Semiconductor laser element

Abstract

Provided is a semiconductor laser element (100) comprising a substrate (101), a semiconductor laminate (100S) disposed above the substrate (101), and a p-side electrode (113) disposed above the semiconductor laminate (100S) and in contact with the semiconductor laminate (100S), wherein the semiconductor laminate (100S) includes: an n-type cladding layer (102) that is a nitride semiconductor layer containing Al; an n-side guide layer (104) disposed above the n-type cladding layer (102); an active layer (105) disposed above the n-side guide layer (104); and a p-type cladding layer (110) that is disposed above the active layer (105) and is a nitride semiconductor layer containing Al, the composition ratio of Al in the n-type cladding layer (102) is greater than the composition ratio of Al in the p-type cladding layer (110), and the p-side electrode (113) is made of at least one of Ag, an Ag alloy, Al, or a translucent conductive film.

Description

semiconductor laser element

[0001] The present disclosure relates to a semiconductor laser device.

[0002] 2. Description of the Related Art Semiconductor laser elements that emit laser light are known (see, for example, Patent Document 1). Patent Document 1 discloses a semiconductor laser element that includes a waveguide layer (in other words, an optical guide layer).

[0003] Special Publication No. 2020-536372

[0004] In the semiconductor laser device disclosed in Patent Document 1, the provision of a waveguide layer allows for a reduction in waveguide loss. However, further reduction in waveguide loss is required in semiconductor laser devices.

[0005] The present disclosure is intended to solve such problems, and has an object to provide a semiconductor laser device that can reduce waveguide loss.

[0006] In order to solve the above problems, one aspect of a semiconductor laser device according to the present disclosure includes a substrate, a semiconductor laminate disposed above the substrate, and a p-side electrode disposed above the semiconductor laminate and in contact with the semiconductor laminate, wherein the semiconductor laminate has an n-type cladding layer which is a nitride semiconductor layer containing Al, an n-side guide layer disposed above the n-side guide layer, an active layer disposed above the n-side guide layer, and a p-type cladding layer which is a nitride semiconductor layer containing Al and disposed above the active layer, wherein the Al composition ratio of the n-type cladding layer is larger than the Al composition ratio of the p-type cladding layer, and the p-side electrode is made of at least one of Ag, an Ag alloy, Al, and a translucent conductive film.

[0007] According to the present disclosure, it is possible to provide a semiconductor laser device capable of reducing waveguide loss.

[0008] 1 is a schematic plan view showing the overall configuration of a semiconductor laser device according to a first embodiment. FIG. 2 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing the configuration of an active layer included in the semiconductor laser device according to the first embodiment. FIG. 4 is a schematic graph showing the refractive index distribution and light intensity distribution in the stacking direction of a semiconductor laser device according to a first comparative example. FIG. 5 is a schematic graph showing the refractive index distribution and light intensity distribution in the stacking direction of a semiconductor laser device according to the first embodiment. FIG. 6 is a first graph showing the relationship between the film thickness of an n-side intermediate layer and the operating voltage of Configuration Example 1. FIG. 7 is a second graph showing the relationship between the film thickness of an n-side intermediate layer and the operating voltage of Configuration Example 1. FIG. 8 is a third graph showing the relationship between the film thickness of an n-side intermediate layer and the operating voltage of Configuration Example 1. FIG. 9 is a graph showing the relationship between the film thickness of an n-side intermediate layer and the waveguide loss of Configuration Example 2. FIG. 10 is a graph showing the relationship between the film thickness of an n-side intermediate layer and the optical confinement factor of Configuration Example 2. FIG. 11 is a graph showing the relationship between the film thickness of an n-side intermediate layer and the effective refractive index difference of Configuration Example 2. FIG. 12 is a graph showing the relationship between the film thickness of an n-side intermediate layer and the peak position of the light intensity distribution of Configuration Example 2. 17 is a graph showing coordinates of positions in the stacking direction of the semiconductor laser device according to the first embodiment. 22 is a graph showing the relationship between the thickness of the n-side guide layer and the waveguide loss in Configuration Example 3. 23 is a graph showing the relationship between the thickness of the n-side guide layer and the optical confinement factor in Configuration Example 3. 24 is a graph showing the relationship between the thickness of the n-side guide layer and the effective refractive index difference in Configuration Example 3. 25 is a graph showing the relationship between the thickness of the n-side guide layer and the peak position of the optical intensity distribution in Configuration Example 3. 26 is a graph enlarging a part of the range of the vertical axis of FIG. 17. 27 is a graph showing the relationship between the thickness of the n-side guide layer and the waveguide loss in Configuration Example 4. 28 is a graph showing the relationship between the thickness of the n-side guide layer and the optical confinement factor in Configuration Example 4. 29 is a graph showing the relationship between the thickness of the n-side guide layer and the effective refractive index difference in Configuration Example 4. 29 is a graph showing the relationship between the thickness of the n-side guide layer and the peak position of the optical intensity distribution in Configuration Example 4. 21 is a graph enlarging a part of the range of the vertical axis of FIG. 22. 22 is a graph showing the relationship between the thickness of the p-type cladding layer and the waveguide loss in Configuration Example 5. 10 is a graph showing the relationship between the thickness of the p-type cladding layer and the optical confinement coefficient in Configuration Example 5. FIG. 11 is a graph showing the relationship between the thickness of the p-type cladding layer and the effective refractive index difference in Configuration Example 5.10 is a graph showing the relationship between the thickness of the p-type cladding layer and the peak position of the light intensity distribution in Configuration Example 5. FIG. 11 is a graph showing the relationship between the thickness of the p-type cladding layer and the waveguide loss in Configuration Example 6. FIG. 12 is a graph showing the relationship between the thickness of the p-type cladding layer and the optical confinement factor in Configuration Example 6. FIG. 13 is a graph showing the relationship between the thickness of the p-type cladding layer and the effective refractive index difference in Configuration Example 6. FIG. 14 is a graph showing the relationship between the thickness of the p-type cladding layer and the peak position of the light intensity distribution in Configuration Example 6. FIG. 15 is a graph showing the distribution of the conduction band potential in the stacking direction between the p-type cladding layer and the p-side guide layer in Comparative Example 2. FIG. 16 is a graph showing the distribution of the conduction band potential in the stacking direction between the p-type cladding layer and the p-side guide layer in Configuration Example 7. FIG. 17 is a graph showing the relationship between the thickness of the n-side intermediate layer and the operating voltage of the semiconductor laser element in Configuration Example 7. FIG. 18 is a graph showing the relationship between the thickness of the n-side intermediate layer and the operating voltage of the semiconductor laser element in Configuration Example 8. FIG. 19 is a graph showing the relationship between the thickness of the n-side guide layer and the waveguide loss in Configuration Example 9. 44 is a graph showing the relationship between the film thickness of the n-side guide layer and the optical confinement factor in Configuration Example 9. FIG. 45 is a graph showing the relationship between the film thickness of the n-side guide layer and the effective refractive index difference in Configuration Example 9. FIG. 46 is a graph showing the relationship between the film thickness of the n-side guide layer and the peak position of the optical intensity distribution in Configuration Example 9. FIG. 47 is a graph enlarging a part of the range of the vertical axis of FIG. 39. FIG. 48 is a graph showing the relationship between the film thickness of the n-side guide layer and the waveguide loss in Configuration Example 10. FIG. 49 is a graph showing the relationship between the film thickness of the n-side guide layer and the optical confinement factor in Configuration Example 10. FIG. 49 is a graph showing the relationship between the film thickness of the n-side guide layer and the effective refractive index difference in Configuration Example 10. FIG. 49 is a graph showing the relationship between the film thickness of the n-side guide layer and the peak position of the optical intensity distribution in Configuration Example 10. FIG. 49 is a graph enlarging a part of the range of the vertical axis of FIG. 44. FIG. 49 is a schematic graph showing an example of the band gap energy distribution of the active layer in Configuration Example 13. FIG. 49 is a graph showing the relationship between the stacking direction position and the optical intensity distribution when a substrate made of GaN is used in Configuration Example 13. 10 is a graph showing the relationship between the stacking direction position and the integrated stress when a substrate made of GaN is used in Configuration Example 13. FIG. 11 is a graph showing the relationship between the stacking direction position and the light intensity distribution when a substrate made of AlGaN is used in Configuration Example 13. FIG. 12 is a graph showing the relationship between the stacking direction position and the integrated stress when a substrate made of AlGaN is used in Configuration Example 13.1 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device according to a second embodiment. FIG. 2 is a graph showing the distribution of the conduction band potential in Structural Example 1 of the semiconductor laser device according to the second embodiment. FIG. 3 is a graph showing the distribution of the valence band potential in Structural Example 1 of the semiconductor laser device according to the second embodiment. FIG. 4 is a graph showing the distribution of the conduction band potential in Structural Example 2 of the semiconductor laser device according to the second embodiment. FIG. 5 is a graph showing the distribution of the valence band potential in Structural Example 2 of the semiconductor laser device according to the second embodiment. FIG. 6 is a graph showing the distribution of the conduction band potential in Structural Example 3 of the semiconductor laser device according to the second embodiment. FIG. 7 is a graph showing the distribution of the valence band potential in Structural Example 3 of the semiconductor laser device according to the second embodiment. FIG. 8 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device according to a third embodiment. FIG. 9 is a schematic cross-sectional view showing the configuration of an n-side guide layer included in the semiconductor laser device according to the third embodiment. FIG. 10 is a schematic cross-sectional view showing the configuration of an active layer included in the semiconductor laser device according to the third embodiment. FIG. 11 is a graph showing the relationship between the Al composition ratio of the substrate of Structural Example C1 and the integrated stress of the semiconductor stack. FIG. 12 is a graph showing the relationship between the stacking direction position and the refractive index of a comparative example. 1 is a graph showing the relationship between stacking direction position and light intensity in a comparative example. FIG. 2 is a graph showing the relationship between stacking direction position and refractive index in Configuration Example C1. FIG. 3 is a graph showing the relationship between stacking direction position and light intensity in Configuration Example C1. FIG. 4 is a graph showing the relationship between the Al composition ratio of the substrate and operating voltage in Configuration Example C1. FIG. 5 is a graph showing the relationship between the Al composition ratio of the substrate and integrated stress of the semiconductor laminate in Configuration Example C2. FIG. 6 is a graph showing the relationship between the Al composition ratio of the substrate and operating voltage in Configuration Example C2. FIG. 7 is a graph showing the relationship between the Al composition ratio of the substrate and integrated stress of the semiconductor laminate in Configuration Example C3. FIG. 8 is a graph showing the relationship between the Al composition ratio of the substrate and operating voltage in Configuration Example 4. FIG. 9 is a graph showing the relationship between the Al composition ratio of the substrate and integrated stress of the semiconductor laminate in Configuration Example C4. FIG. 10 is a graph showing the relationship between the Al composition ratio of the substrate and operating voltage in Configuration Example 4. 10 is a graph showing the relationship between the thickness of the p-type cladding layer and the effective refractive index difference in Configuration Example C1 and Configuration Example C2, respectively.86 is a graph showing the relationship between the thickness of the p-type cladding layer and the optical confinement factor for Configuration Example C2. 87 is a graph showing the relationship between the thickness of the p-type cladding layer and the effective refractive index difference for Configuration Example C2. 88 is a graph showing the relationship between the thickness of the p-type cladding layer and the waveguide loss for Configuration Example C3. 89 is a graph showing the relationship between the thickness of the p-type cladding layer and the optical confinement factor for Configuration Example C3. 89 is a graph showing the relationship between the thickness of the p-type cladding layer and the effective refractive index difference for Configuration Example C3. 89 is a graph showing the relationship between the thickness of the p-type cladding layer and the waveguide loss for Configuration Example C4. 89 is a graph showing the relationship between the thickness of the p-type cladding layer and the optical confinement factor for Configuration Example C4. 89 is a graph showing the relationship between the thickness of the p-type cladding layer and the effective refractive index difference for Configuration Example C4. 89 is a graph showing the relationship between the Al composition ratio of the n-type cladding layer and the Al composition ratio of the substrate according to the third embodiment. 89 is a graph showing the relationship between the ridge width and the number of waveguideable modes according to the third embodiment. 89 is a graph showing an enlarged portion of FIG. 86. 10 is a schematic plan view showing the shape of a ridge in Structural example C51 of the semiconductor laser element according to the third embodiment. FIG. 11 is a schematic plan view showing the shape of a ridge in Structural example C52 of the semiconductor laser element according to the third embodiment. FIG. 12 is a schematic plan view showing the shape of a ridge in Structural example C53 of the semiconductor laser element according to the third embodiment. FIG. 13 is a schematic plan view showing the shape of a ridge in Structural example C61 of the semiconductor laser element according to the third embodiment. FIG. 14 is a schematic plan view showing the shape of a ridge in Structural example C62 of the semiconductor laser element according to the third embodiment. FIG. 15 is a schematic plan view showing the shape of a ridge in Structural example C63 of the semiconductor laser element according to the third embodiment. FIG. 16 is a schematic plan view showing the shape of a ridge in Structural example C71 of the semiconductor laser element according to the third embodiment. FIG. 17 is a schematic plan view showing the shape of the ridge in Structural example C72 of the semiconductor laser element according to the third embodiment. FIG. 18 is a schematic plan view showing the shape of the ridge in Structural example C73 of the semiconductor laser element according to the third embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, and the arrangement and connection of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0010] Furthermore, each figure is a schematic diagram and is not necessarily an exact representation. Therefore, the scales and the like do not necessarily match in each figure. In each figure, the same reference numerals are used to denote substantially the same components, and redundant explanations will be omitted or simplified.

[0011] In this specification, the terms "above" and "below" do not refer to vertically above and below in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. The terms "above" and "below" are used not only when two components are arranged with a gap between them and another component is present between them, but also when two components are arranged in contact with each other.

[0012] First Embodiment A semiconductor laser device according to a first embodiment will be described.

[0013] [1-1. Overall Configuration] First, the overall configuration of the semiconductor laser device according to this embodiment will be described with reference to FIGS. 1 to 3. FIGS. 1 and 2 are a schematic plan view and a cross-sectional view, respectively, showing the overall configuration of the semiconductor laser device 100 according to this embodiment. FIG. 2 shows a cross section taken along line II-II in FIG. 1. FIG. 3 is a schematic cross-sectional view showing the configuration of the active layer 105 included in the semiconductor laser device 100 according to this embodiment. Note that each figure shows an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other. The X-axis, the Y-axis, and the Z-axis are in a right-handed Cartesian coordinate system. The stacking direction of the semiconductor laser device 100 is parallel to the Z-axis direction, and the main emission direction of light (laser light) is parallel to the Y-axis direction.

[0014] As shown in FIG. 2, the semiconductor laser device 100 includes a semiconductor stack 100S and emits light from a facet 100F (see FIG. 1) perpendicular to the stacking direction (i.e., the Z-axis direction) of the semiconductor stack 100S. In this embodiment, the semiconductor laser device 100 has two facets 100F and 100R that form a cavity. The facet 100F is a front facet from which laser light is emitted, and the facet 100R is a rear facet having a higher reflectivity than the facet 100F. The semiconductor laser device 100 also has a waveguide formed between the facets 100F and 100R. In this embodiment, the reflectivity of the facet 100F is lower than that of the facet 100R. The cavity length of the semiconductor laser device 100 according to this embodiment (i.e., the distance between the facets 100F and 100R) is 1200 μm. The semiconductor laser device 100 emits laser light having a peak wavelength of, for example, 450 nm or more and 570 nm or less. The semiconductor laser device 100 may also emit laser light having a peak wavelength shorter than 450 nm or longer than 570 nm.

[0015] As shown in FIG. 2, the semiconductor laser device 100 includes a substrate 101, a semiconductor stack 100S, a current blocking layer 112, a p-side electrode 113, and an n-side electrode 114.

[0016] The semiconductor stack 100S is disposed above the substrate 101 and is a stack in which semiconductor layers are stacked. As shown in Fig. 2, the semiconductor stack 100S has a ridge 110R that protrudes upward. The semiconductor stack 100S also has two grooves 110T that are disposed along the ridge 110R and extend in the Y-axis direction, and two protruding portions 110P that protrude upward. One groove 110T is disposed between the ridge 110R and one of the protruding portions 110P, and the other groove 110T is disposed between the ridge 110R and the other protruding portion 110P.

[0017] The semiconductor laminate 100S according to this embodiment includes an n-type cladding layer 102, an n-side intermediate layer 103, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, a p-side intermediate layer 107, an electron barrier layer 108, a p-type cladding layer 110, and a contact layer 111. In this embodiment, the semiconductor laminate 100S is made of a nitride semiconductor.

[0018] The substrate 101 is a plate-like member that serves as a base for the semiconductor laser device 100. In this embodiment, the substrate 101 is disposed below the n-type cladding layer 102 and is made of AlGaN.

[0019] The n-type cladding layer 102 is disposed above the substrate 101 and is a nitride semiconductor layer containing Al. Here, the cladding layer is a layer in which the change in the light intensity distribution in the layer with respect to the stacking direction can be approximated by an exponential function. The conductivity type of the n-type cladding layer 102 is n-type. The n-type cladding layer 102 has a smaller average refractive index and a larger average band gap energy than the active layer 105. In this embodiment, the n-type cladding layer 102 is made of n-type Al doped with Si. Ｘｎ１ Ga １－Ｘｎ１ N (0<Xn1<1) layers.

[0020] In this disclosure, the average band gap energy of a certain layer refers to the value of the band gap energy obtained by integrating the magnitude of the band gap energy at a certain position in the stacking direction of the layer from the interface position on the substrate side in the stacking direction of the layer to the interface position on the side farther from the substrate in the stacking direction of the layer, and dividing the result by the film thickness of the layer (the distance between the interface on the substrate side and the interface on the side farther from the substrate). Note that in this disclosure, the average band gap energy of a certain layer is also simply referred to as band gap energy.

[0021] The average refractive index of a certain layer is the refractive index value obtained by integrating the magnitude of the refractive index at a certain position in the stacking direction of the layer from the interface position on the substrate side in the stacking direction of the layer to the interface position on the side farther from the substrate in the stacking direction of the layer, and dividing the result by the film thickness of the layer (the distance between the interface on the substrate side and the interface on the side farther from the substrate). Note that in the present disclosure, the average refractive index of a certain layer is also simply referred to as the refractive index.

[0022] The average Al composition ratio of a certain layer is the value of the Al composition ratio 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 farther from the substrate in the stacking direction of the layer, and dividing the result by the film thickness of the layer (the distance between the interface on the substrate side and the interface on the side farther from the substrate). Note that in this disclosure, the average Al composition ratio of a certain layer is also simply referred to as the Al composition ratio. The average In composition ratio is defined in the same way as the average Al composition ratio.

[0023] The average impurity concentration of a layer is the value of the impurity concentration at a certain position in the stacking direction of the layer, integrated in the stacking direction from the interface position on the substrate side in the stacking direction of the layer to the interface position on the side farther from the substrate, and divided by the film thickness of the layer (the distance between the interface on the substrate side and the interface farther from the substrate). In an n-type semiconductor layer, impurity refers to impurities doped to obtain n-type conductivity, and in a p-type semiconductor layer, impurities doped to obtain p-type conductivity. In this disclosure, the average impurity concentration of a layer is also simply referred to as the impurity concentration.

[0024] The n-side intermediate layer 103 is a nitride semiconductor layer disposed between the n-type cladding layer 102 and the n-side guide layer 104. In this embodiment, the n-side intermediate layer 103 is a GaN layer or a compositionally graded layer. The n-side intermediate layer 103 may be a GaN layer with a thickness of 5 nm or more and 30 nm or less. Here, the compositionally graded layer is an Al layer in which the Al composition ratio monotonically decreases with increasing distance from the n-type cladding layer 102. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In Ｙｎｉ N (0≦Xni<1, 0≦Yni<1) layer and Al layer in which the In composition ratio monotonically increases with increasing distance from the n-type cladding layer 302. Ｘｎｊ Ga １－Ｘｎｊ－Ｙｎｊ In Ｙｎｊ The composition gradient layer includes at least one of an AlN (0≦Xnj<1, 0≦Ynj<1) layer and an AlN layer whose band gap energy decreases monotonically with increasing distance from the n-type cladding layer 102. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In ＹｎｉN (0≦Xni<1, 0≦Yni<1) layer. The n-side intermediate layer 103 may be doped with Si. Here, the configuration in which the Al composition ratio of the n-side intermediate layer 103 monotonically decreases with increasing distance from the n-type cladding layer 102 also includes a configuration in which the n-side intermediate layer 103 has a region in which the Al composition ratio does not change with the distance from the n-type cladding layer 102. For example, it also includes a configuration in which the Al composition ratio of the n-side intermediate layer 103 increases stepwise with the distance from the n-type cladding layer 102. Similarly, the configuration in which the In composition ratio of the n-side intermediate layer 103 monotonically increases with increasing distance from the n-type cladding layer 102 also includes a configuration in which the n-side intermediate layer 103 has a region in which the In composition ratio does not change with the distance from the n-type cladding layer 102. The same applies to the terms "monotonically decrease" and "monotonically increase" described below.

[0025] The n-side guide layer 104 is an optical guide layer disposed above the n-type cladding layer 102. The n-side guide layer 104 is disposed between the n-type cladding layer 102 and the active layer 105. The n-side guide layer 104 has a higher refractive index and a smaller band gap energy than the n-type cladding layer 102. In this embodiment, the n-side guide layer 104 is a nitride semiconductor layer containing In. More specifically, the n-side guide layer 104 is made of InGaN. The n-side guide layer 104 is made of, for example, undoped In Ｘｉｎ Ga １－Ｘｉｎ N (0≦Xin<1) layers.

[0026] The active layer 105 is a light-emitting layer disposed above the substrate 101. In this embodiment, the active layer 105 is disposed above the n-side guide layer 104. The active layer 105 has a quantum well structure. Specifically, as shown in FIG. 3 , the active layer 105 has well layers 105b and 105d and barrier layers 105a, 105c, and 105e. The barrier layer 105a is disposed above the n-side guide layer 104. The well layer 105b is disposed above the barrier layer 105a. The barrier layer 105c is disposed above the well layer 105b. The well layer 105d is disposed above the barrier layer 105c. The barrier layer 105e is disposed above the well layer 105d. In this way, the well layer 105b is disposed between the two barrier layers 105a and 105c, and the well layer 105d is disposed between the two barrier layers 105c and 105e. Note that the configuration of the active layer 105 is not limited to this. For example, the active layer 105 may have a single well layer, or may have three or more well layers.

[0027] Each of the barrier layers 105a, 105c, and 105e is a semiconductor layer disposed above the n-side guide layer 104 and functioning as a barrier of the quantum well structure. In this embodiment, the bandgap energy of each of the barrier layers 105a, 105c, and 105e is larger than the bandgap energy of the well layers 105b and 105d, the bandgap energy of the n-type cladding layer 102, and the bandgap energy of the p-type cladding layer 110, and is smaller than the bandgap energy of the electron barrier layer 108. The bandgap energies of the barrier layers 105a, 105c, and 105e may be equal to each other.

[0028] In this embodiment, each of the barrier layers 105a, 105c, and 105e is a nitride semiconductor layer containing In. More specifically, each of the barrier layers 105a, 105c, and 105e is made of InGaN. Each of the barrier layers 105a, 105c, and 105e is made of, for example, undoped In. Ｙｂ１ Ga １－Ｙｂ１N (0<Yb1<1) layer. The In composition ratio of the barrier layer 105a, which is closest to the n-side guide layer 104 among the barrier layers 105a, 105c, and 105e, is equal to or greater than the maximum In composition ratio of the n-side guide layer 104, and the In composition ratio of the barrier layer 105e, which is closest to the p-side guide layer 106, is equal to or greater than the maximum In composition ratio of the p-side guide layer 106. The band gap energy of the barrier layer 105a, which is closest to the n-side guide layer 104 among the barrier layers 105a, 105c, and 105e, is equal to or greater than the minimum band gap energy of the n-side guide layer 104, and the band gap energy of the barrier layer 105e, which is closest to the p-side guide layer 106 among the barrier layers 105a, 105c, and 105e, is equal to or greater than the minimum band gap energy of the p-side guide layer 106.

