Nitride semiconductor light-emitting diodes

Abstract

This nitride semiconductor light emitting element (100) is provided with an N-type cladding layer (102), an N-side first guide layer (103), an N-side second guide layer (104), an active layer (105) which comprises a well layer (105b) and barrier layers (105a, 105c), and a P-type cladding layer (108). The band gap energy of the barrier layers (105a, 105c) is larger than the band gap energy of the N-side second guide layer (104); the band gap energy of the N-side second guide layer (104) is smaller than the band gap energy of the N-side first guide layer (103); the band gap energy of the N-side first guide layer (103) is smaller than the band gap energy of the N-type cladding layer (102); and the cladding layers (102, 108), the guide layers (103, 104) and the barrier layers (105a, 105c) are respectively formed of nitride semiconductors that contain Al.

Description

[Technical Field]

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

[0002] While nitride-based semiconductor light-emitting devices that emit blue light are conventionally known, there is a need for high-power nitride-based semiconductor light-emitting devices that emit shorter-wavelength ultraviolet light (see, for example, Patent Document 1). For example, if a watt-class ultraviolet laser light source can be realized using a nitride-based semiconductor light-emitting device, it can be used as a light source for exposure, a light source for processing, etc. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-131019 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In nitride-based semiconductor light-emitting devices that emit ultraviolet light, for example, an active layer having a quantum well structure with an AlGaN layer as a barrier layer is used. In order to emit ultraviolet light, the bandgap energy of the barrier layer needs to be increased. If the Al composition ratio of the barrier layer is increased to increase the bandgap energy of the barrier layer, the refractive index of the barrier layer will decrease. Therefore, the refractive index of the cladding layer for confining ultraviolet light in the active layer needs to be sufficiently lower than that of the barrier layer. When an AlGaN layer is used as the cladding layer, the Al composition ratio needs to be increased to lower the refractive index of the cladding layer. When a cladding layer made of AlGaN with such a high Al composition ratio is grown on a substrate made of GaN, for example, the tensile strain of the cladding layer on the substrate becomes large. Therefore, when growing cladding layers, active layers, etc. on a GaN wafer to manufacture nitride-based semiconductor light-emitting devices, the wafer is prone to cracking due to the tensile strain caused by the AlGaN layer. To suppress such wafer cracking, one possible measure is to reduce the strain of the cladding layer on the substrate by making the film thickness of the AlGaN cladding layer thinner. Furthermore, since a P-type cladding layer made of P-type AlGaN with a high Al composition ratio has high electrical resistance, the film thickness is set even thinner and the impurity concentration is set higher than that of an N-type cladding layer. Such a P-type cladding layer is compared to an N-type cladding layer. Layer The refractive index increases. As a result, light is biased towards the P-type cladding layer rather than the active layer. Consequently, the optical confinement coefficient in the active layer decreases. Along with this, the thermal saturation level of the optical 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 and provide a nitride-based semiconductor light-emitting element that can reduce strain in a semiconductor stack and increase the light confinement 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 comprises an N-type cladding layer, an N-side first guide layer disposed above the N-side first guide layer, an N-side second guide layer disposed above the N-side second guide layer, an active layer disposed above the N-side second guide layer and having a well layer and a barrier layer, and a P-type cladding layer disposed above the active layer, wherein the band gap energy of the barrier layer is greater than the band gap energy of the N-side second guide layer, the band gap energy of the N-side second guide layer is less than the band gap energy of the N-side first guide layer, the band gap energy of the N-side first guide layer is less than the band gap energy of the N-type cladding layer, and the N-type cladding layer, the N-side first guide layer, the N-side second guide layer, the barrier layer, and the P-type cladding layer are made of a nitride-based semiconductor containing Al.

[0007] Another embodiment of a nitride-based semiconductor light-emitting element according to the present disclosure comprises an N-type cladding layer, an N-side guide layer disposed above the N-type cladding layer, an active layer disposed above the N-side guide layer and including a well layer and a barrier layer, and a P-type cladding layer disposed above the active layer, wherein the band gap energy of the barrier layer is greater than the average band gap energy of the N-side guide layer, the band gap energy of the N-type cladding layer is greater than the average band gap energy of the N-side guide layer, the band gap energy at the lower end of the N-side guide layer is greater than the band gap energy at the upper end, and the N-type cladding layer, the N-side guide layer, the barrier layer, and the P-type cladding layer are made of a nitride-based semiconductor containing Al. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a nitride-based semiconductor light-emitting element that can reduce strain in a semiconductor stack and increase the light confinement coefficient in the active layer. [Brief explanation of the drawing]

[0009] [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 bandgap energy distribution and light intensity distribution in the stacking direction of the semiconductor stack according to Comparative Example 1. [Figure 6] Figure 6 is a schematic graph showing the bandgap energy distribution and light intensity distribution in the stacking direction of the semiconductor stack according to Embodiment 1. [Figure 7] Figure 7 is a schematic graph showing the bandgap energy distribution and light intensity distribution of a semiconductor laminate according to a modified example of Embodiment 1. [Figure 8] Figure 8 is a graph showing the refractive index distribution and light intensity distribution of the semiconductor laminate according to Comparative Example 2. [Figure 9] Figure 9 is a graph showing the refractive index distribution and light intensity distribution of the semiconductor stack according to Embodiment 1. [Figure 10] Figure 10 is a table showing the relationship between the Al composition ratio of each guide layer and the characteristics of nitride-based semiconductor light-emitting devices. [Figure 11] Figure 11 is a graph showing the relationship between the distribution of the conduction band potential energy near the active layer and the electron wave function when the Al composition ratio of each barrier layer is 0.02. [Figure 12]Figure 12 is a graph showing the relationship between the distribution of conduction band potential energy near the active layer and the electron wave function when the Al composition ratio of each barrier layer is 0.05. [Figure 13] Figure 13 is a graph showing the relationship between the Al composition ratio of each barrier layer and the band offset ΔEc. [Figure 14] Figure 14 is a graph showing the relationship between the film thickness of the N-type cladding layer and waveguide loss of the nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 15] Figure 15 is a graph showing the relationship between the film thickness of the N-type cladding layer and the optical confinement coefficient of the nitride-based semiconductor light-emitting element according to Embodiment 1. [Figure 16] Figure 16 is a schematic side view showing the warping of the base material and the semiconductor laminate that occurs when a semiconductor laminate is laminated onto the base material of the substrate according to Embodiment 1. [Figure 17] Figure 17 is a graph showing the amount of warping of the base material and semiconductor laminate that occurs when a semiconductor laminate is laminated onto the base material of the substrate according to Embodiment 1. [Figure 18] Figure 18 is a first graph showing the relationship between each guide layer according to Embodiment 1 and the waveguide loss obtained by simulation. [Figure 19] Figure 19 is a second graph showing the relationship between each guide layer according to Embodiment 1 and the waveguide loss obtained by simulation. [Figure 20] Figure 20 is a third graph showing the relationship between each guide layer according to Embodiment 1 and the waveguide loss obtained by simulation. [Figure 21A] Figure 21A is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 2. [Figure 21B] Figure 21B 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 22] Figure 22 is a schematic graph showing the bandgap energy distribution and light intensity distribution in the stacking direction of the semiconductor stack according to Embodiment 2. [Figure 23] Figure 23 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 3. [Figure 24] Figure 24 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 4. [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 5. [Figure 26] Figure 26 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to a modified example 1 of Embodiment 5. [Figure 27] Figure 27 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to a modified example 2 of Embodiment 5. [Figure 28] Figure 28 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to a modified example 3 of Embodiment 5. [Figure 29] Figure 29 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 6. [Figure 30] Figure 30 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element according to Embodiment 7. [Figure 31] Figure 31 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 8. [Figure 32] Figure 32 is a schematic cross-sectional view showing the overall configuration of a nitride-based semiconductor light-emitting element according to Embodiment 9. [Modes for carrying out the invention]

[0010] 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.

[0011] 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.

[0012] 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.

[0013] (Embodiment 1) A nitride-based semiconductor light-emitting element according to Embodiment 1 will be described.

[0014] [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.

[0015] 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 nitride-based semiconductor light-emitting element 100 also has a waveguide formed between end face 100F and end face 100R. The resonator length (i.e., the distance between end face 100F and end face 100R) of the nitride-based semiconductor light-emitting element 100 according to this embodiment is approximately 1200 μm. The nitride-based semiconductor light-emitting element 100 also emits ultraviolet light having a peak wavelength in the 375 nm band, for example.

[0016] As shown in Figure 2A, the nitride-based semiconductor light-emitting element 100 comprises a substrate 101, a semiconductor laminate 100S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 100S has an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 105, a P-side first guide layer 106, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0017] 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. The substrate 101 contains, for example, an impurity with a concentration of 1 × 10⁻¹⁶ 18 cm -3 The Si is doped.

[0018] The N-type cladding layer 102 is an example of a cladding layer placed on top of the substrate 101. The N-type 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 cladding layer 102 is made of N-type Al with a film thickness of 540 nm. 0.065Ga 0.935 It is an N-layer. The N-type cladding layer 102 is doped with Si having a concentration of 5×10 17 cm -3 . In this embodiment, the N-type cladding layer 102 is laminated above the substrate 101 made of GaN. By laminating the N-type cladding layer 102 above the substrate 101 made of GaN in this way, the lattice constant of the N-type cladding layer 102 becomes equal to the lattice constant of the substrate 101, and when epitaxially laminating a nitride containing at least one kind of element among Al, Ga, and In on the N-type cladding layer 102 while lattice matching, control of the strain, band structure, and refractive index of each layer can be performed by adjusting the composition of each layer, so that the structural control of the nitride semiconductor light-emitting device 100 becomes easy. Therefore, in the nitride semiconductor light-emitting device 100, it becomes easy to obtain desired characteristics.

[0019] The N-side first guide layer 103 is an example of the N-side guide layer disposed above the N-type cladding layer 102. The band gap energy of the N-side first guide layer 103 is smaller than the band gap energy of the N-type cladding layer 102. That is, the refractive index of the N-side first guide layer 103 is larger than the refractive index of the N-type cladding layer 102. The N-side first guide layer 103 is composed of Al Xn1 Ga 1-Xn1 N (0 < Xn1 ≤ 1). In this embodiment, the N-side first guide layer 103 is an N-type Al 0.03 Ga 0.97 N layer with a film thickness of 100 nm. The N-side first guide layer 103 is doped with Si having a concentration of 5×10 17 cm -3 .

[0020] The N-side second guide layer 104 is an example of an N-side guide layer positioned above the N-side first guide layer 103. The N-side second guide layer 104 has a higher refractive index and a lower bandgap energy than the N-type cladding layer 102. Furthermore, the bandgap energy of the N-side second guide layer 104 is smaller than the bandgap energy of the N-side first guide layer 103. In other words, the refractive index of the N-side second guide layer 104 is greater than the refractive index of the N-side first guide layer 103. The N-side second guide layer 104 is made of Al Xn2 Ga 1-Xn2 It consists of N(0≦Xn2≦1). In this embodiment, the N-side second guide layer 104 is an undoped Al with a film thickness of 120 nm. 0.02 Ga 0.98 It is an N-layer structure.

[0021] Thus, in this embodiment, the impurity concentration of the N-side second guide layer 104 is lower than that of the N-side first guide layer 103. In order to reduce the series resistance of the nitride semiconductor light-emitting element 100 and prevent holes from the well layer 105b from leaking to the substrate 101, it is effective to dope the N-side first guide layer 103 and the N-side second guide layer 104 with impurities to reduce the potential of the valence band of each guide layer. In this case, by making the impurity concentration of the N-side second guide layer 104 lower than that of the N-side first guide layer 103, it is possible to suppress the increase in waveguide loss caused by impurities. In other words, by reducing the impurity concentration in the N-side second guide layer 104, which is closer to the active layer 105 than the N-side first guide layer 103, i.e., in a region with higher light intensity, optical loss caused by impurities can be reduced.

[0022] Furthermore, in this embodiment, the N-side second guide layer 104 is not doped with impurities, but the N-side second guide layer 104 may be doped with impurities. This lowers the resistance of the N-side second guide layer 104, making it easier for electrons to flow from the substrate 101 to the active layer 105, and reducing the hole current component leaking from the active layer 105 to the substrate 101. As a result, the thermal saturation level of the optical output during high-temperature operation can be improved.

[0023] The active layer 105 is disposed above the N-side second guide layer 104 and is a light-emitting layer having a quantum well structure. In the present embodiment, as shown in FIG. 2B, the active layer 105 includes a well layer 105b, and barrier layers 105a and 105c.

[0024] The barrier layer 105a is disposed above the N-side second guide layer 104 and functions as a barrier of the quantum well structure. The barrier layer 105a is composed of Al b Ga 1-b N (0 < b ≦ 1). In the present embodiment, the barrier layer 105a is an undoped Al 0.05 Ga 0.95 N layer with a thickness of 12 nm.

[0025] The well layer 105b is disposed above the barrier layer 105a and functions as a well of the quantum well structure. The well layer 105b is disposed between the barrier layer 105a and the barrier layer 105c. In the present embodiment, the well layer 105b is an undoped In 0.01 Ga 0.99 N layer with a thickness of 7.5 nm.

[0026] The barrier layer 105c is disposed above the well layer 105b and functions as a barrier of the quantum well structure. The barrier layer 105c is composed of Al b Ga 1-b N (0 < b ≦ 1). In the present embodiment, the barrier layer 105c is an undoped Al 0.05 Ga0 .95 N layer with a thickness of 10 nm.

