and the portion below the groove 410T is set to be relatively small. Specifically, the effective refractive index difference ΔN is set by adjusting the distance dp (see FIG. 20A ) between the current blocking layer 412 and the active layer 405. Here, the greater the distance dp, the smaller the effective refractive index difference ΔN. In this embodiment, the effective refractive index difference ΔN is 2.1×10 －３ Therefore, in this embodiment, the effective refractive index difference ΔN is about 2.1×10 －３When the ridge 410R is larger than the ridge 410R, the number of higher-order modes (i.e., higher-order transverse modes) that can propagate through the waveguide formed by the ridge 410R is smaller. Therefore, the proportion of each higher-order mode among all transverse modes included in the emitted light from the nitride-based semiconductor light-emitting element 400 becomes relatively large. Therefore, the increase or decrease in the number of modes and the change in the optical confinement factor in the active layer 405 due to inter-mode coupling become relatively large. Therefore, when the increase or decrease in the number of modes and inter-mode coupling occur in the nitride-based semiconductor light-emitting element 400, the linearity of the IL characteristics deteriorates. In other words, a kink occurs in the graph showing the IL characteristics. This may result in a decrease in the stability of the light output from the nitride-based semiconductor light-emitting element 400.

[0145] The nitride-based semiconductor light-emitting device 400 according to this embodiment includes the N-side guide layer 404 and the P-side guide layer 406 having the above-described configuration, and therefore the peak of the light intensity distribution can be positioned in the active layer 405 both below the ridge 410R and below the trench 410T. That is, the difference ΔP between the positions PS1 and PS2 of the light intensity distribution peaks can be reduced. As a result, even if the number of modes increases or decreases and inter-mode coupling occurs, fluctuations in the position in the stacking direction of the peak of the light intensity distribution obtained by adding the light intensity distributions below both the ridge 410R and the trench 410T can be suppressed. Therefore, the stability of the light output can be improved.

[0146] As described above, the distance dp is set to a relatively large value in order to set the effective refractive index difference ΔN to a relatively small value. When the distance dp is set, if the lower end of the ridge 410R (i.e., the bottom of the groove 410T) is set to be lower than the electron barrier layer 409, the electron barrier layer 409 has a large bandgap energy, so holes injected from the contact layer 411 tend to leak from the sidewall of the ridge 410R to the outside of the ridge 410R when passing through the electron barrier layer 409. As a result, the holes flow downward into the groove 410T. Accordingly, the light distribution intensity is low in the active layer 405 below the groove 410T, reducing the probability of radiative recombination between electrons and holes injected into the active layer 405 and increasing non-radiative recombination. Such an increase in non-radiative recombination makes the nitride-based semiconductor light-emitting element 400 more susceptible to degradation. To suppress such degradation, the lower end of the ridge 410R is set to be higher than the electron barrier layer 409. Furthermore, if the distance dc (see FIG. 20A ) from the bottom end of the ridge 410R to the electron barrier layer 409 becomes too large, holes will flow from the ridge 410R into between the groove 410T and the electron barrier layer 409, resulting in leakage current. To prevent this leakage current from increasing, the distance dc is set to as small a value as possible. The distance dc is, for example, 10 nm or more and 70 nm or less.

[0147] 22 to 24, the effects of the respective guide layers of the nitride-based semiconductor light-emitting element 400 according to the present embodiment will be described in comparison with those of comparative nitride-based semiconductor light-emitting elements. FIG. 22 is a graph showing the refractive index distribution and light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting elements of Comparative Examples 7 to 9 and the nitride-based semiconductor light-emitting element 400 according to the present embodiment. Graphs (a) to (c) of FIG. 22 show the refractive index distribution and light intensity distribution of the nitride-based semiconductor light-emitting elements of Comparative Examples 7 to 9, respectively. Graph (d) of FIG. 22 shows the refractive index distribution and light intensity distribution of the nitride-based semiconductor light-emitting element 400 according to the present embodiment. In each graph of FIG. 22, the refractive index distribution is shown by a solid line, and the light intensity distribution is shown by a dashed line.

[0148] 23 is a graph showing the simulation results of the distribution of valence charge potential and hole Fermi level in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9 and the nitride-based semiconductor light-emitting device 400 according to this embodiment. Graphs (a) to (c) of Fig. 23 show the distribution of valence charge potential and hole Fermi level of the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9, respectively. Graph (d) of Fig. 23 shows the distribution of valence charge potential and hole Fermi level of the nitride-based semiconductor light-emitting device 400 according to this embodiment. In each graph of Fig. 23, the valence charge potential is shown by a solid line, and the hole Fermi level is shown by a dashed line.

[0149] 24 is a graph showing the results of a simulation of the carrier concentration distribution in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9, and the nitride-based semiconductor light-emitting device 400 according to the present embodiment. Graphs (a) to (c) of Fig. 24 show the carrier concentration distribution of the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9, respectively. Graph (d) of Fig. 24 shows the carrier concentration distribution of the nitride-based semiconductor light-emitting device 400 according to the present embodiment. In each graph of Fig. 24, the electron concentration distribution is shown by a solid line, and the hole concentration distribution is shown by a dashed line.

[0150] The nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9 differ from the nitride-based semiconductor light-emitting device 400 according to the present embodiment in the configurations of the N-side guide layer and the P-side guide layer. The nitride-based semiconductor light-emitting device of Comparative Example 7 shown in graph (a) of FIG. 22 has an undoped In ０．０４ Ga ０．９６ The N-side guide layer 2104 is made of an N layer, and the undoped In layer 2105 is made of an N layer. ０．０４ Ga ０．９６ The nitride-based semiconductor light-emitting device of Comparative Example 8 shown in graph (b) of FIG. 22 includes an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ The N-side guide layer 2204 is made of an N layer, and the undoped In layer 2205 is made of an N layer. ０．０４ Ga ０．９６The nitride-based semiconductor light-emitting device of Comparative Example 9 shown in graph (c) of FIG. 22 includes an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ The nitride-based semiconductor light-emitting device of Comparative Example 9 includes an N-side guide layer 2304 made of an N layer and a P-side guide layer 2306 having a thickness of 280 nm. The P-side guide layer 2306 of the nitride-based semiconductor light-emitting device of Comparative Example 9 is an undoped InP layer having a thickness of 140 nm arranged above the active layer 405. ０．０４ Ga ０．９６ A P-side first guide layer 2306a made of an N layer and an undoped In layer having a thickness of 140 nm are disposed above the P-side first guide layer 2306a. ０．０２ Ga ０．９８ and a P-side second guide layer 2306b made of an N layer. In the nitride-based semiconductor light-emitting devices of Comparative Examples 7 to 9, the P-side electrode is made of Pd instead of Ag.

[0151] In the nitride-based semiconductor light-emitting device of Comparative Example 7, the N-side guide layer 2104 and the P-side guide layer 2106 have the same composition, and the N-side guide layer 2104 is thicker than the P-side guide layer 2106. Therefore, in the nitride-based semiconductor light-emitting device of Comparative Example 7, the peak of the light intensity distribution in the stacking direction is located in the N-side guide layer 2104, as shown in graph (a) of FIG. 22 . Therefore, the nitride-based semiconductor light-emitting device of Comparative Example 7 has a low optical confinement factor of 1.33%. Furthermore, as shown in graph (a) of FIG. 23 , in the P-side guide layer 2106, in order to conduct holes from the P-side guide layer 2106 to the active layer 405, the hole Fermi level increases from the interface of the P-side guide layer 2106 farther from the active layer 405 to the interface closer to the active layer 405. Meanwhile, the valence electron charge potential is substantially constant in the stacking direction of the P-side guide layer 2106. Therefore, the difference between the hole Fermi level and the valence electron charge potential in the P-side guide layer 2106 increases with increasing distance from the active layer 405. Therefore, as shown in graph (a) of FIG. 24 , the concentration of holes and electrons in the stacking direction of the P-side guide layer 2106, i.e., the free carrier concentration, increases with increasing distance from the active layer 405. As described above, in the nitride-based semiconductor light-emitting device of Comparative Example 7, the free carrier concentration in the stacking direction of the P-side guide layer 2106 cannot be reduced, and therefore reduction in free carrier loss and reduction in the probability of non-radiative recombination cannot be achieved. In the nitride-based semiconductor light-emitting device of Comparative Example 7, the effective refractive index difference ΔN is 3.6×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are −34.1 nm and −75.6 nm, respectively, and the difference ΔP is 41.5 nm. The waveguide loss is 4.5 cm －１ The free carrier loss in the N-side guide layer 2104 and the P-side guide layer 2106 (hereinafter also referred to as "guide layer free carrier loss") is 2.8 cm －１ is.

[0152] In the nitride-based semiconductor light-emitting device of Comparative Example 8, the thickness of the P-side guide layer 2206 is greater than the thickness of the N-side guide layer 2204. Therefore, as shown in graph (b) of FIG. 22 , the peak of the light intensity distribution in the stacking direction is closer to the active layer 405 than in the nitride-based semiconductor light-emitting device of Comparative Example 7. Therefore, in the nitride-based semiconductor light-emitting device of Comparative Example 8, the optical confinement factor is 1.37%, which is slightly improved compared to the nitride-based semiconductor light-emitting device of Comparative Example 7. However, as shown in graph (b) of FIG. 23 , similar to Comparative Example 7, the difference between the hole Fermi level and the valence electron charge potential in the P-side guide layer 2206 increases with increasing distance from the active layer 405. Therefore, as shown in graph (b) of FIG. 24 , the concentration of holes and electrons in the stacking direction of the P-side guide layer 2206, i.e., the free carrier concentration, increases with increasing distance from the active layer 405. In this way, since the free carrier concentration in the stacking direction of the P-side guide layer 2206 cannot be reduced, the nitride-based semiconductor light-emitting device of Comparative Example 8 cannot achieve a reduction in free carrier loss and a reduction in the probability of non-radiative recombination. In the nitride-based semiconductor light-emitting device of Comparative Example 8, the effective refractive index difference ΔN is 3.3×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 31.3 nm and 10.8 nm, respectively, and the difference ΔP is 20.5 nm. The waveguide loss is 5.2 cm －１ and the guide layer free carrier loss is 3.6 cm －１ is.

[0153] In the nitride-based semiconductor light-emitting device of Comparative Example 9, the refractive index of the P-side second guide layer 2306b, which is a region of the P-side guide layer 2306 far from the active layer 405, is made smaller than the refractive index of the P-side first guide layer 2306a, which is a region close to the active layer 405. As a result, as shown in graph (c) of FIG. 22 , the peak of the light intensity distribution in the stacking direction is closer to the active layer 405 than in the nitride-based semiconductor light-emitting device of Comparative Example 8. Therefore, in the nitride-based semiconductor light-emitting device of Comparative Example 9, the optical confinement factor is 1.47%, which is further improved than in the nitride-based semiconductor light-emitting device of Comparative Example 8. However, at the heterobarrier at the interface between the P-side first guide layer 2306a and the P-side second guide layer 2306b, a spike-shaped region is generated in the distribution of valence electron charge potential due to piezoelectric polarization charges, as shown in graph (c) of FIG. 24(c), the electron concentration in the stacking direction of the P-side guide layer 2306 increases in a spike-like manner in the portion where the valence electron charge potential changes discontinuously. １７ cm －３ In this way, since the free carrier concentration in the stacking direction of the P-side guide layer 2306 cannot be reduced, the nitride-based semiconductor light-emitting device of Comparative Example 9 cannot realize a reduction in free carrier loss and a reduction in the probability of non-radiative recombination. In the nitride-based semiconductor light-emitting device of Comparative Example 9, the effective refractive index difference ΔN is 2.5×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 10.7 nm and 4.4 nm, respectively, and the difference ΔP is 6.3 nm. The waveguide loss is 3.93 cm －１ and the guide layer free carrier loss is 2.56 cm －１ is.

[0154] In the nitride-based semiconductor light-emitting device 400 according to this embodiment, as shown in graph (d) of FIG. 22 , the refractive index of the P-side guide layer 406 increases toward the active layer 405, so that the peak of the light intensity distribution in the stacking direction can be moved closer to the active layer 405. Therefore, in the nitride-based semiconductor light-emitting device 400 according to this embodiment, the optical confinement factor is 1.49%, which is further improved compared to the nitride-based semiconductor light-emitting device of Comparative Example 9. Furthermore, since the bandgap energy of the P-side guide layer 406 continuously and monotonically increases with increasing distance from the active layer 405, the valence charge potential continuously decreases with increasing distance from the active layer 405, as shown in graph (d) of FIG. 23 . This makes it possible to maintain a substantially constant difference between the hole Fermi level and the valence charge potential in the P-side guide layer 406. Therefore, as shown in graph (d) of FIG. 24 , the hole and electron concentrations in the stacking direction of the P-side guide layer 406 can be reduced and maintained substantially constant. Here, if the increase in the bandgap energy of the P-side guide layer 406 in the stacking direction (ΔEgp) is small, the effect will be small, so ΔEgp should be 100 meV or more. Conversely, if ΔEgp is made too large, the bandgap energy of the P-side guide layer 406 at the end on the active layer 405 side may become small. In this case, the gradient of the valence electron charge potential of the P-side guide layer 406 becomes too large, causing a leakage current in which holes injected into the active layer 405 leak toward the N-side guide layer 404. Therefore, ΔEgp may be 400 meV or less.

[0155] In this way, the free carrier concentration in the stacking direction of the P-side guide layer 406 can be reduced, and therefore, in the nitride-based semiconductor light-emitting element 400 according to this embodiment, it is possible to achieve a reduction in free carrier loss and a reduction in the probability of non-radiative recombination.

[0156] Furthermore, in the nitride-based semiconductor light-emitting element 400 according to the present embodiment, the P-side electrode 413 contains Ag, similarly to the nitride-based semiconductor light-emitting element 100 according to embodiment 1. This makes it possible to reduce optical loss in the P-side electrode 413 and to improve the efficiency of the nitride-based semiconductor light-emitting element 400.

[0157] In the nitride-based semiconductor light-emitting device 400 according to this embodiment, the effective refractive index difference ΔN is 2.1×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 1.3 nm and -4.3 nm, respectively, and the difference ΔP is 5.6 nm. In this way, in this embodiment, the position PS1 and the difference ΔP can be reduced, so that non-linear portions are less likely to occur in the graph showing the IL characteristics. In addition, the waveguide loss is 3.0 cm －１ and the guide layer free carrier loss is 1.8 cm －１ As described above, in this embodiment, the waveguide loss and the free carrier loss can be reduced compared to the comparative examples.

[0158] [4-3-2. Barrier Layers] Next, the effects of the configuration of each barrier layer of the active layer 405 according to this embodiment will be described in comparison with a comparative example. In this embodiment, as described above, the bandgap energy of each barrier layer is equal to or less than the minimum value of the bandgap energy of the N-side guide layer 404 and the P-side guide layer 406. Here, the results of a simulation of a nitride-based semiconductor light-emitting device of Comparative Example 10, in which the composition of each barrier layer is undoped GaN, the bandgap energy of each barrier layer is equal to or greater than the minimum value of the bandgap energy of the N-side guide layer 404 and the P-side guide layer 406, and the other configuration is the same as that of the nitride-based semiconductor light-emitting device 400 according to this embodiment, are shown. The nitride-based semiconductor light-emitting device of Comparative Example 10 has an optical confinement coefficient of 1.39% and an effective refractive index difference ΔN of 2.3×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 0.35 nm and −21.9 nm, respectively, and the difference ΔP is 22.3 nm. The waveguide loss is 3.4 cm －１ The free carrier loss in the N-side guide layer and the P-side guide layer is 1.84 cm －１As described above, in the nitride-based semiconductor light-emitting device of Comparative Example 10, the band gap energy of each barrier layer is large, that is, the refractive index of each barrier layer is small, so the optical confinement factor is smaller than that of nitride-based semiconductor light-emitting device 400 according to the present embodiment. Accordingly, the other evaluation indexes of the nitride-based semiconductor light-emitting device of Comparative Example 10 are also worse than those of nitride-based semiconductor light-emitting device 400 according to the present embodiment, except for position PS1.

[0159] As described above, in the nitride-based semiconductor light-emitting device 400 according to this embodiment, the optical confinement factor can be increased by setting the band gap energy of each barrier layer to be equal to or less than the minimum value of the band gap energy of the N-side guide layer 404 and the P-side guide layer 406. Accordingly, the difference ΔP can be reduced, and non-linear portions are less likely to occur in the graph showing the IL characteristics.

[0160] 25 and 26, the film thickness of the P-type cladding layer 410 according to this embodiment will be described. Fig. 25 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting device of Comparative Example 11 and each numerical value obtained by simulation. Fig. 26 is a diagram showing the relationship between the film thickness of the P-type cladding layer 410 of the nitride-based semiconductor light-emitting device 400 according to this embodiment and each numerical value obtained by simulation.

[0161] The nitride-based semiconductor light-emitting device of Comparative Example 11 differs from the nitride-based semiconductor light-emitting device 400 according to the present embodiment in that the P-side electrode is made of Pd instead of Ag, but is identical in other respects. １９ cm －３ Mg-doped P-type Al ０．０３５ Ga ０．９６５ By changing the thickness of the N layer, the thickness of the entire P-type cladding layer 410 was changed to 0.45 μm, 0.35 μm, 0.25 μm, and 0.20 μm.

[0162] 25 and 26 , there is no significant difference between Comparative Example 11 and the present embodiment in terms of the values ​​other than the waveguide loss, but the waveguide loss is significantly different between Comparative Example 11 and the present embodiment. Specifically, as the thickness of the P-type cladding layer 410 decreases, the waveguide loss increases in Comparative Example 11. This is because as the thickness of the P-type cladding layer 410 decreases, light seeps into the P-side electrode made of Pd, causing light loss. On the other hand, in the present embodiment, even if the thickness of the P-type cladding layer 410 decreases, light seeps into the P-side electrode 413 containing Ag can be suppressed, so the waveguide loss hardly increases.

[0163] In this way, in the nitride-based semiconductor light-emitting element 400 according to this embodiment, by providing the P-side electrode 413 containing Ag, it is possible to suppress an increase in waveguide loss even when the P-type cladding layer 410 is thinned to about 200 nm.

[0164] Fifth Embodiment A nitride-based semiconductor light-emitting device according to the fifth embodiment will be described. The nitride-based semiconductor light-emitting device according to the fifth embodiment differs from the nitride-based semiconductor light-emitting device 400 according to the fourth embodiment in the band gap energy distribution of the P-side guide layer. The nitride-based semiconductor light-emitting device according to the present embodiment will be described below, focusing on the differences from the nitride-based semiconductor light-emitting device 400 according to the fourth embodiment.

[0165] 27 and 28, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described. Fig. 27 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 500 according to this embodiment. Fig. 28 is a schematic graph showing the distribution of band gap energy in the active layer 405 and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device 500 according to this embodiment.

[0166] 27 , a nitride-based semiconductor light-emitting element 500 according to this embodiment includes a semiconductor stack 500S, a current blocking layer 412, a P-side electrode 413, and an N-side electrode 414. The semiconductor stack 500S includes a substrate 401, an N-type first cladding layer 402, an N-type second cladding layer 403, an N-side guide layer 404, an active layer 405, a P-side guide layer 506, an intermediate layer 408, an electron barrier layer 409, a P-type cladding layer 410, and a contact layer 411.