[0029] The well layer 105b is a nitride semiconductor layer disposed between the barrier layer 105a and the barrier layer 105c, and functions as a well of the quantum well structure. The well layer 105d is a nitride semiconductor layer disposed between the barrier layer 105c and the barrier layer 105e, and functions as a well of the quantum well structure. In this embodiment, the well layers 105b and 105d are nitride semiconductor layers containing In. More specifically, the well layers 105b and 105d are made of InGaN. The well layer 105b is made of undoped In Ｙｗ Ga １－Ｙｗ N (0<Yw<1) layers.

[0030] The p-side guide layer 106 is an optical guide layer disposed above the active layer 105. The p-side guide layer 106 is disposed between the active layer 105 and the p-type cladding layer 110. In this embodiment, the p-side guide layer 106 is disposed between the active layer 105 and the p-side intermediate layer 107. The p-side guide layer 106 has a higher refractive index and a smaller band gap energy than the p-type cladding layer 110. In this embodiment, the p-side guide layer 106 is made of InGaN. That is, the p-side guide layer 106 is made of undoped In Ｘｉｐ Ga １－Ｘｉｐ N (0<Xip<1) layers.

[0031] The p-side intermediate layer 107 is a semiconductor layer disposed between the p-side guide layer 106 and the electron barrier layer 108. The band gap energy of the p-side intermediate layer 107 is equal to or greater than the band gap energy of the p-side guide layer 106 and equal to or less than the band gap energy of the electron barrier layer 108. In this embodiment, the band gap energy of the p-side intermediate layer 107 is equal to or less than the band gap energy of the p-type cladding layer 110. In this embodiment, the p-side intermediate layer 107 is made of GaN.

[0032] The electron barrier layer 108 is a semiconductor layer disposed between the active layer 105 and the p-type cladding layer 110. In this embodiment, the electron barrier layer 108 is disposed between the p-side intermediate layer 107 and the p-type cladding layer 110. The band gap energy of the electron barrier layer 108 is larger than the band gap energy of the barrier layer 105c. This makes it possible to suppress leakage of electrons from the active layer 105 to the p-type cladding layer 110. In this embodiment, the band gap energy of the electron barrier layer 108 is larger than the band gap energy of each of the p-side guide layer 106 and the p-type cladding layer 110. The electron barrier layer 108 is made of p-type Al Ｘｅｂ Ga １－Ｘｅｂ N (0<Xeb<1) layer.

[0033] The p-type cladding layer 110 is disposed above the active layer 105 and is a nitride semiconductor layer containing Al. The Al composition ratio of the p-type cladding layer 110 is lower than the Al composition ratio of the n-type cladding layer 102. In this embodiment, the p-type cladding layer 110 is disposed above the electron barrier layer 108. The p-type cladding layer 110 has a lower refractive index and a larger band gap energy than the active layer 105. The band gap energy of the p-type cladding layer 110 is lower than the band gap energy of the electron barrier layer 108. The p-type cladding layer 110 is a p-type Al Ｘｐｃ Ga １－Ｘｐｃ N (0<Xpc<1) layers.

[0034] The contact layer 111 is a nitride semiconductor layer disposed above the p-type cladding layer 110 and in ohmic contact with the p-side electrode 113. In this embodiment, the contact layer 111 is a p-type GaN layer with a thickness of 60 nm. The contact layer 111 contains impurities with a concentration of 1×10 ２０ cm －３ It is doped with Mg.

[0035] In this embodiment, a ridge 110R, a groove 110T, and a protrusion 110P are formed in the p-type cladding layer 110 and the contact layer 111. As shown in Fig. 2, the width (ridge width) of the ridge 110R is represented by W. Furthermore, the distance between the lower end of the ridge 110R (i.e., the bottom of the groove 110T) and the active layer 105 is represented by dp, and the distance between the lower end of the ridge 110R and the electron barrier layer 108 is represented by dc.

[0036] The current blocking layer 112 is disposed above the p-type cladding layer 110 and is an insulating layer that is transparent to light from the active layer 105. The current blocking layer 112 is disposed on the upper surfaces of the p-type cladding layer 110 and the contact layer 111 in a region other than the upper surface 110Ru of the ridge 110R. That is, the current blocking layer 112 is disposed on the upper surfaces of the two protrusions 110P, the side surfaces of each of the two protrusions 110P facing the ridge 110R, the bottom of the groove 110T, and the side surfaces of the ridge 110R (i.e., the end surfaces of the ridge 110R in the X-axis direction). The current blocking layer 112 may also be disposed on a partial region of the upper surface 110Ru of the ridge 110R. For example, the current blocking layer 112 may be disposed in the edge regions of the upper surface 110Ru of the ridge 110R. In this embodiment, the current blocking layer 112 is formed of SiO ２ It is a layer.

[0037] The p-side electrode 113 is an electrode disposed above the semiconductor stack 100S and in contact with the semiconductor stack 100S. In this embodiment, the p-side electrode 113 is disposed above the contact layer 111. The p-side electrode 113 is disposed on the upper surface 110Ru of the ridge 110R and is in contact with the contact layer 111 at the upper surface 110Ru. In this embodiment, the p-side electrode 113 is disposed above the contact layer 111 and the current blocking layer 112. The p-side electrode 113 is made of at least one of Ag, an Ag alloy, Al, and a translucent conductive film. Here, the translucent conductive film may be a conductive oxide film. The p-side electrode 113 may be made of Ag, Al, or an alloy containing at least one of Ag and Al.

[0038] The n-side electrode 114 is a conductive layer disposed below the substrate 101 (i.e., on the principal surface of the substrate 101 opposite to the principal surface on which the semiconductor stack 100S is disposed). The n-side electrode 114 is a single-layer film or a multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au, for example.

[0039] The semiconductor laser device 100 has the above-described configuration, which generates an effective refractive index difference ΔN between the portion below the ridge 110R and the portion below the groove 110T (see FIG. 2 ). This allows light generated in the portion of the active layer 105 below the ridge 110R to be confined in the horizontal direction (i.e., the X-axis direction).

[0040] The effective refractive index difference ΔN is controlled by adjusting the distance dp between the current blocking layer 112 and the active layer 105. As the distance dp increases, the effective refractive index difference ΔN decreases.

[0041] Here, if the lower end of the ridge 110R is located below the electron barrier layer 108, the electron barrier layer 108 becomes a potential barrier to the electrical conduction of holes from the ridge 110R to the active layer 105. As a result, holes leak from the portions of the electron barrier layer 108 corresponding to the side surfaces of the ridge 110R to the outside of the ridge 110R, causing a leakage current. This deteriorates the semiconductor laser device 100. Therefore, to suppress such deterioration, the lower end of the ridge 110R may be located above the electron barrier layer 108.

[0042] In this case, as the distance dp increases, the distance dc between the electron barrier layer 108 and the current blocking layer 112 also increases. Because the electron barrier layer 108 is an AlGaN layer with a high Al composition ratio, it acts as a potential barrier against hole injection from the p-type cladding layer 110 to the active layer 105. Therefore, when the distance dc is large, a proportion of holes injected from the ridge 110R that flow outside the ridge 110R at the lower end of the ridge 110R increases. These holes that flow outside the ridge 110R do not contribute to the generation and amplification of laser light from the semiconductor laser device 100. This increases the oscillation threshold current of the semiconductor laser device 100. Specifically, the oscillation threshold current increases when the distance dc is 70 nm or greater. To suppress the increase in the oscillation threshold, it is desirable to keep the distance dc as small as possible. To suppress the oscillation threshold current of the semiconductor laser device 100, the distance dc may be, for example, 10 nm or greater and 70 nm or less.

[0043] [1-2. Effects] The effects of the semiconductor laser device 100 according to this embodiment will be described with reference to Fig. 4 and Fig. 5, in comparison with Comparative Example 1. Fig. 4 and Fig. 5 are schematic graphs showing the refractive index distribution and light intensity distribution in the stacking direction of the semiconductor laser devices according to Comparative Example 1 and this embodiment, respectively. In Fig. 5, the light intensity distribution of Comparative Example 1 is shown by a dashed line together with the light intensity distribution according to this embodiment.

[0044] The semiconductor laser device of Comparative Example 1 differs from the semiconductor laser device 100 according to the first embodiment in the configurations of the substrate 901, n-type cladding layer 902, p-type cladding layer 910, and p-side electrode 913, but is otherwise identical. In the semiconductor laser device of Comparative Example 1, the Al composition ratios of the n-type cladding layer 902 and the p-type cladding layer 910 are equal. Therefore, as shown in FIG. 4 , the refractive indices of the n-type cladding layer 902 and the p-type cladding layer 910 are equal. Furthermore, the thickness of the p-type cladding layer 910 in Comparative Example 1 is greater than the thickness of the p-type cladding layer 110 according to the present embodiment. Furthermore, the substrate 901 of Comparative Example 1 is a GaN substrate, and the p-side electrode 913 is made of Pd. Therefore, as shown in FIG. 4 , the refractive index of the p-side electrode 913 in Comparative Example 1 is higher than the refractive index of the p-side electrode 113 according to the present embodiment.

[0045] In this embodiment, the Al composition ratio of the n-type cladding layer 102 is higher than that of the p-type cladding layer 110, and therefore the refractive index of the p-type cladding layer 110 is higher than that of the n-type cladding layer 102. As a result, in this embodiment, the n-side guide layer 104, which has a higher refractive index than the n-type cladding layer 102, improves the controllability of positioning the peak position of the light intensity distribution in the stacking direction near the active layer 105, while increasing the refractive index of the p-type cladding layer 110 can prevent the light intensity distribution from tilting too much in the direction from the active layer 105 to the n-side guide layer 104. Therefore, the light confinement factor in the active layer 105 can be increased, and waveguide loss can be reduced.

[0046] Furthermore, by reducing the Al composition ratio of the p-type cladding layer 110, the hole concentration can be increased, thereby reducing the operating voltage of the semiconductor laser device 100. Furthermore, since the impurity concentration of the p-type cladding layer 110 can be reduced, the free carrier loss due to impurities can be reduced, thereby reducing the waveguide loss.

[0047] Furthermore, in this embodiment, the p-side electrode 113 is made of a metal with a low refractive index, such as Ag, or a transparent conductive oxide film, so that the optical loss at the p-side electrode 113 can be reduced. Therefore, the waveguide loss can be further reduced. Furthermore, since the optical loss at the p-side electrode 113 can be reduced, the thickness of the p-type cladding layer 110 can be made thinner while reducing the waveguide loss. This allows the operating voltage of the semiconductor laser device 100 to be reduced.

[0048] Furthermore, since a conductive oxide film has a higher refractive index than Ag and Al, when the p-side electrode 113 is made of a conductive oxide film, a decrease in the effective refractive index difference ΔN can be suppressed even when the thickness of the p-type cladding layer 110 is small, compared to when the p-side electrode 113 is made of a metal with a low refractive index, such as Ag. Therefore, it is possible to suppress the occurrence of non-linear portions (so-called kinks) in a graph showing the current-light output characteristics of the semiconductor laser device 100.

[0049] Furthermore, when the p-side electrode 113 contains a metal such as Ag, spontaneously emitted light from the active layer 105 may be reflected by the p-side electrode 113 and return to the active layer 105. The spontaneously emitted light that has returned to the active layer 105 is absorbed by the active layer 105 in this manner, thereby increasing the quantum efficiency that contributes to radiative recombination. Therefore, the oscillation threshold current value of the semiconductor laser device 100 can be reduced, and the slope efficiency can be increased.

[0050] The n-side intermediate layer 103 according to this embodiment is a GaN layer or a compositionally graded layer having a thickness of 30 nm or less. FIG. 5 shows an example in which the n-side intermediate layer 103 is a GaN layer. That is, the n-side intermediate layer 103, which is a GaN layer, is disposed between the n-type cladding layer 102, which is a nitride semiconductor layer containing Al, and the n-side guide layer 104, which is a nitride semiconductor layer containing In. When the n-type cladding layer 102 and the n-side guide layer 104 contact each other, a spike-shaped potential barrier is formed at the interface due to the difference in bandgap energy between the two layers. However, by disposing the n-side intermediate layer 103, which is a GaN layer, between the two layers, the potential barrier formed between the n-type cladding layer 102 and the n-side guide layer 104 can be reduced. Therefore, the operating voltage of the semiconductor laser device 100 can be reduced.

[0051] Furthermore, in this embodiment, the n-side guide layer 104 is made of InGaN. This allows the refractive index of the n-side guide layer 104 to be made sufficiently higher than the refractive index of the n-type cladding layer 102, which is a nitride semiconductor layer containing Al. This therefore allows the optical confinement factor in the active layer 105 to be increased. This allows the oscillation threshold current value of the semiconductor laser device 100 to be reduced. Furthermore, since the leakage current can be reduced, the temperature characteristics of the semiconductor laser device 100 can be improved.

[0052] Furthermore, in this embodiment, the p-side guide layer 106 is made of InGaN. This allows the refractive index of the p-side guide layer 106 to be made sufficiently higher than the refractive index of the p-type cladding layer 110, which is a nitride semiconductor layer containing Al. This therefore allows the optical confinement factor in the active layer 105 to be increased. This in turn allows the oscillation threshold current value of the semiconductor laser device 100 to be reduced. Furthermore, increasing the optical confinement factor allows the leakage current to be reduced, thereby improving the temperature characteristics of the semiconductor laser device 100.

[0053] [1-3. Configuration Example 1] Configuration Example 1 of the semiconductor laser device 100 of this embodiment will be described. Configuration Example 1 of the semiconductor laser device 100 is a configuration example that emits laser light in the wavelength band of 445 nm. In Configuration Example 1, the n-type cladding layer 102 is made of n-type Al Ｘｎ１ Ga １－Ｘｎ１ The n-side intermediate layer 103 is an n-type GaN layer having a thickness of T1 [nm]. The n-type cladding layer 102 and the n-side intermediate layer 103 are doped with Si at a concentration of Cn. The n-side guide layer 104 is an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ This is the N layer.

[0054] Each of the barrier layers 105a and 105c is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ The barrier layer 105e is an undoped In layer with a thickness of 5 nm. ０．０５ Ga ０．９５ Each of the well layers 105b and 105d is an undoped In layer having a thickness of 3 nm. ０．１８ Ga ０．８２ This is the N layer.

[0055] The p-side guide layer 106 is an undoped In layer having a thickness of 280 nm. Ｘｉｐ Ga １－Ｘｉｐ In Configuration Example 1, the In composition ratio of the p-side guide layer 106 monotonically increases toward the active layer 105. The In composition ratio Xip is 0.04 at the end face of the p-side guide layer 106 closer to the active layer 105, and the In composition ratio Xip is 0 at the end face of the p-side guide layer 106 farther from the active layer 105. In Configuration Example 1, the rate of change of the In composition ratio in the stacking direction of the p-side guide layer 106 is constant.

[0056] The p-side intermediate layer 107 is a GaN layer with a thickness of 24 nm. The p-side intermediate layer 107 is composed of an undoped GaN layer with a thickness of 21 nm and a 1×10 １９ cm －３ and a 3 nm thick n-type GaN layer doped with Mg.

[0057] The electron barrier layer 108 has a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 5 nm ０．３６ Ga ０．６４ This is the N layer.

[0058] The p-type cladding layer 110 is a p-type Al layer having a thickness of 450 nm. ０．０２６ Ga ０．９７４ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 300 nm ０．０２６ Ga ０．９７４ The contact layer 111 has a concentration of 1×10 ２０ cm －３ The layer is a 10 nm thick p-type GaN layer doped with Mg.

[0059] Here, the p-type cladding layer 110 is a low impurity concentration layer (concentration 2×10 １８ cm－３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer) and a high impurity concentration layer (a layer with a higher impurity concentration than the low impurity concentration layer and arranged above the low impurity concentration layer: concentration 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 300 nm ０．０２６ Ga ０．９７４ Therefore, the free carrier loss caused by impurities can be reduced, and therefore the waveguide loss can be reduced. The low impurity concentration layer may be undoped.

[0060] Furthermore, the impurity concentration of the low impurity concentration layer is lower than the maximum impurity concentration of the electron barrier layer 108. Therefore, the free carrier loss caused by impurities can be reduced, and therefore the waveguide loss can be reduced.

[0061] In addition, in Configuration Example 1, the ridge width W is 45 μm, the cavity length is 1200 μm, and the distance dc between the bottom end of the ridge 110R and the electron barrier layer 108 is 40 nm.

[0062] The relationship between the thickness T1 of the n-side intermediate layer 103 and the operating voltage in Configuration Example 1 will be described with reference to Figs. 6 to 8. Figs. 6 to 8 are graphs showing the relationship between the thickness T1 of the n-side intermediate layer and the operating voltage in Configuration Example 1. Figs. 6, 7, and 8 show the relationship between the thickness T1 of the n-side intermediate layer and the operating voltage when the impurity concentration Cn in the n-type cladding layer 102 and the n-side intermediate layer 103 is 5×10 １７ cm －３ , 1 x 10 １８ cm －３ , and 2 × 10 １８ cm －３ 6 to 8 show graphs for a number of cases where the Al composition ratio Xn1 of the n-type cladding layer 102 is different. Note that each of FIGS. 6 to 8 also shows a case where the Al composition ratio of the n-type cladding layer 102 is equal to the Al composition ratio of the p-type cladding layer 110 (i.e., where Xn1 is 0.026). Also, each of FIGS. 6 to 8 shows the operating voltage when a current of 3 A is supplied to the semiconductor laser device 100.

[0063] As shown in FIGS. 6 to 8, when the impurity concentration Cn is 5×10 １７ cm －３ In this case, the impurity concentration Cn is 1×10 １８ cm －３ , or 2 x 10 １８ cm －３ The operating voltage is higher by 0.2 V or more compared to the case of . Therefore, in order to reduce the operating voltage, the impurity concentration Cn is set to 1×10 １８ cm －３ On the other hand, if the impurity concentration Cn is too high, the free carrier loss increases and the slope efficiency decreases. １８ cm －３ It may be the following:

[0064] As shown in FIG. 6, when the impurity concentration Cn is 5×10 １７ cm －３ When the Al composition ratio Xn1 is 0.055 or less (that is, when the difference in Al composition ratio between the n-type cladding layer 102 and the n-side intermediate layer 103 is 0.055 or less), the thickness T1 of the n-side intermediate layer 103 may be 30 nm or more in order to reduce the operating voltage.

[0065] As shown in FIG. 7, when the impurity concentration Cn is 1×10 １８ cm －３ When the Al composition ratio Xn1 is 0.055 or less, the thickness T1 of the n-side intermediate layer 103 may be 10 nm or more to reduce the operating voltage. When the Al composition ratio Xn1 is greater than 0.055 and less than or equal to 0.075, the thickness T1 of the n-side intermediate layer 103 may be 15 nm or more to reduce the operating voltage. When the Al composition ratio Xn1 is greater than 0.075, the thickness T1 of the n-side intermediate layer 103 may be 20 nm or more to reduce the operating voltage.

[0066] As shown in FIG. 8, when the impurity concentration Cn is 2×10 １７ cm －３When the Al composition ratio Xn1 is 0.055 or less, the thickness T1 of the n-side intermediate layer 103 may be 3 nm or more to reduce the operating voltage. When the Al composition ratio Xn1 is greater than 0.055 and less than or equal to 0.075, the thickness T1 of the n-side intermediate layer 103 may be 5 nm or more to reduce the operating voltage. When the Al composition ratio Xn1 is greater than 0.075, the thickness T1 of the n-side intermediate layer 103 may be 7 nm or more to reduce the operating voltage.

[0067] In addition, in Configuration Example 1, the In composition ratio of the p-side guide layer 106 monotonically decreases with increasing distance from the active layer 105. Furthermore, the bandgap energy of the p-side guide layer 106 monotonically increases with increasing distance from the active layer 105. As a result, the potential of the valence band of the p-side guide layer 106 decreases with increasing distance from the active layer 105. Accordingly, the difference between the potential of the valence band of the p-side guide layer 106 and the Fermi level of holes becomes substantially constant at each position in the stacking direction of the p-side guide layer 106. Therefore, the semiconductor laser device 100 can operate at a low operating voltage without increasing the hole concentration of the p-side guide layer 106. Reducing the hole concentration in this manner reduces free carrier loss, thereby reducing waveguide loss. Therefore, Configuration Example 1 enables the semiconductor laser device 100 to operate at a low operating voltage and a low operating current.

[0068] [1-4. Configuration Example 2] Configuration Example 2 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 2 of the semiconductor laser element 100 differs from Configuration Example 1 in the configuration of the p-type cladding layer 110. Configuration Example 2 will be described below, focusing on the differences from Configuration Example 1.

[0069] The p-type cladding layer 110 of the second example is a p-type Al ０．０２６ Ga ０．９７４ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３p-type Al doped with Mg having a thickness of 200 nm ０．０２６ Ga ０．９７４ In the second configuration example, the impurity concentration Cn in the n-type cladding layer 102 and the n-side intermediate layer 103 is 1×10 １８ cm －３ is.

[0070] The relationship between the thickness T1 of the n-side intermediate layer 103 of Configuration Example 2, the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction will be described with reference to FIGS. 9 to 13. FIGS. 9, 10, 11, and 12 are graphs showing the relationship between the thickness T1 of the n-side intermediate layer of Configuration Example 2, the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution. FIGS. 9 to 12 show graphs for the case where the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.055 and the p-side electrode 113 is made of an Ag film with a thickness of 200 nm, and graphs for the case where the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.055 and the p-side electrode 113 is made of ITO with a thickness of 200 nm (and an Ag film with a thickness of 200 nm disposed above the ITO). 9 to 12 also show, for comparison, a graph in which the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.055 and the p-side electrode 113 is made of Pd, and a graph in which the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.026 and the p-side electrode 113 is made of Ag.

[0071] FIG. 13 is a graph showing coordinates of positions in the stacking direction of the semiconductor laser device 100 according to this embodiment. The vertical axis of FIG. 13 represents the magnitude of the bandgap energy. As shown in FIG. 13, the coordinate of the position in the stacking direction of the n-side end face of the well layer 105b of the active layer 105, i.e., the end face of the well layer 105b closer to the n-side guide layer 104, is defined as zero, the downward direction (toward the n-side guide layer 104) is defined as negative, and the upward direction (toward the p-side guide layer 106) is defined as positive. Here, the peak position of the light intensity distribution mentioned above, P1 [nm], indicates that the position in the stacking direction where the light intensity is maximum in the light intensity distribution in the stacking direction is a distance P1 [nm] from the position in the stacking direction of the end face of the well layer 105b closer to the n-side guide layer 104. When P1 is positive, it indicates that the peak position of the light intensity distribution in the stacking direction is a distance P1 from the position of coordinate zero toward the p-side. In the example shown in FIG. 13, P1 indicates an example in which the active layer 105 has two well layers 105b and 105d. However, whether the active layer 105 has one well layer or a plurality of well layers, the coordinate of the position in the stacking direction of the end face of the well layer closest to the n-side guide layer located nearest to the n-side is set to zero.

[0072] As the thickness T1 of the n-side intermediate layer 103 decreases, the n-type cladding layer 102 approaches the active layer 105, and the spread of the light intensity distribution in the stacking direction from the active layer 105 toward the n-type semiconductor layer decreases. Therefore, as shown in Figures 9 and 10 , as the thickness T1 of the n-side intermediate layer 103 decreases, the optical confinement factor increases, and the effective refractive index difference ΔN increases. Here, the effect of increasing the optical confinement factor is greater when the Al composition ratio of the n-type cladding layer 102 is greater than that of the p-type cladding layer 110.

[0073] When Pd is used as the p-side electrode, the optical loss at the p-side electrode is large, and therefore, there is a significant tendency for the waveguide loss to increase by reducing the thickness T1 of the n-side intermediate layer 103. However, in the semiconductor laser device 100 according to the present embodiment, the optical loss at the p-side electrode 113 can be reduced, and therefore the increase in the waveguide loss that occurs when the thickness T1 of the n-side intermediate layer 103 is reduced can be suppressed.