[0027] The P-side first guide layer 106 is an optical guide layer disposed above the active layer 105. In the present embodiment, the P-side first guide layer 106 is disposed between the active layer 105 and the P-type cladding layer 108. The bandgap energy of the P-side first guide layer 106 is smaller than the bandgap energy of the P-type cladding layer 108. That is, the refractive index of the P-side first guide layer 106 is larger than the refractive index of the P-type cladding layer 108. In the present embodiment, the P-side first guide layer 106 is a P-type Al 0.02 Ga 0.98This is the N layer. The first guide layer 106 on the P side contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 It is doped with magnesium.

[0028] The electron barrier layer 107 is a nitride-based semiconductor layer positioned above the active layer 105. In this embodiment, the electron barrier layer 107 is positioned between the P-side first guide layer 106 and the P-type cladding layer 108. The electron barrier layer 107 is made of Al with a film thickness of 1 nm to 10 nm. Xd Ga1 -Xd The N layer has an Al composition ratio Xd of 0.2 or higher. This allows for improved electron confinement near the active layer 105 while suppressing an increase in the operating voltage of the nitride semiconductor light-emitting element 100. The impurity concentration doped into the electron barrier layer 107 is 1 × 10⁻⁶. 19 cm -3 The above is also acceptable. This makes it possible to increase the conductivity of holes in the electron barrier layer 107. Since the electron barrier layer 107 is thin, with a thickness of 10 nm or less, the influence on the light intensity distribution can be reduced. In this embodiment, the electron barrier layer 107 is made of P-type Al with a thickness of 5 nm. 0.36 Ga 0.64 This is the N layer. The electron barrier layer 107 contains impurities at a concentration of 1 × 10⁻⁶. 19 cm -3 The material is doped with Mg. The electron barrier layer 107 suppresses the leakage of electrons from the active layer 105 to the P-type cladding layer 108, thereby increasing the optical conversion efficiency of the nitride semiconductor light-emitting element 100.

[0029] The P-type cladding layer 108 is a P-type cladding layer positioned above the active layer 105. In this embodiment, the P-type cladding layer 108 is positioned between the electron barrier layer 107 and the contact layer 109. The bandgap energy of the P-type cladding layer 108 is greater than the bandgap energies of the barrier layers 105a and 105c of the active layer 105, and the P-side first guide layer 106. In other words, the refractive index of the P-type cladding layer 108 is smaller than the refractive index of the barrier layers 105a and 105c of the active layer 105, and the P-side first guide layer 106. In this embodiment, the P-type cladding layer 108 is made of P-type Al with a film thickness of 450 nm.0.065 Ga 0.9 35 This is the N layer. The P-type cladding layer 108 is doped with Mg as an impurity. Furthermore, the P-type cladding layer 108 is located below the vertical center (i.e., closer to the active layer 105) and includes a low-concentration region where the impurity concentration is lower than other regions within the P-type cladding layer 108. Specifically, the P-type cladding layer 108 has a lower concentration region of 2 × 10⁻¹⁶ 18 cm -3 P-type Al with Mg doped, 150 nm film thickness. 0.065 Ga 0. 935 The N layer and the concentration 1 × 10⁻¹⁰ located above (i.e., on the side furthest from the active layer 10⁵) 19 cm -3 P-type Al with Mg doped, 300 nm film thickness. 0.065 Ga 0.935 It has an N-layer. This reduces free carrier loss caused by impurities in the P-type cladding layer 108, thereby reducing waveguide loss.

[0030] A ridge 108R is formed in the P-type cladding layer 108 of the nitride-based semiconductor light-emitting element 100. Two grooves 108T are also formed in the P-type cladding layer 108, arranged along the ridge 108R 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 108R (i.e., the bottom of the groove 108T) and the active layer 105 is defined as dp. The film thickness of the P-type cladding layer 108 at the lower end of the ridge 108R (i.e., the distance between the lower end of the ridge 108R and the interface between the P-type cladding layer 108 and the electron barrier layer 107) is defined as dc.

[0031] The contact layer 109 is positioned above the P-type cladding layer 108 and is a layer that makes ohmic contact with the P-side electrode 111. In this embodiment, the contact layer 109 is a P-type GaN layer with a thickness of 100 nm. The contact layer 109 contains impurities with a concentration of 1 × 10⁻⁶ 20 cm - 3 It is doped with magnesium.

[0032] As described above, in the semiconductor laminate 100S according to this embodiment, the N-type cladding layer 102, the N-side first guide layer 103, the N-side second guide layer 104, the barrier layers 105a and 105c, the P-side first guide layer 106, the electron barrier layer 107, and the P-type cladding layer 108 are made of a nitride-based semiconductor containing Al.

[0033] The current blocking layer 110 is positioned above the P-type cladding layer 108 and is an insulating layer that is transparent to light from the active layer 105. The current blocking layer 110 is positioned on the upper surface of the P-type cladding layer 108, in a region other than the upper surface of the ridge 108R. In this embodiment, the current blocking layer 110 is an SiO2 layer.

[0034] The P-side electrode 111 is a conductive layer positioned above the contact layer 109. In this embodiment, the P-side electrode 111 is positioned above the contact layer 109 and the current blocking layer 110. The P-side electrode 111 is, for example, a monolayer or multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au.

[0035] The N-side electrode 112 is a conductive layer located beneath the substrate 101 (i.e., on the main surface opposite to the main surface on which the semiconductor laminate 100S of the substrate 101 is located). The N-side electrode 112 is, for example, a monolayer or multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au.

[0036] As a result of having the above configuration, the nitride semiconductor light-emitting element 100 generates an effective refractive index difference ΔN between the lower portion of the ridge 108R and the lower portion of the groove 108T, as shown in Figure 2A. This allows the light generated in the lower portion of the ridge 108R of the active layer 105 to be confined in the horizontal direction (i.e., in the X-axis direction).

[0037] [1-2.Light intensity distribution] Next, the light intensity distribution of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be described.

[0038] 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 108R and groove 108T, respectively.

[0039] 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 108R and the lower part of the groove 108T, so the light intensity distribution also differs between the lower part of the ridge 108R and the lower part of the groove 108T. As shown in Figure 3, 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 108R is denoted as PS1. The peak position of the light intensity distribution in the stacking direction at the lower part of the groove 108T is denoted as PS2. Here, positions PS1 and PS2 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-type cladding layer 102, is set to zero, the downward direction (towards the N-type cladding layer 102) is set to the negative direction of the coordinate, and the upward direction (towards the P-type cladding layer 108) is set to the positive direction of the coordinate. Furthermore, the absolute value of the difference between position PS1 and position PS2 is defined as the difference in peak positions ΔP.

[0040] Here, the light intensity distribution in the stacking direction at the position corresponding to ridge 108R in this embodiment will be explained using Figures 5 to 7, in comparison with the comparative example. Figures 5 and 6 are schematic graphs showing the bandgap energy distribution and light intensity distribution in the stacking direction of the semiconductor stack according to Comparative Example 1 and this embodiment, respectively. Figure 7 is a schematic graph showing the bandgap energy distribution and light intensity distribution of the semiconductor stack according to a modified example of this embodiment.

[0041] The semiconductor laminate according to Comparative Example 1 shown in Figure 5 has an N-type cladding layer 102, an N-side guide layer 993, an active layer 995, a P-side guide layer 996, an electron barrier layer 107, and a P-type cladding layer 108. The semiconductor laminate according to Comparative Example 1 differs from the semiconductor laminate 100S according to this embodiment in the configuration of the N-side guide layer 993, the active layer 995, and the P-side guide layer 996. In the semiconductor laminate according to Comparative Example 1, the bandgap energy (i.e., refractive index) and film thickness of the N-side guide layer 993 and the P-side guide layer 996 are equal. The active layer 995 also has barrier layers 995a and 995c and a well layer 995b. Each guide layer according to Comparative Example 1 has a larger bandgap energy than the barrier layers 995a and 995c. In other words, each guide layer according to Comparative Example 1 has a smaller refractive index than the barrier layers 995a and 995c.

[0042] In Comparative Example 1 and the semiconductor laminate according to this embodiment, it is necessary to use cladding layers made of AlGaN with a high Al composition ratio in order to emit ultraviolet light. Consequently, the tensile strain of each cladding layer made of AlGaN relative to the substrate 101 made of GaN becomes large, making the base material of the substrate 101 prone to cracking during the manufacturing of nitride-based semiconductor light-emitting elements. To suppress such cracking of the base material, the tensile strain is suppressed by reducing the film thickness of each cladding layer. Furthermore, since the P-type cladding layer 108 made of P-type AlGaN with a high Al composition ratio has high electrical resistance, its film thickness is set to be even thinner and the impurity concentration to be higher than that of the N-type cladding layer 102. Such a P-type cladding layer 108 has a higher refractive index than the N-type cladding layer 102.

[0043] In addition, in the active layer and each guide layer, in order to guide light, it is required to use a layer with a high refractive index. However, when ultraviolet light is generated in the active layer, in the InGaN layer with a high refractive index, the ultraviolet light is absorbed. Therefore, in each guide layer and each barrier layer, the InGaN layer cannot be used. For this reason, an AlGaN layer is used for each guide layer and each barrier layer, and only the InGaN layer is used for the well layer. For this reason, in the semiconductor laminate according to Comparative Example 1, as shown by the broken-line graph in FIG. 5, the peak position of the light intensity distribution is biased in the direction approaching the P-type clad layer 108 with a high refractive index from the active layer 995.

[0044] On the other hand, in the semiconductor laminate 100S according to the present embodiment, the bandgap energies of the barrier layers 105a and 105c are larger than the bandgap energy of the N-side second guide layer 104. That is, the barrier layers 105a and 105c are made of Al b Ga 1-b N (0 < b ≤ 1), and when the N-side second guide layer 104 is made of Al Xn2 Ga 1-Xn2 N (0 ≤ Xn2 ≤ 1), b > Xn2. Also, the bandgap energy of the N-side second guide layer 104 is smaller than the bandgap energy of the N-side first guide layer 103, and the bandgap energy of the N-side first guide layer 103 is smaller than the bandgap energy of the N-type clad layer 102. That is, the N-side first guide layer 103 is Al Xn1 Ga 1-Xn1 N (0 ≤ Xn1 ≤ 1), and the N-type clad layer 102 is Al Xnc Ga 1-XncWhen N is such that 0 ≦ Xnc ≦ 1, Xn2 < Xn1 and Xn1 < Xnc. Thus, in this embodiment, the bandgap energy of the N-side second guide layer 104, which is the guide layer closer to the barrier layer 105a, is smaller than the bandgap energy of the barrier layer 105a. That is, the refractive index of the N-side second guide layer 104 is larger than the refractive index of the barrier layer 105a. Also, the refractive index of the N-side second guide layer 104, which is closer to the active layer 105 than the N-side first guide layer 103, is larger than the refractive index of the N-side first guide layer 103. By having such a refractive index distribution in the semiconductor laminate 100S, the light intensity distribution can be shifted in the direction approaching the N-side second guide layer 104 as compared with the semiconductor laminate according to Comparative Example 1. With such an N-side second guide layer 104, as shown in FIG. 6, it becomes possible to bring the peak position of the light intensity distribution closer to the active layer 105 as compared with the semiconductor laminate according to Comparative Example 1. Further, since the active layer 105 is not doped with impurities, waveguide loss due to light absorption by impurities can be reduced by positioning the peak position of the light intensity distribution in the vicinity of the active layer 105 region.

[0045] Also, the N-side first guide layer 103 and the N-side second guide layer 104 may be collectively referred to as one N-side guide layer. In this case, the bandgap energy at the lower end of the N-side guide layer (that is, the bandgap energy of the N-side first guide layer 103) is larger than the bandgap energy at the upper end (that is, the bandgap energy of the N-side second guide layer 104). Also, the bandgap energies of the barrier layers 105a and 105c are larger than the average bandgap energy of the N-side guide layer. Thereby, as described above, it becomes possible to bring the peak position of the light intensity distribution closer to the active layer 105 as compared with the semiconductor laminate according to Comparative Example 1. Also, as described above, since the film thickness of each cladding layer can be made thin, it is also possible to suppress cracking of the base material of the substrate 101.

[0046] Also, when the Al composition ratio of the N-side first guide layer 103 is represented by Xn1 and the Al composition ratio of the N-side second guide layer 104 is represented by Xn2, Xn1 > Xn2 The following relationship holds: In other words, the band gap energy of the N-side second guide layer 104 is smaller than the band gap energy of the N-side first guide layer 103. Therefore, as described above, compared to the semiconductor laminate according to Comparative Example 1, it is possible to more reliably bring the peak position of the light intensity distribution closer to the active layer 105.

[0047] Furthermore, in the semiconductor laminate according to the modified example of this embodiment shown in Figure 7, the thickness of the N-side second guide layer 104 is thicker than the thickness of the N-side first guide layer 103, which is different from the semiconductor laminate 100S according to this embodiment, but is the same in other respects.

[0048] Thus, by making the thickness of the N-side second guide layer 104, which has a refractive index greater than that of the N-side first guide layer 103, thicker than that of the N-side first guide layer 103, the peak position of the light intensity distribution in the stacking direction tends to spread towards the N-type cladding layer 102. Therefore, it is possible to improve the controllability of positioning the peak position of the light intensity distribution in the region near the active layer 105. As a result, it is possible to suppress the peak position from being too biased toward the P-side first guide layer 106 from the active layer 105.

