Semiconductor laser element

Abstract

To provide a semiconductor laser device that can reduce the operating voltage while suppressing the occurrence of cracks in a semiconductor laminate. 【Solution means】The semiconductor laser device 100 includes a substrate 101 made of Al Xs Ga 1-Xs N (0 < Xs < 1), and a semiconductor laminate 100S disposed above the substrate 101. The semiconductor laminate 100S includes an n-type clad layer 103, an active layer 105 having a quantum well structure disposed above the n-type clad layer 103, and an Al Xpc Ga 1-Xpc N (0 ≦ Xpc ≦ 1)-containing p-type clad layer 110 disposed above the active layer 105. The Al composition ratio of the p-type clad layer 110 gradually decreases as it moves away from the active layer 105. The Al composition ratio of the substrate 101 is smaller than the Al composition ratio at the end face closer to the active layer 105 of the p-type clad layer 110 and larger than the Al composition ratio at the end face farther from the active layer 105 of the p-type clad layer 110.

Description

[Technical Field]

[0001] This disclosure relates to semiconductor laser devices. [Background technology]

[0002] Conventionally, semiconductor laser elements comprising an Al-containing nitride semiconductor layer as a cladding layer are known (see, for example, Patent Document 1 and Patent Document 2).

[0003] The semiconductor laser elements described in Patent Documents 1 and 2 comprise an active layer, a guide layer, and a p-type cladding layer. The Al composition ratio of the p-type cladding layer decreases as it moves away from the guide layer. As a result, negative polarization charges due to spontaneous polarization are distributed within the p-type cladding layer. Consequently, positive charges, or holes, are formed to counteract these negative polarization charges. This increases the concentration of holes within the p-type cladding layer, thereby promoting hole injection into the active layer. By promoting hole injection into the active layer in this way, a reduction in the operating voltage of the semiconductor laser element can be expected. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-98401 [Patent Document 2] Japanese Patent Publication No. 2021-184456 [Overview of the project] [Problems that the invention aims to solve]

[0005] For example, in the semiconductor laser device described in Patent Document 2, when an AlN substrate is used as the substrate, a semiconductor laminate including a cladding layer made of AlGaN having a lattice constant larger than that of AlN is epitaxially grown on the AlN substrate. Therefore, in-plane compressive strain of the semiconductor layer is applied to the cladding layer. Since tensile strain in the stacking direction is generated due to this in-plane compressive strain, positive polarization charges (piezoelectric polarization charges) are generated, and at least a part of the negative polarization charges generated in the p-type cladding layer is canceled out. Therefore, the holes generated along with the negative polarization charges are reduced. Thus, since the holes in the p-type cladding layer are reduced, it becomes difficult for holes to be injected into the active layer.

[0006] On the other hand, when a GaN substrate is used instead of the AlN substrate as the substrate, in-plane tensile strain is applied to a cladding layer made of AlGaN having a lattice constant smaller than that of GaN. Since compressive strain in the stacking direction is generated due to this in-plane tensile strain, negative polarization charges (piezoelectric polarization charges) are generated. Along with this, the concentration of holes generated along with the generation of polarization charges is increased. However, since a large in-plane tensile stress of the semiconductor layer is applied to the semiconductor laminate including the cladding layer, cracks are likely to occur in the semiconductor laminate.

[0007] Therefore, the present disclosure provides a semiconductor laser device that can reduce the operating voltage while suppressing the generation of cracks in the semiconductor laminate.

Means for Solving the Problem

[0008] In order to solve the above problems, one aspect of the semiconductor laser device according to the present disclosure includes a substrate made of Al Xs Ga 1-Xs N (0 < Xs < 1) and a semiconductor laminate disposed above the substrate. The semiconductor laminate includes an n-type cladding layer, an active layer having a quantum well structure disposed above the n-type cladding layer, and an Al Xpc Ga 1-XpcThe substrate has a p-type cladding layer containing N(0≦Xpc≦1), the Al composition ratio of the p-type cladding layer gradually decreases as it moves away from the active layer, and the Al composition ratio of the substrate is smaller than the Al composition ratio of the p-type cladding layer at the end face closer to the active layer and larger than the Al composition ratio of the p-type cladding layer at the end face farther from the active layer. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a semiconductor laser element that can reduce the operating voltage while suppressing the occurrence of cracks in a semiconductor stack. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic plan view showing the overall configuration of the semiconductor laser element according to Embodiment 1. [Figure 2] This is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element according to Embodiment 1. [Figure 3] This is a schematic cross-sectional view showing the configuration of the active layer of the semiconductor laser element according to Embodiment 1. [Figure 4] This graph shows the distribution of polarization charge in the stacking direction of a semiconductor laser element according to Comparative Example 1. [Figure 5] This graph shows the distribution of polarization charge in the stacking direction of a semiconductor laser element according to Embodiment 1. [Figure 6] This graph shows the distribution of in-plane strain in the stacking direction of a semiconductor laser element according to Comparative Example 2. [Figure 7] This graph shows the distribution of in-plane strain in the stacking direction of a semiconductor laser element according to Embodiment 1. [Figure 8] This graph shows the distribution of in-plane stress in the stacking direction of a semiconductor laser element according to Comparative Example 2. [Figure 9] This graph shows the distribution of in-plane stress in the stacking direction of a semiconductor laser element according to Embodiment 1. [Figure 10] This graph shows the distribution of in-plane stress in the stacking direction of a semiconductor laser element according to Comparative Example 2. [Figure 11] This graph shows the distribution of in-plane stress in a semiconductor laser element according to Embodiment 1, in the stacking direction. [Figure 12] This graph shows the current-voltage (IV) characteristics of each semiconductor laser element according to Comparative Example 1 and Embodiment 1. [Figure 13] This is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element according to Embodiment 2. [Figure 14] This figure shows examples of materials that can be used as translucent conductive films. [Figure 15] This is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to Embodiment 3. [Figure 16] This is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to Embodiment 5. [Figure 17] This is a schematic cross-sectional view showing the configuration of the active layer of the semiconductor laser element according to Embodiment 5. [Figure 18] This is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to Embodiment 6. [Figure 19] This is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element according to Embodiment 7. [Figure 20] This graph shows the distribution of in-plane strain in the stacking direction of a semiconductor laser element according to Embodiment 7. [Figure 21] This graph shows the distribution of in-plane stress in the stacking direction of a semiconductor laser element according to Embodiment 7. [Figure 22] This graph shows the distribution of in-plane stress in a semiconductor laser element according to Embodiment 7, in the stacking direction. [Figure 23] This is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to Embodiment 8. [Figure 24] This is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to Embodiment 9. [Figure 25] This is a schematic cross-sectional view showing the configuration of the active layer of the semiconductor laser element according to Embodiment 9. [Modes for carrying out the invention]

[0011] 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.

[0012] 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.

[0013] Furthermore, in this specification, the terms "above" and "below" do not refer to vertically above and vertically below in absolute spatial perception, but rather to terms defined by relative positional relationships based on the stacking order in a stacked configuration. Moreover, the terms "above" and "below" 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.

[0014] Furthermore, in this specification, terms indicating relationships between elements such as parallel, perpendicular, and equal, as well as terms indicating the shape of elements, and numerical ranges, are not expressions that represent only strict meanings, but rather expressions that include substantially equivalent ranges, such as differences of a few percent.

[0015] (Embodiment 1) A semiconductor laser element according to Embodiment 1 will be described.

[0016] [1-1. Overall Structure] First, the overall configuration of the semiconductor laser element according to this embodiment will be explained using Figures 1 to 3. Figures 1 and 2 are schematic plan and cross-sectional views, respectively, showing the overall configuration of the semiconductor laser element 100 according to this embodiment. Figure 2 shows a cross-section along line II-II in Figure 1. Figure 3 is a schematic cross-sectional view showing the configuration of the active layer 105 of the semiconductor laser element 100 according to this embodiment. Figure 3 shows a cross-section of the active layer 105 at the same position as in Figure 2. 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 semiconductor laser 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.

[0017] As shown in Figure 2, the semiconductor laser element 100 comprises a semiconductor stack 100S 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 semiconductor laser element 100 has two end faces 100F and 100R that form a resonator. End face 100F is the front end face from which the laser light is emitted, and end face 100R is the rear end face with a higher reflectivity than end face 100F. The semiconductor laser element 100 also has a waveguide formed between end face 100F and end face 100R. For example, the reflectivity of end face 100F and end face 100R are 16% and 95%, respectively. The resonator length of the semiconductor laser element 100 according to this embodiment (i.e., the distance between end face 100F and end face 100R) is, for example, 800 μm. The semiconductor laser element 100 emits, for example, ultraviolet light. Alternatively, the semiconductor laser element 100 may emit light having a peak wavelength in a wavelength band other than ultraviolet light.

[0018] As shown in Figure 2, the semiconductor laser element 100 comprises a substrate 101 and a semiconductor laminate 100S. In this embodiment, the semiconductor laser element 100 further comprises a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0019] The semiconductor laminate 100S is a laminate in which semiconductor layers are laminated and is disposed above the substrate 101. As shown in FIG. 2, the semiconductor laminate 100S has a ridge 110R that protrudes upward. Further, in the semiconductor laminate 100S, two grooves 110T that are disposed along the ridge 110R on both sides of the ridge 110R and extend in the Y-axis direction, and two protrusions 110P that protrude upward are formed. One groove 110T is disposed between the ridge 110R and one protrusion 110P, and the other groove 110T is disposed between the ridge 110R and the other protrusion 110P.

[0020] The semiconductor laminate 100S according to the present embodiment includes an n-type clad layer 103, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, an intermediate layer 107, an electron barrier layer 108, a p-type clad layer 110, and a contact layer 114.

[0021] The substrate 101 is a plate-like member that serves as a base of the semiconductor laser element 100. The substrate 101 is disposed below the n-type clad layer 103 and is made of Al Xs Ga 1-Xs N (0 < Xs < 1). In the present embodiment, the substrate 101 is an n-type Al 0.55 Ga 0.45 N substrate having a thickness of 80 μm doped with Si as an n-type impurity.

[0022] The n-type clad layer 103 is a clad layer disposed above the substrate 101. The n-type clad layer 103 has a refractive index smaller than that of the active layer 105 and a large average bandgap energy. The n-type clad layer 103 may be an n-type Al Xnc Ga 1-Xnc N (0 < Xnc < 1) layer doped with Si. In the present embodiment, the n-type clad layer 103 is an n-type Al 0.55 Ga 0.45 N layer having a film thickness of 1 μm doped with Si.