[0074] Furthermore, when the thickness T1 of the n-side intermediate layer 103 is reduced, the peak position P1 of the light intensity distribution moves toward the p-side guide layer 106. However, even when the thickness T1 is set to 50 nm or less, the position P1 can be maintained at 10 nm or less (i.e., within the active layer 105).

[0075] From the above, it is assumed that the p-side electrode 113 is made of Ag and the impurity concentration Cn of the n-side intermediate layer 103 is 1×10 １８ cm －３ As described above, by setting the thickness T1 of the n-side intermediate layer 103 to be 10 nm or more and 50 nm or less, it is possible to achieve a reduction in operating voltage, an increase in the optical confinement factor, suppression of an increase in waveguide loss, and control of the position P1 within the active layer 105.

[0076] The same effect can be achieved when an Ag alloy or Al is used as the p-side electrode 113, or when a conductive oxide film such as ITO is used.

[0077] In Configuration Example 2, the semiconductor laminate 100S has an n-side guide layer 104 made of InGaN and a p-side guide layer 106 made of InGaN. Of the barrier layers 105a, 105c, and 105e in the active layer 105, the barrier layer 105a closest to the n-side guide layer 104 has an In composition ratio equal to or greater than the maximum In composition ratio of the n-side guide layer 104, and the barrier layer 105e closest to the p-side guide layer 106 has an In composition ratio equal to or greater than the maximum In composition ratio of the p-side guide layer 106.

[0078] This allows the refractive index of each barrier layer to be equal to or greater than the refractive index of each guide layer, thereby further increasing the optical confinement factor in the active layer 105. As a result, the oscillation threshold current and leakage current can be reduced, and the temperature characteristics can be improved.

[0079] Furthermore, the controllability of positioning the peak position (P1) of the light intensity distribution in the stacking direction in the active layer 105 can be improved, so that the light confinement coefficient in the active layer 105 can be further increased.

[0080] [1-5. Configuration Example 3] Configuration Example 3 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 3 of the semiconductor laser element 100 differs from the configuration of Configuration Example 2 in the configurations of the n-side intermediate layer 103, the n-side guide layer 104, the p-side guide layer 106, and the p-side intermediate layer 107. Configuration Example 3 will be described below, focusing on the differences from Configuration Example 2.

[0081] In the configuration example 3, the n-side intermediate layer 103 has a concentration of 1×10 １８ cm －３ The p-side intermediate layer 107 is an undoped GaN layer having a thickness of 20 nm. In Configuration Example 3, the p-side electrode 113 is an Ag film having a thickness of 200 nm.

[0082] The n-side guide layer 104 is an undoped InN layer having a thickness of Tn1. Ｘｉｎ Ga １－Ｘｉｎ The p-side guide layer 106 is an undoped InN (0≦Xin<1) layer with a thickness of Tp1. Ｘｉｐ Ga １－Ｘｉｐ N (0≦Xip<1) layer. In Configuration Example 3, as in Configuration Example 2, the In composition ratio Xip of the p-side guide layer 106 monotonically increases as it approaches the active layer 105. Furthermore, the band gap energy of the p-side guide layer 106 monotonically decreases as it approaches the active layer 105. The In composition ratio Xip is 0.04 at the end face of the p-side guide layer 106 closer to the active layer 105, and the In composition ratio Xip is 0 at the end face of the p-side guide layer 106 farther from the active layer 105.

[0083] 14 to 18 will be used to explain the relationship between the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 of Configuration Example 3 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction. Figures 14, 15, 16, and 17 are graphs showing the relationship between the thickness Tn1 of the n-side guide layer 104 of Configuration Example 3 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution. Here, the thickness Tp1 of the p-side guide layer 106 is changed according to the thickness Tn1 of the n-side guide layer 104 so that the sum of the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 is 440 nm. In other words, when the film thickness Tn1 is 220 nm, the film thickness Tn1 is equal to the film thickness Tp1, when the film thickness Tn1 is less than 220 nm, the film thickness Tn1 is smaller than the film thickness Tp1, and when the film thickness Tn1 is greater than 220 nm, the film thickness Tn1 is greater than the film thickness Tp1.

[0084] Fig. 18 is a graph in which a part of the range of the vertical axis in Fig. 17 is enlarged. In Fig. 18, the range of the vertical axis shown in Fig. 17 that includes the position corresponding to the active layer 105 is shown enlarged.

[0085] 14 to 18 each show graphs of three distribution examples (Y1, Y2, and Y3) of the In composition ratio Xin of the n-side guide layer 104. In distribution example Y1, the In composition ratio Xin is uniform at 0.04. In distribution example Y2 and distribution example Y3, the In composition ratio Xin of the n-side guide layer 104 monotonically increases as it approaches the active layer 105. Furthermore, the band gap energy of the n-side guide layer 104 monotonically decreases as it approaches the active layer 105. In distribution example Y2, the In composition ratio Xin is 0 at the end face of the n-side guide layer 104 farther from the active layer 105, and the In composition ratio Xin is 0.04 at the end face of the n-side guide layer 104 closer to the active layer 105. In distribution example Y3, the In composition ratio Xin is 0 at the end face of the n-side guide layer 104 farther from the active layer 105, and the In composition ratio Xin is 0.05 at the end face of the n-side guide layer 104 closer to the active layer 105. In distribution example Y2 and distribution example Y3, the rate of change of the In composition ratio Xin in the stacking direction of the n-side guide layer 104 is constant.

[0086] 14 and 16, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to reduce the waveguide loss and the effective refractive index difference ΔN. Here, when the ridge width W is 45 μm or more, the number of modes that can be guided by laser light is very large, and the influence of fluctuations in the light intensity distribution shape due to coupling between modes can be reduced. Therefore, kinks are less likely to occur in the current-light output characteristics of the semiconductor laser device 100. Therefore, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to realize a semiconductor laser device 100 with high light emission efficiency and a narrow horizontal radiation angle.

[0087] 15 , the optical confinement factor can be increased by setting the thickness Tn1 of the n-side guide layer 104 to be equal to or less than the thickness Tp1 of the p-side guide layer 106. When the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, as in the case of distribution examples Y2 and Y3 of the In composition ratio of the n-side guide layer 104, the optical confinement factor is maximized in a configuration in which the thickness Tn1 of the n-side guide layer 104 is equal to the thickness Tp1 of the p-side guide layer 106. Therefore, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, the thickness Tn1 of the n-side guide layer 104 may be equal to or less than the thickness Tp1 of the p-side guide layer 106. On the other hand, when the distribution of the In composition ratio of the n-side guide layer 104 is uniform as in distribution example Y1 of the In composition ratio of the n-side guide layer 104 and the average In composition ratio (i.e., the average refractive index) is larger than distribution examples Y2 and Y3, the thickness Tn1 of the n-side guide layer 104 may be smaller than the thickness Tp1 of the p-side guide layer 106. This can increase the optical confinement factor.

[0088] Furthermore, as in distribution example Y3, the maximum value of the In composition ratio of the n-side guide layer 104 may be greater than the maximum value of the In composition ratio of the p-side guide layer 106. This makes the maximum value of the refractive index of the n-side guide layer 104 greater than the maximum value of the refractive index of the p-side guide layer 106. When the Al composition ratio of the n-type cladding layer 102 is greater than the Al composition ratio of the p-type cladding layer 110, the light intensity distribution in the stacking direction tends to be biased in the direction from the active layer 105 to the p-type cladding layer 110. However, in distribution example Y3, it is easy to control the peak position of the light intensity distribution to the active layer 105. This makes it possible to increase the optical confinement factor while suppressing an increase in waveguide loss.

[0089] 17 and 18 is located within the active layer 105, the optical confinement factor can be increased. As shown in Fig. 18, in distribution example Y1, when the thickness Tp1 of the p-side guide layer 106 is 121 nm or more and 205 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 27.5% or more and 46.6% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled to be within the active layer 105. Therefore, the optical confinement factor can be increased.

[0090] 18 , in distribution example Y2, when the thickness Tp1 of the p-side guide layer 106 is 172 nm or more and 282 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 39.1% or more and 64.1% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0091] 18 , in distribution example Y3, when the thickness Tp1 of the p-side guide layer 106 is 153 nm or more and 252 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 34.8% or more and 57.3% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0092] Furthermore, according to distribution example Y2 and distribution example Y3 of the In composition ratio of the n-side guide layer 104 of configuration example 3, the difference in In composition ratio at the interface between the n-side guide layer 104 and the n-side intermediate layer 103 can be reduced. Therefore, the spike-shaped potential barrier formed near the interface between the n-side guide layer 104 and the n-side intermediate layer 103 can be reduced. This allows the operating voltage of the semiconductor laser device 100 to be reduced. Furthermore, according to distribution example Y2 and distribution example Y3, the band gap energy of the n-side guide layer 104 increases with increasing distance from the active layer 105, thereby preventing holes from leaking from the active layer 105 below the n-side guide layer 104. From the above, according to distribution example Y2 and distribution example Y3, a semiconductor laser device 100 with a low operating voltage and a low operating current can be realized.

[0093] [1-6. Configuration Example 4] Configuration Example 4 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 4 of the semiconductor laser element 100 differs from Configuration Example 3 in the configuration of the p-side electrode 113. Below, Configuration Example 4 will be described, focusing on the differences from Configuration Example 3.

[0094] In the fourth configuration example, the p-side electrode 113 has an ITO film with a thickness of 200 nm and an Ag film with a thickness of 200 nm disposed above the ITO film.

[0095] 19 to 23 will be used to explain the relationship between the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 of Configuration Example 4 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction. Figures 19, 20, 21, and 22 are graphs showing the relationship between the thickness Tn1 of the n-side guide layer 104 of Configuration Example 4 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution. As in Configuration Example 3, the thickness Tp1 of the p-side guide layer 106 is changed according to the thickness Tn1 of the n-side guide layer 104 so that the sum of the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 is 440 nm.

[0096] Fig. 23 is a graph in which a part of the range of the vertical axis in Fig. 22 is enlarged. In Fig. 23, the range of the vertical axis shown in Fig. 22 that includes the position corresponding to the active layer 105 is shown enlarged.

[0097] 19 to 23, similarly to FIGS. 14 to 18, graphs are shown for three distribution examples (Y1, Y2, and Y3) of the In composition ratio Xin of the n-side guide layer 104.

[0098] 19 and 21 , similarly to Configuration Example 3, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to reduce the waveguide loss and the effective refractive index difference ΔN. Furthermore, when the ridge width W is 45 μm or more, the number of modes that can be guided by laser light is very large, and the influence of fluctuations in the light intensity distribution shape due to coupling between modes can be reduced. Therefore, kinks are unlikely to occur in the current-light output characteristics of the semiconductor laser device 100. Therefore, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to realize a semiconductor laser device 100 with high light emission efficiency and a narrow horizontal radiation angle.

[0099] Furthermore, in Configuration Example 4, the p-side electrode 113 includes an ITO film, which is a light-transmitting conductive oxide film. As a result, as shown in FIG. 19 , in Configuration Example 4, the waveguide loss can be further reduced compared to Configuration Example 3.

[0100] 20 , the optical confinement factor can be increased by setting the thickness Tn1 of the n-side guide layer 104 to be equal to or less than the thickness Tp1 of the p-side guide layer 106. As in the case of distribution example Y2 and distribution example Y3 of the In composition ratio of the n-side guide layer 104, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, that is, when the band gap energies of the n-side guide layer 104 and the p-side guide layer 106 monotonically decrease toward the active layer 105, the optical confinement factor is maximized in a configuration in which the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 are equal. Therefore, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, the thickness Tn1 of the n-side guide layer 104 may be equal to or smaller than the thickness Tp1 of the p-side guide layer 106. On the other hand, when the distribution of the In composition ratio of the n-side guide layer 104 is uniform, as in distribution example Y1 of the In composition ratio of the n-side guide layer 104, and the average In composition ratio (i.e., the average refractive index) is larger than those of distribution examples Y2 and Y3, the thickness Tn1 of the n-side guide layer 104 may be smaller than the thickness Tp1 of the p-side guide layer 106. This can increase the optical confinement factor.

[0101] 22 and 23 is located within the active layer 105. As shown in Fig. 23, in distribution example Y1, when the thickness Tp1 of the p-side guide layer 106 is 121 nm or more and 205 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 27.5% or more and 46.6% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled to be within the active layer 105. Therefore, the optical confinement factor can be increased.

[0102] 23 , in distribution example Y2, when the thickness Tp1 of the p-side guide layer 106 is 172 nm or more and 282 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 39.1% or more and 64.1% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0103] 23 , in distribution example Y3, when the thickness Tp1 of the p-side guide layer 106 is 153 nm or more and 252 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 34.8% or more and 57.3% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0104] [1-7. Configuration Example 5] Configuration Example 5 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 5 of the semiconductor laser element 100 differs from Configuration Example 3 in the configuration of the p-type cladding layer 110. Configuration Example 5 will be described below, focusing on the differences from Configuration Example 3.

[0105] The p-type cladding layer 110 of the fifth example is a p-type Al layer having a thickness of 100 nm, 150 nm, 250 nm, or 350 nm. ０．０２６ Ga ０．９７４ This is the N layer.

[0106] When the thickness of the p-type cladding layer 110 is 100 nm, the p-type cladding layer 110 has a concentration of 2×10 １８ cm－３ p-type Al doped with Mg having a thickness of 100 nm ０．０２６ Ga ０．９７４ This is the N layer.

[0107] When the thickness of the p-type cladding layer 110 is 150 nm, the p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 100 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 50 nm ０．０２６ Ga ０．９７４ N layers.

[0108] When the thickness of the p-type cladding layer 110 is 250 nm, the p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 100 nm ０．０２６ Ga ０．９７４ N layers.

[0109] When the thickness of the p-type cladding layer 110 is 350 nm, the p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 200 nm ０．０２６ Ga ０．９７４ N layers.

[0110] 24 to 27 will be used to explain the relationship between the film thickness of the p-type cladding layer 110 of Configuration Example 5 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction. Figures 24, 25, 26, and 27 are graphs showing the relationship between the film thickness of the p-type cladding layer 110 of Configuration Example 5 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution.

[0111] 24 to 27 each show graphs of three distribution examples (Z1, Z2, and Z3) of the In composition ratio Xin of the n-side guide layer 104. In distribution example Z1, the In composition ratio Xin is uniform at 0.04, similar to distribution example Y1 of configuration example 3. In distribution example Z2 and distribution example Z3, the In composition ratio Xin of the n-side guide layer 104 monotonically increases toward the active layer 105, similar to distribution examples Y2 and Y3 of configuration example 3. Furthermore, the band gap energy of the n-side guide layer 104 monotonically decreases toward the active layer 105. In distribution example Z2, the In composition ratio Xin is 0 at the end face of the n-side guide layer 104 farther from the active layer 105, and the In composition ratio Xin is 0.04 at the end face of the n-side guide layer 104 closer to the active layer 105. In distribution example Z3, the In composition ratio Xin is 0 at the end facet of the n-side guide layer 104 farther from the active layer 105, and is 0.05 at the end facet of the n-side guide layer 104 closer to the active layer 105. In distribution example Z1 and distribution example Z3, the film thicknesses of the n-side guide layer 104 and the p-side guide layer 106 are 160 nm and 280 nm, respectively. In distribution example Z2, the film thicknesses of the n-side guide layer 104 and the p-side guide layer 106 are 200 nm and 240 nm, respectively.

[0112] As shown in FIG. 27 , when the thickness of the p-type cladding layer 110 is 100 nm or more and 350 nm or less, the peak position P1 of the light intensity distribution in the stacking direction is located within the active layer 105. On the other hand, as shown in FIGS. 24 to 26 , when the thickness of the p-type cladding layer 110 is 250 nm or less, the p-side electrode 113 is made of Ag, which has a low refractive index. This increases the optical confinement factor, but also increases the waveguide loss, resulting in a decrease in the effective refractive index difference ΔN. In this case, as in distribution example Z1, the average refractive index of the n-side guide layer 104 may be greater than the average refractive index of the p-side guide layer 106. As a result, as shown in FIG. 24 , the waveguide loss can be reduced more than in distribution examples Z2 and Z3, in which the average refractive index of the n-side guide layer 104 is equal to or less than the average refractive index of the p-side guide layer 106.

[0113] In a semiconductor laser device in which the p-side electrode is made of Pd, which has a refractive index significantly higher than that of Ag, when the thickness of the p-type cladding layer is 250 nm or less as in Comparative Example 1, the waveguide loss increases significantly due to light absorption by the p-side electrode compared to Configuration Example 5. Here, the refractive index of Ag is 0.16, and the refractive index of Pd is 1.39.

[0114] [1-8. Structural Example 6] Structural Example 6 of the semiconductor laser element 100 of this embodiment will be described. Structural Example 6 of the semiconductor laser element 100 differs from Structural Example 5 in the configuration of the p-side electrode 113. Below, Structural Example 6 will be described, focusing on the differences from Structural Example 5.

[0115] In Configuration Example 6, the p-side electrode 113 has an ITO film with a thickness of 200 nm and an Ag film with a thickness of 200 nm disposed above the ITO film.

[0116] 28 to 31 will be used to explain the relationship between the film thickness of the p-type cladding layer 110 of Configuration Example 6 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction. Figures 28, 29, 30, and 31 are graphs showing the relationship between the film thickness of the p-type cladding layer 110 of Configuration Example 6 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution, respectively.

[0117] 28 to 31, similarly to FIGS. 24 to 27, graphs are shown for three distribution examples (Z1, Z2, and Z3) of the In composition ratio Xin of the n-side guide layer 104.

[0118] 28 to 31, the same characteristics as those of Configuration Example 5 are obtained in Configuration Example 6. However, as shown in FIGS. 28 and 30, Configuration Example 6 can reduce the waveguide loss and increase the effective refractive index difference ΔN compared to Configuration Example 5. Furthermore, as shown in FIG. 30, even when the thickness of the p-type cladding layer 110 is 100 nm, the effective refractive index difference ΔN is 1.5×10 －３ The above effective refractive index difference ΔN can be obtained.

[0119] The effective refractive index difference ΔN is 1.0×10 －３ If the effective refractive index difference ΔN is less than 1.5×10, the waveguide characteristics of the semiconductor laser device 100 approach those of a gain-guided type, which leads to instability of the horizontal transverse mode of the laser light and an increase in the oscillation threshold current value. However, as in Configuration Example 6, when the p-side electrode 113 has a light-transmitting conductive oxide film, the effective refractive index difference ΔN is 1.5×10 when the thickness of the p-type cladding layer 110 is in the range of 100 nm or more. －３ As a result, the waveguide characteristics of the semiconductor laser device 100 can be maintained as a refractive index waveguide type. Therefore, in Configuration Example 6, it is possible to suppress instability of the horizontal transverse mode of the laser light and an increase in the oscillation threshold current value.

[0120] [1-9. Configuration Example 7] Configuration Example 7 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 7 of the semiconductor laser element 100 differs from Configuration Example 1 mainly in the configuration of the n-side intermediate layer 103. Configuration Example 7 will be described below, focusing on the differences from Configuration Example 1.

[0121] In the configuration example 7, the n-side intermediate layer 103 is a compositionally graded layer. The compositionally graded layer of the configuration example 7 is an Al compositional layer in which the Al composition ratio monotonically decreases and the In composition ratio monotonically increases with increasing distance from the n-type cladding layer 102. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In ＹｎｉN (0≦Xni<1, 0≦Yni<1) layer. That is, the band gap energy of the n-side intermediate layer 103 monotonically decreases with increasing distance from the n-type cladding layer 102. The Al composition ratio Xni of the composition gradient layer is Xn1 at the end face closer to the n-type cladding layer 102 and is 0 at the end face farther from the n-type cladding layer 102. The In composition ratio Yni of the composition gradient layer is 0 at the end face closer to the n-type cladding layer 102 and is 0.04 at the end face farther from the n-type cladding layer 102. Here, the Al composition ratio Xn1 is equal to the Al composition ratio of the n-type cladding layer 102. In Configuration Example 7, the change rates of the Al composition ratio and the In composition ratio in the stacking direction of the composition gradient layer are each constant. Furthermore, in Configuration Example 7, the composition gradient layer and the n-type cladding layer 102 contain In at a concentration of 1×10 １８ cm －３ is doped with Si.

[0122] The p-type cladding layer 110 of the seventh example is a p-type Al ０．０２６ Ga ０．９７４ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 200 nm ０．０２６ Ga ０．９７４ N layers.

[0123] The effect of the compositionally graded layer of Configuration Example 7 will be described with reference to Fig. 32 and Fig. 33 in comparison with the semiconductor laser device of Comparative Example 2. Fig. 32 and Fig. 33 are graphs showing the distribution of the conduction band potential in the stacking direction between the n-type cladding layer 102 and the n-side guide layer 104 of Comparative Example 2 and Configuration Example 7, respectively. In Fig. 32 and Fig. 33, the distribution of the Fermi level in the stacking direction is also shown by a dashed line.

[0124] The semiconductor laser device of Comparative Example 2 differs from Configuration Example 7 in that it does not include the n-side intermediate layer 103, but is the same in other respects.

[0125] As shown in Figure 32, in Comparative Example 2, a spike-shaped potential barrier is formed due to the large potential difference in the conduction band between the n-type cladding layer 102 and the n-side guide layer 104. The height of this potential barrier from the Fermi level (i.e., the potential difference between the Fermi level and the potential barrier) is 0.21 eV. In contrast, in Configuration Example 7, the n-side intermediate layer 103 has a composition-graded layer, which can mitigate fluctuations in the potential of the conduction band between the n-type cladding layer 102 and the n-side guide layer 104. As a result, as shown in Figure 33, the height of the spike-shaped potential barrier from the Fermi level formed between the n-type cladding layer 102 and the n-side guide layer 104 can be reduced to 0.074 eV. Therefore, the operating voltage of the semiconductor laser device 100 can be reduced.

[0126] The composition gradient layer is, for example, undoped Al Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In Ｙｎｉ The composition gradient layer may be an n-type Al layer. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In Ｙｎｉ The potential barrier formed near the interface between the composition gradient layer and the n-type cladding layer 102 is higher than in the case of an N layer. Therefore, in order to reduce the potential barrier, the composition gradient layer may be doped with an impurity at least near the interface with the n-type cladding layer 102. The impurity concentration doped into the composition gradient layer and the n-type cladding layer 102 is 1×10 １７ cm －３ That's it, 2 x 10 １８ cm －３ This can reduce the potential barrier.

[0127] The relationship between the thickness Tn of the n-side intermediate layer 103 (i.e., the thickness of the compositionally graded layer) and the operating voltage of the semiconductor laser device 100 in Configuration Example 7 will be described with reference to FIG. 34 . FIG. 34 is a graph showing the relationship between the thickness Tn of the n-side intermediate layer 103 in Configuration Example 7 and the operating voltage of the semiconductor laser device 100. FIG. 34 shows the graphs for cases where the Al composition ratio Xn1 of the n-type cladding layer 102 (i.e., the maximum Al composition ratio in the n-side intermediate layer 103) is 0.1, 0.075, 0.055, 0.045, and 0.026. Note that the configuration example in which the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.026 is not included in the configuration examples of the semiconductor laser device 100 according to the present embodiment, because the Al composition ratio of the n-type cladding layer 102 and the Al composition ratio of the p-type cladding layer 110 are equal. The configuration example in which the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.026 is one of the comparative examples of this embodiment.

[0128] As shown in FIG. 34 , when the Al composition ratio Xn1 is 0.026, the operating voltage can be almost minimized by setting the thickness Tn of the n-side intermediate layer 103 to 5 nm or more. When the Al composition ratio Xn1 is 0.045, the operating voltage can be almost minimized by setting the thickness Tn of the n-side intermediate layer 103 to 10 nm or more. When the Al composition ratio Xn1 is 0.055, the operating voltage can be almost minimized by setting the thickness Tn of the n-side intermediate layer 103 to 15 nm or more. When the Al composition ratio Xn1 is 0.075, the operating voltage can be almost minimized by setting the thickness Tn of the n-side intermediate layer 103 to 25 nm or more. When the Al composition ratio Xn1 is 0.1, the operating voltage can be almost minimized by setting the thickness Tn of the n-side intermediate layer 103 to 30 nm or more. From these results, the thickness Tn of the n-side intermediate layer 103 may be equal to or greater than the thickness Tnx [nm] expressed by the following formula (1).

