Nitride semiconductor light-emitting diodes

Abstract

To provide a nitride semiconductor light-emitting element capable of reducing an operation voltage and also capable of increasing an optical confinement factor to an active layer.SOLUTION: A nitride semiconductor light-emitting element 100 includes: an N-type first cladding layer 102; an N-side guide layer 104; an active layer 105 including a well layer and a barrier layer and having a quantum well structure; a P-side guide layer 106; and a P-type cladding layer 110. Band gap energy of the N-side guide layer 104 monotonically increases with a distance from the active layer 105, and the N-side guide layer 104 includes a portion where the band gap energy continuously increases with the distance from the active layer 105. Average band gap energy of the P-side guide layer 106 is equal to or greater than average band gap energy of the N-side guide layer 104. When Tp represents a film thickness of the P-side guide layer 106 and Tn represents a film thickness of the N-side guide layer 104, a relationship Tn<Tp is satisfied.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This disclosure relates to nitride-based semiconductor light-emitting devices. [Background technology]

[0002] Conventionally, nitride-based semiconductor light-emitting elements have been used as light sources in processing equipment and the like. In light sources for processing equipment, there is a demand for even higher output power and higher efficiency. To improve the efficiency of nitride-based semiconductor light-emitting elements, techniques such as reducing the operating voltage are known (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-50021 [Overview of the project] [Problems that the invention aims to solve]

[0004] In nitride-based semiconductor light-emitting devices, reducing the thickness of the P-type cladding layer is effective in reducing the operating voltage, in addition to the technique described in Patent Document 1. However, reducing the thickness of the P-type cladding layer causes the peak of the light intensity distribution in the stacking direction (i.e., the direction perpendicular to the main surface of each semiconductor layer) to shift from the active layer toward the N-type cladding layer. As a result, the light confinement coefficient in the active layer decreases, and consequently, the thermal saturation level of the light output decreases. Therefore, it becomes difficult to achieve high output in nitride-based semiconductor light-emitting devices.

[0005] This disclosure aims to solve these problems by providing a nitride-based semiconductor light-emitting element that can reduce the operating voltage and increase the photoconfinement coefficient in the active layer. [Means for solving the problem]

[0006] To solve the above problems, one embodiment of a nitride-based semiconductor light-emitting element according to the present disclosure is a nitride-based semiconductor light-emitting element comprising a semiconductor stack, which emits light from an end face perpendicular to the stacking direction of the semiconductor stack, wherein the semiconductor stack 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 and including a well layer and a barrier layer, 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 band gap energy of the N-side guide layer increases monotonically with increasing distance from the active layer, the N-side guide layer includes a portion in which the band gap energy increases continuously with increasing distance from the active layer, the average band gap energy of the P-side guide layer is greater than or equal to the average band gap energy of the N-side guide layer, and if the film thickness of the P-side guide layer is Tp and the film thickness of the N-side guide layer is Tn, Tn <Tp It satisfies the following relationship. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a nitride-based semiconductor light-emitting element that can reduce the operating voltage and increase the photoconfinement coefficient to the active layer. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic plan view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 2A] Figure 2A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 2B] Figure 2B is a schematic cross-sectional view showing the configuration of the active layer of the nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 3] Figure 3 is a schematic diagram showing an overview of the light intensity distribution in the stacking direction of a nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 4]Figure 4 is a graph showing the coordinates of the position in the stacking direction of the nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 5] Figure 5 is a schematic graph showing the distribution of the bandgap energy of the active layer and each layer in its vicinity in the nitride semiconductor light-emitting element according to Embodiment 1. [Figure 6] Figure 6 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 1 to 3, and the nitride-based semiconductor light-emitting device according to Embodiment 1. [Figure 7] Figure 7 is a graph showing the simulation results of the distribution of valence electron charge levels and hole Fermi levels in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 3, and the nitride-based semiconductor light-emitting device according to Embodiment 1. [Figure 8] Figure 8 is a graph showing the simulation results of the carrier concentration distribution in the stacking direction of the nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 3 and the nitride-based semiconductor light-emitting device according to Embodiment 1. [Figure 9] Figure 9 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 1 and the optical confinement coefficient (Γv). [Figure 10] Figure 10 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 1 and the operating voltage. [Figure 11] Figure 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 3, and the piezoelectric charge density, piezoelectric field, and conduction charge potential. [Figure 12] Figure 12 is a graph showing the relationship between the position in the stacking direction of the nitride semiconductor light-emitting element according to Embodiment 1, and the piezoelectric charge density, piezoelectric field, and conduction charge potential. [Figure 13] Figure 13 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer of the nitride semiconductor light-emitting element according to Embodiment 1 and the photoconfinement coefficient (Γv). [Figure 14]Figure 14 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer of the nitride-based semiconductor light-emitting element according to Embodiment 1 and waveguide loss. [Figure 15] Figure 15 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer of the nitride-based semiconductor light-emitting element according to Embodiment 1 and the operating voltage. [Figure 16] Figure 16 is a graph showing the simulation results of the relationship between the film thickness of the N-side guide layer and position P1 according to Embodiment 1. [Figure 17] Figure 17 is a graph showing the simulation results of the relationship between the film thickness of the N-side guide layer and the difference ΔP according to Embodiment 1. [Figure 18] Figure 18 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer and the optical confinement coefficient (Γv) according to Embodiment 1. [Figure 19] Figure 19 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer and waveguide loss according to Embodiment 1. [Figure 20] Figure 20 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer according to Embodiment 1 and the effective refractive index difference ΔN. [Figure 21] Figure 21 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer and position P1 according to Embodiment 1. [Figure 22] Figure 22 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer and the difference ΔP according to Embodiment 2. [Figure 23A] Figure 23A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 2. [Figure 23B] Figure 23B is a schematic cross-sectional view showing the configuration of the active layer of the nitride-based semiconductor light-emitting element according to Embodiment 2. [Figure 24] Figure 24 is a schematic graph showing the distribution of the bandgap energy of the active layer and each layer in its vicinity in a nitride-based semiconductor light-emitting element according to Embodiment 2. [Figure 25] Figure 25 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 3. [Figure 26] Figure 26 is a schematic graph showing the distribution of the bandgap energy of the active layer and each layer in its vicinity in a nitride-based semiconductor light-emitting element according to Embodiment 3. [Figure 27] Figure 27 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 4. [Figure 28] Figure 28 is a schematic graph showing the distribution of bandgap energies of the active layer and each nearby layer of the nitride-based semiconductor light-emitting element according to Embodiment 4. [Figure 29] Figure 29 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 4 and the optical confinement coefficient (Γv). [Figure 30] Figure 30 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 4 and waveguide loss. [Figure 31] Figure 31 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 4 and the operating voltage. [Figure 32] Figure 32 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 4 and position P1. [Figure 33] Figure 33 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer according to Embodiment 4 and the difference ΔP. [Figure 34] Figure 34 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 5. [Figure 35] Figure 35 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 6. [Figure 36A] Figure 36A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 7. [Figure 36B] Figure 36B is a schematic cross-sectional view showing the configuration of the active layer of the nitride-based semiconductor light-emitting element according to Embodiment 7. [Figure 37] Figure 37 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 8. [Figure 38] Figure 38 is a schematic graph showing the distribution of the bandgap energy of the active layer and each layer in its vicinity in a nitride-based semiconductor light-emitting element according to Embodiment 8. [Figure 39A] Figure 39A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 9. [Figure 39B] Figure 39B is a schematic cross-sectional view showing the configuration of the active layer of the nitride-based semiconductor light-emitting element according to Embodiment 9. [Figure 40] Figure 40 is a schematic graph showing the distribution of bandgap energies of the active layer and each layer in its vicinity in a nitride-based semiconductor light-emitting element according to Embodiment 9. [Figure 41] Figure 41 is a schematic graph showing the distribution of the bandgap energy of the active layer and each layer in its vicinity in a nitride-based semiconductor light-emitting element according to Modification 1 of Embodiment 9. [Figure 42] Figure 42 is a schematic graph showing the distribution of the bandgap energy of the active layer and each layer in its vicinity in a nitride-based semiconductor light-emitting element according to a modified example 2 of Embodiment 9. [Figure 43] Figure 43 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Modification 1. [Figure 44] Figure 44 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Modification 2. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, components, and their arrangement and connection configurations shown in the following embodiments are examples only and are not intended to limit this disclosure.

[0010] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, the scale and other aspects may not necessarily be consistent across all figures. In addition, the same reference numerals are used for substantially identical components in each figure, and redundant explanations are omitted or simplified.

[0011] Furthermore, in this specification, the terms "upper" and "lower" do not refer to the upward (vertically upward) and downward (vertically downward) directions in absolute spatial perception, but rather are used as terms defined by the relative positional relationship based on the stacking order in a stacked configuration. Moreover, the terms "upper" and "lower" apply not only when two components are spaced apart and another component exists between them, but also when two components are placed in contact with each other.

[0012] (Embodiment 1) A nitride-based semiconductor light-emitting element according to Embodiment 1 will be described.

[0013] [1-1. Overall Structure] First, the overall configuration of the nitride-based semiconductor light-emitting element according to this embodiment will be described using Figures 1, 2A, and 2B. Figures 1 and 2A are schematic plan view and cross-sectional view, respectively, showing the overall configuration of the nitride-based semiconductor light-emitting element 100 according to this embodiment. Figure 2A shows a cross-section along line II-II in Figure 1. Figure 2B is a schematic cross-sectional view showing the configuration of the active layer 105 provided in the nitride-based semiconductor light-emitting element 100 according to this embodiment. Note that each figure shows mutually orthogonal X, Y, and Z axes. The X, Y, and Z axes are in a right-handed orthogonal coordinate system. The stacking direction of the nitride-based semiconductor light-emitting element 100 is parallel to the Z-axis direction, and the main emission direction of light (laser light) is parallel to the Y-axis direction.

[0014] As shown in Figure 2A, the nitride-based semiconductor light-emitting element 100 comprises a semiconductor stack 100S including a nitride-based semiconductor layer, and emits light from an end face 100F (see Figure 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 is a semiconductor laser element having two end faces 100F and 100R that form a resonator. End face 100F is the front end face from which laser light is emitted, and end face 100R is the rear end face with a higher reflectivity than end face 100F. In this embodiment, the reflectivity of end faces 100F and 100R is 16% and 95%, respectively. The resonator length of the nitride-based semiconductor light-emitting element 100 according to this embodiment (i.e., the distance between end face 100F and end face 100R) is approximately 1200 μm.

[0015] As shown in Figure 2A, the nitride-based semiconductor light-emitting element 100 comprises a semiconductor laminate 100S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 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 guide layer 106, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 110, and a contact layer 111.

[0016] The substrate 101 is a plate-shaped member that serves as the base for the nitride-based semiconductor light-emitting element 100. In this embodiment, the substrate 101 is an N-type GaN substrate.

[0017] The N-type first cladding layer 102 is an example of an N-type cladding layer placed on top of the substrate 101. The N-type first cladding layer 102 is a layer with a lower refractive index and a larger bandgap energy than the active layer 105. In this embodiment, the N-type first cladding layer 102 is an N-type Al with a film thickness of 1200 nm. 0.035 Ga 0.965 This is an N-type layer. The first N-type cladding layer 102 contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 The Si is doped.

[0018] The N-type second cladding layer 103 is an example of an N-type cladding layer placed on top of the substrate 101. In this embodiment, the N-type second cladding layer 103 is placed on top of the N-type first cladding layer 102. The N-type second cladding layer 103 is a layer with a lower refractive index and a larger bandgap energy than the active layer 105. In this embodiment, the N-type second cladding layer 103 is an N-type GaN layer with a film thickness of 100 nm. The N-type second cladding layer 103 contains impurities with a concentration of 1 × 10⁻¹⁶ 18 cm -3 The silicon is doped into the material. The band gap energy of the N-type second cladding layer 103 is smaller than the band gap energy of the N-type first cladding layer 102, and is greater than or equal to the maximum band gap energy of the P-side guide layer 106.

[0019] The N-side guide layer 104 is an optical guide layer positioned above the N-type second cladding layer 103. The N-side guide layer 104 has a higher refractive index and lower bandgap energy than the N-type first cladding layer 102 and the N-type second cladding layer 103. The bandgap energy of the N-side guide layer 104 increases monotonically as it moves away from the active layer 105 (i.e., as it approaches the N-type first cladding layer 102 in the opposite direction to the crystal growth direction of each semiconductor layer). Here, the configuration in which the bandgap energy increases monotonically includes the configuration in which there is a region in which the bandgap energy is constant in the stacking direction. Furthermore, the N-side guide layer 104 includes a portion in which the bandgap energy increases continuously as it moves away from the active layer 105. Here, the configuration in which the bandgap energy increases monotonically continuously in the stacking direction does not include the configuration in which the bandgap energy changes discontinuously in the stacking direction. In this disclosure, a configuration in which the band gap energy increases continuously and monotonically is a configuration in which the discontinuous increase in the band gap energy is less than 2% of the band gap energy at that position. For example, a configuration in which the band gap energy increases continuously and monotonically as you move away from the active layer 105 in the N-side guide layer 104 is a configuration in which the increase in the band gap energy at a position displaced by a small distance in the opposite direction to the crystal growth direction from a certain position in the N-side guide layer 104 is less than 2% of the band gap energy at that position. For example, a configuration in which the band gap energy increases continuously and monotonically does not include a configuration in which the band gap energy increases in a step-like manner by 2% or more in the direction opposite to the stacking direction, but it does include a configuration in which the band gap energy changes in a step-like manner by less than 2% in the stacking direction. In this embodiment, the band gap energy increases continuously in the entire N-side guide layer 104 as you move away from the active layer 105, but the configuration of the N-side guide layer 104 is not limited to this. For example, the ratio of the film thickness of the portion where the bandgap energy continuously increases as it moves away from the active layer 105 to the total film thickness of the N-side guide layer 104 may be 50% or more.Furthermore, this percentage may be 70% or more, or 90% or more.

[0020] Here, ΔEgn is defined as the increase in the band gap energy of the N-side guide layer 104 in the direction approaching the N-type second cladding layer 103 (the direction opposite to the crystal growth direction). The increase in the band gap energy of the N-side guide layer 104 in the direction opposite to the crystal growth direction is defined, for example, as the difference between the band gap energy at the interface of the N-side guide layer 104 closer to the active layer 105 and the band gap energy at the interface closer to the N-type second cladding layer 103. Furthermore, the ratio of the magnitude of the continuously increasing band gap energy to ΔEgn should be 70% or more. This ratio may also be 80% or more, or 90% or more. In this way, by increasing the band gap energy of the N-side guide layer 104 in the direction opposite to the crystal growth direction, the refractive index of the N-side guide layer 104 increases continuously and monotonically as it approaches the active layer 105. In this case, the refractive index of the N-side guide layer 104 increases as it approaches the active layer 105, so the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 105. Here, if ΔEgn is small, the effect is small, and conversely, if it is too large, the light generated from the active layer 105 is absorbed in the region of the N-side guide layer 104 adjacent to the active layer 105, increasing waveguide loss. To suppress such waveguide loss, ΔEgn may be between 100 meV and 400 meV.

[0021] The N-side guide layer 104 is In Xn Ga 1-XnWhen it consists of N, the In composition ratio Xn of the N-side guide layer 104 monotonically decreases as it moves away from the active layer 105. As a result, the bandgap energy of the N-side guide layer 104 monotonically increases as it moves away from the active layer 105. Here, the configuration in which the In composition ratio Xn monotonically decreases includes a configuration in which there is a region where the In composition ratio Xn is constant in the stacking direction. Also, the N-side guide layer 104 includes a portion where the In composition ratio continuously decreases as it moves away from the active layer 105. 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 discontinuously changes in the stacking direction. The configuration of continuously and monotonically decreasing means that the discontinuous decrease amount of the In composition ratio Xn in the stacking direction at a certain position of the N-side guide layer 104 is less than 20% of the In composition ratio Xn at that position.

[0022] The average bandgap energy of the N-side guide layer 104 is not more than the average bandgap energy of the P-side guide layer 106. In other words, the average value of the In composition ratio of the N-side guide layer 104 is not less than the average value of the In composition ratio of the P-side guide layer 106. In the present embodiment, the average value of the In composition ratio of the N-side guide layer 104 is equal to the average value of the In composition ratio of the P-side guide layer 106. That is, the average bandgap energy of the N-side guide layer 104 is equal to the average bandgap energy of the P-side guide layer 106. Also, when the film thickness of the N-side guide layer 104 is Tn and the film thickness of the P-side guide layer 106 is Tp, Tn < Tp (1) satisfies the relationship.

