Nitride semiconductor laser element

Abstract

A nitride semiconductor laser element (100) comprises: an n-type cladding layer (102); an active layer (105) disposed above the n-type cladding layer (102); a p-type cladding layer (110) disposed above the active layer (105) and having a ridge (110R) formed therein; a conductive oxide film (113) disposed above the p-type cladding layer (110) and translucent with respect to light of the excitation wavelength of the nitride semiconductor laser element (113); and a metal electrode (114) disposed above the conductive oxide film (113) and including a metal that has higher reflectance than palladium with respect to light of the excitation wavelength.

Description

Nitride semiconductor laser device

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

[0002] Conventionally, nitride semiconductor laser elements have been used as light sources for processing equipment, etc. Light sources for processing equipment are required to have even higher efficiency. To improve the efficiency of nitride semiconductor laser elements, for example, techniques for improving quantum efficiency are known (see, for example, Patent Document 1).

[0003] JP 2014-131019 A

[0004] However, nitride semiconductor laser devices are required to have even higher efficiency.

[0005] The present disclosure is intended to solve these problems, and has an object to provide a highly efficient nitride semiconductor laser device.

[0006] In order to solve the above problems, one aspect of the nitride semiconductor laser element according to the present disclosure includes an n-type cladding layer, an active layer disposed above the n-type cladding layer, a p-type cladding layer disposed above the active layer and having a ridge formed thereon, a conductive oxide film disposed above the p-type cladding layer and transparent to light having an oscillation wavelength of the nitride semiconductor laser element, and a metal electrode disposed above the conductive oxide film and containing a metal having a higher reflectivity than Pd for light having the oscillation wavelength.

[0007] According to the present disclosure, a highly efficient nitride semiconductor laser device can be provided.

[0008] 1 is a schematic plan view showing the overall configuration of a nitride semiconductor laser element according to a first embodiment; FIG. 2 is a schematic cross-sectional view showing the overall configuration of the nitride semiconductor laser element according to the first embodiment; FIG. 3 is a schematic cross-sectional view showing the configuration of an active layer included in the nitride semiconductor laser element according to the first embodiment; FIG. 4 is a diagram showing the configuration of each layer included in the nitride semiconductor laser element according to the first embodiment; FIG. 5 is a diagram showing an example of the thickness of a p-type cladding layer, a first p-type cladding layer, and a second p-type cladding layer according to the first embodiment; FIG. 6 is a diagram showing an example of a material that can be used as a conductive oxide film according to the first embodiment; FIG. 7 is a schematic view showing an outline of a light intensity distribution in a stacking direction of the nitride semiconductor laser element according to the first embodiment; FIG. 8 is a graph showing coordinates of positions in the stacking direction of the nitride semiconductor laser element according to the first embodiment; FIG. 9 is a diagram showing a refractive index distribution in the stacking direction of the nitride semiconductor laser element according to the first embodiment; 1 is a graph showing the relationship between the waveguide loss of the nitride semiconductor laser element according to the first embodiment and the film thickness of the conductive oxide film (ITO film thickness). FIG. 2 is a graph showing the relationship between the amount of feedback (FB amount) of spontaneously emitted light to the active layer by the metal electrode according to the first embodiment and the distance from one end of the ridge in the X-axis direction. FIG. 3 is a graph showing the relationship between the film thickness of the p-type cladding layer and the amount of feedback of spontaneously emitted light to the active layer by the metal electrode according to the first embodiment. FIG. 4 is a graph showing the relationship between each characteristic of the nitride semiconductor laser element according to a first modification of the first embodiment and the film thickness of the p-type cladding layer. FIG. 5 is a graph showing the relationship between each characteristic of the nitride semiconductor laser element according to a second modification of the first embodiment and the film thickness of the p-type cladding layer. FIG. 6 is a graph showing the relationship between each characteristic of the nitride semiconductor laser element according to a third modification of the first embodiment and the film thickness of the p-type cladding layer. FIG. 7 is a graph showing the relationship between each characteristic of the nitride semiconductor laser element according to a fourth modification of the first embodiment and the film thickness of the p-type cladding layer.1 is a schematic cross-sectional view showing Structural Example 3 of the nitride semiconductor laser element according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing Structural Example 4 of the nitride semiconductor laser element according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing Structural Example 6 of the nitride semiconductor laser element according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing Structural Example 7 of the nitride semiconductor laser element according to the first embodiment. FIG. 6 is a schematic cross-sectional view showing a first step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 7 is a schematic cross-sectional view showing a first step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 8 is a schematic cross-sectional view showing a second step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 9 is a schematic cross-sectional view showing a third step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 10 is a schematic cross-sectional view showing a fourth step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 11 is a schematic cross-sectional view showing a fifth step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 12 is a schematic cross-sectional view showing a sixth step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 10 is a schematic cross-sectional view showing an eighth step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 11 is a schematic cross-sectional view showing a ninth step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 12 is a schematic cross-sectional view showing a tenth step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 13 is a schematic cross-sectional view showing an eleventh step of a manufacturing method for Structural Example 5 of the nitride semiconductor laser element according to the first embodiment. FIG. 14 is a schematic side view showing an overview of an orbital type sputtering apparatus. FIG. 15 is a schematic plan view showing an overview of an orbital type sputtering apparatus. FIG. 16 is a schematic cross-sectional view showing a first step of a method for forming a conductive oxide film using an orbital type sputtering apparatus. FIG. 17 is a schematic cross-sectional view showing a second step of a method for forming a conductive oxide film using an orbital type sputtering apparatus. FIG. 18 is a schematic cross-sectional view showing a third step of a method for forming a conductive oxide film using an orbital type sputtering apparatus.1 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser element including a conductive oxide film having planar side surfaces. FIG. 1 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser element including a conductive oxide film having convex side surfaces. FIG. 2 is a diagram showing the refractive index distribution in the stacking direction of a nitride semiconductor laser element according to a second embodiment. FIG. 3 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to a second comparative example and the film thickness of a p-type cladding layer. FIG. 4 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to the second embodiment and the film thickness of a p-type cladding layer. FIG. 5 is a diagram showing the refractive index distribution in the stacking direction of a nitride semiconductor laser element according to a third embodiment. FIG. 6 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to the third embodiment and the film thickness of a p-type cladding layer. FIG. 7 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to the fourth embodiment and the film thickness of a p-type cladding layer. FIG. 8 is a diagram showing the refractive index distribution in the stacking direction of a nitride semiconductor laser element according to a fifth embodiment. FIG. 9 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to the fifth embodiment and the film thickness of a p-type cladding layer. 10 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to a sixth embodiment and the thickness of a p-type cladding layer. FIG. 11 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser element according to a seventh embodiment. FIG. 12 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to the seventh embodiment and the thickness of a p-type cladding layer. FIG. 13 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser element according to an eighth embodiment. FIG. 14 is a schematic cross-sectional view showing the configuration of an active layer included in a nitride semiconductor laser element according to the eighth embodiment. FIG. 15 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser element according to the eighth embodiment and the thickness of a p-type cladding layer. FIG. 16 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser element according to a ninth embodiment. FIG. 17 is a schematic cross-sectional view showing the configuration of an active layer included in a nitride semiconductor laser element according to the ninth embodiment. FIG. 18 is a diagram showing the configuration of each layer included in a nitride semiconductor laser element according to the ninth embodiment. FIG. 19 is a diagram showing an example of the thickness of a p-type cladding layer, the thickness of a first p-type cladding layer, and the thickness of a second p-type cladding layer according to the ninth embodiment.75 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser device according to a ninth embodiment and the thickness of a p-type cladding layer. FIG. 76 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser device according to a tenth embodiment. FIG. 77 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser device according to the tenth embodiment and the thickness of a p-type cladding layer. FIG. 78 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser device according to an eleventh embodiment. FIG. 79 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser device according to a twelfth embodiment and the thickness of a p-type cladding layer. FIG. 79 is a diagram showing the relationship between each characteristic of a nitride semiconductor laser device according to a twelfth embodiment and the thickness of a p-type cladding layer. FIG. 79 is a graph showing the relationship between the thickness of an adhesion layer made of Al and the reflectivity of a stacked film made of a conductive oxide film, an adhesion layer, and a metal electrode relative to a nitride semiconductor layer. FIG. 79 is a diagram for explaining the reflectivity shown in FIG. 80. FIG. 81 is a graph showing the relationship between the film thickness of an adhesion layer and the waveguide loss of a nitride semiconductor laser element. FIG. 82 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser element according to an application example of an adhesion layer. FIG. 83 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser element according to a thirteenth embodiment. FIG. 84 is a graph showing the relationship between the film thickness of a hydrogen absorbing layer made of Pd and the reflectance of a stacked film made of a conductive oxide film, a hydrogen absorbing layer, and a metal electrode, relative to a nitride semiconductor layer. FIG. 85 is a diagram for explaining the reflectance shown in FIG. 80. FIG. 86 is a schematic cross-sectional view showing another structural example of the nitride semiconductor laser element according to the thirteenth embodiment. FIG. 87 is a schematic plan view showing the overall configuration of a nitride semiconductor laser element according to a fourteenth embodiment. FIG. 88 is a schematic first cross-sectional view showing the overall configuration of a nitride semiconductor laser element according to the fourteenth embodiment. FIG. 89 is a schematic cross-sectional view showing the configuration of an experimental stack used in an experiment for evaluating the nitride semiconductor laser element according to the fourteenth embodiment. FIG. 89 is a graph showing the relationship between the angle of incidence of laser light on the experimental stack and the reflectance. SiO in the experimental stack. ２1 is a graph showing the relationship between the thickness of a layer and the average reflectance of the SiO layer in the experimental stack. ２16 is a graph showing the relationship between the film thickness of a layer and the average reflectance. FIG. 17 is a schematic diagram showing the configuration of an experimental stack used in an experiment for evaluating other configuration examples of the nitride semiconductor laser device according to embodiment 14. FIG. 18 is a graph showing the relationship between the angle of incidence of laser light on the experimental stack and the reflectance. FIG. 19 is a graph showing the relationship between the number of DBR pairs and the average reflectance in the experimental stack. FIG. 20 is a graph showing the relationship between the number of DBR pairs and the average reflectance in the experimental stack. FIG. 21 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser device according to embodiment 15. FIG. 22 is a schematic cross-sectional view showing the configuration of an active layer included in the nitride semiconductor laser device according to embodiment 15. FIG. 23 is a diagram showing the configuration of each layer included in configuration example 1 of the nitride semiconductor laser device according to embodiment 15. FIG. 24 is a graph showing the wave function of ground level electrons in the well layer of comparative example A when the carrier density is low. FIG. 25 is a graph showing the wave function of ground level heavy holes in the well layer of comparative example A when the carrier density is low. FIG. 26 is a graph showing the wave function of electrons in the well layer of comparative example A when the carrier density is high. 16 is a graph showing the wave function of heavy holes in the well layer of Comparative Example A when the carrier density is high. FIG. 17 is a graph showing the distribution of band gap energy with respect to the stacking direction position in the well layer of Configuration Example 1. FIG. 18 is a graph showing the distribution of band gap energy with respect to the stacking direction position in the well layer of Comparative Example B. FIG. 19 is a graph showing the wave function of ground level electrons in the well layer of Configuration Example 1. FIG. 20 is a graph showing the wave function of ground level heavy holes in the well layer of Configuration Example 1. FIG. 21 is a graph showing the wave function of ground level electrons in the well layer of Comparative Example B. FIG. 22 is a graph showing the relationship between the surface current density and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 1 and Comparative Example B. FIG. 23 is a graph showing the relationship between the current and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 1 and Comparative Example B. FIG. 24 is a diagram showing the configuration of each layer included in Configuration Example 2 of the nitride semiconductor laser device according to Embodiment 15. 10 is a graph showing the relationship between the surface current density and the correlation coefficient in each of the nitride semiconductor laser elements of Configuration Example 2 and Comparative Example C. FIG. 11 is a graph showing the relationship between the current and the correlation coefficient in each of the nitride semiconductor laser elements of Configuration Example 2 and Comparative Example C.Fig. 20 is a diagram showing the configuration of each layer included in Configuration Example 3 of the nitride semiconductor laser device according to Embodiment 15. Fig. 21 is a graph showing the relationship between the surface current density and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 3 and Comparative Example D. Fig. 22 is a graph showing the relationship between the current and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 3 and Comparative Example D.