[0049] Next, the peak position PS1 of the light intensity distribution in the stacking direction at the horizontal center of the lower portion of the ridge 108R of the semiconductor laminate 100S according to this embodiment, and the peak position PS2 of the light intensity distribution in the stacking direction at the lower portion of the groove 108T, will be explained using Figures 8 and 9, in comparison with the semiconductor laminate according to Comparative Example 2. Figures 8 and 9 are graphs showing the refractive index distribution and light intensity distribution of the semiconductor laminate according to Comparative Example 2 and this embodiment. The semiconductor laminate according to Comparative Example 2 differs from the semiconductor laminate 100S according to this embodiment in that the Al composition ratio of the N-side second guide layer 904 is 0.03, the same as that of the N-side first guide layer 103 and the P-side first guide layer 106, but is the same in other respects.

[0050] As shown in Figure 8, the first N-side guide layer 103 and the second N-side guide layer 904 of the semiconductor stack according to Comparative Example 2 have the same Al composition ratio, but different impurity concentrations. Therefore, the refractive index of the first N-side guide layer 106 is higher than that of the first N-side guide layer 103 and the second N-side guide layer 904. Consequently, the peak positions PS1 and PS2 of the light intensity distribution are biased toward the P-side guide layer from the active layer. Specifically, the peak position PS1 is 96.3 nm, and the difference in peak positions ΔP is 33.4 nm.

[0051] On the other hand, in the semiconductor laminate 100S according to this embodiment, since the refractive index of the N-side second guide layer 104 is greater than that of the N-side first guide layer 103, the peak positions PS1 and PS2 of the light intensity distribution are closer to the active layer 105 than in the semiconductor laminate according to Comparative Example 2. Therefore, the optical confinement coefficient to the active layer 105 can be increased, and waveguide loss can be reduced. In addition, both peak positions PS1 and PS2 are brought closer to the active layer 105, and the absolute value of the difference between positions PS1 and PS2 is also reduced. Specifically, the peak position PS1 is 77.1 nm, and the difference in peak positions ΔP is 32.0 nm.

[0052] In the nitride-based semiconductor light-emitting element 100 according to this embodiment, the effective refractive index difference ΔN between the lower part of the ridge 108R and the lower part of the groove 108T is set to be relatively small in order to reduce the divergence angle of the emitted light in the horizontal direction (i.e., in the X-axis direction). Specifically, the effective refractive index difference ΔN is set by adjusting the distance dp (see Figure 2A) between the current blocking layer 110 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 7.4 × 10⁻⁶. -3 It is approximately such that, therefore, in this embodiment, the effective refractive index difference ΔN is 7.4 × 10 - 3When ΔN is larger, the number of higher-order modes (i.e., higher-order transverse modes) that can propagate through the waveguide formed by the ridge 108R is smaller. As ΔN becomes smaller, the number of higher-order modes propagating through the waveguide decreases, so the proportion of each higher-order mode among all transverse modes included in the light emitted from the nitride semiconductor light-emitting element 100 becomes larger. Therefore, the effect of the increase or decrease in the number of modes and the change in the optical confinement coefficient to the active layer 105 due to intermode coupling becomes relatively large. Here, the fundamental mode is considered to be the 0th-order mode. For this reason, 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.

[0053] The decrease in optical output stability described above will be explained below. When viewed from the normal direction of the laser end face, the optical distribution propagating through the waveguide is distributed two-dimensionally in the regions inside and outside the ridge 108R. Higher-order modes have lower effective refractive indices, so the optical distribution tends to spread to the groove 108T in the region outside the ridge 108R and becomes more susceptible to the influence of the current blocking layer 110. The current blocking layer 110 is made of a material with a lower refractive index than the P-type cladding layer 108 in order to confine the light laterally within the ridge 108R. Therefore, the peak position PS2 of the stacking direction optical distribution in the groove 108T in the region outside the ridge 108R is affected by the current blocking layer 110, and tends to show a greater bias toward the substrate 101 in the stacking direction compared to the peak position PS1 of the stacking direction optical distribution in the ridge 108R.

[0054] Because the horizontal optical confinement effect on the highest-order waveguide mode that can be guided in the waveguide is weak, this waveguide mode tends to spread widely into the groove 108T, which is located outside the ridge 108R. As a result, the peak position of this waveguide mode in the groove 108T is closest to the substrate 101 compared to other waveguide mode light, and the average value of the peak position of the optical distribution in the stacking direction relative to the horizontal direction is approximated by the peak position in the groove 108T.

[0055] Therefore, when the optical distribution of modes couples between a higher-order mode (the highest order that can be directed) and a lower-order mode, such as the fundamental mode, or when the order of the highest-order transverse mode (the highest order that can be directed) increases with increasing drive current, the two-dimensional deformation of the optical distribution tends to become large. As a result of such deformation of the optical distribution, the optical confinement coefficient in the active layer 105 fluctuates, which tends to lead to a decrease in the stability of the optical output.

[0056] In the nitride-based semiconductor light-emitting element 100 according to this embodiment, the effective refractive index difference ΔN is reduced in order to reduce the horizontal divergence angle of the emitted light, thereby reducing the number of higher-order modes that can be guided. When the number of higher-order modes that can be guided is reduced in this way, the fluctuation of the optical confinement coefficient becomes larger, which leads to a decrease in the stability of the optical output and makes kinking more likely.

[0057] In the nitride-based semiconductor light-emitting element 100 according to this embodiment, since it includes an N-side first guide layer 103, an N-side second guide layer 104, and a P-side first guide layer 106 having the configuration described above, the peak of the light intensity distribution can be brought closer to the active layer 105 in both the lower portion of the ridge 108R and the lower portion of the groove 108T, and the difference ΔP between the positions PS1 and PS2 of the light intensity distribution peaks can be reduced. As a result, even if the number of modes increases or decreases, 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 108R and the groove 108T, in the stacking direction are suppressed. Therefore, the stability of the light output can be improved.

[0058] 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 108R (i.e., the bottom of the groove 108T) is positioned below the electron barrier layer 107, the electron barrier layer 107 has a large bandgap energy, so holes injected from the contact layer 109 are more likely to leak out of the ridge 108R from the sidewall when passing through the electron barrier layer 107. As a result, the holes flow downwards to the groove 108T. Consequently, the light distribution intensity in the active layer 105 below the groove 108T is small, which reduces the probability of luminescent recombination between electrons and holes injected into the active layer 105, and increases non-luminescent recombination. Consequently, the nitride semiconductor light-emitting element 100 is more prone to degradation. For this reason, the lower end of the ridge 108R is set to be positioned above the electron barrier layer 107. Furthermore, if the distance dc (see Figure 2A) from the lower end of the ridge 108R to the electron barrier layer 107 becomes too large, holes will flow from the ridge 108R into the space between the groove 108T and the electron barrier layer 107, resulting in leakage current. To suppress this increase in leakage current, the distance dc is set to the smallest possible value. A value of 70 nm or less is sufficient. If dc is 45 nm or less, the change in the oscillation threshold due to fluctuations in dc can be further reduced.

[0059] [1-3. Al composition ratio of each guide layer] Next, the Al composition ratios of the N-side first guide layer 103, the N-side second guide layer 104, and the P-side first guide layer 106 of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be explained with reference to Figure 10. Figure 10 is a table showing the relationship between the Al composition ratio configuration of each guide layer and the characteristics of the nitride-based semiconductor light-emitting element. Figure 10 shows the relationship between nine different Al composition ratio configurations, including comparative examples and configuration examples 1 to 8, and the characteristics of the nitride-based semiconductor light-emitting element obtained by simulation. Note that the well thickness normalized photoconfinement coefficient is the value obtained by dividing the photoconfinement coefficient by the film thickness Tw of the well layer.

[0060] The Al composition ratio of each guide layer in the comparative examples is 0.03 (i.e., 3%). Configuration Examples 1 to 8 each have different combinations of Al composition ratios. The Al composition ratios are selected from 0.02 (i.e., 2%), 0.03 (i.e., 3%), and 0.04 (i.e., 4%). Figure 10 also shows the characteristics for three cases where the well layer thickness (well thickness Tw in Figure 10) is 7.5 nm, 12.5 nm, and 17.5 nm.

[0061] As shown in Configuration Examples 1 to 3, when the Al composition ratio Xn2 of the N-side second guide layer is smaller than the Al composition ratio Xn1 of the N-side first guide layer, that is, when the bandgap energy of the N-side second guide layer is smaller than the bandgap energy of the N-side first guide layer, the optical confinement coefficient, waveguide loss, peak position PS1, and peak position difference ΔP are all improved compared to the comparative example. Therefore, as in the nitride-based semiconductor light-emitting element 100 according to this embodiment, it is preferable that the bandgap energy of the N-side second guide layer 104 is smaller than the bandgap energy of the N-side first guide layer 103.

[0062] Furthermore, as shown in Figure 10, as the film thickness Tw of the well layer increases, the optical confinement coefficient, waveguide loss, peak position PS1, and peak position difference ΔP improve. This is because increasing the film thickness of the well layer, which has a high refractive index, causes the light intensity distribution in the stacking direction to approach that of the well layer. For example, the film thickness Tw of the well layer may be 10 nm or more. Alternatively, the film thickness Tw of the well layer may be 20 nm or less in order to realize a quantum well active layer.

[0063] [1-4. Bandgap energy of the barrier layer] Next, the band gap energies of the barrier layers 105a and 105c according to this embodiment will be explained using Figures 11 to 13. Figures 11 and 12 are graphs showing the relationship between the distribution of the conduction band potential energy near the active layer 105 and the electron wave function when the Al composition ratio of each barrier layer is 0.02 and 0.05, respectively. In the graphs of each figure, the horizontal axis represents the distance from a predetermined position, and the vertical axis represents the potential. In the graphs of each figure, the solid line represents the potential of the conduction band of each layer, the dashed line represents the electron quantization energy level, and the dashed line represents the electron wave function. Figure 13 is a graph showing the relationship between the Al composition ratio of each barrier layer and the band offset ΔEc.

[0064] As described above, the band gap energy of the N-side second guide layer 104 adjacent to the active layer 105 is small, so the electron confinement effect of the N-side second guide layer 104 into the well layer 105b is small. For this reason, in the nitride-based semiconductor light-emitting element 100 according to this embodiment, the band offset ΔEc is increased by increasing the size of the barrier layers 105a and 105c. For example, as shown in Figure 11, when the Al composition ratio of the barrier layers 105a and 105c is 0.02, the same as the Al composition ratio of the N-side second guide layer 104, the band offset ΔEc becomes 31 meV, and electron leakage from the barrier layer 105c cannot be sufficiently suppressed, especially during high-power operation. In other words, the electron confinement effect into the well layer 105b is small. Therefore, in this embodiment, by setting the Al composition ratio of barrier layers 105a and 105c to 0.05, the band gap energies of barrier layers 105a and 105c are made larger than the band gap energy of the N-side second guide layer 104, as shown in Figure 12. This makes it possible to set the band offset ΔEc to 80.2 meV. Thus, the electron confinement effect in the well layer 105b can be enhanced. Note that, as shown in Figure 13, the band offset ΔEc increases as the Al composition ratio of each barrier layer increases.

[0065] Furthermore, the bandgap energies of the barrier layers 105a and 105c may be made larger than the bandgap energies of the N-side first guide layer 103. This further reduces electron leakage from the well layer 105b. In addition, since the energy difference between the ground quantum levels of electrons and holes formed in the well layer 105b can be increased, light in the short wavelength band, such as the 375 nm band, can be easily generated in the active layer 105.

[0066] For example, if the barrier layers 105a and 105c are made of AlGaN and the well layer 105b is an InGaN layer with an In composition ratio of 1% and a film thickness of 7.5 nm, then as shown in Figure 13, the Al composition ratio of the barrier layers 105a and 105c is 0.05 By doing so, the band offset ΔEc can be set to 80 meV or more. This suppresses electron leakage from the well layer 105b. Also, if the well layer 105b is an InGaN layer with an In composition ratio of 1% and a film thickness of 7.5 nm, the Al composition ratio of the barrier layers 105a and 105c is 0.10 By doing so, the band offset ΔEc can be set to 167 meV or higher.

[0067] Furthermore, by increasing the thickness of the well layer 105b, the difference between the electron quantum levels and the conduction band potential energy of the well layer 105b becomes smaller, which further increases the band offset ΔEc.

[0068] [1-5. Al composition ratio and film thickness of each cladding layer] Next, the Al composition ratio and film thickness of each cladding layer of the nitride-based semiconductor light-emitting element 100 according to this embodiment will be described.