[0023] Also, the maximum value of the In composition ratio in the N-side guide layer 104 is not more than the In composition ratio of each barrier layer.

[0024] In the present embodiment, the N-side guide layer 104 is an N-type In Xn Ga 1-Xn N layer with a film thickness of 160 nm. The N-side guide layer 104 contains, as an impurity, a concentration of 3×10 17 cm -3Si is doped into it. More specifically, the N-side guide layer 104 is doped with In near the interface closer to the active layer 105. 0.04 Ga 0.96 The N-side guide layer 104 has a composition represented by N, and near the interface farther from the active layer 105, it has a composition represented by GaN. The In composition ratio Xn of the N-side guide layer 104 decreases at a constant rate as it moves away from the active layer 105.

[0025] The active layer 105 is positioned above the N-side guide layer 104 and is a light-emitting layer having a quantum well structure. In this embodiment, the active layer 105 has well layers 105b and 105d and barrier layers 105a, 105c, and 105e, as shown in Figure 2B.

[0026] The barrier layer 105a is positioned above the N-side guide layer 104 and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 105a is an undoped In layer with a thickness of 7 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0027] The well layer 105b is positioned above the barrier layer 105a and functions as a well in the quantum well structure. The well layer 105b is positioned between the barrier layer 105a and the barrier layer 105c. In this embodiment, the well layer 105b is an undoped In 0.18 Ga 0.82 It is an N-layer structure.

[0028] The barrier layer 105c is positioned above the well layer 105b and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 105c is an undoped In layer with a thickness of 7 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0029] The well layer 105d is positioned above the barrier layer 105c and functions as a well in the quantum well structure. The well layer 105d is positioned between the barrier layer 105c and the barrier layer 105e. In this embodiment, the well layer 105d is an undoped In 0.18 Ga0.82 It is an N-layer structure.

[0030] The barrier layer 105e is positioned above the well layer 105d and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 105e is an undoped In layer with a thickness of 5 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0031] The nitride-based semiconductor light-emitting element 100, by having an active layer 105 having the above-described configuration, can emit light with a wavelength of 430 nm to 455 nm.

[0032] In this embodiment, the bandgap energy of each barrier layer is less than or equal to the minimum bandgap energy of the N-side guide layer 104 and the P-side guide layer 106. In other words, the refractive index of each barrier layer is greater than the refractive index of the N-side guide layer 104 and the P-side guide layer 106. Therefore, the optical confinement coefficient to the active layer 105 can be increased. As with each barrier layer in this embodiment, each barrier layer is In Xb Ga 1-Xb When composed of N, the In composition ratio of each barrier layer is greater than or equal to the maximum In composition ratio of the N-side guide layer 104, and greater than or equal to the maximum In composition ratio of the P-side guide layer 106.

[0033] The P-side guide layer 106 is an optical guide layer positioned above the active layer 105. The P-side guide layer 106 has a higher refractive index and a lower bandgap energy than the P-type cladding layer 110. The bandgap energy of the P-side guide layer 106 increases monotonically as it moves away from the active layer 105.

[0034] Here, a configuration in which the band gap energy in the P-side guide layer 106 increases monotonically includes a configuration in which there is a region where the band gap energy is constant in the stacking direction. Furthermore, the P-side guide layer 106 includes a portion in which the band gap energy increases continuously as it moves away from the active layer 105. Here, a configuration in which the band gap energy increases continuously monotonically does not include a configuration in which the band gap energy changes discontinuously in the stacking direction. In this disclosure, a configuration in which the band gap energy increases continuously monotonically is a configuration in which, similar to the N-side guide layer described above, the discontinuous increase in the band gap energy at a certain position is less than 2% of the band gap energy at that position. For example, a configuration in which the band gap energy increases continuously monotonically does not include a configuration in which the band gap energy increases in a step-like manner by 2% or more in the stacking direction, but it does include a configuration in which the band gap energy changes in a step-like manner by less than 2% in the stacking direction. In this embodiment, the bandgap energy of the P-side guide layer 106 increases continuously as it moves away from the active layer 105, but the configuration of the P-side guide layer 106 is not limited to this. For example, the ratio of the film thickness of the portion where the bandgap energy increases continuously as it moves away from the active layer 105 to the total film thickness of the P-side guide layer 106 may be 50% or more. Alternatively, this ratio may be 70% or more, or even 90% or more.

[0035] Here, the band gap energy of the P-side guide layer 106 is N-type second cladding layer 103The increase in the stacking direction is defined as ΔEgp. The increase in the bandgap energy of the P-side guide layer 106 in the stacking direction is defined, for example, as the difference between the bandgap energy at the interface of the P-side guide layer 106 closer to the active layer 105 and the bandgap energy at the interface closer to the P-type cladding layer 110. Furthermore, the ratio of the magnitude of the continuously increasing bandgap energy to ΔEgp should be 70% or more. This ratio may also be 80% or more, or 90% or more. In this way, by increasing the bandgap energy of the P-side guide layer 106 in the stacking direction, the refractive index of the P-side guide layer 106 increases continuously and monotonically as it approaches the active layer 105. In this case, since the refractive index of the P-side guide layer 106 increases as it approaches the active layer 105, the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 105. Here, if ΔEgp is small, the effect is small, and conversely, if it becomes too large, the light generated from the active layer 105 is absorbed in the region of the P-side guide layer 106 adjacent to the active layer 105, increasing waveguide loss. To suppress such waveguide loss, ΔEgp may be between 100 meV and 400 meV.

[0036] The P-side guide layer 106 is In Xp Ga 1-Xp When composed of N, the In composition ratio Xp of the P-side guide layer 106 decreases monotonically as it moves away from the active layer 105. As a result, the band gap energy of the P-side guide layer 106 increases continuously monotonically as it moves away from the active layer 105. Furthermore, the P-side guide layer 106 includes a portion in which the In composition ratio Xp increases continuously as it moves away from the active layer 105. As a result, the band gap energy of the P-side guide layer 106 includes a portion in which it increases continuously as it moves away from the active layer 105.

[0037] As described above, the average bandgap energy of the P-side guide layer 106 is greater than or equal to the average bandgap energy of the N-side guide layer 104. In other words, the average value of the In composition ratio of the P-side guide layer 106 is less than or equal to the average value of the In composition ratio of the N-side guide layer 104. In this embodiment, the average value of the In composition ratio of the P-side guide layer 106 is equal to the average value of the In composition ratio of the N-side guide layer 104. Also, the film thickness Tp of the P-side guide layer 106 is greater than the film thickness Tn of the N-side guide layer 104. The maximum value of the In composition ratio in the P-side guide layer 106 is less than or equal to the In composition ratio of each barrier layer.

[0038] In this embodiment, the P-side guide layer 106 is an undoped In coating with a film thickness of 280 nm. Xp Ga 1-Xp It is an N layer. More specifically, the P-side guide layer 106 has an In layer near the interface closer to the active layer 105. 0.04 Ga 0.96 The P-side guide layer 106 has a composition represented by N, and near the interface farther from the active layer 105, it has a composition represented by GaN. The In composition ratio Xp of the P-side guide layer 106 decreases at a constant rate as it moves away from the active layer 105.

[0039] The intermediate layer 108 is a layer positioned above the active layer 105. In this embodiment, the intermediate layer 108 is positioned between the P-side guide layer 106 and the electron barrier layer 109, reducing stress caused by the difference in lattice constants between the P-side guide layer 106 and the electron barrier layer 109. This suppresses the occurrence of crystal defects in the nitride semiconductor light-emitting element 100. In this embodiment, the intermediate layer 108 is an undoped GaN layer with a thickness of 20 nm.

[0040] The electron barrier layer 109 is positioned 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 positioned between the intermediate layer 108 and the P-type cladding layer 110. The electron barrier layer 109 is a P-type Al layer with a thickness of 5 nm. 0.36 Ga 0.64 This is the N layer. The electron barrier layer 109 contains impurities at a concentration of 1 × 10⁻⁶. 19 cm -3The material is doped with Mg. The electron barrier layer 109 suppresses the leakage of electrons from the active layer 105 to the P-type cladding layer 110.

[0041] The P-type cladding layer 110 is a P-type cladding layer positioned above the active layer 105. In this embodiment, the P-type cladding layer 110 is positioned 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 bandgap energy than the active layer 105. The thickness of the P-type cladding layer 110 may be 460 nm or less. This suppresses the electrical resistance of the nitride semiconductor light-emitting element 100. Therefore, the operating voltage of the nitride semiconductor light-emitting element 100 can be reduced. Furthermore, since self-heating during operation of the nitride semiconductor light-emitting element 100 can be reduced, the temperature characteristics of the nitride semiconductor light-emitting element 100 can be improved. Therefore, high-power operation of the nitride semiconductor light-emitting element 100 becomes possible. In the nitride semiconductor light-emitting element 100 according to this embodiment, in order for the P-type cladding layer 110 to fully exhibit its function as a cladding layer, the thickness of the P-type cladding layer 110 should be 200 nm or more. Furthermore, 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 made of P-type Al with a thickness of 450 nm. 0.035 Ga 0.965 This is an N layer. The P-type cladding layer 110 is doped with Mg as an impurity. Furthermore, 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 further away from the active layer 105. Specifically, the concentration of the P-type cladding layer 110 located closer to the active layer 105 is 2 × 10⁻¹⁰. 18 cm -3 P-type Al with Mg doped, 150 nm film thickness. 0.035 Ga 0.965 The N layer and the concentration 1 × 10 located on the side furthest from the active layer 105. 19 cm -3 P-type Al with Mg doped, 300 nm film thickness. 0.035 Ga 0.965 It has N layers.

[0042] A ridge 110R is formed in the P-type cladding layer 110 of the nitride-based semiconductor light-emitting element 100. Two grooves 110T are also 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 Figure 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.

[0043] The contact layer 111 is positioned above the P-type cladding layer 110 and is a layer that makes ohmic contact with the P-side electrode 113. In this embodiment, the contact layer 111 is a P-type GaN layer with a thickness of 60 nm. The contact layer 111 contains impurities with a concentration of 1 × 10⁻⁶ 20 cm -3 It is doped with magnesium.

[0044] The current blocking layer 112 is positioned 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 positioned 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 an SiO2 layer.

[0045] The P-side electrode 113 is a conductive layer positioned above the contact layer 111. In this embodiment, the P-side electrode 113 is positioned above the contact layer 111 and the current blocking layer 112. The P-side electrode 113 is, for example, a monolayer or multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au.

[0046] The N-side electrode 114 is a conductive layer positioned below the substrate 101 (i.e., on the main surface opposite to the main surface on which the N-type first cladding layer 102, etc., of the substrate 101 is located). The N-side electrode 114 is, for example, a monolayer or multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au.

[0047] As a result of having the above configuration, the nitride-based semiconductor light-emitting element 100 generates an effective refractive index difference ΔN between the lower portion of the ridge 110R and the lower portion of the groove 110T, as shown in Figure 2A. This allows the light generated in the lower portion of the ridge 110R of the active layer 105 to be confined in the horizontal direction (i.e., in the X-axis direction).

[0048] [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.

[0049] First, the light intensity distribution in the stacking direction (Z-axis direction in each figure) of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be explained using Figure 3. Figure 3 is a schematic diagram showing the outline of the light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting element 100 according to this embodiment. Figure 3 shows a schematic cross-sectional view of the nitride-based semiconductor light-emitting element 100 and a graph showing the outline of the light intensity distribution in the stacking direction at positions corresponding to the ridge 110R and groove 110T, respectively.

[0050] 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 is not necessarily located in the active layer. Furthermore, in the nitride-based semiconductor light-emitting device 100 according to this embodiment, the stacking structure differs between the lower part of the ridge 110R and the lower part of the groove 110T, so the light intensity distribution also differs between the lower part of the ridge 110R and the lower part of the groove 110T. As shown in Figure 3, let P1 be the peak position of the light intensity distribution in the stacking direction at the center of the horizontal direction (i.e., the X-axis direction) of the lower part of the ridge 110R. Let P2 be the peak position of the light intensity distribution in the stacking direction at the lower part of the groove 110T. Here, positions P1 and P2 will be explained using Figure 4. Figure 4 is a graph showing the coordinates of the positions in the stacking direction of the nitride-based semiconductor light-emitting device 100 according to this embodiment. As shown in Figure 4, the coordinate of the position in the stacking direction of the N-side end face of the well layer 105b of the active layer 105, that is, the end face of the well layer 105b closer to the N-side guide layer 104, is set to zero, downward (towards the N-side guide layer 104) is set to the negative direction of the coordinate, and upward (towards the P-side guide layer 106) is set to the positive direction of the coordinate. Furthermore, the absolute value of the difference between position P1 and position P2 is defined as the difference in peak positions ΔP.

[0051] The light intensity distribution in the stacking direction of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be described below with reference to Figure 5. Figure 5 is a schematic graph showing the distribution of the bandgap energy of the active layer 105 and each layer in its vicinity in the nitride-based semiconductor light-emitting element 100 according to this embodiment.

[0052] In the nitride-based semiconductor light-emitting element 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 groove 110T of the ridge 110R from the bottom surface) is also set to be relatively low. Generally, in semiconductor light-emitting elements having such a configuration, the peak position of the light intensity distribution in the stacking direction shifts in the direction from the active layer 105 towards the N-type second cladding layer 103. As a result, the light confinement coefficient to the active layer 105 decreases, and consequently, the thermal saturation level of the light output decreases. Therefore, it becomes difficult to operate the semiconductor light-emitting element at high power. In this embodiment, as described above, the average bandgap energy of the P-side guide layer 106 is equal to the average bandgap energy of the N-side guide layer 104. On the other hand, the thickness Tp of the P-side guide layer 106 is greater than the thickness Tn of the N-side guide layer 104 (inequality (1) above). Thus, by increasing the thickness of the P-side guide layer 106, which has a higher refractive index than each cladding layer, it becomes possible to shift the light intensity distribution from the active layer 105 towards the P-side guide layer 106. Therefore, according to the nitride-based semiconductor light-emitting element 100 of 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 105.

[0053] Furthermore, in this embodiment, the bandgap energies of the N-side guide layer 104 and the P-side guide layer 106 increase continuously and monotonically as they move away from the active layer 105. In other words, the refractive indices of the N-side guide layer 104 and the P-side guide layer 106 increase continuously and monotonically as they approach the active layer 105. Because the refractive indices of the N-side guide layer 104 and the P-side guide layer 106 increase as they approach the active layer 105, the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 105.

[0054] In this embodiment, the compositions of the N-side guide layer 104 and the P-side guide layer 106 are, respectively, In Xn Ga 1-Xn N and In Xp Ga 1-XpIt is represented by N. The composition near the interface of the N-side guide layer 104 closer to the active layer 105 and near the interface further away from it are, respectively, In Xn1 Ga 1-Xn1 N and In Xn2 Ga 1-Xn2 It is represented by N. The composition near the interface of the P-side guide layer 106 closer to the active layer 105 and near the interface further away from it are, respectively, In Xp1 Ga 1-Xp1 N and In Xp2 Ga 1-Xp2 It is represented by N. As described above, in this embodiment, Xn1=Xp1=0.04 and Xn2=Xp2=0.

[0055] Furthermore, in this embodiment, the barrier layers 105a, 105c, and 105e of the active layer 105 are In Xb Ga 1-Xb The In composition ratios Xb, Xn, and Xp of each barrier layer, N-side guide layer 104, and P-side guide layer 106 are as follows: Xp ≤ Xb (2) Xn ≤ Xb (3) This satisfies the following relationship. As a result, the bandgap energy of each barrier layer is less than or equal to the minimum bandgap energy of the N-side guide layer 104 and the P-side guide layer 106. In other words, the refractive index of each barrier layer can be made larger than that of the P-side 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 brought closer to the active layer 105. It also suppresses excessive shift of the light intensity distribution from the active layer 105 towards the P-type cladding layer 110. This effect is greater when the bandgap energy of each barrier layer is less than the minimum bandgap energy of the N-side guide layer 104 and the P-side guide layer 106, and the light confinement coefficient also increases.

[0056] With the above configuration, in this embodiment, the position P1 of the peak of the light intensity distribution in the stacking direction in the lower part of the ridge 110R can be set to 15.9 nm. In other words, the peak of the light intensity distribution can be positioned in the active layer 105 (see Figure 4). Furthermore, ΔP can be suppressed to 6.2 nm. As a result, the light confinement coefficient in the active layer 105 can be increased to approximately 1.44%.