[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] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel, terms indicating the shape of elements, such as flat plate and uniform film thickness, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about several percent.

[0013] First Embodiment A nitride semiconductor laser device according to a first embodiment will be described.

[0014] [1-1. Overall Configuration] First, the overall configuration of the nitride semiconductor laser device according to this embodiment will be described with reference to FIGS. 1 to 4. FIGS. 1 and 2 are a schematic plan view and a cross-sectional view, respectively, showing the overall configuration of nitride 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 active layer 105 included in nitride semiconductor laser device 100 according to this embodiment. FIG. 3 shows an enlarged view of only the cross section of active layer 105 among the cross sections shown in FIG. 2. Note that each drawing shows an X-axis, a Y-axis, and a Z-axis, which are orthogonal to each other. The X-axis, the Y-axis, and the Z-axis represent a right-handed Cartesian coordinate system. The stacking direction of nitride 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. FIG. 4 is a diagram showing the configuration of each layer included in nitride semiconductor laser device 100 according to this embodiment.

[0015] As shown in FIG. 2 , the nitride semiconductor laser device 100 includes a semiconductor stack 100S including nitride semiconductor layers, and emits light from a facet 100F (see FIG. 1 ) perpendicular to the stacking direction (i.e., the Z-axis direction) of the semiconductor stack 100S. In this embodiment, the nitride semiconductor laser device 100 emits light in the 445 nm wavelength band. In this embodiment, the nitride semiconductor laser device 100 is a semiconductor laser device having two facets 100F and 100R that form a cavity. The facet 100F is a front facet from which laser light is emitted, and the facet 100R is a rear facet having a higher reflectivity than the facet 100F. In this embodiment, the reflectivities of the facets 100F and 100R are 16% and 95%, respectively. The cavity length of nitride semiconductor laser device 100 according to this embodiment (that is, the distance between facet 100F and facet 100R) is about 1200 μm.

[0016] 2 , the nitride semiconductor laser device 100 includes a semiconductor stack 100S, a current blocking layer 112, a conductive oxide film 113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117. The semiconductor stack 100S also includes a substrate 101, an n-type cladding layer 102, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, an intermediate layer 108, an electron barrier layer 109, a p-type cladding layer 110, and a contact layer 111.

[0017] The substrate 101 is a plate-like member that serves as a base for the nitride semiconductor laser device 100. In this embodiment, the substrate 101 is an n-type GaN substrate.

[0018] The n-type cladding layer 102 is an n-type cladding layer disposed above the substrate 101. The n-type cladding layer 102 has a smaller refractive index than the active layer 105 and a larger band gap energy. In this embodiment, the n-type cladding layer 102 is made of a nitride semiconductor containing Al. The n-type cladding layer 102 has a first n-type cladding layer 102a and a second n-type cladding layer 102b. As shown in FIG. 4, the first n-type cladding layer 102a is made of an n-type Al cladding layer having a thickness of 1200 nm. ０．０２６ Ga ０．９７４ The first n-type cladding layer 102a contains an impurity of 1×10 １８ cm －３ The second n-type cladding layer 102b is disposed above the first n-type cladding layer 102a. As shown in FIG. 4, the second n-type cladding layer 102b is an n-type GaN layer with a thickness of 100 nm. The second n-type cladding layer 102b contains an impurity of 1×10 １８ cm －３ is doped with Si.

[0019] 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 refractive index higher than that of the n-type cladding layer 102 and a band gap energy lower than that of the n-type cladding layer 102. In this embodiment, as shown in FIG. 4, the n-side guide layer 104 is an undoped InP layer having a thickness of 280 nm.０．０３ Ga ０．９７ This is the N layer.

[0020] The active layer 105 is a light-emitting layer disposed above the n-type cladding layer 102. In this embodiment, the active layer 105 is disposed above the n-side guide layer 104 and has a quantum well structure. As shown in FIG. 3 , the active layer 105 has well layers 105b and 105d and barrier layers 105a, 105c, and 105e.

[0021] The barrier layer 105a is disposed above the n-side guide layer 104 and functions as a barrier for the quantum well structure. In this embodiment, as shown in FIG. 4, the barrier layer 105a is an undoped In layer having a thickness of 7 nm. ０．０４ Ga ０．９６ This is the N layer.

[0022] The well layer 105b is disposed above the barrier layer 105a and functions as a well of the quantum well structure. The well layer 105b is disposed between the barrier layer 105a and the barrier layer 105c. In this embodiment, as shown in FIG. 4, the well layer 105b is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0023] The barrier layer 105c is disposed above the well layer 105b and functions as a barrier for the quantum well structure. In this embodiment, as shown in FIG. 4, the barrier layer 105c is a 7 nm thick undoped In ０．０４ Ga ０．９６ This is the N layer.

[0024] The well layer 105d is disposed above the barrier layer 105c and functions as a well of the quantum well structure. The well layer 105d is disposed between the barrier layer 105c and the barrier layer 105e. In this embodiment, as shown in FIG. 4, the well layer 105d is a 3-nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0025] The barrier layer 105e is disposed above the well layer 105d and functions as a barrier for the quantum well structure. In this embodiment, as shown in FIG. 4, the barrier layer 105e is an undoped In layer having a thickness of 5 nm. ０．０４ Ga ０．９６ This is the N layer.

[0026] In this embodiment, the active layer 105 has a multiple quantum well structure including two well layers, but the active layer 105 may have a multiple quantum well structure including three or more well layers, or may have a single quantum well structure including one well layer.

[0027] 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. 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, as shown in FIG. 4, the p-side guide layer 106 is an undoped InP layer having a thickness of 160 nm. ０．０３ Ga ０．９７ This is the N layer.

[0028] The intermediate layer 108 is a layer disposed above the active layer 105. In this embodiment, the intermediate layer 108 is disposed between the p-side guide layer 106 and the electron barrier layer 109, and reduces stress caused by the difference in lattice constant between the p-side guide layer 106 and the electron barrier layer 109. This makes it possible to suppress the occurrence of crystal defects in the nitride semiconductor laser device 100. In this embodiment, as shown in FIG. 4 , the intermediate layer 108 is an undoped GaN layer with a thickness of 20 nm.

[0029] The electron barrier layer 109 is a nitride semiconductor layer disposed above the active layer 105. In this embodiment, the electron barrier layer 109 is disposed between the intermediate layer 108 and the p-type cladding layer 110. As shown in FIG. 4, the electron barrier layer 109 is a p-type Al ０．３６ Ga ０．６４ The electron barrier layer 109 contains an impurity of 1×10 １９ cm －３The electron barrier layer 109 can prevent electrons from leaking from the active layer 105 to the p-type cladding layer 110.

[0030] The p-type cladding layer 110 is a p-type cladding layer disposed above the active layer 105. In this embodiment, the p-type cladding layer 110 is disposed between the electron barrier layer 109 and the contact layer 111. The p-type cladding layer 110 has a lower refractive index than the active layer 105 and a higher band gap energy. In this embodiment, the p-type cladding layer 110 is made of a nitride semiconductor containing Al. In this embodiment, as shown in FIG. 4, the p-type cladding layer 110 has a first p-type cladding layer 110a and a second p-type cladding layer 110b disposed above the first p-type cladding layer 110a. The first p-type cladding layer 110a is made of a p-type Al ０．０２６ Ga ０．９７４ The first p-type cladding layer 110a contains an impurity of 2×10 １８ cm －３ The second p-type cladding layer 110b is a p-type AlN layer having a thickness of Tcp2 [nm]. ０．０２６ Ga ０．９７４ The second p-type cladding layer 110b contains an impurity of 1×10 １９ cm －３ As described above, the impurity concentration of the first p-type cladding layer 110a is lower than the impurity concentration of the second p-type cladding layer 110b.

[0031] Here, the thickness Tcp (=Tcp1+Tcp2) of the p-type cladding layer 110 will be described with reference to FIG. 5 . FIG. 5 is a diagram showing configuration examples of the thickness Tcp of the p-type cladding layer 110, the thickness Tcp1 of the first p-type cladding layer 110a, and the thickness Tcp2 of the second p-type cladding layer 110b according to this embodiment. As shown in FIG. 5 , in this embodiment, studies were conducted on examples where the thickness Tcp of the p-type cladding layer 110 was 0.1 μm, 0.2 μm, 0.25 μm, 0.35 μm, and 0.45 μm. The results of the study will be described later.

[0032] As shown in FIGS. 1 and 2 , the p-type cladding layer 110 has a ridge 110R that protrudes upward. The p-type cladding layer 110 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. A groove 110T is formed between each of the two protruding portions 110P and the ridge 110R. In this embodiment, the ridge width W is approximately 45 μm. As shown in FIG. 2 , the distance between the lower end of the ridge 110R (i.e., the bottom of the groove 110T) and the active layer 105 is defined as dp. The film thickness of the p-type cladding layer 110 at the lower end of the ridge 110R (i.e., the distance between the lower end of the ridge 110R and the interface between the p-type cladding layer 110 and the electron barrier layer 109) is defined as dc.

[0033] The contact layer 111 is a p-type semiconductor layer disposed above the p-type cladding layer 110. In this embodiment, the contact layer 111 is a p-type GaN layer with a thickness of 10 nm, and is in contact with the conductive oxide film 113. The contact layer 111 contains impurities with a concentration of 1×10 ２０ cm －３ It is doped with Mg.

[0034] The current blocking layer 112 is disposed above the p-type cladding layer 110 and is an electrically insulating layer that is transparent to light from the active layer 105. In the example shown in FIG. 2, the current blocking layer 112 is disposed on the upper surface of the p-type cladding layer 110 in a region other than the upper surface of the ridge 110R. In this embodiment, the current blocking layer 112 is made of SiO ２ It is a layer.