[0069] [1-5-1. Waveguide Loss and Optical Confinement Coefficient] First, the relationship between the Al composition ratio and film thickness of each cladding layer of the nitride semiconductor light-emitting element 100, and the waveguide loss and optical confinement coefficient will be explained using Figures 14 and 15. Figures 14 and 15 are graphs showing the relationship between the film thickness of the N-type cladding layer 102 of the nitride semiconductor light-emitting element 100 according to this embodiment, and the waveguide loss and optical confinement coefficient, respectively. The graphs shown in Figures 14 and 15 are graphs obtained by simulation. In this simulation, the Al composition ratio Xc of both the N-type cladding layer 102 and the P-type cladding layer 108 was set to the same Al composition ratio Xc, and the waveguide loss and optical confinement coefficient were calculated when the Al composition ratio Xc and the film thickness of the N-type cladding layer 102 were varied. Figures 14 and 15 show the waveguide loss and optical confinement coefficient for each case where the Al composition ratio Xc is 0.05, 0.06, 0.07, 0.08, and 0.09, respectively. In the nitride-based semiconductor light-emitting element 100 calculated in this simulation, a buffer layer is provided between the substrate 101 and the N-type cladding layer 102. The buffer layer is made of N-type Al with a thickness of 1000 nm, which is sequentially stacked on the substrate 101. 0.007 Ga 0.993 N layer and N-type In 0.05 Ga 0.95 It includes an N layer. The buffer layer contains impurities with a concentration of 5 × 10⁻⁶. 17 cm -3 The Si is doped.

[0070] As shown in Figure 14, when the thickness of the N-type cladding layer 102 is less than 0.5 μm, waveguide loss tends to increase. This is thought to be due to light leaking to the outside of the N-type cladding layer 102 (substrate 101 and buffer layer), where the leaked light is absorbed or propagates within the substrate as substrate mode. By increasing the thickness of the N-type cladding layer 102 to 0.5 μm or more, such waveguide loss can be reduced. Furthermore, as the Al composition ratio increases, the refractive index of each cladding layer decreases, and as shown in Figure 15, the optical confinement coefficient increases, thus reducing waveguide loss. In particular, by setting the Al composition ratio to 0.06 or higher, waveguide loss can be significantly reduced compared to the case where the Al composition ratio is 0.05. However, even when the Al composition ratio is greater than 0.08, the reduction in waveguide loss is small compared to the case where the Al composition ratio is 0.08. On the other hand, increasing the Al composition ratio increases the tensile strain of the semiconductor laminate 100S relative to the substrate 101. To suppress this increase in tensile strain, the Al composition ratio may be set to 0.08.

[0071] [1-5-2. Curvature] Next, the amount of warping caused by strain in the nitride-based semiconductor light-emitting element 100 according to this embodiment will be explained using Figure 16. Figure 16 is a schematic side view showing the warping of the base material 101M and the semiconductor laminate 100S that occurs when a semiconductor laminate 100S is laminated onto the base material 101M of the substrate 101 according to this embodiment. The base material 101M of the substrate 101 shown in Figure 16 is, for example, a GaN substrate with a diameter of 2 inches. As shown in Figure 16, when a semiconductor laminate 100S is laminated onto the base material 101M (i.e., crystal growth is performed), warping occurs in the base material 101M and the semiconductor laminate 100S due to the tensile strain on the base material 101M caused by the AlGaN layer in the semiconductor laminate 100S. In this embodiment, the tensile strain on the base material 101M caused by the AlGaN layer results in warping in a direction that causes the upper surface of the semiconductor laminate 100S to become concave.

[0072] Here, the amount of warpage of the base material 101M and the semiconductor laminate 100S will be explained using Figure 17. Figure 17 is a graph showing the amount of warpage of the base material 101M and the semiconductor laminate 100S that occurs when the semiconductor laminate 100S is laminated onto the base material 101M of the substrate 101 according to this embodiment. The horizontal axis of Figure 17 represents the amount of Al contained in the semiconductor laminate 100S. Xc Ga 1-Xc The total thickness of the N-type cladding layer 102 and the P-type cladding layer 108, which are made of N, is shown, and the vertical axis represents the amount of warpage. Here, as shown in Figure 16, the amount of warpage when the upper surface of the semiconductor laminate 100S is concave (i.e., the depth of the concave part indicated by the arrow in Figure 16) is expressed as a negative number. On the other hand, the amount of warpage when the upper surface of the semiconductor laminate 100S is convex (i.e., the height of the convex part) is expressed as a positive number.

[0073] Figure 17 shows the simulation results of the amount of warpage in the nitride-based semiconductor light-emitting element 100 described above, when the thickness of the N-type cladding layer 102 is changed, with solid lines representing the results. Figure 17 also shows the amount of warpage for cases where the Al composition ratio Xc of the N-type cladding layer 102 and the P-type cladding layer 108 is 0.05, 0.06, 0.07, and 0.08. In the simulation, a 2-inch diameter disc-shaped GaN substrate was used as the base material 101M.

[0074] In Figure 17, the amount of warpage when a buffer layer is provided between the base material 101M and the N-type cladding layer 102 to reduce strain and warpage is also shown by a dashed line. The buffer layer is made of N-type Al with a thickness of 300 nm, which is sequentially laminated on the base material 101M. 0.007 Ga 0.993 N layer and N-type In 0.05 Ga 0.95 It includes an N layer. The buffer layer contains impurities with a concentration of 5 × 10⁻⁶. 17 cm -3 The Si is doped.

[0075] As shown in Figure 17, the absolute value of the warpage increases as the Al composition ratio in each cladding layer increases, and as the total film thickness of each cladding layer increases. This is because the tensile strain on the GaN base material 101M increases as the Al composition ratio in the AlGaN layer increases and the film thickness increases.

[0076] When a 2-inch diameter GaN substrate is used as the base material 101M, the risk of cracking in the base material 101M increases if the absolute value of the warpage exceeds 800 μm. Therefore, in order to keep the absolute value of the warpage of the base material 101M below 700 μm, for example, if the Al composition ratio Xc is between 0.06 and 0.07, the total thickness of the cladding layer should be 1.1 μm or less. Furthermore, as described above based on Figures 14 and 15, by making the thickness of the N-type cladding layer 102 0.5 μm or more, that is, by making the total thickness of the P-type cladding layer 108 with a thickness of 450 nm (i.e., 0.45 μm) and the N-type cladding layer 102 0.95 μm or more, waveguide loss can be suppressed and the optical confinement coefficient can be increased. Therefore, by setting the Al composition ratio Xc to 0.06 or more and 0.07 or less, and the total thickness of the cladding layer to 0.95 μm or more and 1.1 μm or less, it is possible to realize a waveguide with low loss and a large optical confinement coefficient while suppressing cracking of the base material 101M. Furthermore, by setting the total thickness of the cladding layer to 1.0 μm or less, the absolute value of the warpage of the base material 101M can be further reduced, thereby more reliably suppressing cracking of the base material 101M.

[0077] Furthermore, as shown by the dashed line in Figure 17, the absolute value of the warpage can be reduced by providing a buffer layer between the base material 101M and the N-type cladding layer 102. Therefore, when a buffer layer is provided, it becomes possible to increase the total thickness of the cladding layer and the Al composition ratio while suppressing cracking of the base material 101M.

[0078] [1-6. Thickness of each guide layer] Next, the relationship between the film thickness of the N-side first guide layer 103, the N-side second guide layer 104, and the P-side first guide layer 106 and the waveguide loss will be explained using Figures 18 to 20. Figures 18 to 20 are graphs showing the relationship between each guide layer according to this embodiment and the waveguide loss obtained by simulation. In Figures 18 to 20, the horizontal axis represents the film thickness Tp1 of the P-side first guide layer 106, and the vertical axis represents the waveguide loss. Each of Figures 18 to 20 shows a graph for each case in which the film thickness Tn2 of the N-side second guide layer 104 is changed in 30 nm increments from 50 nm to 200 nm. The film thickness Tn1 of the N-side first guide layer 103 is 100 nm. Figures 18, 19, and 20 show the relationships when the Al composition ratio Xp1 of the P-side first guide layer 106 is 0.02, 0.03, and 0.04, respectively.

[0079] As shown in Figures 18 to 20, waveguide loss can be reduced as the film thickness Tn2 of the N-side second guide layer 104 increases. This is because, as described above, increasing the film thickness Tn2 of the N-side second guide layer 104, which has a higher refractive index than the N-type cladding layer 102 and the N-side first guide layer 103, shifts the peak position of the light intensity distribution in the stacking direction from the P-type cladding layer 108 towards the active layer 105. Furthermore, since the active layer 105 is not doped with impurities, the peak position of the light intensity distribution is shifted towards the active layer 105 By getting closer to the target area, waveguide losses caused by impurities can be reduced.

[0080] Furthermore, as shown in Figures 18 to 20, waveguide loss can be further reduced when the film thickness Tn2 of the N-side second guide layer 104 is thicker than the film thickness Tn1 (=100 nm) of the N-side first guide layer 103.

[0081] When the film thickness Tp1 of the P-side first guide layer 106 is thin, waveguide loss tends to increase. Therefore, to reduce waveguide loss, the film thickness Tp1 of the P-side first guide layer 106 may be 65 nm or more. Also, when the film thickness Tn2 of the N-side second guide layer 104 is 150 nm or more, the influence of the film thickness Tp1 of the P-side first guide layer 106 on waveguide loss becomes small. In other words, when the film thickness Tn2 of the N-side second guide layer 104 is 150 nm or more, waveguide loss remains almost constant even if the film thickness Tp1 of the P-side first guide layer 106 changes. Therefore, to increase the degree of freedom of the film thickness Tp1 of the P-side first guide layer 106, the film thickness Tn2 of the N-side second guide layer 104 may be 150 nm or more.

[0082] (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 configuration of the well layer. Below, the nitride-based semiconductor light-emitting element according to this embodiment will be described using Figures 21A to 22, focusing on the differences from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0083] Figure 21A is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 200 according to this embodiment. Figure 21B is a schematic cross-sectional view showing the configuration of the active layer 205 provided in the nitride-based semiconductor light-emitting element 200 according to this embodiment. Figure 22 is a schematic graph showing the bandgap energy distribution and light intensity distribution in the stacking direction of the semiconductor laminate 200S according to this embodiment.

[0084] As shown in Figure 21A, the nitride-based semiconductor light-emitting element 200 according to this embodiment comprises a substrate 101, a semiconductor laminate 200S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 200S has an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 205, a P-side first guide layer 206, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0085] As shown in FIG. 21B, the active layer 205 according to this embodiment has a well layer 205b, barrier layers 105a and 105c. The well layer 205b according to this embodiment is an undoped In 0.01 Ga 0.99 N layer with a thickness of 17.5 nm. Thus, in this embodiment, the thickness of the well layer 205b is 10 nm or more. By increasing the thickness of the well layer 205b having a large refractive index in this way, the light intensity distribution in the stacking direction can be made closer to the well layer 205b. Therefore, the light confinement factor, waveguide loss, peak position PS1, and difference ΔP in peak position of the nitride semiconductor light-emitting device 200 can be further improved.

[0086] In this embodiment, the P-side first guide layer 206 is a P-type Al 0.04 Ga 0.96 N layer with a thickness of 200 nm. The P-side first guide layer 206 is doped with Mg at a concentration of 1×10 18 cm -3 as an impurity. Thus, in this embodiment, the bandgap energy of the P-type clad layer 108 made of Al 0.065 Ga0 .935 N is larger than the bandgap energy of the P-side first guide layer 206. Also, the bandgap energy of the P-side first guide layer 206 is larger than the average bandgap energy of the N-side guide layer including the N-side first guide layer 103 made of Al 0.03 Ga 0.97 N and the N-side second guide layer 104 made of Al 0.02 Ga 0.98 N. That is, the refractive index of the P-side first guide layer 206 is smaller than the average refractive index of the N-side guide layer. Thereby, the peak position of the light intensity distribution can be shifted in the direction from the P-side first guide layer 206 to the N-side guide layer (that is, downward). Therefore, in this embodiment, as shown in FIG. 22, it is possible to make the peak position of the light intensity distribution closer to the active layer 205 than in Comparative Example 1 described in Embodiment 1.

[0087] In addition, in the present embodiment, the N-type clad layer 102 is made of Al Xnc Ga 1-Xnc N, the N-side guide layer is made of AlGaN, and the barrier layers 105a and 105c are made of Al b Ga 1-b N, the P-side first guide layer 206 is made of AlGaN, and the electron barrier layer 107 is made of Al Xd Ga 1-Xd N, the P-type clad layer 108 is made of Al Xpc Ga 1-Xpc N. When the average Al composition ratio of the N-side guide layer is Xn and the average Al composition ratio of the P-side first guide layer 206 is Xp1, b>Xn, Xp1≧X n , Xnc>Xn, Xpc>Xp1 hold. Thus, since b>Xn holds, the bandgap energies of the barrier layers 105a and 105c are larger than the average bandgap energy of the N-side guide layer. That is, the refractive indices of the barrier layers 105a and 105c are smaller than the refractive index of the N-side guide layer. Thereby, the peak position of the light intensity distribution can be shifted in the direction from the barrier layers 105a and 105c to the N-side guide layer (that is, downward). Therefore, it becomes possible to bring the peak position of the light intensity distribution closer to the active layer 205 than in Comparative Example 1 described in Embodiment 1.

[0088] According to the present embodiment, the effective refractive index difference ΔN is 4.3×10 -3 , the position PS1 of the peak of the light intensity distribution in the stacking direction below the ridge 108R is 8.9 nm, ΔP is 4.2 nm, the light confinement factor to the active layer 205 is 5.2%, and the waveguide loss is 3.7 cm -1 , and a nitride semiconductor light-emitting device 200 can be realized.

[0089] (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 that it includes a hole barrier layer. Below, the nitride-based semiconductor light-emitting element according to this embodiment will be described with reference to Figure 23, focusing on the differences from the nitride-based semiconductor light-emitting element 200 according to Embodiment 2.