[0167] In the P-side guide layer 506, similarly to the P-side guide layer 406 according to the fourth embodiment, the band gap energy of the P-side guide layer 506 increases monotonically with increasing distance from the active layer 405. The P-side guide layer 506 also includes a portion in which the band gap energy increases continuously with increasing distance from the active layer 405. In this embodiment, the P-side guide layer 506 is made of undoped In Ｘｐ Ga １－Ｘｐ The P-side guide layer 506 is an N layer, and the average rate of change in the In composition ratio in the stacking direction in a region from the interface of the P-side guide layer 506 closer to the active layer 405 to the center of the P-side guide layer 506 in the stacking direction is greater than the average rate of change in the In composition ratio in the stacking direction in a region from the center to the interface of the P-side guide layer 506 closer to the P-type cladding layer 410. In other words, the curve showing the relationship between the position in the stacking direction of the P-side guide layer 506 and the In composition ratio has a downward convex shape. In further words, the curve showing the relationship between the position in the stacking direction of the P-side guide layer 506 and the band gap energy has an upward convex shape (see FIG. 28 ).

[0168] In this embodiment, the P-side guide layer 506 includes a P-side first guide layer 506a and a P-side second guide layer 506b. The P-side first guide layer 506a is an undoped InP layer having a thickness of 140 nm. Ｘｐ Ga １－Ｘｐ More specifically, the P-side first guide layer 506a is an In layer near the interface on the side closer to the active layer 405. Ｘｐ１ Ga １－Ｘｐ１ N, and in the vicinity of the interface farther from the active layer 405 Ｘｐｍ Ga １－ＸｐｍThe P-side first guide layer 506a has a composition represented by the formula: In composition ratio Xp of the P-side first guide layer 506a decreases at a constant rate as it moves away from the active layer 405. The P-side second guide layer 506b has a thickness of 140 nm and is made of undoped In Ｘｐ Ga １－Ｘｐ More specifically, the P-side second guide layer 506b is an In layer near the interface on the side closer to the active layer 405. Ｘｐｍ Ga １－Ｘｐｍ N, and in the vicinity of the interface farther from the active layer 405 Ｘｐ２ Ga １－Ｘｐ２ N. The In composition ratio Xp of the P-side second guide layer 506b decreases at a constant rate with increasing distance from the active layer 405. In this embodiment, Xp1=0.04, Xpm=0.02, and Xp2=0.

[0169] [5-2. Effects] [5-2-1. Free Carrier Loss] Next, the free carrier loss reduction effect of the nitride-based semiconductor light-emitting element 500 according to this embodiment will be described with reference to Fig. 29 and Fig. 30. Fig. 29 is a graph showing the simulation results of the distribution of valence electron charge potential and hole Fermi level in the stacking direction of the nitride-based semiconductor light-emitting element 500 according to this embodiment. Fig. 30 is a graph showing the simulation results of the distribution of carrier concentration in the stacking direction of the nitride-based semiconductor light-emitting element 500 according to this embodiment.

[0170] 29 , in the nitride-based semiconductor light-emitting device 500 according to this embodiment, the curve representing the valence charge potential in the P-side guide layer 506 can be made convex downward. Here, the curve representing the hole Fermi level in the P-side guide layer 506 has a convex downward shape. Therefore, by making the curve representing the valence charge potential in the P-side guide layer 506 convex downward, the difference between the hole Fermi level and the valence charge potential in the P-side guide layer 506 can be made more uniform than in the P-side guide layer 406 according to the fourth embodiment. Therefore, as shown in FIG. 30 , the hole concentration can be reduced in the P-side guide layer 506, particularly in a region close to the active layer 405. This further reduces free carrier loss in the P-side guide layer 506.

[0171] [5-2-2. Barrier Layers] Next, the effects of the configuration of each barrier layer of the active layer 405 according to this embodiment will be described in comparison with a comparative example. In this embodiment, the band gap energy of each barrier layer is equal to or less than the minimum value of the band gap energy of the N-side guide layer 404 and the P-side guide layer 506. This can increase the optical confinement factor. As a result, the difference ΔP can be reduced, making it less likely that a non-linear portion will occur in a graph showing the IL characteristics.

[0172] Sixth Embodiment A nitride-based semiconductor light-emitting device according to the sixth embodiment will be described. The nitride-based semiconductor light-emitting device according to the sixth embodiment differs from nitride-based semiconductor light-emitting device 400 according to the fourth embodiment in the relationship between the Al composition ratios of the N-type first cladding layer and the P-type cladding layer, and in the configuration of the electron barrier layer. The nitride-based semiconductor light-emitting device according to the sixth embodiment will be described below with reference to FIG. 31 , focusing on the differences from nitride-based semiconductor light-emitting device 400 according to the fourth embodiment.

[0173] FIG. 31 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 600 according to this embodiment.

[0174] 31 , a nitride-based semiconductor light-emitting element 600 according to this embodiment includes a semiconductor stack 600S, a current blocking layer 412, a P-side electrode 413, and an N-side electrode 414. The semiconductor stack 600S includes a substrate 401, an N-type first cladding layer 602, an N-type second cladding layer 403, an N-side guide layer 404, an active layer 405, a P-side guide layer 406, an intermediate layer 408, an electron barrier layer 609, a P-type cladding layer 410, and a contact layer 411.

[0175] The N-type first cladding layer 602 according to this embodiment is an N-type Al 1N 2 O 3 layer having a thickness of 1200 nm. ０．０３６ Ga ０．９６４ The N-type first cladding layer 602 contains an impurity with a concentration of 1×10 １８ cm －３ is doped with Si.

[0176] The P-type cladding layer 410 according to this embodiment is a P-type Al layer having a thickness of 450 nm as described above.０．０２６ Ga ０．９７４ This is the N layer.

[0177] In this embodiment, the N-type first cladding layer 602 and the P-type cladding layer 410 contain Al, and when the Al composition ratios of the N-type first cladding layer 602 and the P-type cladding layer 410 are Ync and Ypc, respectively, the relationship Ync>Ypc (24) is satisfied.

[0178] Here, when at least one of the N-type first cladding layer 602 and the P-type cladding layer 410 has a superlattice structure, the composition ratios Ync and Ypc represent average Al composition ratios. For example, when the N-type first cladding layer 602 includes multiple 2-nm-thick GaN layers and multiple 2-nm-thick AlGaN layers with an Al composition ratio of 0.07, and the multiple GaN layers and the multiple AlGaN layers are alternately stacked, Ync is 0.035, which is the average Al composition ratio of the entire N-type first cladding layer 602. When the P-type cladding layer 410 includes multiple 2-nm-thick GaN layers and multiple 2-nm-thick AlGaN layers with an Al composition ratio of 0.07, and the multiple GaN layers and the multiple AlGaN layers are alternately stacked, Ypc is 0.035, which is the average Al composition ratio of the entire P-type cladding layer 410.

[0179] This allows the refractive index of the N-type first cladding layer 602 to be lower than the refractive index of the P-type cladding layer 410. Therefore, even if the film thickness of the P-type cladding layer 410 is reduced in order to reduce the operating voltage of the nitride-based semiconductor light-emitting device 600, the refractive index of the N-type first cladding layer 602 is lower than the refractive index of the P-type cladding layer 410, and therefore it is possible to prevent the peak of the light intensity distribution in the stacking direction from shifting in a direction approaching from the active layer 405 toward the N-type first cladding layer 602.

[0180] The electron barrier layer 609 is disposed above the active layer 405 and is a nitride-based semiconductor layer containing at least Al. In this embodiment, the electron barrier layer 609 is disposed between the intermediate layer 408 and the P-type cladding layer 410. The electron barrier layer 609 is a P-type AlGaN layer with a thickness of 5 nm. The electron barrier layer 609 also has an Al composition ratio increasing region in which the Al composition ratio monotonically increases toward the P-type cladding layer 410. Here, the configuration in which the Al composition ratio monotonically increases also includes a configuration including a region in which the Al composition ratio is constant in the stacking direction. For example, the configuration in which the Al composition ratio monotonically increases also includes a configuration in which the Al composition ratio increases stepwise. In the electron barrier layer 609 according to this embodiment, the entire electron barrier layer 609 is an Al composition ratio increasing region, and the Al composition ratio increases at a constant rate of change in the stacking direction. Specifically, the electron barrier layer 609 has an Al composition ratio increasing region near the interface with the intermediate layer 408. ０．０２ Ga ０．９８ The Al composition ratio increases monotonically as the layer approaches the P-type cladding layer 410. ０．３６ Ga ０．６４ The electron barrier layer 609 contains impurities at a concentration of 1×10 １９ cm －３ It is doped with Mg.

[0181] The electron barrier layer 609 can prevent electrons from leaking from the active layer 405 to the P-type cladding layer 410. Furthermore, since the electron barrier layer 609 has an Al composition ratio increasing region where the Al composition ratio monotonically increases, the potential barrier of the valence band of the electron barrier layer 609 can be reduced compared to when the Al composition ratio is uniform. This facilitates the flow of holes from the P-type cladding layer 410 to the active layer 405. Therefore, even when the P-side guide layer 406, which is an undoped layer, has a large thickness, as in this embodiment, an increase in the electrical resistance of the nitride-based semiconductor light-emitting element 600 can be suppressed. This allows the operating voltage of the nitride-based semiconductor light-emitting element 600 to be reduced. Furthermore, self-heating of the nitride-based semiconductor light-emitting element 600 during operation can be reduced, thereby improving the temperature characteristics of the nitride-based semiconductor light-emitting element 600. Therefore, high-power operation of the nitride-based semiconductor light-emitting element 600 is possible.

[0182] According to this embodiment, the effective refractive index difference ΔN is 1.9×10 －３ The position PS1 is 5.3 nm, the difference ΔP is 4.2 nm, the optical confinement factor in the active layer 405 is 1.55%, and the waveguide loss is 3.6 cm －１ and the guide layer free carrier loss is 2.4 cm －１ Thus, a nitride-based semiconductor light-emitting device 600 can be realized.

[0183] Seventh Embodiment A nitride-based semiconductor light-emitting device according to the seventh embodiment will be described. The nitride-based semiconductor light-emitting device according to the present embodiment differs from nitride-based semiconductor light-emitting device 400 according to the fourth embodiment mainly in the configuration of the P-type cladding layer. The nitride-based semiconductor light-emitting device according to the present embodiment will be described below with reference to FIG. 32 , focusing on the differences from nitride-based semiconductor light-emitting device 400 according to the fourth embodiment.

[0184] 32 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 700 according to this embodiment. As shown in FIG. 32 , the nitride-based semiconductor light-emitting device 700 according to this embodiment includes a semiconductor stack 700S, a current blocking layer 412, a P-side electrode 413, and an N-side electrode 414. The semiconductor stack 700S includes a substrate 401, an N-type first cladding layer 402, an N-type second cladding layer 403, an N-side guide layer 404, an active layer 405, a P-side guide layer 406, an intermediate layer 408, an electron barrier layer 709, a P-type cladding layer 710, and a contact layer 411.

[0185] The electron barrier layer 709 according to this embodiment is a P-type Al layer having a thickness of 1.6 nm. ０．３６ Ga ０．６４ The electron barrier layer 709 contains an impurity of 1.5×10 １９ cm －３ It is doped with Mg.

[0186] The P-type cladding layer 710 according to this embodiment is disposed between the electron barrier layer 709 and the contact layer 411. The P-type cladding layer 710 has a smaller refractive index and a higher band gap energy than the active layer 405. A ridge 710R is formed in the P-type cladding layer 710, similar to the P-type cladding layer 410 according to the fourth embodiment. Furthermore, two grooves 710T are formed in the P-type cladding layer 710, which are disposed along the ridge 710R and extend in the Y-axis direction.

[0187] The P-type cladding layer 710 is a P-type Al layer having a thickness of 450 nm. ０．０２６ Ga ０．９７４ The P-type cladding layer 710 is an N layer. The P-type cladding layer 710 is doped with Mg as an impurity. In this embodiment, the impurity concentration at the end of the P-type cladding layer 710 closer to the active layer 405 is lower than the impurity concentration at the end farther from the active layer 405. The P-type cladding layer 710 also has a region in which the impurity concentration monotonically increases with increasing distance from the active layer 405. Here, the configuration in which the impurity concentration monotonically increases also includes a configuration in which there is a region in which the impurity concentration is constant in the stacking direction. Specifically, the P-type cladding layer 710 has a concentration of 2×10 ... １８ cm －３ P-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 180 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1.3 × 10 １９ cm －３ P-type Al doped with Mg having a thickness of 120 nm ０．０２６ Ga ０．９７４ In this manner, in this embodiment, the P-type cladding layer 710 has a first layer closest to the active layer 405, a second layer having a higher impurity concentration than the first layer, and a third layer having a higher impurity concentration than the second layer.

[0188] In this embodiment, the thickness of the P-side guide layer 406 is greater than the thickness of the N-side guide layer 404. In this case, the peak of the light intensity distribution in the stacking direction is located in the region near the active layer 405, thereby suppressing the spread of light into the P-type cladding layer 710. Therefore, the light intensity in the P-type cladding layer 710 is weak. Therefore, even if the Mg concentration in the region of the P-type cladding layer 710 near the contact layer 411 is increased, an increase in waveguide loss can be suppressed. Furthermore, by increasing the Mg concentration, it is possible to reduce the series resistance of the nitride-based semiconductor light-emitting device 700 (i.e., the resistance between the P-side electrode 413 and the N-side electrode 414).

[0189] For example, when the thickness of the P-side guide layer 406 is 200 nm or more, the Mg concentration is set to 1.3×10 in a region within 0.15 μm from the interface between the P-type cladding layer 710 and the contact layer 411. １９ cm －３ Even if the Mg concentration in the P-type cladding layer 710 is increased above this level, the optical intensity is sufficiently reduced to the extent that an increase in waveguide loss can be suppressed. Increasing the Mg concentration in the P-type cladding layer 710 in this manner makes it possible to reduce the series resistance of the nitride-based semiconductor light-emitting element 700. The Mg concentration in the P-type cladding layer 710 is 1.6×10 １９ cm －３ This can suppress a decrease in carrier mobility caused by an excessively high Mg concentration, thereby suppressing an increase in series resistance.

[0190] When the thickness of the P-side guide layer 406 is 250 nm or more, the light intensity in the P-type cladding layer 710 becomes even weaker, and therefore, even if the thickness of the low-concentration region in the P-type cladding layer 710 where the Mg concentration is lowest is set to 20 nm or less, an increase in waveguide loss can be suppressed.

[0191] Furthermore, in the P-type cladding layer 710, the Mg concentration does not need to be changed stepwise in the stacking direction, but may be changed continuously. For example, the Mg concentration in the P-type cladding layer 710 may have the following structure: At the interface of the P-type cladding layer 710 closer to the active layer 405, the Mg concentration is 1.5×10 5 times the Mg concentration in the electron barrier layer 709. １９ cm －３In the region of the P-type cladding layer 710 within 100 nm from the interface, the Mg concentration is approximately equal to 1×10 １８ cm －３ From 3 x 10 １８ cm －３ The Mg concentration may monotonically decrease with increasing distance from the interface so as to reach the range below. In this way, the P-type cladding layer 710 may have a concentration decreasing region in the region closest to the active layer 405, in which the impurity concentration monotonically decreases with increasing distance from the active layer 405. Furthermore, the P-type cladding layer 710 may have a low concentration region disposed above the concentration decreasing region, in which the change in Mg concentration in the stacking direction is small and in which the Mg concentration is the lowest in the P-type cladding layer 710. In the low concentration region, the Mg concentration is, for example, 1×10 １８ cm －３ 3x10 or more １８ cm －３ Furthermore, the P-type cladding layer 710 may have a concentration increasing region disposed above the low concentration region, in which the Mg concentration monotonically increases with increasing distance from the active layer 405. In the concentration increasing region, the Mg concentration is, for example, 1×10 １８ cm －３ 3x10 or more １８ cm －３ From the following range, 1.3 x 10 １９ cm －３ increases monotonically until

[0192] The concentration increasing region may have a high increasing rate region located closer to the active layer 405 and a low increasing rate region located above the high increasing rate region. The rate of change in the Mg concentration in the stacking direction in the high increasing rate region is greater than the rate of change in the Mg concentration in the low increasing rate region in the stacking direction.

[0193] According to this embodiment, the effective refractive index difference ΔN is 1.9×10 －３ The position PS1 is 3.6 nm, the difference ΔP is 2.8 nm, the optical confinement factor in the active layer 405 is 1.54%, and the waveguide loss is 3.6 cm －１ and the guide layer free carrier loss is 2.4 cm －１ It is possible to realize a nitride-based semiconductor light-emitting device 700 having the above structure.

[0194] Eighth Embodiment A nitride-based semiconductor light-emitting device according to the eighth embodiment will be described. The nitride-based semiconductor light-emitting device according to the present embodiment differs from nitride-based semiconductor light-emitting device 700 according to the seventh embodiment in the configuration of the electron barrier layer. The nitride-based semiconductor light-emitting device according to the present embodiment will be described below with reference to FIGS. 33 and 34 , focusing on the differences from nitride-based semiconductor light-emitting device 700 according to the seventh embodiment.

[0195] Fig. 33 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 800 according to this embodiment. Fig. 34 is a graph showing the distribution of the Al composition ratio in the stacking direction of an electron barrier layer 809 according to this embodiment. The horizontal axis of the graph shown in Fig. 34 represents the position x in the stacking direction, and the vertical axis represents the Al composition ratio. Fig. 34 also shows the distribution of the Al composition ratio in the intermediate layer 408 and a part of the P-type cladding layer 710, in addition to the electron barrier layer 809.

[0196] 33 , a nitride-based semiconductor light-emitting device 800 according to this embodiment includes a semiconductor stack 800S, a current blocking layer 412, a P-side electrode 413, and an N-side electrode 414. The semiconductor stack 800S includes a substrate 401, an N-type first cladding layer 402, an N-type second cladding layer 403, an N-side guide layer 404, an active layer 405, a P-side guide layer 406, an intermediate layer 408, an electron barrier layer 809, a P-type cladding layer 710, and a contact layer 411.

[0197] The electron barrier layer 809 according to this embodiment is a P-type AlGaN layer. The electron barrier layer 809 contains impurities at a concentration of 1.5×10 １９ cm －３The electron barrier layer 809 is doped with Mg. The electron barrier layer 809 has an Al composition ratio increasing region in which the Al composition ratio monotonically increases toward the P-type cladding layer 710, and an Al composition ratio decreasing region located above the Al composition ratio increasing region in which the Al composition ratio monotonically decreases toward the P-type cladding layer 710. Here, the configuration in which the Al composition ratio monotonically decreases includes a configuration including a region in which the Al composition ratio is constant in the stacking direction. For example, the configuration in which the Al composition ratio monotonically decreases includes a configuration in which the Al composition ratio decreases stepwise. In the graph shown in FIG. 34 , position x=Xs indicates the interface of the electron barrier layer 809 with the intermediate layer 408, and position x=Xe indicates the interface of the electron barrier layer 809 with the P-type cladding layer 710. Note that position x=Xs may be defined as the end of the region in which the Al composition ratio increases toward the P-type cladding layer 710. The position x=Xe may be defined as the end of a region where the Al composition ratio decreases toward the P-type cladding layer 710, in other words, the end of a region where the Al composition ratio is constant in the stacking direction. The position x=Xm is the position where the Al composition ratio is maximum in the electron barrier layer 809. The region from the position x=Xs to the position x=Xm is the region where the Al composition ratio increases, and the region from the position x=Xm to the position x=Xe is the region where the Al composition ratio decreases.

[0198] The thickness of the electron barrier layer 809 is 5 nm or less. The thickness of the Al composition ratio increasing region is 2 nm or less. The thickness of the Al composition ratio decreasing region is greater than the thickness of the Al composition ratio increasing region. The thickness of the region in the electron barrier layer 809 where the Al composition ratio is maximum is 0.5 nm or less. Here, the region where the Al composition ratio is maximum means a region where the Al composition ratio is 95% or more of the maximum value of the Al composition ratio in the electron barrier layer 809.