[0129] Tnx=360・Xn1-4.67 (1)

[0130] Furthermore, the thickness Tn of the n-side intermediate layer 103 may be equal to or greater than half the thickness Tnx. When the thickness Tn of the n-side intermediate layer 103 is equal to or greater than half the thickness Tnx, the operating voltage can be reduced more than when the thickness Tn is less than half the thickness Tnx.

[0131] In the configuration example 7, the n-side guide layer 104 was undoped, but the concentration was 1×10 １７ cm －３ That's it, 2 x 10 １８ cm －３ The semiconductor laser device 100 may be doped with the following impurities, which allows the operating voltage of the semiconductor laser device 100 to be reduced.

[0132] [1-10. Structural Example 8] Structural Example 8 of the semiconductor laser element 100 of this embodiment will be described. Structural Example 8 of the semiconductor laser element 100 differs from Structural Example 7 in the configuration of the n-side intermediate layer 103. Below, Structural Example 8 will be described, focusing on the differences from Structural Example 7.

[0133] In the configuration example 8, the n-side intermediate layer 103 is a compositionally graded layer, similar to the configuration example 7. The compositionally graded layer of the configuration example 8 is an Al layer in which the Al composition ratio monotonically decreases with increasing distance from the n-type cladding layer 102. Ｘｎｉ Ga １－Ｘｎｉ N layer (0≦Xni<1) and the Al Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ The In layer is disposed above the N layer, and the In composition ratio increases monotonically with increasing distance from the n-type cladding layer 102. Ｙｎｉ Ga １－Ｙｎｉ The composition gradient layer has an Al layer and an N layer (0≦Yni<1). Ｘｎｉ Ga １－Ｘｎｉ The Al composition ratio Xni of the N layer is Al Ｘｎｉ Ga １－Ｘｎｉ At the end face closer to the n-type cladding layer 102 of the N layer, Xn1, and Al Ｘｎｉ Ga １－Ｘｎｉ The In content of the composition gradient layer is 0 at the end face farther from the n-type cladding layer 102 of the N layer. Ｙｎｉ Ga １－Ｙｎｉ The In composition ratio Yni of the N layer is In Ｙｎｉ Ga １－Ｙｎｉ At the end face closer to the n-type cladding layer 102 of the N layer, it is 0, and In Ｙｎｉ Ga １－Ｙｎｉ At the end face of the N layer farther from the n-type cladding layer 102, the Al composition ratio Xn1 is 0.04. Here, the Al composition ratio Xn1 is equal to the Al composition ratio of the n-type cladding layer 102. In Configuration Example 8, Al ＸｎｉGa １－Ｘｎｉ The change rate of the Al composition ratio in the stacking direction of the N layer, and the Ｙｎｉ Ga １－Ｙｎｉ In the configuration example 8, the change rate of the In composition ratio in the stacking direction of the N layer is constant. １８ cm －３ The Al of the composition gradient layer is doped. Ｘｎｉ Ga １－Ｘｎｉ N layer and In Ｙｎｉ Ga １－Ｙｎｉ The thickness of each of the N layers is Tn / 2, where Tn is the thickness of the n-side intermediate layer 103.

[0134] In the configuration example 8, it is also possible to reduce the spike-shaped potential barrier formed between the n-type cladding layer 102 and the n-side guide layer 104. Ｙｎｉ Ga １－Ｙｎｉ The N layer can reduce the potential barrier even if it is undoped. Ｙｎｉ Ga １－Ｙｎｉ The potential barrier becomes higher than when the N layer is doped with impurities. Ｙｎｉ Ga １－Ｙｎｉ The N layer may be doped with an impurity. The impurity concentration doped into the composition gradient layer and the n-type cladding layer 102 is 1×10 １７ cm －３ That's it, 2 x 10 １８ cm －３ This can reduce the potential barrier.

[0135] The relationship between the thickness Tn of the n-side intermediate layer 103 (i.e., the thickness of the compositionally graded layer) and the operating voltage of the semiconductor laser device 100 in Configuration Example 8 will be described with reference to FIG. 35 . FIG. 35 is a graph showing the relationship between the thickness Tn of the n-side intermediate layer 103 in Configuration Example 8 and the operating voltage of the semiconductor laser device 100. FIG. 35 shows the graphs for cases where the Al composition ratio Xn1 of the n-type cladding layer 102 (i.e., the maximum Al composition ratio in the n-side intermediate layer 103) is 0.1, 0.075, 0.055, 0.045, and 0.026. Note that the configuration example in which the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.026 is not included in the configuration examples of the semiconductor laser device 100 according to the present embodiment, because the Al composition ratio of the n-type cladding layer 102 and the Al composition ratio of the p-type cladding layer 110 are equal. The configuration example in which the Al composition ratio Xn1 of the n-type cladding layer 102 is 0.026 is one of the comparative examples of this embodiment.

[0136] 35 , in Configuration Example 8, as in Configuration Example 7, the thickness Tn of the n-side intermediate layer 103 may be equal to or greater than the thickness Tnx [nm] expressed by the above formula (1). This allows the operating voltage to be substantially minimized. Furthermore, the thickness Tn of the n-side intermediate layer 103 may be equal to or greater than half the thickness Tnx. If the thickness Tn of the n-side intermediate layer 103 is equal to or greater than half the thickness Tnx, the operating voltage can be reduced more than when the thickness Tn is less than half the thickness Tnx.

[0137] [1-11. Configuration Example 9] Configuration Example 9 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 9 of the semiconductor laser element 100 differs from Configuration Example 7 in the configurations of the n-side guide layer 104 and the p-side guide layer 106, but is the same in other configurations. Below, Configuration Example 9 will be described, focusing on the differences from Configuration Example 7.

[0138] In the configuration example 9, the n-side guide layer 104 is an undoped InN layer having a thickness of Tn1. Ｘｉｎ Ga １－Ｘｉｎ The p-side guide layer 106 is an undoped InN (0≦Xin<1) layer with a thickness of Tp1. Ｘｉｐ Ga １－Ｘｉｐ N (0≦Xip<1) layers.

[0139] In Configuration Example 9, the Al composition ratio of the n-type cladding layer 102 is 0.055. The impurity concentration in the n-type cladding layer 102 and the n-side intermediate layer 103 is 1×10 １８ cm －３ is.

[0140] 36 to 40 will be used to explain the relationship between the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 of Configuration Example 9 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction. Figures 36, 37, 38, and 39 are graphs showing the relationship between the thickness Tn1 of the n-side guide layer 104 of Configuration Example 9 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution. Here, the thickness Tp1 of the p-side guide layer 106 is changed according to the thickness Tn1 of the n-side guide layer 104 so that the sum of the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 is 440 nm.

[0141] Fig. 40 is a graph in which a part of the range of the vertical axis in Fig. 39 is enlarged. In Fig. 40, the range of the vertical axis shown in Fig. 39 that includes the position corresponding to the active layer 105 is shown enlarged.

[0142] 36 to 40, similar to Configuration Example 3 and the like, graphs are shown for three distribution examples (Y1, Y2, and Y3) of the In composition ratio Xin of the n-side guide layer 104.

[0143] 36 and 38, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to reduce the waveguide loss and the effective refractive index difference ΔN. Here, when the ridge width W is 45 μm or more, the number of modes that can be guided by laser light is very large, and the influence of fluctuations in the light intensity distribution shape due to coupling between modes can be reduced. Therefore, kinks are less likely to occur in the current-light output characteristics of the semiconductor laser device 100. Therefore, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to realize a semiconductor laser device 100 with high light emission efficiency and a narrow horizontal radiation angle.

[0144] 37 , the optical confinement factor can be increased by setting the thickness Tn1 of the n-side guide layer 104 to be equal to or less than the thickness Tp1 of the p-side guide layer 106. As in the case of distribution example Y2 and distribution example Y3 of the In composition ratio of the n-side guide layer 104, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, that is, when the band gap energies of the n-side guide layer 104 and the p-side guide layer 106 monotonically decrease toward the active layer 105, the optical confinement factor is maximized in a configuration in which the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 are equal. Therefore, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, the thickness Tn1 of the n-side guide layer 104 may be equal to or smaller than the thickness Tp1 of the p-side guide layer 106. On the other hand, when the distribution of the In composition ratio of the n-side guide layer 104 is uniform, as in distribution example Y1 of the In composition ratio of the n-side guide layer 104, and the average In composition ratio (i.e., the average refractive index) is larger than those of distribution examples Y2 and Y3, the thickness Tn1 of the n-side guide layer 104 may be smaller than the thickness Tp1 of the p-side guide layer 106. This can increase the optical confinement factor.

[0145] 39 and 40 is located within the active layer 105, the optical confinement factor can be increased. As shown in Fig. 40, in distribution example Y1, when the thickness Tp1 of the p-side guide layer 106 is 119 nm or more and 200 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 27.0% or more and 45.5% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled to be within the active layer 105. Therefore, the optical confinement factor can be increased.

[0146] 40 , in distribution example Y2, when the thickness Tp1 of the p-side guide layer 106 is 170 nm or more and 280 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 38.6% or more and 63.6% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0147] 40 , in distribution example Y3, when the thickness Tp1 of the p-side guide layer 106 is 150 nm or more and 250 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 34.1% or more and 56.8% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0148] [1-12. Configuration Example 10] Configuration Example 10 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 10 of the semiconductor laser element 100 differs from Configuration Example 9 in the configuration of the p-side electrode 113. Below, Configuration Example 10 will be described, focusing on the differences from Configuration Example 9.

[0149] In Configuration Example 10, the p-side electrode 113 has an ITO film with a thickness of 200 nm and an Ag film with a thickness of 200 nm disposed above the ITO film.

[0150] 41 to 45 are used to explain the relationship between the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 of Configuration Example 10 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position of the light intensity distribution in the stacking direction. FIGS. 41 , 42 , 43 , and 44 are graphs showing the relationship between the thickness Tn1 of the n-side guide layer 104 of Configuration Example 10 and the waveguide loss, the optical confinement factor, the effective refractive index difference ΔN, and the peak position (P1) of the light intensity distribution. As in Configuration Example 9, the thickness Tp1 of the p-side guide layer 106 is changed according to the thickness Tn1 of the n-side guide layer 104 so that the sum of the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 is 440 nm.

[0151] Fig. 45 is a graph in which a part of the range of the vertical axis in Fig. 44 is enlarged. In Fig. 45, the range of the vertical axis shown in Fig. 44 that includes the position corresponding to the active layer 105 is shown enlarged.

[0152] 41 to 45, similarly to FIGS. 36 to 40, graphs are shown for three distribution examples (Y1, Y2, and Y3) of the In composition ratio Xin of the n-side guide layer 104.

[0153] 41 and 43 , similarly to Configuration Example 9, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to reduce the waveguide loss and the effective refractive index difference ΔN. Furthermore, when the ridge width W is 45 μm or more, the number of modes that can be guided by laser light is very large, and the influence of fluctuations in the light intensity distribution shape due to coupling between modes can be reduced. Therefore, kinks are unlikely to occur in the current-light output characteristics of the semiconductor laser device 100. Therefore, by making the thickness Tn1 of the n-side guide layer 104 larger than the thickness Tp1 of the p-side guide layer 106, it is possible to realize a semiconductor laser device 100 with high light emission efficiency and a narrow horizontal radiation angle.

[0154] Furthermore, in Configuration Example 10, the p-side electrode 113 has an ITO film, which is a light-transmitting conductive oxide film. As a result, as shown in FIG. 41 , in Configuration Example 10, the waveguide loss can be further reduced compared to Configuration Example 9.

[0155] 42 , the optical confinement factor can be increased by setting the thickness Tn1 of the n-side guide layer 104 to be equal to or less than the thickness Tp1 of the p-side guide layer 106. As in the case of distribution example Y2 and distribution example Y3 of the In composition ratio of the n-side guide layer 104, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, that is, when the band gap energies of the n-side guide layer 104 and the p-side guide layer 106 monotonically decrease toward the active layer 105, the optical confinement factor is maximized in a configuration in which the thickness Tn1 of the n-side guide layer 104 and the thickness Tp1 of the p-side guide layer 106 are equal. Therefore, when the In composition ratios of the n-side guide layer 104 and the p-side guide layer 106 monotonically increase toward the active layer 105, the thickness Tn1 of the n-side guide layer 104 may be equal to or smaller than the thickness Tp1 of the p-side guide layer 106. On the other hand, when the distribution of the In composition ratio of the n-side guide layer 104 is uniform, as in distribution example Y1 of the In composition ratio of the n-side guide layer 104, and the average In composition ratio (i.e., the average refractive index) is larger than those of distribution examples Y2 and Y3, the thickness Tn1 of the n-side guide layer 104 may be smaller than the thickness Tp1 of the p-side guide layer 106. This can increase the optical confinement factor.

[0156] 44 and 45 is located within the active layer 105, the optical confinement factor can be increased. As shown in Fig. 45, in distribution example Y1, when the thickness Tp1 of the p-side guide layer 106 is 119 nm or more and 200 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 27.0% or more and 45.5% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled to be within the active layer 105. Therefore, the optical confinement factor can be increased.

[0157] 45 , in distribution example Y2, when the thickness Tp1 of the p-side guide layer 106 is 170 nm or more and 280 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 38.6% or more and 63.6% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0158] 45 , in distribution example Y3, when the thickness Tp1 of the p-side guide layer 106 is 150 nm or more and 250 nm or less (that is, when the thickness Tn1 of the n-side guide layer 104 is 34.1% or more and 56.8% or less of the sum of the thickness Tn1 and the thickness Tn1 of the p-side guide layer 106), the position P1 can be controlled within the active layer 105. Therefore, the optical confinement factor can be increased.

[0159] [1-13. Configuration Example 11] Configuration Example 11 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 11 of the semiconductor laser element 100 differs from Configuration Example 1 mainly in the configuration of the active layer 105. Configuration Example 11 will be described below, focusing on the differences from Configuration Example 1.

[0160] The active layer 105 of Configuration Example 11 has a single quantum well structure. That is, the active layer 105 has a barrier layer 105a, a well layer 105b disposed above the barrier layer 105a, and a barrier layer 105c disposed above the well layer 105b. The barrier layer 105a is made of undoped InP with a thickness of 7 nm. ０．０５ Ga ０．９５ The well layer 105b is an undoped In layer having a thickness of 4.5 nm. ０．１８ Ga ０．８２ The barrier layer 105c is an undoped In layer with a thickness of 5 nm. ０．０５ Ga ０．９５ In this way, of the plurality of barrier layers 105 a and 105 c, the barrier layer 105 a closest to the n-type cladding layer 102 has a larger film thickness than the barrier layer 105 c closest to the p-type cladding layer 110 .

[0161] The n-type cladding layer 102 of Configuration Example 11 has a concentration of 1×10 １８ cm －３ n-type Al doped with Si having a thickness of 1500 nm ０．０４５ Ga ０．９５５ This is the N layer.

[0162] The n-side intermediate layer 103 of Configuration Example 11 has a concentration of 1×10 １８ cm －３The composition gradient layer of Configuration Example 11 is an n-type Si-doped composition gradient layer having a thickness of 30 nm. The composition gradient layer of Configuration Example 11 is an Al composition gradient layer in which the Al composition ratio monotonically decreases and the In composition ratio monotonically increases with increasing distance from the n-type cladding layer 102. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In Ｙｎｉ N (0≦Xni<1, 0≦Yni<1) layer. The band gap energy of the n-side intermediate layer 103 monotonically decreases with increasing distance from the n-type cladding layer 102. The Al composition ratio Xni of the composition gradient layer is 0.045 at the end facet closer to the n-type cladding layer 102 and is 0 at the end facet farther from the n-type cladding layer 102. The In composition ratio Yni of the composition gradient layer is 0 at the end facet closer to the n-type cladding layer 102 and is 0.04 at the end facet farther from the n-type cladding layer 102.

[0163] The n-side guide layer 104 of the configuration example 11 is an undoped In layer having a thickness of 160 nm or 200 nm. Ｘｉｎ Ga １－Ｘｉｎ This is the N layer.

[0164] The p-side guide layer 106 of the configuration example 11 is an undoped In layer having a thickness of 280 nm or 240 nm. Ｘｉｐ Ga １－Ｘｉｐ The p-side guide layer 106 has an In composition ratio Xip of 0.04 at the end face of the p-side guide layer 106 closer to the active layer 105, and an In composition ratio Xip of 0.04 at the end face of the p-side guide layer 106 farther from the active layer 105.

[0165] The p-type cladding layer 110 of the configuration example 11 is a p-type Al ０．０２６ Ga ０．９７４ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 100 nm０．０２６ Ga ０．９７４ N layers.

[0166] In Configuration Example 11, the characteristics of the semiconductor laser device 100 will be described when the In composition ratio Xin of the n-side guide layer 104 is uniform at 0.04, similar to Distribution Example Y1 of Configuration Example 3, the thickness of the n-side guide layer 104 is 160 nm, and the thickness of the p-side guide layer 106 is 280 nm. In this case, the waveguide loss of the semiconductor laser device 100 is 3.4 cm －１ The optical confinement coefficient is 1.2%, and the effective refractive index difference ΔN is 2.2×10 －３ and the position P1 was 1.5 nm.

[0167] In Configuration Example 11, the In composition ratio Xin of the n-side guide layer 104 increases from 0 to 0.04 as it moves away from the n-type cladding layer 102, similar to Distribution Example Y2 of Configuration Example 3, and the characteristics of the semiconductor laser device 100 will be described when the thickness of the n-side guide layer 104 is 200 nm and the thickness of the p-side guide layer 106 is 240 nm. In this case, the waveguide loss of the semiconductor laser device 100 is 3.5 cm －１ The optical confinement coefficient is 1.2%, and the effective refractive index difference ΔN is 3.3×10 －３ and the position P1 was 3.8 nm.

[0168] In Configuration Example 11, the In composition ratio Xin of the n-side guide layer 104 increases from 0 to 0.05 as it moves away from the n-type cladding layer 102, similar to Distribution Example Y3 of Configuration Example 3, and the characteristics of the semiconductor laser device 100 will be described when the thickness of the n-side guide layer 104 is 200 nm and the thickness of the p-side guide layer 106 is 240 nm. In this case, the waveguide loss of the semiconductor laser device 100 is 3.5 cm －１ The optical confinement coefficient is 1.2%, and the effective refractive index difference ΔN is 3.0×10 －３ and the position P1 was 1.5 nm.

[0169] In the configuration example 11, low waveguide loss and a large optical confinement factor can also be realized. In particular, in the semiconductor laser device 100 including the active layer 105 having a single quantum well structure as in the configuration example 11, the optical confinement factor in the active layer 105 tends to be low, so the effect of the configuration as in the configuration example 11, which can increase the optical confinement factor, is particularly remarkable. In addition, when the effective refractive index difference ΔN is 2×10 －３ That's it, 3 x 10 －３ or less, the horizontal divergence angle of the laser light can be reduced.

[0170] In Configuration Example 11, the n-side intermediate layer 103 is a compositionally graded layer, but it may be an n-type GaN layer with a thickness of 30 nm.

[0171] Furthermore, of the multiple barrier layers 105a and 105c included in the active layer 105 of Configuration Example 11, the band gap energy of the barrier layer 105c closest to the p-type cladding layer 110 may be larger than the band gap energy of the barrier layer 105a closest to the n-type cladding layer 102. Furthermore, of the multiple barrier layers 105a and 105c, the Al composition ratio of the barrier layer 105c closest to the p-type cladding layer 110 may be larger than the Al composition ratio of the barrier layer 105a closest to the n-type cladding layer 102.

[0172] [1-14. Configuration Example 12] Configuration Example 12 of the semiconductor laser element 100 of this embodiment will be described. Configuration Example 12 of the semiconductor laser element 100 differs from Configuration Example 11 in the configuration of the p-side electrode 113. Configuration Example 12 will be described below, focusing on the differences from Configuration Example 11.

[0173] In Configuration Example 12, the p-side electrode 113 has an ITO film with a thickness of 200 nm and an Ag film with a thickness of 200 nm disposed above the ITO film.

[0174] In Configuration Example 12, the characteristics of the semiconductor laser device 100 will be described when the In composition ratio Xin of the n-side guide layer 104 is uniform at 0.04, similar to Distribution Example Y1 of Configuration Example 3, the thickness of the n-side guide layer 104 is 160 nm, and the thickness of the p-side guide layer 106 is 280 nm. In this case, the waveguide loss of the semiconductor laser device 100 is 3.1 cm. －１The optical confinement coefficient is 1.2%, and the effective refractive index difference ΔN is 2.4×10 －３ and the position P1 was 1.6 nm.

[0175] In Configuration Example 12, the In composition ratio Xin of the n-side guide layer 104 increases from 0 to 0.04 as it moves away from the n-type cladding layer 102, similar to Distribution Example Y2 of Configuration Example 3, and the characteristics of the semiconductor laser device 100 will be described when the thickness of the n-side guide layer 104 is 200 nm and the thickness of the p-side guide layer 106 is 240 nm. In this case, the waveguide loss of the semiconductor laser device 100 is 3.1 cm. －１ The optical confinement coefficient is 1.2%, and the effective refractive index difference ΔN is 3.5×10 －３ and the position P1 was 4.0 nm.

[0176] In Configuration Example 12, the In composition ratio Xin of the n-side guide layer 104 increases from 0 to 0.05 as it moves away from the n-type cladding layer 102, similar to Distribution Example Y3 of Configuration Example 3, and the characteristics of the semiconductor laser device 100 will be described when the thickness of the n-side guide layer 104 is 200 nm and the thickness of the p-side guide layer 106 is 240 nm. In this case, the waveguide loss of the semiconductor laser device 100 is 3.5 cm －１ The optical confinement coefficient is 1.2%, and the effective refractive index difference ΔN is 3.0×10 －３ and the position P1 was 1.5 nm.

[0177] In the configuration example 12, low waveguide loss and a large optical confinement factor can also be realized. In particular, in the semiconductor laser device 100 including the active layer 105 having a single quantum well structure as in the configuration example 12, the optical confinement factor in the active layer 105 tends to be low, so the effect of the configuration as in the configuration example 12, which can increase the optical confinement factor, is particularly remarkable. In addition, when the effective refractive index difference ΔN is 2×10 －３ That's it, 3 x 10 －３ Furthermore, in Configuration Example 12, the p-side electrode 113 includes an ITO film, which is a conductive oxide film having light transmission properties, and therefore the waveguide loss can be further reduced compared to Configuration Example 11.

[0178] In Configuration Example 11, the n-side intermediate layer 103 is a compositionally graded layer, but it may be an n-type GaN layer with a thickness of 30 nm.

[0179] [1-15. Configuration Example 13] Configuration Example 13 of the semiconductor laser device 100 of this embodiment will be described. Configuration Example 13 of the semiconductor laser device 100 is a configuration example that emits laser light in the wavelength band of 530 nm. In Configuration Example 13, the n-type cladding layer 102 is made of n-type Al ０．０８ Ga ０．９２ The n-side intermediate layer 103 is an n-type GaN layer having a thickness of 200 nm. １８ cm －３ The n-side guide layer 104 is an undoped In layer with a thickness of 180 nm. ０．０４ Ga ０．９６ This is the N layer.

[0180] Each of the barrier layers 105a and 105c is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ The barrier layer 105e is an undoped In layer with a thickness of 5 nm. ０．０５ Ga ０．９５ Each of the well layers 105b and 105d is an undoped In layer having a thickness of 3 nm. ０．２５ Ga ０．７５ This is the N layer.

[0181] The p-side guide layer 106 is an undoped In layer having a thickness of 260 nm. Ｘｉｐ Ga １－Ｘｉｐ The p-side guide layer 106 is an N layer. The In composition ratio of the p-side guide layer 106 monotonically decreases with increasing distance from the active layer 105. The band gap energy of the p-side guide layer 106 monotonically increases with increasing distance from the active layer 105. The In composition ratio Xip is 0.03 at the end face of the p-side guide layer 106 closer to the active layer 105, and is 0 at the end face of the p-side guide layer 106 farther from the active layer 105. In configuration example 13, the rate of change of the In composition ratio in the stacking direction of the p-side guide layer 106 is constant.