[0090] Figure 23 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 300 according to this embodiment. As shown in Figure 23, the nitride-based semiconductor light-emitting element 300 according to this embodiment comprises a substrate 101, a semiconductor laminate 300S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 300S has an N-type cladding layer 102, an N-side first guide layer 103, a hole barrier layer 313, an N-side second guide layer 104, an active layer 205, a P-side first guide layer 206, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0091] The hole barrier layer 313 is a nitride-based semiconductor layer positioned between the N-type cladding layer 102 and the active layer 205 to suppress the leakage of holes from the active layer 205 to the N-type cladding layer 102. In this embodiment, the hole barrier layer 313 is positioned between the N-side first guide layer 103 and the N-side second guide layer 104. The hole barrier layer 313 is made of N-type Al with a film thickness of 4 nm. 0.30 Ga 0.70 This is the N layer. The hole barrier layer 313 contains impurities at a concentration of 5 × 10⁻¹⁶. 17 cm -3 The silicon is doped into the material. Thus, the nitride semiconductor light-emitting element 300 comprises an N-type cladding layer 102 and a hole barrier layer 313 having a higher Al composition ratio than the Al composition ratio of the barrier layers 105a and 105c. This makes it possible to improve the confinement effect of holes near the active layer 205 while suppressing an increase in the operating voltage. The hole barrier layer 313 contains 5 × 10 impurities. 17 cm -3The above doping is also possible. This increases the electron conductivity in the hole barrier layer 313. The thickness of the hole barrier layer 313 is, for example, 1 nm to 10 nm. By making the thickness of the hole barrier layer 313 thinner in this way, the influence on the light intensity distribution of the hole barrier layer 313 can be reduced, and the nitride-based semiconductor light-emitting element 300 according to this embodiment also exhibits the same effects as the nitride-based semiconductor light-emitting element 200 according to Embodiment 2.

[0092] According to this embodiment, the effective refractive index difference ΔN is 4.9 × 10 -3 The peak position PS1 of the light intensity distribution in the stacking direction in the lower part of ridge 108R is 10.8 nm, ΔP is 4.3 nm, the light confinement coefficient to the active layer 205 is 5.2%, and the waveguide loss is 5.2 cm. -1 This enables the realization of a nitride-based semiconductor light-emitting element 300.

[0093] (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 200 according to Embodiment 2 in that it includes a P-side second guide layer. Hereinafter, the nitride-based semiconductor light-emitting element according to this embodiment will be described with reference to Figure 24, focusing on the differences from the nitride-based semiconductor light-emitting element 200 according to Embodiment 2.

[0094] Figure 24 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 400 according to this embodiment. As shown in Figure 24, the nitride-based semiconductor light-emitting element 400 according to this embodiment comprises a substrate 101, a semiconductor laminate 400S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 400S has an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 205, a P-side first guide layer 406, an electron barrier layer 107, a P-side second guide layer 414, a P-type cladding layer 108, and a contact layer 109.

[0095] The P-side second guide layer 414 is an optical guide layer positioned between the P-side first guide layer 406 and the P-type cladding layer 108. In this embodiment, the P-side second guide layer 414 is positioned between the electron barrier layer 107 and the P-type cladding layer 108. The P-side second guide layer 414 is made of P-type Al with a film thickness of 50 nm. 0.04 Ga 0.96 This is the N layer. The P-side second guide layer 414 contains impurities with a concentration of 2 × 10⁻¹⁶. 18 cm -3 It is doped with magnesium.

[0096] Furthermore, in this embodiment, the P-side first guide layer 406 is made of P-type Al with a film thickness of 150 nm. 0. 04 Ga 0.96 This is the N layer. The first guide layer 406 on the P side contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 The material is doped with Mg. In other words, in this embodiment, the film thickness of the P-side first guide layer 406 is 50 nm thinner than the film thickness of the P-side first guide layer 206 according to Embodiment 2. Thus, when the nitride semiconductor light-emitting element 400 includes a P-side second guide layer 414, the film thickness of the P-side first guide layer 406 may be reduced by the film thickness of the P-side second guide layer 414.

[0097] Thus, in this embodiment, the nitride semiconductor light-emitting element 400 includes a P-side second guide layer 414 positioned between the electron barrier layer 107 and the P-type cladding layer 108, and the thickness of the P-side first guide layer 406 is thinner than the thickness of the P-side first guide layer 206 in Embodiment 2 by the thickness of the P-side second guide layer 414. In other words, in this embodiment, the electron barrier layer 107 is positioned closer to the well layer 205b of the active layer 205 than the electron barrier layer 107 in Embodiment 2 by the thickness of the P-side second guide layer 414. By positioning the electron barrier layer 107 closer to the well layer 205b in this way, the current leaking from the active layer 205 to the P-type cladding layer 108 by the electron barrier layer 107 can be further suppressed.

[0098] According to this embodiment, the effective refractive index difference ΔN is 7.4 × 10 -3The peak position PS1 of the light intensity distribution in the stacking direction in the lower part of ridge 108R is 9.1 nm, ΔP is 6.9 nm, the light confinement coefficient to the active layer 205 is 5.4%, and the waveguide loss is 4.5 cm. -1 This enables the realization of a nitride-based semiconductor light-emitting element 400.

[0099] (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 that it includes a buffer layer. Below, the nitride-based semiconductor light-emitting element according to this embodiment will be described with reference to Figure 25, focusing on the differences from the nitride-based semiconductor light-emitting element 100 according to Embodiment 1.

[0100] Figure 25 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 500 according to this embodiment. As shown in Figure 25, the nitride-based semiconductor light-emitting element 500 according to this embodiment comprises a substrate 101, a semiconductor laminate 500S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 500S has a first buffer layer 521, an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 105, a P-side first guide layer 106, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0101] The first buffer layer 521 is a buffer layer containing In, disposed between the substrate 101 and the N-type cladding layer 102. In this embodiment, the first buffer layer 521 is an N-type In with a film thickness of 150 nm. 0.05 Ga 0.95 This is the N layer. The first buffer layer 521 contains impurities with a concentration of 5 × 10⁻⁶. 17 cm -3The silicon is doped into the substrate. When a first buffer layer 521 made of InGaN, which has compressible strain relative to the substrate 101, is placed between the GaN substrate 101 and the N-type cladding layer 102 in this manner, the amount of tensile strain in the entire semiconductor laminate 500S is reduced. Therefore, the concave warping of the base material 101M of the substrate 101 described in Embodiment 1 can be reduced. In other words, the flatness of the base material 101M can be improved. Consequently, cracking of the base material 101M can be suppressed.

[0102] According to this embodiment, the effective refractive index difference ΔN is 7.4 × 10 -3 The peak position PS1 of the light intensity distribution in the stacking direction in the lower part of ridge 108R is 96.0 nm, ΔP is -26.3 nm, the light confinement coefficient to the active layer 105 is 1.69%, and the waveguide loss is 4.65 cm -1 This enables the realization of a nitride-based semiconductor light-emitting element 500.

[0103] (Modification 1 of Embodiment 5) A nitride-based semiconductor light-emitting element according to a modification 1 of Embodiment 5 will be described. This modification differs from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5 in that it further comprises a second buffer layer. Hereinafter, the nitride-based semiconductor light-emitting element according to this modification will be described with reference to Figure 26, focusing on the differences from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5.

[0104] Figure 26 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 500A according to this modified example. As shown in Figure 26, the nitride-based semiconductor light-emitting element 500A according to this modified example comprises a substrate 101, a semiconductor laminate 500AS, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 500AS has a first buffer layer 521, second buffer layers 522a and 522b, an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 105, a P-side first guide layer 106, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0105] The second buffer layers 522a and 522b are buffer layers made of GaN and are arranged on at least one main surface of the first buffer layer 521. In this modified example, the second buffer layer 522a is arranged on the main surface of the first buffer layer 521 facing the substrate 101 (i.e., the lower main surface), and the second buffer layer 522b is arranged on the main surface of the first buffer layer 521 facing the N-type cladding layer 102 (i.e., the upper main surface). In other words, the second buffer layer 522a, the first buffer layer 521, the second buffer layer 522b, and the N-type cladding layer 102 are sequentially stacked on the substrate 101. In this modified example, the second buffer layers 522a and 522b are N-type GaN layers with a film thickness of 10 nm. The second buffer layers 522a and 522b each contain impurities with a concentration of 5 × 10⁻¹⁶ 17 cm -3 and 1 × 10 18 cm -3 The Si is doped.

[0106] In this way, by stacking a second buffer layer 522a made of GaN on top of the substrate 101, and then stacking a first buffer layer 521 made of InGaN having compressible strain, the occurrence of lattice defects on the lower main surface of the first buffer layer 521 (i.e., the interface with the second buffer layer 522a) can be suppressed. Furthermore, by stacking the second buffer layer 522b between the first buffer layer 521 and the N-type cladding layer 102, the difference between compressible stress and tensile stress between the first buffer layer 521 and the N-type cladding layer 102 can be reduced. This reduces the shear stress between the first buffer layer 521 and the N-type cladding layer 102. Therefore, in the processing step after crystal growth of the semiconductor laminate 500AS on the base material 101M of the substrate 101, the occurrence of cracks in the nitride-based semiconductor light-emitting element 500A can be reduced.

[0107] In this modified example, as in Embodiment 5, the effective refractive index difference ΔN is 7.4 × 10 -3The peak position PS1 of the light intensity distribution in the stacking direction in the lower part of ridge 108R is 96.0 nm, ΔP is -26.3 nm, the light confinement coefficient to the active layer 105 is 1.69%, and the waveguide loss is 4.65 cm -1 This enables the realization of a nitride-based semiconductor light-emitting element 500A.

[0108] (Modification 2 of Embodiment 5) A nitride-based semiconductor light-emitting element according to a modified example 2 of Embodiment 5 will be described. This modified example differs from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5 in that it further comprises a third buffer layer. Hereinafter, the nitride-based semiconductor light-emitting element according to this modified example will be described with reference to Figure 27, focusing on the differences from the nitride-based semiconductor light-emitting element 500 according to Embodiment 5.

[0109] Figure 27 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 500B according to this modified example. As shown in Figure 27, the nitride-based semiconductor light-emitting element 500B according to this modified example comprises a substrate 101, a semiconductor laminate 500BS, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 500BS has a third buffer layer 523, a first buffer layer 521, an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 105, a P-side first guide layer 106, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0110] The third buffer layer 523 is placed between the substrate 101 and the first buffer layer 521 and contains Al. middle Buffer layer An example In this modified example, the third buffer layer 523 is made of N-type Al with a film thickness of 1000 nm (i.e., 1 μm). 0.007 Ga 0.993 This is the N layer. The third buffer layer 523 contains impurities with a concentration of 5 × 10⁻⁶. 17 cm -3 The Si is doped.

[0111] As described above, by stacking a third buffer layer 523 made of AlGaN between a substrate 101 made of GaN and a first buffer layer 521 made of InGaN, the flatness of the surface of the first buffer layer 521 during crystal growth can be improved. Therefore, the flatness of the growth surface of each semiconductor layer grown on the first buffer layer 521 can be improved. If the Al composition ratio of the third buffer layer 523 is large, the tensile strain increases, and the amount of concave warping of the base material 101M of the substrate 101 increases. To reduce such warping, the Al composition ratio of the third buffer layer 523 is set to 0.01 or less.

[0112] By laminating a first buffer layer 521 having compressive strain relative to the substrate 101 onto the third buffer layer 523, the warping of the base material 101M of the substrate 101 can be reduced. In other words, the flatness of the base material 101M can be improved. Therefore, cracking in the processing steps after crystal growth of the base material 101M can be suppressed.

[0113] In this modified example, as in Embodiment 5, the effective refractive index difference ΔN is 7.4 × 10 -3 The peak position PS1 of the light intensity distribution in the stacking direction in the lower part of ridge 108R is 96.0 nm, ΔP is -26.3 nm, the light confinement coefficient to the active layer 105 is 1.69%, and the waveguide loss is 4.65 cm -1 This enables the realization of the nitride-based semiconductor light-emitting element 500B.

[0114] (Modification 3 of Embodiment 5) A nitride-based semiconductor light-emitting element according to Modification 3 of Embodiment 5 will be described. This modified nitride-based semiconductor light-emitting element differs from the nitride-based semiconductor light-emitting element 500B according to Modification 2 of Embodiment 5 in that it further comprises a second buffer layer. Hereinafter, the nitride-based semiconductor light-emitting element according to this modified example will be described with reference to Figure 28, focusing on the differences from the nitride-based semiconductor light-emitting element 500B according to Modification 2 of Embodiment 5.

[0115] Figure 28 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 500C according to this modified example. As shown in Figure 28, the nitride-based semiconductor light-emitting element 500C according to this modified example comprises a substrate 101, a semiconductor laminate 500CS, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 500CS has a third buffer layer 523, a first buffer layer 521, second buffer layers 522a and 522b, an N-type cladding layer 102, an N-side first guide layer 103, an N-side second guide layer 104, an active layer 105, a P-side first guide layer 106, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0116] Book Variation The second buffer layer 522a is placed between the third buffer layer 523 and the first buffer layer 521. The second buffer layer 522b is placed between the first buffer layer 521 and the N-type cladding layer 102.

[0117] This configuration provides the same effects as the nitride semiconductor light-emitting element 500B according to Modification 2 of Embodiment 5. Furthermore, by including the second buffer layers 522a and 522b, the nitride semiconductor light-emitting element 500C provides the same effects as Modification 1 of Embodiment 5.