[0035] The conductive oxide film 113 is disposed above the p-type cladding layer 110 and is a film that is translucent to light having the oscillation wavelength of the nitride semiconductor laser device 100. In this embodiment, the conductive oxide film 113 is disposed on the upper surface 110Ru of the ridge 110R and is in contact with the contact layer 111. The conductive oxide film 113 has a uniform thickness in the width direction of the ridge 110R (the X-axis direction in FIG. 2 ). The conductive oxide film 113 is disposed continuously (i.e., without interruption) in the width direction of the ridge 110R in a cross section parallel to the width direction and stacking direction of the ridge 110R. Materials that can be used for the conductive oxide film 113 will be described with reference to FIG. 6 . FIG. 6 shows examples of materials that can be used for the conductive oxide film 113 according to this embodiment. FIG. 6 lists the band gap energy Eg [eV] and refractive index of each material. Note that in FIG. 6 , rutile-type GeO ２ The refractive indexes of IGZO and IGZO, and the band gap energy Eg and refractive index of rutile-type oxide semiconductor alloys are omitted. As shown in Fig. 6, the refractive index of materials that can be used as the conductive oxide film 113 is lower than the refractive index of nitride semiconductors (about 2.5), so the conductive oxide film 113 can also function as a cladding layer. Among the conductive oxide film materials shown in Fig. 6, MgO, CaO, NiO, and Ta-added SnO, which have relatively large band gap energies, are ｘ Ge １－ｘ O ２ , rutile-type GeO ２ (r-GeO ２ ), and rutile-type oxide semiconductor mixed crystal (GeO ２ -SnO ２ -SiO ２ ) are suitable for nitride semiconductor laser elements that emit laser light in the ultraviolet region, for example. Furthermore, ITO, GZO, AZO, and IGZO, which have smaller band gap energies than these conductive oxide film materials, are suitable for nitride semiconductor laser elements that emit laser light in the blue region or green region, for example. In this embodiment, as shown in FIG. 4, the conductive oxide film 113 is ITO with a film thickness of 200 nm.

[0036] Metal electrode 114 is an electrode disposed above conductive oxide film 113. In this embodiment, metal electrode 114 is an electrode containing a metal having a higher reflectivity than Pd for light having the oscillation wavelength of nitride semiconductor laser device 100. Metal electrode 114 is made of, for example, Ag, an Ag alloy, Al, or Rh. Metal electrode 114 made of Ag, an Ag alloy, Al, or Rh can provide a higher reflectivity at any incident angle for light having a wavelength of approximately 375 nm or more and 780 nm or less than that of Pd. In this embodiment, metal electrode 114 is made of Ag with a film thickness of 200 nm.

[0037] The barrier electrode 115 is an electrode disposed above the metal electrode 114. In this embodiment, the barrier electrode 115 is disposed between the metal electrode 114 and the cover electrode 116, and prevents metal atoms diffusing in the cover electrode 116 from reaching the metal electrode 114. In this embodiment, the barrier electrode 115 is made of, for example, Pt, Ti, or Cr. As a result, when the cover electrode 116 is mounted on a submount or the like via AuSn solder or the like, the barrier electrode 115 can prevent Sn diffusing in the cover electrode 116 from reaching the metal electrode 114. As a result, changes in the characteristics of the metal electrode 114 can be suppressed.

[0038] The cover electrode 116 is an electrode that covers the metal electrode 114. In this embodiment, the cover electrode 116 is electrically connected to the metal electrode 114 via the barrier electrode 115. In this embodiment, the cover electrode 116 is made of Au with a film thickness of 2000 nm.

[0039] The n-side electrode 117 is a conductive layer disposed below the substrate 101 (i.e., on the main surface of the substrate 101 opposite to the main surface on which the components of the semiconductor stack 100S other than the substrate 101 are disposed). The n-side electrode 117 is a single-layer film or a multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au, for example.

[0040] 2, the nitride semiconductor laser device 100 has the above-described configuration, and as a result, an effective refractive index difference ΔN occurs between the portion below the ridge 110R and the portion below the groove 110T, which allows light generated in the portion of the active layer 105 below the ridge 110R to be confined in the horizontal direction (i.e., the X-axis direction).

[0041] [1-2. Light Intensity Distribution] Next, the light intensity distribution and stability of the light output of nitride semiconductor laser device 100 according to this embodiment will be described.

[0042] First, the light intensity distribution in the stacking direction (Z-axis direction in each drawing) of nitride semiconductor laser device 100 according to this embodiment will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing an outline of the light intensity distribution in the stacking direction of nitride semiconductor laser device 100 according to this embodiment. Fig. 7 shows a schematic cross-sectional view of nitride semiconductor laser device 100 and a graph showing an outline of the light intensity distribution in the stacking direction at positions corresponding to ridge 110R and groove 110T.

[0043] In general, in nitride semiconductor laser devices, light is generated in the active layer, but the light intensity distribution in the stacking direction depends on the stacking structure, and the peak of the light intensity distribution does not necessarily lie in the active layer. Furthermore, since the stacking structure of nitride semiconductor laser device 100 according to this embodiment differs between the portion below ridge 110R and the portion below groove 110T, the light intensity distribution also differs between the portion below ridge 110R and the portion below groove 110T. As shown in FIG. 7 , the peak position of the light intensity distribution in the stacking direction at the center in the horizontal direction (i.e., the X-axis direction) of the portion below ridge 110R is designated PS1. Furthermore, the peak position of the light intensity distribution in the stacking direction below groove 110T is designated PS2. Positions PS1 and PS2 will now be described with reference to FIG. 8 . FIG. 8 is a graph showing coordinates of positions in the stacking direction of nitride semiconductor laser device 100 according to this embodiment. 8 , of the well layers 105b and 105d included in the active layer 105, the n-side end face of the well layer 105b that is closest to the n-side guide layer 104, i.e., the end face of the well layer 105b closer to the n-side guide layer 104, has a coordinate of zero in the stacking direction, with the downward direction (toward the n-side guide layer 104) being the negative coordinate direction and the upward direction (toward the p-side guide layer 106) being the positive coordinate direction. In this embodiment, of the peak positions of the light intensity distribution, a peak position PS1 below the ridge 110R, which is the most important, is evaluated.

[0044] [1-3. Effects] The effects of the nitride semiconductor laser device 100 according to the present embodiment will be described with reference to FIGS. 9 to 13 , in comparison with nitride semiconductor laser devices of comparative examples. FIGS. 9 and 10 are diagrams showing the refractive index distribution in the stacking direction of the nitride semiconductor laser devices of Comparative Example 1 and the present embodiment, respectively. FIGS. 9 and 10 also schematically show the light intensity distribution in the stacking direction. FIGS. 11 and 12 are diagrams showing the relationship between the characteristics of the nitride semiconductor laser devices of Comparative Example 1 and the present embodiment, respectively, and the thickness Tcp of the p-type cladding layer 110. FIG. 13 is a diagram showing the relationship between the waveguide loss of the nitride semiconductor laser device 100 according to the present embodiment and the thickness (ITO film thickness) of the conductive oxide film 113. Note that the characteristics shown in FIGS. 11 to 13 and the following characteristics were calculated by simulation.

[0045] The nitride semiconductor laser element according to Comparative Example 1 shown in FIG. 9 differs from nitride semiconductor laser element 100 according to the present embodiment in that it does not include conductive oxide film 113 according to the present embodiment and that it includes metal electrode 114c made of Pd instead of metal electrode 114, but is the same in other respects.

[0046] In the nitride semiconductor laser device according to Comparative Example 1, the absorption loss in metal electrode 114c is large, and therefore, as the thickness Tcp of p-type cladding layer 110 decreases, the light intensity in the vicinity of metal electrode 114c increases, resulting in a larger absorption loss in metal electrode 114c, as shown in Fig. 11. For this reason, as the thickness Tcp of p-type cladding layer 110 decreases, the waveguide loss increases sharply.

[0047] In contrast, in this embodiment, by providing conductive oxide film 113 which has a small refractive index and small absorption loss for light having the oscillation wavelength of nitride semiconductor laser device 100, conductive oxide film 113 also functions as a cladding layer, making it possible to reduce absorption loss and enhance the light confinement effect. Furthermore, in this embodiment, metal electrode 114 which has high reflectivity and small absorption loss is disposed above conductive oxide film 113, making it possible to further reduce absorption loss. Therefore, as shown in FIG. 12 , in this embodiment, waveguide loss can be suppressed even when film thickness Tcp of p-type cladding layer 110 is small.

[0048] Furthermore, in this embodiment, by reducing the thickness Tcp of the p-type cladding layer 110, free carrier loss in the p-type cladding layer 110 can be reduced, thereby further reducing waveguide loss. Furthermore, by reducing the thickness Tcp of the p-type cladding layer 110, electrical resistance in the p-type cladding layer 110 can be reduced, thereby reducing power loss in the nitride semiconductor laser device 100. The thickness Tcp of the p-type cladding layer 110 may be, for example, not less than 0.1 μm (100 nm) and not more than 0.45 μm (450 nm). The thickness Tcp of the p-type cladding layer 110 may be not less than 0.1 μm (100 nm) and not more than 0.3 μm (300 nm). This allows for further reductions in waveguide loss and power loss in the nitride semiconductor laser device 100.

[0049] As described above, in the nitride semiconductor laser device 100 according to this embodiment, the waveguide loss and power loss can be reduced, and therefore high efficiency can be achieved.

[0050] Furthermore, in this embodiment, by providing the n-side guide layer 104 and the p-side guide layer 106, the light intensity distribution can be suppressed from spreading into the p-type cladding layer 110, thereby further suppressing waveguide loss.

[0051] Furthermore, as shown in FIGS. 11 and 12 , in the nitride semiconductor laser device 100 according to the present embodiment, characteristics equivalent to or better than those of the nitride semiconductor laser device according to Comparative Example 1 can be obtained in terms of the optical confinement coefficient (in the active layer 105), the effective refractive index difference ΔN, and the peak position PS1 of the light intensity distribution.

[0052] 13 , if the film thickness (ITO film thickness) of conductive oxide film 113 is 0.1 μm or more, waveguide loss can be suppressed even more reliably. The film thickness of conductive oxide film 113 may be 0.4 μm or less. This makes it possible to suppress the operating voltage of nitride semiconductor laser device 100 and also to prevent the size of nitride semiconductor laser device 100 from increasing.