[0199] The graph shown in FIG. 34 shows lines g(x) and h(x) together with a curve f(x) indicating the distribution of the Al composition ratio with respect to the position in the stacking direction of the electron barrier layer 809. The line g(x) is a line passing through a point on the curve f(x) at position x=Xs and a point on the curve f(x) at position x=Xm. The line h(x) is a line passing through a point on the curve f(x) at position x=Xm and a point on the curve f(x) at position x=Xe. As shown in FIG. 34, the curve f(x) is a downward convex curve in the range from position x=Xs to position x=Xm. Furthermore, the curve f(x) is a downward convex curve in the range from position x=Xm to position x=Xe. In other words, f(Xd1)<g(Xd1) holds at position x=Xd1, which corresponds to the midpoint between positions x=Xs and x=Xm (i.e., a point between positions x=Xs and x=Xm that is equidistant from positions x=Xs and x=Xm).Furthermore, f(Xd2)<h(Xd2) holds at position x=Xd2, which corresponds to the midpoint between positions x=Xm and x=Xe.

[0200] As described above, by grading the Al composition ratio on the side of the electron barrier layer 809 closer to the active layer 405, the positive piezoelectric polarization charge formed at the interface of the electron barrier layer 809 with the intermediate layer 408 can be dispersed into a region with an increased Al composition ratio. Accordingly, the concentration of electrons attracted by the positive piezoelectric polarization charge is reduced at the interface of the electron barrier layer 809 with the intermediate layer 408. As a result, a decrease in the potential energy of the valence band at the interface of the electron barrier layer 809 with the intermediate layer 408 can be suppressed. This reduces the potential barrier against holes flowing from the P-type cladding layer 710 to the active layer 405, thereby reducing the operating voltage.

[0201] Furthermore, by setting the thickness of the region where the Al composition ratio is maximum to 0.5 nm or less, the potential barrier in the valence band for holes can be reduced, and the operating voltage can be reduced.

[0202] Furthermore, by setting the film thickness of the electron barrier layer 809 to 5 nm or less, it is possible to narrow the width (i.e., thickness) of the potential barrier of the valence band formed by the electron barrier layer 809. As a result, it is possible to reduce the electrical conduction barrier for holes from the P-type cladding layer 710 to the active layer 405, thereby reducing the operating voltage. Here, if the film thickness of the electron barrier layer 809 is thinner than 2 nm, the number of electrons that flow from the active layer 405 to the P-type cladding layer 710 beyond the electron barrier layer 809 increases, so the film thickness of the electron barrier layer 809 needs to be 2 nm or more.

[0203] Furthermore, when the film thickness of the Al composition ratio increasing region is 2 nm or less, by setting the film thickness of the electron barrier layer 809 to 5 nm or less and making the film thickness of the Al composition ratio decreasing region of the electron barrier layer 809 larger than the film thickness of the Al composition ratio increasing region, it is possible to suppress the generation of electrons that flow from the active layer 405 to the P-type cladding layer 710 across the electron barrier layer 809.

[0204] Furthermore, the positive piezoelectric polarization charge formed near the interface of the electron barrier layer 809 with the intermediate layer 408 is greater in the region where the rate of change in the Al composition ratio is relatively large than in the region close to the intermediate layer 408 where the rate of change in the Al composition ratio is relatively small. By making the shape of the curve f(x) in the region of increasing Al composition ratio of the electron barrier layer 809 convex downward, the rate of change in the Al composition ratio near the interface of the electron barrier layer 809 with the intermediate layer 408 can be reduced, thereby reducing the positive piezoelectric polarization charge at the interface. Therefore, the concentration of electrons attracted by the positive piezoelectric polarization charge at the interface is reduced. Accordingly, the potential barrier of the valence band for holes at the interface of the electron barrier layer 809 with the intermediate layer 408 can be reduced.

[0205] Furthermore, by making the shape of the curve f(x) in the region of decreasing Al composition ratio of the electron barrier layer 809 convex downward, it is possible to reduce the film thickness of the region of high Al composition ratio in the vicinity of the position x = Xm, and further narrow the width of the potential barrier of the valence band formed by the electron barrier layer 809. As a result, it is possible to reduce the electrical conduction barrier of holes from the P-type cladding layer 710 to the active layer 405, and the operating voltage is reduced.

[0206] The Mg concentration in the electron barrier layer 809 according to this embodiment is 1.5×10１９ cm －３ Since the Al composition is graded in the region of the electron barrier layer 809 closer to the active layer 405 (i.e., the region with an increased Al composition ratio), the Mg concentration may be 1.5×10 １９ cm －３ Even if the Al composition ratio of the electron barrier layer 809 is increased to 30% or more, the potential barrier against holes in the electron barrier layer 809 can be reduced. This makes it possible to suppress an increase in the operating voltage even if the Al composition ratio of the electron barrier layer 809 is increased to 30% or more.

[0207] Furthermore, by making the shape of the curve f(x) in the region of the electron barrier layer 809 closer to the active layer 405 (i.e., the region where the Al composition ratio is increased) convex downward, the effect of suppressing the formation of a potential barrier in the valence band is enhanced, and the Mg concentration is increased to 1×10 １９ cm －３ It is possible to make the Mg concentration 0.7×10 or less. １８ cm －３ This can prevent the potential of the valence band of the electron barrier layer 809 from being excessively lowered.

[0208] In this embodiment, the electron barrier layer 809 is made of Al ０．０２ Ga ０．９８ The electron barrier layer 809 has a composition represented by N, and the Al composition ratio of the electron barrier layer 809 increases monotonically as it approaches the P-type cladding layer 710. At a position x=Xm where the distance from the interface of the electron barrier layer 809 with the intermediate layer 408 is 1 nm, the electron barrier layer 809 has a composition represented by Al ０．３６ Ga ０．６４ The electron barrier layer 809 has a composition represented by the formula: AlN. As it approaches the P-type cladding layer 710 from the position x=Xm, the Al composition ratio of the electron barrier layer 809 monotonically decreases. The electron barrier layer 809 has a composition represented by the formula: AlN. ０．０２６ Ga ０．９７４ It has a composition represented by N.

[0209] The nitride-based semiconductor light-emitting element 800 according to this embodiment also achieves the same effects as the nitride-based semiconductor light-emitting element 700 according to embodiment 7. Furthermore, in the nitride-based semiconductor light-emitting element 800 according to this embodiment, by further grading the Al composition ratio on the side of the electron barrier layer 809 closer to the active layer 405, it is possible to suppress a decrease in the potential energy of the valence band at the interface between the electron barrier layer 809 and the intermediate layer 408. This makes it possible to reduce the operating voltage of the nitride-based semiconductor light-emitting element 800.

[0210] Ninth Embodiment A nitride-based semiconductor light-emitting device according to the ninth embodiment will be described. The nitride-based semiconductor light-emitting device according to the present embodiment differs from the nitride-based semiconductor light-emitting device 100 according to the first embodiment in the configuration of the N-side guide layer. The nitride-based semiconductor light-emitting device according to the present embodiment will be described below with reference to FIGS. 35A to 41.

[0211] [9-1. Overall Configuration] First, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described with reference to Figures 35A and 35B. Figure 35A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 900 according to this embodiment. Figure 35B is a schematic cross-sectional view showing the configuration of an active layer 905 included in the nitride-based semiconductor light-emitting device 900 according to this embodiment.

[0212] 35A , the nitride-based semiconductor light-emitting element 900 includes a semiconductor stack 900S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor stack 900S includes a substrate 901, an N-type first cladding layer 902, an N-type second cladding layer 903, an N-side guide layer 904, an active layer 905, a P-side guide layer 906, an intermediate layer 908, an electron barrier layer 909, a P-type cladding layer 910, and a contact layer 911.

[0213] The substrate 901 is a plate-like member that serves as a base for the nitride-based semiconductor light-emitting device 900. In this embodiment, the substrate 901 is an N-type GaN substrate.

[0214] The N-type first cladding layer 902 is an example of an N-type cladding layer disposed above the substrate 901. The N-type first cladding layer 902 has a smaller refractive index than the active layer 905 and a larger band gap energy. In this embodiment, the N-type first cladding layer 902 is a 1200 nm thick N-type Al ０．０３５ Ga ０．９６５ The N-type first cladding layer 902 contains an impurity with a concentration of 1×10 １８ cm －３ is doped with Si.

[0215] The N-type second cladding layer 903 is an example of an N-type cladding layer disposed above the substrate 901. In this embodiment, the N-type second cladding layer 903 is disposed above the N-type first cladding layer 902. The N-type second cladding layer 903 is a layer having a smaller refractive index than the active layer 905 and a larger band gap energy. In this embodiment, the N-type second cladding layer 903 is an N-type GaN layer having a film thickness of 100 nm. The N-type second cladding layer 903 contains impurities at a concentration of 1×10 １８ cm －３ The band gap energy of the N-type second cladding layer 903 is smaller than the band gap energy of the N-type first cladding layer 902 and is equal to or larger than the maximum value of the band gap energy of the P-side guide layer 906.

[0216] The N-side guide layer 904 is an optical guide layer disposed above the N-type second cladding layer 903. The N-side guide layer 904 has a higher refractive index and a smaller bandgap energy than the N-type first cladding layer 902 and the N-type second cladding layer 903. The bandgap energy of the N-side guide layer 904 monotonically increases with increasing distance from the active layer 905 (i.e., as it approaches the N-type first cladding layer 902 in the direction opposite to the crystal growth direction of each semiconductor layer). Here, a configuration in which the bandgap energy monotonically increases also includes a configuration in which there is a region in which the bandgap energy is constant in the stacking direction. Furthermore, the N-side guide layer 904 includes a portion in which the bandgap energy continuously increases with increasing distance from the active layer 905. Here, a configuration in which the bandgap energy continuously and monotonically increases in the stacking direction does not include a configuration in which the bandgap energy changes discontinuously in the stacking direction. In the present disclosure, a configuration in which the bandgap energy increases continuously and monotonically refers to a configuration in which the discontinuous increase in the bandgap energy is less than 2% of the bandgap energy at that position. For example, a configuration in which the bandgap energy in the N-side guide layer 904 increases continuously and monotonically with increasing distance from the active layer 905 refers to a configuration in which the increase in the bandgap energy at a position in the N-side guide layer 904 displaced a small distance from the position in the direction opposite to the crystal growth direction is less than 2% of the bandgap energy at that position. For example, a configuration in which the bandgap energy increases continuously and monotonically does not include a configuration in which the bandgap energy increases stepwise by 2% or more in the direction opposite to the stacking direction, but does include a configuration in which the bandgap energy changes stepwise by less than 2% in the stacking direction. In this embodiment, the bandgap energy in the entire N-side guide layer 904 increases continuously with increasing distance from the active layer 905, but the configuration of the N-side guide layer 904 is not limited to this. For example, the ratio of the thickness of the portion of the N-side guide layer 904 whose band gap energy increases continuously with increasing distance from the active layer 905 to the entire thickness of the N-side guide layer 904 may be 50% or more.The percentage may be 70% or more, or 90% or more.

[0217] Here, the increase in the bandgap energy of the N-side guide layer 904 in the direction toward the N-type second cladding layer 903 (the direction opposite to the direction of crystal growth) is defined as ΔEgn. The increase in the bandgap energy of the N-side guide layer 904 in the direction opposite to the direction of crystal growth is defined, for example, as the difference between the bandgap energy at the interface of the N-side guide layer 904 closer to the active layer 905 and the bandgap energy at the interface closer to the N-type second cladding layer 903. The proportion of the magnitude of the continuously increasing bandgap energy in ΔEgn to ΔEgn may be 70% or more. Alternatively, this proportion may be 80% or more, or may be 90% or more. In this way, by increasing the bandgap energy of the N-side guide layer 904 in the direction opposite to the direction of crystal growth, the refractive index of the N-side guide layer 904 continuously and monotonically increases as it approaches the active layer 905. In this case, the refractive index of the N-side guide layer 904 increases toward the active layer 905, so the peak of the light intensity distribution in the stacking direction can be moved closer to the active layer 905. Here, if ΔEgn is small, the effect is small, but conversely, if it is too large, the light generated from the active layer 905 is absorbed in a region of the N-side guide layer 904 with small band gap energy adjacent to the active layer 905, thereby increasing waveguide loss. In order to suppress such waveguide loss, ΔEgn may be 100 meV or more and 400 meV or less.

[0218] The N-side guide layer 904 is In Ｘｎ Ga １－ＸｎWhen the N-side guide layer 904 is made of N, the In composition ratio Xn of the N-side guide layer 904 monotonically decreases with increasing distance from the active layer 905. As a result, the band gap energy of the N-side guide layer 904 monotonically increases with increasing distance from the active layer 905. Here, the configuration in which the In composition ratio Xn monotonically decreases includes a configuration in which there is a region in which the In composition ratio Xn is constant in the stacking direction. Furthermore, the N-side guide layer 904 includes a portion in which the In composition ratio continuously decreases with increasing distance from the active layer 905. Here, the configuration in which the In composition ratio Xn continuously and monotonically decreases does not include a configuration in which the In composition ratio Xp changes discontinuously in the stacking direction. The configuration in which the In composition ratio continuously and monotonically decreases means a configuration in which the discontinuous decrease in the In composition ratio Xn at a certain position in the N-side guide layer 904 in the stacking direction is less than 20% of the In composition ratio Xn at that position.

[0219] The average band gap energy of the N-side guide layer 904 is equal to or less than the average band gap energy of the P-side guide layer 906. In other words, the average value of the In composition ratio of the N-side guide layer 904 is equal to or greater than the average value of the In composition ratio of the P-side guide layer 906. In this embodiment, the average value of the In composition ratio of the N-side guide layer 904 is equal to the average value of the In composition ratio of the P-side guide layer 906. In other words, the average band gap energy of the N-side guide layer 904 is equal to the average band gap energy of the P-side guide layer 906. Furthermore, when the thickness of the N-side guide layer 904 is Tn and the thickness of the P-side guide layer 906 is Tp, the following relationship is satisfied: Tn<Tp (31)

[0220] The maximum value of the In composition ratio in the N-side guide layer 904 is equal to or less than the In composition ratio of each barrier layer.

[0221] In this embodiment, the N-side guide layer 904 is an N-type InP layer having a thickness of 160 nm. Ｘｎ Ga １－Ｘｎ The N-side guide layer 904 contains an impurity of 3×10 １７ cm －３ More specifically, the N-side guide layer 904 is doped with In near the interface closer to the active layer 905. ０．０４ Ga ０．９６The N-side guide layer 904 has a composition represented by N, and a composition represented by GaN near the interface farther from the active layer 905. The In composition ratio Xn of the N-side guide layer 904 decreases at a constant rate with increasing distance from the active layer 905.

[0222] The active layer 905 is a light-emitting layer having a quantum well structure and is disposed above the N-side guide layer 904. In this embodiment, the active layer 905 includes well layers 905b and 905d and barrier layers 905a, 905c, and 905e, as shown in FIG.

[0223] The barrier layer 905a is disposed above the N-side guide layer 904 and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 905a is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0224] The well layer 905b is disposed above the barrier layer 905a and functions as a well of the quantum well structure. The well layer 905b is disposed between the barrier layer 905a and the barrier layer 905c. In this embodiment, the well layer 905b is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0225] The barrier layer 905c is disposed above the well layer 905b and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 905c is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0226] The well layer 905d is disposed above the barrier layer 905c and functions as a well of the quantum well structure. The well layer 905d is disposed between the barrier layer 905c and the barrier layer 905e. In this embodiment, the well layer 905d is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0227] The barrier layer 905e is disposed above the well layer 905d and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 905e is an undoped In layer having a thickness of 5 nm.０．０５ Ga ０．９５ This is the N layer.

[0228] The nitride-based semiconductor light-emitting element 900 includes the active layer 905 having the above-described configuration, and can emit light with a wavelength of 430 nm or more and 455 nm or less.

[0229] In this embodiment, the band gap energy of each barrier layer is equal to or less than the minimum value of the band gap energy of the N-side guide layer 904 and the P-side guide layer 906. In other words, the refractive index of each barrier layer is greater than the refractive index of the N-side guide layer 904 and the P-side guide layer 906. Therefore, the optical confinement coefficient in the active layer 905 can be increased. Ｘｂ Ga １－Ｘｂ When made of N, the In composition ratio of each barrier layer is equal to or greater than the maximum value of the In composition ratio of the N-side guide layer 904 and equal to or greater than the maximum value of the In composition ratio of the P-side guide layer 906 .

[0230] The P-side guide layer 906 is an optical guide layer disposed above the active layer 905. The P-side guide layer 906 has a higher refractive index and a smaller bandgap energy than the P-type cladding layer 910. The bandgap energy of the P-side guide layer 906 increases monotonically with increasing distance from the active layer 905.

[0231] Here, the configuration in which the bandgap energy in the P-side guide layer 906 increases monotonically includes a configuration in which there is a region in which the bandgap energy is constant in the stacking direction. The P-side guide layer 906 also includes a portion in which the bandgap energy continuously increases with increasing distance from the active layer 905. Here, the configuration in which the bandgap energy continuously and monotonically increases does not include a configuration in which the bandgap energy changes discontinuously in the stacking direction. In the present disclosure, the configuration in which the bandgap energy continuously and monotonically increases means, as with the N-side guide layer described above, a configuration in which the discontinuous increase in the bandgap energy at a certain position is less than 2% of the bandgap energy at that position. For example, the configuration in which the bandgap energy continuously and monotonically increases does not include a configuration in which the bandgap energy increases stepwise by 2% or more in the stacking direction, but does include a configuration in which the bandgap energy changes stepwise by less than 2% in the stacking direction. In this embodiment, the bandgap energy continuously increases with increasing distance from the active layer 905 throughout the entire P-side guide layer 906, but the configuration of the P-side guide layer 906 is not limited to this. For example, the ratio of the film thickness of the portion of the P-side guide layer 906 where the bandgap energy continuously increases with increasing distance from the active layer 905 to the entire film thickness of the P-side guide layer 906 may be 50% or more. Alternatively, this ratio may be 70% or more, or 90% or more.

[0232] Here, the increase in the bandgap energy of the P-side guide layer 906 in the direction toward the N-type second cladding layer 903 is defined as ΔEgp. The increase in the bandgap energy of the P-side guide layer 906 in the stacking direction is defined, for example, as the difference between the bandgap energy at the interface of the P-side guide layer 906 closer to the active layer 905 and the bandgap energy at the interface closer to the P-type cladding layer 910. The proportion of the continuously increasing bandgap energy in ΔEgp to ΔEgp may be 70% or more. This proportion may also be 80% or more, or 90% or more. In this way, by increasing the bandgap energy of the P-side guide layer 906 in the stacking direction, the refractive index of the P-side guide layer 906 increases continuously and monotonically as it approaches the active layer 905. In this case, the refractive index of the P-side guide layer 906 increases as it approaches the active layer 905, so that the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 905. Here, if ΔEgp is small, the effect is small, but conversely, if it is too large, the light generated from the active layer 905 is absorbed in a region of the P-side guide layer 906 with small band gap energy that is adjacent to the active layer 905, thereby increasing waveguide loss. In order to suppress such waveguide loss, ΔEgp may be 100 meV or more and 400 meV or less.

[0233] The P-side guide layer 906 is In Ｘｐ Ga １－Ｘｐ When the P-side guide layer 906 is made of N, the In composition ratio Xp of the P-side guide layer 906 monotonically decreases with increasing distance from the active layer 905. As a result, the band gap energy of the P-side guide layer 906 continuously and monotonically increases with increasing distance from the active layer 905. Furthermore, the P-side guide layer 906 includes a portion where the In composition ratio Xp continuously increases with increasing distance from the active layer 905. As a result, the band gap energy of the P-side guide layer 906 includes a portion where the In composition ratio Xp continuously increases with increasing distance from the active layer 905.