[0118] In this modified example, as in Embodiment 5, the effective refractive index difference ΔN is 7.4 × 10 -3 The peak position PS1 of the light intensity distribution in the stacking direction in the lower part of ridge 108R is 96.0 nm, ΔP is -26.3 nm, the light confinement coefficient to the active layer 105 is 1.69%, and the waveguide loss is 4.65 cm -1 This enables the realization of a nitride-based semiconductor light-emitting element 500C.

[0119] (Modification 4 of Embodiment 5) A nitride-based semiconductor light-emitting element according to Modification 4 of Embodiment 5 will be described. The nitride-based semiconductor light-emitting element according to this modification differs from the nitride-based semiconductor light-emitting element 500C according to Modification 3 of Embodiment 5 in the composition of each layer of the semiconductor laminate. The following description of the nitride-based semiconductor light-emitting element according to this modification will focus on the differences between it and the nitride-based semiconductor light-emitting element 500C according to Modification 3 of Embodiment 5.

[0120] The nitride-based semiconductor light-emitting element according to this modified example comprises a substrate 101, a semiconductor laminate, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112, similar to the modified example 3 of Embodiment 5. The semiconductor laminate includes a third buffer layer, a first buffer layer, two second buffer layers, an N-type cladding layer, an N-side first guide layer, an N-side second guide layer, an active layer, a P-side first guide layer, an electron barrier layer, a P-type cladding layer, and a contact layer.

[0121] The third buffer layer in this modified example is made of N-type Al with a film thickness of 1000 nm. 0.02 Ga 0.98 This is the N layer. The third buffer layer contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 The Si is doped.

[0122] The first buffer layer in this modified example is made of N-type In 0.04 Ga 0.96 This is the N layer. The first buffer layer contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 The Si is doped.

[0123] Each of the two second buffer layers in this modified example is an N-type GaN layer with a thickness of 10 nm. Each of the two second buffer layers contains an impurity with a concentration of 1 × 10⁻⁶ 18 cm -3 The Si is doped.

[0124] The N-type cladding layer in this modified example is made of N-type Al with a film thickness of 540 nm. 0.065 Ga 0.93This is a 5N layer. The N-type cladding layer contains impurities at a concentration of 1 × 10⁻⁶. 18 cm -3 The Si is doped.

[0125] The first guide layer on the N side in this modified example is made of N-type Al with a film thickness of 100 nm. 0.03 Ga 0.97 This is the N layer. The first guide layer on the N side contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 The Si is doped.

[0126] The N-side second guide layer in this modified example is an undoped aluminum layer with a thickness of 120 nm. 0.02 Ga0 .98 It is an N-layer structure.

[0127] The active layer in this modified example has two barrier layers and a well layer disposed between the two barrier layers, similar to the active layer in Modified Example 3 of Embodiment 5.

[0128] Each of the two barrier layers in this modified example is an undoped aluminum layer with a thickness of 12 nm. 0.04 Ga 0.96 It is an N-layer structure.

[0129] The well layer in this modified example is an undoped aluminum layer with a thickness of 17.5 nm. 0.078 Ga 0.8 92 In 0.03 It is an N-layer structure.

[0130] The first guide layer on the P side in this modified example is P-type Al with a film thickness of 200 nm. 0.035 Ga 0.9 65 This is the N layer. The first guide layer on the P side contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 It is doped with magnesium.

[0131] The electron barrier layer, P-type cladding layer, and contact layer in this modified example have the same configuration as the electron barrier layer 107, P-type cladding layer 108, and contact layer 109 in Modified Example 3 of Embodiment 5, respectively.

[0132] In the nitride-based semiconductor light-emitting element according to this modified example, which has the configuration described above, each layer placed between the N-type cladding layer and the P-type cladding layer has a lower refractive index than GaN, except for the well layer. Therefore, the effective refractive index in the region where light propagating through the waveguide is distributed is lower than that of the GaN substrate 101. Furthermore, since the wavelength corresponding to the bandgap energy of GaN is approximately 365 nm, the substrate 101 is transparent to laser light in the 375 nm wavelength band.

[0133] As a result, the light that reaches the substrate 101 spreads across the entire substrate 101 without attenuation, increasing waveguide loss.

[0134] One way to reduce the proportion of light reaching the substrate 101 is to increase the thickness of the N-type cladding layer. However, in this case, the tensile strain generated in the semiconductor laminate increases. Therefore, after growing the semiconductor laminate on the base material 101M of the substrate 101, temperature changes during various processing steps to form a laser element including the semiconductor laminate make the base material 101M on which the semiconductor laminate is formed more prone to cracking.

[0135] Therefore, the thickness of the N-type cladding layer with a high Al composition ratio must be, for example, 1 μm or less. In this modified example, it is set to 540 nm to suppress the increase in tensile strain. In this case, since the attenuation of light in the N-type cladding layer is insufficient, a first buffer layer, which is an N-type InGaN buffer layer with an In composition ratio of 0.04, is placed below the N-type cladding layer to attenuate light by absorption.

[0136] In Modification 3 of Embodiment 5, the In composition ratio of the first buffer layer 521 was 0.05, but in the first buffer layer according to this modification, the In composition ratio is 0.04, which is lower than the In composition ratio of the first buffer layer 521 according to Modification 3 of Embodiment 5. Increasing the In composition ratio of the first buffer layer increases the absorption of laser light in this layer and can increase the attenuation of light, but it makes it easier for pits to occur in the first buffer layer. On the other hand, if the In composition ratio of the first buffer layer is low, the light absorption in this layer is small, so the light is not sufficiently attenuated in the first buffer layer and is more likely to reach the substrate 101.

[0137] Therefore, in the buffer layer structure of this modified example, the Al composition ratio of the third buffer layer, which is made of N-type AlGaN, is set to 0.02, which is higher than the Al composition ratio of 0.007 of the third buffer layer 523 in modified example 3 of Embodiment 5. This lowers the refractive index of the third buffer layer and increases the attenuation of light in this layer. As a result, in the buffer layer structure of this modified example, the tensile strain in the third buffer layer increases, but the occurrence of pits in the first buffer layer is suppressed while suppressing the light distribution intensity reaching the substrate 101.

[0138] If the In composition ratio of the first buffer layer is less than 0.05, the effect of attenuating light in this layer becomes small. Therefore, it is necessary to increase the Al composition ratio of the third buffer layer to more than 0.01 and lower the refractive index of the third buffer layer to increase the attenuation of light and reduce the light intensity reaching the substrate 101. However, if the Al composition ratio of the third buffer layer is made too large, the tensile strain will become too large, so the Al composition ratio of the third buffer layer must be less than or equal to one-third (33.3%) of the average Al composition ratio of the N-type cladding layer made of N-type AlGaN. In this modified example, the Al composition ratio of the third buffer layer is 30.7% of the Al composition ratio of the N-type cladding layer, which is 0.065.

[0139] Furthermore, if the In composition ratio of the first buffer layer is made too small, the optical attenuation effect in this layer will decrease, and the compressive strain of the first buffer layer will also decrease. As a result, the effect of the first buffer layer in compensating for the tensile strain of the N-type and P-type cladding layers, which have a high Al composition ratio and large tensile strain, and reducing the warping of the wafer after crystal growth will be diminished. For this reason, the In composition ratio of the first buffer layer should be 0.03 or higher.

[0140] If the In composition ratio of the first buffer layer is 0.05 or higher, the light attenuation effect due to light absorption in this layer can be greatly increased, so it is not necessary to increase the Al composition ratio of the third buffer layer. By making the third buffer layer an AlGaN layer with an Al composition ratio of 0.01 or lower, the flatness of the surface of the first buffer layer during crystal growth can be improved, and furthermore, by reducing the tensile strain generated in the third buffer layer, the warping of the base material 101M of the substrate 101 can be reduced.

[0141] Next, the Al composition ratio of each guide layer in this modified example will be explained.

[0142] The Al composition ratio of the N-side first guide layer is 0.03, the Al composition ratio of the N-side second guide layer is 0.02, and the Al composition ratio of the P-side first guide layer is 0.035. Thus, in this modified example, the average refractive index of the N-side first guide layer and the N-side second guide layer is higher than that of the P-side first guide layer, and furthermore, the refractive index of the N-side second guide layer is higher than that of the N-side first guide layer. This makes it possible to improve the controllability of positioning the peak position PS1 of the light intensity distribution in the stacking direction in the region near the well layer.

[0143] Next, the well layer relating to this modified example will be explained.

[0144] As shown in this modified example, by making the well layer an AlGaInN layer containing Al, the In composition ratio of the well layer required to obtain laser oscillation in the 375 nm band can be increased compared to the In composition ratio when the well layer is an InGaN layer. In the well layer of this modified example, by setting the In composition ratio to 0.03 and the Al composition ratio to 0.047, laser oscillation in the 375 nm band can be obtained in a nitride semiconductor light-emitting device. Thus, the In composition ratio can be increased to 0.03 compared to the In composition ratio of 0.01 required to obtain laser oscillation light in the 375 nm band when the well layer is an InGaN layer. Furthermore, if the In composition ratio of the well layer is 0.05, laser oscillation in the 375 nm band can be obtained in a nitride semiconductor light-emitting device by setting the Al composition ratio to 0.093.

[0145] Thus, by making the well layer an Al-containing AlGaInN layer, the In composition ratio of the well layer increases, resulting in increased compressible strain in the well layer. In this case, the tensile strain accumulated in the N-type cladding layer, the N-side first guide layer, and the N-side second guide layer can be compensated for by the compressible strain of the well layer, thereby suppressing the occurrence of wafer cracking. Furthermore, because the compressible strain of the well layer increases, the difference in ground state energy levels between heavy holes and light holes formed in the well layer increases, and the carrier density of heavy holes present in the ground state increases. As a result, the amplification gain of the active layer increases with a small injection current, and the oscillation threshold current value can be reduced.

[0146] Here, if we let the Al composition ratio of the well layer be x (0 ≤ x ≤ 1) and the In composition ratio be y (0 ≤ y ≤ 1), then by determining the respective composition ratios x and y such that the following relationship is satisfied, it is possible to obtain ultraviolet laser oscillation light in the 375 nm wavelength band in a nitride-based semiconductor light-emitting element.

[0147] 2.34y≧x≧2.34y―0.234 y≧0.234 Here, the lattice constants in the a-axis direction of AlN, GaN, and InN constituting AlGaInN are 3.08 Å, 3.16 Å, and 3.5 Å, respectively, with the lattice constant of InN being larger than that of AlN and GaN. Therefore, the sum of internal strain energies arising from the difference between the stable interatomic spacing based on the lattice constant difference between each group 3 atom (Al, Ga, In) and the nitrogen atom is smaller when the In atoms in the AlGaInN layer are locally segregated and unevenly distributed rather than uniformly distributed within the crystal growth plane. Furthermore, because the difference in lattice constants between AlN and GaN is small, the unevenness in the distribution of Al atoms is smaller than the unevenness in the distribution of In atoms.

[0148] As a result, increasing the In composition ratio makes it easier to form high-In composition regions with an average diameter of several tens to several nanometers within the growth plane. These high-In composition regions have a small bandgap energy and function as quantum dot active layers. When quantum dot regions are formed, quantum levels are formed not only in the stacking direction (growth layer direction) but also in the direction within the growth layer plane, making it possible to increase the electron and hole concentrations present in the ground state of the quantum levels. Therefore, the oscillation threshold (oscillation threshold current value) of nitride-based semiconductor light-emitting devices can be reduced.

[0149] In semiconductor laser devices operating in the 375nm wavelength band, the difference in bandgap energy between the guide layer and the well layer is small, making it easy for electrons injected into the well layer to leak into the P-side first guide layer. Therefore, by using a quaternary AlGaInN well layer, the oscillation threshold can be reduced, electron leakage can be minimized, and the temperature characteristics of nitride-based semiconductor light-emitting devices can be improved.

[0150] (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 500C according to Modification 3 of Embodiment 5 mainly in that the Al composition ratio of each cladding layer is increased. Below, the nitride-based semiconductor light-emitting element according to this embodiment will be described with reference to Figure 29, focusing on the differences from the nitride-based semiconductor light-emitting element 500C according to Modification 3 of Embodiment 5.

[0151] Figure 29 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 29, the nitride-based semiconductor light-emitting element 600 according to this embodiment comprises a substrate 101, a semiconductor laminate 600S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 600S has a third buffer layer 523, a first buffer layer 521, second buffer layers 522a and 522b, an N-type cladding layer 602, an N-side first guide layer 603, an N-side second guide layer 604, an active layer 105, a P-side first guide layer 606, an electron barrier layer 107, a P-type cladding layer 608, and a contact layer 109.

[0152] The N-type cladding layer 602 is made of N-type Al with a thickness of 540 nm. 0.11 Ga 0.89 This is an N-type cladding layer. The N-type cladding layer 602 contains impurities at a concentration of 5 × 10⁻¹⁶. 17 cm -3 The Si is doped.

[0153] The N-side first guide layer 603 is made of N-type Al with a film thickness of 100 nm. 0.06 Ga 0.94 This is the N layer. The first guide layer 603 on the N side contains impurities with a concentration of 5 × 10⁻⁶. 17 cm -3 The Si is doped.