[0053] Next, the effect of the metal electrode 114 according to this embodiment in feeding back spontaneously emitted light from the active layer 105 to the active layer 105 will be described with reference to FIGS. 14 and 15 . FIG. 14 is a graph showing the relationship between the amount of feedback (FB amount) of spontaneously emitted light to the active layer 105 by the metal electrode 114 according to this embodiment and the distance from one end of the ridge 110R in the X-axis direction. FIG. 14 shows the feedback amount when the thickness Tcp of the p-type cladding layer 110 is 0.1 μm, 0.15 μm, 0.25 μm, 0.35 μm, and 0.45 μm. FIG. 15 is a graph showing the relationship between the thickness Tcp of the p-type cladding layer 110 according to this embodiment and the amount of feedback of spontaneously emitted light to the active layer 105 by the metal electrode 114. 14 and 15 show the amount of feedback when Ag is used as metal electrode 114, as in nitride semiconductor laser device 100 according to the present embodiment, and when a metal electrode made of Pd is used instead of metal electrode 114 made of Ag. Note that although Figures 14 and 15 show results calculated using the configuration of a nitride semiconductor laser device according to embodiment 3, which will be described later, it is expected that similar calculation results will be obtained when the configuration of a nitride semiconductor laser device according to any embodiment other than embodiment 3 is used.

[0054] 14 and 15 , regardless of whether the thickness Tcp of the p-type cladding layer 110 is 0.1 μm, 0.15 μm, 0.25 μm, 0.35 μm, or 0.45 μm, using the metal electrode 114 made of Ag can increase the amount of spontaneously emitted light feedback by about 1.7 times compared to using a metal electrode made of Pd. Components of the fed-back spontaneously emitted light with wavelengths shorter than the oscillation wavelength are absorbed in the active layer 105 and can contribute to the generation of electron-hole pairs. As a result, the quantum efficiency of the nitride semiconductor laser device 100 can be improved. The increased quantum efficiency can reduce the oscillation threshold of the nitride semiconductor laser device 100 and improve its slope efficiency. In this way, the nitride semiconductor laser device 100 according to this embodiment can achieve high efficiency.

[0055] The film thickness of the metal electrode 114 may be 100 nm or more. This makes it possible to prevent the spontaneously emitted light from passing through the metal electrode 114, thereby ensuring a sufficient reflectance for the spontaneously emitted light. The film thickness of the metal electrode 114 may be 400 nm or less. This makes it possible to prevent defects such as burrs and residues from occurring during electrode formation on the nitride semiconductor laser device 100.

[0056] Furthermore, in this embodiment, nitride semiconductor laser device 100 includes electron barrier layer 109. This can prevent electrons injected into active layer 105 from leaking into p-type cladding layer 110. Therefore, it is possible to improve the temperature characteristics of nitride semiconductor laser device 100 and reduce the oscillation threshold value.

[0057] [1-4. Modifications] Nitride semiconductor laser devices according to Modifications 1 to 4 of this embodiment will be described. The nitride semiconductor laser devices according to Modifications 1 to 4 differ from the nitride semiconductor laser device 100 according to the first embodiment in the configurations of the n-side guide layer 104 and the p-side guide layer 106, but are the same in other respects. The nitride semiconductor laser devices according to each modification will be described below with reference to FIGS. 16 to 19, focusing on the differences from the nitride semiconductor laser device 100 according to this embodiment. FIGS. 16, 17, 18, and 19 are diagrams showing the relationship between the characteristics of the nitride semiconductor laser devices according to Modifications 1, 2, 3, and 4 of this embodiment and the thickness Tcp of the p-type cladding layer 110, respectively.

[0058] The nitride semiconductor laser devices according to Modifications 1 and 2 differ from the nitride semiconductor laser device 100 according to Embodiment 1 in the film thickness of each guide layer, but are otherwise the same. In Modification 1, the n-side guide layer 104 and the p-side guide layer 106 each have a film thickness of 220 nm. In Modification 2, the n-side guide layer 104 has a film thickness of 160 nm, and the p-side guide layer 106 has a film thickness of 280 nm.

[0059] The nitride semiconductor laser devices according to Modifications 3 and 4 differ from the nitride semiconductor laser device 100 according to Embodiment 1 in the film thickness of each guide layer and the composition of the p-side guide layer 106, but are the same in other respects. In Modification 3, the film thickness of each of the n-side guide layer 104 and the p-side guide layer 106 is 220 nm. In Modification 4, the film thickness of the n-side guide layer 104 is 160 nm, and the film thickness of the p-side guide layer 106 is 280 nm. In Modifications 3 and 4, the p-side guide layer 106 is made of undoped In ０．０２ Ga ０．９８ This is the N layer.

[0060] In the nitride semiconductor laser device 100 according to the present embodiment, the thickness of the p-side guide layer 106 is smaller than the thickness of the n-side guide layer 104, but in the nitride semiconductor laser devices according to Modifications 1 to 4, the thickness of the p-side guide layer 106 is equal to or greater than the thickness of the n-side guide layer 104. This allows the peak position of the light intensity distribution to be shifted upward (i.e., in the direction from the active layer 105 to the p-side guide layer 106). In this embodiment, since the thickness Tcp of the p-type cladding layer 110 is small, the peak position of the light intensity distribution tends to be shifted downward from the active layer 105. However, in the nitride semiconductor laser devices according to Modifications 1 to 4, this tendency can be suppressed by making the thickness of the p-side guide layer 106 equal to or greater than the thickness of the n-side guide layer 104. This allows the peak position of the light intensity distribution to be closer to the active layer 105. Accordingly, as shown in FIGS. 16 to 19, in the nitride semiconductor laser devices according to Modifications 1 to 4, the optical confinement coefficient in active layer 105 can be increased more than in nitride semiconductor laser device 100 according to the present embodiment.

[0061] Furthermore, in the nitride semiconductor laser devices according to Modifications 1 to 4, the thickness of the p-side guide layer 106 is equal to or greater than the thickness of the n-side guide layer 104, thereby reducing the effective refractive index difference ΔN. This reduces the horizontal divergence angle of the laser beam (the angle at which the beam spreads in a direction parallel to the X-axis direction). Furthermore, since the vertical divergence angle of the laser beam (the angle at which the beam spreads in a direction parallel to the Z-axis direction) can be reduced, the absorption loss of the laser beam can be reduced even when the thickness Tcp of the p-type cladding layer 110 is small. As a result, a nitride semiconductor laser device can be realized that has a small horizontal divergence angle of the laser beam and is capable of low-voltage, high-temperature, and high-power operation.

[0062] In the third and fourth modifications, the p-side guide layer 106 is In ０．０２ Ga ０．９８ N layer, and the n-side guide layer 104 is In ０．０３ Ga ０．９７Since the p-side guide layer 106 is an N layer, the average refractive index of the p-side guide layer 106 is smaller than the average refractive index of the n-side guide layer 104. In other words, the average bandgap energy of the p-side guide layer 106 is larger than the average bandgap energy of the n-side guide layer 104. This makes it possible to prevent the peak position of the light intensity distribution from shifting upward too much, compared to when the average refractive index of the p-side guide layer 106 is equal to the average refractive index of the n-side guide layer 104, as in Modifications 1 and 2. Therefore, as shown in FIGS. 18 and 19 , the nitride semiconductor laser devices according to Modifications 3 and 4 can further reduce waveguide loss.

[0063] In this disclosure, the average refractive index of each layer refers to 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 position of the interface closer to the substrate 101 in the stacking direction of the layer to the position of the interface farther from the substrate 101, and dividing the result by the film thickness of the layer (the distance between the interface closer to the substrate 101 and the interface farther from the substrate 101).

[0064] In addition, in the present disclosure, the average band gap energy of each 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 in the stacking direction from the position of the interface closer to the substrate 101 in the stacking direction of the layer to the position of the interface farther from the substrate 101, and dividing the result by the film thickness of the layer (the distance between the interface closer to the substrate 101 and the interface farther from the substrate 101).

[0065] [1-5. Structural Examples of Conductive Oxide Film and Metal Electrode] Structural examples of conductive oxide film 113 and metal electrode 114 according to this embodiment will be described with reference to Figures 20 to 26. Figures 20, 21, 22, 23, 24, 25, and 26 are schematic cross-sectional views showing Structural Example 1, Structural Example 2, Structural Example 3, Structural Example 4, Structural Example 5, Structural Example 6, and Structural Example 7, respectively, of nitride semiconductor laser element 100 according to this embodiment. Figures 20 to 26 show only a portion of the same cross section as Figure 2.

[0066] In Structural Example 1 of the nitride semiconductor laser device 100, as shown in FIG. 20 , the conductive oxide film 113 is disposed over the entire top surface 110Ru of the ridge 110R. The dimension of the conductive oxide film 113 in the X-axis direction is equal to the dimension of the top surface 110Ru of the ridge 110R in the X-axis direction. The conductive oxide film 113 has a uniform film thickness in the X-axis direction. The side surface 113s of the conductive oxide film 113 is parallel to the stacking direction (Z-axis direction). Here, the side surface 113s of the conductive oxide film 113 is an end surface located at the end of the conductive oxide film 113 in the X-axis direction. In Structural Example 1, the side surface 113s of the conductive oxide film 113 is parallel to the YZ plane.

[0067] The metal electrode 114 is disposed over the entire upper surface 113u of the conductive oxide film 113. In other words, the metal electrode 114 covers the upper surface 110Ru of the ridge 110R via the conductive oxide film 113. This increases the amount of spontaneously emitted light fed back to the active layer 105 by the metal electrode 114. In Structural Example 1, the metal electrode 114 is disposed only above the upper surface 110Ru of the ridge 110R. The metal electrode 114 has a uniform film thickness in the X-axis direction.

[0068] The current blocking layer 112 covers the side surface 110Rs of the ridge 110R. Here, the side surface 110Rs of the ridge 110R is an end surface located at the end of the ridge 110R in the X-axis direction. The current blocking layer 112 covers at least a portion of the side surface 113s of the conductive oxide film 113. In other words, the current blocking layer 112 continuously covers the side surface 110Rs of the ridge 110R and at least a portion of the side surface 113s of the conductive oxide film 113. The current blocking layer 112 has a smaller refractive index than the p-type cladding layer 110. In Structural Example 1, the current blocking layer 112 covers the side surface 110Rs of the ridge 110R, the bottom surface 110Tu of the trench 110T, and the entire side surface 113s of the conductive oxide film 113, but does not cover the top surface 113u of the conductive oxide film 113.

[0069] The current blocking layer 112 having the above-described configuration can increase the effective refractive index difference ΔN of the nitride semiconductor laser device 100. Furthermore, because the current blocking layer 112 has small absorption loss for light of the oscillation wavelength of the nitride semiconductor laser device 100, the laser light is stably guided within the waveguide formed by the ridge 110R even when the thickness Tcp of the p-type cladding layer 110 is small.

[0070] 21 , in Structural Example 2 of the nitride semiconductor laser element 100, the current blocking layer 112 continuously covers the side surface 113s of the conductive oxide film 113 and the end of the top surface 113u of the conductive oxide film 113. More specifically, the current blocking layer 112 continuously covers the entire surface of the side surface 113s of the conductive oxide film 113 and the end in the X-axis direction of the top surface 113u. The current blocking layer 112 has an opening 112a at a position facing the top surface 113u of the conductive oxide film 113.

[0071] The metal electrode 114 is disposed in a region of the upper surface 113u of the conductive oxide film 113 that corresponds to the opening 112a of the current blocking layer 112. In the second structural example, the metal electrode 114 is disposed with a uniform thickness over the entire area of ​​the upper surface 113u of the conductive oxide film 113 that corresponds to the opening 112a of the current blocking layer 112.