[0234] As described above, the average band gap energy of the P-side guide layer 906 is equal to or greater than the average band gap energy of the N-side guide layer 904. In other words, the average value of the In composition ratio of the P-side guide layer 906 is equal to or less than the average value of the In composition ratio of the N-side guide layer 904. In this embodiment, the average value of the In composition ratio of the P-side guide layer 906 is equal to the average value of the In composition ratio of the N-side guide layer 904. In addition, the thickness Tp of the P-side guide layer 906 is greater than the thickness Tn of the N-side guide layer 904. The maximum value of the In composition ratio in the P-side guide layer 906 is equal to or less than the In composition ratio of each barrier layer.

[0235] In this embodiment, the p-side guide layer 906 is an undoped In layer having a thickness of 280 nm. Ｘｐ Ga １－Ｘｐ More specifically, the P-side guide layer 906 has an In layer near the interface closer to the active layer 905. ０．０４ Ga ０．９６ The p-side guide layer 906 has a composition represented by N, and a composition represented by GaN near the interface farther from the active layer 905. The In composition ratio Xp of the p-side guide layer 906 decreases at a constant rate as it becomes farther from the active layer 905.

[0236] The intermediate layer 908 is a layer disposed above the active layer 905. In this embodiment, the intermediate layer 908 is disposed between the P-side guide layer 906 and the electron barrier layer 909, and reduces stress caused by the difference in lattice constant between the P-side guide layer 906 and the electron barrier layer 909. This makes it possible to suppress the occurrence of crystal defects in the nitride-based semiconductor light-emitting element 900. In this embodiment, the intermediate layer 908 is an undoped GaN layer with a thickness of 20 nm.

[0237] The electron barrier layer 909 is a nitride-based semiconductor layer that is disposed above the active layer 905 and contains at least Al. In this embodiment, the electron barrier layer 909 is disposed between the intermediate layer 908 and the P-type cladding layer 910. The electron barrier layer 909 is a 5-nm-thick P-type Al ０．３６ Ga ０．６４ The electron barrier layer 909 contains an impurity of 1×10 １９ cm －３The electron barrier layer 909 can prevent electrons from leaking from the active layer 905 to the P-type cladding layer 910.

[0238] The P-type cladding layer 910 is a P-type cladding layer disposed above the active layer 905. In this embodiment, the P-type cladding layer 910 is disposed between the electron barrier layer 909 and the contact layer 911. The P-type cladding layer 910 has a lower refractive index and a higher bandgap energy than the active layer 905. The thickness of the P-type cladding layer 910 may be 460 nm or less. This reduces the electrical resistance of the nitride-based semiconductor light-emitting device 900. Therefore, the operating voltage of the nitride-based semiconductor light-emitting device 900 can be reduced. Furthermore, self-heating during operation of the nitride-based semiconductor light-emitting device 900 can be reduced, thereby improving the temperature characteristics of the nitride-based semiconductor light-emitting device 900. Therefore, high-power operation of the nitride-based semiconductor light-emitting device 900 is possible. In the nitride-based semiconductor light-emitting device 900 according to this embodiment, the thickness of the P-type cladding layer 910 may be 200 nm or more in order for the P-type cladding layer 910 to fully function as a cladding layer. The thickness of the P-type cladding layer 910 may be 250 nm or more. In this embodiment, the P-type cladding layer 910 is a P-type Al 1N 2 O 3 layer having a thickness of 450 nm. ０．０３５ Ga ０．９６５ The P-type cladding layer 910 is an N layer. The P-type cladding layer 910 is doped with Mg as an impurity. The impurity concentration at the end of the P-type cladding layer 910 closer to the active layer 905 is lower than the impurity concentration at the end farther from the active layer 905. Specifically, the P-type cladding layer 910 has a dopant concentration of 2×10 １８ cm －３ P-type Al doped with Mg having a thickness of 150 nm ０．０３５ Ga ０．９６５ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 300 nm ０．０３５ Ga ０．９６５ N layers.

[0239] A ridge 910R is formed in the P-type cladding layer 910 of the nitride-based semiconductor light-emitting device 900. Two grooves 910T are formed in the P-type cladding layer 910, arranged along the ridge 910R and extending in the Y-axis direction. In this embodiment, the ridge width W is approximately 30 μm. As shown in FIG. 35A , the distance between the lower end of the ridge 910R (i.e., the bottom of the groove 910T) and the active layer 905 is defined as dp. The film thickness of the P-type cladding layer 910 at the lower end of the ridge 910R (i.e., the distance between the lower end of the ridge 910R and the interface between the P-type cladding layer 910 and the electron barrier layer 909) is defined as dc.

[0240] The contact layer 911 is disposed above the P-type cladding layer 910 and is in ohmic contact with the P-side electrode 913. In this embodiment, the contact layer 911 is a P-type GaN layer with a film thickness of 60 nm. The contact layer 911 contains impurities with a concentration of 1×10 ２０ cm －３ It is doped with Mg.

[0241] The current blocking layer 912 is disposed above the P-type cladding layer 910 and is an insulating layer that is transparent to light from the active layer 905. The current blocking layer 912 is disposed on the upper surface of the P-type cladding layer 910 in a region other than the upper surface of the ridge 910R. In this embodiment, the current blocking layer 912 is made of SiO ２ It is a layer.

[0242] The P-side electrode 913 is a conductive layer disposed above the semiconductor stack 900S. In this embodiment, the P-side electrode 913 is disposed above the contact layer 911 and the current blocking layer 912 and is in contact with the contact layer 911. The P-side electrode 913 is, for example, a single-layer film or a multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au.

[0243] The N-side electrode 914 is a conductive layer disposed below the substrate 901 (i.e., on the principal surface of the substrate 901 opposite to the principal surface on which the N-type first cladding layer 902 and the like are disposed). The N-side electrode 914 is a single-layer film or a multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au, for example.

[0244] 35A , the nitride-based semiconductor light-emitting element 900 has the above-described configuration, and therefore an effective refractive index difference ΔN occurs between the portion below the ridge 910R and the portion below the groove 910T, which allows light generated in the portion of the active layer 905 below the ridge 910R to be confined in the horizontal direction (i.e., the X-axis direction).

[0245] 9-2. Stability of Light Intensity Distribution and Light Output Next, the stability of light intensity distribution and light output of the nitride-based semiconductor light-emitting element 900 according to this embodiment will be described.

[0246] The light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting element 900 according to this embodiment will be described with reference to Fig. 36. Fig. 36 is a schematic graph showing the distribution of band gap energy in the active layer 905 and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting element 900 according to this embodiment.

[0247] In the nitride-based semiconductor light-emitting device 900 according to this embodiment, the thickness of the P-type cladding layer 910 is set to be relatively thin in order to reduce the operating voltage. Accordingly, the height of the ridge 910R (i.e., the height of the ridge 910R from the bottom surface of the groove 910T) is also set to be relatively low. In general, in a semiconductor light-emitting device having such a configuration, the peak position of the light intensity distribution in the stacking direction shifts from the active layer 905 toward the N-type second cladding layer 903. This reduces the optical confinement factor of the active layer 905, and therefore reduces the thermal saturation level of the optical output. This makes it difficult for the semiconductor light-emitting device to operate at high output. In this embodiment, as described above, the average bandgap energy of the P-side guide layer 906 is equal to the average bandgap energy of the N-side guide layer 904. Meanwhile, the thickness Tp of the P-side guide layer 906 is greater than the thickness Tn of the N-side guide layer 904 (see the above inequality (31)). In this way, by increasing the film thickness of the P-side guide layer 906, which has a refractive index higher than that of each cladding layer, it is possible to shift the light intensity distribution in a direction from the active layer 905 toward the P-side guide layer 906. Therefore, with the nitride-based semiconductor light-emitting element 900 according to this embodiment, it is possible to control the peak of the light intensity distribution in the stacking direction so that it is located in the active layer 905.

[0248] Furthermore, in this embodiment, the band gap energies of the N-side guide layer 904 and the P-side guide layer 906 continuously and monotonically increase with increasing distance from the active layer 905. In other words, the refractive indexes of the N-side guide layer 904 and the P-side guide layer 906 continuously and monotonically increase with increasing distance from the active layer 905. Since the refractive indexes of the N-side guide layer 904 and the P-side guide layer 906 increase with increasing distance from the active layer 905 in this manner, the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 905.

[0249] In this embodiment, the compositions of the N-side guide layer 904 and the P-side guide layer 906 are In, Ｘｎ Ga １－Ｘｎ N and In Ｘｐ Ga １－ＸｐThe composition of the N-side guide layer 904 near the interface closer to the active layer 905 and near the interface farther from the active layer 905 is In. Ｘｎ１ Ga １－Ｘｎ１ N and In Ｘｎ２ Ga １－Ｘｎ２ The composition of the P-side guide layer 906 near the interface closer to the active layer 905 and near the interface farther from the active layer 905 is In. Ｘｐ１ Ga １－Ｘｐ１ N and In Ｘｐ２ Ga １－Ｘｐ２ N. As described above, in this embodiment, Xn1=Xp1=0.04, and Xn2=Xp2=0.

[0250] In this embodiment, the barrier layers 905a, 905c, and 905e of the active layer 905 are made of In. Ｘｂ Ga １－Ｘｂ The In composition ratios Xb, Xn, and Xp of each barrier layer, the N-side guide layer 904, and the P-side guide layer 906 satisfy the following relationships: Xp≦Xb (32) Xn≦Xb (33). As a result, the bandgap energy of each barrier layer is equal to or less than the minimum value of the bandgap energy of the N-side guide layer 904 and the P-side guide layer 906. That is, the refractive index of each barrier layer can be made larger than that of the P-side guide layer 906 and the N-side guide layer 904. As a result, the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 905. Furthermore, excessive movement of the light intensity distribution from the active layer 905 toward the P-type cladding layer 910 can be suppressed. This effect is enhanced when the bandgap energy of each barrier layer is made less than the minimum value of the bandgap energy of the N-side guide layer 904 and the P-side guide layer 906, and the optical confinement factor also increases.

[0251] With the above-described configuration, in this embodiment, the position PS1 of the peak of the light intensity distribution in the stacking direction below the ridge 910R can be set to 15.9 nm. In other words, the peak of the light intensity distribution can be positioned in the active layer 905. Furthermore, ΔP can be suppressed to 6.2 nm. This allows the light confinement factor in the active layer 905 to be increased to approximately 1.44%.

[0252] As described above, according to the nitride-based semiconductor light-emitting device 900 of this embodiment, the peak of the light intensity distribution in the stacking direction can be positioned in the active layer 905. Note that "the peak of the light intensity distribution in the stacking direction is positioned in the active layer 905" means that the peak of the light intensity distribution in the stacking direction is positioned in the active layer 905 at least one position in the horizontal direction of the nitride-based semiconductor light-emitting device 900, and is not limited to a state in which the peak of the light intensity distribution in the stacking direction is positioned in the active layer 905 at all positions in the horizontal direction.

[0253] When the peak of the light intensity distribution in the stacking direction is positioned in the active layer 905 as in this embodiment, the proportion of the portion of the light located in the P-type cladding layer 910 can be increased compared to when the peak of the light intensity distribution is positioned in the N-side guide layer 904. Here, since the P-type cladding layer 910 has a higher impurity concentration than the N-type first cladding layer 902 and the N-type second cladding layer 903, the increase in the proportion of the portion of the light located in the P-type cladding layer 910 raises concerns about an increase in free carrier loss in the P-type cladding layer 910. However, in this embodiment, the P-side guide layer 906 is an undoped layer, and the thickness Tp of the P-side guide layer 906 is relatively large, thereby increasing the proportion of the portion of the light intensity distribution located in the undoped layer. Therefore, an increase in free carrier loss can be suppressed. Specifically, in this embodiment, the waveguide loss is reduced to 2.8 cm －１ It can be suppressed to a certain extent.

[0254] Furthermore, in the nitride-based semiconductor light-emitting device 900 according to this embodiment, the effective refractive index difference ΔN between the portion below the ridge 910R and the portion below the groove 910T is set to be relatively small in order to reduce the divergence angle of the emitted light in the horizontal direction (i.e., the X-axis direction). Specifically, the effective refractive index difference ΔN is set by adjusting the distance dp (see FIG. 35A ) between the current blocking layer 912 and the active layer 905. Here, the greater the distance dp, the smaller the effective refractive index difference ΔN. In this embodiment, the effective refractive index difference ΔN is 2.9×10 －３ Therefore, in this embodiment, the effective refractive index difference ΔN is about 2.9×10 －３ When the ridge 910R is larger than the ridge 910R, the number of higher-order modes (i.e., higher-order transverse modes) that can propagate through the waveguide formed by the ridge 910R is smaller. Therefore, the proportion of each higher-order mode among all transverse modes included in the emitted light from the nitride-based semiconductor light-emitting device 900 becomes relatively large. Therefore, the increase or decrease in the number of modes and the change in the optical confinement factor in the active layer 905 due to inter-mode coupling become relatively large. Therefore, when the increase or decrease in the number of modes and inter-mode coupling occur in the nitride-based semiconductor light-emitting device 900, the linearity of the optical output characteristic with respect to the supplied current (the so-called IL characteristic) decreases. In other words, a non-linear portion (a so-called kink) appears in the graph showing the IL characteristic. This can lead to a decrease in the stability of the optical output from the nitride-based semiconductor light-emitting device 900.

[0255] The above-described decrease in the stability of the optical output will be explained below. In the nitride-based semiconductor light-emitting device 900, the optical intensity distribution in the portion below the ridge 910R is dominated by the fundamental mode (i.e., the zeroth-order mode), while the optical intensity distribution in the portion below the groove 910T is dominated by a higher-order mode. Therefore, when the difference ΔP between the peak position PS1 of the optical intensity distribution in the stacking direction in the portion below the ridge 910R of the nitride-based semiconductor light-emitting device 900 and the peak position PS2 of the optical intensity distribution in the stacking direction in the portion below the groove 910T is large, an increase or decrease in the number of modes and inter-mode coupling occur, which fluctuates the optical confinement factor in the active layer 905, thereby decreasing the stability of the optical output.

[0256] For example, if the number of higher-order modes decreases, the peak of the light intensity distribution obtained by adding together the light intensity distributions below both the ridge 910R and the groove 910T moves to a position closer to position PS1. Therefore, the larger the difference ΔP between positions PS1 and PS2, the greater the fluctuation in the light confinement factor in the active layer 905 when the number of modes changes. Therefore, the stability of the light output decreases.

[0257] The nitride-based semiconductor light-emitting device 900 according to this embodiment includes the N-side guide layer 904 and the P-side guide layer 906 having the above-described configuration, and therefore the peak of the light intensity distribution can be positioned in the active layer 905 both below the ridge 910R and below the trench 910T. That is, the difference ΔP between the positions PS1 and PS2 of the light intensity distribution peaks can be reduced. As a result, even if the number of modes increases or decreases and inter-mode coupling occurs, fluctuations in the position in the stacking direction of the peak of the light intensity distribution obtained by adding the light intensity distributions below both the ridge 910R and the trench 910T can be suppressed. Therefore, the stability of the light output can be improved.

[0258] As described above, the distance dp is set to a relatively large value in order to set the effective refractive index difference ΔN to a relatively small value. When the distance dp is set, if the lower end of the ridge 910R (i.e., the bottom of the trench 910T) is set to be lower than the electron barrier layer 909, the electron barrier layer 909 has a large bandgap energy, so holes injected from the contact layer 911 tend to leak from the sidewall of the ridge 910R to the outside of the ridge 910R when passing through the electron barrier layer 909. As a result, the holes flow downward into the trench 910T. Accordingly, the light intensity in the active layer 905 below the trench 910T is low, so the probability of radiative recombination between electrons and holes injected into the active layer 905 decreases, and non-radiative recombination increases. Such an increase in non-radiative recombination makes the nitride-based semiconductor light-emitting element 900 more susceptible to degradation. To suppress such degradation, the lower end of the ridge 910R is set to be higher than the electron barrier layer 909. Furthermore, if the distance dc (see FIG. 35A ) from the bottom end of the ridge 910R to the electron barrier layer 909 becomes too large, holes will flow from the ridge 910R into between the groove 910T and the electron barrier layer 909, resulting in leakage current. To prevent this increase in leakage current, the distance dc is set to as small a value as possible. The distance dc is, for example, not less than 10 nm and not more than 70 nm. In this embodiment, the distance dc is 40 nm.

[0259] [9-3. Effects] [9-3-1. Guide Layers] The effects of each guide layer of the nitride-based semiconductor light-emitting device 900 according to the present embodiment will be described with reference to FIGS. 37 to 39 , in comparison with nitride-based semiconductor light-emitting devices of comparative examples. FIG. 37 is a graph showing the refractive index distribution and light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14 and the nitride-based semiconductor light-emitting device 900 according to the present embodiment. Graphs (a) to (c) of FIG. 37 show the refractive index distribution and light intensity distribution of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14, respectively. Graph (d) of FIG. 37 shows the refractive index distribution and light intensity distribution of the nitride-based semiconductor light-emitting device 900 according to the present embodiment. In each graph of FIG. 37 , the refractive index distribution is shown by a solid line, and the light intensity distribution is shown by a dashed line.

[0260] 38 is a graph showing the simulation results of the distribution of valence charge potential and hole Fermi level in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14 and the nitride-based semiconductor light-emitting device 900 according to this embodiment. Graphs (a) to (c) of Fig. 38 show the distributions of valence charge potential and hole Fermi level of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14, respectively. Graph (d) of Fig. 38 shows the distributions of valence charge potential and hole Fermi level of the nitride-based semiconductor light-emitting device 900 according to this embodiment. In each graph of Fig. 38, the valence charge potential is shown by a solid line, and the hole Fermi level is shown by a dashed line.

[0261] 39 is a graph showing the results of a simulation of the carrier concentration distribution in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14, and the nitride-based semiconductor light-emitting device 900 according to the present embodiment. Graphs (a) to (c) of Fig. 39 show the carrier concentration distribution of the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14, respectively. Graph (d) of Fig. 39 shows the carrier concentration distribution of the nitride-based semiconductor light-emitting device 900 according to the present embodiment. In each graph of Fig. 39, the electron concentration distribution is shown by a solid line, and the hole concentration distribution is shown by a dashed line.

[0262] The nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14 differ from the nitride-based semiconductor light-emitting device 900 according to the present embodiment in the configurations of the N-side guide layer and the P-side guide layer. The nitride-based semiconductor light-emitting device of Comparative Example 12 shown in graph (a) of FIG. 37 has an undoped In ０．０４ Ga ０．９６ The N-side guide layer 2104 is made of an N layer, and the undoped In layer 2105 is made of an N layer. ０．０４ Ga ０．９６ The nitride-based semiconductor light-emitting device of Comparative Example 13 shown in graph (b) of FIG. 37 includes an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ The N-side guide layer 2204 is made of an N layer, and the undoped In layer 2205 is made of an N layer. ０．０４ Ga ０．９６The nitride-based semiconductor light-emitting device of Comparative Example 14 shown in graph (c) of FIG. 37 has an undoped In layer with a thickness of 160 nm. ０．０４ Ga ０．９６ It includes an N-side guide layer 404 made of an N layer and a P-side guide layer 406 with a film thickness of 280 nm. The P-side guide layer 406 of the nitride-based semiconductor light-emitting device of Comparative Example 14 has a configuration similar to that of the P-side guide layer 906 according to the present embodiment. In the nitride-based semiconductor light-emitting devices of Comparative Examples 12 to 14, the P-side electrode is made of Pd instead of Ag.