[0023] Here, in the present disclosure, the average bandgap energy of a certain layer refers to the value obtained by integrating the magnitude of the bandgap energy at a certain position in the stacking direction of the layer from the position of the interface on the substrate side in the stacking direction of the layer to the position of the interface on the side far from the substrate in the stacking direction, and then dividing by the film thickness of the layer (the distance between the interface on the substrate side and the interface on the side far from the substrate). In the present disclosure, the average bandgap energy of a certain layer is also simply referred to as the bandgap energy.

[0024] The average refractive index of a certain layer refers to the value obtained by integrating the magnitude of the refractive index at a certain position in the stacking direction of the layer from the position of the interface on the substrate side in the stacking direction of the layer to the position of the interface on the side far from the substrate in the stacking direction, and then dividing by the film thickness of the layer (the distance between the interface on the substrate side and the interface on the side far from the substrate). In the present disclosure, the average refractive index of a certain layer is also simply referred to as the refractive index.

[0025] The average Al composition ratio of a certain layer refers to the value obtained by integrating the magnitude of the Al composition ratio at a certain position in the stacking direction of the layer from the position of the interface on the substrate side in the stacking direction of the layer to the position of the interface on the side far from the substrate in the stacking direction, and then dividing by the film thickness of the layer (the distance between the interface on the substrate side and the interface on the side far from the substrate). In the present disclosure, the average Al composition ratio of a certain layer is also simply referred to as the Al composition ratio.

[0026] The n-side guide layer 104 is an optical guide layer disposed above the n-type cladding layer 103. In the present embodiment, the n-side guide layer 104 is disposed between the n-type cladding layer 103 and the active layer 105 and contains Al. The n-side guide layer 104 has a refractive index greater than that of the n-type cladding layer 103 and a smaller bandgap energy. The n-side guide layer 104 is an Al Xng Ga 1-Xng N (0 < Xng < 1) layer may be used. In the present embodiment, the n-side guide layer 104 is an undoped Al 0.45 Ga 0.55 N layer with a film thickness of 158 nm.

[0027] The active layer 105 is disposed above the n-type cladding layer 103 and is a light-emitting layer having a quantum well structure. The active layer 105 has one or more well layers and a plurality of barrier layers. In the present embodiment, the active layer 105 has a single quantum well (SQW) structure. Further, the active layer 105 is disposed above the n-side guide layer 104. Also, in the present embodiment, the active layer 105 emits ultraviolet light. As shown in FIG. 3, the active layer 105 has an SQW structure and includes a well layer 105b and barrier layers 105a and 105c. The well layer 105b is disposed between the two barrier layers 105a and 105c. Note that the configuration of the active layer 105 is not limited to this. For example, the active layer 105 may have a multiple quantum well structure. Specifically, the active layer 105 may have three or more barrier layers and two or more well layers.

[0028] Each of the barrier layers 105a and 105c is a semiconductor layer that is disposed above the n-side guide layer 104 and functions as a barrier of the quantum well structure. The barrier layer 105c is disposed above the barrier layer 105a. That is, the barrier layer 105a is an example of an n-side barrier layer that is disposed at the position closest to the substrate 101 among the plurality of barrier layers 105a and 105c included in the active layer 105. The barrier layer 105c is an example of a p-side barrier layer that is disposed at the position farthest from the substrate 101 among the plurality of barrier layers 105a and 105c included in the active layer 105.

[0029] In the present embodiment, the band gap energy of each of the barrier layers 105a and 105c is larger than the band gap energy of the well layer 105b and smaller than the band gap energy of the electron barrier layer 108. The band gap energy of the barrier layer 105a may be equal to the band gap energy of the barrier layer 105c. Each of the barrier layers 105a and 105c may be a nitride semiconductor layer containing Al. More specifically, each of the barrier layers 105a and 105c may be made of AlGaN. That is, the barrier layer 105a is an undoped Al Xb1 Ga 1-Xb1 N (0 < Xb1 ≦ 1) layer, and the barrier layer 105c is an undoped Al Xb2 Ga 1-Xb2It may be an N (0 < Xb2 ≤ 1) layer. In the present embodiment, each of the barrier layers 105a and 105c is an undoped Al 0.45 Ga 0.55 N layer.

[0030] The well layer 105b is disposed above the barrier layer 105a and is a nitride semiconductor layer that functions as a well of a quantum well structure. The well layer 105b is disposed between the barrier layer 105a and the barrier layer 105c. The well layer 105b may be an undoped Al Xw Ga 1-Xw N (0 ≤ Xw < 1) layer. In the present embodiment, the well layer 105b is an undoped Al 0.35 Ga 0.65 N layer.

[0031] The p-side guide layer 106 is an optical guide layer disposed above the active layer 105. In the present embodiment, the p-side guide layer 106 is disposed between the active layer 105 and the p-type clad layer 110 and contains Al. In the present embodiment, the p-side guide layer 106 is disposed between the active layer 105 and the electron barrier layer 108. The p-side guide layer 106 has a refractive index larger than that of the p-type clad layer 110 and a smaller bandgap energy. The p-side guide layer 106 may be an Al Xpg Ga 1-Xpg N (0 < Xpg < 1) layer. In the present embodiment, the p-side guide layer 106 is an undoped Al 0.45 Ga 0.55 N layer.

[0032] The intermediate layer 107 is a semiconductor layer disposed between the p-side guide layer 106 and the p-type clad layer 110. The intermediate layer 107 is disposed between the p-side guide layer 106 and the p-type clad layer 110 and is an example of a composition gradient layer whose composition changes in the stacking direction. In the present embodiment, the intermediate layer 107 is disposed between the p-side guide layer 106 and the electron barrier layer 108 and is made of AlGaN. More specifically, the intermediate layer 107 is an undoped Al Xpi Ga 1-XpiIt is an N (0 < Xpi < 1) layer, and the Al composition ratio Xpi of the intermediate layer 107 gradually increases as it moves away from the active layer 105. In the present embodiment, the intermediate layer 107 is an undoped Al with a film thickness of 20 nm Xpi Ga 1-Xpi It is an N (0 < Xpi < 1) layer. The Al composition ratio Xpi of the intermediate layer 107 is 0.55 at the end face closer to the active layer 105 and 0.65 at the end face farther from the active layer 105.

[0033] In the present disclosure, the gradual increase includes not only a configuration that continuously increases but also a configuration that increases stepwise. Also, in the present disclosure, the gradual decrease includes not only a configuration that continuously decreases but also a configuration that decreases stepwise.

[0034] The electron barrier layer 108 is a semiconductor layer disposed between the active layer 105 and the p-type clad layer 110. In the present embodiment, the electron barrier layer 108 is disposed between the p-side guide layer 106 and the p-type clad layer 110. Also, the electron barrier layer 108 is disposed between the intermediate layer 107 and the p-type clad layer 110. The bandgap energy of the electron barrier layer 108 is larger than the bandgap energy of the barrier layer 105c. Thereby, leakage of electrons from the active layer 105 to the p-type clad layer 110 can be suppressed. The bandgap energy of the electron barrier layer 108 may be larger than the bandgap energy of each of the p-side guide layer 106 and the p-type clad layer 110. Further, the bandgap energy of the electron barrier layer 108 may be larger than the maximum bandgap energy of each of the p-side guide layer 106 and the p-type clad layer 110.

[0035] In the present embodiment, the electron barrier layer 108 is disposed between the p-side guide layer 106 and the p-type clad layer 110 and is an example of a compositionally graded layer whose composition changes in the stacking direction. The electron barrier layer 108 is made of AlGaN. More specifically, the electron barrier layer 108 is Al Xeb Ga 1-XebIt is an N(0 < Xeb < 1) layer, and the Al composition ratio Xeb of the electron barrier layer 108 gradually increases as it moves away from the active layer 105. In the present embodiment, the electron barrier layer 108 is an undoped Al with a thickness of 10 nm Xeb Ga 1-Xeb N(0 < Xeb < 1) layer. The Al composition ratio Xeb of the electron barrier layer 108 is 0.65 at the end face closer to the active layer 105 and 0.75 at the end face farther from the active layer 105.

[0036] The p-type cladding layer 110 is a cladding layer disposed above the active layer 105. The p-type cladding layer 110 contains Al Xpc Ga 1-Xpc N(0 ≦ Xpc ≦ 1). In the present embodiment, the p-type cladding layer 110 is disposed above the electron barrier layer 108. The p-type cladding layer 110 has a refractive index smaller than that of the active layer 105 and a larger bandgap energy. The bandgap energy of the p-type cladding layer 110 is smaller than the bandgap energy of the electron barrier layer 108.

[0037] In the present embodiment, the p-type cladding layer 110 is a p-type Al Xpc Ga 1-Xpc N(0 ≦ Xpc ≦ 1) layer. The Al composition ratio of the p-type cladding layer 110 gradually decreases as it moves away from the active layer 105. Also, the Al composition ratio of the substrate 101 is smaller than the Al composition ratio at the end face closer to the active layer 105 of the p-type cladding layer 110 and larger than the Al composition ratio at the end face farther from the active layer 105 of the p-type cladding layer 110. Also, the Al composition ratios of the plurality of barrier layers 105a and 105c are larger than the Al composition ratio at the end face farther from the active layer 105 of the p-type cladding layer 110. Also, the average Al composition ratio of the p-type cladding layer 110 is larger than the Al composition ratio of the n-type cladding layer 103. In the present embodiment, the p-type cladding layer 110 includes a first p-type cladding layer 111 and a second p-type cladding layer 112 disposed above the first p-type cladding layer 111.

[0038] The first p-type cladding layer 111 is a p-type Al disposed above the active layer 105 Xpc1 Ga 1-Xpc1It is an N(0 < Xpc1 < 1) layer. The Al composition ratio of the first p-type clad layer 111 gradually decreases as it moves away from the active layer 105. In this embodiment, the first p-type clad layer 111 is a p-type Al Xpc1 [Ga 1-Xpc1 ]N layer with a thickness of 261 nm doped with Mg. Xpc1 Ga 1-Xpc1 The Al composition ratio Xpc1 of the first p-type clad layer 111 is 0.9 at the end face closer to the active layer 105 and 0.45 at the end face farther from the active layer 105.