[0072] Structural Example 2 of the nitride semiconductor laser device 100 having the above-described structure also achieves the same effects as Structural Example 1. In Structural Example 2, the current blocking layer 112, which has a small refractive index, completely covers the side surface 113s of the conductive oxide film 113, so that the laser light can be confined within the conductive oxide film 113. This makes it possible to prevent the laser light propagating through the waveguide from leaking to the barrier electrode 115 and the cover electrode 116 and causing absorption loss. Therefore, even if the thickness Tcp of the p-type cladding layer 110 is reduced, it is possible to achieve lateral confinement of the light distribution while suppressing an increase in waveguide loss.

[0073] 22 , in Structural Example 3 of the nitride semiconductor laser element 100, the current blocking layer 112 continuously covers the side surface 113s of the conductive oxide film 113 and the end of the upper surface 113u of the conductive oxide film 113, similar to Structural Example 2. The current blocking layer 112 has an opening 112a at a position facing the upper surface 113u of the conductive oxide film 113.

[0074] The metal electrode 114 is disposed on the upper surface 113u of the conductive oxide film 113 at a position corresponding to the opening 112a of the current blocking layer 112, and covers the upper surface 110Ru of the ridge 110R. The metal electrode 114 covers at least a portion of the current blocking layer 112 facing the upper surface 110Ru of the ridge 110R.

[0075] Structural Example 3 of the nitride semiconductor laser device 100 having the above-described structure also achieves the same effects as Structural Example 2. Furthermore, in Structural Example 3, the metal electrode 114 covers the upper surface 110Ru of the ridge 110R, so that the spontaneously emitted light (indicated by the dashed arrow in FIG. 22 ) propagating outside the opening 112a of the current blocking layer 112 can be reflected by the metal electrode 114. This allows the spontaneously emitted light to be fed back to the active layer 105. In this way, Structural Example 3 can further increase the amount of spontaneously emitted light that is fed back.

[0076] In Structural Example 4 of the nitride semiconductor laser device 100, as shown in FIG. 23 , the current blocking layer 112 has a configuration similar to that of Structural Examples 2 and 3. In Structural Example 4, the metal electrode 114 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side portion 112s of the current blocking layer 112 facing the side surface 113s of the conductive oxide film 113. In other words, the metal electrode 114 continuously covers the upper surface 113u of the conductive oxide film 113 and at least a portion of the side portion 112s. As shown in FIG. 23 , the metal electrode 114 may continuously cover the side portion 112s of the current blocking layer 112 and at least a portion of the bottom portion 112b disposed in the groove 110T. Note that the metal electrode 114 may cover the entire upper surface of the semiconductor stack 100S.

[0077] Structural Example 4 of the nitride semiconductor laser device 100 having the above-described structure also achieves the same effects as Structural Example 3. Furthermore, in Structural Example 4, the metal electrode 114 covers at least a portion of the side portion 112s of the current blocking layer 112, so that the spontaneously emitted light propagating along the side surface 110Rs of the ridge 110R (indicated by the dashed arrow on the right side in FIG. 23 ) can be reflected (or multiple-reflected) by the metal electrode 114. This allows the spontaneously emitted light to be fed back to the active layer 105. In this way, Structural Example 4 can increase the amount of spontaneously emitted light fed back compared to Structural Example 3. If Ag, Al, or Rh is used, loss during reflection is small even when the spontaneously emitted light is multiple-reflected, as indicated by the dashed arrow passing through the side surface 110Rs on the right side in FIG. 23 , and the amount of spontaneously emitted light fed back can be increased.

[0078] In Structural Example 5 of the nitride semiconductor laser device 100, as shown in FIG. 24 , the film thickness of the conductive oxide film 113 decreases toward the side surface 110Rs of the ridge 110R. In other words, the side surface 113s of the conductive oxide film 113 is inclined with respect to the XY plane and the YZ plane. The current blocking layer 112 continuously covers the inclined side surface 113s of the conductive oxide film 113 and the end of the top surface 113u of the conductive oxide film 113. More specifically, the current blocking layer 112 continuously covers the entire side surface 113s of the conductive oxide film 113 and the end of the top surface 113u in the X-axis direction. The current blocking layer 112 has a side portion 112s arranged along the side surface 113s of the conductive oxide film 113. The top surface of the side portion 112s of the current blocking layer 112 is inclined along the side surface 113s of the conductive oxide film 113. The current blocking layer 112 has an opening 112 a at a position facing the upper surface 113 u of the conductive oxide film 113 .

[0079] The metal electrode 114 continuously covers the top surface 110Ru of the ridge 110R and at least a part of the side portion 112s of the current blocking layer 112 that faces the side surface 113s of the conductive oxide film 113. As shown in Fig. 24, the metal electrode 114 may continuously cover the side portion 112s of the current blocking layer 112 and at least a part of the bottom portion 112b disposed in the trench 110T.

[0080] Structural Example 5 of the nitride semiconductor laser device 100 having the above-described structure also achieves the same effects as Structural Example 4. Furthermore, in Structural Example 5, the portion of the metal electrode 114 that covers at least a part of the side portion 112s of the current blocking layer 112 is inclined along the side portion 112s, and therefore it is possible to increase the proportion of the spontaneous emission light reflected by the metal electrode 114 that is fed back to the active layer 105. Therefore, in Structural Example 5, it is possible to increase the amount of spontaneous emission light that is fed back more than in Structural Example 4.

[0081] 25 , in Structural Example 6 of the nitride semiconductor laser device 100, as in Structural Example 5, the film thickness of the conductive oxide film 113 decreases toward the side surface 110Rs of the ridge 110R. In Structural Example 6, the current blocking layer 112 covers only a portion of the lower side of the inclined side surface 113s of the conductive oxide film 113. The current blocking layer 112 continuously covers the side surface 110Rs of the ridge 110R and at least a portion of the side surface 113s of the conductive oxide film 113. The current blocking layer 112 has a side portion 112s disposed along the side surface 113s of the conductive oxide film 113. The upper surface of the side portion 112s of the current blocking layer 112 is inclined along the side surface 113s of the conductive oxide film 113. The current blocking layer 112 has an opening 112a at a position facing the side surface 113s of the conductive oxide film 113.

[0082] The metal electrode 114 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side surface 113s of the conductive oxide film 113. In Structural Example 6, the metal electrode 114 contacts at least a portion of the side surface 113s of the conductive oxide film 113. As shown in FIG. 25 , the metal electrode 114 may continuously cover the side portion 112s of the current blocking layer 112 and at least a portion of the bottom portion 112b disposed in the trench 110T.

[0083] Structural Example 6 of the nitride semiconductor laser element 100 having the above-described structure also achieves the same effects as Structural Example 5. Furthermore, in Structural Example 6, the metal electrode 114 contacts at least a part of the side surface 113s of the conductive oxide film 113, thereby improving the adhesion between the metal electrode 114 and the conductive oxide film 113, and therefore peeling of the metal electrode 114 can be suppressed. Furthermore, the improved adhesion between the metal electrode 114 and the conductive oxide film 113 reduces the electrical resistance between the metal electrode 114 and the conductive oxide film 113. Therefore, the operating voltage of the nitride semiconductor laser element 100 can be reduced.

[0084] 26 , in Structural Example 7 of the nitride semiconductor laser element 100, the film thickness of the conductive oxide film 113 decreases toward the side surface 110Rs of the ridge 110R, as in Structural Examples 5 and 6. In Structural Example 7, the current blocking layer 112 covers the side surface of the ridge 110R but does not cover the inclined side surface 113s of the conductive oxide film 113.

[0085] The metal electrode 114 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side surface 113s of the conductive oxide film 113. In a structural example, the metal electrode 114 contacts at least a portion of the side surface 113s of the conductive oxide film 113. As shown in FIG. 26 , the metal electrode 114 may continuously cover the entire side surface 113s of the conductive oxide film 113 and a portion of the current blocking layer 112.

[0086] Structural Example 7 of the nitride semiconductor laser element 100 having the above-described structure also achieves the same effects as Structural Example 6. Furthermore, in Structural Example 7, the metal electrode 114 contacts the entire side surface 113s of the conductive oxide film 113, thereby further improving the adhesion between the metal electrode 114 and the conductive oxide film 113, and therefore peeling of the metal electrode 114 can be further suppressed. Furthermore, the improved adhesion between the metal electrode 114 and the conductive oxide film 113 further reduces the electrical resistance between the metal electrode 114 and the conductive oxide film 113. Therefore, the operating voltage of the nitride semiconductor laser element 100 can be further reduced.

[0087] Next, a manufacturing method for Structural Example 5 of nitride semiconductor laser element 100 according to the present embodiment will be described. Here, the description will focus on methods for forming conductive oxide film 113, current blocking layer 112, and metal electrode 114, which have characteristic structures, with reference to FIGS. 27 to 37. FIGS. 27 to 37 are schematic cross-sectional views showing the steps of the manufacturing method for Structural Example 5 of nitride semiconductor laser element 100 according to the present embodiment. FIGS. 27 to 37 show cross sections of nitride semiconductor laser element 100 corresponding to the cross section shown in FIG.

[0088] As shown in Fig. 27, semiconductor layers from the n-type cladding layer 102 to the contact layer 111 are formed on the substrate 101. Note that the substrate 101 is not shown in Figs. 27 to 37. Next, a resist consisting of two layers, a lower layer Rb and an upper layer Ru, is applied onto the contact layer 111. The lower layer Rb is applied onto the contact layer 111, and the upper layer Ru is applied onto the lower layer Rb. Here, the upper layer Ru dissolves more slowly in a developer than the lower layer Rb.

[0089] 28, a predetermined region of the resist is exposed to light using a mask Msk. Here, the predetermined region is a region corresponding to a region where conductive oxide film 113 of nitride semiconductor laser device 100 is to be formed.

[0090] Next, the resist is developed, and predetermined areas of the resist are removed, as shown in Fig. 29. Here, the upper layer Ru dissolves in the developer at a slower rate than the lower layer Rb, so undercuts are formed in the resist. In other words, a larger area of ​​the resist is removed in the lower layer Rb than in the upper layer Ru.

[0091] Subsequently, as shown in Fig. 30, a conductive oxide film 113 is formed by, for example, sputtering. Here, the conductive oxide film 113 is formed on the contact layer 111 by parallel plate sputtering. In this case, the conductive oxide film 113 can be formed to have a trapezoidal cross section as shown in Fig. 30. In other words, the conductive oxide film 113 can be formed to have side surfaces 113s inclined with respect to the XY plane and the YZ plane.

[0092] 31 , the resist is removed and heat treatment is performed on the conductive oxide film 113. By forming the conductive oxide film 113 by the above-described method, it is possible to form the conductive oxide film 113 in which the angle θ113 between the side surface 113s and the upper surface of the contact layer 111 is 10° or more and 30° or less.

[0093] 32, a resist R0 is formed on the conductive oxide film 113. Specifically, the resist is applied as described above, and exposure and development are performed, so that the resist R0 remains only on the conductive oxide film 113.