[0154] The N-side second guide layer 604 is made of undoped aluminum with a thickness of 120 nm. 0.04 Ga 0.96 It is an N-layer structure.

[0155] The first guide layer 606 on the P side is made of P-type Al with a film thickness of 200 nm. 0.08 Ga 0.92 This is the N layer. The first guide layer 606 on the P side contains impurities with a concentration of 1 × 10⁻⁶. 18 cm -3 It is doped with magnesium.

[0156] The P-type cladding layer 608 is made of P-type Al with a thickness of 450 nm. 0.11 Ga 0.89 This is the N layer. The P-type cladding layer 608 is doped with Mg as an impurity. Furthermore, the P-type cladding layer 608 is located below the vertical center (i.e., closer to the active layer 105) and includes a low-concentration region where the impurity concentration is lower than other regions within the P-type cladding layer 608. Specifically, the P-type cladding layer 608 has a lower concentration region of 2 × 10⁻¹⁶. 18 cm -3 P-type Al with Mg doped, 150 nm film thickness. 0.11 Ga 0.89 The N layer and the concentration 1 × 10⁻¹⁰ located above (i.e., on the side furthest from the active layer 10⁵) 19 cm -3 P-type Al with Mg doped, 300 nm film thickness. 0.11 Ga 0.89 It has N layers.

[0157] Furthermore, a ridge 608R is formed in the P-type cladding layer 608. In addition, two grooves 608T are formed in the P-type cladding layer 608, which are arranged along the ridge 608R and extend in the Y-axis direction.

[0158] As described above, in this embodiment, the refractive indices of the N-type cladding layer 602 and the P-type cladding layer 608 can be reduced by increasing the Al composition ratio of the N-type cladding layer 602 and the P-type cladding layer 608. Therefore, in this embodiment, waveguide loss can be reduced and the optical confinement coefficient can be increased. In addition, both the peak position PS1 and the difference ΔP of the peak position in the optical intensity distribution in the stacking direction in the lower part of the ridge 608R can be reduced. As a result, IL characteristics with excellent temperature characteristics and linearity can be achieved.

[0159] According to this embodiment, the effective refractive index difference ΔN is 4.8 × 10 -3 The peak position PS1 of the light intensity distribution in the stacking direction in the lower portion of ridge 608R is 6.9 nm, ΔP is -3.3 nm, the light confinement coefficient to the active layer 105 is 5.3%, and the waveguide loss is 4.0 cm. -1 This enables the realization of a nitride-based semiconductor light-emitting element 600.

[0160] (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 200 according to Embodiment 2 in the configuration of the N-side guide layer. Hereinafter, the nitride-based semiconductor light-emitting element according to this embodiment will be described with reference to Figure 30, focusing on the differences from the nitride-based semiconductor light-emitting element 200 according to Embodiment 2.

[0161] Figure 30 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 700 according to this embodiment. As shown in Figure 30, the nitride-based semiconductor light-emitting element 700 according to this embodiment comprises a substrate 101, a semiconductor laminate 700S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 700S has an N-type cladding layer 102, an N-side guide layer 740, an active layer 205, a P-side first guide layer 206, an electron barrier layer 107, a P-type cladding layer 108, and a contact layer 109.

[0162] The N-side guide layer 740 in this embodiment is an optical guide layer positioned above the N-type cladding layer 102. The composition of the N-side guide layer 740 is not uniform in the stacking direction. Specifically, the N-side guide layer 740 is an N-type AlGaN layer with a thickness of 220 nm. The Al composition ratio of the N-side guide layer 740 changes from 0.03 to 0.02 from bottom to top in the stacking direction. The manner in which the Al composition ratio changes is not particularly limited. In this embodiment, the Al composition ratio of the N-side guide layer 740 changes at a constant rate in the stacking direction. In addition, the portion of the N-side guide layer 740 with a thickness of 100 nm below it contains impurities with a concentration of 5 × 10⁻¹⁶ 17 cm -3 The silicon is doped into the material. On the other hand, the 100 nm thick portion above the N-side guide layer 740 is not doped with impurities.

[0163] Thus, the bandgap energy of the N-type cladding layer 102 is greater than the average bandgap energy of the N-side guide layer 740. As a result, the average refractive index of the N-side guide layer 740 is greater than the average refractive index of the N-type cladding layer 102, and the N-side guide layer 740 functions as an optical guide layer. Furthermore, the bandgap energies of the barrier layers 105a and 105c are greater than the average bandgap energy of the N-side guide layer 740. In other words, the refractive indices of the barrier layers 105a and 105c are smaller than the average refractive index of the N-side guide layer 740. Therefore, similar to the nitride-based semiconductor light-emitting element 100 according to Embodiment 1, it is possible to bring the peak position of the light intensity distribution closer to the active layer 205.

[0164] Furthermore, the band gap energy at the lower end of the N-side guide layer 740 (the end closer to the N-type cladding layer 102) is greater than the band gap energy at the upper end (the end closer to the active layer 205). Thus, in this embodiment, the band gap energy at the upper end of the N-side guide layer 740, which is the guide layer closer to the barrier layer 105a, is smaller than the band gap energy of the barrier layer 105a. In other words, the refractive index at the upper end of the N-side guide layer 740, which is the guide layer closer to the barrier layer 105a, is greater than the refractive index of the barrier layer 105a. Also, the refractive index at the upper end of the N-side guide layer 740, which is closer to the active layer 205 than the lower end of the N-side guide layer 740, is greater than the refractive index at the lower end. Because the semiconductor laminate 700S has such a refractive index distribution, the light intensity distribution can be shifted toward the upper end of the N-side guide layer 740, similar to the nitride-based semiconductor light-emitting element 100 according to Embodiment 1. Furthermore, since the active layer 205 is not doped with impurities, the peak position of the light intensity distribution can be positioned in the region near the active layer 205, thereby reducing waveguide losses caused by light absorption due to impurities.

[0165] Furthermore, the bandgap energy of the P-type cladding layer 108 is greater than the bandgap energy of the P-side first guide layer 206. Also, the bandgap energy of the P-side first guide layer 206 is greater than the average bandgap energy of the N-side guide layer 740. In other words, the refractive index of the P-side first guide layer 206 is smaller than the average refractive index of the N-side guide layer 740. This allows the peak position of the light intensity distribution to be shifted from the P-side first guide layer 206 toward the N-side guide layer 740 (i.e., downward). Therefore, in this embodiment, similar to the nitride-based semiconductor light-emitting element 100 according to Embodiment 1, it is possible to bring the peak position of the light intensity distribution closer to the active layer 205.

[0166] (Embodiment 8) A nitride-based semiconductor light-emitting element according to Embodiment 8 will now be described. The nitride-based semiconductor light-emitting element according to this embodiment differs from the nitride-based semiconductor light-emitting element 600 according to Embodiment 6 in that a separation groove is formed in the substrate and that it does not have a buffer 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 600 according to Embodiment 6, using Figure 31.

[0167] Figure 31 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 800 according to this embodiment. As shown in Figure 31, the nitride-based semiconductor light-emitting element 800 according to this embodiment comprises a substrate 801, a semiconductor laminate 800S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 800S has an N-type cladding layer 602, an N-side first guide layer 603, an N-side second guide layer 604, an active layer 105, a P-side first guide layer 606, an electron barrier layer 107, a P-type cladding layer 608, and a contact layer 109.

[0168] The substrate 801 is made of GaN. Multiple separation grooves 801T are formed on the substrate 801. In this embodiment, the separation grooves 801T are formed on the upper main surface of the substrate 801 along the ridge 608R.

[0169] Multiple isolation grooves 801T are laminated with semiconductor stacks 800S. Specifically, multiple isolation grooves 801T are laminated with an N-type cladding layer 602, an N-side first guide layer 603, an N-side second guide layer 604, an active layer 105, a P-side first guide layer 606, an electron barrier layer 107, a P-type cladding layer 608, and a contact layer 109.

[0170] In this way, by forming separation grooves 801T in the substrate 801 and stacking the semiconductor laminate 800S on top of them, the width W2 of the nitride-based semiconductor light-emitting element 800 can be effectively narrowed to the distance W1 between the separation grooves 801T. The semiconductor laminate 800S stacked on the substrate 801 has an N-type cladding layer 602 and a P-type cladding layer 608 with a relatively high Al composition ratio, which causes tensile strain on the GaN substrate 801.

[0171] Here, since the P-type cladding layer 608 is further away from the substrate 801 than the N-type cladding layer 602, the lattice constant of the P-type cladding layer 608 is more likely to change to a value corresponding to the atomic composition than the lattice constant of the N-type cladding layer 602. For this reason, a shear stress is applied to the semiconductor laminate 800S formed on the end of the separation groove 801T closer to the ridge 608R, causing the P-type cladding layer 608 to shrink horizontally.

[0172] The effect of this shear stress on the region sandwiched between two adjacent separation grooves 801T is greater when the distance W1 is small. Therefore, a smaller distance W1 results in less tensile stress in the P-type cladding layer 608, making it less likely for cracks to occur in the base material after the semiconductor laminate 800S is laminated onto the base material of the substrate 801. For this reason, the distance W1 may be, for example, 2500 μm or less.

[0173] However, if the distance W1 is too small, the thermal resistance of the nitride semiconductor light-emitting element 800 increases. For this reason, the distance W1 may be 1000 μm or more.

[0174] Furthermore, if the width W2 of the nitride semiconductor light-emitting element 800, which includes the two separation grooves 801T, is too small, the thermal resistance of the nitride semiconductor light-emitting element 800 will increase. Also, when separating each of the multiple nitride semiconductor light-emitting elements 800, which are fabricated in an array-like manner and connected to each other, along the direction of the resonator, the processability decreases, making it difficult to separate each of the multiple nitride semiconductor light-emitting elements 800. For this reason, the width W2 may be 150 μm or more. On the other hand, if the width W2 is too large, the effect of reducing the thermal resistance of the nitride semiconductor light-emitting element 800 will decrease. For this reason, the width W2 may be 400 μm or less.

[0175] Furthermore, if the difference between the distance W1 and the width W2 becomes too small, debris tends to adhere to the side walls of the nitride semiconductor light-emitting elements 800 during the separation process, which separates each of the multiple nitride semiconductor light-emitting elements 800 fabricated in an array along the resonator direction. Such debris increases the risk of leakage current generation when the nitride semiconductor light-emitting elements 800 are mounted in a junction-down configuration. For this reason, the difference between the distance W1 and the width W2 (W2-W1) may be 8 μm or more.

[0176] The greater the depth of the separation groove 801T, the longer the region where shear stress occurs in the semiconductor laminate 800S formed on the end of the separation groove 801T closer to the ridge 608R, thus increasing the crack suppression effect described above. The depth of the separation groove 801T should be greater than or equal to the thickness from the N-type cladding layer 602 to the contact layer 109 of the semiconductor laminate 800S (i.e., greater than or equal to the distance from the lower end of the N-type cladding layer 602 to the upper end of the contact layer 109).

[0177] As described above, by forming separation grooves 801T in the substrate 801, even if the Al composition ratio of each cladding layer is 8% or more, as in this embodiment, it is possible to suppress the occurrence of cracks in the base material of the substrate 801 after crystal growth of the semiconductor laminate 800S.

[0178] (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 800 according to Embodiment 8 in that it includes a buffer layer. Below, the nitride-based semiconductor light-emitting element according to this embodiment will be described with reference to Figure 32, focusing on the differences from the nitride-based semiconductor light-emitting element 800 according to Embodiment 8.

[0179] Figure 32 is a schematic cross-sectional view showing the overall configuration of the nitride-based semiconductor light-emitting element 900 according to this embodiment. As shown in Figure 32, the nitride-based semiconductor light-emitting element 900 according to this embodiment comprises a substrate 801, a semiconductor laminate 600S, a current blocking layer 110, a P-side electrode 111, and an N-side electrode 112. The semiconductor laminate 600S has a third buffer layer 523, a first buffer layer 521, second buffer layers 522a and 522b, an N-type cladding layer 602, an N-side first guide layer 603, an N-side second guide layer 604, an active layer 105, a P-side first guide layer 606, an electron barrier layer 107, a P-type cladding layer 608, and a contact layer 109.

[0180] The substrate 801 according to this embodiment also has a plurality of separation grooves 801T formed therein. A semiconductor laminate 600S is stacked in the plurality of separation grooves 801T. Therefore, the same effects as in Embodiment 8 are achieved in this embodiment as well.

[0181] Furthermore, since the semiconductor laminate 600S according to this embodiment includes a first buffer layer 521, second buffer layers 522a and 522b, and a third buffer layer 523, it achieves the same effects as in Embodiment 6.

[0182] (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.