[0039] The first p-type clad layer 111 has a first portion 111a and a second portion 111b disposed above the first portion 111a. The lattice constant of the first portion 111a is less than or equal to the lattice constant of the substrate 101. In this embodiment, the first portion 111a is a p-type Al Xpc1 [Ga 1-Xpc1 ]N layer with a thickness of 203 nm doped with Mg. Xpc1 Ga 1-Xpc1 The Al composition ratio Xpc1 of the first portion 111a is 0.9 at the end face closer to the active layer 105 and 0.55 at the end face farther from the active layer 105. The lattice constant of the second portion 111b is greater than or equal to the lattice constant of the substrate 101. In this embodiment, the second portion 111b is a p-type Al Xpc1 [Ga 1-Xpc1 ]N layer with a thickness of 58 nm doped with Mg. Xpc1 Ga 1-Xpc1 The Al composition ratio Xpc1 of the second portion 111b is 0.55 at the end face closer to the active layer 105 and 0.45 at the end face farther from the active layer 105.

[0040] The second p-type clad layer 112 is a p-type Al Xpc2 [Ga 1-Xpc2 ]N(0 ≦ Xpc2 < 1) layer disposed above the first p-type clad layer 111. The Al composition ratio of the second p-type clad layer 112 gradually decreases as it moves away from the active layer 105. In this embodiment, the second p-type clad layer 112 is a p-type Al Xpc2 [Ga 1-Xpc2 ]N layer with a thickness of 75 nm doped with Mg. Xpc2 Ga 1-Xpc2 The Al composition ratio Xpc2 of the second p-type clad layer 112 is 0.45 at the end face closer to the active layer 105 and 0 at the end face farther from the active layer 105. Xpc2 Ga 1-Xpc2 ​

[0041] The contact layer 114 is a nitride semiconductor layer positioned above the p-type cladding layer 110 and making ohmic contact with the p-side electrode 131. In this embodiment, the contact layer 114 is a Mg-doped p-type GaN layer with a thickness of 10 nm.

[0042] In this embodiment, ridges 110R, grooves 110T, and protrusions 110P are formed on the p-type cladding layer 110 and the contact layer 114. As shown in Figure 2, the width of the ridge 110R (ridge width) (in the X-axis direction) is represented by W. The ridge width W is, for example, 45 μm. The distance between the lower end 110Rb of the ridge 110R and the electron barrier layer 108 (in other words, the end face of the p-type cladding layer 110 closer to the active layer 105) is represented by dc. In this embodiment, the distance dc is 45 nm. The lower end 110Rb is located in the p-type cladding layer 110. More specifically, the lower end 110Rb is located in the first portion 111a of the first p-type cladding layer 111. Furthermore, the Al composition ratio of the p-type cladding layer 110 at the lower end 110Rb is greater than the Al composition ratio of the substrate 101.

[0043] The center of the ridge 110R in the stacking direction is located in the p-type cladding layer 110. The dimensions of the ridge 110R in the stacking direction (i.e., the height from the bottom edge 110Rb to the top surface 110Ru of the ridge 110R) are 301 nm. The Al composition ratio of the p-type cladding layer 110 at the center of the ridge 110R in the stacking direction is greater than the Al composition ratio of the substrate 101.

[0044] Here, if the lower end of the ridge 110R is below the electron barrier layer 108, the electron barrier layer 108 acts as a potential barrier to the electrical conduction of holes from the ridge 110R to the active layer 105. As a result, a leakage current is generated due to holes leaking out of the ridge 110R from the portion of the electron barrier layer 108 corresponding to the side surface of the ridge 110R. Consequently, the semiconductor laser element 100 deteriorates. Therefore, in order to suppress such deterioration, the lower end of the ridge 110R may be located above the electron barrier layer 108.

[0045] Since the electron barrier layer 108 is an AlGaN layer with a high Al composition ratio, it acts as a potential barrier to hole injection from the p-type cladding layer 110 to the active layer 105. Therefore, when the distance dc is large, the proportion of holes injected from the ridge 110R that flow outside the ridge 110R at the lower end of the ridge 110R increases. Holes that flow outside the ridge 110R in this way do not contribute to the generation and amplification of laser light from the semiconductor laser element 100. Therefore, the oscillation threshold current value of the semiconductor laser element 100 increases. Specifically, the oscillation threshold current value increases when the distance dc is 70 nm or more. To suppress the increase in the oscillation threshold current value, the distance dc should be as small as possible. To suppress the oscillation threshold current value of the semiconductor laser element 100, the distance dc may be, for example, between 10 nm and 70 nm.

[0046] The current blocking layer 120 is positioned above the p-type cladding layer 110 and is an insulating layer that is transparent to light from the active layer 105. The current blocking layer 120 is positioned on the upper surfaces of the p-type cladding layer 110 and the contact layer 114, excluding the upper surface 110Ru. In other words, the current blocking layer 120 is positioned on the upper surfaces of the two protrusions 110P, on the ridge 110R side of each of the two protrusions 110P, at the bottom of the groove 110T, and on the side of the ridge 110R (i.e., the end face of the ridge 110R in the X-axis direction). The current blocking layer 120 may also be positioned in a part of the upper surface 110Ru. For example, the current blocking layer 120 may be positioned in the edge region of the upper surface 110Ru. In this embodiment, the current blocking layer 120 is an SiO2 layer.

[0047] The p-side electrode 131 is an electrode that is in contact with the semiconductor laminate 100S above the semiconductor laminate 100S. In this embodiment, the p-side electrode 131 is positioned above the contact layer 114. The p-side electrode 131 is positioned on the upper surface 110Ru and is in contact with the contact layer 114 on the upper surface 110Ru. In this embodiment, the p-side electrode 131 is positioned above the contact layer 114 and the current blocking layer 120. The p-side electrode 131 is, for example, a single-layer or multilayer film formed of at least one of Ag, Al, Pd, Cr, Ti, Ni, Pt, and Au. The p-side electrode 131 may be made of Ag, Al, or an alloy containing at least one of Ag and Al. By making the p-side electrode 131 out of a metal with a low refractive index, waveguide loss of the semiconductor laser element 100 can be reduced. In this embodiment, the p-side electrode 131 is made of Pd. Furthermore, an adhesion layer made of Ti or the like, a barrier metal layer made of Pt or the like, and a pad electrode made of Au or the like may be sequentially formed on the p-side electrode 131.

[0048] The n-side electrode 141 is a conductive layer positioned below 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 141 is, for example, a single-layer or multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au. A bonding layer made of Ti, a barrier metal layer made of Pt, and a pad electrode made of Au may be sequentially formed on the n-side electrode 141.

[0049] [1-2. Effects] The effects of the semiconductor laser element 100 according to this embodiment will be explained using Figures 4 to 12, in comparison with the semiconductor laser elements according to Comparative Examples 1 and 2.

[0050] Figures 4 and 5 are graphs showing the distribution of polarization charge in the stacking direction for each semiconductor laser element according to Comparative Example 1 and this embodiment, respectively. Figures 4 and 5 show the spontaneous polarization charge (dashed line), the polarization charge due to strain (dotted line), and the total polarization charge (solid line) for each semiconductor laser element. The horizontal axis in Figures 4 and 5 indicates the position in the stacking direction. The vertical axis in Figures 4 and 5 indicates the polarization charge.

[0051] Figures 6 and 7 are graphs showing the stacking direction distribution of in-plane strain for each semiconductor laser element according to Comparative Example 2 and this embodiment, respectively. Here, the in-plane direction is the direction parallel to the plane perpendicular to the stacking direction of the semiconductor laser element. Figures 8 and 9 are graphs showing the stacking direction distribution of in-plane stress for each semiconductor laser element according to Comparative Example 2 and this embodiment, respectively. Figures 10 and 11 are graphs showing the stacking direction distribution of integrated in-plane stress for each semiconductor laser element according to Comparative Example 2 and this embodiment, respectively. Figures 10 and 11 show the integrated in-plane stress from the substrate to each position in the stacking direction of the semiconductor stack (i.e., the value obtained by integrating the in-plane stress at each position in the stacking direction of the semiconductor stack in the stacking direction). Hereafter, integrated in-plane stress will also be simply referred to as integrated stress. Note that in Figures 6 to 11, tensile strain and tensile stress are represented by negative values, and compressive strain and compressive stress are represented by positive values. Figure 12 is a graph showing the current-voltage (IV) characteristics of each semiconductor laser element according to Comparative Example 1 and this embodiment.

[0052] The semiconductor laser element according to Comparative Example 1 differs from the semiconductor laser element 100 according to this embodiment in that it comprises an AlN substrate 2101 and does not have an intermediate layer 107 and an electron barrier layer 108, but is otherwise identical. The semiconductor laser element according to Comparative Example 2 differs from the semiconductor laser element 100 according to this embodiment in that it comprises a GaN substrate 2201 and does not have an intermediate layer 107 and an electron barrier layer 108, but is otherwise identical.

[0053] The semiconductor laser element according to Comparative Example 1 has a p-type cladding layer 110, similar to the semiconductor laser element 100 according to this embodiment. The Al composition ratio of the p-type cladding layer 110 decreases as it moves away from the guide layer. As a result, negative polarization charges (spontaneous polarization charges) are distributed within the p-type cladding layer 110, as shown in Figure 4.

[0054] On the other hand, in the semiconductor laser element according to Comparative Example 1, since AlGaN has a larger lattice constant than the substrate 2101 made of AlN, compressive strain is applied to the p-type cladding layer 110. As a result, as shown in Figure 4, positive polarization charges are generated in the p-type cladding layer 110 of the semiconductor laser element according to Comparative Example 1 due to the strain. Since the positive polarization charges generated by the strain cancel out some of the negative spontaneous polarization charges, the total polarization charge in the p-type cladding layer 110 becomes smaller than the spontaneous polarization charge. Consequently, the concentration of holes generated by the polarization charges in the p-type cladding layer 110 is reduced. As a result, as shown in Figure 12, the operating voltage of the semiconductor laser element according to Comparative Example 1 increases.

[0055] Furthermore, in the semiconductor laser element according to Comparative Example 2, the AlGaN, which makes up the majority of the semiconductor laminate, has a smaller lattice constant than the GaN substrate 2201, and as shown in Figure 6, tensile strain is applied to the semiconductor laminate. In other words, as shown in Figure 8, tensile stress is applied to the semiconductor laminate. As shown in Figure 10, the integral stress applied to the entire semiconductor laminate is -7021.5 Pa·m. In the semiconductor laser element according to Comparative Example 2, as described above, a large tensile strain is applied to the semiconductor laminate, making it prone to crack formation. In other words, the reliability of the semiconductor laser element is reduced.