[0057] As described above, the nitride-based semiconductor light-emitting element 100 according to this embodiment allows the peak of the light intensity distribution in the stacking direction to be located in the active layer 105. Note that the statement that the peak of the light intensity distribution in the stacking direction is located in the active layer 105 means that at least one position in the horizontal direction of the nitride-based semiconductor light-emitting element 100 has the peak of the light intensity distribution in the stacking direction located in the active layer 105, and is not limited to the state where the peak of the light intensity distribution in the stacking direction is located in the active layer 105 at all positions in the horizontal direction.

[0058] As in this embodiment, if the peak of the light intensity distribution in the stacking direction is located in the active layer 105, the proportion of light located in the P-type cladding layer 110 may increase compared to when the peak of the light intensity distribution is located 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 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, by making the P-side guide layer 106 an undoped layer and making the film thickness Tp of the P-side guide layer 106 relatively large, the proportion of the light intensity distribution located in the undoped layer can be increased. Therefore, the increase in free carrier loss can be suppressed. Specifically, in this embodiment, the waveguide loss is 3.4 cm -1 It can be suppressed to a certain extent.

[0059] Furthermore, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, in order to reduce the divergence angle of the emitted light in the horizontal direction (i.e., the X-axis direction), the effective refractive index difference ΔN between the lower part of the ridge 110R and the lower part of the groove 110T is set to be relatively small. Specifically, the effective refractive index difference ΔN is set by adjusting the distance dp (see Figure 2A) between the current blocking layer 112 and the active layer 105. Here, the larger the distance dp, the smaller the effective refractive index difference ΔN becomes. In this embodiment, the effective refractive index difference ΔN is 2.9 × 10⁻⁶. -3 It is approximately such that, therefore, in this embodiment, the effective refractive index difference ΔN is 2.9 × 10 -3 In cases where the ridge is larger, 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 contained in the light emitted from the nitride semiconductor light-emitting element 100 is relatively large. Consequently, the change in the number of modes and the change in the optical confinement coefficient to the active layer 105 due to intermode coupling are relatively large. Therefore, when the number of modes increases or decreases and intermode coupling occurs in the nitride semiconductor light-emitting element 100, the linearity of the optical output characteristics with respect to the supplied current (so-called IL characteristics) decreases. In other words, a non-linear portion (so-called kink) occurs in the graph showing the IL characteristics. Consequently, the stability of the optical output of the nitride semiconductor light-emitting element 100 may decrease.

[0060] The decrease in optical output stability described above will be explained below. In the nitride semiconductor light-emitting element 100, the optical intensity distribution in the lower part of the ridge 110R is dominated by the fundamental mode (i.e., the 0th-order mode), while the optical intensity distribution in the lower part of the groove 110T is dominated by higher-order modes. Therefore, when the difference ΔP between the peak position P1 of the optical intensity distribution in the stacking direction in the lower part of the ridge 110R of the nitride semiconductor light-emitting element 100 and the peak position P2 of the optical intensity distribution in the stacking direction in the lower part of the groove 110T is large, the number of modes increases or decreases, and intermode coupling occurs, causing the optical confinement coefficient in the active layer 105 to fluctuate, thus reducing the stability of the optical output.

[0061] For example, if higher-order modes decrease, the peak of the light intensity distribution, which is the sum of the light intensity distributions in the lower parts of both the ridge 110R and the groove 110T, shifts to a position closer to position P1. Therefore, the larger the difference ΔP between position P1 and position P2, the greater the fluctuation in the light confinement coefficient in the active layer 105 when the number of modes changes. Consequently, the stability of the light output decreases.

[0062] In the nitride-based semiconductor light-emitting element 100 according to this embodiment, since it includes an N-side guide layer 104 and a P-side guide layer 106 having the configuration described above, the peak of the light intensity distribution can be positioned in the active layer 105 in both the lower portion of the ridge 110R and the lower portion of the groove 110T. In other words, the difference ΔP between the positions P1 and P2 of the light intensity distribution peak can be reduced. As a result, even if the number of modes increases or decreases, or intermode coupling occurs, fluctuations in the position of the peak of the light intensity distribution, which is the sum of the light intensity distributions in the lower portions of both the ridge 110R and the groove 110T, in the stacking direction are suppressed. Therefore, the stability of the light output can be improved.

[0063] As mentioned above, in order to set the effective refractive index difference ΔN to a relatively small value, the distance dp is set to a relatively large value. When setting the distance dp, if the lower end of the ridge 110R (i.e., the bottom of the groove 110T) is positioned below the electron barrier layer 109, the electron barrier layer 109 has a large bandgap energy, so holes injected from the contact layer 111 are more likely to leak out of the ridge 110R from the sidewall when passing through the electron barrier layer 109. As a result, the holes flow downwards to the groove 110T. Consequently, because the light intensity in the active layer 105 below the groove 110T is low, the probability of luminescent recombination between electrons and holes injected into the active layer 105 decreases, and non-luminescent recombination increases. This increase in non-luminescent recombination makes the nitride semiconductor light-emitting element 100 more susceptible to degradation. To suppress such degradation, the lower end of the ridge 110R is set to be positioned above the electron barrier layer 109. Furthermore, if the distance dc (see Figure 2A) from the lower end of the ridge 110R to the electron barrier layer 109 becomes too large, holes will flow from the ridge 110R into the space between the groove 110T and the electron barrier layer 109, resulting in leakage current. To suppress this increase in leakage current, the distance dc is set to the smallest possible value. For example, the distance dc is between 10 nm and 70 nm. In this embodiment, the distance dc is 40 nm.

[0064] [1-3. Effects] [1-3-1. Each guide layer] The effects of each guide layer of the nitride-based semiconductor light-emitting element 100 according to the above-described embodiment will be explained using Figures 6 to 8, in comparison with the nitride-based semiconductor light-emitting elements of the comparative examples. Figure 6 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 1 to 3 and the nitride-based semiconductor light-emitting element 100 according to this embodiment. Graphs (a) to (c) in Figure 6 show the refractive index distribution and light intensity distribution of the nitride-based semiconductor light-emitting elements of Comparative Examples 1 to 3, respectively. Graph (d) in Figure 6 shows the refractive index distribution and light intensity distribution of the nitride-based semiconductor light-emitting element 100 according to this embodiment. In each graph in Figure 6, the refractive index distribution is shown by a solid line and the light intensity distribution is shown by a dashed line.

[0065] Figure 7 is a graph showing the simulation results of the distribution of valence electron charge and hole Fermi level in the stacking direction of the nitride semiconductor light-emitting devices of Comparative Examples 1 to 3 and the nitride semiconductor light-emitting device 100 according to this embodiment. Graphs (a) to (c) in Figure 7 show the distribution of valence electron charge and hole Fermi level of the nitride semiconductor light-emitting devices of Comparative Examples 1 to 3, respectively. Graph (d) in Figure 7 shows the distribution of valence electron charge and hole Fermi level of the nitride semiconductor light-emitting device 100 according to this embodiment. In each graph in Figure 7, the valence electron charge is shown by a solid line and the hole Fermi level is shown by a dashed line.

[0066] Figure 8 is a graph showing the simulation results of the carrier concentration distribution in the stacking direction for the nitride semiconductor light-emitting devices of Comparative Examples 1 to 3 and the nitride semiconductor light-emitting device 100 according to this embodiment. Graphs (a) to (c) in Figure 8 show the carrier concentration distribution for the nitride semiconductor light-emitting devices of Comparative Examples 1 to 3, respectively. Graph (d) in Figure 8 shows the carrier concentration distribution for the nitride semiconductor light-emitting device 100 according to this embodiment. In each graph in Figure 8, the electron concentration distribution is shown by a solid line, and the hole concentration distribution is shown by a dashed line.

[0067] The nitride-based semiconductor light-emitting devices of Comparative Examples 1 to 3 differ from the nitride-based semiconductor light-emitting device 100 according to this embodiment in the configuration of the N-side guide layer and the P-side guide layer. The nitride-based semiconductor light-emitting device of Comparative Example 1, shown in Graph (a) of Figure 6, has an undoped In layer with a film thickness of 280 nm. 0.04 Ga 0.96 An N-side guide layer 1104 consisting of an N layer and an undoped In layer with a film thickness of 160 nm. 0.04 Ga 0.96 It comprises a P-side guide layer 1106 consisting of an N layer. The nitride semiconductor light-emitting device of Comparative Example 2 shown in Graph (b) of Figure 6 has an undoped In 0.04 Ga 0.96 An N-side guide layer 1204 consisting of an N layer and an undoped In layer with a film thickness of 280 nm. 0.04 Ga 0.96 It comprises a P-side guide layer 1206 consisting of an N layer. The nitride semiconductor light-emitting device of Comparative Example 3 shown in Graph (c) of Figure 6 has an undoped In 0.04 Ga 0.96 The device comprises an N-side guide layer 1304 consisting of an N layer and a P-side guide layer 1306 with a thickness of 280 nm. The P-side guide layer 1306 of the nitride-based semiconductor light-emitting element of Comparative Example 3 has the same configuration as the P-side guide layer 106 according to this embodiment.

[0068] In the nitride-based semiconductor light-emitting device of Comparative Example 1, the compositions of the N-side guide layer 1104 and the P-side guide layer 1106 are identical, and the N-side guide layer 1104 has a greater film thickness than the P-side guide layer 1106. Therefore, in the nitride-based semiconductor light-emitting device of Comparative Example 1, as shown in graph (a) of Figure 6, the peak of the light intensity distribution in the stacking direction is located in the N-side guide layer 1104. As a result, the photoconfinement coefficient of the nitride-based semiconductor light-emitting device of Comparative Example 1 is a low value of 1.33%. Also, as shown in graph (a) of Figure 7, in the P-side guide layer 1106, in order to conduct holes from the P-side guide layer 1106 to the active layer 105, the hole Fermi level increases as you approach the interface closer to the active layer 105, rather than from the interface further away from the active layer 105. On the other hand, the valence electron charge is almost constant in the stacking direction of the P-side guide layer 1106. Therefore, the difference between the hole Fermi level and the valence electron charge level in the P-side guide layer 1106 increases as it approaches the active layer 105. As a result, as shown in graph (a) of Figure 8, the concentration of holes and electrons in the stacking direction of the P-side guide layer 1106, i.e., the free carrier concentration, increases as it moves away from the active layer 105. Thus, in the nitride-based semiconductor light-emitting device of Comparative Example 1, the free carrier concentration in the stacking direction of the P-side guide layer 1106 cannot be reduced, and therefore, a reduction in free carrier loss and a reduction in the non-luminescent recombination probability cannot be achieved. In the nitride-based semiconductor light-emitting device of Comparative Example 1, the effective refractive index difference ΔN is 3.6 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are -34.1 nm and -75.6 nm, respectively, and the difference ΔP is 41.5 nm. Furthermore, the waveguide loss is 4.5 cm. -1 Therefore, the free carrier loss in the N-side guide layer 1104 and the P-side guide layer 1106 (hereinafter also referred to as "guide layer free carrier loss") is 2.8 cm -1 That is the case.

[0069] In the nitride semiconductor light-emitting element of Comparative Example 2, the thickness of the P-side guide layer 1206 is greater than that of the N-side guide layer 1204. As shown in graph (b) of Figure 6, the peak of the light intensity distribution in the stacking direction is closer to the active layer 105 than in the nitride semiconductor light-emitting element of Comparative Example 1. Therefore, the light confinement coefficient of the nitride semiconductor light-emitting element of Comparative Example 2 is 1.37%, which is a slight improvement over the nitride semiconductor light-emitting element of Comparative Example 1. However, as shown in graph (b) of Figure 7, similar to Comparative Example 1, the difference between the hole Fermi level and the valence electron charge level in the P-side guide layer 1206 increases as it approaches the active layer 105. Therefore, as shown in graph (b) of Figure 8, the concentration of holes and electrons in the stacking direction of the P-side guide layer 1206, i.e., the free carrier concentration, increases as it moves away from the active layer 105. Thus, because the free carrier concentration in the stacking direction of the P-side guide layer 1206 cannot be reduced, the nitride-based semiconductor light-emitting device of Comparative Example 2 cannot achieve a reduction in free carrier loss and a reduction in the non-luminescent recombination probability. In the nitride-based semiconductor light-emitting device of Comparative Example 2, the effective refractive index difference ΔN is 3.3 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are 31.3 nm and 10.8 nm, respectively, and the difference ΔP is 20.5 nm. Furthermore, the waveguide loss is 5.2 cm. -1 Therefore, the guide layer free carrier loss is 3.6 cm -1 That is the case.

[0070] In the nitride-based semiconductor light-emitting element of Comparative Example 3, as shown in graph (c) of Figure 6, the refractive index of the P-side guide layer 1306 increases as it approaches the active layer 105, so that the peak of the light intensity distribution in the stacking direction can be brought closer to the active layer 105. For this reason, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the light confinement coefficient is 1.49%, which is an improvement over the nitride-based semiconductor light-emitting element of Comparative Example 2. Also, since the bandgap energy of the P-side guide layer 1306 increases monotonically as it moves away from the active layer 105, the valence electron charge level decreases continuously as it moves away from the active layer 105, as shown in graph (d) of Figure 7. This makes it possible to keep the difference between the hole Fermi level and the valence electron charge level almost constant in the P-side guide layer 1306. For this reason, as shown in graph (c) of Figure 8, the concentrations of holes and electrons in the stacking direction of the P-side guide layer 1306 can be reduced and kept almost constant. In this way, the free carrier concentration in the stacking direction of the P-side guide layer 1306 can be reduced. However, at the interface of the N-side guide layer 1304 furthest from the active layer 105 (i.e., the interface with the N-type second cladding layer 103), the band gap energy becomes discontinuous, and as shown in graph (c) of Figure 8, the hole concentration at that interface increases in a spike-like manner. For this reason, the comparative example 3 Even in the nitride-based semiconductor light-emitting element, non-luminescent recombination and free carrier loss in the N-side guide layer 1304 cannot be reduced. Comparative Example 3 Nitride-based semiconductor light-emitting element Child The effective refractive index difference ΔN is 2.1 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are 1.3 nm and -4.3 nm, respectively, and the difference ΔP is 5.6 nm. Furthermore, the waveguide loss is 3.20 cm. -1 Therefore, the guide layer free carrier loss is 1.8 cm -1 That is the case.

[0071] In the nitride-based semiconductor light-emitting element 100 according to this embodiment, as shown in graph (d) of Figure 6, not only the refractive index of the P-side guide layer 106 but also the refractive index of the N-side guide layer 104 increases as it approaches the active layer 105, making it easier to bring the peak of the light intensity distribution in the stacking direction closer to the active layer 105. In the nitride-based semiconductor light-emitting element 100 according to this embodiment, the light confinement coefficient is 1.44%, which is equivalent to that of the nitride-based semiconductor light-emitting element of Comparative Example 3. Furthermore, since the bandgap energy of the N-side guide layer 104 increases continuously and monotonically as it moves away from the active layer 105, the discontinuity in the bandgap energy at the interface of the N-side guide layer 104 that is farther from the active layer 105 can be reduced. Therefore, as shown in graph (d) of Figure 8, the hole concentration at the interface and in the N-side guide layer 104 can be significantly reduced compared to the nitride-based semiconductor light-emitting element of Comparative Example 3. Thus, since the free carrier concentration in the P-side guide layer 106 and the N-side guide layer 104 can be reduced, the nitride-based semiconductor light-emitting element 100 according to this embodiment can achieve a reduction in free carrier loss and a reduction in the non-luminescent recombination probability. In the nitride-based semiconductor light-emitting element 100 according to this embodiment, the effective refractive index difference ΔN is 2.9 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are 15.9 nm and 9.7 nm, respectively, and the difference ΔP is 6.2 nm. Thus, in this embodiment, since the positions P1 and the difference ΔP can be reduced, non-linear portions are less likely to occur in the graph showing the IL characteristics. Furthermore, the waveguide loss is 3.40 cm. -1 Therefore, the guide layer free carrier loss is 1.45 cm -1 Thus, in this embodiment, waveguide loss and free carrier loss can be reduced. In particular, in this embodiment, free carrier loss can be reduced compared to each of the comparative examples.