[0094] 33, dry etching is performed to etch the contact layer 111 and the p-type cladding layer 110 in the regions not covered by the resist R0. This forms a ridge 110R and a groove 110T. Although not shown in FIG. 33, in this embodiment, a protrusion 110P is also formed at the same time.

[0095] Subsequently, the resist R0 is removed, and the current blocking layer 112 is formed as shown in Fig. 34. In this embodiment, the current blocking layer 112 is formed on the entire upper surfaces of the conductive oxide film 113, the p-type cladding layer 110, and the contact layer 111.

[0096] 35, an opening 112a is formed in the current blocking layer 112. Specifically, a resist is formed on the current blocking layer 112, and the resist is removed from the region corresponding to the opening 112a by exposure and development. Next, the region of the current blocking layer 112 corresponding to the opening 112a is removed by dry etching. In this way, the opening 112a can be formed.

[0097] Next, as shown in Fig. 36, a metal electrode 114 is formed. Specifically, a resist R1 is formed, and the resist is exposed and developed to remove the resist in the region corresponding to the metal electrode 114. Next, the metal electrode 114 is formed using electron beam (EB) evaporation or the like. Note that the metal electrode 114 may be formed only in a predetermined region as shown in Fig. 36, or may be formed over the entire top surface of the semiconductor stack 100S.

[0098] Next, as shown in Fig. 37 , the resist R1 is removed. Next, although not shown in Fig. 37 , a barrier electrode 115 and a cover electrode 116 are formed above the metal electrode 114 and the current blocking layer 112. This allows fabrication of Structural Example 5 of the nitride semiconductor laser device 100 according to the present embodiment. Note that Structural Examples 6 and 7 of the nitride semiconductor laser device 100 can also be fabricated in the same manner as Structural Example 5 of the nitride semiconductor laser device 100.

[0099] Although the conductive oxide film 113 having flat side surfaces 113s has been described above, the side surfaces 113s may be concave. In other words, the side surfaces 113s may have a shape that protrudes toward the inside of the conductive oxide film 113. A method for forming the conductive oxide film 113 having such side surfaces 113s will be described with reference to FIGS.

[0100] To form the conductive oxide film 113 having the concave side surface 113s, for example, a revolution-type sputtering apparatus in which the sputtering target is eccentric from the center of the susceptor can be used. Such a revolution-type sputtering apparatus will be described with reference to Figures 38 and 39. Figures 38 and 39 are a schematic side view and a plan view, respectively, showing an overview of the revolution-type sputtering apparatus.

[0101] As shown in FIGS. 38 and 39 , the revolution-type sputtering apparatus includes a disk-shaped susceptor St and a target Tg. As shown in FIG. 39 , the susceptor St rotates around the center of the susceptor St as the rotation axis. The wafer Wf on which the conductive oxide film 113 is formed is positioned on the main surface of the susceptor St at a position away from the center of the susceptor St. As shown in FIG. 38 , the target Tg is positioned away from the main surface of the susceptor St on which the wafer Wf is positioned. As shown in FIGS. 38 and 39 , the target Tg is spaced apart from the rotation axis passing through the center of the susceptor St. In such a revolution-type sputtering apparatus, sputtering is performed while rotating the susceptor St, thereby achieving sputtering with a large oblique incidence component of particles from the target onto the wafer Wf. The process of forming the conductive oxide film 113 using such a revolution-type sputtering apparatus will be described with reference to FIGS. 40 to 42 . 40 to 42 are schematic cross-sectional views showing the steps of a method for forming conductive oxide film 113 using an orbital sputtering apparatus, each showing a cross section of nitride semiconductor laser element 100 corresponding to the cross section shown in FIG.

[0102] As shown in FIG. 40 , a resist consisting of a lower layer Rb and an upper layer Ru is formed on the contact layer 111, followed by sputtering. In a revolution-type sputtering apparatus, there is a greater obliquely incident component of particles from the target than in parallel-plate sputtering. Therefore, a deposition film Mt is formed not only on the upper surface of the upper layer Ru of the resist, but also on the side surfaces of the portions where the resist has been removed. As a result, as sputtering continues, the deposition film Mt formed on the side surfaces of the upper layer Ru of the resist becomes thicker, and as shown in FIG. 41 , the gaps in the portions where the resist has been removed become narrower. This makes it more difficult for the obliquely incident component of particles from the target to reach the contact layer 111. Therefore, the inclination of the side surfaces of the deposition film Mt formed on the contact layer 111 relative to the upper surface of the contact layer 111 gradually approaches vertical. Therefore, as shown in FIG. 42 , a conductive oxide film 113 having concave side surfaces 113s is formed.

[0103] The effects of a nitride semiconductor laser device 100 including a conductive oxide film 113 having such concave side surfaces 113s will be described with reference to Figures 43 to 45. Figure 43 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device 100 including a conductive oxide film 113 having concave side surfaces 113s. Figure 44 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device 100 including a conductive oxide film 113 having planar side surfaces 113s. Figure 45 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device 100 including a conductive oxide film 113 having convex side surfaces 113s.

[0104] In the nitride semiconductor laser device 100 including the conductive oxide film 113 having the concave side surface 113s, spontaneous emission light emitted from the light-emitting point Ep is reflected by the metal electrode 114, as indicated by the dashed arrow in FIG. 43 . The metal electrode 114 has a side portion 114s disposed opposite the concave side surface 113s. The surface of the side portion 114s of the metal electrode 114 facing the conductive oxide film 113 has a convex region facing the conductive oxide film 113. Such a side portion 114s functions as a convex reflection surface along the side surface 113s for the spontaneous emission light. Therefore, the spontaneous emission light is fed back almost uniformly over a wide range of the active layer 105. This makes it possible to uniformize the gain of the laser light in the active layer 105, thereby preventing the gain of a specific high-order transverse mode from being selectively increased. This makes it possible to suppress amplification of higher-order transverse modes, thereby suppressing degradation in the linearity of the characteristic of optical output versus current supplied to nitride semiconductor laser device 100 (the so-called IL characteristic). In other words, it is possible to suppress the occurrence of non-linear portions (so-called kinks) in a graph showing the IL characteristic. In this way, in nitride semiconductor laser device 100 including conductive oxide film 113 having concave side surface 113s, optical output can be stabilized.

[0105] In contrast, in a nitride semiconductor laser device 100 including a conductive oxide film 113 having a planar side surface 113s as shown in Fig. 44, the degree of dispersion of the spontaneously emitted light reflected by one side portion 114s of the metal electrode 114 is smaller, as indicated by the dashed arrow in Fig. 44, than the degree of dispersion of the spontaneously emitted light shown in Fig. 43. For this reason, the uniformity of the gain of the laser light in the active layer 105 is lower in Fig. 44.

[0106] In addition, in a nitride semiconductor laser device 100 including a conductive oxide film 113 having a convex side surface 113s as shown in Fig. 45, a side portion 114s of a metal electrode 114 functions as a concave reflecting surface. Therefore, as shown by the dashed arrow in Fig. 45, spontaneous emission light can be focused on a predetermined region of the active layer 105. This can increase the gain for a specific higher-order transverse mode, which can induce a kink.

[0107] As described above, nitride semiconductor laser device 100 including conductive oxide film 113 having concave side surface 113s shown in FIG. 43 can stabilize the optical output more than nitride semiconductor laser device 100 including conductive oxide film 113 having planar or convex side surface 113s.

[0108] Furthermore, in this embodiment, as shown in FIGS. 43 to 45 , the side surface 113s of the conductive oxide film 113 may be inclined with respect to the stacking direction (more specifically, the YZ plane) so that the cross-sectional shape of the conductive oxide film 113 in the ZX plane has a forward tapered shape. The effect of such a side surface 113s will be described in comparison with the structural example shown in FIG. 23 . When the side surface 113s extends parallel to the stacking direction, as in the structural example shown in FIG. 23 , the spontaneously emitted light is multiple-reflected before being fed back to the active layer 105. Since the spontaneously emitted light is attenuated with each reflection, the attenuation of the spontaneously emitted light is relatively large in the structural example shown in FIG. 23 . In contrast, when the side surface 113s and the side portion 114s of the metal electrode 114 arranged at a position opposite the side surface 113s are inclined with respect to the stacking direction, as shown in FIGS. 43 to 45 , the spontaneously emitted light can be fed back to the active layer 105 with just one reflection from the side surface 114s. Therefore, spontaneous emission light can be more efficiently fed back to the active layer 105. The side surface 113s inclined with respect to the stacking direction may be, for example, flat, or may have a convex or concave region. Furthermore, the surface of the side portion 114s facing the conductive oxide film 113 may be flat, may have a convex region (i.e., convex toward the conductive oxide film 113), or may have a concave region (i.e., convex toward the interior of the metal electrode 114).

[0109] (Embodiment 2) A nitride semiconductor laser device according to embodiment 2 will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to embodiment 1 in the configuration of each guide layer, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 46 , focusing on the differences from nitride semiconductor laser device 100 according to embodiment 1. FIG. 46 is a diagram showing the refractive index distribution in the stacking direction of the nitride semiconductor laser device according to this embodiment. FIG. 46 also schematically shows the light intensity distribution in the stacking direction.

[0110] As shown in FIG. 46, the nitride semiconductor laser device according to the present embodiment includes an n-side guide layer 204 and a p-side guide layer 206 instead of the n-side guide layer 104 and the p-side guide layer 106 according to the first embodiment.

[0111] The n-side guide layer 204 according to this embodiment is disposed between the n-type cladding layer 102 and the active layer 105. The n-side guide layer 204 is an undoped In layer having a thickness of 150 nm. ０．０３ Ga ０．９７ This is the N layer.

[0112] The p-side guide layer 206 according to this embodiment is disposed between the active layer 105 and the p-type cladding layer 110. The p-side guide layer 206 has a first p-side guide layer 206a and a second p-side guide layer 206b. The average refractive index of the first p-side guide layer 206a is equal to or greater than the average refractive index of the n-side guide layer 204, and the average refractive index of the second p-side guide layer 206b is less than the average refractive index of the n-side guide layer 204. The thickness of the p-side guide layer 206 is equal to or greater than the thickness of the n-side guide layer 204. In this embodiment, the first p-side guide layer 206a is an undoped InP layer having a thickness of 100 nm. ０．０３ Ga ０．９７ The first p-side guide layer 206a is an N layer, and the average refractive index of the first p-side guide layer 206a is equal to the average refractive index of the n-side guide layer 204. The second p-side guide layer 206b is an undoped InP layer with a thickness of 190 nm. ０．０１ Ga ０．９９ The second p-side guide layer 206 b is an N layer, and the average refractive index of the second p-side guide layer 206 b is lower than the average refractive index of the n-side guide layer 204 .

[0113] 47 and 48, the effects of the nitride semiconductor laser device according to the present embodiment will be described in comparison with the nitride semiconductor laser device according to Comparative Example 2. Figures 47 and 48 are diagrams showing the relationship between the characteristics of the nitride semiconductor laser devices according to Comparative Example 2 and the present embodiment and the thickness Tcp of p-type cladding layer 110, respectively.