[0056] In the semiconductor laser element 100 according to this embodiment, the Al composition ratio of the substrate 101 is smaller than the Al composition ratio of the p-type cladding layer 110 at the end face closer to the active layer 105, and larger than the Al composition ratio of the p-type cladding layer 110 at the end face further from the active layer 105. As a result, the Al composition ratio of the p-type cladding layer 110 is approximately the same as that of the substrate 101, and as shown in Figure 7, tensile strain is applied to a part of the p-type cladding layer 110 (i.e., the first part 111a), and compressive strain is applied to the other parts of the p-type cladding layer 110 (i.e., the second part 111b and the second p-type cladding layer 112). In other words, as shown in Figure 9, tensile stress is applied to a part of the p-type cladding layer 110 (i.e., the first part 111a), and compressive stress is applied to the other parts of the p-type cladding layer 110 (i.e., the second part 111b and the second p-type cladding layer 112). As a result, as shown in Figure 11, the integral stress applied to the entire semiconductor laminate 100S is 222.6 Pa·m. Thus, in this embodiment, no in-plane tensile stress is applied to the semiconductor laminate 100S, and a small in-plane compressive stress is applied. Therefore, compared to the semiconductor laser element according to Comparative Example 2, the occurrence of cracks in the semiconductor laminate 100S can be suppressed in the semiconductor laser element 100 according to this embodiment.

[0057] Furthermore, as shown in Figure 5, in the semiconductor laser element 100 according to this embodiment, the positive polarization charge generated by strain is small, so the decrease in negative spontaneous polarization charge can be suppressed. In other words, the decrease in total polarization charge in the semiconductor laminate can be suppressed. Consequently, the reduction in the concentration of holes generated by polarization charge in the p-type cladding layer 110 can be suppressed. As a result, as shown in Figure 12, the semiconductor laser element 100 according to this embodiment can reduce the operating voltage compared to the semiconductor laser element according to Comparative Example 1.

[0058] Furthermore, in the semiconductor laser element 100 according to this embodiment, the semiconductor laminate 100S is arranged between the n-type cladding layer 103 and the active layer 105 and has an n-side guide layer 104 containing Al.

[0059] By including Al in the n-side guide layer 104, the refractive index of the n-side guide layer 104 is reduced. This increases the optical confinement coefficient to the active layer 105 of the semiconductor laser element 100, thereby reducing the oscillation threshold current. Furthermore, the inclusion of Al in the n-side guide layer 104 increases the bandgap energy of the n-side guide layer 104, thus reducing leakage current. Consequently, the temperature characteristics of the semiconductor laser element 100 can be improved.

[0060] Furthermore, in the semiconductor laser element 100 according to this embodiment, the semiconductor laminate 100S is arranged between the active layer 105 and the p-type cladding layer 110 and has a p-side guide layer 106 containing Al.

[0061] By including Al in the p-side guide layer 106, the refractive index of the p-side guide layer 106 is reduced. This increases the optical confinement coefficient to the active layer 105 of the semiconductor laser element 100, thereby reducing the oscillation threshold current. Furthermore, the inclusion of Al in the p-side guide layer 106 increases the bandgap energy of the p-side guide layer 106, thus reducing leakage current. Consequently, the temperature characteristics of the semiconductor laser element 100 can be improved.

[0062] Furthermore, in the semiconductor laser element 100 according to this embodiment, the semiconductor laminate 100S has an electron barrier layer 108 disposed between the active layer 105 and the p-type cladding layer 110.

[0063] This suppresses electron leakage from the active layer 105 to the p-type cladding layer 110, thereby improving the temperature characteristics of the semiconductor laser element 100.

[0064] Furthermore, in the semiconductor laser element 100 according to this embodiment, the multiple barrier layers 105a and 105c contain Al.

[0065] This allows for an increase in the bandgap energy of the multiple barrier layers 105a and 105c, thereby enhancing the effect of confining electrons in the well layer 105b. Consequently, the temperature characteristics of the semiconductor laser element 100 can be improved.

[0066] Furthermore, in the semiconductor laser element 100 according to this embodiment, the Al composition ratio of the multiple barrier layers 105a and 105c is greater than the Al composition ratio at the end face of the p-type cladding layer 110 that is farther from the active layer 105.

[0067] This allows the overall Al composition ratio of the p-type cladding layer 110 to be greater than the Al composition ratio of the multiple barrier layers 105a and 105c. Therefore, the electrical resistance of the p-type cladding layer 110 can be reduced, and thus the operating voltage of the semiconductor laser element 100 can be reduced.

[0068] Furthermore, in the semiconductor laminate 100S of the semiconductor laser element 100 according to this embodiment, if the in-plane tensile stress occurring in layers with a lattice constant smaller than that of the substrate 101 is represented by a negative stress, and the in-plane compressive stress occurring in layers with a lattice constant larger than that of the substrate 101 is represented by a positive stress, then the integral value (integral stress) of the in-plane stress in the stacking direction of the semiconductor laminate 100S is -900 Pa·m or more.

[0069] This suppresses the occurrence of cracks in the semiconductor laminate 100S. Furthermore, it suppresses cracking of the wafer, which is the base material of the substrate 101, during the manufacturing of the semiconductor laser element 100. Additionally, by setting the integrated stress to -400 Pa·m or higher and 400 Pa·m or lower, warping of the substrate 101 and the wafer can be suppressed. Therefore, handling of the wafer during processing steps such as the individualization of the semiconductor laser element 100 becomes easier.

[0070] Furthermore, in the semiconductor laser element 100 according to this embodiment, the average Al composition ratio of the p-type cladding layer 110 is greater than the Al composition ratio of the n-type cladding layer 103.

[0071] This reduces the refractive index of the ridge 110R, thereby reducing the effective refractive index difference between the ridge 110R and the area outside the ridge 110R (i.e., the area outside the ridge 110R in the width direction of the ridge 110R). Consequently, it becomes easier to cut off higher-order transverse modes, making it easier to realize a semiconductor laser element 100 that performs single-transverse-mode operation.

[0072] Furthermore, in the semiconductor laser element 100 according to this embodiment, a ridge 110R is formed on the semiconductor laminate 100S.

[0073] This allows the current to be confined within the ridge 110R and a waveguide to be formed.

[0074] Furthermore, in the semiconductor laser element 100 according to this embodiment, the lower end 110Rb is located in the p-type cladding layer 110, and the Al composition ratio of the p-type cladding layer 110 at the lower end 110Rb may be greater than the Al composition ratio of the substrate 101.

[0075] (Embodiment 2) A semiconductor laser element according to Embodiment 2 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 100 according to Embodiment 1 mainly in that a translucent conductive film is arranged on top of the semiconductor laminate. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 100 according to Embodiment 1.

[0076] [2-1. Overall Structure] The semiconductor laser element according to this embodiment will be described with reference to Figure 13. Figure 13 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element 200 according to this embodiment. In Figure 13, similar to Figure 2, a cross-section perpendicular to the laser beam emission direction of the semiconductor laser element 200 is shown.

[0077] As shown in Figure 13, the semiconductor laser element 200 according to this embodiment comprises a substrate 201, a semiconductor laminate 200S, a current blocking layer 120, a translucent conductive film 232, a p-side electrode 231, and an n-side electrode 141.

[0078] The semiconductor laminate 200S according to this embodiment includes an n-type cladding layer 203, an n-side guide layer 204, an active layer 105, a p-side guide layer 106, an intermediate layer 107, an electron barrier layer 108, a p-type cladding layer 210, and a contact layer 114.

[0079] The substrate 201 according to this embodiment is an 80 μm thick n-type Al doped with Si as an n-type impurity. 0.5 Ga 0.5 This is an N substrate.

[0080] The n-type cladding layer 203 in this embodiment is an n-type Al doped with Si and with a film thickness of 1 μm. 0.45 Ga 0.55 It is an N-type cladding layer. In this embodiment, the Al composition ratio of the n-type cladding layer 203 is smaller than the Al composition ratio of the substrate 201. The n-side guide layer 204 in this embodiment is an undoped Al layer with a film thickness of 158 nm. 0.4 Ga 0.6 It is an N-layer structure.

[0081] The p-type cladding layer 210 according to this embodiment has a first p-type cladding layer 211 and a second p-type cladding layer 212 positioned above the first p-type cladding layer 211.

[0082] The first p-type cladding layer 211 in this embodiment is a p-type Al doped with Mg and with a thickness of 99 nm. Xpc1 Ga 1-Xpc1 This is an N layer. The Al composition ratio Xpc1 of the first p-type cladding layer 211 is 0.9 at the end face closer to the active layer 105 and 0.45 at the end face further away from the active layer 105.

[0083] The first p-type cladding layer 211 has a first portion 211a and a second portion 211b positioned above the first portion 211a. The lattice constant of the first portion 211a is less than or equal to the lattice constant of the substrate 201. In this embodiment, the first portion 211a is a p-type Al doped with Mg and with a film thickness of 88 nm. Xpc1 Ga 1-Xpc1 This is an N layer. The Al composition ratio Xpc1 of the first portion 211a is 0.9 at the end face closer to the active layer 105 and 0.5 at the end face further from the active layer 105. In this embodiment, the second portion 211b is a p-type Al layer with a thickness of 11 nm and doped with Mg. Xpc1 Ga 1-Xpc1 This is the N layer. The Al composition ratio Xpc1 of the second portion 211b is 0.5 at the end face closer to the active layer 105 and 0.45 at the end face further away from the active layer 105.

[0084] The second p-type cladding layer 212 in this embodiment is a p-type Al doped with Mg and with a film thickness of 40 nm. Xpc2 Ga 1-Xpc2 This is an N layer. The Al composition ratio Xpc2 of the second p-type cladding layer 212 is 0.45 at the end face closer to the active layer 105 and 0 at the end face further away from the active layer 105.