[0072] Next, the effect of the In composition ratio distribution in the N-side guide layer 104 of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be explained using Figures 9 and 10. Figures 9 and 10 are graphs showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer 104 according to this embodiment, the photoconfinement coefficient (Γv), and the operating voltage, respectively.

[0073] Figures 9 and 10 show the photoconfinement coefficient and operating voltage when the In composition ratio Xn1 near the interface of the N-side guide layer 104 closer to the active layer 105 is 4%, and the In composition ratio Xn2 near the interface further from the active layer 105 is 0%, 1%, 2%, 3%, and 4%, and the In composition ratio decreases at a constant rate as the distance from the active layer 105 increases. Here, the operating voltage is shown as the voltage applied to the nitride semiconductor light-emitting element when the supply current to the nitride semiconductor light-emitting element is 3A. In addition, the simulation results when the In composition ratio in the N-side guide layer is uniform are also shown as dashed lines in Figures 9 and 10.

[0074] As shown in Figures 9 and 10, when the In composition ratio in the N-side guide layer 104 decreases continuously and monotonically as it moves away from the active layer 105, the high refractive index region of the N-side guide layer 104 can be brought closer to the active layer 105 than when the In composition ratio in the N-side guide layer is uniform. This allows for an increase in the optical confinement coefficient and a reduction in the operating voltage. Furthermore, when the average In composition ratio is less than 2%, waveguide loss can be reduced even further, and the optical confinement coefficient can be increased.

[0075] For example, as shown in Figures 9 and 10, when the In composition ratio in the N-side guide layer is uniformly 2%, the optical confinement coefficient is 1.39%, and the effective refractive index difference ΔN is 3.0 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are 20.4 nm and 10.4 nm, respectively, and the difference ΔP is 10.0 nm. Furthermore, the waveguide loss is 3.4 cm. -1 Therefore, the guide layer free carrier loss is 1.38 cm-1 That is, when the In composition ratio is uniform, the peak of the light intensity distribution cannot be positioned in the active layer, and the light confinement factor is also lower than that of the nitride semiconductor light-emitting device 100 according to this embodiment.

[0076] Next, the effect of reducing the operating voltage of the nitride semiconductor light-emitting device 100 according to this embodiment will be described with reference to FIGS. 11 and 12 while comparing it with the nitride semiconductor light-emitting device of Comparative Example 3 described above. FIG. 11 is a graph showing the relationship between the position in the stacking direction of the nitride semiconductor light-emitting device of Comparative Example 3, the piezoelectric polarization charge density, the piezoelectric polarization electric field, and the conduction band potential. FIG. 12 is a graph showing the relationship between the position in the stacking direction of the nitride semiconductor light-emitting device 100 according to this embodiment, the piezoelectric polarization charge density, the piezoelectric polarization electric field, and the conduction band potential. In the graphs (a), (b), and (c) of FIGS. 11 and 12, the relationships between the position in the stacking direction of each nitride semiconductor light-emitting device, the piezoelectric polarization charge density, the piezoelectric polarization electric field, and the conduction band potential are shown, respectively. In addition, in the graph (c) of FIGS. 11 and 12, the hole Fermi level is also shown by a broken line.

[0077] As shown in the graph (a) of FIG. 11, the piezoelectric polarization charge density of the N-side guide layer 1304 of the nitride semiconductor light-emitting device of Comparative Example 3 is constant in the stacking direction. Therefore, the gap in the piezoelectric polarization charge density at each interface between the N-side guide layer 1304, the N-type second clad layer 103, and the active layer 105 is large. Along with this, piezoelectric polarization charges are locally formed at each interface between the N-side guide layer 1304, the N-type second clad layer 103, and the active layer 105. As a result, a large piezoelectric polarization electric field is generated. Therefore, as shown in the graph (b) of FIG. 11, spike-shaped piezoelectric polarization electric fields are generated at each interface between the N-side guide layer 1304, the N-type second clad layer 103, and the active layer 105. As a result, holes are attracted near each interface between the N-side guide layer 1304, the N-type second clad layer 103, and the active layer 105, and the conduction band potential at the interface increases (see ΔE1 shown in the graph (c) of FIG. 11).

[0078] On the other hand, as shown in graph (a) of Figure 12, the polarization charge density of the N-side guide layer 104 of the nitride semiconductor light-emitting element 100 according to this embodiment decreases monotonically as it approaches the interface further away from the interface closer to the active layer 105. Therefore, the gap in piezoelectric polarization charge density at each interface between the N-side guide layer 104 and the N-type second cladding layer 103 and the active layer 105 is suppressed. As a result, the piezoelectric polarization charge is dispersed in the stacking direction of the N-side guide layer 104. Therefore, as shown in graph (b) of Figure 12, the piezoelectric polarization field at each interface between the N-side guide layer 104 and the N-type second cladding layer 103 and the active layer 105 can be suppressed. As a result, as shown in graph (c) of Figure 12, the increase in conduction charge (ΔE1 shown in graph (c) of Figure 12) caused by the induction of holes near each interface between the N-side guide layer 104 and the N-type second cladding layer 103 and the active layer 105 can be suppressed. This makes it possible to improve the conductivity of electrons flowing from the N-type second cladding layer 103 to the active layer 105 in the nitride-based semiconductor light-emitting element 100 according to this embodiment, and thus reduce the operating voltage.

[0079] [1-3-2. Impurities in the N-side guide layer] Next, the effect of impurities in the N-side guide layer 104 according to this embodiment will be explained using Figures 13 to 15. Figures 13, 14, and 15 are graphs showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer 104 of the nitride-based semiconductor light-emitting element 100 according to this embodiment, and the optical confinement coefficient (Γv), waveguide loss, and operating voltage, respectively. Graphs (a), (b), (c), and (d) in Figures 13 to 15 show the relationships between the impurity (Si) concentration in the N-side guide layer 104 when it is 0 (i.e., undoped), 3 × 10⁻¹⁰, and 15 × 10⁻¹⁰, respectively. 17 cm -3 , 6×10 17 cm -3 , and 1 × 10 18 cm -3 The simulation results for this case are shown.

[0080] In FIGS. 13 to 15, the In composition ratio Xn1 near the interface closer to the active layer 105 of the N-side guide layer 104 is 4%, and the In composition ratio Xn2 near the interface farther from the active layer 105 is 0%, 1%, 2%, 3%, and 4%. As the distance from the active layer 105 increases, the light confinement coefficient and the operating voltage when the In composition ratio decreases at a constant rate of change are shown. Also, in FIGS. 13 to 15, the simulation results when the In composition ratio in the N-side guide layer is uniform are also shown by broken lines.

[0081] As shown in FIG. 13, in the nitride semiconductor light-emitting device 100 according to the present embodiment, the light confinement coefficient can be increased as compared with the nitride semiconductor light-emitting device of the comparative example in which the In composition ratio of the N-side guide layer is uniform. Also, from FIG. 13, it can be seen that in the nitride semiconductor light-emitting device 100 according to the present embodiment, the light confinement coefficient hardly depends on the impurity concentration.

[0082] As shown in FIG. 14, in the nitride semiconductor light-emitting device 100 according to the present embodiment, except when no impurity is added, the waveguide loss can be reduced as compared with the nitride semiconductor light-emitting device of the comparative example in which the In composition ratio of the N-side guide layer is uniform. This is considered to be due to the fact that although the electron concentration increases due to the addition of the impurity, the hole concentration decreases due to the bandgap energy distribution in the stacking direction of the N-side guide layer 104.

[0083] As shown in FIG. 15, in the nitride semiconductor light-emitting device 100 according to the present embodiment, the operating voltage can be reduced as compared with the nitride semiconductor light-emitting device of the comparative example in which the In composition ratio of the N-side guide layer is uniform. Also, by increasing the concentration of the impurity added to the nitride semiconductor light-emitting device 100, the electron concentration in the N-side guide layer 104 can be increased, so that the operating voltage can be further reduced.

[0084] From FIGS. 14 and 15, in the nitride semiconductor light-emitting device 100 according to the present embodiment, the impurity concentration in the N-side guide layer 104 is 1×10 17 cm -3 or more and 6×1017 cm -3 By doing the following, it is possible to reduce the operating voltage while suppressing a significant increase in waveguide losses.

[0085] [1-3-3. Film thickness of N-side guide layer and P-side guide layer] Next, the effect of the relationship between the film thickness of the N-side guide layer 104 and the P-side guide layer 106 according to this embodiment will be explained using Figures 16 and 17. Figures 16 and 17 are graphs showing the simulation results of the relationship between the film thickness of the N-side guide layer 104, position P1, and difference ΔP according to this embodiment, respectively. In the simulations shown in Figures 16 and 17, the sum of the film thicknesses of the N-side guide layer 104 and the P-side guide layer 106 is kept constant at 440 nm, while the individual film thicknesses of the N-side guide layer 104 and the P-side guide layer 106 are varied. The In composition ratio of the N-side guide layer 104 and the P-side guide layer 106 is 4% near the interface closer to the active layer 105, and 0% near the interface further from the active layer 105. The In composition ratio of the N-side guide layer 104 and the P-side guide layer 106 is varied at a constant rate in the stacking direction. Furthermore, Figures 16 and 17 also show, as a comparative example, the simulation results for an example where the In composition ratio of the N-side guide layer is constant at 2%, indicated by dashed lines.

[0086] As shown in Figure 16, by setting the film thickness Tn of the N-side guide layer 104 to 160 nm or more and 250 nm or less, position P1 can be positioned in the active layer 105. In other words, the film thickness of the N-side guide layer 104 may be set to 36% or more and 57% or less of the sum of the film thicknesses of the N-side guide layer 104 and the P-side guide layer 106. This makes it possible to set position P1 to -7 nm or more and 18 nm or less, that is, to position the peak of the light intensity distribution within the active layer 105.

[0087] As shown in Figure 17, the difference ΔP can be reduced by making the film thickness Tn of the N-side guide layer 104 less than 220 nm, that is, by making it smaller than the film thickness Tp of the P-side guide layer 106. In particular, the film thickness of the N-side guide layer 104 and the P-side guide layer 106By setting the sum of the film thicknesses to 23% or more and 43% or less, the difference ΔP can be made 20 nm or less. Also, as shown in Figure 17, even when the In composition ratio of the P-side guide layer 106 is kept constant at 2%, the N-side guide layer 104 The difference ΔP can be reduced by making the film thickness of the P-side guide layer 106 smaller than the film thickness of the P-side guide layer 106. However, the difference ΔP can be reduced even more if the In composition ratio is continuously and monotonically decreased as it moves away from the active layer 105, as in the P-side guide layer 106 of this embodiment.

[0088] [1-3-4. P-type cladding layer] Next, the film thickness of the P-type cladding layer 110 according to this embodiment will be explained using Figures 18 to 22. Figure 18 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer 110 according to this embodiment and the optical confinement coefficient (Γv). Figure 19 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer 110 according to this embodiment and the waveguide loss. Figure 20 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer 110 according to this embodiment and the effective refractive index difference ΔN. Figure 21 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer 110 according to this embodiment and the position P1. Figure 22 is a graph showing the simulation results of the relationship between the film thickness of the P-type cladding layer 110 according to this embodiment and the difference ΔP. In addition, Figures 18 to 22 also show the simulation results of a comparative example in which the In composition ratio of both the N-side guide layer and the P-side guide layer is constant at 2%. Figures 18 to 22 also show the simulation results of the nitride-based semiconductor light-emitting element 300 according to Embodiment 3, which will be described later.

[0089] As shown in Figure 18, the nitride-based semiconductor light-emitting element 100 according to this embodiment can achieve a higher photoconfinement coefficient than the nitride-based semiconductor light-emitting element of the comparative example. Furthermore, in this embodiment, due to the configuration of each guide layer and each barrier layer described above, the photoconfinement coefficient does not decrease even when the film thickness of the P-type cladding layer 110 is reduced to 250 nm.

[0090] As shown in Figure 19, the nitride-based semiconductor light-emitting element 100 according to this embodiment can reduce waveguide loss compared to the nitride-based semiconductor light-emitting element of the comparative example. Furthermore, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, even if the film thickness of the P-type cladding layer 110 is reduced to about 300 nm, a significant increase in waveguide loss can be suppressed.

[0091] As shown in Figure 20, the nitride-based semiconductor light-emitting element 100 according to this embodiment can reduce the effective refractive index difference ΔN compared to the nitride-based semiconductor light-emitting element of the comparative example.

[0092] As shown in Figure 21, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, position P1 can be positioned on the active layer 105 over the entire range of P-type cladding layer 110 thickness from 250 nm to 820 nm, similar to the nitride-based semiconductor light-emitting element of the comparative example. Furthermore, as shown in Figure 22, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the difference ΔP can be reduced over the entire range of P-type cladding layer 110 thickness from 250 nm to 820 nm compared to the nitride-based semiconductor light-emitting element of the comparative example.

[0093] As described above, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the film thickness of the P-type cladding layer 110 can be reduced, and therefore the operating voltage can be reduced.

[0094] [1-3-5. Each barrier layer] Next, the effects of the configuration of each barrier layer in the active layer 105 according to this embodiment will be explained in comparison with the comparative example. In this embodiment, as described above, the bandgap energy of each barrier layer is less than or equal to the minimum bandgap energy of the N-side guide layer 104 and the P-side guide layer 106. Here, as a comparative example, the simulation results of a nitride-based semiconductor light-emitting device of Comparative Example 4 are shown, in which the composition of each barrier layer is made undoped GaN, thereby making the bandgap energy of each barrier layer greater than the minimum bandgap energy of the N-side guide layer 104 and the P-side guide layer 106, and the other configurations are the same as those of the nitride-based semiconductor light-emitting device 100 according to this embodiment. In the nitride-based semiconductor light-emitting device of Comparative Example 4, the photoconfinement coefficient is 1.34%, and the effective refractive index difference ΔN is 3.2 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are 33.9 nm and 10.3 nm, respectively, and the difference ΔP is 23.6 nm. Furthermore, the waveguide loss is 3.6 cm. -1 Therefore, the guide layer free carrier loss is 1.32 cm -1 Thus, in the nitride-based semiconductor light-emitting element of Comparative Example 4, the bandgap energy of each barrier layer is large, that is, the refractive index of each barrier layer is small, so the light confinement coefficient is lower than that of the nitride-based semiconductor light-emitting element 100 according to this embodiment. Consequently, other evaluation indicators of the nitride-based semiconductor light-emitting element of Comparative Example 4 are also worse than those of the nitride-based semiconductor light-emitting element 100 according to this embodiment, except for position P1.

[0095] As described above, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the photoconfinement coefficient can be increased by setting the bandgap energy of each barrier layer to be less than or equal to the minimum bandgap energy of the N-side guide layer 104 and the P-side guide layer 106. Consequently, the difference ΔP can be reduced, making it less likely for non-linear portions to occur in the graph showing the IL characteristics.

[0096] (Embodiment 2) A nitride-based semiconductor light-emitting element according to Embodiment 2 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1 mainly in the bandgap energy distribution of the P-side guide layer. The following description will focus on the differences between the nitride-based semiconductor light-emitting element according to this embodiment and the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0097] First, the overall configuration of the nitride-based semiconductor light-emitting element according to this embodiment will be explained using Figures 23A, 23B, and 24. Figure 23A is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 200 according to this embodiment. Figure 23B is a schematic graph showing the configuration of the active layer 205 of the nitride-based semiconductor light-emitting element 200 according to this embodiment. Figure 24 is a schematic graph showing the distribution of the bandgap energy of the active layer 205 and each layer in its vicinity in the nitride-based semiconductor light-emitting element 200 according to this embodiment.

[0098] As shown in Figure 23A, the nitride-based semiconductor light-emitting element 200 according to this embodiment comprises a semiconductor laminate 200S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 200S has 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 205, a P-side guide layer 206, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 110, and a contact layer 111.

[0099] The active layer 205 has well layers 105b and 105d and barrier layers 205a, 105c, and 205e, as shown in Figure 23B.

[0100] The barrier layer 205a is positioned above the N-side guide layer 104 and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 205a is an undoped In- 0.05 Ga 0.95 It is an N-layer structure.

[0101] The barrier layer 205e is positioned above the well layer 105d and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 105e is an undoped In layer with a thickness of 6 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0102] The P-side guide layer 206 in this embodiment differs from the P-side guide layer 106 in Embodiment 1 in that the bandgap energy is constant in the stacking direction, as shown in Figure 24. In this embodiment, the P-side guide layer 206 is an undoped In Xp Ga 1-Xp It is an N layer, and the In composition ratio Xp of the P-side guide layer 206 is 2%.