[0183] For example, in each of the above embodiments, the Al composition ratio of the electron barrier layer was uniform within the layer, but the electron barrier layer may have a region in which the Al composition ratio gradually increases as it moves upward (i.e., as it approaches the P-type cladding layer). Configurations in which the Al composition ratio increases monotonically also include configurations that include a region in which the Al composition ratio is constant in the stacking direction. For example, configurations in which the Al composition ratio increases monotonically also include configurations in which the Al composition ratio increases in a step-like manner. For example, the electron barrier layer may include an Al composition ratio change region in which the Al composition ratio increases monotonically as it approaches the P-type cladding layer in the stacking direction, and an Al composition ratio constant region in which the Al composition ratio is constant in the stacking direction. The Al composition ratio change region is located, for example, at the end of the electron barrier layer closer to the active layer, and the Al composition ratio constant region is located at the end of the electron barrier layer closer to the P-type cladding layer. In the Al composition ratio change region, the Al composition ratio increases at a constant rate of change as it approaches the P-type cladding layer in the stacking direction. Specifically, the region where the Al composition ratio changes is at a film thickness of 3 nm, and near the interface on the side closer to the active layer, Al 0.04 Ga0 .96 Having a composition represented by N, the Al composition ratio increases monotonically as it approaches the region with a constant Al composition ratio, and near the interface with the region with a constant Al composition ratio, Al 0.36 Ga 0.64 It has a composition represented by N. The region with a constant Al composition ratio has a film thickness of 2 nm, and throughout the entire region, Al 0.36 Ga 0.64 It has a composition represented by N. The electron barrier layer contains impurities at a concentration of 1 × 10⁻⁶. 19 cm -3 It is doped with magnesium.

[0184] In this way, the electron barrier layer has a region where the Al composition ratio changes monotonically, which reduces the potential barrier in the valence band of the electron barrier layer compared to when the Al composition ratio is uniform. Therefore, holes flow more easily from the P-type cladding layer to the active layer. Consequently, the increase in electrical resistance of the nitride semiconductor light-emitting device can be suppressed. This allows for a reduction in the operating voltage of the nitride semiconductor light-emitting device. Furthermore, since self-heating during operation of the nitride semiconductor light-emitting device can be reduced, the temperature characteristics of the nitride semiconductor light-emitting device can be improved. Consequently, high-power operation of the nitride semiconductor light-emitting device becomes possible.

[0185] Furthermore, in the above embodiments, the Al composition ratios of the N-type cladding layer and the P-type cladding layer were the same, but they do not necessarily have to be the same. For example, the Al composition ratio of the N-type cladding layer may be smaller than that of the P-type cladding layer. As a result, the refractive index of the N-type cladding layer becomes larger than that of the P-type cladding layer, so that the light intensity distribution in the stacking direction can be shifted toward the N-type cladding layer. Note that the N-type cladding layer and the P-type cladding layer may be, for example, a superlattice layer consisting of a multilayer film of thin films of GaN and AlGaN. In this case, the Al composition ratio of each cladding layer is expressed as the average Al composition ratio of the entire superlattice layer.

[0186] Furthermore, although the above embodiments show examples where the nitride-based semiconductor light-emitting element is a semiconductor laser element, 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.

[0187] In each of the above embodiments, the nitride semiconductor light-emitting device had a structure including one well layer as the structure of the active layer 105, but a structure including a plurality of well layers may also be used.

[0188] In addition, the nitride semiconductor light-emitting device according to each of the above embodiments includes the electron barrier layer 107 and the current blocking layer 110, but these layers are not necessarily provided.

[0189] In the nitride semiconductor light-emitting device according to each of the above embodiments, at least one of the barrier layer, the N-side guide layer (such as the N-side first guide layer and the N-side second guide layer), the P-side first guide layer, the P-side second guide layer, and the N-type clad layer may be formed of AlGaInN. By using AlGaInN, at least a part of the tensile strain in the semiconductor laminate can be offset, so that the occurrence of cracks can be reduced. In particular, by using AlGaInN that generates compressive strain as AlGaInN, the effect of offsetting the tensile strain in the semiconductor laminate becomes greater. For example, it is conceivable to use AlGaInN that generates compressive strain only for the N-side guide layer (such as the N-side first guide layer and the N-side second guide layer), and use AlGaN for other layers (barrier layer, P-side guide layer, N-type clad layer).

[0190] In addition, forms obtained by applying various modifications conceivable by those skilled in the art to each of the above embodiments, and forms realized by arbitrarily combining the components and functions in each of the above embodiments without departing from the spirit of the present disclosure are also included in the present disclosure.

Industrial Applicability

[0191] The nitride semiconductor light-emitting device of the present disclosure can be applied, for example, as a high-output and high-efficiency light source to a light source for a processing machine.

Explanation of Signs

[0192] 100, 200, 300, 400, 500, 500A, 500B, 500C, 600, 700, 800, 900 Nitride-based semiconductor light-emitting devices 100F, 100R end face 100S, 200S, 300S, 400S, 500S, 500AS, 500BS, 500CS, 600S, 700S, 800S semiconductor laminates 101, 801 circuit boards 101M Base material 102, 602 N-type cladding layer 103, 603 N-side first guide layer 104, 604 N-side second guide layer 105, 205 active layer 105a, 105c barrier layer 105b, 205b well layers 106, 206, 406, 606 P-side first guide layer 107 Electron barrier layer 108,608 P-type cladding layers 108R, 608R Ridge 108T, 608T groove 109 Contact Layer 110 Current Blocking Layer 111 P side electrode 112 N side electrode 313 Hole barrier layer 414 P-side second guide layer 521 First Buffer Layer 522a, 522b Second buffer layer 523 Third Buffer Layer 740 N-side guide layer 801T separation groove

Claims

1. N-type cladding layer, An N-side first guide layer is positioned above the aforementioned N-type cladding layer, An N-side second guide layer is positioned above the N-side first guide layer, An active layer having a well layer and a barrier layer is positioned above the N-side second guide layer, The active layer comprises a P-type cladding layer positioned above the active layer, The band gap energy of the barrier layer is greater than the band gap energies of the N-side first guide layer and the N-side second guide layer, The band gap energy of the N-side second guide layer is smaller than the band gap energy of the N-side first guide layer. The band gap energy of the N-side first guide layer is smaller than the band gap energy of the N-type cladding layer. The N-type cladding layer, the N-side first guide layer, the N-side second guide layer, the barrier layer, and the P-type cladding layer are made of a nitride-based semiconductor containing Al. Nitride semiconductor light-emitting element.

2. A nitride-based semiconductor light-emitting element, N-type cladding layer, An N-side first guide layer is positioned above the aforementioned N-type cladding layer, An N-side second guide layer is positioned above the N-side first guide layer, An active layer having a well layer and a barrier layer is positioned above the N-side second guide layer, The active layer comprises a P-type cladding layer positioned above the active layer, The band gap energy of the barrier layer is greater than the band gap energy of the N-side second guide layer. The band gap energy of the N-side second guide layer is smaller than the band gap energy of the N-side first guide layer. The band gap energy of the N-side first guide layer is smaller than the band gap energy of the N-type cladding layer. The N-type cladding layer, the N-side first guide layer, the N-side second guide layer, the barrier layer, and the P-type cladding layer are made of a nitride-based semiconductor containing Al. The aforementioned N-type cladding layer is laminated on top of a substrate made of GaN. The nitride-based semiconductor light-emitting device is Displaced between the substrate and the N-type cladding layer, a first buffer layer containing In is provided. The third buffer layer, which contains Al, is disposed between the substrate and the first buffer layer. Nitride semiconductor light-emitting element.

3. The band gap energy of the barrier layer is greater than the average band gap energy of the N-side first guide layer and the N-side second guide layer. Nitride-based semiconductor light-emitting element according to claim 1 or 2.

4. The aforementioned barrier layer is Al ｂ Ga １－ｂ N consists of (0 < b ≤ 1) Nitride-based semiconductor light-emitting element according to any one of claims 1 to 3.

5. The N-side first guide layer is Al Ｘｎ１ Ga １－Ｘｎ１ N consists of (0 < Xn1 ≤ 1) Nitride-based semiconductor light-emitting element according to any one of claims 1 to 4.

6. The N-side second guide layer is Al Ｘｎ２ Ga １－Ｘｎ２ N consists of (0 ≤ Xn² ≤ 1) Nitride-based semiconductor light-emitting element according to any one of claims 1 to 5.

7. The thickness of the N-side second guide layer is thicker than the thickness of the N-side first guide layer. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 6.

8. The impurity concentration of the N-side first guide layer is higher than the impurity concentration of the N-side second guide layer. Nitride-based semiconductor light-emitting element according to any one of claims 1 to 7.

9. N-type cladding layer, An N-side guide layer is positioned above the aforementioned N-type cladding layer, An active layer, which is positioned above the N-side guide layer and includes a well layer and a barrier layer, A P-type cladding layer is positioned above the aforementioned active layer, A P-side first guide layer is disposed between the active layer and the P-type cladding layer, The system comprises an electron barrier layer disposed between the P-side first guide layer and the P-type cladding layer, The band gap energy of the barrier layer is greater than the average band gap energy of the N-side guide layer. The band gap energy of the N-type cladding layer is greater than the average band gap energy of the N-side guide layer. The band gap energy at the lower end of the N-side guide layer is greater than the band gap energy at the upper end. The N-type cladding layer, the N-side guide layer, the barrier layer, and the P-type cladding layer are made of a nitride-based semiconductor containing Al. The band gap energy of the P-type cladding layer is greater than the band gap energy of the P-side first guide layer. The band gap energy of the P-side first guide layer is greater than the average band gap energy of the N-side guide layer. The P-side first guide layer and the electron barrier layer are made of a nitride-based semiconductor containing Al. Nitride semiconductor light-emitting element.

10. A nitride-based semiconductor light-emitting element, N-type cladding layer, An N-side guide layer is positioned above the aforementioned N-type cladding layer, An active layer, which is positioned above the N-side guide layer and includes a well layer and a barrier layer, The active layer comprises a P-type cladding layer positioned above the active layer, The band gap energy of the barrier layer is greater than the average band gap energy of the N-side guide layer. The band gap energy of the N-type cladding layer is greater than the average band gap energy of the N-side guide layer. The band gap energy at the lower end of the N-side guide layer is greater than the band gap energy at the upper end. The N-type cladding layer, the N-side guide layer, the barrier layer, and the P-type cladding layer are made of a nitride-based semiconductor containing Al. The aforementioned N-type cladding layer is laminated on top of a substrate made of GaN. The nitride-based semiconductor light-emitting device is Displaced between the substrate and the N-type cladding layer, a first buffer layer containing In is provided. The third buffer layer, which contains Al, is disposed between the substrate and the first buffer layer. Nitride semiconductor light-emitting element.

11. A P-side first guide layer is disposed between the active layer and the P-type cladding layer, The system comprises an electron barrier layer disposed between the P-side first guide layer and the P-type cladding layer, The band gap energy of the P-type cladding layer is greater than the band gap energy of the P-side first guide layer. The band gap energy of the P-side first guide layer is greater than the average band gap energy of the N-side guide layer. The P-side first guide layer and the electron barrier layer are made of a nitride-based semiconductor containing Al. Nitride-based semiconductor light-emitting element according to claim 10.

12. The aforementioned N-type cladding layer is Al Ｘｎｃ Ga １－Ｘｎｃ Consists of N, The N-side guide layer is made of AlGaN, The barrier layer is Al ｂ Ga １－ｂ and consists of N The first guide layer on the P side is made of AlGaN, The aforementioned electron barrier layer is Al Ｘｄ Ga １－Ｘｄ Consists of N, The aforementioned P-type cladding layer is Al Ｘｐｃ Ga １－Ｘｐｃ Consists of N, If we denote the average Al composition ratio of the N-side guide layer as Xn and the average Al composition ratio of the P-side first guide layer as Xp1, b>Xn, Xp1≧Xn, Xnc>Xn, Xpc>Xp1 The relationship holds true. The nitride-based semiconductor light-emitting element according to claim 11.

13. The N-side guide layer comprises an N-side first guide layer made of AlGaN and an N-side second guide layer made of AlGaN, which is disposed between the N-side first guide layer and the active layer. If the Al composition ratio of the first guide layer on the N side is denoted as Xn1, and the Al composition ratio of the second guide layer on the N side is denoted as Xn2, Xn1 > Xn2 The relationship holds true. The nitride-based semiconductor light-emitting element according to claim 12.

14. The thickness of the N-side second guide layer is thicker than the thickness of the N-side first guide layer. The nitride-based semiconductor light-emitting element according to claim 13.

15. The electron barrier layer has a region in which the Al composition ratio gradually increases as it extends upward. The nitride-based semiconductor light-emitting element according to any one of claims 11 to 14.

16. The P-type cladding layer includes a low-concentration region located below the vertical center within the P-type cladding layer, where the impurity concentration is lower than in other areas of the P-type cladding layer. A nitride-based semiconductor light-emitting element according to any one of claims 9 to 15.

17. The Al composition ratio Xnc of the N-type cladding layer is smaller than the Al composition ratio Xpc of the P-type cladding layer. Nitride-based semiconductor light-emitting element according to any one of claims 9 to 16.

18. The thickness of the well layer is 10 nm or more. Nitride-based semiconductor light-emitting element according to any one of claims 9 to 17.

19. The aforementioned N-type cladding layer is laminated on top of a substrate made of GaN. The nitride-based semiconductor light-emitting element according to claim 1.

20. Displaced between the substrate and the N-type cladding layer, the first buffer layer includes In. The nitride-based semiconductor light-emitting element according to claim 19.

21. The first buffer layer comprises a second buffer layer made of GaN, which is disposed on at least one main surface of the first buffer layer. The nitride-based semiconductor light-emitting element according to claim 20.

22. A third buffer layer containing Al is disposed between the substrate and the first buffer layer. Nitride-based semiconductor light-emitting element according to claim 20 or 21.

23. Multiple separation grooves are formed in the substrate. The N-type cladding layer, the active layer, and the P-type cladding layer are laminated in the plurality of separation grooves. Nitride-based semiconductor light-emitting element according to any one of claims 19 to 22.

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