[0114] The nitride semiconductor laser element of Comparative Example 2 differs from the nitride semiconductor laser element of the present embodiment in that it does not include the conductive oxide film 113 of the present embodiment and that it includes a metal electrode made of Pd instead of the metal electrode 114, but is the same in other respects.

[0115] The nitride semiconductor laser element according to the present embodiment exhibits the same effects as those of nitride semiconductor laser element 100 according to embodiment 1. For example, as shown in Figures 47 and 48, in the nitride semiconductor laser element according to comparative example 2, the waveguide loss increases sharply as the thickness Tcp of p-type cladding layer 110 decreases, but in the nitride semiconductor laser element according to the present embodiment, the waveguide loss can be suppressed even when the thickness Tcp of p-type cladding layer 110 is small.

[0116] Furthermore, in the nitride semiconductor laser device according to the present embodiment, the thickness of the p-side guide layer 206 is equal to or greater than the thickness of the n-side guide layer 204. This makes it possible to shift the peak position of the light intensity distribution upward, as in the first to fourth modifications of the first embodiment. Therefore, it becomes possible to move the peak position of the light intensity distribution closer to the active layer 105. Accordingly, in the nitride semiconductor laser device according to the present embodiment, the optical confinement coefficient in the active layer 105 can be increased more than in the nitride semiconductor laser device 100 according to the first embodiment.

[0117] Furthermore, in the nitride semiconductor laser element according to the present embodiment, the film thickness of the p-side guide layer 206 is equal to or greater than the film thickness of the n-side guide layer 204, and therefore, similar to the first to fourth modifications of the first embodiment, a nitride semiconductor laser element can be realized which has a small horizontal divergence angle of laser light and is capable of low-voltage, high-temperature, and high-output operation.

[0118] Moreover, in this embodiment, the p-side guide layer 206 has a first p-side guide layer 206a whose average refractive index is equal to or greater than that of the n-side guide layer 204, and a second p-side guide layer 206b whose average refractive index is less than that of the n-side guide layer 204. This improves the controllability of positioning the peak position of the light intensity distribution near the active layer 105, thereby enabling an increase in the light confinement coefficient in the active layer 105.

[0119] (Third Embodiment) A nitride semiconductor laser device according to the third embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment in the configurations of the guide layers and active layer, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 49 , focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment. FIG. 49 is a diagram showing the refractive index distribution in the stacking direction of the nitride semiconductor laser device according to this embodiment. FIG. 49 also schematically shows the light intensity distribution in the stacking direction.

[0120] As shown in FIG. 49 , the nitride semiconductor laser device according to the present embodiment includes an n-side guide layer 304, an active layer 305, and a p-side guide layer 306, instead of the n-side guide layer 104, the active layer 105, and the p-side guide layer 106 according to the first embodiment.

[0121] The n-side guide layer 304 according to this embodiment is disposed between the n-type cladding layer 102 and the active layer 305. The n-side guide layer 304 is an undoped In layer having a thickness of 160 nm. ０．０４ Ga ０．９６ This is the N layer.

[0122] The p-side guide layer 306 according to this embodiment is disposed between the active layer 305 and the p-type cladding layer 110. The refractive index of the p-side guide layer 306 monotonically decreases with increasing distance from the active layer 305. In other words, the bandgap energy of the p-side guide layer 306 monotonically increases with increasing distance from the active layer 305. Here, the configuration in which the refractive index monotonically decreases also includes a configuration in which there is a region in which the refractive index is constant in the stacking direction. The average refractive index of the p-side guide layer 306 is equal to or less than the average refractive index of the n-side guide layer 304. In other words, the average bandgap energy of the p-side guide layer 306 is equal to or greater than the average bandgap energy of the n-side guide layer 304. The thickness of the p-side guide layer 306 is equal to or greater than the thickness of the n-side guide layer 304. In this embodiment, the p-side guide layer 306 is a 280 nm-thick undoped In Ｘｐｇ Ga １－ＸｐｇThe p-side guide layer 306 is an In layer near the interface closer to the active layer 305. ０．０４ Ga ０．９６ The composition ratio of In monotonically decreases toward the p-type cladding layer 110, and the composition ratio of In near the interface closer to the p-type cladding layer 110 is GaN.

[0123] The active layer 305 is a light-emitting layer disposed above the n-type cladding layer 102. In this embodiment, the active layer 305 is disposed above the n-side guide layer 304 and has a quantum well structure. As shown in Fig. 49, the active layer 305 has well layers 105b and 105d and barrier layers 305a, 305c, and 305e.

[0124] The barrier layer 305a is disposed above the n-side guide layer 304 and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 305a is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0125] The well layer 105b is disposed above the barrier layer 305a and functions as a well of the quantum well structure. The well layer 105b is disposed between the barrier layer 305a and the barrier layer 305c. In this embodiment, the well layer 105b is a 3-nm-thick undoped In layer, similar to the well layer 105b in the first embodiment. ０．１８ Ga ０．８２ This is the N layer.

[0126] The barrier layer 305c is disposed above the well layer 105b and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 305c is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0127] The well layer 105d is disposed above the barrier layer 305c and functions as a well of the quantum well structure. The well layer 105d is disposed between the barrier layer 305c and the barrier layer 305e. In this embodiment, the well layer 105d is a 3-nm-thick undoped In layer, similar to the well layer 105d in the first embodiment. ０．１８ Ga０．８２ This is the N layer.

[0128] The barrier layer 305e is disposed above the well layer 105d and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 305e is an undoped In layer having a thickness of 5 nm. ０．０５ Ga ０．９６ This is the N layer.

[0129] The effects of the nitride semiconductor laser device according to this embodiment will be described with reference to Fig. 50. Fig. 50 is a diagram showing the relationship between each characteristic of the nitride semiconductor laser device according to this embodiment and the thickness Tcp of p-type cladding layer 110.

[0130] The nitride semiconductor laser device according to this embodiment achieves the same effects as those of nitride semiconductor laser device 100 according to embodiment 1. For example, as shown in Fig. 50 , in the nitride semiconductor laser device according to this embodiment, waveguide loss can be suppressed even when the thickness Tcp of p-type cladding layer 110 is small.

[0131] Furthermore, in the nitride semiconductor laser device according to the present embodiment, the thickness of the p-side guide layer 306 is equal to or greater than the thickness of the n-side guide layer 304. This makes it possible to shift the peak position of the light intensity distribution upward, as in the first to fourth modifications of the first embodiment and the second embodiment. Therefore, it becomes possible to move the peak position of the light intensity distribution closer to the active layer 305. Accordingly, in the nitride semiconductor laser device according to the present embodiment, the optical confinement coefficient in the active layer 305 can be increased more than in the nitride semiconductor laser device 100 according to the first embodiment.

[0132] Furthermore, in the nitride semiconductor laser element according to the present embodiment, the film thickness of the p-side guide layer 306 is equal to or greater than the film thickness of the n-side guide layer 304. Therefore, similar to the first to fourth modifications of the first embodiment and the second embodiment, a nitride semiconductor laser element can be realized which has a small horizontal divergence angle of laser light and is capable of low-voltage, high-temperature, and high-output operation.

[0133] Furthermore, in this embodiment, the refractive index of the p-side guide layer 306 monotonically decreases with increasing distance from the active layer 305. In other words, the bandgap energy of the p-side guide layer 306 monotonically increases with increasing distance from the active layer 305. Since the bandgap energy of the p-side guide layer 306 monotonically increases with increasing distance from the active layer 305 in this manner, the conductivity of holes in the p-side guide layer 306 is improved. This makes it possible to reduce the hole concentration in the p-side guide layer 306. This makes it possible to reduce free carrier loss due to holes. Therefore, the nitride semiconductor laser device according to this embodiment can reduce waveguide loss, thereby enabling high efficiency.

[0134] (Fourth Embodiment) A nitride semiconductor laser device according to the fourth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from the nitride semiconductor laser device according to the third embodiment in the configuration of each guide layer, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 51 , focusing on the differences from the nitride semiconductor laser device according to the third embodiment. FIG. 51 is a diagram showing the refractive index distribution in the stacking direction of the nitride semiconductor laser device according to this embodiment. FIG. 51 also schematically shows the light intensity distribution in the stacking direction.

[0135] As shown in FIG. 51, the nitride semiconductor laser device according to the present embodiment includes an n-side guide layer 404 and a p-side guide layer 406 instead of the n-side guide layer 304 and the p-side guide layer 306 according to the third embodiment.

[0136] The n-side guide layer 404 according to this embodiment is disposed between the n-type cladding layer 102 and the active layer 305. The refractive index of the n-side guide layer 404 monotonically decreases with increasing distance from the active layer 305. In other words, the band gap energy of the n-side guide layer 404 monotonically increases with increasing distance from the active layer 305. In this embodiment, the n-side guide layer 404 is an undoped InP layer with a thickness of 160 nm. Ｘｎｇ Ga １－ＸｎｇThe n-side guide layer 404 is an In layer near the interface closer to the active layer 305. ０．０４ Ga ０．９６ The composition ratio of In monotonically decreases toward the n-type cladding layer 102, and the composition ratio of In near the interface closer to the n-type cladding layer 102 is expressed as GaN.

[0137] The p-side guide layer 406 according to this embodiment is disposed between the active layer 305 and the p-type cladding layer 110. The refractive index of the p-side guide layer 406 monotonically decreases with increasing distance from the active layer 305. In other words, the bandgap energy of the p-side guide layer 406 monotonically increases with increasing distance from the active layer 305. The average refractive index of the p-side guide layer 406 is equal to or lower than the average refractive index of the n-side guide layer 404. In other words, the average bandgap energy of the p-side guide layer 406 is equal to the average bandgap energy of the n-side guide layer 404. In this embodiment, the average refractive index of the p-side guide layer 406 is equal to the average refractive index of the n-side guide layer 404.

[0138] The thickness of the p-side guide layer 406 is equal to or greater than the thickness of the n-side guide layer 404. In this embodiment, the p-side guide layer 406 is an undoped InN layer having a thickness of 280 nm. Ｘｐｇ Ga １－Ｘｐｇ The p-side guide layer 406 is an In layer near the interface closer to the active layer 305. ０．０４ Ga ０．９６ The composition ratio of In monotonically decreases toward the p-type cladding layer 110, and the composition ratio of In near the interface closer to the p-type cladding layer 110 is GaN.

[0139] The effects of the nitride semiconductor laser device according to this embodiment will be described with reference to Fig. 52. Fig. 52 is a diagram showing the relationship between each characteristic of the nitride semiconductor laser device according to this embodiment and the thickness Tcp of p-type cladding layer 110.

[0140] The nitride semiconductor laser element according to this embodiment achieves the same effects as those of nitride semiconductor laser element 100 according to embodiment 1. For example, as shown in Fig. 52, in the nitride semiconductor laser element according to this embodiment, waveguide loss can be suppressed even when the thickness Tcp of p-type cladding layer 110 is small.