[0103] In a nitride-based semiconductor light-emitting element 200 having such an active layer 205 and P-side guide layer 206, the operating voltage can be reduced and the photoconfinement coefficient to the active layer 205 can be increased, similar to the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0104] According to this embodiment, the effective refractive index difference ΔN is 3.5 × 10 -3 The position P1 is 11.0 nm, the position P2 is 2.5 nm, the difference ΔP is 8.5 nm, the optical confinement coefficient to the active layer 205 is 1.33%, and the waveguide loss is 5.1 cm -1 Therefore, the guide layer free carrier loss is 2.6 cm -1 This enables the realization of a nitride-based semiconductor light-emitting element 200.

[0105] (Embodiment 3) A nitride-based semiconductor light-emitting element according to Embodiment 3 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 200 according to Embodiment 2 in the bandgap energy distribution of the P-side guide layer. Below, the nitride-based semiconductor light-emitting element according to this embodiment will be described, focusing on the differences from the nitride-based semiconductor light-emitting element 200 according to Embodiment 2.

[0106] First, the overall configuration of the nitride-based semiconductor light-emitting element according to this embodiment will be described using Figures 25 and 26. Figure 25 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 300 according to this embodiment. Figure 26 is a schematic graph showing the distribution of the bandgap energy of the active layer 205 and each layer in its vicinity in the nitride-based semiconductor light-emitting element 300 according to this embodiment.

[0107] As shown in Figure 25, the nitride-based semiconductor light-emitting element 300 according to this embodiment comprises a semiconductor laminate 300S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 300S has 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 205, a P-side guide layer 306, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 110, and a contact layer 111.

[0108] The P-side guide layer 306 in this embodiment differs from the P-side guide layer 206 in embodiment 2 in that the band gap energy changes in a step-like manner in the stacking direction, as shown in Figure 24. The P-side guide layer 306 has a P-side first guide layer 306a and a P-side second guide layer 306b. The P-side first guide layer 306a is a guide layer positioned above the active layer 205 and having a band gap energy greater than that of the active layer 205. The P-side second guide layer 306b is a guide layer positioned above the P-side first guide layer 306a and having a band gap energy greater than that of the P-side first guide layer 306a. In this embodiment, the P-side first guide layer 306a is an undoped In 0.04 Ga 0.96 It is an N layer, and the P-side second guide layer 306b is an undoped In layer with a film thickness of 200 nm. 0.01 Ga 0.99 This is an N layer. Thus, the P-side first guide layer 306a has a higher In composition ratio than the P-side second guide layer 306b.

[0109] In a nitride-based semiconductor light-emitting element 300 having such a P-side guide layer 306, the operating voltage can be reduced and the photoconfinement coefficient to the active layer 205 can be increased, similar to the nitride-based semiconductor light-emitting element 200 according to Embodiment 3.

[0110] According to this embodiment, the effective refractive index difference ΔN is 2.8 × 10 -3 The position P1 is 13.0 nm, the position P2 is 9.1 nm, the difference ΔP is 3.9 nm, the optical confinement coefficient to the active layer 205 is 1.47%, and the waveguide loss is 3.9 cm. -1 The guide layer free carrier loss is 1.9 cm². -1 This enables the realization of a nitride-based semiconductor light-emitting element 300.

[0111] The effects of the nitride-based semiconductor light-emitting element 300 according to this embodiment will be explained in comparison with the nitride-based semiconductor light-emitting elements of Comparative Examples 5 to 7.

[0112] The nitride-based semiconductor light-emitting element of Comparative Example 5 differs from the nitride-based semiconductor light-emitting element 300 of this embodiment in that the N-side guide layer has a constant bandgap energy in the stacking direction. The N-side guide layer of the nitride-based semiconductor light-emitting element of Comparative Example 5 is an N-type In 0.02 Ga 0.98 It is an N layer, and contains impurities with a concentration of 3 × 10⁻⁶ 17 cm -3 Si is doped. In the nitride-based semiconductor light-emitting element of Comparative Example 5, the effective refractive index difference ΔN is 3.5 × 10 -3 The position P1 is 12.6 nm, the position P2 is 4.7 nm, the difference ΔP is 7.9 nm, the optical confinement coefficient to the active layer 205 is 1.27%, and the waveguide loss is 5.1 cm -1 Therefore, the guide layer free carrier loss is 2.5 cm -1 That is the case.

[0113] Thus, the nitride-based semiconductor light-emitting element 300 according to this embodiment is equipped with an N-side guide layer 104 having the above-described configuration, and therefore the photoconfinement coefficient can be increased compared to the nitride-based semiconductor light-emitting element of Comparative Example 5.

[0114] The nitride semiconductor light-emitting devices of Comparative Examples 6 and 7 differ from the nitride semiconductor light-emitting device 300 of this embodiment in that the average bandgap energy of the P-side guide layer is smaller than the average bandgap energy of the N-side guide layer. The P-side guide layer of the nitride semiconductor light-emitting devices of Comparative Examples 6 and 7 is an undoped In 0.04 Ga 0.96 The first guide layer on the P side is an N layer, and an undoped In layer is placed above the first guide layer on the P side with a film thickness of 100 mm. 0.04 Ga 0.96 It has an N-layer, which is a P-side second guide layer. The N-side guide layer of the nitride semiconductor light-emitting element of Comparative Example 6 has the same configuration as the N-side guide layer 104 in this embodiment. The N-side guide layer of the nitride semiconductor light-emitting element of Comparative Example 7 has a constant bandgap energy in the stacking direction. Specifically, the N-side guide layer of the nitride semiconductor light-emitting element of Comparative Example 7 is an N-type In 0.04 Ga 0.96 It is an N layer, and contains impurities at a concentration of 3 × 10⁻⁶ 17 cm -3 The Si is doped.

[0115] In the nitride-based semiconductor light-emitting devices of Comparative Example 6 and Comparative Example 7, the positions P1 are 32.7 nm and 38.3 nm, respectively, and the peak position of the light intensity distribution is outside the active layer and in the P-side guide layer. Therefore, when coupling occurs between higher-order modes that can propagate in the waveguide formed by the ridge 110R and lower-order modes that are stably confined in the waveguide, light confinement occurs. coefficient This is prone to change. In other words, the linearity of the IL characteristics tends to decrease. In particular, as in Comparative Examples 6 and 7, when the effective refractive index difference ΔN is 3.0 × 10 -3When the value is small, the number of higher-order modes that can propagate through the waveguide decreases, which increases the impact on the IL characteristics due to intermode coupling. For this reason, the linearity of the IL characteristics tends to decrease in the nitride-based semiconductor light-emitting devices of Comparative Examples 6 and 7.

[0116] On the other hand, in the nitride-based semiconductor light-emitting element 300 according to this embodiment, position P1 is 13.0 nm, which is significantly smaller than the position P1 of the nitride-based semiconductor light-emitting elements of Comparative Examples 6 and 7. Therefore, a decrease in the linearity of the IL characteristics can be suppressed.

[0117] (Embodiment 4) A nitride-based semiconductor light-emitting element according to Embodiment 4 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1 mainly in the bandgap energy distribution of the N-side guide layer. The following description will focus on the differences between the nitride-based semiconductor light-emitting element according to this embodiment and the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0118] [4-1. Overall Structure] First, the overall configuration of the nitride-based semiconductor light-emitting element according to this embodiment will be described using Figures 27 and 28. Figure 27 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 400 according to this embodiment. Figure 28 is a schematic graph showing the distribution of the bandgap energy of the active layer 205 and each layer in its vicinity in the nitride-based semiconductor light-emitting element 400 according to this embodiment.

[0119] As shown in Figure 27, the nitride-based semiconductor light-emitting element 400 according to this embodiment comprises a semiconductor laminate 400S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 400S has a substrate 101, an N-type first cladding layer 102, an N-type second cladding layer 103, an N-side guide layer 404, an active layer 205, a P-side guide layer 106, an intermediate layer 108, an electron barrier layer 109, a P-type cladding layer 110, and a contact layer 111.

[0120] In the N-side guide layer 404 according to this embodiment, similar to the N-side guide layer 104 according to Embodiment 1, the band gap energy increases monotonically and continuously as it moves away from the active layer 205. In this embodiment, the N-side guide layer 404 is made of N-type In Xn Ga 1-Xn It is an N layer, and the N-side guide layer 404 contains impurities with a concentration of 3 × 10⁻⁶ 17 cm -3 Si is doped into it. Furthermore, the absolute value of the average rate of change of the In composition ratio in the stacking direction in the region from the interface of the N-side guide layer 404 on the side closer to the active layer 205 to the center of the N-side guide layer 404 in the stacking direction is smaller than the absolute value of the average rate of change of the In composition ratio in the stacking direction in the region from the center to the interface of the N-side guide layer 404 on the side closer to the N-type first cladding layer 102. In other words, the curve showing the relationship between the position of the N-side guide layer 404 in the stacking direction and the In composition ratio has an upward convex shape. To put it another way, the curve showing the relationship between the position of the N-side guide layer 404 in the stacking direction and the band gap energy has a downward convex shape (see Figure 28).

[0121] The N-side guide layer 404 has an N-side first guide layer 404a and an N-side second guide layer 404b. The N-side first guide layer 404a is a guide layer positioned above the N-type second cladding layer 103. The N-side first guide layer 404a has a film thickness of 80 nm. Xn Ga 1-Xn It is an N layer. More specifically, the N-side first guide layer 404a has In near the interface furthest from the active layer 205. Xn2 Ga 1-Xn2 It has a composition represented by N, and near the interface closer to the active layer 205, In Xnm Ga 1-Xnm It has a composition represented by N (see Figure 28). The In composition ratio Xn of the N-side first guide layer 404a decreases at a constant rate as it moves away from the active layer 105. The N-side second guide layer 404b is a guide layer positioned above the N-side first guide layer 404a. In other words, the N-side second guide layer 404b is positioned between the N-side first guide layer 404a and the active layer 205. The N-side second guide layer 404b has a film thickness of 80 nm and is N-type InXn Ga 1-Xn It is an N layer. More specifically, the N-side second guide layer 404b has In near the interface closer to the active layer 205. Xn1 Ga 1-Xn1 It has a composition represented by N, and near the interface furthest from the active layer 205, In Xnm Ga 1-Xnm It has a composition represented by N. The In composition ratio Xn of the N-side second guide layer 404b decreases at a constant rate as it moves away from the active layer 105. In this embodiment, Xn1=0.04, Xnm=0.03, and Xn2=0.

[0122] [4-2. Effects] [4-2-1.In composition ratio distribution] Next, the effect of the In composition ratio distribution in the N-side guide layer 404 of the nitride-based semiconductor light-emitting element 400 according to this embodiment will be explained using Figures 29 to 33. Figure 29 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer 404 according to this embodiment and the optical confinement coefficient (Γv). Figure 30 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer 404 according to this embodiment and waveguide loss. Figure 31 is a graph showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer 404 according to this embodiment and the operating voltage. Figures 32 and 33 are graphs showing the simulation results of the relationship between the average In composition ratio in the N-side guide layer 404 according to this embodiment and the position P1 and the difference ΔP, respectively. Figures 29 to 33 show the waveguide loss and optical confinement coefficient when the In composition ratio Xp1 near the interface of the N-side guide layer 404 closer to the active layer 205 is 4%, and the In composition ratio Xp2 near the interface further from the active layer 205 is 0%, and the In composition ratio is continuously and monotonically decreased as the distance from the active layer 205 increases. More specifically, Figures 29 to 33 show the simulation results when the average In composition ratio in the N-side guide layer 404 is changed by changing the In composition ratio Xnm in the central part of the stacking direction of the N-side guide layer 404. In addition, the simulation results when the In composition ratio in the N-side guide layer is uniform are also shown as dashed lines in Figures 29 to 33.

[0123] In the examples shown in Figures 29 to 33, when the average In composition ratio is greater than 2%, the curve showing the relationship between the position of the N-side guide layer 404 in the stacking direction and the In composition ratio has a convex shape. For example, when the average In composition ratio is 2.5%, it corresponds to the nitride-based semiconductor light-emitting element 400 according to this embodiment.

[0124] As shown in Figures 29 and 30, when the In composition ratio in the N-side guide layer 404 decreases continuously and monotonically as it moves away from the active layer 205, the optical confinement coefficient can be increased and waveguide losses can be reduced compared to when the In composition ratio in the N-side guide layer is uniform. Furthermore, when the average In composition ratio is greater than 2%, the optical confinement coefficient can be increased even further and waveguide losses can be reduced even more.

[0125] Furthermore, as shown in Figure 31, the operating voltage can be reduced more effectively when the In composition ratio in the N-side guide layer 404 decreases continuously and monotonically as it moves away from the active layer 205, compared to when the In composition ratio in the N-side guide layer is uniform. Moreover, the operating voltage can be reduced even further when the average In composition ratio is greater than 2%.

[0126] Furthermore, as shown in Figures 32 and 33, when the In composition ratio in the N-side guide layer 404 decreases continuously and monotonically as it moves away from the active layer 205, the position P1 of the peak of the light intensity distribution can be brought closer to the active layer 205, and the difference ΔP can be reduced, compared to when the In composition ratio in the N-side guide layer is uniform. Moreover, when the average In composition ratio is greater than 2%, the position P1 can be located within the active layer 205, and the difference ΔP can be reduced even further. This is thought to be because when the average In composition ratio is greater than 2%, the refractive index of the region of the N-side guide layer 404 closer to the active layer 205 can be increased, thus guiding light to the vicinity of the active layer 205.

[0127] [4-2-2. Each barrier layer] Next, the effects of the configuration of each barrier layer in the active layer 205 according to this embodiment will be explained in comparison with the comparative example. In this embodiment, as described above, the bandgap energy of each barrier layer is less than or equal to the minimum bandgap energy of the N-side guide layer 404 and the P-side guide layer 106. Here, as a comparative example, the simulation results of a nitride-based semiconductor light-emitting device of Comparative Example 8 are shown, in which the composition of each barrier layer is undoped GaN, the bandgap energy of each barrier layer is greater than the minimum bandgap energy of the N-side guide layer 404 and the P-side guide layer 106, and the other configurations are the same as those of the nitride-based semiconductor light-emitting device 400 according to this embodiment. In the nitride-based semiconductor light-emitting device of Comparative Example 8, the photoconfinement coefficient is 1.36%, and the effective refractive index difference ΔN is 3.4 × 10⁻⁶. -3 The peak positions P1 and P2 of the light intensity distribution are 22.8 nm and 2.2 nm, respectively, and the difference ΔP is 20.6 nm. Furthermore, the waveguide loss is 3.4 cm. -1 Therefore, the free carrier loss in the N-side guide layer and the P-side guide layer is 1.4 cm -1 That is the case.

[0128] In contrast, in this embodiment, the optical confinement coefficient is 1.44%, and the effective refractive index difference ΔN is 3.4 × 10 -3 The peak positions P1 and P2 of the light intensity distribution are 10.9 nm and 5.5 nm, respectively, and the difference ΔP is 5.4 nm. Furthermore, the waveguide loss is 3.4 cm. -1 Therefore, the guide layer free carrier loss is 1.7 cm -1 That is the case.

[0129] Thus, in this embodiment, since the bandgap energy of each barrier layer is less than or equal to that of each guide layer, that is, since the refractive index of each barrier layer is greater than that of each guide layer, the optical confinement coefficient can be increased compared to the nitride-based semiconductor light-emitting element of Comparative Example 8. Consequently, in this embodiment, the position P1 and the difference ΔP can also be reduced compared to the nitride-based semiconductor light-emitting element of Comparative Example 8. In this embodiment, since the difference ΔP can be reduced, non-linear portions are less likely to occur in the graph showing the IL characteristics.

[0130] (Embodiment 5) A nitride-based semiconductor light-emitting element according to Embodiment 5 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1 in the relationship between the Al composition ratio 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 element according to this embodiment will be described below, focusing on the differences from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1, using Figure 34.

[0131] Figure 34 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 500 according to this embodiment.

[0132] As shown in Figure 34, the nitride-based semiconductor light-emitting element 500 according to this embodiment comprises a semiconductor laminate 500S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 500S has a substrate 101, an N-type first cladding layer 502, an N-type second cladding layer 103, an N-side guide layer 104, an active layer 105, a P-side guide layer 106, an intermediate layer 108, an electron barrier layer 509, a P-type cladding layer 510, and a contact layer 111.