[0182] The p-side intermediate layer 107 is a GaN layer with a thickness of 20 nm. The p-side intermediate layer 107 is composed of an undoped GaN layer with a thickness of 17 nm and a 1×10 １９ cm －３ and a 3 nm thick n-type GaN layer doped with Mg.

[0183] The electron barrier layer 108 has a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 5 nm ０．３６ Ga ０．６４ This is the N layer.

[0184] The p-type cladding layer 110 is a p-type Al layer having a thickness of 250 nm. ０．０４ Ga ０．９６ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０４ Ga ０．９６ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 100 nm ０．０４ Ga ０．９６ The contact layer 111 has a concentration of 1×10 ２０ cm －３ The layer is a 10 nm thick p-type GaN layer doped with Mg.

[0185] In Configuration Example 13, the ridge width W is 45 μm, the cavity length is 1200 μm, and the distance dc between the bottom end of the ridge 110R and the electron barrier layer 108 is 40 nm.

[0186] In the configuration example 13, when the p-side electrode 113 is an Ag film with a thickness of 200 nm, the waveguide loss of the semiconductor laser device 100 is 5.3 cm －１ The optical confinement coefficient is 1.18%, and the effective refractive index difference ΔN is 4.2×10 －３ and the position P1 was 1.1 nm.

[0187] In the configuration example 13, when the p-side electrode 113 has an ITO film with a thickness of 200 nm and Pd with a thickness of 200 nm arranged above the ITO film, the waveguide loss of the semiconductor laser device 100 is 4.9 cm －１ The optical confinement coefficient is 1.15%, and the effective refractive index difference ΔN is 5.5×10 －３ and the position P1 was 2.7 nm.

[0188] In this way, the p-side electrode 113 includes ITO, which is a light-transmitting conductive oxide film, thereby reducing waveguide loss. In Configuration Example 13, the thickness of the p-type cladding layer 110 is 250 nm, but even if the thickness of the p-type cladding layer 110 is 100 nm, waveguide loss can be reduced. Furthermore, when the thickness of the p-type cladding layer 110 is 100 nm or more and 300 nm or less, position P1 can be controlled within the active layer 105.

[0189] In the configuration example 13, when the p-side electrode 113 has an ITO film with a thickness of 200 nm and an Ag film with a thickness of 200 nm arranged above the ITO film, the waveguide loss of the semiconductor laser device 100 is 4.72 cm －１ The optical confinement coefficient is 1.15%, and the effective refractive index difference ΔN is 5.5×10 －３ and the position P1 was 2.8 nm. Thus, by including the ITO film and the Ag film in the p-side electrode 113, the waveguide loss can be further reduced. Furthermore, as described above, by including the Ag film in the p-side electrode 113, the effect of feeding back spontaneously emitted light to the active layer 105 can be enhanced. Therefore, the effect of reducing the oscillation threshold current value and the effect of increasing the slope efficiency due to the increased quantum efficiency can be obtained. This effect is particularly effective in the semiconductor laser device 100 that emits laser light in the 530 nm band, since the temperature characteristics tend to deteriorate as the optical confinement factor in the active layer 105 decreases.

[0190] As in Configuration Example 13, by including In in each barrier layer, it is possible to suppress the light intensity distribution from spreading to the p-type cladding layer 110. This makes it possible to increase the light confinement factor and reduce the waveguide loss. Furthermore, as in Configuration Example 13, by making the film thickness of the p-side guide layer 106 thicker than the film thickness of the n-side guide layer 104, it is possible to further suppress the light intensity distribution from spreading to the p-type cladding layer 110. This makes it possible to further increase the light confinement factor and further reduce the waveguide loss.

[0191] Furthermore, the configuration of the active layer 105 in Configuration Example 13 is not limited to the above-described configuration. For example, the composition of each barrier layer may be GaN. This reduces the tensile stress in the semiconductor laminate 100S, thereby improving the crystallinity of the semiconductor laminate 100S. Furthermore, by using GaN as the composition of each barrier layer, the difference between the energy of each quantum level of electrons in each well layer and the energy (potential) of the conduction band of each barrier layer, and the difference between the energy of each quantum level of holes in each well layer and the energy of the valence band of each barrier layer, can be increased. This makes it possible to suppress leakage of electrons or holes from each well layer to each guide layer.

[0192] Furthermore, when the composition of each barrier layer is GaN, the active layer 105 may have an intermediate barrier layer disposed between each well layer and each barrier layer. Such a configuration of the active layer 105 will be described with reference to Fig. 46. Fig. 46 is a schematic graph showing an example of the bandgap energy distribution of the active layer 105 of Configuration Example 13. The horizontal axis of Fig. 46 represents the position in the stacking direction of the active layer 105, and the vertical axis represents the bandgap energy.

[0193] 46, the active layer 105 may have intermediate barrier layers 105i and 105j. The intermediate barrier layer 105i is a layer disposed between the barrier layer 105a and the well layer 105b. The bandgap energy of the intermediate barrier layer 105i is lower than that of the barrier layer 105a and higher than that of the well layer 105b. The intermediate barrier layer 105j is a layer disposed between the barrier layer 105c and the well layer 105d. The bandgap energy of the intermediate barrier layer 105j is lower than that of the barrier layer 105c and higher than that of the well layer 105d.

[0194] Here, if the bandgap energy of the intermediate barrier layer is too close to that of the barrier layer, the refractive index of the intermediate barrier layer will be small, and the optical confinement factor of the well layer will be small. Furthermore, if the bandgap energy of the intermediate barrier layer is too close to that of the well layer, the well layer, which has a large In composition ratio, will be thick, which may result in a decrease in crystallinity. Therefore, if the average bandgap energy of the intermediate barrier layer is represented by Egm and the average bandgap energies of the barrier layer and well layer in contact with the intermediate barrier layer are represented by Egb and Egw, respectively, the average bandgap energy Egm of the intermediate barrier layer may be equal to or greater than Egw + (Egb - Egw) × 0.3 and equal to or less than Egw + (Egb - Egw) × 0.7. When the barrier layer, intermediate barrier layer, and well layer are each made of InGaN, the average In composition ratio of each layer is represented by Inb, Inm, and Inw, respectively. Inm may be Inb + (Inw - Inb) x 0.3 or more and Inb + (Inw - Inb) x 0.7 or less. If the thickness of the intermediate barrier layer is too thin, the effect of increasing the optical confinement coefficient of the well layer is small, and if it is too thick, the region with a high In composition ratio becomes thick, which may lead to a decrease in crystallinity. Therefore, the film thickness of the intermediate barrier layer may be 1 nm or more and 10 nm or less. The intermediate barrier layers 105i and 105j are made of undoped In with a film thickness of 1 nm or more and 10 nm or less. ０．１０ Ga ０．９０ An N layer or the like can be used.

[0195] The active layer 105 includes these intermediate barrier layers 105i and 105j, which increases the refractive index of the active layer 105. This increases the optical confinement factor of the active layer 105, allowing the peak position (P1) of the light intensity distribution in the stacking direction to be controlled within the active layer 105. The intermediate barrier layers 105i and 105j may be configured so that the band gap energy monotonically decreases from the n-side to the p-side. This configuration allows the position in the stacking direction where the amplitude of the wave function of the ground quantum level of electrons formed in the conduction band of the well layers 105b and 105d is maximized to be closer to the position in the stacking direction where the amplitude of the wave function of the ground quantum level of holes formed in the valence band is maximized. This increases the correlation coefficient between the ground quantum levels of electrons and holes, improving the amplification gain. This reduces the oscillation threshold current. In this case, as described above, if the average value of the band gap energy of the intermediate barrier layer is represented by Egm and the average band gap energies of the barrier layer and well layer in contact with the intermediate barrier layer are represented by Egb and Egw, respectively, the average value of the band gap energy Egm of the intermediate barrier layer may be Egw + (Egb - Egw) × 0.3 or more and Egw + (Egb - Egw) × 0.7 or less. If the barrier layer, intermediate barrier layer, and well layer are each made of InGaN, if the average In composition ratio of each layer is represented by Inb, Inm, and Inw, respectively, Inm may be Inb + (Inw - Inb) × 0.3 or more and Inb + (Inw - Inb) × 0.7 or less.

[0196] Furthermore, when the semiconductor laser element 100 emits laser light in a wavelength band longer than the 455 nm band, the In composition ratio of each well layer becomes high, which tends to deteriorate the crystallinity of the semiconductor laminate 100S. Even in such a case, by including the intermediate barrier layers 105i and 105j in the active layer 105, the difference in lattice constant between the intermediate barrier layers 105i and 105j and the well layers 105b and 105d becomes smaller than the difference in lattice constant between the barrier layer 105a, the barrier layer 105c and the well layers 105b and 105d, which facilitates crystal growth and makes it possible to improve the crystallinity of the semiconductor laminate 100S.

[0197] The active layer 105 may have a single quantum well structure. In the semiconductor laser device 100 including the active layer 105 having a single quantum well structure, the optical confinement coefficient of the active layer 105 tends to be low, and therefore the effect of the above-described configuration that can increase the optical confinement coefficient is particularly remarkable.

[0198] In Configuration Example 13, the substrate 101 may be made of AlGaN. The effects of using an AlGaN substrate 101 will be described with reference to FIGS. 47 to 50 , comparing the effects with the effects of using a GaN substrate 101. FIGS. 47 and 48 are graphs showing the relationship between the stacking direction position and the light intensity distribution and the integrated stress when a GaN substrate 101 is used in Configuration Example 13. FIGS. 49 and 50 are graphs showing the relationship between the stacking direction position and the light intensity distribution and the integrated stress when an AlGaN substrate 101 is used in Configuration Example 13. FIG. 47 shows graphs for cases where the n-type cladding layer 102 has a thickness of 1 μm, 2 μm, and 3 μm. FIG. 48 shows graphs for cases where the n-type cladding layer 102 has a thickness of 2.3 μm. FIGS. 49 and 50 show graphs for cases where the n-type cladding layer 102 has a thickness of 1 μm.

[0199] 48 and 50 is an integral value obtained by integrating the stress applied to the semiconductor stack in the stacking direction, where the value of tensile stress occurring in a layer in the semiconductor stack 100S that has a smaller lattice constant than the substrate 101 is expressed as a negative value and the value of compressive stress occurring in a layer in the semiconductor stack 100S that has a larger lattice constant than the substrate 101 is expressed as a positive value. In other words, the greater the absolute value of the integrated stress, the greater the stress applied to the semiconductor stack 100S; a negative value for the integrated stress indicates that tensile stress is applied to the semiconductor stack 100S, and a positive value for the integrated stress indicates that compressive stress is applied to the semiconductor stack 100S.

[0200] When using a substrate 101 made of GaN, the refractive index of the substrate 101 is higher than the effective refractive index for the guided mode in which laser light having a wavelength in the 530 nm band propagates through the waveguide of the semiconductor laser element, and so when the light reaches the substrate 101, the light propagates within the substrate 101. This causes light leakage into the substrate 101. As a result, the light emission efficiency decreases and a kink occurs in the current-light output characteristics. In order to suppress such light leakage into the substrate 101, the light intensity at the interface between the substrate 101 and the n-type cladding layer 102 is reduced to 10% of the peak light intensity. －６ It is necessary to suppress the stress distribution to 1 / 2 times or less. To achieve such a light intensity distribution, the film thickness of the n-type cladding layer 102 in Configuration Example 13 needs to be 2.3 μm or more. In this case, as shown in FIG. 48 , the integrated stress accumulated throughout the semiconductor laminate 100S is −1033 Pa m. In this case, cracks in the wafer and lattice defects in the semiconductor laminate 100S may occur when and after the semiconductor laminate 100S is stacked on the wafer that is the base material of the substrate 101.

[0201] In contrast, when using a substrate 101 made of AlGaN having a refractive index smaller than the effective refractive index for the guided mode of laser light, it is possible to suppress the occurrence of light leakage into the substrate 101. In Configuration Example 13, by using a substrate 101 made of AlGaN having an Al composition ratio of 0.035 or more, it is possible to suppress the occurrence of light leakage into the substrate 101.

[0202] Furthermore, by using the substrate 101 made of AlGaN, the difference in lattice constant between the substrate 101 and each cladding layer can be reduced, so that the integrated stress accumulated in the entire semiconductor laminate 100S becomes 258.3 Pa m. Therefore, the occurrence of cracks and lattice defects in the wafer can be suppressed.

[0203] If the n-type cladding layer 102 is too thin, the influence of the substrate 101 on the light intensity distribution in the stacking direction increases, so the thickness of the n-type cladding layer 102 may be 0.5 μm or more.

[0204] Furthermore, the Al composition ratio of the AlGaN substrate 101 may be 50% or more and less than the Al composition ratio of the n-type cladding layer 102. This reduces the spike-shaped potential barrier caused by piezoelectric polarization charges generated in the conduction band structure at the interface between the substrate 101 and the n-type cladding layer 102. Therefore, the refractive index of the substrate 101 can be made smaller than the effective refractive index for the waveguide mode while suppressing an increase in the operating voltage of the semiconductor laser device 100.

[0205] (Embodiment 2) A semiconductor laser device according to embodiment 2 will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 100 according to embodiment 1 mainly in that the thickness of the p-type cladding layer 110 is thin and that the lower end of the ridge is located below the electron barrier layer. The semiconductor laser device according to this embodiment will be described below with reference to FIG. 51 , focusing on the differences from the semiconductor laser device 100 according to embodiment 1.

[0206] Fig. 51 is a schematic cross-sectional view showing the overall configuration of the semiconductor laser device 200 according to this embodiment. Similar to Fig. 2, Fig. 51 shows a cross section perpendicular to the direction of emission of laser light from the semiconductor laser device 200.

[0207] As shown in FIG. 51, the semiconductor laser device 200 includes a substrate 101, a semiconductor stack 200S, a current blocking layer 112, a p-side electrode 113, and an n-side electrode 114.

[0208] The semiconductor stack 200S has a ridge 110R that protrudes upward. The semiconductor stack 100S also has two grooves 110T that are arranged along the ridge 110R and extend in the Y-axis direction, and two protruding portions 110P that protrude upward. One groove 110T is arranged between the ridge 110R and one of the protruding portions 110P, and the other groove 110T is arranged between the ridge 110R and the other protruding portion 110P.

[0209] The semiconductor laminate 200S has an n-type cladding layer 102, an n-side intermediate layer 103, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, a p-side intermediate layer 207, an electron barrier layer 108, a p-type cladding layer 110, and a contact layer 111. In this embodiment, the semiconductor laminate 100S is made of a nitride semiconductor.

[0210] The n-type cladding layer 102 has a concentration of 1×10 １８ cm －３ Si-doped Al film with a thickness of 1500 nm ０．０５５ Ga ０．９４５ This is the N layer.

[0211] The n-side intermediate layer 103 has a concentration of 1×10 １８ cm －３ The n-side intermediate layer 103 is a 30 nm thick GaN layer doped with Si. The n-side intermediate layer 103 may be a compositionally graded layer.

[0212] The n-side guide layer 104 is an In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ The n-side guide layer 104 may have an In composition ratio similar to the distribution examples Y2 and Y3.

[0213] The active layer 105 and the p-side guide layer 106 have the same configurations as the active layer 105 and the p-side guide layer 106 of the first structural example of the semiconductor laser device 100 according to the first embodiment.

[0214] The p-side intermediate layer 207 is a semiconductor layer disposed between the p-side guide layer 106 and the electron barrier layer 108. The band gap energy of the p-side intermediate layer 207 is equal to or greater than the band gap energy of the p-side guide layer 106 and equal to or less than the band gap energy of the electron barrier layer 108. In this embodiment, the band gap energy of the p-side intermediate layer 207 is equal to or less than the band gap energy of the p-type cladding layer 110. In this embodiment, the p-side intermediate layer 207 is composed of an undoped GaN layer with a thickness of 20 nm and an undoped Al layer with a thickness of 50 nm disposed above the GaN layer. ０．０２６ Ga ０．９７４ N layers.

[0215] The electron barrier layer 108 has a concentration of 1×10１９ cm －３ p-type Al doped with Mg having a thickness of 10 nm Ｘｅｂ Ga １－Ｘｅｂ In this embodiment, the electron barrier layer 108 has a lower layer with a thickness of 7 nm and an upper layer with a thickness of 3 nm disposed above the lower layer. The lower layer is a p-type Al layer whose Al composition ratio monotonically increases with increasing distance from the active layer 105. Ｘｅｂ Ga １－Ｘｅｂ The Al composition ratio Xeb is 0.026 at the end face closer to the lower active layer 105, and 0.2 at the end face farther from the active layer 105. The upper layer is a p-type Al layer in which the Al composition ratio monotonically decreases with increasing distance from the active layer 105. Ｘｅｂ Ga １－Ｘｅｂ The Al composition ratio Xeb is 0.2 at the end face closer to the upper active layer 105, and 0.026 at the end face farther from the active layer 105.

[0216] The p-type cladding layer 110 is a p-type Al layer having a thickness of 150 nm. ０．０２６ Ga ０．９７４ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 50 nm ０．０２６ Ga ０．９７４ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 100 nm ０．０２６ Ga ０．９７４ N layers.

[0217] The contact layer 111 has a concentration of 1×10 ２０ cm －３ The layer is a 10 nm thick p-type GaN layer doped with Mg.

[0218] The p-side electrode 113 is made of at least one of Ag, an Ag alloy, and Al.

[0219] 51 , the lower end of the ridge 110R according to this embodiment is located below the electron barrier layer 108. In this embodiment, the lower end of the ridge 110R is located in the p-side intermediate layer 207. In this manner, the electron barrier layer 108 is located inside the ridge 110R.

[0220] When the thickness of the p-type cladding layer 110 is 150 nm or less as in this embodiment, the effective refractive index difference ΔN is 1.5×10 －３ or less, which poses a risk of kink occurrence. For this reason, in this embodiment, the ridge 110R is formed to extend below the electron barrier layer 108, thereby improving the effective refractive index difference ΔN.

[0221] By positioning the lower end of the ridge 110R in the GaN layer of the p-side intermediate layer 207, which has a uniform composition, it is possible to improve the uniformity of the effective refractive index difference ΔN in the horizontal plane (in the plane parallel to the XY plane in FIG. 51 ). Increasing the thickness of the GaN layer of the p-side intermediate layer 207 makes it easier to form the lower end of the ridge 110R in this GaN layer, but if the thickness of the GaN layer is made too thick, the optical confinement effect in the stacking direction will be weakened, resulting in increased waveguide loss.

[0222] Therefore, by forming an AlGaN layer having a constant Al composition ratio between the GaN layer of the p-side intermediate layer 207 and the electron barrier layer 108 and positioning the lower end of the ridge 110R within this AlGaN layer, the position of the lower end of the ridge 110R can be easily controlled without weakening the optical confinement effect in the stacking direction. In this case, the Al composition ratio of the AlGaN layer of the p-side intermediate layer 207 may be equal to or less than the Al composition ratio of the p-type cladding layer 110. This makes it possible to suppress an increase in operating voltage.

[0223] In this embodiment, the p-side intermediate layer 207 includes a GaN layer and an AlGaN layer, but may include only one of the GaN layer and the AlGaN layer.

[0224] In this embodiment, the p-side electrode 113 is made of at least one of Ag, an Ag alloy, and Al, which have a low refractive index, so that an increase in waveguide loss can be suppressed even if the thickness of the p-type cladding layer 110 is thin.

[0225] If an electron barrier layer 108 having an Al composition ratio of 0.26 or more, which is 0.234 or more greater than the average Al composition ratio of the p-type cladding layer 110, is disposed inside the ridge 110R, the band gap energy of the electron barrier layer 108 is large, making current leakage from the sidewalls of the ridge 110R more likely. To prevent this, the maximum Al composition ratio of the electron barrier layer 108 may be set to 0.245 or less, which is 0.219 greater than the average Al composition ratio of the p-type cladding layer 110, and the electron barrier layer 108 may have an Al composition gradient portion with a thickness of 7 nm or more, in which the Al composition ratio monotonically increases with increasing distance from the active layer 105. If the maximum Al composition ratio of the electron barrier layer 108 is low, electrons leaking from the active layer 105 to the p-type cladding layer 110 cannot be prevented, resulting in deterioration of the temperature characteristics of the semiconductor laser device 200. Therefore, the maximum Al composition ratio of the electron barrier layer 108 may be 0.1 or more higher than the average Al composition ratio of the p-type cladding layer 110 .

[0226] In this embodiment, as described above, the Al composition ratio at the interface between the lower electron barrier layer 108 and the p-side intermediate layer 207 is set equal to the Al composition ratio of the AlGaN layer of the p-side intermediate layer 207, and the Al composition ratio of the lower layer monotonically increases with increasing distance from the active layer 105. In addition, the Al composition ratios at the interface between the upper and lower layers of the electron barrier layer 108 are set equal, and the Al composition ratio at the interface between the upper electron barrier layer 108 and the p-type cladding layer 110 is set equal to the Al composition ratio of the p-type cladding layer 110. Furthermore, the Al composition ratio of the upper layer monotonically decreases with increasing distance from the active layer 105.

[0227] As a result, piezoelectric polarization charges formed near the interface between the electron barrier layer 108 and the p-side intermediate layer 207 are dispersed throughout the entire lower layer, reducing the potential barrier against holes formed in the valence band and thereby reducing the operating voltage. Furthermore, since the electron barrier layer 108 does not have a high Al composition region with an Al composition ratio of 0.26 or more, the potential barrier against holes formed in the valence band of the electron barrier layer 108 is reduced. Therefore, current leakage from the side surfaces of the ridge 110R of the electron barrier layer 108 can be suppressed.

[0228] In this embodiment, the p-side electrode 113 may have a conductive oxide film such as ITO having light transmission, thereby reducing waveguide loss.

[0229] In the first and second embodiments, the n-side guide layer 104 is undoped and doped with impurities. １７ cm －３ That's it, 2 x 10 １８ cm －３ The n-side intermediate layer 103 may be doped with the following impurities. This allows the operating voltage of the semiconductor laser device 100 to be reduced. In particular, when the n-side guide layer 104 is made of n-type InGaN and is an In composition gradient layer in which the In composition ratio increases toward the active layer 105, the operating voltage can be further reduced. The effects of such an In composition gradient layer and the effects of the n-side intermediate layer 103 will be described with reference to FIGS. 52 to 57 . FIGS. 52 and 53 are graphs showing the potential distributions of the conduction band and valence band in Configuration Example 1 of the semiconductor laser device 200 according to this embodiment. FIGS. 54 and 55 are graphs showing the potential distributions of the conduction band and valence band in Configuration Example 2 of the semiconductor laser device 200 according to this embodiment. FIGS. 56 and 57 are graphs showing the potential distributions of the conduction band and valence band in Configuration Example 3 of the semiconductor laser device 200 according to this embodiment. In FIGS. 52 , 54 , and 56 , the Fermi levels of electrons are also indicated by long dashed lines. The Fermi levels of holes are also shown by long dashed lines in Figures 53, 55, and 57. In Figures 52 to 57, short dashed lines are shown at positions in the stacking direction that correspond to the boundaries of each semiconductor layer.

[0230] Configuration example 1 of the semiconductor laser device 200 according to this embodiment differs from the configuration of the semiconductor laser device 200 according to the above-described embodiment in the configurations of the n-side intermediate layer 103 and the n-side guide layer 104.

[0231] The n-side intermediate layer 103 of Configuration Example 1 is a compositionally graded layer. The n-side intermediate layer 103 of Configuration Example 1 is a 10 nm thick n-type Al layer whose Al composition ratio monotonically decreases with increasing distance from the n-type cladding layer 102.Ｘｎｉ Ga １－Ｘｎｉ N (0≦Xni<1) layer. The band gap energy of the n-side intermediate layer 103 monotonically decreases with increasing distance from the n-type cladding layer 102. The Al composition ratio Xni of the n-side intermediate layer 103 is 0.055 at the end face closer to the n-type cladding layer 102 and is 0 at the end face farther from the n-type cladding layer 102. The n-side intermediate layer 103 has an Al composition ratio Xni of 1×10 １８ cm －３ is doped with Si.