[0263] In the nitride-based semiconductor light-emitting device of Comparative Example 12, the N-side guide layer 2104 and the P-side guide layer 2106 have the same composition, and the N-side guide layer 2104 is thicker than the P-side guide layer 2106. Therefore, in the nitride-based semiconductor light-emitting device of Comparative Example 12, the peak of the light intensity distribution in the stacking direction is located in the N-side guide layer 2104, as shown in graph (a) of FIG. 37 . Therefore, the nitride-based semiconductor light-emitting device of Comparative Example 12 has a low optical confinement factor of 1.33%. Furthermore, as shown in graph (a) of FIG. 38 , in the P-side guide layer 2106, in order to conduct holes from the P-side guide layer 2106 to the active layer 905, the hole Fermi level increases from the interface of the P-side guide layer 2106 farther from the active layer 905 to the interface closer to the active layer 905. Meanwhile, the valence electron charge potential is substantially constant in the stacking direction of the P-side guide layer 2106. Therefore, the difference between the hole Fermi level and the valence electron charge potential in the P-side guide layer 2106 increases with increasing distance from the active layer 905. Therefore, as shown in graph (a) of Figure 39, the concentration of holes and electrons in the stacking direction of the P-side guide layer 2106, i.e., the free carrier concentration, increases with increasing distance from the active layer 905. As described above, in the nitride-based semiconductor light-emitting device of Comparative Example 12, the free carrier concentration in the stacking direction of the P-side guide layer 2106 cannot be reduced, and therefore reduction in free carrier loss and reduction in the probability of non-radiative recombination cannot be achieved. In the nitride-based semiconductor light-emitting device of Comparative Example 12, the effective refractive index difference ΔN is 3.6 × 10 －３The peak positions PS1 and PS2 of the light intensity distribution are −34.1 nm and −75.6 nm, respectively, and the difference ΔP is 41.5 nm. The waveguide loss is 4.5 cm －１ The free carrier loss in the N-side guide layer 2104 and the P-side guide layer 2106 is 2.8 cm －１ is.

[0264] In the nitride-based semiconductor light-emitting device of Comparative Example 13, the thickness of the P-side guide layer 2206 is greater than the thickness of the N-side guide layer 2204. Therefore, as shown in graph (b) of FIG. 37 , the peak of the light intensity distribution in the stacking direction is closer to the active layer 905 than in the nitride-based semiconductor light-emitting device of Comparative Example 12. Therefore, in the nitride-based semiconductor light-emitting device of Comparative Example 13, the optical confinement factor is slightly improved compared to that of the nitride-based semiconductor light-emitting device of Comparative Example 12. However, as shown in graph (b) of FIG. 38 , similar to Comparative Example 12, the difference between the hole Fermi level and the valence electron charge potential in the P-side guide layer 2206 increases with increasing distance from the active layer 905. Therefore, as shown in graph (b) of FIG. 39 , the concentration of holes and electrons in the stacking direction of the P-side guide layer 2206, i.e., the free carrier concentration, increases with increasing distance from the active layer 905. In this way, since the free carrier concentration in the stacking direction of the P-side guide layer 2206 cannot be reduced, the nitride-based semiconductor light-emitting device of Comparative Example 13 cannot achieve a reduction in free carrier loss and a reduction in the probability of non-radiative recombination. In the nitride-based semiconductor light-emitting device of Comparative Example 13, the effective refractive index difference ΔN is 3.3×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 31.3 nm and 10.8 nm, respectively, and the difference ΔP is 20.5 nm. The waveguide loss is 5.2 cm －１ and the guide layer free carrier loss is 3.6 cm －１ is.

[0265] In the nitride-based semiconductor light-emitting device of Comparative Example 14, as shown in graph (c) of FIG. 37 , the refractive index of the P-side guide layer 406 increases toward the active layer 905, so the peak of the light intensity distribution in the stacking direction can be moved closer to the active layer 905. Therefore, in the nitride-based semiconductor light-emitting device 900 according to this embodiment, the optical confinement factor is further improved than that of the nitride-based semiconductor light-emitting device of Comparative Example 13. Furthermore, since the bandgap energy of the P-side guide layer 406 continuously and monotonically increases with increasing distance from the active layer 905, the valence charge potential continuously decreases with increasing distance from the active layer 905, as shown in graph (d) of FIG. 38 . This makes it possible to maintain a substantially constant difference between the hole Fermi level and the valence charge potential in the P-side guide layer 406. Therefore, as shown in graph (c) of FIG. 39 , the hole and electron concentrations in the stacking direction of the P-side guide layer 406 can be reduced and maintained substantially constant. In this way, the free carrier concentration in the stacking direction of the P-side guide layer 406 can be reduced. However, since the band gap energy is discontinuous at the interface of the N-side guide layer 404 farther from the active layer 905 (i.e., the interface with the N-type second cladding layer 903), the hole concentration increases in a spike-like manner at the interface, as shown in graph (c) of FIG. 39 . Therefore, even in the nitride-based semiconductor light-emitting device of Comparative Example 14, non-radiative recombination and free carrier loss in the N-side guide layer 404 cannot be reduced. In the nitride-based semiconductor light-emitting device of Comparative Example 14, the effective refractive index difference ΔN is 2.1×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 1.3 nm and −4.3 nm, respectively, and the difference ΔP is 5.6 nm. The waveguide loss is 3.20 cm －１ and the guide layer free carrier loss is 1.8 cm －１ is.

[0266] In the nitride-based semiconductor light-emitting device 900 according to this embodiment, as shown in graph (d) of FIG. 37 , not only the refractive index of the P-side guide layer 906 but also the refractive index of the N-side guide layer 904 increases toward the active layer 905, making it easier to move the peak of the light intensity distribution in the stacking direction closer to the active layer 905. In the nitride-based semiconductor light-emitting device 900 according to this embodiment, an optical confinement coefficient equivalent to that of the nitride-based semiconductor light-emitting device of Comparative Example 14 can be obtained. Furthermore, since the bandgap energy of the N-side guide layer 904 increases continuously and monotonically with increasing distance from the active layer 905, discontinuity in the bandgap energy at the interface of the N-side guide layer 904 farther from the active layer 905 can be reduced. Therefore, as shown in graph (d) of FIG. 39 , the hole concentration at the interface and the N-side guide layer 904 can be significantly reduced compared to the nitride-based semiconductor light-emitting device of Comparative Example 14. In this way, since the free carrier concentrations in the P-side guide layer 906 and the N-side guide layer 904 can be reduced, the nitride-based semiconductor light-emitting device 900 according to this embodiment can achieve a reduction in free carrier loss and a reduction in the probability of non-radiative recombination. In the nitride-based semiconductor light-emitting device 900 according to this embodiment, the effective refractive index difference ΔN is 2.9×10 －３ The peak positions PS1 and PS2 of the light intensity distribution are 15.9 nm and 9.7 nm, respectively, and the difference ΔP is 6.2 nm. As described above, in this embodiment, by bringing the peak of the light intensity distribution closer to the active layer 905, the position PS1 and the difference ΔP can be reduced, and therefore non-linear portions are less likely to occur in the graph showing the IL characteristics. Furthermore, in this embodiment, the waveguide loss and free carrier loss can be reduced. In particular, in this embodiment, the free carrier loss can be reduced compared to each comparative example.

[0267] Next, the effect of reducing the operating voltage of the nitride-based semiconductor light-emitting device 900 according to this embodiment will be described with reference to FIGS. 40 and 41 , while comparing it with the nitride-based semiconductor light-emitting device of Comparative Example 14. FIG. 40 is a graph showing the relationship between the position in the stacking direction of the nitride-based semiconductor light-emitting device of Comparative Example 14 and the piezoelectric polarization charge density, piezoelectric polarization electric field, and conduction field potential. FIG. 41 is a graph showing the relationship between the position in the stacking direction of the nitride-based semiconductor light-emitting device 900 according to this embodiment and the piezoelectric polarization charge density, piezoelectric polarization electric field, and conduction field potential. Graphs (a), (b), and (c) in FIGS. 40 and 41 respectively show the relationship between the position in the stacking direction of each nitride-based semiconductor light-emitting device and the piezoelectric polarization charge density, piezoelectric polarization electric field, and conduction field potential. Note that graphs (c) in FIGS. 40 and 41 also show the hole Fermi levels with dashed lines.

[0268] As shown in graph (a) of Figure 40 , the piezoelectric polarization charge density of the N-side guide layer 404 of the nitride-based semiconductor light-emitting device of Comparative Example 14 is constant in the stacking direction. Therefore, there is a large gap in the piezoelectric polarization charge density at each interface between the N-side guide layer 404 and the N-type second cladding layer 903 and the active layer 905. Accordingly, piezoelectric polarization charges are locally formed at each interface between the N-side guide layer 404 and the N-type second cladding layer 903 and the active layer 905. This generates a large piezoelectric polarization electric field. Therefore, as shown in graph (b) of Figure 40 , a spike-shaped piezoelectric polarization electric field is generated at each interface between the N-side guide layer 404 and the N-type second cladding layer 903 and the active layer 905. As a result, holes are attracted to the vicinity of each interface between the N-side guide layer 404 and the N-type second cladding layer 903 and the active layer 905, and the conduction field potential at the interface increases (see ΔE1 shown in graph (c) of Figure 40).

[0269] 41A, the polarization charge density of the N-side guide layer 904 of the nitride-based semiconductor light-emitting device 900 according to this embodiment monotonically decreases from the interface closer to the active layer 905 to the interface farther from it. This reduces the gap in the piezoelectric polarization charge density at each interface between the N-side guide layer 904 and the N-type second cladding layer 903 and the active layer 905. This allows the piezoelectric polarization charges to be dispersed in the stacking direction of the N-side guide layer 904. This reduces the piezoelectric polarization electric field at each interface between the N-side guide layer 904 and the N-type second cladding layer 903 and the active layer 905, as shown in graph (b) of FIG. 41 (c), it is possible to suppress an increase in the conduction band potential (ΔE1 shown in graph (c) of FIG. 41 ) caused by the attraction of holes near the interfaces between the N-side guide layer 904 and the N-type second cladding layer 903 and between the N-side guide layer 904 and the active layer 905. As a result, in the nitride-based semiconductor light-emitting device 900 according to this embodiment, it is possible to improve the conductivity of electrons flowing from the N-type second cladding layer 903 toward the active layer 905, thereby reducing the operating voltage.

[0270] [9-3-2. Impurities in N-Side Guide Layer] Next, the effect of impurities in the N-side guide layer 904 according to this embodiment will be described.

[0271] In the nitride-based semiconductor light-emitting device 900 according to this embodiment, the optical confinement coefficient can be made higher than that of a nitride-based semiconductor light-emitting device in which the In composition ratio of the N-side guide layer is uniform. Moreover, in the nitride-based semiconductor light-emitting device 900 according to this embodiment, the optical confinement coefficient is almost independent of the impurity concentration.

[0272] In the nitride-based semiconductor light-emitting device 900 according to this embodiment, except when no impurities are added, the waveguide loss can be reduced compared to a nitride-based semiconductor light-emitting device in which the In composition ratio of the N-side guide layer is uniform. This is thought to be because the electron concentration increases when impurities are added, but the hole concentration decreases due to the band gap energy distribution in the stacking direction of the N-side guide layer 904.

[0273] In the nitride-based semiconductor light-emitting device 900 according to this embodiment, the operating voltage can be reduced compared to a nitride-based semiconductor light-emitting device of a comparative example in which the N-side guide layer has a uniform In composition ratio. Furthermore, by increasing the concentration of impurities added to the nitride-based semiconductor light-emitting device 900, the electron concentration in the N-side guide layer 904 can be increased, thereby further reducing the operating voltage.

[0274] In the nitride-based semiconductor light-emitting device 900 according to this embodiment, the impurity concentration in the N-side guide layer 904 is set to 1×10 １７ cm －３ 6 x 10 or more １７ cm －３ By setting the above, it is possible to reduce the operating voltage while suppressing a significant increase in waveguide loss.

[0275] Furthermore, by doping the N-side guide layer 904 with N-type impurities, the band gap energy of the N-side guide layer 904 increases with increasing distance from the active layer 905, as shown in the valence band band structure of graph (d) in FIG. 38 . Therefore, the potential of the valence band of the N-side guide layer 904 decreases with increasing distance from the active layer 905. Therefore, the potential of the valence band of the N-side guide layer 904 functions as a potential barrier that suppresses leakage of hole current injected from the P-type layer to the active layer 905 to the N-type layer. Here, increasing the N-type impurity concentration enhances the effect of suppressing hole leakage, thereby improving the probability of radiative recombination of electrons and holes in the active layer 905. This increases the quantum efficiency of the nitride-based semiconductor light-emitting device 900, thereby improving light-emitting efficiency.

[0276] Furthermore, doping the N-side guide layer 904 with an N-type impurity increases the electrical conductivity of electrons in the N-side guide layer 904, thereby reducing the operating voltage of the nitride-based semiconductor light-emitting element 900. The N-type impurity concentration in the N-side guide layer 904 is, for example, 3×10 １７ cm －３The N-type impurity concentration in the N-side guide layer 904 may be 2×10 or more. This ensures the above-mentioned effects. If the N-type impurity concentration in the N-side guide layer 904 is too high, the free carrier loss in the N-side guide layer 904 increases and the effect of suppressing hole leakage may become saturated. Therefore, the N-type impurity concentration in the N-side guide layer 904 should be 2×10 or more. １８ cm －３ In this way, the N-type impurity in the N-side guide layer 904 may be 3×10 １７ cm －３ That's it, 2 x 10 １８ cm －３ By satisfying the following conditions, it is possible to suppress the increase in free carrier loss due to doping with N-type impurities, while suppressing hole leakage and achieving a lower operating voltage by improving the electrical conductivity of electrons, thereby improving the luminous efficiency of the nitride-based semiconductor light-emitting element 900.

[0277] [9-3-3. Film Thickness of N-Side Guide Layer and P-Side Guide Layer] Next, the effect of the relationship between the film thicknesses of the N-side guide layer 904 and the P-side guide layer 906 according to this embodiment will be described.

[0278] By setting the thickness Tn of the N-side guide layer 904 to be 160 nm or more and 250 nm or less, the position PS1 can be located in the active layer 905. In other words, the thickness of the N-side guide layer 904 may be set to be 36% or more and 57% or less of the sum of the thicknesses of the N-side guide layer 904 and the P-side guide layer 906. This allows the position PS1 to be set to be -7 nm or more and 18 nm or less, that is, the peak of the light intensity distribution can be located in the active layer 905.

[0279] The difference ΔP can be reduced by setting the thickness Tn of the N-side guide layer 904 to less than 220 nm, that is, by setting it to be smaller than the thickness Tp of the P-side guide layer 906. In particular, the difference ΔP can be reduced to 20 nm or less by setting the thickness of the N-side guide layer 904 to be 23% to 43% of the sum of the thicknesses of the N-side guide layer 904 and the P-side guide layer. Even when the In composition ratio of the P-side guide layer 906 is constant at 2%, the difference ΔP can be reduced by setting the thickness of the N-side guide layer to be smaller than the thickness of the P-side guide layer 906. However, the difference ΔP can be further reduced by continuously and monotonically decreasing the In composition ratio with increasing distance from the active layer 905, as in the P-side guide layer 906 according to this embodiment.

[0280] [9-3-4. P-Type Cladding Layer] Next, the film thickness of the P-type cladding layer 910 according to this embodiment will be described with reference to FIGS. 42 and 43. FIG. 42 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting device of Comparative Example 15 and each numerical value obtained by simulation. Here, the nitride-based semiconductor light-emitting device of Comparative Example 15 differs from the nitride-based semiconductor light-emitting device 900 according to this embodiment in that the P-side electrode is made of Pd, but is the same in other respects. FIG. 43 is a diagram showing the relationship between the film thickness of the P-type cladding layer 910 of the nitride-based semiconductor light-emitting device 900 according to this embodiment and each numerical value obtained by simulation. In this simulation, the P-type cladding layer 910 having a concentration of 1×10 １９ cm －３ Mg-doped P-type Al ０．０３５ Ga ０．９６５ By changing the film thickness of the N layer, the film thickness of the entire P-type cladding layer 910 was changed to 0.45 μm, 0.35 μm, 0.25 μm, and 0.20 μm.

[0281] 42 and 43 , there is no significant difference between Comparative Example 15 and the present embodiment in terms of values ​​other than the waveguide loss, but the waveguide loss is significantly different between Comparative Example 15 and the present embodiment. Specifically, as the thickness of the P-type cladding layer decreases, the waveguide loss increases in Comparative Example 15. This is because as the thickness of the P-type cladding layer decreases, light seeps into the P-side electrode made of Pd, causing light loss. On the other hand, in the present embodiment, even if the thickness of the P-type cladding layer 910 decreases, light seeps into the P-side electrode 913 containing Ag can be suppressed, so the waveguide loss hardly increases.

[0282] In this way, in the nitride-based semiconductor light-emitting element 900 according to this embodiment, by providing the P-side electrode 913 containing Ag, it is possible to suppress an increase in waveguide loss even when the P-type cladding layer 910 is thinned to about 200 nm.

[0283] As described above, the nitride-based semiconductor light-emitting device 900 according to this embodiment can increase the optical confinement factor. Furthermore, in this embodiment, due to the configurations of the guide layers and barrier layers described above, the optical confinement factor does not decrease even when the thickness of the P-type cladding layer 910 is reduced to 200 nm.

[0284] As described above, in the nitride-based semiconductor light-emitting device 900 according to this embodiment, it is possible to reduce the film thickness of the P-type cladding layer 910, and therefore the operating voltage can be reduced.

[0285] [9-3-5. Barrier Layers] Next, the effects of the configuration of each barrier layer of the active layer 905 according to this embodiment will be described in comparison with a comparative example. In this embodiment, as described above, the band gap energy of each barrier layer is equal to or less than the minimum value of the band gap energy of the N-side guide layer 904 and the P-side guide layer 906. This makes it possible to increase the optical confinement factor. Accordingly, the difference ΔP can be reduced, making it less likely that a non-linear portion will occur in a graph showing the IL characteristics.

[0286] P-Side Electrode In the nitride-based semiconductor light-emitting element 900 according to the present embodiment, the P-side electrode 913 contains Ag, as in the nitride-based semiconductor light-emitting element 100 according to embodiment 1. This reduces optical loss in the P-side electrode 913 and improves the efficiency of the nitride-based semiconductor light-emitting element 900.

[0287] Tenth Embodiment A nitride-based semiconductor light-emitting device according to a tenth embodiment will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment in the band gap energy distribution of the P-side guide layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below, focusing on the differences from the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment.

[0288] First, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described with reference to Figures 44 and 45. Figure 44 is a schematic cross-sectional view showing the overall configuration of nitride-based semiconductor light-emitting device 1000 according to this embodiment. Figure 45 is a schematic graph showing the distribution of band gap energy in active layer 905 and each layer in the vicinity thereof of nitride-based semiconductor light-emitting device 1000 according to this embodiment.

[0289] 44 , the nitride-based semiconductor light-emitting element 1000 according to this embodiment includes a semiconductor laminate 1000S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor laminate 1000S includes a substrate 901, an N-type first cladding layer 902, an N-type second cladding layer 903, an N-side guide layer 904, an active layer 905, a P-side guide layer 1006, an intermediate layer 908, an electron barrier layer 909, a P-type cladding layer 910, and a contact layer 911.

[0290] 45, the P-side guide layer 1006 according to this embodiment differs from the P-side guide layer 906 according to the ninth embodiment in that the band gap energy is constant in the stacking direction. In this embodiment, the P-side guide layer 1006 is an undoped InP layer having a thickness of 280 nm. Ｘｐ Ga １－Ｘｐ The P-side guide layer 1006 is an N-layer, and the In composition ratio Xp is 2%.