[0133] The N-type first cladding layer 502 in this embodiment is made of N-type Al with a film thickness of 1200 nm. 0.036 Ga 0.964 This is an N-type layer. The first N-type cladding layer 502 contains impurities at a concentration of 1 × 10⁻⁶. 18 cm -3 The Si is doped.

[0134] In this embodiment, the P-type cladding layer 510 is placed between the electron barrier layer 509 and the contact layer 111. The P-type cladding layer 510 has a lower refractive index and a higher bandgap energy than the active layer 105. In this embodiment, the P-type cladding layer 510 is made of P-type Al with a film thickness of 450 nm. 0.026 Ga 0.974This is the N layer. The P-type cladding layer 510 is doped with Mg as an impurity. Furthermore, the impurity concentration at the end of the P-type cladding layer 510 closer to the active layer 105 is lower than the impurity concentration at the end further away from the active layer 105. Specifically, the concentration of the P-type cladding layer 510 located closer to the active layer 105 is 2 × 10⁻¹⁰. 18 cm -3 P-type Al with Mg doped, 150 nm film thickness. 0.026 Ga 0.974 The N layer and the concentration 1 × 10 located on the side furthest from the active layer 105. 19 cm -3 P-type Al with Mg doped, 300 nm film thickness. 0.026 Ga 0.974 It has N layers.

[0135] The P-type cladding layer 510 has ridges 510R formed on it, similar to the nitride-based semiconductor light-emitting element 100 according to Embodiment 1. In addition, the P-type cladding layer 510 has two grooves 510T formed on it, which are arranged along the ridges 510R and extend in the Y-axis direction.

[0136] In this embodiment, the N-type first cladding layer 502 and the P-type cladding layer 510 contain Al, and the Al composition ratios of the N-type first cladding layer 502 and the P-type cladding layer 510 are Ync and Ypc, respectively. Ync>Ypc (4) It satisfies the following relationship.

[0137] Here, if at least one of the N-type first cladding layer 502 and the P-type cladding layer 510 has a superlattice structure, the composition ratios Ync and Ypc represent the average Al composition ratio. For example, if the N-type first cladding layer 502 includes multiple GaN layers with a thickness of 2 nm and multiple AlGaN layers with a thickness of 2 nm and an Al composition ratio of 0.07, and each of the multiple GaN layers and each of the multiple AlGaN layers are stacked alternately, then Ync will be 0.035, which is the average Al composition ratio for the entire N-type first cladding layer 502. If the P-type cladding layer 510 includes multiple GaN layers with a thickness of 2 nm and multiple AlGaN layers with a thickness of 2 nm and an Al composition ratio of 0.07, and each of the multiple GaN layers and each of the multiple AlGaN layers are stacked alternately, then Ypc will be 0.035, which is the average Al composition ratio for the entire P-type cladding layer 510.

[0138] As equation (4) above holds true, the refractive index of the N-type first cladding layer 502 can be reduced to that of the P-type cladding layer 510. Therefore, even if the film thickness of the P-type cladding layer 510 is reduced in order to reduce the operating voltage of the nitride semiconductor light-emitting element 500, the refractive index of the N-type first cladding layer 502 is smaller than that of the P-type cladding layer 510, so it is possible to suppress the shift of the peak of the light intensity distribution in the stacking direction from the active layer 105 towards the N-type first cladding layer 502.

[0139] The electron barrier layer 509 is positioned above the active layer 105 and is a nitride-based semiconductor layer containing at least Al. In this embodiment, the electron barrier layer 509 is positioned between the intermediate layer 108 and the P-type cladding layer 510. The electron barrier layer 509 is a P-type AlGaN layer with a thickness of 5 nm. The electron barrier layer 509 also has an Al composition ratio gradient region in which the Al composition ratio increases monotonically as it approaches the P-type cladding layer 510. Here, the configuration in which the Al composition ratio increases monotonically also includes a configuration in which the Al composition ratio is constant in the stacking direction. For example, the configuration in which the Al composition ratio increases monotonically also includes a configuration in which the Al composition ratio increases in a step-like manner. In the electron barrier layer 509 according to this embodiment, the entire electron barrier layer 509 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 509 has Al near the interface with the intermediate layer 108. 0.02 Ga 0.98 It has a composition represented by N, and as it approaches the P-type cladding layer 510, the Al composition ratio increases monotonically, and near the interface with the P-type cladding layer 510, Al 0.36 Ga 0.64 It has a composition represented by N. The electron barrier layer 509 contains impurities at a concentration of 1 × 10⁻⁶. 19 cm -3 It is doped with magnesium.

[0140] The electron barrier layer 509 suppresses electron leakage from the active layer 105 to the P-type cladding layer 510. Furthermore, because the electron barrier layer 509 has an Al composition change region where the Al composition ratio increases monotonically, the potential barrier in the valence band of the electron barrier layer 509 can be reduced compared to when the Al composition ratio is uniform. This makes it easier for holes to flow from the P-type cladding layer 510 to the active layer 105. Therefore, even when the thickness of the P-side guide layer 106, which is an undoped layer, is large, as in this embodiment, the increase in the electrical resistance of the nitride semiconductor light-emitting element 500 can be suppressed. This allows the operating voltage of the nitride semiconductor light-emitting element 500 to be reduced. In addition, since self-heating during operation of the nitride semiconductor light-emitting element 500 can be reduced, the temperature characteristics of the nitride semiconductor light-emitting element 500 can be improved. Therefore, high-power operation of the nitride semiconductor light-emitting element 500 becomes possible.

[0141] According to this embodiment, the effective refractive index difference ΔN is 3.0 × 10 -3 The position P1 is 17.3 nm, the difference ΔP is 7.0 nm, the optical confinement coefficient to the active layer 105 is 1.45%, and the waveguide loss is 3.3 cm. -1 Therefore, the guide layer free carrier loss is 1.3 cm -1 This enables the realization of a nitride-based semiconductor light-emitting element 500.

[0142] (Embodiment 6) A nitride-based semiconductor light-emitting element according to Embodiment 6 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5 mainly in that it has a translucent conductive film on the contact layer of the ridge. The nitride-based semiconductor light-emitting element according to this embodiment will be described below, focusing on the differences from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5, using Figure 35.

[0143] Figure 35 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 600 according to this embodiment. As shown in Figure 35, the nitride-based semiconductor light-emitting element 600 according to this embodiment comprises a semiconductor laminate 600S, a current blocking layer 112, a P-side electrode 113, an N-side electrode 114, and a translucent conductive film 620. The semiconductor laminate 600S has a substrate 101, an N-type first cladding layer 502, an N-type second cladding layer 103, an N-side guide layer 104, an active layer 105, a P-side guide layer 106, an intermediate layer 108, an electron barrier layer 509, a P-type cladding layer 610, and a contact layer 611.

[0144] In this embodiment, the P-type cladding layer 610 is placed between the electron barrier layer 509 and the contact layer 611. The P-type cladding layer 610 has a lower refractive index and a higher bandgap energy than the active layer 105. In this embodiment, the P-type cladding layer 610 is made of P-type Al with a film thickness of 330 nm. 0.026 Ga 0.974 This is the N layer. The P-type cladding layer 610 is doped with Mg as an impurity. Furthermore, the impurity concentration at the end of the P-type cladding layer 610 closer to the active layer 105 is lower than the impurity concentration at the end further away from the active layer 105. Specifically, the concentration of the P-type cladding layer 610 located closer to the active layer 105 is 2 × 10⁻¹⁰. 18 cm -3 P-type Al with Mg doped, 150 nm film thickness. 0.026 Ga 0.974 The N layer and the concentration 1 × 10 located on the side furthest from the active layer 105. 19 cm -3 P-type Al with Mg doped, 180 nm film thickness. 0.026 Ga 0.974 It has N layers.

[0145] The P-type cladding layer 610 has ridges 610R formed on it, similar to the nitride-based semiconductor light-emitting element 500 according to Embodiment 5. In addition, the P-type cladding layer 610 has two grooves 610T formed on it, which are arranged along the ridges 610R and extend in the Y-axis direction.

[0146] The contact layer 611 is positioned above the P-type cladding layer 610 and is a layer that makes ohmic contact with the P-side electrode 113. In this embodiment, the contact layer 611 is a P-type GaN layer with a thickness of 10 nm. The contact layer 611 contains impurities with a concentration of 1 × 10⁻⁶ 20 cm -3 It is doped with magnesium.

[0147] The translucent conductive film 620 according to this embodiment is a conductive film that is placed above the P-type cladding layer 610 and transmits at least a portion of the light generated by the nitride-based semiconductor light-emitting element 600. As the translucent conductive film 620, for example, an oxide film that is transparent to visible light and exhibits low electrical conductivity can be used, such as tin-doped indium oxide (ITO), Ga-doped zinc oxide, Al-doped zinc oxide, or In and Ga-doped zinc oxide.

[0148] The nitride-based semiconductor light-emitting element 600 according to this embodiment also provides the same effects as the nitride-based semiconductor light-emitting element 100 according to Embodiment 1, as shown in Figures 18 to 22 above.

[0149] Furthermore, in this embodiment, since a translucent conductive film 620 is provided above the P-type cladding layer 610, the loss of light propagating above the P-type cladding layer 610 can be reduced. As shown in Figure 19, this effect is particularly pronounced when the thickness of the P-type cladding layer 610 is small. In addition, since the thickness of the P-type cladding layer 610 can be further reduced, the electrical resistance of the nitride semiconductor light-emitting element 600 can be further reduced. As a result, the slope efficiency of the nitride semiconductor light-emitting element 600 can be increased and the operating voltage can be reduced.

[0150] According to this embodiment, the effective refractive index difference ΔN is 2.7 × 10 -3 The position P1 is 15.1 nm, the difference ΔP is 5.4 nm, the optical confinement coefficient to the active layer 105 is 1.47%, and the waveguide loss is 4.0 cm. -1 Therefore, the guide layer free carrier loss is 1.3 cm -1This enables the realization of a nitride-based semiconductor light-emitting element 600.

[0151] (Embodiment 7) A nitride-based semiconductor light-emitting element according to Embodiment 7 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5 in the configuration of the active layer. Hereinafter, the nitride-based semiconductor light-emitting element according to this embodiment will be described using Figures 36A and 36B, focusing on the differences from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5.

[0152] Figure 36A is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 700 according to this embodiment. Figure 36B is a cross-sectional view showing the configuration of the active layer 705 provided in the nitride-based semiconductor light-emitting element 700 according to this embodiment.

[0153] As shown in Figure 36A, the nitride-based semiconductor light-emitting element 700 according to this embodiment comprises a semiconductor laminate 700S, a current blocking layer 112, a P-side electrode 113, an N-side electrode 114, and a translucent conductive film 620. The semiconductor laminate 700S has a substrate 101, an N-type first cladding layer 502, an N-type second cladding layer 103, an N-side guide layer 104, an active layer 705, a P-side guide layer 106, an intermediate layer 108, an electron barrier layer 509, a P-type cladding layer 510, and a contact layer 111.

[0154] The active layer 705 according to this embodiment has a single quantum well structure, as shown in Figure 36B, and comprises a single well layer 105b and barrier layers 105a and 105c sandwiching the well layer 105b. The well layer 105b has the same configuration as the well layer 105b according to Embodiment 1, and the barrier layers 105a and 105c have the same configuration as the barrier layers 105a and 105c according to Embodiment 1.

[0155] According to the nitride semiconductor light-emitting device 700 according to this embodiment, the same effects as those of the nitride semiconductor light-emitting devices according to Embodiment 5 and Embodiment 6 are achieved. In particular, in the nitride semiconductor light-emitting device 700 having a single quantum well structure as described above, the active layer 705 has a single well layer 105b. Thus, even in the nitride semiconductor light-emitting device 700 in which the number of well layers 105b having a large refractive index is small, due to the configurations such as the N-side guide layer 104 and the P-side guide layer 106, the peak of the light intensity distribution in the stacking direction can be positioned at the active layer 705 or in its vicinity. Therefore, the light confinement factor can be increased.

[0156] According to this embodiment, the effective refractive index difference ΔN is 2.9×10 -3 , the position P1 is 9.7 nm, the difference ΔP is 8.6 nm, the light confinement factor to the active layer 705 is 0.75%, and the waveguide loss is 3.3 cm -1 , and the guide layer free carrier loss is 1.4 cm -1 . Thus, the nitride semiconductor light-emitting device 700 can be realized. In this embodiment, since the total film thickness of the active layer 705 is 8 nm smaller than that of the active layer 105 according to Embodiment 5, the light confinement factor is smaller than that of Embodiment 5.

[0157] (Embodiment 8) The nitride semiconductor light-emitting device according to Embodiment 8 will be described. The nitride semiconductor light-emitting device according to this embodiment is different from the nitride semiconductor light-emitting device 100 according to Embodiment 1 in that the average bandgap energy of the P-side guide layer is larger than the average bandgap energy of the N-side guide layer. Hereinafter, the nitride semiconductor light-emitting device according to this embodiment will be described with reference to FIGS. 37 and 38, focusing on the differences from the nitride semiconductor light-emitting device 100 according to Embodiment 1.

[0158] FIG. 37 is a schematic cross-sectional view showing the overall configuration of the nitride semiconductor light-emitting device 800 according to this embodiment. FIG. 38 is a schematic graph showing the distribution of the bandgap energy of the active layer 105 and the layers in its vicinity of the nitride semiconductor light-emitting device 800 according to this embodiment.

[0159] As shown in FIG. 37, the nitride semiconductor light-emitting device 800 according to the present embodiment includes a semiconductor laminate 800S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 800S 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 guide layer 806, an intermediate layer 108, an electron blocking layer 109, a P-type cladding layer 110, and a contact layer 111.

[0160] In the present embodiment, the P-side guide layer 806 is an undoped In Xp Ga 1-Xp N layer with a film thickness of 280 nm. More specifically, the P-side guide layer 806 has a composition represented by In 0.03 Ga 0.97 N near the interface closer to the active layer 105, and has a composition represented by GaN near the interface farther from the active layer 105. The In composition ratio Xp of the P-side guide layer 806 decreases at a constant rate as it moves away from the active layer 105.

[0161] Thus, the average value of the In composition ratio of the P-side guide layer 806 according to the present embodiment is less than the average value of the In composition ratio of the N-side guide layer 104. Therefore, the average bandgap energy of the P-side guide layer 806 is larger than the average bandgap energy of the N-side guide layer 104 (see FIG. 38). In other words, the average refractive index of the P-side guide layer 806 is less than the average refractive index of the N-side guide layer 104. Here, since the film thickness of the P-side guide layer 806 is larger than the film thickness of the N-side guide layer 104, the peak of the light intensity distribution can be biased closer to the P-side guide layer 806 with respect to the active layer 105. In the present embodiment, since the average refractive index of the P-side guide layer 806 is less than the average refractive index of the N-side guide layer 104, it is possible to suppress the peak of the light intensity distribution from being biased closer to the P-side guide layer 806 with respect to the active layer 105.

[0162] Furthermore, the In composition ratio of the P-side guide layer 806 decreases continuously and monotonically as it moves away from the active layer 105. In other words, the refractive index of the P-side guide layer 806 increases continuously and monotonically as it approaches the active layer 105. This allows the peak of the light intensity distribution in the stacking direction to be brought closer to the active layer 105.

[0163] According to this embodiment, the effective refractive index difference ΔN is 2.8 × 10 -3 The position P1 is 9.9 nm, the position P2 is 2.1 nm, the difference ΔP is 7.8 nm, the optical confinement coefficient to the active layer 105 is 1.42%, and the waveguide loss is 3.4 cm -1 The guide layer free carrier loss is 1.30 cm². -1 This enables the realization of a nitride-based semiconductor light-emitting element 800. In this embodiment, since the average bandgap energy of the P-side guide layer 806 is greater than the average bandgap energy of the N-side guide layer 104, the peak of the light intensity distribution in the stacking direction can be brought closer to the center of the active layer 105 in the stacking direction than in the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0164] (Embodiment 9) A nitride-based semiconductor light-emitting element according to Embodiment 9 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1 mainly in the wavelength band of the emitted light. Hereinafter, the nitride-based semiconductor light-emitting element according to this embodiment will be described using Figures 39A, 39B, and 40, focusing on the differences from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0165] Figure 39A is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 900 according to this embodiment. Figure 39B is a schematic cross-sectional view showing the configuration of the active layer 905 of the nitride-based semiconductor light-emitting element 900 according to this embodiment. Figure 40 is a schematic graph showing the distribution of the bandgap energy of the active layer 905 and each layer in its vicinity of the nitride-based semiconductor light-emitting element 900 according to this embodiment.