[0232] The n-side guide layer 104 of the first configuration example has a concentration of 1×10 １８ cm －３ 160 nm thick n-type In ０．０４ Ga ０．９６ This is the N layer.

[0233] The second configuration example of the semiconductor laser device 200 according to this embodiment differs from the first configuration example in the configuration of the n-side guide layer 104 .

[0234] The n-side guide layer 104 of the second example has a concentration of 1×10 １８ cm －３ 160 nm thick n-type In Ｘｉｎ Ga １－Ｘｉｎ N (0≦Xin<1) layer. The In composition ratio Xin of the n-side guide layer 104 monotonically increases toward the active layer 105. The band gap energy of the n-side guide layer 104 monotonically decreases toward the active layer 105. The In composition ratio Xin is 0 at the end face of the n-side guide layer 104 farther from the active layer 105, and the In composition ratio Xin is 0.04 at the end face of the n-side guide layer 104 closer to the active layer 105.

[0235] Configuration example 3 of the semiconductor laser device 200 according to this embodiment differs from configuration example 2 in that it does not include the n-side intermediate layer 103 .

[0236] 53 , when the n-side guide layer 104 has a uniform composition, the potential of the valence band in the n-side guide layer 104 is constant, and holes tend to leak from the active layer 105 to the n-type cladding layer 102. In contrast, when the n-side guide layer 104 is an In composition gradient layer as in Configuration Example 2 (and Configuration Example 3), and an impurity exhibiting n-type conductivity is introduced into the n-side guide layer 104 at a concentration of 4×10 １７ cm －３ When doped in the above range, as shown in FIG. 55 (and FIG. 57), the potential of the valence band of the n-side guide layer 104 increases as it approaches the active layer 105. In other words, the potential of the valence band of the n-side guide layer 104 decreases as it moves away from the active layer, so the n-side guide layer 104 functions as a potential barrier that makes it difficult for holes injected into the active layer 105 to leak to the n-type cladding layer 102 side. This not only reduces the operating voltage as described above, but also reduces hole leakage current and improves light emission efficiency. The magnitude of this effect is as follows: when the doping concentration is 2×10 １８ cm －３ At this point, the n-side guide layer 104 is doped with an impurity exhibiting n-type conductivity at a concentration of 4×10 １７ cm －３ That's it, 2 x 10 １８ cm －３ The doping may be in the following range: The effect of improving the light emission efficiency by reducing the hole leakage current is enhanced in the case of a single quantum well structure in which leakage current is likely to occur.

[0237] Furthermore, by providing the n-side intermediate layer 103, which is a compositionally graded layer, between the n-type cladding layer 102 and the n-side guide layer 104 as in Configuration Example 2, the potential barrier of the conduction band formed between the n-type cladding layer 102 and the n-side guide layer 104 can be reduced compared to Configuration Example 3, which does not include the n-side intermediate layer 103 (see FIGS. 54 and 56 ). Therefore, the operating voltage can be reduced.

[0238] The effect of reducing the potential barrier of the conduction band is greater when the n-side guide layer 104 is an In compositionally graded layer as in Configuration Example 2 than when the n-side guide layer 104 has a uniform composition as in Configuration Example 1. Therefore, as shown in FIGS. 52 and 54 , the potential barrier of the conduction band formed between the n-type cladding layer 102 and the n-side guide layer 104 is smaller in Configuration Example 2 than in Configuration Example 1, thereby further reducing the operating voltage. The effect of reducing the potential barrier of the conduction band is achieved by forming the n-side guide layer 104 as an In compositionally graded layer, thereby distributing piezoelectric polarization charges throughout the n-side guide layer 104. Distributing the piezoelectric polarization charges throughout the n-side guide layer 104 can suppress the concentration of potential changes in the conduction band at the interface between the n-side intermediate layer 103 and the n-side guide layer 104, which would otherwise be caused by the concentration of piezoelectric polarization charges near the interface.

[0239] In Configuration Example 1 and Configuration Example 2, the n-side intermediate layer 103 may further include an n-type GaN layer with a thickness of 100 nm or less that is disposed between the compositionally graded layer and the n-side guide layer 104. However, in this case, if the thickness of the n-type GaN layer is increased, the distance between the active layer 105 and the n-type cladding layer 102 increases, thereby reducing the optical confinement coefficient. For this reason, it is preferable that the n-type GaN layer is thin; for example, the thickness of the n-type GaN layer may be 30 nm or less.

[0240] In Configuration Examples 1 to 3, the n-type cladding layer 102 and the n-side guide layer 104 have the same impurity concentration. However, because the n-type cladding layer 102 is farther from the active layer 105 than the n-side guide layer 104, the impurity concentration of the n-type cladding layer 102 may be higher than the impurity concentration of the n-side guide layer 104. In this case, in the light intensity distribution in the stacking direction, the light intensity in the n-type cladding layer 102 is smaller than the light intensity in the n-side guide layer 104. This makes it possible to suppress the influence of free carrier loss caused by doping the n-type cladding layer 102 with an impurity, and to reduce the resistance value of the n-type cladding layer 102. This makes it possible to reduce the operating voltage while suppressing a decrease in light emission efficiency.

[0241] Furthermore, in the first and second embodiments, the In composition ratio of each barrier layer is higher than the maximum In composition ratio of the n-side guide layer 104 and the p-side guide layer 106, but the configuration of each barrier layer is not limited to this. For example, the In composition ratio of the barrier layer closest to the substrate 101 may be equal to or greater than the maximum In composition ratio of the n-side guide layer 104, and the In composition ratio of the barrier layer closest to the p-type cladding layer 110 may be equal to or greater than the maximum In composition ratio of the p-side guide layer 106. With this configuration, the refractive index of the barrier layer closest to the substrate 101 is equal to or greater than the maximum refractive index of the n-side guide layer 104, and the refractive index of the barrier layer closest to the p-type cladding layer 110 is equal to or greater than the maximum refractive index of the p-side guide layer 106. Therefore, the controllability of positioning the peak position P1 of the light intensity distribution in the stacking direction near the active layer 105 is improved, and the optical confinement factor is increased.

[0242] Furthermore, the barrier layer closest to the substrate 101 may be doped with an impurity. In this case, by doping the barrier layer closest to the substrate 101 with an impurity exhibiting n-type conductivity, it is possible to shield the piezoelectric polarization charge at the interface between the barrier layer and the well layer, thereby reducing the potential barrier of the conduction band generated at the interface between the barrier layer closest to the substrate 101 and the well layer. As a result, electrons can be easily injected into the active layer 105 at a low voltage, thereby reducing the operating voltage. The concentration of the impurity doped into the barrier layer closest to the substrate 101 is 5×10 １８ cm －３ The above is necessary. Also, 5 x 10 １９ cm －３ When the impurity is doped at a concentration above this, the effect of reducing the potential barrier becomes almost constant. Therefore, the impurity concentration doped into the barrier layer closest to the substrate 101 is set to 5×10 １８ cm －３ That's it, 5 x 10 １９ cm －３ Here, the barrier layer closest to the substrate 101 may have a thickness of 5×10 １８ cm －３When doping with impurities at a concentration above this, the effect of shielding piezoelectric polarization charges at the interface between the barrier layer closest to the substrate 101 and the well layer is increased, so the thickness of the barrier layer closest to the substrate 101 can be set to 3 nm or less. If the thickness of the impurity-doped barrier layer closest to the substrate 101 is set to 1 nm or less, the effect of shielding piezoelectric polarization charges decreases, so a thickness of 1 nm or more is necessary.

[0243] (Embodiment 3) A semiconductor laser device according to embodiment 3 will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 100 according to embodiment 1 mainly in that the semiconductor laser device according to this embodiment emits laser light in the ultraviolet region. The following description of the semiconductor laser device according to this embodiment will focus on the differences from the semiconductor laser device 100 according to embodiment 1.

[0244] [3-1. Basic Configuration] The basic configuration of the semiconductor laser device according to this embodiment will be described with reference to Figs. 58 to 60. Fig. 58 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 300 according to this embodiment. Figs. 59 and 60 are schematic cross-sectional views showing the configurations of an n-side guide layer 304 and an active layer 305 included in the semiconductor laser device 300 according to this embodiment, respectively. Figs. 58 to 60 show cross sections perpendicular to the emission direction of laser light from the semiconductor laser device 200, similar to Fig. 2.

[0245] As shown in FIG. 58, the semiconductor laser device 300 includes a substrate 301, a semiconductor stack 300S, a current blocking layer 312, a p-side electrode 313, and an n-side electrode 314.

[0246] The semiconductor stack 300S is disposed above the substrate 301 and is a stack in which semiconductor layers are stacked. As shown in Fig. 58, the semiconductor stack 300S has a ridge 310R that protrudes upward. The semiconductor stack 300S also has two grooves 310T that are disposed along the ridge 310R and extend in the Y-axis direction, and two protruding portions 310P that protrude upward. One groove 310T is disposed between the ridge 310R and one of the protruding portions 310P, and the other groove 310T is disposed between the ridge 310R and the other protruding portion 310P.

[0247] The semiconductor laminate 300S according to this embodiment has an n-type cladding layer 302, an n-side guide layer 304, an active layer 305, a p-side guide layer 306, a p-side intermediate layer 307, an electron barrier layer 308, a p-type cladding layer 310, and a contact layer 311.

[0248] The substrate 301 is made of AlGaN. The substrate 301 is made of n-type AlGaN doped with Si at a concentration Cn. Ｘｓ Ga １－Ｘｓ N (0<Xs<1) substrate.

[0249] The n-type cladding layer 302 is an n-type Al doped with Si at a concentration Cn. Ｘｎｃ Ga １－Ｘｎｃ The Al composition ratio Xnc of the n-type cladding layer 302 is greater than the Al composition ratio of the p-type cladding layer 310.

[0250] The n-side guide layer 304 is made of AlGaN. In this embodiment, as shown in Fig. 59, the n-side guide layer 304 has a first n-side guide layer 304a and a second n-side guide layer 304b. The first n-side guide layer 304a is disposed above the second n-side guide layer 304b.

[0251] The first n-side guide layer 304a is an undoped layer included in the n-side guide layer 304. In this embodiment, the first n-side guide layer 304a is an undoped Al Ｘｎｇ１ Ga １－Ｘｎｇ１ N (0<Xng1<1) layers.

[0252] The second n-side guide layer 304b is an n-type layer included in the n-side guide layer 304. The second n-side guide layer 304b is disposed between the n-type cladding layer 302 and the first n-side guide layer 304a. In this embodiment, the second n-side guide layer 304b is an n-type Al doped with Si. Ｘｎｇ２ Ga １－Ｘｎｇ２ N (0<Xng2<1) layer. The Al composition ratio of the second n-side guide layer 304b may be equal to the Al composition ratio of the first n-side guide layer 304a.

[0253] The active layer 305 is disposed above the n-side guide layer 304. The active layer 305 has a quantum well structure and emits ultraviolet light. Specifically, as shown in FIG. 60 , the active layer 305 has a single quantum well structure and includes a well layer 305 b and barrier layers 305 a and 305 c. The well layer 305 b is disposed between the two barrier layers 305 a and 305 c. Note that the configuration of the active layer 305 is not limited to this. For example, the active layer 305 may have a multiple quantum well structure. Specifically, the active layer 305 may include three or more barrier layers and two or more well layers.

[0254] Each of the barrier layers 305a and 305c is a semiconductor layer disposed above the first n-side guide layer 304a and functions as a barrier of the quantum well structure. The barrier layer 305c is disposed above the barrier layer 305a. In this embodiment, each of the barrier layers 305a and 305c is a nitride semiconductor layer containing Al. More specifically, each of the barrier layers 305a and 305c is made of AlGaN. That is, the barrier layer 305a is made of undoped Al. Ｘｂ１ Ga １－Ｘｂ１ N (0<Xb1<1) layer, and the barrier layer 305c is an undoped Al Ｘｂ２ Ga １－Ｘｂ２ N (0<Xb2<1) layer.

[0255] The well layer 305b is a nitride semiconductor layer disposed above the barrier layer 305a and functions as a well of the quantum well structure. In this embodiment, the well layer 305b is an undoped In Ｘｗ１ Ga １－Ｘｗ１ N (0<Xw1<1) layer or undoped Al Ｘｗ２ Ga １－Ｘｗ２N (0<Xw2<1) layers.

[0256] The p-side guide layer 306 is made of AlGaN. That is, the p-side guide layer 306 is made of undoped Al Ｘｐｇ１ Ga １－Ｘｐｇ１ N (0<Xpg1<1) layers.

[0257] The p-side intermediate layer 307 is made of AlGaN. More specifically, the p-side intermediate layer 307 is made of Al Ｘｐｉ Ga １－Ｘｐｉ N (0<Xpi<1) layers.

[0258] The electron barrier layer 308 is made of p-type Al Ｘｅｂ Ga １－Ｘｅｂ N (0<Xeb<1) layer.

[0259] The p-type cladding layer 310 is made of p-type Al Ｘｐｃ Ga １－Ｘｐｃ The Al composition ratio Xpc of the p-type cladding layer 310 is smaller than the Al composition ratio Xnc of the n-type cladding layer 302.

[0260] The contact layer 311 is a p-type GaN layer with a thickness of 60 nm. The contact layer 311 contains impurities with a concentration of 1×10 ２０ cm －３ It is doped with Mg.

[0261] In this embodiment, a ridge 310R, a groove 310T, and a protrusion 310P are formed in the p-type cladding layer 310 and the contact layer 311.

[0262] The current blocking layer 312, the p-side electrode 313, and the n-side electrode 314 according to this embodiment have the same configurations as the current blocking layer 112, the p-side electrode 113, and the n-side electrode 114 according to the first embodiment, respectively.

[0263] In a semiconductor laser device emitting laser light in the ultraviolet region with a wavelength shorter than 380 nm, such as the semiconductor laser device 300 according to this embodiment, the band gap energy of the well layer 305b is large, so electrons injected into the active layer 305 tend to leak into the p-side guide layer 306. As a result, the operating carrier density of the well layer 305b tends to be high during laser oscillation. Therefore, the portion of the well layer 305b located below the ridge 310R experiences a greater decrease in refractive index due to the plasma effect than the other portions of the well layer 305b. As a result, the effective refractive index below the ridge 310R decreases, and a refractive index anti-guiding state in which the effective refractive index difference ΔN becomes negative tends to occur.

[0264] In this case, in a semiconductor laser device using a GaN substrate, the refractive index of the GaN substrate may be higher than the effective refractive index for the guided mode of the laser light, so that light that reaches the GaN substrate leaks into the GaN substrate with a higher refractive index, resulting in a decrease in light emission efficiency.

[0265] Furthermore, the light intensity distribution below the current blocking layer 312, compared to the light intensity distribution below the ridge 310R, tends to spread toward the substrate due to the presence of the current blocking layer 312, which has a lower refractive index. Therefore, for example, in a semiconductor laser device using a GaN substrate, light leakage into the GaN substrate occurs, making it impossible to achieve confinement of the horizontal transverse mode of the laser light. This increases the waveguide loss of the semiconductor laser device. In this case, the slope efficiency in the current-light output characteristics of the semiconductor laser device decreases, and the oscillation threshold current value increases.

[0266] In order to suppress the occurrence of such a phenomenon, in a semiconductor laser element using a GaN substrate, the effective refractive index difference ΔN is set to 10×10 －３ The configuration of the semiconductor laser element is adjusted so that the above is achieved.

[0267] In this embodiment, by using the substrate 301 made of AlGaN, the refractive index of the substrate 301 can be made smaller than the effective refractive index for the guided mode of the laser light, so that the leakage of light into the substrate 301 as described above can be suppressed. －３ The following 5 x 10 －３Even if the degree is small, the occurrence of light leakage to the substrate 301 can be suppressed.

[0268] Furthermore, by using the substrate 301 made of AlGaN, the difference in lattice constant with the n-type cladding layer 302 made of AlGaN is reduced. This reduces the stress applied to the semiconductor laminate 300S laminated on the substrate 301. Therefore, even when the film thickness of the n-type cladding layer 302 is 1 μm or more, cracking of the wafer and the occurrence of lattice defects in the semiconductor laminate 300S can be suppressed when and after the semiconductor laminate 300S is laminated on the wafer that is the base material of the substrate 301.

[0269] [3-2. Configuration Example C1] Configuration example C1 of the semiconductor laser device 300 according to this embodiment will be described. In configuration example C1, the laser light has a peak wavelength in the 375 nm band. In configuration example C1, the n-type cladding layer 302 is made of n-type Al ０．１０ Ga ０．９０ The first n-side guide layer 304a is an undoped AlN layer with a thickness of 180 nm. ０．０３ Ga ０．９７ The second n-side guide layer 304b is an n-type AlN layer having a thickness of 127 nm. ０．０３ Ga ０．９７ The substrate 301, the n-type cladding layer 302, and the second n-side guide layer 304b are doped with Si at a concentration Cn.

[0270] Each of the barrier layers 305a and 305c is an undoped Al layer having a thickness of 11 nm. ０．０４ Ga ０．９６ The well layer 105b is an undoped In layer having a thickness of 17.5 nm. ０．０１ Ga ０．９９ This is the N layer.

[0271] The p-side guide layer 306 is an undoped Al layer with a thickness of 66 nm. ０．０３ Ga ０．９７ The p-side intermediate layer 307 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 3 nm ０．０３ Ga ０．９７ N layer, and the electron barrier layer 308 has a concentration of 1.5×10 １９ cm－３ p-type Al doped with Mg having a thickness of 5 nm ０．３６ Ga ０．６４ This is the N layer.

[0272] The p-type cladding layer 310 is a p-type Al layer having a thickness of 450 nm. ０．０６５ Ga ０．９３５ The p-type cladding layer 310 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．０６５ Ga ０．９３５ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 300 nm ０．０６５ Ga ０．９３５ The contact layer 311 has a concentration of 1×10 ２０ cm －３ The p-side electrode 313 is made of Ag.

[0273] In addition, in Configuration Example 1, the ridge width W is 15 μm and the cavity length is 800 μm.

[0274] The effects of configuration example C1 of the semiconductor laser device 300 according to this embodiment will be described with reference to FIGS. 61 to 65, comparing configuration example C1 with a comparative example. FIG. 61 is a graph showing the relationship between the Al composition ratio of the substrate 301 of configuration example C1 and the integrated stress of the semiconductor stack 300S. FIGS. 62 and 63 are graphs showing the relationship between the stacking direction position, the refractive index, and the light intensity of the comparative example. FIGS. 64 and 65 are graphs showing the relationship between the stacking direction position, the refractive index, and the light intensity of configuration example C1. In configuration example C1 shown in FIGS. 64 and 65, the substrate 301 is made of Al. ０．０５ Ga ０．９５ It consists of N.

[0275] The comparative example differs from configuration example C1 in that the substrate is made of GaN, but is identical in other respects. As shown in Fig. 62, in the comparative example, the substrate 1001 is made of GaN, which has a higher refractive index than the n-side guide layer 304. For this reason, light leaks into the substrate 1001, as shown in Fig. 63. As a result, in the comparative example, the light emission efficiency decreases and a kink occurs in the current-light output characteristics.

[0276] In contrast, in Configuration Example C1, as shown in FIG. 64, the bandgap energy of the substrate 301 is equal to or lower than the bandgap energy of the n-side guide layer 304. That is, the Al composition ratio of the substrate 301 is equal to or higher than the Al composition ratio of the n-side guide layer 304, and the refractive index of the substrate 301 is equal to or lower than the refractive index of the n-side guide layer 304. Therefore, as shown in FIG. 65, leakage of light into the substrate 301 can be suppressed. Furthermore, the Al composition ratio of the substrate 301 may be set to 0.045 or higher. This allows the refractive index of the substrate 301 to be equal to or lower than the effective refractive index of the guided mode of the laser light in Configuration Example C1. Therefore, leakage of light into the substrate 301 can be further suppressed. Therefore, Configuration Example C1 can improve the light emission efficiency compared to the comparative example, and suppress the occurrence of kinks in the current-light output characteristics.

[0277] Furthermore, since the substrate 301 is made of AlGaN, the difference in lattice constant between the substrate 301 and each cladding layer of the semiconductor laminate 300S can be reduced. This effect will be explained using FIG. 61. As shown in FIG. 61, when a substrate made of GaN is used, the integrated stress is about -948.3 Pa m, which increases the risk of wafer cracking. In contrast, when a substrate made of Al ０．０５ Ga ０．９５ In the configuration example C1 using the substrate 301 made of N, the tensile stress applied to the semiconductor laminate 300S can be significantly reduced without reducing the Al composition ratio of each cladding layer, etc. ０．０５ Ga ０．９５ In the configuration example C1 using the substrate 301 made of N, the integrated stress is reduced to -278.9 Pa·m, and the risk of wafer cracking can be reduced.

[0278] By reducing the tensile stress applied to the semiconductor stack 300S in this manner, the bandgap energy of each layer of the semiconductor stack 300S of Configuration Example C1 can be increased and the refractive index can be reduced compared to the comparative example. This allows the optical confinement factor of Configuration Example C1 to be increased compared to the comparative example. Furthermore, since the bandgap energy of the barrier layer 105c can be increased, leakage electrons from the well layer 105b over the barrier layer 105c can be reduced. This improves the temperature characteristics of the semiconductor laser device 300. Furthermore, by reducing the tensile stress applied to the semiconductor stack 300S, cracking of the wafer and the occurrence of lattice defects in the semiconductor stack 300S can be suppressed when and after stacking the semiconductor stack 300S on the wafer, which is the base material of the substrate 301.

[0279] Furthermore, the band gap energy of the substrate 301 in configuration example C1 is equal to or lower than the band gap energy of the n-type cladding layer 302. In other words, the Al composition ratio of the substrate 301 made of AlGaN is equal to or lower than the Al composition ratio of the n-type cladding layer 302 made of AlGaN. This makes it possible to prevent the compressive stress in the semiconductor stack 100S from increasing too much.

[0280] In addition, in configuration example C1, the Al composition ratio of the barrier layers 305 a and 305 c is higher than the Al composition ratio of the n-side guide layer 304 and lower than the Al composition ratio of the substrate 301. In this case, the stress applied to the barrier layers 305 a and 305 c becomes compressive. This increases the bandgap energy of the barrier layer 305 c, thereby reducing leakage of electrons from the well layer 305 b toward the p-type cladding layer 310.

[0281] In this embodiment, the Al composition ratio of the substrate 301 may be higher than that of the p-side guide layer 306 and lower than that of the barrier layers 305a and 305c. This makes it possible to increase the bandgap energy of the p-side guide layer 306 by making the stress applied to the p-side guide layer 306 compressive, thereby reducing the leakage of electrons from the well layer 305b toward the p-type cladding layer 310. Furthermore, the refractive index of the p-side guide layer 306 can be reduced, thereby increasing the optical confinement coefficient in the active layer 305.

[0282] Next, the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C1 and the operating voltage will be described with reference to FIG. 66. FIG. 66 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example C1 and the operating voltage. FIG. 66 also shows the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300 (hereinafter also referred to as the operating voltage during 800 mA operation). FIG. 66 also shows the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C1 and the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300 (hereinafter also referred to as the operating voltage during 800 mA operation). Furthermore, FIG. 66 shows the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C1 and the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300 (hereinafter also referred to as the operating voltage during 800 mA operation). １８ cm －３ , 5 x 10 １８ cm －３ , and 1 × 10 １９ cm －３ The operating voltages for each case are shown.

[0283] As shown in FIG. 66, when the impurity concentration Cn is 1×10 １８ cm －３ That's it, 1 x 10 １９ cm －３ In the following cases, the operating voltage is minimized when the Al composition ratio of the substrate 301 is 0.04. In order to further reduce the operating voltage, the impurity concentration Cn is set to 5×10 １８ cm －３ It may be more than that.

[0284] For example, the first n-side guide layer 304a may also be doped with Si as an impurity to reduce the operating voltage. However, this increases the free carrier loss in the first n-side guide layer 304a. Therefore, in order to achieve both a reduction in the operating voltage and a reduction in the FC loss, the first n-side guide layer 304a may be doped with 3×10 １７ That's it, 1 x 10 １８ cm －３ The following impurities may be doped.