[0085] In this embodiment, ridges 210R, grooves 210T, and protrusions 210P are formed on the p-type cladding layer 210 and the contact layer 114. In this embodiment, as in Embodiment 1, the ridge width W is 45 μm, and the distance dc between the lower end 210Rb of the ridge 210R and the electron barrier layer 108 is 45 nm. The center of the ridge 210R in the stacking direction is located in the p-type cladding layer 210. The dimension of the ridge 210R in the stacking direction (i.e., the height from the lower end 210Rb to the upper surface 210Ru of the ridge 210R) is 94 nm. The Al composition ratio of the p-type cladding layer 210 at the center of the ridge 210R in the stacking direction is smaller than the Al composition ratio of the substrate 201.

[0086] The translucent conductive film 232 is a conductive film positioned above the semiconductor laminate 200S. The translucent conductive film 232 is translucent to laser light emitted from the semiconductor laser element 200. The translucent conductive film 232 is positioned between the semiconductor laminate 200S and the p-side electrode 231. In this embodiment, the translucent conductive film 232 is positioned above the contact layer 114 and is in contact with the contact layer 114 and the p-side electrode 231. The translucent conductive film 232 is also positioned on the upper surface 210Ru. In this embodiment, the side surface (end face in the X-axis direction) of the translucent conductive film 232 is covered by the current blocking layer 120. The thickness of the translucent conductive film 232 may be greater than the thickness of the p-type cladding layer 210. In this embodiment, the thickness of the translucent conductive film 232 is 150 nm.

[0087] The band gap energy of the translucent conductive film 232 is greater than the band gap energy of the active layer 105. In other words, the band gap energy of the translucent conductive film 232 is greater than the band gap energy of the well layer 105b of the active layer 105. Examples of materials that can be used as the translucent conductive film 232 will be explained using Figure 14. Figure 14 shows examples of materials that can be used as the translucent conductive film 232. Figure 14 also shows the band gap energy (Eg) and refractive index of each material. Examples of materials that can be used as the translucent conductive film 232 include MgO, CaO, NiO, and Ta-doped Sn shown in Figure 14. X Ge 1-X By using materials such as O2, rutile-type GeO2 (r-GeO2), and rutile-type oxide semiconductor mixed crystal systems (GeO2-SnO2-SiO2), the translucent conductive film 232 can function as a cladding layer while suppressing laser light loss in the translucent conductive film 232.

[0088] In this embodiment, the p-side electrode 231 is positioned above the semiconductor laminate 200S and the translucent conductive film 232. In this embodiment, the p-side electrode 231 is made of Al.

[0089] [2-2. Effects] In the semiconductor laser element 200 according to this embodiment, similar to the semiconductor laser element 100 according to Embodiment 1, the Al composition ratio of the substrate 201 is smaller than the Al composition ratio at the end face of the p-type cladding layer 210 closer to the active layer 105, and larger than the Al composition ratio at the end face of the p-type cladding layer 210 further from the active layer 105. As a result, the Al composition ratio of the p-type cladding layer 210 becomes approximately the same as the Al composition ratio of the substrate 201, and tensile strain is applied to a part of the p-type cladding layer 210 (i.e., the first part 211a), while compressive strain is applied to the other parts of the p-type cladding layer 210 (i.e., the second part 211b and the second p-type cladding layer 212). In other words, tensile stress is applied to a part of the p-type cladding layer 210 (i.e., the first part 211a), and compressive stress is applied to the other parts of the p-type cladding layer 210 (i.e., the second part 211b and the second p-type cladding layer 212). As a result, the integral stress applied to the entire semiconductor laminate 200S becomes greater than 0 Pa·m. Thus, in this embodiment, no in-plane tensile stress is applied to the semiconductor laminate 200S, and a small in-plane compressive stress is applied. Therefore, compared to the semiconductor laser element according to Comparative Example 2 described above, the semiconductor laser element 200 according to this embodiment can suppress the occurrence of cracks in the semiconductor laminate 200S.

[0090] Furthermore, in the semiconductor laser element 200 according to this embodiment, the Al composition ratio of the n-type cladding layer 203 is smaller than the Al composition ratio of the substrate 201.

[0091] This makes it possible to make the refractive index of the substrate 201 smaller than that of the n-type cladding layer 203, thereby suppressing light leakage into the substrate 201. Consequently, the luminescence efficiency of the semiconductor laser element 200 can be improved.

[0092] Furthermore, since in-plane compressive strain is applied to the n-type cladding layer 203, the occurrence of wafer cracks and fractures during the crystal growth process and the wafer processing process of the substrate 201 can be suppressed. In addition, since the compressive strain in the well layer 105b can be increased, the bandgap energy in the well layer 105b can be increased. Therefore, the oscillation wavelength of the semiconductor laser element 200 can be shortened.

[0093] Furthermore, since the generation of spike-like potential distributions in the conduction charge at the interface between the substrate 201 and the n-type cladding layer 203 can be suppressed, the operating voltage of the semiconductor laser element 200 can be reduced.

[0094] Furthermore, in the semiconductor laser element 200 according to this embodiment, the center of the ridge 210R in the stacking direction of the semiconductor laminate 200S is located in the p-type cladding layer 210, and the Al composition ratio of the p-type cladding layer 210 at the center of the ridge 210R in the stacking direction of the semiconductor laminate 200S is smaller than the Al composition ratio of the substrate 201.

[0095] This reduces the tensile strain applied within the ridge 210R. Consequently, the maximum value of the applied stress can be reduced in the layer located near the edge of the lower end 210Rb in the width direction of the ridge 210R (part of the active layer 105, etc.).

[0096] Furthermore, the semiconductor laser element 200 according to this embodiment includes a translucent conductive film 232 positioned above the semiconductor laminate 200S.

[0097] This allows for a reduction in the light intensity at the end face of the translucent conductive film 232 that is farther from the p-type cladding layer 210, even when the thickness of the p-type cladding layer 210 is reduced. Consequently, the light loss at the p-side electrode 231 can be reduced.

[0098] Furthermore, in the semiconductor laser element 200 according to this embodiment, the thickness of the translucent conductive film 232 is greater than the thickness of the p-type cladding layer 210.

[0099] In this way, by reducing the thickness of the p-type cladding layer 210, light absorption and electrical resistance in the p-type cladding layer 210 can be reduced. Furthermore, since the stress applied to the p-type cladding layer 210 can be reduced, cracking of the wafer, which is the base material of the substrate 201, and the occurrence of cracks in the wafer and semiconductor laminate 200S can be reduced.

[0100] (Embodiment 3) A semiconductor laser element according to Embodiment 3 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 100 according to Embodiment 1 mainly in the configuration of the p-type cladding layer. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 100 according to Embodiment 1.

[0101] [3-1. Overall Structure] The semiconductor laser element according to this embodiment will be described with reference to Figure 15. Figure 15 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element 300 according to this embodiment. In Figure 15, similar to Figure 2, a cross-section perpendicular to the laser beam emission direction of the semiconductor laser element 300 is shown.

[0102] As shown in Figure 15, the semiconductor laser element 300 according to this embodiment comprises a substrate 101, a semiconductor laminate 300S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0103] The semiconductor laminate 300S according to this embodiment includes an n-type cladding layer 103, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, an intermediate layer 107, an electron barrier layer 108, a p-type cladding layer 310, and a contact layer 114.

[0104] The p-type cladding layer 310 according to this embodiment has a first p-type cladding layer 111 and a second p-type cladding layer 312 positioned above the first p-type cladding layer 111.

[0105] The second p-type cladding layer 312 in this embodiment is a p-type Al doped with Mg and with a film thickness of 105 nm. Xpc2 Ga 1-Xpc2 This is an N layer. The Al composition ratio Xpc2 of the second p-type cladding layer 312 is 0.45 at the end face closer to the active layer 105 and 0 at the end face further away from the active layer 105.

[0106] In this embodiment, ridges 310R, grooves 310T, and protrusions 310P are formed on the p-type cladding layer 310 and the contact layer 114. In this embodiment, as in Embodiment 1, the ridge width W is 45 μm, and the distance dc between the lower end 310Rb of the ridge 310R and the electron barrier layer 108 is 45 nm. The center of the ridge 310R in the stacking direction is located in the p-type cladding layer 310. The dimension of the ridge 310R in the stacking direction (i.e., the height from the lower end 310Rb to the upper surface 310Ru of the ridge 310R) is 331 nm. The Al composition ratio of the p-type cladding layer 310 at the center of the ridge 310R in the stacking direction is smaller than the Al composition ratio of the substrate 101.

[0107] [3-2. Effects] In the semiconductor laser element 300 according to this embodiment, similar to the semiconductor laser element 100 according to Embodiment 1, the Al composition ratio of the substrate 101 is smaller than the Al composition ratio at the end face of the p-type cladding layer 310 closer to the active layer 105, and larger than the Al composition ratio at the end face of the p-type cladding layer 310 further from the active layer 105. As a result, the Al composition ratio of the p-type cladding layer 310 becomes approximately the same as the Al composition ratio of the substrate 101, so that tensile strain is applied to a part of the p-type cladding layer 310 (i.e., the first part 111a) and compressive strain is applied to the other parts of the p-type cladding layer 310 (i.e., the second part 111b and the second p-type cladding layer 312). In other words, tensile stress is applied to a part of the p-type cladding layer 310 (i.e., the first part 111a), and compressive stress is applied to the other parts of the p-type cladding layer 310 (i.e., the second part 111b and the second p-type cladding layer 312). As a result, the integral stress applied to the entire semiconductor laminate 300S becomes 299.3 Pa·m. Thus, in this embodiment, the semiconductor laminate 300S is no longer subjected to in-plane tensile stress, and a small in-plane compressive stress is applied. Therefore, compared to the semiconductor laser element according to Comparative Example 2 described above, the semiconductor laser element 300 according to this embodiment can suppress the occurrence of cracks in the semiconductor laminate 300S.

[0108] Furthermore, in the semiconductor laser element 300 according to this embodiment, the center of the ridge 310R in the stacking direction of the semiconductor laminate 300S is located in the p-type cladding layer 310, and the Al composition ratio of the p-type cladding layer 310 at the center of the ridge 310R in the stacking direction of the semiconductor laminate 300S is smaller than the Al composition ratio of the substrate 101.

[0109] This reduces the tensile strain applied within the ridge 310R. Consequently, the maximum value of the applied stress can be reduced in the layer located near the edge of the lower end 310Rb in the width direction of the ridge 310R (part of the active layer 105, etc.).

[0110] (Embodiment 4) A semiconductor laser element according to Embodiment 4 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 300 according to Embodiment 3 in the configuration of the substrate. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 300 according to Embodiment 3.