[0166] As shown in Figure 39A, the nitride-based semiconductor light-emitting element 900 according to this embodiment comprises a semiconductor laminate 900S, a current blocking layer 112, a P-side electrode 113, and an N-side electrode 114. The semiconductor laminate 900S has a substrate 101, an N-type first cladding layer 902, an N-side guide layer 904, an active layer 905, a P-side guide layer 906, an electron barrier layer 909, a P-type cladding layer 910, and a contact layer 111.

[0167] The N-type first cladding layer 902 in this embodiment is made of N-type Al with a film thickness of 740 nm. 0.10 Ga 0.90 This is an N-type layer. The first N-type cladding layer 902 contains impurities at a concentration of 5 × 10⁻¹⁶. 17 cm -3 The Si is doped.

[0168] The N-side guide layer 904 in this embodiment is made of N-type Al with a film thickness of 130 nm. Xna Ga 1-Xna This is the N layer. The N-side guide layer 904 contains impurities with a concentration of 5 × 10⁻⁶. 17 cm -3 Si is doped into it. More specifically, the N-side guide layer 904 has Al near the interface closer to the active layer 905. Xna1 Ga 1-Xna1 It has a composition represented by N, and Al is present near the interface furthest from the active layer 905. Xna2 Ga 1-Xna2 It has a composition represented by N. In this embodiment, the Al composition ratio Xna1 near the interface of the N-side guide layer 904 closer to the active layer 905 is 0, and the Al composition ratio Xna2 near the interface of the N-side guide layer 904 further from the active layer 905 is 0.06 (i.e., 6%). The Al composition ratio Xna of the N-side guide layer 904 increases at a constant rate as it moves away from the active layer 905.

[0169] The active layer 905 according to this embodiment has a well layer 905b and barrier layers 905a and 905c, as shown in Figure 39B.

[0170] The barrier layer 905a is positioned above the N-side guide layer 904 and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 905a is made of undoped Al with a thickness of 11 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0171] The well layer 905b is positioned above the barrier layer 905a and functions as a well in the quantum well structure. The well layer 905b is positioned between the barrier layer 905a and the barrier layer 905c. In this embodiment, the well layer 905b is made of undoped In with a film thickness of 17.5 nm. 0.01 Ga 0.99 It is an N-layer structure.

[0172] The barrier layer 905c is positioned above the well layer 905b and functions as a barrier to the quantum well structure. In this embodiment, the barrier layer 905c is made of undoped Al with a thickness of 11 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0173] The nitride-based semiconductor light-emitting element 900 according to this embodiment is equipped with an active layer 905 having the above-described configuration, and is capable of emitting light with a wavelength of 350 nm to 390 nm.

[0174] The P-side guide layer 906 in this embodiment is made of undoped Al with a film thickness of 280 nm. 0.05 Ga 0.95 It is an N-layer structure.

[0175] The electron barrier layer 909 in this embodiment is P-type Al with a film thickness of 5 nm. 0.36 Ga 0.64 This is the N layer. The electron barrier layer 909 contains impurities at a concentration of 1 × 10⁻¹⁶. 19 cm -3 It is doped with magnesium.

[0176] In this embodiment, the P-type cladding layer 910 is placed between the electron barrier layer 909 and the contact layer 111. The P-type cladding layer 910 has a lower refractive index and a higher bandgap energy than the active layer 905. In this embodiment, the P-type cladding layer 910 is made of P-type Al with a film thickness of 660 nm. 0.10 Ga 0.90 This is an N layer. The P-type cladding layer 910 is doped with Mg as an impurity. Furthermore, 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 further away from the active layer 905. Specifically, the concentration of the P-type cladding layer 910 located closer to the active layer 905 is 2 × 10⁻¹⁴. 18 cm -3 P-type Al with Mg doped, 250 nm film thickness. 0.10 Ga 0.90 The N layer and the concentration 1 × 10 located on the side furthest from the active layer 905. 19 cm -3 Mg-doped P-type Al film with a thickness of 410 nm 0.10 Ga 0.90 It has N layers.

[0177] The P-type cladding layer 910 has a ridge 910R formed on it, similar to the nitride-based semiconductor light-emitting element 100 according to Embodiment 1. Furthermore, the P-type cladding layer 910 has two grooves 910T formed on it, which are arranged along the ridge 910R and extend in the Y-axis direction. In this embodiment, the film thickness dc of the P-type cladding layer 910 at the lower end of the ridge 910R is 30 nm.

[0178] As described above, in the nitride-based semiconductor light-emitting element 900 according to this embodiment, the Al composition ratio Xna of the N-side guide layer 904 increases monotonically as it moves away from the active layer 905. In other words, the refractive index of the N-side guide layer 904 increases monotonically as it approaches the active layer 905. This makes it possible to bring the peak of the light intensity distribution in the stacking direction closer to the active layer 905.

[0179] Also, in the present embodiment, the film thickness of the P-side guide layer 906 is larger than the film thickness of the N-side guide layer 904. Thereby, since the distance dp between the lower end portion of the ridge 910R and the active layer 905 becomes larger than the case where the film thickness of the P-side guide layer 906 is equal to or less than the film thickness of the N-side guide layer 904, the effective refractive index difference ΔN can be reduced. Therefore, the stability of the light output of the nitride semiconductor light-emitting device 900 can be enhanced.

[0180] Also, in the present embodiment, the Al composition ratio of the P-side guide layer 906 is larger than the average Al composition ratio of the N-side guide layer 904. That is, the average bandgap energy of the P-side guide layer 906 is larger than the average bandgap energy of the N-side guide layer 904 (see FIG. 40). Therefore, the average refractive index of the P-side guide layer 906 is less than the average refractive index of the N-side guide layer 904. As described above, since the film thickness of the P-side guide layer 906 is larger than the film thickness of the N-side guide layer 904, the peak of the light intensity distribution can be biased toward the P-side guide layer 906 with respect to the active layer 905. In the present embodiment, since the average refractive index of the P-side guide layer 906 is less than the average refractive index of the N-side guide layer 904, it is possible to suppress the peak of the light intensity distribution from being biased toward the P-side guide layer 906 with respect to the active layer 905.

[0181] Also, in the present embodiment, by doping the N-side guide layer 904 with an N-type impurity, the series resistance of the nitride semiconductor light-emitting device 900 can be reduced in the same manner as in the first embodiment. Further, in the present embodiment, as shown in FIG. 40, the minimum bandgap energy of the N-side guide layer 904 (that is, the bandgap energy near the interface between the N-side guide layer 904 and the active layer 905) is smaller than the bandgap energy of the barrier layer 905a. Thus, even when the bandgap energy near the interface between the N-side guide layer 904 and the active layer 905 becomes smaller than the bandgap energy of the barrier layer 905a, by doping the N-side guide layer 904 with an N-type impurity, an increase in the hole concentration in the N-side guide layer 904 can be suppressed. As a result, since the non-radiative recombination probability of electrons and holes in the N-side guide layer 904 can be reduced, a decrease in the light-emitting efficiency and long-term reliability of the nitride semiconductor light-emitting device 900 can be suppressed.

[0182] Furthermore, according to the nitride-based semiconductor light-emitting element 900 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 905a and 905c are made of Al with an Al composition of 0.04 or higher. 0.05 Ga 0.95 Because it is formed of an N layer, the bandgap energy of the barrier layers 905a and 905c is 3.47 eV or higher, which is sufficiently larger than the energy of 3.28 eV corresponding to a wavelength of 375 nm. Therefore, a quantum level corresponding to an emission wavelength in the 375 nm band can be easily formed in the well layer 905b. Furthermore, since electrons and holes can be confined to the quantum levels of the quantum well region, leakage of electrons and holes from the quantum well region to the N-side guide layer 904 and the P-side guide layer 906 can be suppressed. Consequently, the luminescence efficiency of the nitride semiconductor light-emitting element 900 can be increased, and the temperature characteristics of the nitride semiconductor light-emitting element 900 can be improved.

[0183] According to this embodiment, the effective refractive index difference ΔN is 2.2 × 10 -3 The position P1 is 2.9 nm, the position P2 is 2.3 nm, the difference ΔP is 0.6 nm, the optical confinement coefficient to the active layer 905 is 6.7%, and the waveguide loss is 2.8 cm. -1 This enables the realization of a nitride-based semiconductor light-emitting element 900.

[0184] To explain the effects of the nitride-based semiconductor light-emitting element 900 according to this embodiment, Comparative Example 9 、10、 The characteristics of the nitride-based semiconductor light-emitting element (type 3) will be explained.

[0185] The nitride-based semiconductor light-emitting devices of Comparative Examples 9 and 10 differ from the nitride-based semiconductor light-emitting device 900 of this embodiment in that the Al composition ratio of the P-side guide layer is 3% and 2%, respectively, but they are otherwise identical. In the nitride-based semiconductor light-emitting device of Comparative Example 9, the average bandgap energy of the P-side guide layer is equal to the average bandgap energy of the N-side guide layer 904. In the nitride-based semiconductor light-emitting device of Comparative Example 10, the average bandgap energy of the P-side guide layer is less than the average bandgap energy of the N-side guide layer 904.

[0186] In the nitride-based semiconductor light-emitting element of Comparative Example 9, the effective refractive index difference ΔN is 1.8 × 10⁻⁶. -3 The position P1 is 10.8 nm, the position P2 is 9.9 nm, the difference ΔP is 0.9 nm, the optical confinement coefficient to the active layer 905 is 5.7%, and the waveguide loss is 3.2 cm -1 In the nitride-based semiconductor light-emitting element of Comparative Example 10, the effective refractive index difference ΔN is 3.1 × 10⁻⁶. -3 The position P1 is 80.4 nm, the position P2 is 68.9 nm, the difference ΔP is 11.5 nm, the optical confinement coefficient to the active layer 905 is 4.7%, and the waveguide loss is 3.5 cm. -1 That is the case.

[0187] Thus, in this embodiment, since the average bandgap energy of the P-side guide layer is greater than the average bandgap energy of the N-side guide layer 904, the optical confinement coefficient, waveguide loss, and peak position of the optical intensity distribution can be improved compared to the nitride-based semiconductor light-emitting devices of Comparative Examples 9 and 10.

[0188] The nitride-based semiconductor light-emitting element of Comparative Example 3 differs from the nitride-based semiconductor light-emitting element 900 of this embodiment in that the composition of the N-side guide layer is uniform, but otherwise it is the same. The N-side guide layer of the nitride-based semiconductor light-emitting element of Comparative Example 3 is made of N-type Al with a film thickness of 130 nm. 0.03 Ga 0.97 This is the N layer. The N-side guide layer contains impurities with a concentration of 5 × 10⁻¹⁶. 17 cm -3 The Si is doped.

[0189] In the nitride-based semiconductor light-emitting element of Comparative Example 3, the effective refractive index difference ΔN is 4.1 × 10⁻⁶. -3 The position P1 is 49.5 nm, the position P2 is 35.7 nm, the difference ΔP is 13.8 nm, the optical confinement coefficient to the active layer 905 is 5.0%, and the waveguide loss is 3.4 cm -1 That is the case.

[0190] Thus, in this embodiment, the bandgap energy of the N-side guide layer 904 increases monotonically and continuously as it moves away from the active layer 905, thereby improving the effective refractive index difference ΔN, the optical confinement coefficient, and the peak position of the optical intensity distribution compared to the nitride-based semiconductor light-emitting element of Comparative Example 3.

[0191] (Modification 1 of Embodiment 9) Next, a nitride-based semiconductor light-emitting element according to Modification 1 of Embodiment 9 will be described. The nitride-based semiconductor light-emitting element according to this modification differs from the nitride-based semiconductor light-emitting element 900 according to Embodiment 9 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 element according to this modification will be described below with reference to Figure 41. Figure 41 is a schematic graph showing the bandgap energy distribution of the active layer 905 and each layer in its vicinity in the nitride-based semiconductor light-emitting element according to this modification.

[0192] As shown in Figure 41, the P-side guide layer 906A of the nitride semiconductor light-emitting element according to this modified example has a P-side first guide layer 906a and a P-side second guide layer 906b. The P-side first guide layer 906a is a guide layer positioned above the active layer 905. The P-side second guide layer 906b is a guide layer positioned above the P-side first guide layer 906a and has a larger bandgap energy than the P-side first guide layer 906a. In this modified example, the P-side first guide layer 906a is an undoped Al with a film thickness of 70 nm. 0.01 Ga 0.99 It is an N layer, and the P-side second guide layer 906b is an undoped Al with a film thickness of 210 nm. 0.05 Ga0.95 This is the N layer. Thus, the first guide layer 906a on the P side has a higher Al composition ratio than the second guide layer 906b on the P side.

[0193] In the nitride-based semiconductor light-emitting element according to this modified example, the same effects as those of the nitride-based semiconductor light-emitting element 900 according to Embodiment 9 are achieved. Furthermore, in this modified example, the Al composition ratio of the P-side guide layer 906A increases in a step-like manner as it moves away from the active layer 905. As a result, the refractive index of the region of the P-side guide layer 906A close to the active layer 905 can be made higher than the refractive index of the region farther from the active layer 905, thereby bringing the peak of the light intensity distribution closer to the active layer 905.

[0194] According to this modified example, the effective refractive index difference ΔN is 1.24 × 10⁻⁴. -3 The position P1 is 11.6 nm, the position P2 is 11.3 nm, the difference ΔP is 0.3 nm, the optical confinement coefficient to the active layer 905 is 7.7%, and the waveguide loss is 2.5 cm. -1 This enables the realization of nitride-based semiconductor light-emitting devices.

[0195] To explain the effect of the nitride-based semiconductor light-emitting element in this modified example, the characteristics of the nitride-based semiconductor light-emitting elements of Comparative Example 11 and Comparative Example 12 will be described.

[0196] The nitride-based semiconductor light-emitting devices of Comparative Examples 11 and 12 differ from the nitride-based semiconductor light-emitting device 900 of this modification in that the Al composition ratio of the P-side second guide layer is 3.67% and 2.3%, respectively, but are otherwise identical. In the nitride-based semiconductor light-emitting device of Comparative Example 11, the average bandgap energy of the P-side guide layer is equal to the average bandgap energy of the N-side guide layer 904. In the nitride-based semiconductor light-emitting device of Comparative Example 12, the average bandgap energy of the P-side guide layer is less than the average bandgap energy of the N-side guide layer 904.

[0197] In the nitride-based semiconductor light-emitting element of Comparative Example 11, the effective refractive index difference ΔN is 1.7 × 10⁻⁶. -3The position P1 is 34.8 nm, the position P2 is 33.3 nm, the difference ΔP is 1.5 nm, the optical confinement coefficient to the active layer 905 is 6.8%, and the waveguide loss is 2.8 cm. -1 In the nitride-based semiconductor light-emitting element of Comparative Example 12, the effective refractive index difference ΔN is 2.5 × 10⁻⁶. -3 The position P1 is 60.1 nm, the position P2 is 56.6 nm, the difference ΔP is 3.5 nm, the optical confinement coefficient to the active layer 905 is 5.4%, and the waveguide loss is 3.3 cm. -1 That is the case.

[0198] Thus, in this modified example, since the average bandgap energy of the P-side guide layer 906A is greater than the average bandgap energy of the N-side guide layer 904, the optical confinement coefficient, waveguide loss, and peak position of the optical intensity distribution can be improved compared to the nitride-based semiconductor light-emitting devices of Comparative Examples 11 and 12.

[0199] (Modification 2 of Embodiment 9) Next, a nitride-based semiconductor light-emitting element according to a modification 2 of Embodiment 9 will be described. The nitride-based semiconductor light-emitting element according to this modification differs from the nitride-based semiconductor light-emitting element 900 according to Embodiment 9 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 element according to this modification will be described below with reference to Figure 42. Figure 42 is a schematic graph showing the bandgap energy distribution of the active layer 905 and each layer in its vicinity in the nitride-based semiconductor light-emitting element according to this modification.

[0200] In this modified example, the P-side guide layer 906B is made of undoped aluminum with a film thickness of 280 nm. Xpa Ga 1-Xpa It is an N layer. More specifically, the P-side guide layer 906B has a composition represented by GaN near the interface closer to the active layer 905, and Al near the interface further away from the active layer 905. 0.08 Ga 0.92It has a composition represented by N. The Al composition ratio Xpa of the P-side guide layer 906B increases at a constant rate as it moves away from the active layer 905. Therefore, the band gap energy of the P-side guide layer 906B increases continuously and monotonically as it moves away from the active layer 905.