[0285] Furthermore, spike-shaped potential barriers are formed due to piezoelectric polarization charges in the conduction bands at the interface between the substrate 301 and the n-type cladding layer 302 and at the interface between the n-type cladding layer 302 and the second n-side guide layer 304b. In order to suppress an increase in operating voltage due to these potential barriers, a 1×10 １８ cm －３That's it, 1 x 10 １９ cm －３ The following Si may be doped.

[0286] Note that the compositionally graded layer according to the first embodiment may be disposed between the n-type cladding layer 302 and the n-side guide layer 304 in the configuration example C1, thereby achieving the same effect as that of the compositionally graded layer according to the first embodiment.

[0287] The compositionally graded layer may be disposed at a position other than between the n-type cladding layer 302 and the n-side guide layer 304. For example, the compositionally graded layer may be disposed between the substrate 301 and the n-type cladding layer 302. In this case, the compositionally graded layer is, for example, an n-type AlGaN layer in which the Al composition ratio approaches that of the substrate 301 toward the substrate 301 and approaches that of the n-type cladding layer 302 toward the n-type cladding layer 302. Such a compositionally graded layer can reduce the potential barrier formed between the substrate 301 and the n-type cladding layer 302, thereby reducing the operating voltage of the semiconductor laser device 300.

[0288] The thickness of the compositionally graded layer may be, for example, 10 nm or more. This ensures the effect of reducing the potential barrier. Furthermore, for example, the n-side guide layer 104 may include a compositionally graded layer. In this case, it is preferable that the compositionally graded layer is not too thick in order to prevent a decrease in the refractive index of the n-side guide layer 104. For example, the thickness of the compositionally graded layer included in the n-side guide layer 104 may be thinner than the thickness of the compositionally graded layer disposed between the substrate 301 and the n-type cladding layer 302.

[0289] Furthermore, as in configuration example C1, the Al composition ratio of the barrier layer 305a, of the barrier layers 305a and 305c of the active layer 305, which is closest to the n-side guide layer 304, may be equal to or greater than the maximum Al composition ratio of the n-side guide layer 304, and the Al composition ratio of the barrier layer 305c, of the barrier layers 305a and 305c, which is closest to the p-side guide layer 306, may be equal to or greater than the maximum Al composition ratio of the p-side guide layer 306. The bandgap energy of the barrier layer 305a, of the barrier layers 305a and 305c of the active layer 305, which is closest to the n-side guide layer 304, may be equal to or greater than the maximum bandgap energy of the n-side guide layer 304, and the bandgap energy of the barrier layer 305c, of the barrier layers 305a and 305c, which is closest to the p-side guide layer 306, may be equal to or greater than the maximum bandgap energy of the p-side guide layer 306.

[0290] This increases the difference between the quantum level formed in the well layer 305b and the conduction band potential of the barrier layers 105a and 105c, making it easier to confine electrons within the well layer 105b, thereby reducing the oscillation threshold current value.

[0291] In addition, in the configuration example C1, the Al composition ratio of at least one of the n-side guide layer 304 and the p-side guide layer 306 may monotonically decrease toward the active layer 305. Furthermore, the band gap energy of at least one of the n-side guide layer 304 and the p-side guide layer 306 may monotonically decrease toward the active layer 305.

[0292] This allows the refractive indexes of the n-side guide layer 304 and the p-side guide layer 306 to monotonically increase toward the active layer 305, improving the controllability of positioning the peak position of the light intensity distribution in the stacking direction in the active layer, thereby reducing waveguide loss while increasing the light confinement factor in the active layer 305.

[0293] Furthermore, when the lattice constant of each guide layer is smaller than that of the substrate 301, it becomes possible to reduce the tensile stress in the region of each guide layer closer to the active layer 305, thereby suppressing cracks in the wafer when and after stacking the semiconductor laminate 300S on the wafer, which is the base material of the substrate 301.

[0294] Furthermore, as in configuration example C1, the thickness of the n-side guide layer 304 may be thicker than the thickness of the p-side guide layer 306. In a semiconductor laser device 300 that emits laser light in the ultraviolet range, using a p-type GaN layer for the contact layer 311 increases light absorption in the contact layer 311. Furthermore, GaN has a higher refractive index than the waveguide mode of the laser light, causing light leakage into the contact layer 311. Furthermore, if the Al composition ratio of the n-type cladding layer 302 is higher than that of the p-type cladding layer 310, the light intensity distribution in the stacking direction tends to be biased in the direction from the active layer 305 to the p-type cladding layer 310. Therefore, in each guide layer whose refractive index is higher than that of each cladding layer, by making the thickness of the n-side guide layer 304 larger than the thickness of the p-side guide layer 306, it is possible to improve the controllability of positioning the peak position of the light intensity distribution in the stacking direction in the active layer 305.

[0295] [3-3. Configuration Example C2] Configuration example C2 of the semiconductor laser device 300 of this embodiment will be described. Configuration example C2 differs from configuration example C1 in that the laser light has a peak wavelength in the 365 nm band. Below, configuration example C2 will be described, focusing on the differences from configuration example C1.

[0296] In the configuration example C2, the n-type cladding layer 302 is an n-type Al ０．１７ Ga ０．８３ The first n-side guide layer 304a is an undoped AlN layer with a thickness of 180 nm. ０．０７ Ga ０．９３ The second n-side guide layer 304b is an n-type AlN layer having a thickness of 127 nm. ０．０７ Ga ０．９３ The substrate 301, the n-type cladding layer 302, and the second n-side guide layer 304b are doped with Si at a concentration Cn.

[0297] Each of the barrier layers 305a and 305c is an undoped Al layer having a thickness of 11 nm. ０．０９ Ga ０．９１ The well layer 305b is an undoped Al layer having a thickness of 17.5 nm. ０．０４ Ga ０．９６ This is the N layer.

[0298] The p-side guide layer 306 is an undoped Al layer with a thickness of 66 nm. ０．０７ Ga ０．９３ The p-side intermediate layer 307 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 3 nm ０．０７ Ga ０．９３ N layer, and the electron barrier layer 308 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 5 nm ０．３６ Ga ０．６４ This is the N layer.

[0299] The p-type cladding layer 310 is a p-type Al layer having a thickness of 450 nm. ０．１３ Ga ０．８７ The p-type cladding layer 110 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．１３ Ga ０．８７ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 300 nm ０．１３ Ga ０．８７ The contact layer 311 has a concentration of 1×10 ２０ cm －３ The layer is a p-type GaN layer doped with Mg and having a thickness of 60 nm.

[0300] The effects of the configuration example C2 will be described below. The configuration example C2 also has the same effects as the configuration example C1.

[0301] Furthermore, because the substrate 301 is made of AlGaN, the difference in lattice constant between the substrate 301 and each cladding layer of the semiconductor stack 300S can be reduced. This effect will be explained using Fig. 67. Fig. 67 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example C2 and the integrated stress of the semiconductor stack 300S.

[0302] As shown in Fig. 67, when a substrate made of GaN is used, the integrated stress is about -1352.7 Pa m, and the risk of wafer cracking increases. ０．１１ Ga０．８９ In the configuration example C2 using the substrate 301 made of N, the tensile stress applied to the semiconductor laminate 100S can be significantly reduced without reducing the Al composition ratio of each cladding layer, etc. ０．１１ Ga ０．８９ In the configuration example C2 using the substrate 301 made of N, the integrated stress is reduced to -133.1 Pa m, reducing the risk of wafer cracking. Furthermore, the effective refractive index for the guided mode of the laser light is greater than the refractive index of the substrate 301, reducing light leakage into the substrate 301. This makes it possible to prevent a decrease in light emission efficiency and the occurrence of kinks.

[0303] Furthermore, the band gap energy of the substrate 301 in Configuration Example C2 is equal to or lower than the band gap energy of the n-type cladding layer 302. In other words, the Al composition ratio of the substrate 301 made of AlGaN is equal to or lower than the Al composition ratio of the n-type cladding layer 302 made of AlGaN. This makes it possible to prevent the compressive stress in the semiconductor stack 300S from increasing too much.

[0304] Next, the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C2 and the operating voltage will be described with reference to Fig. 68. Fig. 68 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example C2 and the operating voltage. Fig. 68 also shows the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300. Fig. 68 also shows the operating voltage when the impurity concentration (i.e., Si concentration) Cn in the substrate 301 etc. is 1×10 １８ cm －３ , 5 x 10 １８ cm －３ , and 1 × 10 １９ cm －３ The operating voltages for each case are shown.

[0305] As shown in FIG. 68, when the impurity concentration Cn is 1×10 １８ cm －３ That's it, 1 x 10 １９ cm －３ In the following cases, the operating voltage is minimized when the Al composition ratio of the substrate 301 is 0.11. In order to further reduce the operating voltage, the impurity concentration Cn is set to 5×10 １８ cm －３It may be more than that.

[0306] [3-4. Configuration Example C3] Configuration example C3 of the semiconductor laser element 300 of this embodiment will be described. Configuration example C3 differs from configuration example C1 in that the laser light has a peak wavelength in the 355 nm band. Below, configuration example C3 will be described, focusing on the differences from configuration example C1.

[0307] In the configuration example C3, the n-type cladding layer 302 is an n-type Al ０．２２ Ga ０．７８ The first n-side guide layer 304a is an undoped AlN layer with a thickness of 180 nm. ０．１４ Ga ０．８６ The second n-side guide layer 304b is an n-type AlN layer having a thickness of 127 nm. ０．１４ Ga ０．８６ The substrate 301, the n-type cladding layer 302, and the second n-side guide layer 304b are doped with Si at a concentration Cn.

[0308] Each of the barrier layers 305a and 305c is an undoped Al layer having a thickness of 11 nm. ０．１３ Ga ０．８７ The well layer 305b is an undoped Al layer having a thickness of 17.5 nm. ０．０９３ Ga ０．９０７ This is the N layer.

[0309] The p-side guide layer 306 is an undoped Al layer with a thickness of 66 nm. ０．１４ Ga ０．８６ The p-side intermediate layer 307 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 3 nm ０．１４ Ga ０．８６ N layer, and the electron barrier layer 308 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 5 nm ０．３６ Ga ０．６４ This is the N layer.

[0310] The p-type cladding layer 310 is a p-type Al layer having a thickness of 450 nm. ０．１８ Ga ０．８２ The p-type cladding layer 310 has a concentration of 2×10 １８ cm－３ p-type Al doped with Mg having a thickness of 150 nm ０．１８ Ga ０．８２ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 300 nm ０．１８ Ga ０．８２ The contact layer 311 has a concentration of 1×10 ２０ cm －３ The layer is a p-type GaN layer doped with Mg and having a thickness of 100 nm.

[0311] The effects of the configuration example C3 will be described below. The configuration example C3 also provides the same effects as the configuration example C1.

[0312] Furthermore, because the substrate 301 is made of AlGaN, the difference in lattice constant between the substrate 301 and each cladding layer of the semiconductor stack 300S can be reduced. This effect will be explained using Fig. 69. Fig. 69 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example C3 and the integrated stress of the semiconductor stack 300S.

[0313] As shown in Fig. 69, when a substrate made of GaN is used, the integrated stress is about -2456.0 Pa m, and the risk of wafer cracking increases. ０．１６ Ga ０．８４ In the configuration example C3 using the substrate 301 made of N, the tensile stress applied to the semiconductor laminate 300S can be significantly reduced without reducing the Al composition ratio of each cladding layer, etc. ０．１６ Ga ０．８４ In the configuration example C3 using the substrate 301 made of N, the integrated stress is reduced to -306.4 Pa m, reducing the risk of wafer cracking. Furthermore, the effective refractive index of the guided mode of the laser light is greater than the refractive index of the substrate 301, reducing light leakage into the substrate 301. This prevents a decrease in light emission efficiency and the occurrence of kinks.

[0314] Furthermore, the band gap energy of the substrate 301 in Configuration Example C3 is equal to or lower than the band gap energy of the n-type cladding layer 302. In other words, the Al composition ratio of the substrate 301 made of AlGaN is equal to or lower than the Al composition ratio of the n-type cladding layer 302 made of AlGaN. This makes it possible to prevent the compressive stress in the semiconductor stack 300S from increasing too much.

[0315] Next, the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C3 and the operating voltage will be described with reference to Fig. 70. Fig. 70 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example 4 and the operating voltage. Fig. 70 also shows the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300. Fig. 70 also shows the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C3 and the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300. １８ cm －３ , 5 x 10 １８ cm －３ , and 1 × 10 １９ cm －３ The operating voltages for each case are shown.

[0316] As shown in FIG. 70, when the impurity concentration Cn is 1×10 １８ cm －３ That's it, 1 x 10 １９ cm －３ In the following cases, the operating voltage is minimized when the Al composition ratio of the substrate 301 is 0.16. In addition, in order to further reduce the operating voltage, the impurity concentration Cn is set to 5×10 １８ cm －３ It may be more than that.

[0317] [3-5. Configuration Example C4] Configuration example C4 of the semiconductor laser element 300 of this embodiment will be described. Configuration example C4 differs from configuration example C1 in that the laser light has a peak wavelength in the 340 nm band. Below, configuration example C4 will be described, focusing on the differences from configuration example C1.

[0318] In the configuration example C4, the n-type cladding layer 302 is an n-type Al ０．５０ Ga ０．５０ The first n-side guide layer 304a is an undoped AlN layer with a thickness of 180 nm. ０．３０ Ga０．７０ The second n-side guide layer 304b is an n-type AlN layer having a thickness of 127 nm. ０．３０ Ga ０．７０ The substrate 301, the n-type cladding layer 302, and the second n-side guide layer 304b are doped with Si at a concentration Cn.

[0319] Each of the barrier layers 305a and 305c is an undoped Al layer having a thickness of 11 nm. ０．３０ Ga ０．７０ The well layer 305b is an undoped Al layer having a thickness of 17.5 nm. ０．２０ Ga ０．８０ This is the N layer.

[0320] The p-side guide layer 306 is an undoped Al layer with a thickness of 66 nm. ０．３０ Ga ０．７０ The p-side intermediate layer 307 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 3 nm ０．３０ Ga ０．７０ N layer, and the electron barrier layer 308 has a concentration of 1.5×10 １９ cm －３ p-type Al doped with Mg having a thickness of 5 nm ０．５０ Ga ０．５０ This is the N layer.

[0321] The p-type cladding layer 310 is a p-type Al layer having a thickness of 450 nm. ０．４０ Ga ０．６０ The p-type cladding layer 310 has a concentration of 2×10 １８ cm －３ p-type Al doped with Mg having a thickness of 150 nm ０．４０ Ga ０．６０ N layer and a layer with a concentration of 1×10 １９ cm －３ p-type Al doped with Mg having a thickness of 300 nm ０．４０ Ga ０．６０ The contact layer 311 has a concentration of 1×10 ２０ cm －３ The layer is a p-type GaN layer doped with Mg and having a thickness of 100 nm.

[0322] The effects of the configuration example C4 will be described below. The configuration example C4 also has the same effects as the configuration example C1.

[0323] Furthermore, because the substrate 301 is made of AlGaN, the difference in lattice constant between the substrate 301 and each cladding layer of the semiconductor stack 300S can be reduced. This effect will be explained using Fig. 71. Fig. 71 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example C4 and the integrated stress of the semiconductor stack 300S.

[0324] As shown in Fig. 71, when a substrate made of GaN is used, the integrated stress is about -5515.5 Pa m, and the risk of wafer cracking increases. ０．３５ Ga ０．６５ In the configuration example C4 using the substrate 301 made of N, the tensile stress applied to the semiconductor laminate 300S can be significantly reduced without reducing the Al composition ratio of each cladding layer, etc. ０．３５ Ga ０．６５ In the configuration example C4 using the substrate 301 made of N, the integrated stress is reduced to -238.8 Pa m, reducing the risk of wafer cracking. Furthermore, the effective refractive index of the guided mode of the laser light is greater than the refractive index of the substrate 301, reducing light leakage into the substrate 301. This prevents a decrease in light emission efficiency and the occurrence of kinks.

[0325] Furthermore, the band gap energy of the substrate 301 in Configuration Example C4 is equal to or lower than the band gap energy of the n-type cladding layer 302. In other words, the Al composition ratio of the substrate 301 made of AlGaN is equal to or lower than the Al composition ratio of the n-type cladding layer 302 made of AlGaN. This makes it possible to prevent the compressive stress in the semiconductor stack 300S from increasing too much.

[0326] Next, the relationship between the Al composition ratio and impurity concentration of the substrate 301 of Configuration Example C3 and the operating voltage will be described with reference to Fig. 72. Fig. 72 is a graph showing the relationship between the Al composition ratio of the substrate 301 of Configuration Example 4 and the operating voltage. Fig. 72 also shows the operating voltage when a current of 800 mA is supplied to the semiconductor laser device 300. Fig. 72 also shows the operating voltage when the impurity concentration (i.e., Si concentration) Cn in the substrate 301 etc. is 1×10 １８ cm －３ , 5 x 10 １８ cm －３ , and 1 × 10 １９ cm －３ The operating voltages for each case are shown.

[0327] As shown in FIG. 72, when the impurity concentration Cn is 1×10 １８ cm －３ That's it, 1 x 10 １９ cm －３ In the following cases, the operating voltage is minimized when the Al composition ratio of the substrate 301 is 0.50. In order to further reduce the operating voltage, the impurity concentration Cn is set to 5×10 １８ cm －３ It may be more than that.

[0328] 73 to 84 illustrate the relationship between the characteristics of the semiconductor laser device 300 according to this embodiment and the thickness of the p-type cladding layer 310. Each of FIGS. 73, 74, and 75 is a graph showing the relationship between the thickness of the p-type cladding layer 310 of Configuration Example C1 and the waveguide loss, the optical confinement factor, and the effective refractive index difference ΔN. Each of FIGS. 73 to 75 also illustrates the relationship between Comparative Examples C11 and C12.

[0329] 76, 77, and 78 are graphs showing the relationship between the thickness of the p-type cladding layer 310 of Configuration Example C2 and the waveguide loss, the optical confinement factor, and the effective refractive index difference ΔN, respectively. The relationships between Comparative Examples C21 and C22 are also shown in FIGS.

[0330] 79, 80, and 81 are graphs showing the relationship between the thickness of the p-type cladding layer 310 of Configuration Example C3 and the waveguide loss, the optical confinement factor, and the effective refractive index difference ΔN, respectively. Figures 79 to 81 also show the relationships between Comparative Examples C31 and C32.

[0331] 82, 83, and 84 are graphs showing the relationship between the thickness of the p-type cladding layer 310 of Configuration Example C4 and the waveguide loss, the optical confinement factor, and the effective refractive index difference ΔN, respectively. The relationships between Comparative Examples C41 and C42 are also shown in Figures 82 to 84.

[0332] Comparative Examples C11, C21, C31, and C41 differ from Structural Examples C1, C2, C3, and C4, respectively, in that the Al composition ratio of the n-type cladding layer is equal to the Al composition ratio of the p-type cladding layer 310, but are identical in other respects. Comparative Examples C12, C22, C32, and C42 differ from Structural Examples C1, C2, C3, and C4, respectively, in that the p-side electrode is made of Pd, but are identical in other respects.

[0333] 73, 76, 79, and 82, in Comparative Examples C12, C22, C32, and C42 in which the p-side electrode is made of Pd, the waveguide loss increases rapidly as the thickness of the p-type cladding layer 310 decreases. In contrast, in this embodiment, the p-side electrode 113 is made of Ag, which has a low refractive index, and therefore the increase in waveguide loss can be suppressed even if the thickness of the p-type cladding layer 310 is reduced to 0.15 μm.

[0334] Furthermore, as shown in Figures 74, 77, 80, and 83, in this embodiment, the Al composition ratio of the n-type cladding layer 302 is larger than the Al composition ratio of the p-type cladding layer 310, and therefore the optical confinement factor can be increased compared to Comparative Examples C11, C21, C31, and C41.

[0335] Furthermore, as shown in Figures 75, 78, 81, and 84, the effective refractive index difference ΔN decreases as the thickness of the p-type cladding layer 310 decreases. In particular, the decrease in the effective refractive index difference ΔN is significant when the thickness of the p-type cladding layer 310 is 0.15 μm or less. As the effective refractive index difference ΔN decreases, the number of horizontal-lateral modes operating in laser oscillation decreases, the influence of coupling between each mode increases, and kinks tend to occur in the current-light output characteristics. To suppress this phenomenon, the lower end of the ridge 310R may be positioned below the electron barrier layer 308. This increases the effective refractive index difference ΔN. For example, the lower end of the ridge 310R may be positioned in the p-side intermediate layer 307 or the p-side guide layer 306. Because the p-side intermediate layer 307 and the p-side guide layer 306 have uniform compositions, the amount of variation in the effective refractive index difference ΔN due to variations in the position at which the lower end of the ridge 310R is formed can be reduced.

[0336] [3-7. Al composition ratio of substrate] The Al composition ratio of the substrate 301 according to this embodiment will be described with reference to FIG. 85. FIG. 85 is a graph showing the relationship between the Al composition ratio of the n-type cladding layer 302 according to this embodiment and the Al composition ratio of the substrate 301. The white circles shown in FIG. 85 represent the Al composition ratios of the n-type cladding layer 302 and the substrate 301, respectively, where the impurity concentration Cn of the substrate 301 is 5×10 １８ cm －３ 3 shows the relationship between the Al composition ratios of the substrate 301 and the n-type cladding layer 302 in which the operating voltage during 800 mA operation is minimum when the above formula is used.

[0337] 85 is an approximation curve of the curve connecting the white circles. That is, the curve Alc is an approximation curve of the curve connecting the white circles when the impurity concentration Cn of the substrate 301 is 5×10 １８ cm －３ 3c is a curve approximating the relationship between the Al composition ratios of the substrate 301 and the n-type cladding layer 302 at which the operating voltage during 800 mA operation is minimized when x is the Al composition ratio of the n-type cladding layer 302 and y is the Al composition ratio of the substrate 301. The curve Alc is expressed by the following equation:

[0338] y = 0.510x ２ +0.843x-0.0491

[0339] The black circles and squares shown in FIG. 85 indicate that the impurity concentration Cn of the substrate 301 is 5×10 １８ cm －３ 1 shows the relationship between the Al composition ratios of the substrate 301 and the n-type cladding layer 302 when the operating voltage during 800 mA operation is 0.07 V higher than the minimum value when the substrate 301 is in this state. Here, when the operating voltage during 800 mA operation is 0.07 V higher than the minimum value, the Al composition ratio of the substrate 301 has two values: one that is higher than the Al composition ratio of the n-type cladding layer 302, and one that is lower than the Al composition ratio of the n-type cladding layer 302. The black circles indicate the lower Al composition ratio, and the squares indicate the higher Al composition ratio.

[0340] The curve Almin shown in Fig. 85 is an approximation curve of the curve connecting the black circles. The curve Almin is expressed by the following formula.

[0341] y = 1.515x ２ +0.206x-0.0326

[0342] The curve Almax shown in Fig. 85 is an approximation curve of the curve connecting the square marks. The curve Almax is expressed by the following formula.

[0343] y = 2.144x ２ -0.494x+0.270

[0344] Therefore, the Al composition ratio x of each n-type cladding layer 302 and the Al composition ratio y of the substrate 301 may be set so that the following two equations simultaneously hold between the Al composition ratio x of each n-type cladding layer 302 and the Al composition ratio y of the substrate 301:

[0345] y≧1.515x ２ +0.206x-0.0326 y≦2.144x ２ -0.494x+0.270

[0346] This makes it possible to suppress the operating voltage during 800 mA operation to a value close to the minimum value.

[0347] [3-8. Shape of Ridge] The shape of the ridge 310R of the semiconductor laser device 300 according to this embodiment will be described. First, the relationship between the ridge width (W) and the number of wave-guiding modes will be described with reference to FIGS. 86 and 87. FIG. 86 is a graph showing the relationship between the ridge width and the number of wave-guiding modes according to this embodiment. FIG. 87 is a graph showing an enlargement of a part of FIG. 86. FIG. 87 shows an enlarged view of only the range of the graph in FIG. 86 where the ridge width is 3 μm or less. Furthermore, FIGS. 86 and 87 show the effective refractive index difference ΔN of 1×10 in a configuration in which the laser light of the semiconductor laser device 300 according to this embodiment has a peak wavelength in the 355 nm band. －３ , 2 × 10 －３ , 3 x 10 －３ , 5 x 10 －３ , 10 x 10 －３ , and 15 × 10 －３ The number of modes that can be guided is shown for each case.