[0291] In the nitride-based semiconductor light-emitting element 1000 having such an active layer 905 and P-side guide layer 1006, the operating voltage can be reduced and the optical confinement coefficient in the active layer 905 can be increased, similar to the nitride-based semiconductor light-emitting element 900 according to the ninth embodiment.

[0292] According to this embodiment, the effective refractive index difference ΔN is 3.5×10 －３ The position PS1 is 11.0 nm, the position PS2 is 2.5 nm, the difference ΔP is 8.5 nm, the optical confinement factor in the active layer 905 is 1.33%, and the waveguide loss is 4.3 cm －１ It is possible to realize a nitride-based semiconductor light-emitting device 1000 having the above structure.

[0293] Next, the film thickness of the P-type cladding layer 910 according to this embodiment will be described with reference to FIGS. 46 and 47 . FIG. 46 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting device of Comparative Example 16 and each numerical value obtained by simulation. Here, the nitride-based semiconductor light-emitting device of Comparative Example 16 differs from the nitride-based semiconductor light-emitting device 1000 according to this embodiment in that the P-side electrode is made of Pd, but is the same in other respects. FIG. 47 is a diagram showing the relationship between the film thickness of the P-type cladding layer 910 of the nitride-based semiconductor light-emitting device 1000 according to this embodiment and each numerical value obtained by simulation. In this simulation, the P-type cladding layer 910 having a concentration of 1×10 １９ cm －３ Mg-doped P-type Al ０．０３５ Ga ０．９６５ By changing the film thickness of the N layer, the film thickness of the entire P-type cladding layer 910 was changed to 0.45 μm, 0.35 μm, 0.25 μm, and 0.20 μm.

[0294] 46 and 47 , there is no significant difference between Comparative Example 16 and the present embodiment in terms of values ​​other than the waveguide loss, but the waveguide loss is significantly different between Comparative Example 16 and the present embodiment. Specifically, as the thickness of the P-type cladding layer decreases, the waveguide loss increases in Comparative Example 16. This is because as the thickness of the P-type cladding layer decreases, light seeps into the P-side electrode made of Pd, causing light loss. On the other hand, in the present embodiment, even if the thickness of the P-type cladding layer 910 decreases, light seeps into the P-side electrode 913 containing Ag can be suppressed, so the waveguide loss hardly increases.

[0295] In this way, in the nitride-based semiconductor light-emitting element 1000 according to this embodiment, by providing the P-side electrode 913 containing Ag, it is possible to suppress an increase in waveguide loss even when the P-type cladding layer 910 is thinned to about 200 nm.

[0296] As described above, in the nitride-based semiconductor light-emitting device 1000 according to this embodiment, it is possible to reduce the film thickness of the P-type cladding layer 910, and therefore the operating voltage can be reduced.

[0297] Eleventh Embodiment A nitride-based semiconductor light-emitting device according to an eleventh embodiment will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from the nitride-based semiconductor light-emitting device 1000 according to the tenth embodiment in the band gap energy distribution of the P-side guide layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below, focusing on the differences from the nitride-based semiconductor light-emitting device 1000 according to the tenth embodiment.

[0298] First, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described with reference to Figures 48 and 49. Figure 48 is a schematic cross-sectional view showing the overall configuration of nitride-based semiconductor light-emitting device 1100 according to this embodiment. Figure 49 is a schematic graph showing the distribution of band gap energy in active layer 905 and each layer in the vicinity thereof of nitride-based semiconductor light-emitting device 1100 according to this embodiment.

[0299] 48 , the nitride-based semiconductor light-emitting device 1100 according to this embodiment includes a semiconductor laminate 1100S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor laminate 1100S includes a substrate 901, an N-type first cladding layer 902, an N-type second cladding layer 903, an N-side guide layer 904, an active layer 905, a P-side guide layer 1106, an intermediate layer 908, an electron barrier layer 909, a P-type cladding layer 910, and a contact layer 911.

[0300] As shown in FIG. 45 , the P-side guide layer 1106 according to this embodiment differs from the P-side guide layer 1006 according to the tenth embodiment in that the band gap energy changes stepwise in the stacking direction. The P-side guide layer 1106 has a P-side first guide layer 1106a and a P-side second guide layer 1106b. The P-side first guide layer 1106a is disposed above the active layer 905 and is a guide layer having a band gap energy larger than that of the active layer 905. The P-side second guide layer 1106b is disposed above the P-side first guide layer 1106a and is a guide layer having a band gap energy larger than that of the P-side first guide layer 1106a. In this embodiment, the P-side first guide layer 1106a is an undoped InP layer having a thickness of 80 nm. ０．０４ Ga ０．９６ The P-side second guide layer 1106b is an undoped In layer with a thickness of 200 nm. ０．０１ Ga ０．９９ The P-side first guide layer 1106a is an N layer. In this way, the In composition ratio of the P-side first guide layer 1106a is larger than that of the P-side second guide layer 1106b.

[0301] In the nitride-based semiconductor light-emitting device 1100 having such a P-side guide layer 1106, the operating voltage can be reduced and the optical confinement coefficient in the active layer 905 can be increased, similar to the nitride-based semiconductor light-emitting device 1000 according to the tenth embodiment.

[0302] According to this embodiment, the effective refractive index difference ΔN is 2.8×10 －３ The position PS1 is 13.1 nm, the difference ΔP is 4.0 nm, the optical confinement coefficient in the active layer 905 is 1.47%, and the waveguide loss is 3.4 cm －１It is possible to realize a nitride-based semiconductor light-emitting device 1100 having the above structure.

[0303] Next, the film thickness of the P-type cladding layer 910 according to this embodiment will be described with reference to FIGS. 50 and 51 . FIG. 50 is a diagram showing the relationship between the film thickness of the P-type cladding layer of the nitride-based semiconductor light-emitting device of Comparative Example 17 and each numerical value obtained by simulation. Here, the nitride-based semiconductor light-emitting device of Comparative Example 17 differs from the nitride-based semiconductor light-emitting device 1100 according to this embodiment in that the P-side electrode is made of Pd, but is the same in other respects. FIG. 51 is a diagram showing the relationship between the film thickness of the P-type cladding layer 910 of the nitride-based semiconductor light-emitting device 1100 according to this embodiment and each numerical value obtained by simulation. In this simulation, the P-type cladding layer 910 having a concentration of 1×10 １９ cm －３ Mg-doped P-type Al ０．０３５ Ga ０．９６５ By changing the film thickness of the N layer, the film thickness of the entire P-type cladding layer 910 was changed to 0.45 μm, 0.35 μm, 0.25 μm, and 0.20 μm.

[0304] 50 and 51 , there is no significant difference between Comparative Example 17 and the present embodiment in terms of values ​​other than the waveguide loss, but the waveguide loss is significantly different between Comparative Example 17 and the present embodiment. Specifically, as the thickness of the P-type cladding layer decreases, the waveguide loss increases in Comparative Example 17. This is because as the thickness of the P-type cladding layer decreases, light seeps into the P-side electrode made of Pd, causing light loss. On the other hand, in the present embodiment, even if the thickness of the P-type cladding layer 910 decreases, light seeps into the P-side electrode 913 containing Ag can be suppressed, so the waveguide loss hardly increases.

[0305] In this way, in the nitride-based semiconductor light-emitting element 1100 according to this embodiment, by providing the P-side electrode 913 containing Ag, it is possible to suppress an increase in waveguide loss even when the P-type cladding layer 910 is thinned to about 200 nm.

[0306] As described above, in the nitride-based semiconductor light-emitting device 1100 according to this embodiment, it is possible to reduce the film thickness of the P-type cladding layer 910, and therefore the operating voltage can be reduced.

[0307] Twelfth Embodiment A nitride-based semiconductor light-emitting device according to a twelfth embodiment will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment mainly in the band gap energy distribution of the N-side guide layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below, focusing on the differences from the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment.

[0308] [12-1. Overall Configuration] First, the overall configuration of the nitride-based semiconductor light-emitting device according to this embodiment will be described with reference to Figures 52 and 53. Figure 52 is a schematic cross-sectional view showing the overall configuration of nitride-based semiconductor light-emitting device 1200 according to this embodiment. Figure 53 is a schematic graph showing the distribution of band gap energy in active layer 905 and each layer in the vicinity thereof of nitride-based semiconductor light-emitting device 1200 according to this embodiment.

[0309] 52 , a nitride-based semiconductor light-emitting device 1200 according to this embodiment includes a semiconductor laminate 1200S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor laminate 1200S includes a substrate 901, an N-type first cladding layer 902, an N-type second cladding layer 903, an N-side guide layer 1204, an active layer 905, a P-side guide layer 906, an intermediate layer 908, an electron barrier layer 909, a P-type cladding layer 910, and a contact layer 911.

[0310] In the N-side guide layer 1204 according to this embodiment, similarly to the N-side guide layer 904 according to the ninth embodiment, the band gap energy increases continuously and monotonically with increasing distance from the active layer 905. In this embodiment, the N-side guide layer 1204 is made of N-type In Ｘｎ Ga １－Ｘｎ The N-side guide layer 1204 is an N layer, and the impurity is a 3×10 １７ cm －３The N-side guide layer 1204 is doped with Si. The absolute value of the average rate of change in the In composition ratio in the stacking direction in the region from the interface of the N-side guide layer 1204 closer to the active layer 905 to the center of the N-side guide layer 1204 in the stacking direction is smaller than the absolute value of the average rate of change in the In composition ratio in the stacking direction in the region from the center to the interface of the N-side guide layer 1204 closer to the N-type first cladding layer 902. In other words, the curve showing the relationship between the position in the stacking direction of the N-side guide layer 1204 and the In composition ratio has an upward convex shape. In further words, the curve showing the relationship between the position in the stacking direction of the N-side guide layer 1204 and the band gap energy has a downward convex shape (see FIG. 53 ).

[0311] The N-side guide layer 1204 includes an N-side first guide layer 1204a and an N-side second guide layer 1204b. The N-side first guide layer 1204a is a guide layer disposed above the N-type second cladding layer 903. The N-side first guide layer 1204a is an In Ｘｎ Ga １－Ｘｎ More specifically, the N-side first guide layer 1204a is an In layer near the interface farther from the active layer 905. Ｘｎ２ Ga １－Ｘｎ２ N, and in the vicinity of the interface closer to the active layer 905 Ｘｎｍ Ga １－Ｘｎｍ N (see FIG. 53). The In composition ratio Xn of the N-side first guide layer 1204a decreases at a constant rate as it moves away from the active layer 905. The N-side second guide layer 1204b is a guide layer disposed above the N-side first guide layer 1204a. In other words, the N-side second guide layer 1204b is disposed between the N-side first guide layer 1204a and the active layer 905. The N-side second guide layer 1204b is an 80 nm thick N-type In Ｘｎ Ga １－Ｘｎ More specifically, the N-side second guide layer 1204b is an In layer near the interface closer to the active layer 905. Ｘｎ１ Ga １－Ｘｎ１ N, and in the vicinity of the interface farther from the active layer 905 Ｘｎｍ Ga １－ＸｎｍThe In composition ratio Xn of the N-side second guide layer 1204b decreases at a constant rate with increasing distance from the active layer 905. In this embodiment, Xn1=0.04, Xnm=0.03, and Xn2=0.

[0312] [12-2. Effects] The effects of the configuration of each barrier layer of the active layer 905 according to this embodiment will be described below in comparison with a comparative example. In this embodiment, as described above, the band gap energy of each barrier layer is equal to or less than the minimum value of the band gap energy of the N-side guide layer 1204 and the P-side guide layer 906.

[0313] In this embodiment, the bandgap energy of each barrier layer is equal to or less than that of each guide layer, i.e., the refractive index of each barrier layer is greater than that of each guide layer. Therefore, the optical confinement factor can be increased compared to when the bandgap energy of each barrier layer is greater than the minimum value of the bandgap energy of the N-side guide layer 1204 and the P-side guide layer 906. Accordingly, in this embodiment, the position PS1 and the difference ΔP can also be reduced. In this way, since the difference ΔP can be reduced in this embodiment, non-linear portions are less likely to occur in the graph showing the IL characteristics.

[0314] (Embodiment 13) A nitride-based semiconductor light-emitting device according to embodiment 13 will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from the nitride-based semiconductor light-emitting device 900 according to embodiment 9 in the relationship between the Al composition ratios of the N-type first cladding layer and the P-type cladding layer, and in the configuration of the electron barrier layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below with reference to FIG. 54 , focusing on the differences from the nitride-based semiconductor light-emitting device 900 according to embodiment 9.

[0315] FIG. 54 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting device 1300 according to this embodiment.

[0316] 54 , a nitride-based semiconductor light-emitting device 1300 according to this embodiment includes a semiconductor stack 1300S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor stack 1300S includes a substrate 901, an N-type first cladding layer 1302, an N-type second cladding layer 903, an N-side guide layer 904, an active layer 905, a P-side guide layer 906, an intermediate layer 908, an electron barrier layer 1309, a P-type cladding layer 1310, and a contact layer 911.

[0317] The N-type first cladding layer 1302 according to this embodiment is an N-type Al 1N 2 O 3 layer having a thickness of 1200 nm. ０．０３６ Ga ０．９６４ The N-type first cladding layer 1302 contains an impurity of 1×10 １８ cm －３ is doped with Si.

[0318] The P-type cladding layer 1310 according to this embodiment is disposed between the electron barrier layer 1309 and the contact layer 911. The P-type cladding layer 1310 has a lower refractive index than the active layer 905 and a higher band gap energy. In this embodiment, the P-type cladding layer 1310 is a P-type Al 1000 SiO 2 layer having a thickness of 450 nm. ０．０２６ Ga ０．９７４ The P-type cladding layer 1310 is an N layer. The P-type cladding layer 1310 is doped with Mg as an impurity. The impurity concentration at the end of the P-type cladding layer 1310 closer to the active layer 905 is lower than the impurity concentration at the end farther from the active layer 905. Specifically, the P-type cladding layer 1310 has a concentration of 2×10 １８ cm －３ P-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 300 nm ０．０２６ Ga ０．９７４ N layers.

[0319] A ridge 1310R is formed in the P-type cladding layer 1310, similar to the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment. Furthermore, two grooves 1310T are formed in the P-type cladding layer 1310, arranged along the ridge 1310R and extending in the Y-axis direction.

[0320] In this embodiment, the N-type first cladding layer 1302 and the P-type cladding layer 1310 contain Al, and when the Al composition ratios of the N-type first cladding layer 1302 and the P-type cladding layer 1310 are Ync and Ypc, respectively, the relationship Ync>Ypc (34) is satisfied.

[0321] Here, when at least one of the N-type first cladding layer 1302 and the P-type cladding layer 1310 has a superlattice structure, the composition ratios Ync and Ypc represent average Al composition ratios. For example, when the N-type first cladding layer 1302 includes multiple 2-nm-thick GaN layers and multiple 2-nm-thick AlGaN layers with an Al composition ratio of 0.07, and the multiple GaN layers and the multiple AlGaN layers are alternately stacked, Ync is 0.035, which is the average Al composition ratio of the entire N-type first cladding layer 1302. When the P-type cladding layer 1310 includes multiple 2-nm-thick GaN layers and multiple 2-nm-thick AlGaN layers with an Al composition ratio of 0.07, and the multiple GaN layers and the multiple AlGaN layers are alternately stacked, Ypc is 0.035, which is the average Al composition ratio of the entire P-type cladding layer 1310.

[0322] Since the above formula (34) is satisfied, the refractive index of the N-type first cladding layer 1302 can be made lower than the refractive index of the P-type cladding layer 1310. Therefore, even if the film thickness of the P-type cladding layer 1310 is reduced in order to reduce the operating voltage of the nitride-based semiconductor light-emitting device 1300, the refractive index of the N-type first cladding layer 1302 is lower than the refractive index of the P-type cladding layer 1310, and therefore, it is possible to prevent the peak of the light intensity distribution in the stacking direction from shifting in a direction approaching the N-type first cladding layer 1302 from the active layer 905.

[0323] The electron barrier layer 1309 is disposed above the active layer 905 and is a nitride-based semiconductor layer containing at least Al. In this embodiment, the electron barrier layer 1309 is disposed between the intermediate layer 908 and the P-type cladding layer 1310. The electron barrier layer 1309 is a P-type AlGaN layer with a thickness of 5 nm. The electron barrier layer 1309 also has an Al composition ratio gradient region in which the Al composition ratio monotonically increases toward the P-type cladding layer 1310. Here, the configuration in which the Al composition ratio monotonically increases also includes a configuration including a region in which the Al composition ratio is constant in the stacking direction. For example, the configuration in which the Al composition ratio monotonically increases also includes a configuration in which the Al composition ratio increases stepwise. In the electron barrier layer 1309 according to this embodiment, the entire electron barrier layer 1309 is an Al composition ratio increasing region, and the Al composition ratio increases at a constant rate in the stacking direction. Specifically, the electron barrier layer 1309 has an Al composition ratio gradient region near the interface with the intermediate layer 908. ０．０２ Ga ０．９８ The Al composition ratio increases monotonically as the layer approaches the P-type cladding layer 1310. ０．３６ Ga ０．６４ The electron barrier layer 1309 has a composition represented by the formula: N. The electron barrier layer 1309 contains impurities at a concentration of 1×10 １９ cm －３ It is doped with Mg.

[0324] The electron barrier layer 1309 can prevent electrons from leaking from the active layer 905 to the P-type cladding layer 1310. Furthermore, since the electron barrier layer 1309 has an Al composition ratio increasing region where the Al composition ratio monotonically increases, the potential barrier of the valence band of the electron barrier layer 1309 can be reduced compared to when the Al composition ratio is uniform. This facilitates the flow of holes from the P-type cladding layer 1310 to the active layer 905. Therefore, even when the P-side guide layer 906, which is an undoped layer, has a large thickness, as in this embodiment, an increase in the electrical resistance of the nitride-based semiconductor light-emitting device 1300 can be suppressed. This allows the operating voltage of the nitride-based semiconductor light-emitting device 1300 to be reduced. Furthermore, self-heating of the nitride-based semiconductor light-emitting device 1300 during operation can be reduced, thereby improving the temperature characteristics of the nitride-based semiconductor light-emitting device 1300. Therefore, high-power operation of the nitride-based semiconductor light-emitting device 1300 is possible.

[0325] Fourteenth Embodiment A nitride-based semiconductor light-emitting device according to a fourteenth embodiment will be described. The nitride-based semiconductor light-emitting device according to this embodiment differs from the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment in that the average band gap energy of the P-side guide layer is larger than the average band gap energy of the N-side guide layer. The nitride-based semiconductor light-emitting device according to this embodiment will be described below with reference to FIGS. 55 and 56 , focusing on the differences from the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment.

[0326] Fig. 55 is a schematic cross-sectional view showing the overall configuration of nitride-based semiconductor light-emitting device 1400 according to this embodiment. Fig. 56 is a schematic graph showing the distribution of band gap energy in active layer 905 and each layer in the vicinity thereof of nitride-based semiconductor light-emitting device 1400 according to this embodiment.

[0327] 55 , a nitride-based semiconductor light-emitting device 1400 according to this embodiment includes a semiconductor laminate 1400S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor laminate 1400S includes a substrate 901, an N-type first cladding layer 902, an N-type second cladding layer 903, an N-side guide layer 904, an active layer 905, a P-side guide layer 1406, an intermediate layer 908, an electron barrier layer 909, a P-type cladding layer 910, and a contact layer 911.