[0111] The semiconductor laser element according to this embodiment comprises a substrate 101, a semiconductor laminate 300S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0112] In this embodiment, the substrate 101 is doped with Ge as an n-type impurity. 18 cm -3 Ge is doped into the substrate. Furthermore, Si is doped into the substrate 101 as an n-type impurity, and the Si concentration in the substrate 101 may be lower than the Ge concentration. 17 cm -3 Even if the Si is doped.

[0113] When growing a substrate 101 made of Si-doped AlGaN, Si readily reacts with Al, so Al and Si tend to bond together during crystal growth. This leads to uneven Si concentration in the substrate 101, which in turn makes it easier for through-dislocations to occur. Consequently, strain and piezoelectric polarization in the AlGaN cladding layers of the semiconductor laminate 300S tend to be uneven. In contrast, Ge reacts less readily with Al than Si, allowing for a more uniform Ge concentration in the substrate 101. This suppresses the generation of through-dislocations in the substrate 101. For example, if the dislocation density in the substrate 101 is 1 × 10⁻⁶, 4 cm -2 The following is possible. In this embodiment, the dislocation density is 1 × 10⁻⁶ 3 cm -2Consequently, it is possible to suppress the non-uniformity of strain and piezoelectric polarization in each cladding layer made of AlGaN in the semiconductor laminate 300S.

[0114] (Embodiment 5) A semiconductor laser element according to Embodiment 5 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 300 according to Embodiment 3 in the configuration of the active layer. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 300 according to Embodiment 3.

[0115] [5-1. Overall Structure] The semiconductor laser element according to this embodiment will be described with reference to Figures 16 and 17. Figure 16 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element 500 according to this embodiment. In Figure 16, a cross-section perpendicular to the laser light emission direction of the semiconductor laser element 500 is shown, similar to Figure 2. Figure 17 is a schematic cross-sectional view showing the configuration of the active layer 505 provided in the semiconductor laser element 500 according to this embodiment.

[0116] As shown in Figure 16, the semiconductor laser element 500 according to this embodiment comprises a substrate 101, a semiconductor laminate 500S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0117] The semiconductor laminate 500S according to this embodiment includes an n-type cladding layer 103, an n-side guide layer 104, an active layer 505, a p-side guide layer 106, an intermediate layer 107, an electron barrier layer 108, a p-type cladding layer 310, and a contact layer 114.

[0118] The active layer 505 according to this embodiment, as shown in Figure 17, has one or more well layers 505b and a plurality of barrier layers 505a, 505c. In this embodiment, the active layer 505 has an SQW structure.

[0119] The barrier layer 505a is an example of an n-side barrier layer among multiple barrier layers 505a and 505c, which is positioned closest to the substrate 101. The barrier layer 505a has a first barrier layer 505a1 positioned below one or more well layers 505b, and a second barrier layer 505a2 positioned below the first barrier layer 505a1.

[0120] The first barrier layer 505a1 is an example of a first lower barrier layer located below one or more well layers 505b. In this embodiment, the first barrier layer 505a1 is made of undoped Al with a film thickness of 2 nm. 0.4 Ga 0.6 It is an N-layer structure.

[0121] The second barrier layer 505a2 is an example of a second lower barrier layer positioned below the first lower barrier layer. In this embodiment, the second barrier layer 505a2 is an undoped Al with a film thickness of 8 nm. 0.45 Ga 0.55 It is an N-layer structure.

[0122] The barrier layer 505c is an example of a p-side barrier layer among multiple barrier layers 505a and 505c, which is positioned furthest from the substrate 101. The barrier layer 505c has a first barrier layer 505c1 positioned above one or more well layers 505b, and a second barrier layer 505c2 positioned above the first barrier layer 505c1.

[0123] The first barrier layer 505c1 is an example of a first upper barrier layer positioned above one or more well layers 505b. In this embodiment, the first barrier layer 505c1 is an undoped aluminum layer with a thickness of 1 nm. 0.4 Ga 0.6 It is an N-layer structure.

[0124] The second barrier layer 505c2 is an example of a second upper barrier layer positioned above the first upper barrier layer. In this embodiment, the second barrier layer 505c2 is an undoped aluminum layer with a thickness of 8 nm. 0.45 Ga 0.55 It is an N-layer structure.

[0125] The well layer 505b is disposed between the barrier layer 505a and the barrier layer 505c. In the present embodiment, the well layer 505b is an undoped Al 0.35 Ga 0.65 N layer with a film thickness of 3 nm.

[0126] [5-2. Effect] In the semiconductor laser device 500 according to the present embodiment as well, similar to the semiconductor laser device 100 according to the first embodiment, the Al composition ratio of the substrate 101 is smaller than the Al composition ratio at the end face closer to the active layer 505 of the p-type clad layer 310, and larger than the Al composition ratio at the end face farther from the active layer 505 of the p-type clad layer 310. As a result, the Al composition ratio of the p-type clad layer 310 becomes approximately the same as the Al composition ratio of the substrate 101, tensile strain is applied to a part of the p-type clad layer 310 (that is, the first portion 111a), and compressive strain is applied to the other parts of the p-type clad layer 310 (that is, the second portion 111b and the second p-type clad layer 312). That is, tensile stress is applied to a part of the p-type clad layer 310 (that is, the first portion 111a), and compressive stress is applied to the other parts of the p-type clad layer 310 (that is, the second portion 111b and the second p-type clad layer 312). As a result, the integrated stress applied to the entire semiconductor laminate 500S is 302.9 Pa·m. Thus, in the semiconductor laminate 500S according to the present embodiment, in-plane tensile stress is not applied, and small in-plane compressive stress is applied. Therefore, compared with the semiconductor laser device according to Comparative Example 2 described above, in the semiconductor laser device 500 according to the present embodiment, the occurrence of cracks in the semiconductor laminate 500S can be suppressed.

[0127] Furthermore, in the semiconductor laser element 500 according to this embodiment, the active layer 505 has an SQW structure. Of the multiple barrier layers 505a and 505c, the average bandgap energy of the barrier layer 505a located closest to the substrate 101 is smaller than the average bandgap energy of the barrier layer 505c located furthest from the substrate 101. In this embodiment, the barrier layer 505a has a first barrier layer 505a1 located below the well layer 505b and a second barrier layer 505a2 located below the first barrier layer 505a1. The bandgap energy of the second barrier layer 505a2 is greater than the bandgap energy of the first barrier layer 505a1. In this embodiment, the barrier layer 505c has a first barrier layer 505c1 located above the well layer 505b and a second barrier layer 505c2 located above the first barrier layer 505c1. The band gap energy of the second barrier layer 505c2 is greater than the band gap energy of the first barrier layer 505c1. In this embodiment, barrier layer 505a has a first barrier layer 505a1 and a second barrier layer 505a2, and barrier layer 505c has a first barrier layer 505c1 and a second barrier layer 505c2. The first barrier layer 505a1 and the first barrier layer 505c1 have the same composition. The second barrier layer 505a2 and the second barrier layer 505c2 have the same composition and the same film thickness. In this embodiment, the above configuration regarding the average band gap energy is achieved by making the film thickness of the first barrier layer 505a1 thicker than the film thickness of the first barrier layer 505c1.

[0128] This configuration enhances the effect of confining light into the well layer 505b of the active layer 505, which has an SQW structure. Therefore, the luminescence efficiency of the semiconductor laser element 500 can be increased.

[0129] Furthermore, by making the bandgap energy of the first barrier layer 505a1 smaller than the bandgap energy of the first barrier layer 505c1, the average bandgap energy of the barrier layer 505a, which is located closest to the substrate 101, can be made smaller than the average bandgap energy of the barrier layer 505c, which is located furthest from the substrate 101.

[0130] (Embodiment 6) A semiconductor laser element according to Embodiment 6 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 300 according to Embodiment 3 in the shape of its ridge. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 300 according to Embodiment 3.

[0131] The semiconductor laser element according to this embodiment will be described with reference to Figure 18. Figure 18 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element 600 according to this embodiment. In Figure 18, similar to Figure 2, a cross-section perpendicular to the laser beam emission direction of the semiconductor laser element 600 is shown.

[0132] As shown in Figure 18, the semiconductor laser element 600 according to this embodiment comprises a substrate 101, a semiconductor laminate 300S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0133] In this embodiment, ridges 610R, grooves 310T, and protrusions 310P are formed on the p-type cladding layer 310 and the contact layer 114.

[0134] In this embodiment, the width Wb of the lower end 610Rb of the ridge 610R is greater than the width Wu of the upper end of the ridge 610R (i.e., the width of the upper surface 610Ru of the ridge 610R). In other words, the ridge 610R in this embodiment has a forward tapered shape, and its end face in the width direction is inclined. In this embodiment, the width Wb is 45 μm, and the inclination angle θr of the end face in the width direction of the ridge 610R is 60 degrees.

[0135] In the layer located near the end of the lower end 610Rb in the width direction of the ridge 610R (part of the active layer 105, etc.), the applied shear stress becomes locally large. In this embodiment, this localized shear stress can be reduced by inclining the end face in the width direction of the ridge 610R.

[0136] (Embodiment 7) A semiconductor laser element according to Embodiment 7 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 100 according to Embodiment 1 in the configuration of the substrate. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 100 according to Embodiment 1.

[0137] [7-1. Overall Structure] The semiconductor laser element according to this embodiment will be described with reference to Figure 19. Figure 19 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element 700 according to this embodiment. In Figure 19, similar to Figure 2, a cross-section perpendicular to the laser beam emission direction of the semiconductor laser element 700 is shown.

[0138] As shown in Figure 19, the semiconductor laser element 700 according to this embodiment comprises a substrate 701, a semiconductor laminate 100S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0139] The semiconductor laminate 100S according to this embodiment includes an n-type cladding layer 103, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, an intermediate layer 107, an electron barrier layer 108, a p-type cladding layer 110, and a contact layer 114.

[0140] The substrate 701 according to this embodiment is an 80 μm thick n-type Al doped with Si as an n-type impurity. 0.85 Ga 0.15 This is an N substrate.