[0348] In a configuration using a GaN substrate, the effective refractive index difference ΔN is set to 10×10 －３ In contrast, in the semiconductor laser device 300 according to the present embodiment, as described above, the leakage of light to the substrate 301 can be suppressed, and therefore the effective refractive index difference ΔN needs to be 3×10 －３ This can be about 1 / 2.5. Therefore, the ridge width required to achieve single transverse mode operation in the semiconductor laser device 300 according to this embodiment (i.e., the ridge width required to set the number of waveguide modes to 1) can be increased. Here, single transverse mode operation means operation in which the transverse mode of laser light oscillated in the semiconductor laser device 300 is a single transverse mode. In single transverse mode operation, the horizontal far-field pattern (FFP) of the semiconductor laser device 300 is unimodal. Note that, as defined in the present disclosure, the state in which the horizontal FFP is unimodal includes not only a state in which the horizontal FFP includes only a peak corresponding to the fundamental transverse mode, but also a state in which the horizontal FFP includes a peak corresponding to the fundamental transverse mode and a small peak. A small peak means, for example, a peak whose magnitude is 10% or less of the peak corresponding to the fundamental transverse mode.

[0349] Specifically, when the radiation angle indicating the radiation direction of the FFP in the horizontal direction is represented by x, and the horizontal FFP is approximated by a Gaussian function (f(x)) having a half-width equal to the half-width of the horizontal FFP, the absolute value of the difference (h(x)) between the horizontal FFP value and the Gaussian function value in each radiation direction (i.e., each radiation angle x) should be within 10% of the maximum magnitude of the function g(x) indicating the actual FFP in the horizontal direction. Here, the function g(x) is normalized so that its maximum value is 1. The Gaussian function f(x) is expressed by the following formula.

[0350] f(x)=exp{-(x-a) ２ / (2σ ２ )} x: radiation angle (deg.) a: radiation angle (deg.) at which g(x) is maximum σ: standard deviation of Gaussian function f(x)

[0351] In this case, the half-width of the Gaussian function f(x) is 2σ (2 log ｅ 2) ２ By calculating σ assuming that the magnitude of this value is the same as the half-width of the actual FFP radiation pattern and finding the Gaussian function f(x), the function h(x) expressed by the following equation can be obtained.

[0352] h(x)=|f(x)−g(x)|

[0353] As shown in FIGS. 86 and 87, for example, when the effective refractive index difference ΔN is 10×10 －３ When the effective refractive index difference ΔN is 3×10, the maximum ridge width that can be used for single transverse mode operation is about 0.7 μm. －３ In this way, when the effective refractive index difference ΔN is 10×10, the maximum value of the ridge width that can be operated in a single transverse mode is about 1.4 μm. －３ When the effective refractive index difference ΔN is 3×10 －３ In this case, the ridge width can be increased by approximately double. Accordingly, the area of ​​the upper surface 310Ru of the ridge 310R, which is the region into which current is injected, can be increased, thereby reducing the series resistance of the semiconductor laser device 300. Therefore, the operating voltage of the semiconductor laser device 300 can be reduced.

[0354] As shown in FIGS. 86 and 87, the effective refractive index difference ΔN is 1×10 －３ When the effective refractive index difference ΔN is 2×10, the maximum ridge width that can be used for single transverse mode operation is approximately 2.4 μm. －３ When the effective refractive index difference ΔN is 5×10, the maximum ridge width that can be used for single transverse mode operation is approximately 1.7 μm. －３ When the effective refractive index difference ΔN is 15×10, the maximum ridge width that can be used for single transverse mode operation is approximately 1.1 μm. －３ In this case, the maximum value of the ridge width that can be used for single transverse mode operation is about 0.6 μm.

[0355] In addition, in the configuration in which the laser light of the semiconductor laser device 300 according to the present embodiment has a peak wavelength in the 375 nm band, the effective refractive index difference ΔN is 1×10 －３ When the effective refractive index difference ΔN is 2×10, the maximum ridge width that can be used for single transverse mode operation is approximately 2.6 μm. －３ When the effective refractive index difference ΔN is 3×10, the maximum ridge width that can be used for single transverse mode operation is approximately 1.8 μm. －３ When the effective refractive index difference ΔN is 5×10, the maximum ridge width that can be used for single transverse mode operation is approximately 1.5 μm. －３ When the effective refractive index difference ΔN is 10×10, the maximum ridge width that can be used for single transverse mode operation is approximately 1.1 μm. －３ When the effective refractive index difference ΔN is 15×10, the maximum ridge width that can be used for single transverse mode operation is approximately 0.8 μm. －３ In this case, the maximum value of the ridge width that can be used for single transverse mode operation is about 0.6 μm.

[0356] Although the above describes configuration examples in which the ridge width is constant, the ridge width does not have to be constant. Configuration examples in which the ridge width is not constant will be described with reference to FIGS. 88 to 96 . FIGS. 88 , 89 , and 90 are schematic plan views showing the shapes of the ridges 310R in Configuration Examples C51, C52, and C53 of the semiconductor laser device 300 according to this embodiment, respectively. FIGS. 91 , 92 , and 93 are schematic plan views showing the shapes of the ridges 310R in Configuration Examples C61, C62, and C63 of the semiconductor laser device 300 according to this embodiment, respectively. FIGS. 94 , 95 , and 96 are schematic plan views showing the shapes of the ridges 310R in Configuration Examples C71, C72, and C73 of the semiconductor laser device 300 according to this embodiment, respectively.

[0357] The ridge 310R of configuration example C51 shown in FIG. 88 has a region Rm where the ridge width is constant at a minimum value Wm, and a region Rf that is closer to the end facet 100F than region Rm. In configuration example C51, the minimum ridge width Wm is equal to the ridge width Wr at the end facet 100R. The length of region Rm in the Y-axis direction is Lm, and the length of region Rf in the Y-axis direction is Lf. Region Rf has a region R1 where the ridge width is constant at Wf (>Wm) and a tapered region Rfc whose ridge width increases as it approaches the end facet 100F. The inclination angle of tapered region Rfc of the end facet in the X-axis direction with respect to the Y-axis direction is constant at θf. The length of region R1 in the Y-axis direction is L1, and the length of tapered region Rfc in the Y-axis direction is Lfc.

[0358] Higher-order transverse modes may be cut off in the region Rm where the ridge width of the configuration example C51 is minimum. This shape suppresses laser oscillation in higher-order transverse modes, thereby making the horizontal FFP unimodal and widening the current injection area. This reduces the series resistance of the semiconductor laser device 300, thereby reducing the operating voltage.

[0359] 88 , regions (regions Rm and R1) with constant ridge widths of 100 μm or more may be formed in the Y-axis direction from each of end faces 100F and 100R. This makes it possible to suppress errors in the ridge widths of end faces 100F and 100R even if deviations occur in the cleavage positions when end faces 100F and 100R are formed by cleavage.

[0360] Furthermore, the minimum value Wm of the ridge width does not necessarily have to be narrowed to a ridge width that can cut off all modes except the fundamental transverse mode (i.e., horizontal zero-order mode). Since the propagation loss experienced by each order of transverse mode in the tapered region Rfc is greater for higher orders of modes, higher-order transverse modes can be attenuated in the region where the stripe width changes. As a result, laser oscillation can be performed so that the fundamental transverse mode is the main component. For example, when the effective refractive index difference ΔN is 3×10 －３ When the laser light has a peak wavelength in the 375 nm band, if the minimum value Wm is 2 μm and the maximum ridge width (Wf) is 3 μm, the first-order transverse mode can also propagate, but the propagation loss of the first-order transverse mode in the tapered region Rfc is greater than that of the fundamental transverse mode, so the first-order transverse mode can be attenuated. Therefore, the semiconductor laser device 300 can operate with the fundamental transverse mode as the main mode component. For example, the minimum value Wm of the ridge width may be W0 + 1 μm or less, where W0 represents the maximum ridge width that can cut off modes other than the fundamental transverse mode (i.e., the horizontal zeroth-order mode). Furthermore, the ridge width Wf at the end facet 100F may be Wm + 1 μm or more. For example, the minimum width of the ridge 310R may be 0.6 μm or more or 1.6 μm or less.

[0361] Furthermore, when the energy corresponding to the peak wavelength of the laser light is greater than the bandgap energy of GaN, if the ridge width is narrower than 3 μm, the light intensity distribution in the stacking direction of the fundamental transverse mode propagating through the waveguide will be more spread toward the substrate 301. This will increase the effect of light absorption loss in the substrate 301.

[0362] By using a substrate 301 having a band gap energy larger than the energy corresponding to the peak wavelength of the laser light, the optical absorption loss in the substrate 301 is reduced, thereby reducing the waveguide loss, and as a result, the slope efficiency of the semiconductor laser device 300 is improved.

[0363] Furthermore, if the reflectivity of facet 100F is lower than that of facet 100R, the light intensity distribution in the Y-axis direction will be higher on the facet 100F side. This will result in carrier hole burning, such that the carrier distribution in the active layer 105 is lower on the facet 100F side and higher on the facet 100R side. This will make it easier for carriers on the facet 100R side, where the carrier concentration is higher, to leak from the active layer 105, lowering the thermal saturation level in the current-light output characteristics. To prevent this, the ridge width on the facet 100R side can be narrowed to increase the light density and increase the amount of carriers consumed by stimulated emission.

[0364] The length Lm of the region Rm may be 0 μm or more, but the longer it is, the more reliably the highest-order transverse mode capable of propagation in the region Rm can be selected. However, if the length Lm is too long, the length Lfc of the tapered region Rfc becomes small, and the propagation loss of the fundamental transverse mode also increases. Therefore, in order to attenuate higher-order transverse modes while suppressing the increase in the propagation loss of the fundamental transverse mode, the average value of the inclination angle θf of the tapered region Rfc may be set to 0.01 degrees (deg.) or more and 0.1 degrees or less. The inclination angle θf may be constant in the tapered region Rfc, or may vary discontinuously or continuously. In this case, the average value of the inclination angle θf is defined by the following equation:

[0365] atan((Wf-Wm) / 2Lfc)×180 / π

[0366] The ridge 310R of the configuration example C52 shown in Figure 89 has a region Rm where the ridge width is constant at a minimum value Wm, a region Rf that is closer to the end face 100F than region Rm, and a region Rr that is closer to the end face 100R than region Rm. The length of region Rm in the Y-axis direction is Lm, the length of region Rf in the Y-axis direction is Lf, and the length of region Rr in the Y-axis direction is Lr. Region Rf has a region R1 where the ridge width is constant at Wf (>Wm) and a tapered region Rfc whose ridge width increases as it approaches the end face 100F. Region Rr has a region R2 where the ridge width is constant at Wr (>Wm) and a tapered region Rrc whose ridge width increases as it approaches the end face 100R. The inclination angle of tapered region Rrc from the end face in the X-axis direction to the Y-axis direction is constant at θr. The length of the region R2 in the Y-axis direction is L2, and the length of the tapered region Rrc in the Y-axis direction is Lrc.

[0367] In configuration example C52, the ridge width Wf at facet 100F is equal to the ridge width Wr at facet 100R and is greater than the minimum ridge width Wm. The reflectance of facet 100F is smaller than the reflectance of facet 100R. The length Lf of region Rf is equal to the length Lr of region Rr.

[0368] In configuration example C52, similarly to configuration example C51, tilt angle θf and tilt angle θr may be 0.01 degrees or more and 0.1 degrees or less. In configuration example C52, ridge width Wf at facet 100F is equal to ridge width Wr at facet 100R, which simplifies the ridge formation process. This facilitates the manufacture of the semiconductor laser device 300.

[0369] The ridge 310R of the configuration example C53 shown in FIG. 90 differs from the configuration example C52 in that the length Lf of the region Rf is longer than the length Lr of the region Rr.

[0370] In this configuration example C53, since the length Lf is longer than the length Lr, similarly to configuration example C51, the ridge width can be narrowed in the region close to the facet 100R where the carrier concentration is high, thereby increasing the optical density and the amount of carriers consumed by stimulated emission. Therefore, the decrease in the thermal saturation level in the current-light output characteristics can be suppressed.

[0371] 91 differs from configuration example C51 in that it has two tapered regions Rfc1 and Rfc2 with different inclination angles. In configuration example C61, the inclination angle θf1 of tapered region Rfc1 closer to facet 100F is smaller than the inclination angle θf2 of tapered region Rfc2 closer to facet 100R. In the light intensity distribution in the Y-axis direction, the light intensity is high near facets 100F and 100R and is minimized at a position in the Y-axis direction determined by the reflectance of each facet.

[0372] When the reflectance of end face 100F is smaller than that of end face 100R, the light intensity in the Y-axis direction decreases once and becomes minimum as the light approaches end face 100F from end face 100R. The light intensity increases from the Y-axis position where the light intensity is minimum as the light approaches end face 100F.

[0373] When the reflectivity of facet 100F is lower than that of facet 100R, the position where the light intensity is minimum is located between the center in the Y-axis direction and facet 100R. Therefore, by making the inclination angle θf1 of tapered region Rfc1 close to facet 100F smaller than the inclination angle θf2 of tapered region Rfc2 close to facet 100R, the propagation loss of the laser light in the Y-axis direction can be reduced. In configuration example C61, the inclination angle is changed in two stages, but the inclination angle may be changed in three or more stages.

[0374] 92 differs from configuration example C52 in that region Rf has two tapered regions Rfc1 and Rfc2 with different inclination angles, and region Rr has two tapered regions Rrc1 and Rrc2 with different inclination angles. In configuration example C62, the inclination angle θf1 of tapered region Rfc1 closer to facet 100F is smaller than the inclination angle θf2 of tapered region Rfc2 closer to facet 100R, and the inclination angle θr1 of tapered region Rrc1 closer to facet 100F is larger than the inclination angle θr2 of tapered region Rrc2 closer to facet 100R.

[0375] In configuration example C62, the inclination angle is changed in two stages between region Rm and facet 100F. The inclination angle is also changed in two stages between region Rm and facet 100R. As described above, the optical intensity is maximized near each facet, so by reducing the inclination angle closer to each facet, it is possible to reduce the waveguide loss in each tapered region. In configuration example C62, the inclination angle is changed in two stages, but the inclination angle may be changed in three or more stages.

[0376] 93 differs from configuration example C53 in that region Rf has two tapered regions Rfc1 and Rfc2 with different inclination angles, and region Rr has two tapered regions Rrc1 and Rrc2 with different inclination angles. In configuration example C63, the inclination angle θf1 of tapered region Rfc1 closer to facet 100F is smaller than the inclination angle θf2 of tapered region Rfc2 closer to facet 100R, and the inclination angle θr1 of tapered region Rrc1 closer to facet 100F is larger than the inclination angle θr2 of tapered region Rrc2 closer to facet 100R.

[0377] In configuration example C63, the inclination angle is changed in two steps between region Rm and facet 100F. The inclination angle is also changed in two steps between region Rm and facet 100R. As described above, the optical intensity is maximized near each facet, so by reducing the inclination angle closer to each facet, it is possible to reduce the waveguide loss in each tapered region. While the inclination angle is changed in two steps in configuration example C63, it may also be changed in three or more steps.

[0378] 94 differs from configuration example C61 in that the inclination angle θfc of the tapered region Rfc continuously decreases as the angle approaches the end face 100F. In configuration example C71, the same effects as those of configuration example C61 are achieved.

[0379] 95 differs from configuration example C62 in that the inclination angle θfc of tapered region Rfc continuously decreases as it approaches facet 100F, and the inclination angle θrc of tapered region Rrc continuously decreases as it approaches facet 100R. Configuration example C72 like this also achieves the same effects as configuration example C62.

[0380] 96 differs from configuration example C63 in that the inclination angle θfc of tapered region Rfc continuously decreases as it approaches the facet 100F, and the inclination angle θrc of tapered region Rrc continuously decreases as it approaches the facet 100R. In configuration example C73, the same effects as those of configuration example C63 are achieved.

[0381] (Modifications, etc.) Although the semiconductor laser device according to the present disclosure has been described above based on the embodiments, the present disclosure is not limited to the above-described embodiments.

[0382] For example, in each of the above embodiments, the semiconductor laser element is an example of a semiconductor laser element using a resonator, but the semiconductor laser element may be a superluminescent diode.

[0383] In addition, although the p-type cladding layer in each embodiment has a uniform Al composition ratio, the configuration of the p-type cladding layer is not limited to this. For example, the p-type cladding layer may have a superlattice structure in which multiple AlGaN layers and multiple GaN layers are alternately stacked.

[0384] In the third embodiment, the average Al composition ratio of the first p-side guide layer is equal to the average Al composition ratio of the n-side guide layer. However, the average Al composition ratio of the first p-side guide layer may be greater than the average Al composition ratio of the n-side guide layer. The average bandgap energy of the first p-side guide layer may be greater than the average bandgap energy of the n-side guide layer. This shifts the peak position of the light intensity distribution in the stacking direction from the active layer toward the n-side guide layer, thereby reducing free carrier loss in the p-type cladding layer and the like, and thus reducing waveguide loss.

[0385] This disclosure also includes forms obtained by applying various modifications to the above-mentioned embodiments that a person skilled in the art would conceive, and forms realized by arbitrarily combining the components and functions of the above-mentioned embodiments within the scope of the present disclosure.

[0386] The semiconductor laser device of the present disclosure can be applied, for example, as a high-output, highly efficient light source for exposure devices and processing machines.

[0387] 100, 200, 300 Semiconductor laser element 100F, 100R Facet 100S, 200S, 300S Semiconductor laminate 101, 301, 901, 1001 Substrate 102, 302, 902 N-type cladding layer 103 N-side intermediate layer 104, 304 N-side guide layer 105, 305 Active layer 105a, 105c, 105e, 305a, 305c Barrier layer 105b, 105d, 305b Well layer 105i, 105j Intermediate barrier layer 106, 306 P-side guide layer 107, 207, 307 P-side intermediate layer 108, 308 Electron barrier layer 110, 310, 910 P-type cladding layer 110P, 310P protrusion 110R, 310R ridge 110Ru, 310Ru upper surface 110T, 310T groove 111, 311 contact layer 112, 312 current blocking layer 113, 313, 913 p-side electrode 114, 314 n-side electrode 304a first n-side guide layer 304b second n-side guide layer

Claims

1. A semiconductor laser element comprising: a substrate; a semiconductor laminate disposed above the substrate; and a p-side electrode disposed above the semiconductor laminate and in contact with the semiconductor laminate, wherein the semiconductor laminate has: an n-type cladding layer which is a nitride semiconductor layer containing Al; an n-side guide layer disposed above the n-type cladding layer; an active layer disposed above the n-side guide layer; and a p-type cladding layer which is a nitride semiconductor layer containing Al and disposed above the active layer, wherein the Al composition ratio of the n-type cladding layer is larger than the Al composition ratio of the p-type cladding layer; and the p-side electrode is made of at least one of Ag, an Ag alloy, Al, and a translucent conductive film.

2. The semiconductor laser device according to claim 1, wherein the transparent conductive film is a conductive oxide film.

3. The n-side guide layer is a nitride semiconductor layer containing In, the semiconductor laminate has an n-side intermediate layer disposed between the n-type cladding layer and the n-side guide layer, the n-side intermediate layer is a GaN layer or a compositionally graded layer having a thickness of 30 nm or less, and the compositionally graded layer is an Al layer in which the Al composition ratio monotonically decreases with increasing distance from the n-type cladding layer. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In Ｙｎｉ N (0≦Xni<1, 0≦Yni<1) layer and an Al layer in which the In composition ratio monotonically increases with increasing distance from the n-type cladding layer. Ｘｎｊ Ga １－Ｘｎｊ－Ｙｎｊ In Ｙｎｊ 3. The semiconductor laser device according to claim 1, further comprising at least one of N (0≦Xnj<1, 0≦Ynj<1) layers.

4. The semiconductor laser device according to any one of claims 1 to 3, wherein the n-side guide layer is made of InGaN.

5. The semiconductor laser device according to claim 4, wherein the semiconductor laminate has a p-side guide layer made of InGaN, disposed between the active layer and the p-type cladding layer.

6. The semiconductor laser device according to claim 5, wherein the active layer has one or more well layers and a plurality of barrier layers, each of the plurality of barrier layers being made of InGaN, the In composition ratio of the barrier layer closest to the n-side guide layer being equal to or greater than the maximum In composition ratio of the n-side guide layer, and the In composition ratio of the barrier layer closest to the p-side guide layer being equal to or greater than the maximum In composition ratio of the p-side guide layer.

7. The semiconductor laser device according to claim 6, wherein the In composition ratio of at least one of the n-side guide layer and the p-side guide layer monotonically increases with increasing distance from the active layer.

8. The semiconductor laser device according to claim 7, wherein the thickness of said n-side guide layer is smaller than the thickness of said p-side guide layer.

9. The semiconductor laser device according to claim 7, wherein the In composition ratios of the n-side guide layer and the p-side guide layer monotonically increase toward the active layer, and the thickness of the n-side guide layer is equal to or greater than the thickness of the p-side guide layer.

10. The semiconductor laser device according to any one of claims 6 to 9, wherein the maximum value of the In composition ratio of said n-side guide layer is greater than the maximum value of the In composition ratio of said p-side guide layer.

11. The semiconductor laser device according to claim 3, wherein the n-side intermediate layer is a GaN layer having a thickness of 5 nm or more and 30 nm or less.

12. The semiconductor laser device according to claim 1 or 2, wherein the p-type cladding layer has a thickness of 350 nm or less.

13. The semiconductor laser device according to claim 1 or 2, wherein the n-side guide layer is made of AlGaN.

14. The semiconductor laser device according to claim 13, wherein the semiconductor laminate has a p-side guide layer disposed between the active layer and the p-type cladding layer, and the p-side guide layer is made of AlGaN.

15. The semiconductor laser device according to claim 14, wherein the active layer has one or more well layers and a plurality of barrier layers, each of the plurality of barrier layers being made of AlGaN, the Al composition ratio of the barrier layer closest to the n-side guide layer being equal to or greater than the maximum Al composition ratio of the n-side guide layer, and the Al composition ratio of the barrier layer closest to the p-side guide layer being equal to or greater than the maximum Al composition ratio of the p-side guide layer.

16. The semiconductor laser device according to claim 14, wherein the Al composition ratio of at least one of the n-side guide layer and the p-side guide layer monotonically decreases with increasing proximity to the active layer.

17. The semiconductor laser device according to claim 14, wherein the n-side guide layer has a thickness greater than that of the p-side guide layer.

18. The semiconductor laminate has a composition gradient layer disposed between the n-type cladding layer and the n-side guide layer, and the composition gradient layer has an Al composition ratio that monotonically decreases with increasing distance from the n-type cladding layer. Ｘｎｉ Ga １－Ｘｎｉ－Ｙｎｉ In Ｙｎｉ N (0≦Xni<1, 0≦Yni<1) layer and an Al layer in which the In composition ratio monotonically increases with increasing distance from the n-type cladding layer. Ｘｎｊ Ga １－Ｘｎｊ－Ｙｎｊ In Ｙｎｊ 3. The semiconductor laser device according to claim 1, further comprising at least one of N (0≦Xnj<1, 0≦Ynj<1) layers.

19. The semiconductor laser device according to any one of claims 1 to 18, wherein the substrate is made of AlGaN.

20. The semiconductor laser device according to claim 19, wherein the semiconductor laser device has a waveguide, and the refractive index of the substrate is smaller than the effective refractive index for a guided mode propagating through the waveguide.

21. The semiconductor laser device according to any one of claims 1 to 20, wherein the semiconductor laminate has an electron barrier layer disposed between the active layer and the n-type cladding layer, a ridge is formed in the semiconductor laminate, and the electron barrier layer is located inside the ridge.

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