[0328] In this embodiment, the P-side guide layer 1406 is an undoped In layer having a thickness of 280 nm. Ｘｐ Ga １－Ｘｐ More specifically, the P-side guide layer 1406 is an In layer near the interface closer to the active layer 905. ０．０３ Ga ０．９７ The p-side guide layer 1406 has a composition represented by N in the vicinity of the interface farther from the active layer 905, and a composition represented by GaN in the vicinity of the interface farther from the active layer 905. The In composition ratio Xp of the p-side guide layer 1406 decreases at a constant rate as it becomes farther from the active layer 905.

[0329] As described above, the average In composition ratio of the P-side guide layer 1406 according to this embodiment is less than the average In composition ratio of the N-side guide layer 904. Therefore, the average bandgap energy of the P-side guide layer 1406 is greater than the average bandgap energy of the N-side guide layer 904 (see FIG. 56 ). In other words, the average refractive index of the P-side guide layer 1406 is less than the average refractive index of the N-side guide layer 904. Here, because the thickness of the P-side guide layer 1406 is greater than the thickness of the N-side guide layer 904, the peak of the light intensity distribution may be biased toward the P-side guide layer 1406 relative to the active layer 905. In this embodiment, because the average refractive index of the P-side guide layer 1406 is less than the average refractive index of the N-side guide layer 904, the peak of the light intensity distribution can be prevented from being biased toward the P-side guide layer 1406 relative to the active layer 905.

[0330] Furthermore, the In composition ratio of the P-side guide layer 1406 continuously and monotonically decreases with increasing distance from the active layer 905. In other words, the refractive index of the P-side guide layer 1406 continuously and monotonically increases with increasing distance from the active layer 905. This allows the peak of the light intensity distribution in the stacking direction to be closer to the active layer 905.

[0331] Fifteenth Embodiment A nitride-based semiconductor light-emitting element according to a fifteenth embodiment will be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 900 according to the ninth embodiment mainly in the wavelength band of emitted light. The nitride-based semiconductor light-emitting element according to this embodiment will be described below with reference to Figures 57A, 57B, and 58, focusing on the differences from the nitride-based semiconductor light-emitting element 900 according to the ninth embodiment.

[0332] Fig. 57A is a schematic cross-sectional view showing the overall configuration of nitride-based semiconductor light-emitting device 1500 according to this embodiment. Fig. 57B is a schematic cross-sectional view showing the configuration of active layer 1505 included in nitride-based semiconductor light-emitting device 1500 according to this embodiment. Fig. 58 is a schematic graph showing the distribution of band gap energy in active layer 1505 and each layer in the vicinity thereof of nitride-based semiconductor light-emitting device 1500 according to this embodiment.

[0333] 57A , the nitride-based semiconductor light-emitting device 1500 according to this embodiment includes a semiconductor stack 1500S, a current blocking layer 912, a P-side electrode 913, and an N-side electrode 914. The semiconductor stack 1500S includes a substrate 901, an N-type first cladding layer 1502, an N-side guide layer 1504, an active layer 1505, a P-side guide layer 1506, an electron barrier layer 1509, a P-type cladding layer 1510, and a contact layer 911.

[0334] The N-type first cladding layer 1502 according to this embodiment is an N-type Al 1N 2 O 3 layer having a thickness of 740 nm. ０．１０ Ga ０．９０ The N-type first cladding layer 1502 contains an impurity of 5×10 １７ cm －３ is doped with Si.

[0335] The N-side guide layer 1504 according to this embodiment is an N-type AlN layer having a thickness of 130 nm. Ｘｎａ Ga １－Ｘｎａ The N-side guide layer 1504 contains an impurity of 5×10 １７ cm －３ More specifically, the N-side guide layer 1504 is doped with Al in the vicinity of the interface closer to the active layer 1505. Ｘｎａ１ Ga １－Ｘｎａ１ N, and in the vicinity of the interface farther from the active layer 1505 Ｘｎａ２ Ga １－Ｘｎａ２ In this embodiment, the Al composition ratio Xna1 of the N-side guide layer 1504 near the interface closer to the active layer 1505 is 0, and the Al composition ratio Xna2 of the N-side guide layer 1504 near the interface farther from the active layer 1505 is 0.06 (i.e., 6%). The Al composition ratio Xna of the N-side guide layer 1504 increases at a constant rate with increasing distance from the active layer 1505.

[0336] As shown in FIG. 57B, the active layer 1505 according to this embodiment includes a well layer 1505b and barrier layers 1505a and 1505c.

[0337] The barrier layer 1505a is disposed above the N-side guide layer 1504 and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 1505a is an undoped AlN layer having a thickness of 11 nm. ０．０５ Ga ０．９５ This is the N layer.

[0338] The well layer 1505b is disposed above the barrier layer 1505a and functions as a well of the quantum well structure. The well layer 1505b is disposed between the barrier layer 1505a and the barrier layer 1505c. In this embodiment, the well layer 1505b is an undoped In layer having a thickness of 17.5 nm. ０．０１ Ga ０．９９ This is the N layer.

[0339] The barrier layer 1505c is disposed above the well layer 1505b and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 1505c is an undoped Al layer having a thickness of 11 nm. ０．０５ Ga０．９５ This is the N layer.

[0340] The nitride-based semiconductor light-emitting device 1500 according to this embodiment includes the active layer 1505 having the above-described configuration, and can emit light with a wavelength of 350 nm or more and 390 nm or less.

[0341] The p-side guide layer 1506 according to this embodiment is an undoped AlN layer having a thickness of 280 nm. ０．０５ Ga ０．９５ This is the N layer.

[0342] The electron barrier layer 1509 according to this embodiment is a P-type Al layer having a thickness of 5 nm. ０．３６ Ga ０．６４ The electron barrier layer 1509 contains an impurity of 1×10 １９ cm －３ It is doped with Mg.

[0343] The P-type cladding layer 1510 according to this embodiment is disposed between the electron barrier layer 1509 and the contact layer 911. The P-type cladding layer 1510 has a lower refractive index than the active layer 1505 and a higher band gap energy. In this embodiment, the P-type cladding layer 1510 is a P-type Al 1000 SiO 2 layer having a thickness of 660 nm. ０．１０ Ga ０．９０ The P-type cladding layer 1510 is an N layer. The P-type cladding layer 1510 is doped with Mg as an impurity. The impurity concentration at the end of the P-type cladding layer 1510 closer to the active layer 1505 is lower than the impurity concentration at the end farther from the active layer 1505. Specifically, the P-type cladding layer 1510 has a concentration of 2×10 １８ cm －３ P-type Al doped with Mg having a thickness of 250 nm ０．１０ Ga ０．９０ N layer and a layer with a concentration of 1×10 １９ cm －３ P-type Al doped with Mg having a thickness of 410 nm ０．１０ Ga ０．９０ N layers.

[0344] A ridge 1510R is formed in the P-type cladding layer 1510, similar to the nitride-based semiconductor light-emitting device 900 according to the ninth embodiment. Two grooves 1510T are formed in the P-type cladding layer 1510, arranged along the ridge 1510R and extending in the Y-axis direction. In this embodiment, the thickness dc of the P-type cladding layer 1510 at the lower end of the ridge 1510R is 30 nm.

[0345] As described above, in the nitride-based semiconductor light-emitting device 1500 according to this embodiment, the Al composition ratio Xna of the N-side guide layer 1504 monotonically increases with increasing distance from the active layer 1505. In other words, the refractive index of the N-side guide layer 1504 monotonically increases with increasing distance from the active layer 1505. This allows the peak of the light intensity distribution in the stacking direction to be closer to the active layer 1505.

[0346] Furthermore, in this embodiment, the thickness of the P-side guide layer 1506 is greater than the thickness of the N-side guide layer 1504. This increases the distance dp between the bottom end of the ridge 1510R and the active layer 1505 compared to when the thickness of the P-side guide layer 1506 is equal to or less than the thickness of the N-side guide layer 1504, thereby reducing the effective refractive index difference ΔN. This therefore increases the stability of the light output of the nitride-based semiconductor light-emitting element 1500.

[0347] Furthermore, in this embodiment, the Al composition ratio of the P-side guide layer 1506 is larger than the average Al composition ratio of the N-side guide layer 1504. That is, the average bandgap energy of the P-side guide layer 1506 is larger than the average bandgap energy of the N-side guide layer 1504 (see FIG. 58 ). Therefore, the average refractive index of the P-side guide layer 1506 is smaller than the average refractive index of the N-side guide layer 1504. As described above, because the thickness of the P-side guide layer 1506 is larger than the thickness of the N-side guide layer 1504, the peak of the light intensity distribution may be biased toward the P-side guide layer 1506 relative to the active layer 1505. In this embodiment, because the average refractive index of the P-side guide layer 1506 is smaller than the average refractive index of the N-side guide layer 1504, it is possible to prevent the peak of the light intensity distribution from being biased toward the P-side guide layer 1506 relative to the active layer 1505.

[0348] In this embodiment, the series resistance of the nitride-based semiconductor light-emitting device 1500 can be reduced by doping the N-side guide layer 1504 with an N-type impurity, as in the ninth embodiment. Furthermore, in this embodiment, as shown in FIG. 58 , the minimum bandgap energy of the N-side guide layer 1504 (i.e., the bandgap energy of the N-side guide layer 1504 near the interface with the active layer 1505) is smaller than the bandgap energy of the barrier layer 1505 a. Thus, even when the bandgap energy of the N-side guide layer 1504 near the interface with the active layer 1505 is smaller than the bandgap energy of the barrier layer 1505 a, an increase in the hole concentration in the N-side guide layer 1504 can be suppressed by doping the N-side guide layer 1504 with an N-type impurity. As a result, the probability of non-radiative recombination of electrons and holes in the N-side guide layer 1504 can be reduced, thereby suppressing a decrease in the luminous efficiency and long-term reliability of the nitride-based semiconductor light-emitting device 1500.

[0349] Furthermore, according to the nitride-based semiconductor light-emitting device 1500 of this embodiment, even if the wavelength corresponding to the energy difference between the ground quantum levels of electrons and holes is 380 nm or less, the barrier layers 1505 a and 1505 c have an Al composition of 0.04 or more. ０．０５ Ga ０．９５ Because the barrier layers 1505a and 1505c are formed of N layers, the bandgap energy of the barrier layers 1505a and 1505c is 3.47 eV or more, which is sufficiently greater than the energy of 3.28 eV corresponding to a wavelength of 375 nm. Therefore, a quantum level that results in an emission wavelength in the 375 nm band can be easily formed in the well layer 1505b. Furthermore, because electrons and holes can be confined to the quantum level of the quantum well region, leakage of electrons and holes in the quantum well region to the N-side guide layer 1504 and the P-side guide layer 1506 can be suppressed. Therefore, the light-emitting efficiency of the nitride-based semiconductor light-emitting element 1500 can be improved, and the temperature characteristics of the nitride-based semiconductor light-emitting element 1500 can be improved.

[0350] (First Modification of Fifteenth Embodiment) Next, a nitride-based semiconductor light-emitting device according to a first modification of the fifteenth embodiment will be described. The nitride-based semiconductor light-emitting device according to this modification differs from the nitride-based semiconductor light-emitting device 1500 according to the fifteenth embodiment in the bandgap energy distribution in the stacking direction of the P-side guide layer, but is the same in other respects. The nitride-based semiconductor light-emitting device according to this modification will be described below with reference to FIG. 59. FIG. 59 is a schematic graph showing the bandgap energy distribution of the active layer 1505 and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device according to this modification.

[0351] 59, the P-side guide layer 1506A of the nitride-based semiconductor light-emitting device according to this modification has a P-side first guide layer 1506a and a P-side second guide layer 1506b. The P-side first guide layer 1506a is a guide layer disposed above the active layer 1505. The P-side second guide layer 1506b is a guide layer disposed above the P-side first guide layer 1506a and has a larger bandgap energy than the P-side first guide layer 1506a. In this modification, the P-side first guide layer 1506a is a 70 nm-thick undoped Al ０．０１ Ga ０．９９ The P-side second guide layer 1506b is an undoped Al layer with a thickness of 210 nm. ０．０５ Ga ０．９５ The P-side first guide layer 1506a is an N layer. Thus, the Al composition ratio of the P-side first guide layer 1506a is larger than that of the P-side second guide layer 1506b.

[0352] The nitride-based semiconductor light-emitting element according to this modification also achieves the same effects as the nitride-based semiconductor light-emitting element 1500 according to the fifteenth embodiment. Furthermore, in this modification, the Al composition ratio of the P-side guide layer 1506A increases stepwise with increasing distance from the active layer 1505. This makes it possible to make the refractive index of the region of the P-side guide layer 1506A close to the active layer 1505 higher than the refractive index of the region far from the active layer 1505, thereby bringing the peak of the light intensity distribution closer to the active layer 1505. This makes it possible to improve the optical confinement factor, the waveguide loss, and the peak position of the light intensity distribution.

[0353] (Second Modification of Fifteenth Embodiment) Next, a nitride-based semiconductor light-emitting device according to a second modification of the fifteenth embodiment will be described. The nitride-based semiconductor light-emitting device according to this modification differs from the nitride-based semiconductor light-emitting device 1500 according to the fifteenth embodiment in the bandgap energy distribution in the stacking direction of the P-side guide layer, but is the same in other respects. The nitride-based semiconductor light-emitting device according to this modification will be described below with reference to FIG. 60. FIG. 60 is a schematic graph showing the bandgap energy distribution of the active layer 1505 and each layer in the vicinity thereof of the nitride-based semiconductor light-emitting device according to this modification.

[0354] The p-side guide layer 1506B according to this modification is an undoped Al Ｘｐａ Ga １－Ｘｐａ More specifically, the P-side guide layer 1506B has a composition represented by GaN near the interface closer to the active layer 1505, and an Al layer near the interface farther from the active layer 1505. ０．０８ Ga ０．９２ N. The Al composition ratio Xpa of the P-side guide layer 1506B increases at a constant rate with increasing distance from the active layer 1505. Therefore, the band gap energy of the P-side guide layer 1506B increases continuously and monotonically with increasing distance from the active layer 1505.

[0355] The nitride-based semiconductor light-emitting element according to this modification also achieves the same effects as the nitride-based semiconductor light-emitting element 1500 according to embodiment 15. Furthermore, in this modification, the Al composition ratio of the P-side guide layer 1506B continuously and monotonically increases with increasing distance from the active layer 1505. This increases the refractive index of the P-side guide layer 1506B with increasing distance from the active layer 1505, allowing the peak of the light intensity distribution to be closer to the active layer 1505.

[0356] (Modifications, etc.) Although the nitride-based semiconductor light-emitting device according to the present disclosure has been described above based on the respective embodiments, the present disclosure is not limited to the above-described respective embodiments.

[0357] For example, in the above-described embodiments, examples have been shown in which the nitride-based semiconductor light-emitting element is a semiconductor laser element. However, the nitride-based semiconductor light-emitting element is not limited to a semiconductor laser element. For example, the nitride-based semiconductor light-emitting element may be a superluminescent diode. In this case, the reflectance of the end face of the semiconductor stack included in the nitride-based semiconductor light-emitting element with respect to light emitted from the semiconductor stack may be 0.1% or less. Such a reflectance can be achieved, for example, by forming an anti-reflection film made of a dielectric multilayer film or the like on the end face. Alternatively, by using an inclined stripe structure in which the ridge serving as the waveguide intersects with the front end face at an angle of 5° or more from the normal direction of the front end face, the proportion of the component of the guided light reflected at the front end face that recouples with the waveguide and becomes guided light can be reduced to a small value of 0.1% or less.

[0358] Furthermore, in the first and second embodiments, the nitride-based semiconductor light-emitting element has an active layer structure including two well layers, but may have a structure including only a single well layer. Thus, even when the active layer includes only one high-refractive-index well layer, by using the N-side guide layer 104, P-side first guide layer 106, and P-side second guide layer 107 of the present disclosure, it is possible to improve the controllability of the position of the light distribution in the vertical direction (i.e., the stacking direction), thereby positioning the peak of the light distribution in the vertical direction near the well layer. Therefore, it is possible to realize a nitride-based semiconductor light-emitting element having a low lasing threshold, low waveguide loss, a high optical confinement factor, and current-light output (IL) characteristics with excellent linearity.

[0359] Furthermore, although the nitride-based semiconductor light-emitting element in each of the above-described embodiments has a single ridge, the nitride-based semiconductor light-emitting element may have multiple ridges. Such a nitride-based semiconductor light-emitting element will be described with reference to FIG. 61 . FIG. 61 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element 1600 according to Modification 1. As shown in FIG. 61 , the nitride-based semiconductor light-emitting element 1600 according to Modification 1 has a configuration in which a plurality of nitride-based semiconductor light-emitting elements 100 according to Embodiment 1 are horizontally arranged in an array. In FIG. 61 , the nitride-based semiconductor light-emitting element 1600 has a configuration in which three nitride-based semiconductor light-emitting elements 100 are integrally arranged, but the number of nitride-based semiconductor light-emitting elements 100 included in the nitride-based semiconductor light-emitting element 1600 is not limited to three. The number of nitride-based semiconductor light-emitting elements 100 included in the nitride-based semiconductor light-emitting element 1600 may be two or more. Each nitride-based semiconductor light-emitting element 100 has a light-emitting portion 100E that emits light. Light-emitting portion 100E is a portion of active layer 105 that emits light, and corresponds to a portion of active layer 105 that is located below ridge 110R. In this manner, nitride-based semiconductor light-emitting element 1600 according to Modification 1 has a plurality of light-emitting portions 100E arranged in an array. This makes it possible to obtain a plurality of emitted lights from one nitride-based semiconductor light-emitting element 1600, thereby achieving a high-output nitride-based semiconductor light-emitting element 1600. Note that, although nitride-based semiconductor light-emitting element 1600 according to Modification 1 includes a plurality of nitride-based semiconductor light-emitting elements 100, the plurality of nitride-based semiconductor light-emitting elements included in nitride-based semiconductor light-emitting element 1600 is not limited thereto and may include nitride-based semiconductor light-emitting elements according to other embodiments.

[0360] 62 , the individual light-emitting portions 100E may be separated by separation grooves 100T having a width (dimension in the X-axis direction) of 8 μm to 20 μm and a depth (dimension in the Z-axis direction) of 1.0 μm to 1.5 μm. By employing such a structure, even if the spacing between adjacent light-emitting portions 100E is narrowed to 300 μm or less, it is possible to reduce thermal interference due to self-heating of the individual light-emitting portions 100E during operation.

[0361] Furthermore, since the nitride-based semiconductor light-emitting element of the present invention has a small ΔN and can have a small horizontal spread angle, even if the distance between the centers of the light-emitting portions 100E shown in Figures 61 and 62 is narrowed, the light emitted from each light-emitting portion 100E is less likely to interfere with each other, and the distance between the centers of the light-emitting portions 100E can be narrowed to 250 μm or less. In Modification 2, this distance is 225 μm.

[0362] Furthermore, although the nitride-based semiconductor light-emitting elements according to the first to third embodiments include the N-type second cladding layer 103, the intermediate layer 108, the electron barrier layer 409, and the current blocking layer 112, these layers are not necessarily required.

[0363] Furthermore, the nitride-based semiconductor light-emitting elements according to the fourth to eighth embodiments include the N-type second cladding layer 403, the intermediate layer 408, the electron barrier layer 409, and the current blocking layer 412, but these layers are not necessarily required.

[0364] Furthermore, although the nitride-based semiconductor light-emitting devices according to the ninth to fifteenth embodiments include an N-type second cladding layer, an intermediate layer, an electron barrier layer, and a current blocking layer, these layers do not necessarily have to be included.