[0201] In the nitride-based semiconductor light-emitting element according to this modified example, the same effects as those of the nitride-based semiconductor light-emitting element 900 according to Embodiment 9 are achieved. Furthermore, in this modified example, the Al composition ratio of the P-side guide layer 906B increases continuously and monotonically as it moves away from the active layer 905. As a result, the refractive index of the P-side guide layer 906B increases as it approaches the active layer 905, making it possible to bring the peak of the light intensity distribution closer to the active layer 905.

[0202] According to this modified example, the effective refractive index difference ΔN is 1.13 × 10⁻⁶. -3 The position P1 is 22.2 nm, the position P2 is 21.3 nm, the difference ΔP is 0.9 nm, the optical confinement coefficient to the active layer 905 is 7.3%, and the waveguide loss is 2.6 cm. -1 This enables the realization of nitride-based semiconductor light-emitting devices.

[0203] To explain the effect of the nitride-based semiconductor light-emitting element in this modified example, the characteristics of the nitride-based semiconductor light-emitting elements of Comparative Example 13 and Comparative Example 14 will be described.

[0204] The nitride-based semiconductor light-emitting devices of Comparative Examples 13 and 14 differ from the nitride-based semiconductor light-emitting device of this modification in that the Al composition ratio at the interface of the P-side guide layer furthest from the active layer 905 is 6% and 4%, respectively, but are otherwise identical. In the nitride-based semiconductor light-emitting device of Comparative Example 13, the average bandgap energy of the P-side guide layer is equal to the average bandgap energy of the N-side guide layer 904. In the nitride-based semiconductor light-emitting device of Comparative Example 14, the average bandgap energy of the P-side guide layer is less than the average bandgap energy of the N-side guide layer 904.

[0205] In the nitride-based semiconductor light-emitting element of Comparative Example 13, the effective refractive index difference ΔN is 1.43 × 10⁻⁶. -3 The position P1 is 36.4 nm, the position P2 is 34.9 nm, the difference ΔP is 1.5 nm, the optical confinement coefficient to the active layer 905 is 6.6%, and the waveguide loss is 2.8 cm. -1 In the nitride-based semiconductor light-emitting element of Comparative Example 14, the effective refractive index difference ΔN is 1.9 × 10⁻⁶. -3 The position P1 is 54.6 nm, the position P2 is 52.3 nm, the difference ΔP is 2.3 nm, the optical confinement coefficient to the active layer 905 is 5.7%, and the waveguide loss is 3.1 cm -1 That is the case.

[0206] Thus, in this modified example, since the average bandgap energy of the P-side guide layer 906B is greater than the average bandgap energy of the N-side guide layer 904, the optical confinement coefficient, waveguide loss, and peak position of the optical intensity distribution can be improved compared to the nitride-based semiconductor light-emitting devices of Comparative Examples 13 and 14.

[0207] (Torture, etc.) The nitride-based semiconductor light-emitting devices described above have been explained based on various embodiments, but this disclosure is not limited to the above embodiments.

[0208] For example, in the embodiments described above, the nitride-based semiconductor light-emitting element is shown to be a semiconductor laser element, but 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 laminate of the nitride-based semiconductor light-emitting element with respect to the light emitted from the semiconductor laminate may be 0.1% or less. Such reflectance can be achieved, for example, by forming an anti-reflective film made of a dielectric multilayer film on the end face. Alternatively, if the ridge that becomes the waveguide is tilted at 5° or more from the normal direction of the front end face and intersects the front end face, the proportion of the component in which the waveguided light reflected from the front end face re-couples with the waveguide and becomes waveguided light can be made to a small value of 0.1% or less. In particular, when the wavelength of the emitted light is in the band of 430 nm to 455 nm, the film thickness of the well layers 105b and 105d of the active layer 105 becomes 35 Å or less. In this case, the effect of reducing waveguide loss and increasing the optical confinement coefficient in the active layer 105 by the nitride semiconductor light-emitting element according to this disclosure allows for securing optical amplification gain even when the reflectivity of the end face is reduced. Furthermore, when such a nitride semiconductor light-emitting element is placed in an external resonator including a wavelength-selective element, the self-heating of the nitride semiconductor light-emitting element can be reduced, and wavelength fluctuations of the emitted light can be suppressed, making it easier to achieve oscillation at a desired selected wavelength.

[0209] Furthermore, in embodiments 1 to 6 described above, the nitride-based semiconductor light-emitting element had a structure in which the active layer 105 included two well layers, but it may also have a structure that includes only a single well layer. In this way, even when there is only one well layer with a high refractive index included in the active layer, by using the N-side guide layer and P-side guide layer of this disclosure, the controllability of the position of the light intensity distribution in the stacking direction can be improved, so that the peak of the light intensity distribution in the stacking direction can be positioned near the well layer. Therefore, it is possible to realize a nitride-based semiconductor light-emitting element with a low oscillation threshold, low waveguide loss, a high optical confinement coefficient, and current-optical output (IL) characteristics with excellent linearity.

[0210] Furthermore, in each of the above embodiments, the nitride semiconductor light-emitting element had a single ridge, but the nitride semiconductor light-emitting element may have multiple ridges. Such a nitride semiconductor light-emitting element will be explained with reference to Figure 43. Figure 43 is a schematic cross-sectional view showing the overall configuration of the nitride semiconductor light-emitting element 1000 according to Modification 1. As shown in Figure 43, the nitride semiconductor light-emitting element 1000 according to Modification 1 has a configuration in which multiple nitride semiconductor light-emitting elements 100 according to Embodiment 1 are arranged in a horizontal array. In Figure 43, the nitride semiconductor light-emitting element 1000 has a configuration in which three nitride semiconductor light-emitting elements 100 are integrally arranged, but the number of nitride semiconductor light-emitting elements 100 in the nitride semiconductor light-emitting element 1000 is not limited to three. The number of nitride semiconductor light-emitting elements 100 in the nitride semiconductor light-emitting element 1000 may be two or more. Each nitride semiconductor light-emitting element 100 has a light-emitting section 100E that emits light. The light-emitting portion 100E is the part of the active layer 105 that emits light, and corresponds to the part of the active layer 105 located below the ridge 110R. Thus, the nitride semiconductor light-emitting element 1000 according to Modification 1 has a plurality of light-emitting portions 100E arranged in an array. As a result, multiple emitted lights can be obtained from a single nitride semiconductor light-emitting element 1000, thus realizing a high-power nitride semiconductor light-emitting element 1000. In Modification 1, the nitride semiconductor light-emitting element 1000 comprises a plurality of nitride semiconductor light-emitting elements 100, but the plurality of nitride semiconductor light-emitting elements comprising the nitride semiconductor light-emitting element 1000 are not limited to this and may be nitride semiconductor light-emitting elements according to other embodiments.

[0211] Furthermore, as shown in the modified example 2 of the nitride-based semiconductor light-emitting element 1000a in Figure 44, each individual light-emitting section 100E may be separated by a separation groove 100T with 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 adopting such a structure, even when the distance between adjacent light-emitting sections 100E is narrowed to 300 μm or less, thermal interference due to self-heating during the operation of each individual light-emitting section 100E can be reduced.

[0212] Furthermore, the disclosure Nitride semiconductor light-emitting diodes Since ΔN is small and the horizontal spread angle can be reduced, even if the distance between the centers of the light-emitting units 100E shown in Figures 43 and 44 is narrowed, the light emitted from each light-emitting unit 100E is less likely to interfere with each other, and the distance between the centers of the light-emitting units 100E can be narrowed to 250 μm or less. In the modified example 2, this distance is 225 μm.

[0213] Furthermore, in each of the above embodiments and its modified forms, each guide layer is In Xn Ga 1-Xn Although it was 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, then the N-side guide layer is Al Xna Ga 1-Xna It consists of N, and the N-side guide layer is, Xpa Ga 1-Xpa It may also consist of N. In this case, the Al composition ratio of the N-side guide layer increases monotonically and continuously as it moves away 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 photoconfinement coefficient to the active layer. Furthermore, the absolute value of the average rate of change of the Al composition ratio in the stacking direction in the region from the interface of the N-side guide layer closer to the active layer to the center of the stacking direction of the N-side guide layer may be smaller than the absolute value of the average rate of change of the Al composition ratio in the stacking direction in the region from the center to the interface of the N-side guide layer closer to the N-type first cladding layer.

[0214] Furthermore, while the nitride-based semiconductor light-emitting element according to each of the above embodiments includes an N-type second cladding layer 103, an intermediate layer 108, an electron barrier layer 109, and a current blocking layer 112, these layers are not necessarily required.

[0215] Furthermore, while the P-type cladding layers 110, 510, and 610 were layers with a uniform Al composition ratio, the composition 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, an AlGaN layer with a thickness of 1.85 nm and an Al composition ratio of 0.052 (5.2%) is alternately stacked with a GaN layer with a thickness of 1.85 nm. In this case, the Al composition ratio of each P-type cladding layer is defined as the average Al composition ratio in the superlattice structure, which is 0.026 (2.6%).

[0216] Furthermore, this disclosure also includes forms obtained by applying various modifications to each of the above embodiments that a person skilled in the art could conceive, and forms realized by arbitrarily combining the components and functions of each of the above embodiments without departing from the spirit of this disclosure.

[0217] For example, the configuration of each cladding layer according to Embodiment 1 may be applied to each nitride-based semiconductor light-emitting element according to Embodiments 5 and 6. Alternatively, the translucent conductive film according to Embodiment 6 may be applied to each nitride-based semiconductor light-emitting element according to Embodiments 1 to 5. [Industrial applicability]

[0218] The nitride-based semiconductor light-emitting element of this disclosure can be applied, for example, as a high-power and high-efficiency light source for processing machines and the like. [Explanation of Symbols]

[0219] 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1000a Nitride-based semiconductor light-emitting diodes 100E Light Emitting Section 100F, 100R end face 100T separation groove 100S, 200S, 300S, 400S, 500S, 600S, 700S, 800S, 900S semiconductor stacks 101 circuit board 102, 502, 902 N-type first cladding layer 103 N-type second cladding layer 104, 404, 904, 1104, 1204, 1304 N-side guide layer 105, 205, 705, 905 active layer 105a, 105c, 105e, 205a, 205e, 905a, 905c barrier layer 105b, 105d, 905b well layers 106, 206, 306, 806, 906, 906A, 906B, 1106, 1206, 1306 P-side guide layer 108 Middle Class 10⁹, 50⁹, 90⁹ electron barrier layer 110, 510, 610, 910 P-type cladding layers 110R, 510R, 610R, 910R Ridge 110T, 510T, 610T, 910T groove 111, 611 Contact Layer 112 Current Blocking Layer 113 P side electrode 114 N side electrode 306a, 906a P-side first guide layer 306b, 906b P-side second guide layer 404a N-side first guide layer 404b N-side second guide layer 620 Transparent conductive film

Claims

1. A nitride-based semiconductor light-emitting element comprising a semiconductor stack, wherein light is emitted 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, An electron barrier layer positioned above the P-side guide layer, It has a P-type cladding layer disposed above the electron barrier layer, Ridges are formed in the aforementioned P-type cladding layer. The P-side guide layer is an undoped 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 the average bandgap energy of the N-side guide layer. 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, The thickness of the N-side guide layer is 190 nm or less. The thickness of the N-side guide layer is 36% or more and 43% or less of the sum of the thickness of the N-side guide layer and the thickness of the P-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, respectively. Nitride semiconductor light-emitting element.

2. The thickness of the N-side guide layer is 160 nm or more. The nitride-based semiconductor light-emitting element according to claim 1.

3. The N-side guide layer is In Ｘｎ Ga １－Ｘｎ Consists 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-based semiconductor light-emitting element according to claim 1 or 2.

4. 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. Nitride-based semiconductor light-emitting element according to claim 1 or 2.

5. The absolute value of the average rate of change of the In composition ratio in the stacking direction in the region from the interface of the N-side guide layer closest to the active layer to the central part of the N-side guide layer in the stacking direction is smaller than the absolute value of the average rate of change of the In composition ratio in the stacking direction in the region from the central part to the interface of the N-side guide layer closest to the N-type first cladding layer. The nitride-based semiconductor light-emitting element according to claim 3.

6. The absolute value of the average rate of change in the Al composition ratio in the stacking direction in the region from the interface of the N-side guide layer on the side closer to the active layer to the central part of the N-side guide layer in the stacking direction is smaller than the absolute value of the average rate of change in the Al composition ratio in the stacking direction in the region from the central part to the interface of the N-side guide layer on the side closer to the N-type first cladding layer. The nitride-based semiconductor light-emitting device according to claim 4.

7. The barrier layer is In Ｘｂ Ga １－Ｘｂ composed 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. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 6.

8. The N-side guide layer has 1 × 10 １７ cm －３ The above 6 x 10 １７ cm －３ The following concentrations of impurities are doped into the product. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 7.

9. The peak of the light intensity distribution in the stacking direction is located in the active layer. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 8.

10. The impurity concentration at the end of the P-type cladding layer closer to the active layer is lower than the impurity concentration at the end of the P-type cladding layer further from the active layer. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 9.

11. The Al composition ratio of the electron barrier layer increases monotonically as it moves away from the active layer. It has a region where the Al composition changes. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 10.

12. The distance between the lower end of the ridge and the electron barrier layer is 10 nm or more and 70 nm or less. The nitride-based semiconductor light-emitting element according to any one of claims 1 to 11.

13. The aforementioned N-type first cladding layer and the P-type cladding layer contain Al, If the Al composition ratios of the N-type first cladding layer and the P-type cladding layer are Ync and Ypc, respectively, Ync > Ypc Satisfying the relationship Nitride-based semiconductor light-emitting element according to any one of claims 1 to 12.

14. The thickness of the P-type cladding layer is 460 nm or less. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 13.

15. The P-type cladding layer is provided with a translucent conductive film positioned above it. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 14.

16. The system comprises an N-type second cladding layer disposed between the N-type first cladding layer and the N-side guide layer, The band gap energy of the N-type second cladding layer is smaller than the band gap energy of the N-type first cladding layer and is greater than or equal to the maximum band gap energy of the P-side guide layer. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 15.

17. It has multiple light-emitting parts arranged in an array. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 16.

18. The reflectance of the end face of the semiconductor laminate is 0.1% or less. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 17.

19. A nitride-based semiconductor light-emitting element comprising a semiconductor stack, wherein light is emitted 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, An electron barrier layer positioned above the P-side guide layer, It has a P-type cladding layer disposed above the electron barrier layer, Ridges are formed in the aforementioned P-type cladding layer. The P-side guide layer is an undoped 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 the average bandgap energy of the N-side guide layer. 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, The thickness of the N-side guide layer is 190 nm or less. The thickness of the N-side guide layer is 36% or more and 43% or less of the sum of the thickness of the N-side guide layer and the thickness of the P-side guide layer. The electron barrier layer has an Al composition change region in which the Al composition ratio increases monotonically as it moves away from the active layer. The active layer has a single quantum well structure. Nitride semiconductor light-emitting element.

20. The thickness of the N-side guide layer is 160 nm or more. The nitride-based semiconductor light-emitting element according to claim 19.

21. The N-side guide layer has 3 × 10 １７ cm －３ The above 1 x 10 １８ cm －３ The following concentrations of impurities are doped into the product. Nitride-based semiconductor light-emitting element according to claim 19 or 20.

22. The aforementioned N-type first cladding layer and the P-type cladding layer contain Al, If the Al composition ratios of the N-type first cladding layer and the P-type cladding layer are Ync and Ypc, respectively, Ync > Ypc Satisfying the relationship Nitride-based semiconductor light-emitting element according to any one of claims 19 to 21.

23. The average In composition ratio of the N-side guide layer is 2% or more. Nitride-based semiconductor light-emitting element according to any one of claims 19 to 22.

24. The semiconductor laminate has an intermediate layer disposed between the P-side guide layer and the electron barrier layer, The aforementioned intermediate layer reduces stress caused by the difference in lattice constants between the P-side guide layer and the electron barrier layer. Nitride-based semiconductor light-emitting element according to any one of claims 19 to 23.

25. The peak of the light intensity distribution in the stacking direction is located in the active layer. Nitride-based semiconductor light-emitting element according to any one of claims 19 to 24.

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