[0141] The first p-type cladding layer 111 of the p-type cladding layer 110 has a first portion 711a whose lattice constant is less than or equal to the lattice constant of the substrate 701, and a second portion 711b whose lattice constant is greater than or equal to the lattice constant of the substrate 701. In this embodiment, the first portion 711a is p-type Al with a film thickness of 29 nm and doped with Mg. Xpc1 Ga 1-Xpc1 This is an N layer. The Al composition ratio Xpc1 of the first portion 711a is 0.9 at the end face closer to the active layer 105 and 0.85 at the end face further from the active layer 105. In this embodiment, the second portion 711b is a p-type Al doped with Mg and with a film thickness of 232 nm. Xpc1 Ga 1-Xpc1 This is an N layer. The Al composition ratio Xpc1 of the second portion 711b is 0.85 at the end face closer to the active layer 105 and 0.45 at the end face further away from the active layer 105. Also, the lower end 110Rb of the ridge 110R is located in the second portion 711b of the first p-type cladding layer 111. The Al composition ratio of the p-type cladding layer 110 at the lower end 110Rb is smaller than the Al composition ratio of the substrate 101.

[0142] [7-2. Effects] The effects of the semiconductor laser element 700 according to this embodiment will be explained using Figures 20 to 22. Figures 20, 21, and 22 are graphs showing the stacking direction distribution of in-plane strain, in-plane stress, and integrated in-plane stress of the semiconductor laser element 700 according to this embodiment, respectively.

[0143] In the semiconductor laser element 700 according to this embodiment, similar to the semiconductor laser element 100 according to Embodiment 1, the Al composition ratio of the substrate 701 is smaller than the Al composition ratio at the end face of the p-type cladding layer 110 closer to the active layer 105, and larger than the Al composition ratio at the end face of the p-type cladding layer 110 further from the active layer 105. As a result, the Al composition ratio of the p-type cladding layer 110 becomes approximately the same as the Al composition ratio of the substrate 701, and as shown in Figure 20, tensile strain is applied to a part of the p-type cladding layer 110 (i.e., the first part 711a), and compressive strain is applied to the other parts of the p-type cladding layer 310 (i.e., the second part 711b and the second p-type cladding layer 112). In other words, as shown in Figure 21, a tensile stress is applied to a part of the p-type cladding layer 310 (i.e., the first part 711a), and a compressive stress is applied to the other parts of the p-type cladding layer 310 (i.e., the second part 711b and the second p-type cladding layer 112). In this embodiment, because the lattice constant of the substrate 701 is small, the integral stress applied to the entire semiconductor laminate 100S is relatively large at 4343.0 Pa·m, as shown in Figure 22. However, because the stress applied to the semiconductor laminate 100S is compressive stress, the occurrence of cracks in the semiconductor laminate 100S can be suppressed compared to the case where tensile stress is applied.

[0144] Furthermore, in the semiconductor laser element 700 according to this embodiment, the center of the ridge 110R in the stacking direction of the semiconductor laminate 100S is located in the p-type cladding layer 110, and the Al composition ratio of the p-type cladding layer 110 at the center of the ridge 110R in the stacking direction of the semiconductor laminate 100S is smaller than the Al composition ratio of the substrate 701.

[0145] This reduces the tensile strain applied within the ridge 110R. Consequently, the maximum value of the applied stress can be reduced in the layer below the widthwise end of the ridge 110Rb at the lower end 110Rb.

[0146] (Embodiment 8) A semiconductor laser element according to Embodiment 8 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 300 according to Embodiment 3 in that it does not have a p-side guide layer. The following description of the semiconductor laser element according to this embodiment will focus on the differences from the semiconductor laser element 300 according to Embodiment 3.

[0147] [8-1. Overall Structure] The semiconductor laser element according to this embodiment will be described with reference to Figure 23. Figure 23 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser element 800 according to this embodiment. In Figure 23, similar to Figure 2, a cross-section perpendicular to the laser beam emission direction of the semiconductor laser element 800 is shown.

[0148] As shown in Figure 23, the semiconductor laser element 800 according to this embodiment comprises a substrate 101, a semiconductor laminate 800S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0149] The semiconductor laminate 800S according to this embodiment has an n-type cladding layer 103, an n-side guide layer 104, an active layer 105, an intermediate layer 107, an electron barrier layer 108, a p-type cladding layer 310, and a contact layer 114. Thus, the semiconductor laminate 800S does not have a p-side guide layer.

[0150] [8-2. Effects] In the semiconductor laser element 800 according to this embodiment, similar to the semiconductor laser element 100 according to Embodiment 1, the Al composition ratio of the substrate 101 is smaller than the Al composition ratio at the end face of the p-type cladding layer 310 closer to the active layer 105, and larger than the Al composition ratio at the end face of the p-type cladding layer 310 further from the active layer 105. As a result, the Al composition ratio of the p-type cladding layer 310 becomes approximately the same as the Al composition ratio of the substrate 101, so that tensile strain is applied to a part of the p-type cladding layer 310 (i.e., the first part 111a) and compressive strain is applied to the other parts of the p-type cladding layer 310 (i.e., the second part 111b and the second p-type cladding layer 312). In other words, tensile stress is applied to a part of the p-type cladding layer 310 (i.e., the first part 111a), and compressive stress is applied to the other parts of the p-type cladding layer 310 (i.e., the second part 111b and the second p-type cladding layer 312). As a result, the integral stress applied to the entire semiconductor laminate 800S becomes 173.9 Pa·m. Thus, in this embodiment, the semiconductor laminate 800S is no longer subjected to in-plane tensile stress, and instead is subjected to small in-plane compressive stress. Therefore, compared to the semiconductor laser element according to Comparative Example 2 described above, the semiconductor laser element 800 according to this embodiment can suppress the occurrence of cracks in the semiconductor laminate 800S.

[0151] (Embodiment 9) A semiconductor laser element according to Embodiment 9 will now be described. The semiconductor laser element according to this embodiment differs from the semiconductor laser element 300 according to Embodiment 3 in the configuration of each guide layer and the active layer. The following description will focus on the differences between the semiconductor laser element according to this embodiment and the semiconductor laser element 300 according to Embodiment 3.

[0152] [9-1. Overall Structure] The semiconductor laser device according to this embodiment will be described with reference to FIGS. 24 and 25. FIG. 24 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser device 900 according to this embodiment. In FIG. 24, a cross-section perpendicular to the emission direction of the laser light of the semiconductor laser device 900 is shown as in FIG. 2. FIG. 25 is a schematic cross-sectional view showing the configuration of the active layer 905 included in the semiconductor laser device 900 according to this embodiment.

[0153] As shown in FIG. 24, the semiconductor laser device 900 according to this embodiment includes a substrate 101, a semiconductor laminate 900S, a current blocking layer 120, a p-side electrode 131, and an n-side electrode 141.

[0154] The semiconductor laminate 900S according to this embodiment has an n-type clad layer 103, an n-side guide layer 904, an active layer 905, a p-side guide layer 906, an intermediate layer 107, an electron barrier layer 108, a p-type clad layer 310, and a contact layer 114.

[0155] The n-side guide layer 904 according to this embodiment is disposed between the n-type clad layer 103 and the active layer 905 and contains Al. The bandgap energy at the end face of the n-side guide layer 904 closer to the active layer 905 is smaller than the bandgap energy at the end face of the n-side guide layer 904 farther from the active layer 905. In this embodiment, the bandgap energy of the n-side guide layer 904 gradually increases as it moves away from the active layer 905. The n-side guide layer 904 is an undoped Al Xng Ga 1-Xng N (0 < Xng < 1) layer. The Al composition ratio Xng of the n-side guide layer 904 is 0.4 at the end face closer to the active layer 905 and 0.45 at the end face farther from the active layer 905. Note that the n-side guide layer 904 may be doped with n-type impurities.

[0156] As shown in FIG. 25, the active layer 905 according to this embodiment has one or more well layers 905b and a plurality of barrier layers 905a, 905c. In this embodiment, the active layer 905 has a SQW structure.

[0157] The barrier layer 905a is an example of an n-side barrier layer among multiple barrier layers 905a and 905c, which is positioned closest to the substrate 101. The barrier layer 905a has a first barrier layer 905a1 positioned below one or more well layers 905b, and a second barrier layer 905a2 positioned below the first barrier layer 905a1.

[0158] The first barrier layer 905a1 is an example of a first lower barrier layer located below one or more well layers 905b. In this embodiment, the first barrier layer 905a1 is made of undoped Al with a film thickness of 6 nm. 0.4 Ga 0.6 It is an N-layer structure.

[0159] The second barrier layer 905a2 is an example of a second lower barrier layer located below the first lower barrier layer. In this embodiment, the second barrier layer 905a2 is an undoped Al with a film thickness of 5 nm. 0.45 Ga 0.55 It is an N-layer structure.

[0160] The barrier layer 905c is an example of a p-side barrier layer among the multiple barrier layers 905a and 905c, which is positioned furthest from the substrate 101. In this embodiment, the barrier layer 905c is an undoped aluminum layer with a thickness of 3 nm. 0.45 Ga 0.55 It is an N-layer structure.

[0161] The well layer 905b is placed between the barrier layer 905a and the barrier layer 905c. In this embodiment, the well layer 905b is made of undoped aluminum with a film thickness of 4 nm. 0.35 Ga 0.65 It is an N-layer structure.

[0162] The p-side guide layer 906 according to this embodiment is disposed between the active layer 905 and the p-type clad layer 310 and contains Al. The bandgap energy at the end face closer to the active layer 905 of the p-side guide layer 906 is smaller than the bandgap energy at the end face farther from the active layer 905 of the p-side guide layer 906. In this embodiment, the bandgap energy of the p-side guide layer 906 gradually increases as it moves away from the active layer 905. The p-side guide layer 906 is an undoped Al Xpg Ga 1-Xpg N (0 < Xng < 1) layer. The Al composition ratio Xpg of the p-side guide layer 906 is 0.41 at the end face closer to the active layer 905 and 0.45 at the end face farther from the active layer 905.