[0365] In the above-mentioned ninth to fifteenth embodiments and their modifications, each guide layer is made of In Ｘｎ Ga １－Ｘｎ Although the composition of each guide layer is an N layer, the composition of each guide layer is not limited to this. For example, if the Al composition ratio of the N-side guide layer is Xna and the Al composition ratio of the P-side guide layer is Xpa, the N-side guide layer will have an Al Ｘｎａ Ga １－Ｘｎａ N, and the P-side guide layer is Al Ｘｐａ Ga １－ＸｐａThe nitride semiconductor light-emitting element may be made of N. In this case, the Al composition ratio of the N-side guide layer may continuously and monotonically increase with increasing distance from the active layer, and the average value of the Al composition ratio of the N-side guide layer may be smaller than the average value of the Al composition ratio of the P-side guide layer. A nitride-based semiconductor light-emitting element having such a configuration can also reduce the operating voltage and increase the optical confinement factor in the active layer. Furthermore, the absolute value of the average rate of change in the Al composition ratio in the stacking direction in a region from the interface of the N-side guide layer closer to the active layer to the center of the N-side guide layer in the stacking direction may be smaller than the absolute value of the average rate of change in the Al composition ratio in the stacking direction in a region of the N-side guide layer from the center to the interface of the N-side guide layer closer to the N-type first cladding layer.

[0366] Although the P-type cladding layers 410, 910, and 1310 described above have a uniform Al composition ratio, the configuration of each P-type cladding layer is not limited to this. For example, each P-type cladding layer may have a superlattice structure in which multiple AlGaN layers and multiple GaN layers are alternately stacked. Specifically, each P-type cladding layer may have a superlattice structure in which, for example, 1.85-nm-thick AlGaN layers with an Al composition ratio of 0.052 (5.2%) and 1.85-nm-thick GaN layers are alternately stacked. In this case, the Al composition ratio of each P-type cladding layer is defined as the average Al composition ratio of 0.026 (2.6%) in the superlattice structure.

[0367] Furthermore, in each embodiment, whether the N-side guide layer is made of InGaN or AlGaN, by doping the N-side guide layer with an N-type impurity, the N-side guide layer can function as a potential barrier that suppresses holes injected from the P-type layer into the active layer from leaking into the N-type layer. Here, increasing the N-type impurity concentration enhances the effect of suppressing hole leakage, thereby improving the probability of radiative recombination of electrons and holes in the active layer. This increases the quantum efficiency of the nitride-based semiconductor light-emitting device, thereby improving its luminous efficiency.

[0368] Furthermore, by doping the N-type guide layer with an N-type impurity, the electrical conductivity of electrons in the N-side guide layer is increased, thereby reducing the operating voltage of the nitride-based semiconductor light-emitting device. The N-type impurity concentration in the N-side guide layer is, for example, 3×10１７ cm －３ The N-type impurity concentration in the N-side guide layer may be 2×10 or more. This ensures the above-mentioned effects. If the N-type impurity concentration in the N-side guide layer is too high, the free carrier loss in the N-side guide layer increases and the effect of suppressing hole leakage may become saturated. Therefore, the N-type impurity concentration in the N-side guide layer should be 2×10 or more. １８ cm －３ In this way, the N-type impurity in the N-side guide layer may be 3×10 １７ cm －３ That's it, 2 x 10 １８ cm －３ By satisfying the following, it is possible to suppress the increase in free carrier loss caused by doping with N-type impurities, while suppressing hole leakage and achieving a lower operating voltage by improving the electrical conductivity of electrons. This makes it possible to improve the light-emitting efficiency of the nitride-based semiconductor light-emitting element. The effect of suppressing hole leakage by doping the N-side guide layer with N-type impurities can be obtained even in a structure in which the band gap energy of the N-side guide layer is constant, but is more pronounced in a structure in which the band gap energy increases with increasing distance from the active layer.

[0369] In addition, in the embodiment in which the N-side guide layer is made of InGaN, a structure has been shown in which an N-type second cladding layer made of N-type GaN is disposed between the N-side guide layer and the N-type first cladding layer made of AlGaN. In such a structure, in order to reduce the oscillation threshold current value by increasing the optical confinement factor in the direction perpendicular to the active layer, it is effective to configure the N-type first cladding layer with a small refractive index to have a small thickness between the active layer. Specifically, for example, the thickness of the N-type second cladding layer made of N-type GaN may be 30 nm or less. Furthermore, an N-side guide layer made of InGaN may be disposed immediately above the N-type first cladding layer made of AlGaN and immediately below the active layer.

[0370] In this case, the N-type first cladding layer may have a composition change region in which the atomic composition changes in the stacking direction in a region including the interface with the N-side guide layer. The composition change region changes in atomic composition so as to complement the atomic composition of the region other than the composition change region of the N-type first cladding layer and the atomic composition of the N-side guide layer. That is, the atomic composition of the composition change region approaches the atomic composition of the N-side guide layer as it approaches the N-side guide layer, and approaches the atomic composition of the region other than the composition change region of the N-type first cladding layer as it moves away from the N-side guide layer.

[0371] Alternatively, the semiconductor light emitting device may include an Al composition gradient layer disposed between the N-side first cladding layer and the N-side guide layer, wherein the Al composition ratio of the Al composition gradient layer decreases toward the active layer.

[0372] When the N-type first cladding layer does not have a composition-change region, and when the semiconductor light-emitting device does not have an Al composition-gradient layer, negative piezoelectric polarization charges are concentrated and generated at the interface between the N-type first cladding layer and the N-side guide layer. Therefore, the hole concentration in the region near the interface increases to satisfy the electrical neutrality condition at the interface, and the band structure in the region near the interface changes. As a result, a spike-shaped potential barrier is formed in the conduction band potential. This potential barrier in the conduction band reduces the electrical conductivity of electrons flowing from the N-type first cladding layer to the active layer, increasing the operating voltage.

[0373] On the other hand, when the N-type first cladding layer has a composition change region, or when the semiconductor light-emitting device has an Al composition gradient layer, the negative piezoelectric polarization charge generated between the N-type first cladding layer and the N-side guide layer can be dispersed in the composition change region or the Al composition gradient layer. This can suppress an increase in the hole concentration in the region near the interface. This reduces the potential barrier formed in the conduction band, improving the electrical conductivity of electrons. As a result, it is possible to simultaneously achieve a reduction in operating voltage and an increase in the optical confinement factor.

[0374] The effect of reducing the oscillation threshold current value by increasing the optical confinement factor is greater when the active layer has a single quantum well structure consisting of only one well layer with a high refractive index and when the N-side guide layer has an In compositionally graded structure in which the In composition ratio decreases toward the active layer. When the N-side guide layer has an In compositionally graded structure, the refractive index of the region with a low In composition ratio is relatively small compared to the refractive index of the region with a high In composition ratio. As a result, the vertical optical intensity distribution tends to spread toward the N-type first cladding layer, thereby reducing the optical confinement factor of the active layer. Therefore, when the N-side guide layer has an In compositionally graded structure, the effect of reducing the oscillation threshold current value by the above configuration is greater.

[0375] Furthermore, when the active layer has a single quantum well structure, an intermediate barrier layer having a thickness of 1 nm to 8 nm may be disposed between the well layer and the N-side barrier layer. Here, the bandgap energy of the intermediate barrier layer is smaller than that of the barrier layer but larger than that of the well layer. Such an intermediate barrier layer can further increase the optical confinement factor in the well layer and reduce the oscillation threshold current. The bandgap energy of the intermediate barrier layer may decrease toward the well layer. In this case, the bandgap energy at the interface of the intermediate barrier layer facing the barrier layer may be smaller than that of the interface of the barrier layer facing the intermediate barrier layer, and the bandgap energy at the interface of the intermediate barrier layer facing the well layer may be larger than that of the interface of the well layer facing the intermediate barrier layer. This allows piezoelectric polarization charges formed at the interfaces between the intermediate barrier layer and each of the well layer and the N-side barrier layer to be dispersed into the intermediate barrier layer, whose bandgap energy decreases toward the well layer. As a result, the spike-shaped potential barrier in the conduction band formed between the N-side barrier layer and the well layer when no intermediate barrier layer is present can be reduced. Therefore, the electrical conductivity of electrons flowing from the N-type layer toward the well layer is improved, thereby reducing the operating voltage of the nitride-based semiconductor light-emitting device. In order to decrease the bandgap energy of the intermediate barrier layer toward the well layer, if the intermediate barrier layer is made of InGaN, the In composition ratio may be increased toward the well layer. Whether the bandgap energy of the intermediate barrier layer is constant or decreases toward the well layer, it is sufficient that the average bandgap energy of the intermediate barrier layer is greater than the average bandgap energy of the well layer and smaller than the average bandgap energy of the N-side barrier layer. Alternatively, it is sufficient that the average In composition ratio of the intermediate barrier layer is smaller than the average In composition ratio of the well layer and larger than the average In composition ratio of the N-side barrier layer.

[0376] When a p-side electrode made of Ag is used, spontaneously emitted light from the active layer is reflected by the p-side electrode and fed back to the active layer. This fed-back spontaneously emitted light is reabsorbed in the active layer, resulting in improved quantum efficiency and enhanced luminous efficiency. Here, when an intermediate barrier layer that absorbs the short-wavelength component of the fed-back spontaneously emitted light is used, the quantum efficiency can be further improved. To achieve this effect, when the intermediate barrier layer and well layer are formed of InGaN, the difference between the maximum In composition ratio of the intermediate barrier layer and the average In composition ratio of the well layer should be 0.06 or less.

[0377] Furthermore, in a region including the interface of the N-type first cladding layer made of AlGaN on the active layer side, if the Al composition ratio of the N-type first cladding layer decreases toward the active layer, the spike-shaped potential barrier in the conduction band due to piezoelectric polarization charges formed at the interface can be reduced, thereby increasing the electrical conductivity of electrons and reducing the operating voltage of the semiconductor light-emitting device.

[0378] Furthermore, a transparent conductive oxide film may be disposed between the Ag P-side electrode and the contact layer. This allows the P-type cladding layer to be thinned to 0.3 μm or less. Therefore, free carrier loss in the P-type cladding layer can be suppressed, thereby reducing waveguide loss. Furthermore, the series resistance of the semiconductor light-emitting device can be reduced. Furthermore, the effect of improving light emission efficiency due to improved quantum efficiency caused by feedback of spontaneously emitted light from the active layer to the active layer can be obtained. When the semiconductor light-emitting device is a ridge-type semiconductor laser device in which a ridge is formed in the P-type cladding layer, if the P-type cladding layer is made too thin, the horizontal lateral light confinement effect within the ridge, which occurs due to the refractive index difference between the ridge and the current blocking layer disposed on the ridge sidewall, is weakened, resulting in a smaller effective refractive index difference ΔN. This weakens the refractive index guiding effect, increasing the oscillation threshold and making it more likely that kinks will occur in the current-light output characteristics. Therefore, the P-type cladding layer thickness may be 0.1 μm or more.

[0379] Furthermore, when the P-type cladding layer is 0.2 μm or less, the lower end of the ridge may be formed between the electron barrier layer and the active layer to increase ΔN. In this case, the electron barrier layer is formed inside the ridge. Therefore, when the electron barrier layer is made of AlGaN, increasing the Al composition ratio to 0.3 or more increases the electron concentration at the active layer-side interface of the electron barrier layer due to positive piezoelectric polarization charges formed at the active layer-side interface, thereby lowering the valence band potential. As a result, the potential barrier against holes flowing from the P-type cladding layer to the active layer increases, and the electron barrier layer contacts the current blocking layer at the ridge sidewalls, making the band structure of the electron barrier layer in the width direction of the ridge discontinuous at the ridge sidewalls. This allows holes to leak near the interface of the electron barrier layer at the ridge sidewalls, resulting in a decrease in light-emitting efficiency and degradation of the semiconductor light-emitting device in laser operation reliability tests.

[0380] To prevent such holes from leaking out of the ridge, the electron barrier layer may have an Al composition gradient portion in which the Al composition ratio monotonically increases with increasing distance from the active layer. This allows the positive piezoelectric polarization charge of the electron barrier layer to be dispersed in the Al composition gradient portion, thereby preventing the positive piezoelectric polarization charge from concentrating at the interface of the electron barrier layer on the active layer side. The reduced electron concentration at the interface of the electron barrier layer on the active layer side prevents a decrease in the valence band potential, thereby preventing holes generated on the ridge sidewalls from leaking out of the ridge.

[0381] The thickness of the Al composition gradient portion may be 5 nm or more, which can more reliably obtain the effect of dispersing the piezoelectric polarization charge.

[0382] 5 × 10 for the electron barrier layer １８ cm －３ Since it is necessary to dope the electron barrier layer with Mg at such a high concentration, the thickness of the electron barrier layer may be 30 nm or less, which makes it possible to suppress waveguide loss due to free carrier loss in the electron barrier layer.

[0383] Furthermore, by having an Al composition gradient portion in the electron barrier layer, it is possible to suppress a decrease in the v...

Claims

1. A nitride-based semiconductor light-emitting element comprises a semiconductor stack and a P-side electrode positioned above the semiconductor stack, and emits light from an end face perpendicular to the stacking direction of the semiconductor stack, The semiconductor laminate is N-type first cladding layer, An N-side guide layer is positioned above the N-type first cladding layer, An active layer having a quantum well structure is disposed above the N-side guide layer and includes a well layer and a barrier layer. A P-side first guide layer is positioned above the active layer, A second guide layer on the P side is positioned above the first guide layer on the P side, It has a P-type cladding layer positioned above the P-side second guide layer, The band gap energy of the P-side second guide layer is greater than the band gap energy of the N-side guide layer. The band gap energy of the N-side guide layer is greater than or equal to the band gap energy of the P-side first guide layer. The P-side electrode contains Ag Nitride semiconductor light-emitting element.

2. If the film thickness of the first guide layer on the P side is Tp1, the film thickness of the second guide layer on the P side is Tp2, and the film thickness of the guide layer on the N side is Tn1, Tn1<Tp1+Tp2 Satisfying the relationship The nitride-based semiconductor light-emitting element according to claim 1.

3. Tp1 < Tp2 Satisfying the relationship The nitride-based semiconductor light-emitting element according to claim 2.

4. Tp1 < Tn1 Satisfying the relationship Nitride-based semiconductor light-emitting element according to claim 2 or 3.

5. The average refractive index of the first guide layer on the P side and the second guide layer on the P side is smaller than the average refractive index of the guide layer on the N side. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 3.

6. The first guide layer on the P side is In Ｘｐ１ Ga １－Ｘｐ１ Consists of N, The N-side guide layer is In Ｘｎ１ Ga １－Ｘｎ１ Consists of N, Xn1 ≤ Xp1 Satisfying the relationship Nitride-based semiconductor light-emitting element according to any one of claims 1 to 3.

7. The P-side second guide layer is In Ｘｐ２ Ga １－Ｘｐ２ Consists of N, Xp2 < Xn1 Satisfying the relationship Nitride semiconductor light-emitting element according to claim 6.

8. The aforementioned barrier layer is In Ｘｂ Ga １－Ｘｂ Consists of N, Xp1 < Xb Satisfying the relationship Nitride semiconductor light-emitting element according to claim 6.

9. The band gap energy of the N-side guide layer is greater than the band gap energy of the P-side first guide layer. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 3.

10. A nitride-based semiconductor light-emitting element comprises a semiconductor stack and a P-side electrode positioned above the semiconductor stack, and emits light from an end face perpendicular to the stacking direction of the semiconductor stack, The semiconductor laminate is N-type first cladding layer, An N-side guide layer is positioned above the N-type first cladding layer, An active layer having a quantum well structure is disposed above the N-side guide layer and includes a well layer and a barrier layer. A P-side guide layer is positioned above the active layer, It has a P-type cladding layer positioned above the P-side guide layer, The band gap energy of the P-side guide layer increases monotonically as it moves away from the active layer. The P-side guide layer includes a portion in which the band gap energy continuously increases as it moves away from the active layer. The average bandgap energy of the P-side guide layer is greater than or equal to the average bandgap energy of the N-side guide layer. The band gap energy of the barrier layer is less than or equal to the minimum band gap energy of the N-side guide layer and the P-side guide layer. The P-side electrode contains Ag Nitride semiconductor light-emitting element.

11. A nitride-based semiconductor light-emitting element comprises a semiconductor stack and a P-side electrode positioned above the semiconductor stack, and emits light from an end face perpendicular to the stacking direction of the semiconductor stack, The semiconductor laminate is N-type first cladding layer, An N-side guide layer is positioned above the N-type first cladding layer, An active layer having a quantum well structure is disposed above the N-side guide layer and includes a well layer and a barrier layer. A P-side guide layer is positioned above the active layer, It has a P-type cladding layer positioned above the P-side guide layer, The band gap energy of the N-side guide layer increases monotonically as it moves away from the active layer. The N-side guide layer includes a portion in which the band gap energy continuously increases as it moves away from the active layer. The average bandgap energy of the P-side guide layer is greater than or equal to the average bandgap energy of the N-side guide layer. The P-side electrode contains Ag Nitride semiconductor light-emitting element.

12. If the thickness of the P-side guide layer is Tp and the thickness of the N-side guide layer is Tn, Tn < Tp Satisfying the relationship Nitride semiconductor light-emitting element according to claim 10 or 11.

13. The N-side guide layer is In Ｘｎ Ga １－Ｘｎ composed of N, The P-side guide layer is In Ｘｐ Ga １－Ｘｐ Consists of N, The In composition ratio of the N-side guide layer decreases monotonically as it moves away from the active layer. The average value of the In composition ratio of the N-side guide layer is equal to or greater than the average value of the In composition ratio of the P-side guide layer. Nitride semiconductor light-emitting element according to claim 10 or 11.

14. The average value of the In composition ratio of the N-side guide layer is greater than the average value of the In composition ratio of the P-side guide layer. The nitride-based semiconductor light-emitting element according to claim 13.

15. The average rate of change in the In composition ratio in the stacking direction of the P-side guide layer from the interface on the side of the P-side guide layer closest to the active layer to the central part of the P-side guide layer in the stacking direction is greater than the average rate of change in the In composition ratio in the stacking direction of the region from the central part to the interface on the side of the P-side guide layer closest to the P-type cladding layer. The nitride-based semiconductor light-emitting element according to claim 13.

16. The aforementioned barrier layer is In Ｘｂ Ga １－Ｘｂ Consists of N, The maximum value of the In composition ratio in the P-side guide layer is less than or equal to the In composition ratio of the barrier layer. The nitride-based semiconductor light-emitting element according to claim 13.

17. The aforementioned barrier layer is In Ｘｂ Ga １－Ｘｂ Consists of N, The maximum value of the In composition ratio in the N-side guide layer is less than or equal to the In composition ratio of the barrier layer. The maximum value of the In composition ratio in the P-side guide layer is less than or equal to the In composition ratio of the barrier layer. The nitride-based semiconductor light-emitting element according to claim 11.

18. The N-side guide layer is Al Ｘｎａ Ga １－Ｘｎａ Consists of N, The P-side guide layer is Al Ｘｐａ Ga １－Ｘｐａ Consists of N, The Al composition ratio of the N-side guide layer increases monotonically as it moves away from the active layer. The average Al composition ratio of the N-side guide layer is less than or equal to the average Al composition ratio of the P-side guide layer. The nitride-based semiconductor light-emitting element according to claim 11.

19. The average bandgap energy of the P-side guide layer is greater than the average bandgap energy of the N-side guide layer. Nitride-based semiconductor light-emitting element according to any one of claims 11, 17, or 18.

20. The band gap energy of the barrier layer is less than or equal to the minimum band gap energy of the N-side guide layer and the P-side guide layer, respectively. Nitride-based semiconductor light-emitting element according to any one of claims 11, 17, or 18.

21. The thickness of the P-type cladding layer is 460 nm or less. A nitride-based semiconductor light-emitting element according to any one of claims 1 to 3, 10, 11, 17, or 18.