[0163] [9-2. Effect] In the semiconductor laser element 900 according to this embodiment as well, similar to the semiconductor laser element 100 according to Embodiment 1, the Al composition ratio of the substrate 101 is smaller than the Al composition ratio at the end face closer to the active layer 905 of the p-type clad layer 310 and larger than the Al composition ratio at the end face farther from the active layer 905 of the p-type clad layer 310. As a result, the Al composition ratio of the p-type clad layer 310 becomes approximately the same as the Al composition ratio of the substrate 101, tensile strain is applied to a part of the p-type clad layer 310 (that is, the first part 111a), and compressive strain is applied to other parts of the p-type clad layer 310 (that is, the second part 111b and the second p-type clad layer 312). That is, tensile stress is applied to a part of the p-type clad layer 310 (that is, the first part 111a), and compressive stress is applied to other parts of the p-type clad layer 310 (that is, the second part 111b and the second p-type clad layer 312). As a result, the integrated stress applied to the entire semiconductor laminate 500S is 356.3 Pa·m. Thus, in the semiconductor laminate 900S according to this embodiment, in-plane tensile stress is not applied, and small in-plane compressive stress is applied. Therefore, compared with the semiconductor laser element according to Comparative Example 2 described above, in the semiconductor laser element 900 according to this embodiment, the occurrence of cracks in the semiconductor laminate 900S can be suppressed.

[0164] Furthermore, in the semiconductor laser element 900 according to this embodiment, the active layer 905 has an SQW structure. Of the multiple barrier layers 905a and 905c, the average bandgap energy of the barrier layer 905a located closest to the substrate 101 is smaller than the average bandgap energy of the barrier layer 905c located furthest from the substrate 101. In this embodiment, the barrier layer 905a has a first barrier layer 905a1 located below the well layer 905b and a second barrier layer 905a2 located below the first barrier layer 905a1. The bandgap energy of the second barrier layer 905a2 is greater than the bandgap energy of the first barrier layer 905a1.

[0165] This configuration enhances the effect of confining light from the active layer 905, which has an SQW structure, to the well layer 905b. Therefore, the luminescence efficiency of the semiconductor laser element 900 can be increased.

[0166] Furthermore, in the semiconductor laser element 900 according to this embodiment, the band gap energy at the end face of the n-side guide layer 904 closer to the active layer 905 is smaller than the band gap energy at the end face of the n-side guide layer 904 further from the active layer 905.

[0167] This n-side guide layer 904 can suppress the leakage of holes from the active layer 905 to the n-type cladding layer 103. Therefore, the temperature characteristics of the semiconductor laser element 900 can be improved.

[0168] Furthermore, the n-side guide layer 904 may be doped with n-type impurities.

[0169] This allows the energy of the conduction band in the n-side guide layer 904 to be aligned with the energy of the conduction band in the barrier layer 905a of the active layer 905. Therefore, leakage of holes from the active layer 905 to the n-type cladding layer 103 can be further suppressed.

[0170] Furthermore, in the semiconductor laser element 900 according to this embodiment, the band gap energy at the end face of the p-side guide layer 906 closer to the active layer 905 is smaller than the band gap energy at the end face of the p-side guide layer 906 further from the active layer 905.

[0171] The refractive index of the p-side guide layer 906 increases as it approaches the active layer 905. This allows the peak of the light intensity distribution in the stacking direction to be brought closer to the active layer 905. Therefore, it becomes easier to confine light to the active layer 905.

[0172] Furthermore, in the semiconductor laser element 900 according to this embodiment, the average band gap energy of the p-side guide layer 906 is greater than the average band gap energy of the n-side guide layer 904.

[0173] This makes it possible to make the average refractive index of the n-side guide layer 904 higher than the average refractive index of the p-side guide layer 906. Therefore, when using a substrate 101 with a relatively low refractive index, as in the semiconductor laser element 900 according to this embodiment, it is possible to suppress the bias of the light intensity distribution towards the p-side relative to the active layer 905.

[0174] (Torture, etc.) The semiconductor laser elements related to this disclosure have been described above based on various embodiments, but this disclosure is not limited to the above embodiments.

[0175] For example, in the embodiments described above, the semiconductor laser element is shown to be equipped with a resonator, but the semiconductor laser element does not need to be equipped with a resonator. For example, the semiconductor laser element may be a superluminescent diode.

[0176] Furthermore, this disclosure also includes forms obtained by applying various modifications to each of the above embodiments that a person skilled in the art could conceive, and forms realized by arbitrarily combining the components and functions of each of the above embodiments without departing from the spirit of this disclosure.

[0177] For example, the configuration of n-type impurities in the substrate according to Embodiment 4 may be applied to each substrate according to other embodiments.

[0178] Furthermore, the configuration of the ridge 610R according to the above embodiment 6 may be applied to each ridge according to the other embodiments. [Industrial applicability]

[0179] The semiconductor laser element of this disclosure can be applied, for example, as a high-power and high-efficiency light source for exposure equipment and processing machines. [Explanation of Symbols]

[0180] 100, 200, 300, 500, 600, 700, 800, 900 Semiconductor Laser Elements 100F, 100R end face 100S, 200S, 300S, 500S, 800S, 900S semiconductor stacks 101, 201, 701, 2101, 2201 circuit boards 103, 203 n-type cladding layers 104, 204, 904 n-side guide layer 105, 505, 905 active layer 105a, 105c, 505a, 505c, 905a, 905c barrier layer 105b, 505b, 905b well layer 106, 906 p-side guide layer 107 Middle Class 108 Electron barrier layer 110, 210, 310 p-type cladding layers 110P, 210P, 310P protrusion 110R, 210R, 310R, 610R Ridge 110Rb, 210Rb, 310Rb, 610Rb bottom end 110Ru, 210Ru, 310Ru, 610Ru top surface 110T, 210T, 310T groove 111, 211 First p-type cladding layer 111a, 211a, 711a first part 111b, 211b, 711b second part 112, 212, 312 Second p-type cladding layer 114 Contact Layer 120 Current Block Layer 131, 231 p side electrode 141 n-side electrode 232 Transparent conductive film 505a1, 505c1, 905a1 First barrier layer 505a2, 505c2, 905a2 second barrier layer

Claims

1. A semiconductor laser element, Al Ｘｓ Ga １－Ｘｓ A substrate consisting of N (0 < Xs < 1), The substrate comprises a semiconductor laminate disposed above the substrate, The semiconductor laminate is n-type cladding layer, An active layer having a quantum well structure is disposed above the aforementioned n-type cladding layer, Displaced above the active layer, Al Ｘｐｃ Ga １－Ｘｐｃ It has a p-type cladding layer containing N (0 ≤ Xpc ≤ 1), The Al composition ratio of the p-type cladding layer gradually decreases as it moves away from the active layer. The Al composition ratio of the substrate is smaller than the Al composition ratio at the end face of the p-type cladding layer closer to the active layer, and larger than the Al composition ratio at the end face of the p-type cladding layer further from the active layer. Semiconductor laser element.

2. The semiconductor laminate has an n-side guide layer containing Al, which is disposed between the n-type cladding layer and the active layer. The semiconductor laser element according to claim 1.

3. The band gap energy at the end face of the n-side guide layer closer to the active layer is smaller than the band gap energy at the end face of the n-side guide layer further from the active layer. The semiconductor laser element according to claim 2.

4. The n-side guide layer is doped with n-type impurities. The semiconductor laser element according to claim 3.

5. The semiconductor laminate has a p-side guide layer containing Al, which is disposed between the active layer and the p-type cladding layer. The semiconductor laser element according to claim 2.

6. The band gap energy at the end face of the p-side guide layer closer to the active layer is smaller than the band gap energy at the end face of the p-side guide layer further from the active layer. The semiconductor laser element according to claim 5.

7. The average bandgap energy of the p-side guide layer is greater than the average bandgap energy of the n-side guide layer. The semiconductor laser element according to claim 5 or 6.

8. The semiconductor laminate has an electron barrier layer disposed between the active layer and the p-type cladding layer. A semiconductor laser element according to any one of claims 1 to 7.

9. The active layer has one or more well layers and a plurality of barrier layers. The aforementioned multiple barrier layers include Al The semiconductor laser element according to claim 1.

10. The Al composition ratio of the plurality of barrier layers is greater than the Al composition ratio at the end face of the p-type cladding layer furthest from the active layer. The semiconductor laser element according to claim 9.

11. The active layer has a single quantum well structure consisting of one well layer and two barrier layers. Of the two barrier layers, the average bandgap energy of the n-side barrier layer, which is the barrier layer located closest to the substrate, is smaller than the average bandgap energy of the p-side barrier layer, which is the barrier layer located furthest from the substrate. The semiconductor laser element according to claim 1.

12. The n-side barrier layer is, A first barrier layer is located below the aforementioned well layer, It has a second barrier layer positioned below the first barrier layer, The band gap energy of the second barrier layer is greater than the band gap energy of the first barrier layer. The semiconductor laser element according to claim 11.

13. In the aforementioned semiconductor laminate, when the in-plane tensile stress occurring in a layer with a lattice constant smaller than that of the substrate is represented by a negative stress, and the in-plane compressive stress occurring in a layer with a lattice constant larger than that of the substrate is represented by a positive stress, the integral value of the in-plane stress in the stacking direction of the semiconductor laminate is -900 Pa·m or greater. A semiconductor laser element according to any one of claims 1 to 12.

14. The Al composition ratio of the n-type cladding layer is smaller than that of the substrate. The semiconductor laser element according to claim 1.

15. The average Al composition ratio of the p-type cladding layer is greater than the Al composition ratio of the n-type cladding layer. The semiconductor laser element according to claim 1.

16. Ridges are formed in the aforementioned semiconductor stack. The semiconductor laser element according to claim 1.

17. The lower end of the ridge is located in the p-type cladding layer. The Al composition ratio of the p-type cladding layer at the lower end is greater than the Al composition ratio of the substrate. The semiconductor laser element according to claim 16.

18. The center of the ridge in the stacking direction of the semiconductor laminate is located in the p-type cladding layer. The Al composition ratio of the p-type cladding layer at the center of the ridge in the stacking direction of the semiconductor laminate is smaller than the Al composition ratio of the substrate. The semiconductor laser element according to claim 16 or 17.

19. The width of the lower end of the ridge is greater than the width of the upper end of the ridge. The semiconductor laser element according to claim 16.

20. The semiconductor laminate is further provided with a translucent conductive film positioned above it. The semiconductor laser element according to claim 1.

21. The thickness of the light-transmitting conductive film is greater than the thickness of the p-type cladding layer. The semiconductor laser element according to claim 20.

22. The aforementioned substrate is doped with Ge as an n-type impurity. The semiconductor laser element according to claim 1.

23. The aforementioned substrate is further doped with Si as an n-type impurity. The Si concentration in the aforementioned substrate is lower than the Ge concentration. The semiconductor laser element according to claim 22.

24. The dislocation density of the substrate is 1 × 10 ４ cm －２ Less than The semiconductor laser element according to claim 22.

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