[0141] Furthermore, in the nitride semiconductor laser device according to the present embodiment, the thickness of the p-side guide layer 406 is equal to or greater than the thickness of the n-side guide layer 404. Moreover, the refractive index of the p-side guide layer 406 monotonically decreases with increasing distance from the active layer 305. As a result, the nitride semiconductor laser device according to the present embodiment exhibits the same effects as the nitride semiconductor laser device according to the second embodiment.

[0142] Furthermore, in the nitride semiconductor laser device according to this embodiment, the refractive index of the n-side guide layer 404 monotonically decreases with increasing distance from the active layer 305. That is, the bandgap energy of the n-side guide layer 404 monotonically increases with increasing distance from the active layer 305. In this way, the bandgap energy of the n-side guide layer 404 monotonically increases with increasing distance from the active layer 305, improving the electron conductivity in the n-side guide layer 404. Therefore, it is possible to reduce holes leaking from the active layer 305 to the n-side guide layer 404 and the n-type cladding layer 102. This allows the operating voltage of the nitride semiconductor laser device to be reduced.

[0143] (Fifth Embodiment) A nitride semiconductor laser device according to a fifth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from the nitride semiconductor laser device according to the fourth embodiment in the configuration of the p-side guide layer, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 53 , focusing on the differences from the nitride semiconductor laser device according to the fourth embodiment. FIG. 53 is a diagram showing the refractive index distribution in the stacking direction of the nitride semiconductor laser device according to this embodiment. FIG. 53 also schematically shows the light intensity distribution in the stacking direction.

[0144] As shown in FIG. 53, the nitride semiconductor laser device according to this embodiment includes a p-side guide layer 506 instead of the p-side guide layer 406 according to the fourth embodiment.

[0145] The p-side guide layer 506 according to this embodiment is disposed between the active layer 305 and the p-type cladding layer 110. The average refractive index of the p-side guide layer 506 is equal to or less than the average refractive index of the n-side guide layer 404. In other words, the average band gap energy of the p-side guide layer 506 is equal to or greater than the average band gap energy of the n-side guide layer 404. In this embodiment, the average refractive index of the p-side guide layer 506 is equal to the average refractive index of the n-side guide layer 404. The thickness of the p-side guide layer 506 is equal to or greater than the thickness of the n-side guide layer 404. In this embodiment, the p-side guide layer 506 is an undoped InP layer having a thickness of 280 nm. ０．０２ Ga ０．９８ This is the N layer.

[0146] The effects of the nitride semiconductor laser device according to this embodiment will be described with reference to Fig. 54. Fig. 54 is a diagram showing the relationship between each characteristic of the nitride semiconductor laser device according to this embodiment and the thickness Tcp of p-type cladding layer 110.

[0147] The nitride semiconductor laser device according to this embodiment achieves the same effects as those of nitride semiconductor laser device 100 according to embodiment 1. For example, as shown in Fig. 54, in the nitride semiconductor laser device according to this embodiment, waveguide loss can be suppressed even when the thickness Tcp of p-type cladding layer 110 is small.

[0148] Furthermore, in the nitride semiconductor laser device according to the present embodiment, the thickness of the p-side guide layer 506 is equal to or greater than the thickness of the n-side guide layer 404. This makes it possible to increase the optical confinement coefficient in the active layer 305, similar to the first to fourth modifications of the first embodiment.

[0149] Furthermore, in the nitride semiconductor laser element according to the present embodiment, the film thickness of the p-side guide layer 506 is equal to or greater than the film thickness of the n-side guide layer 404, and therefore, similar to the first to fourth modifications of the first embodiment, a nitride semiconductor laser element can be realized which has a small horizontal divergence angle of laser light and is capable of low-voltage, high-temperature, and high-output operation.

[0150] Furthermore, in the nitride semiconductor laser device according to the present embodiment, similarly to the fourth embodiment, the refractive index of the n-side guide layer 404 monotonically decreases with increasing distance from the active layer 305. This allows the operating voltage of the nitride semiconductor laser device to be reduced, similarly to the fourth embodiment.

[0151] Sixth Embodiment A nitride semiconductor laser device according to the sixth embodiment will be described. The nitride semiconductor laser device according to the sixth embodiment differs from the nitride semiconductor laser device according to the fourth embodiment in the configuration of the p-side guide layer, but is the same in other respects. The nitride semiconductor laser device according to the sixth embodiment will be described below with reference to FIG. 55 , focusing on the differences from the nitride semiconductor laser device according to the fourth embodiment. FIG. 55 is a diagram showing the refractive index distribution in the stacking direction of the nitride semiconductor laser device according to the sixth embodiment. FIG. 55 also schematically shows the light intensity distribution in the stacking direction.

[0152] As shown in FIG. 55, the nitride semiconductor laser device according to this embodiment includes a p-side guide layer 606 instead of the p-side guide layer 406 according to the fourth embodiment.

[0153] The p-side guide layer 606 according to this embodiment is disposed between the active layer 305 and the p-type cladding layer 110. The p-side guide layer 606 includes a first p-side guide layer 606a and a second p-side guide layer 606b. The average refractive index of the first p-side guide layer 606a is equal to or greater than the average refractive index of the n-side guide layer 404, and the average refractive index of the second p-side guide layer 606b is less than the average refractive index of the n-side guide layer 404. The film thickness of the p-side guide layer 606 is equal to or greater than the film thickness of the n-side guide layer 404. The average refractive index of the p-side guide layer 606 is equal to or less than the average refractive index of the n-side guide layer 404. In other words, the average band gap energy of the p-side guide layer 606 is equal to or greater than the average band gap energy of the n-side guide layer 404. In this embodiment, the average refractive index of the p-side guide layer 606 is less than the average refractive index of the n-side guide layer 404.

[0154] In this embodiment, the first p-side guide layer 606a is an undoped In layer having a thickness of 80 nm. ０．０４ Ga０．９６ The second p-side guide layer 606b is an undoped In layer with a thickness of 200 nm. ０．０１ Ga ０．９９ This is the N layer.

[0155] The effects of the nitride semiconductor laser device according to this embodiment will be described with reference to Fig. 56. Fig. 56 is a diagram showing the relationship between each characteristic of the nitride semiconductor laser device according to this embodiment and the thickness Tcp of p-type cladding layer 110.

[0156] The nitride semiconductor laser element according to this embodiment achieves the same effects as those of nitride semiconductor laser element 100 according to embodiment 1. For example, as shown in Fig. 56, in the nitride semiconductor laser element according to this embodiment, waveguide loss can be suppressed even when the thickness Tcp of p-type cladding layer 110 is small.

[0157] Furthermore, in the nitride semiconductor laser device according to this embodiment, the thickness of the p-side guide layer 606 is equal to or greater than the thickness of the n-side guide layer 404. This makes it possible to increase the optical confinement coefficient in the active layer 305, similar to the first to fourth modifications of the first embodiment.

[0158] Furthermore, in the nitride semiconductor laser element according to the present embodiment, the film thickness of the p-side guide layer 606 is equal to or greater than the film thickness of the n-side guide layer 404, and therefore, similar to the first to fourth modifications of the first embodiment, a nitride semiconductor laser element can be realized which has a small horizontal divergence angle of laser light and is capable of low-voltage, high-temperature, and high-power operation.

[0159] Furthermore, in the nitride semiconductor laser device according to the present embodiment, similarly to the fourth embodiment, the refractive index of the n-side guide layer 404 monotonically decreases with increasing distance from the active layer 305. This allows the operating voltage of the nitride semiconductor laser device to be reduced, similarly to the fourth embodiment.

[0160] Moreover, in this embodiment, the p-side guide layer 606 has a first p-side guide layer 606a whose average refractive index is equal to or greater than that of the n-side guide layer 404, and a second p-side guide layer 606b whose average refractive index is less than that of the n-side guide layer 404. This improves the controllability of positioning the peak position of the light intensity distribution near the active layer 305, thereby enabling an increase in the light confinement coefficient in the active layer 305.

[0161] Seventh Embodiment A nitride semiconductor laser device according to the seventh embodiment will be described. The nitride semiconductor laser device according to the present embodiment differs from nitride semiconductor laser device 100 according to the first embodiment in the configurations of the cladding layers and active layer, but is the same in other respects. The nitride semiconductor laser device according to the present embodiment will be described below with reference to FIG. 57 , focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment. FIG. 57 is a schematic cross-sectional view showing the overall configuration of nitride semiconductor laser device 700 according to the present embodiment. Like FIG. 2 , FIG. 57 shows a cross section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 700.

[0162] 57 , the nitride semiconductor laser device 700 according to this embodiment includes a semiconductor stack 700S, a current blocking layer 112, a conductive oxide film 113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117. The semiconductor stack 700S includes a substrate 101, an n-type cladding layer 702, an n-side guide layer 104, an active layer 305, a p-side guide layer 106, an intermediate layer 108, an electron barrier layer 109, a p-type cladding layer 710, and a contact layer 111.

[0163] The n-type cladding layer 702 according to this embodiment is an n-type cladding layer disposed above the substrate 101. The n-type cladding layer 702 has a smaller refractive index than the active layer 305 and a larger band gap energy. In this embodiment, the n-type cladding layer 702 includes a first n-type cladding layer 702a and a second n-type cladding layer 102b. The first n-type cladding layer 702a is an n-type Al 102b with a thickness of 1200 nm. ０．０７ Ga ０．９３The first n-type cladding layer 702a contains an impurity of 1×10 １８ cm －３ The second n-type cladding layer 102b is disposed above the first n-type cladding layer 702a. The second n-type cladding layer 102b is an n-type GaN layer with a thickness of 100 nm, similar to the second n-type cladding layer 102b according to the first embodiment. The second n-type cladding layer 102b contains an impurity of 1×10 １８ cm －３ is doped with Si.

[0164] The active layer 305 according to this embodiment is a light-emitting layer disposed above the n-type cladding layer 702. The active layer 305 according to this embodiment has the same configuration as the active layer 305 according to the third embodiment.

[0165] The p-type cladding layer 710 according to this embodiment is a p-type cladding layer disposed above the active layer 305. In this embodiment, the p-type cladding layer 710 is disposed between the electron barrier layer 109 and the contact layer 111. The p-type cladding layer 710 has a smaller refractive index than the active layer 305 and a higher band gap energy.

[0166] In this embodiment, the average refractive index of the p-type cladding layer 710 is greater than the average refractive index of the n-type cladding layer 702. Such a relationship is realized, for example, by each of the n-type cladding layer 702 and the p-type cladding layer 710 being made of a nitride semiconductor containing Al, and the Al composition ratio of the p-type cladding layer 710 being smaller than the Al composition ratio of the n-type cladding layer 702.

[0167] In this embodiment, the p-type cladding layer 710 includes a first p-type cladding layer and a second p-type cladding layer disposed above the first p-type cladding layer. The first p-type cladding layer is made of p-type Al ０．０２ Ga ０．９８ The first p-type cladding layer contains an impurity of 2×10 １８ cm －３ The second p-type cladding layer is a p-type Al layer having a thickness of Tcp2 [nm]. ０．０２ Ga ０．９８The second p-type cladding layer is an N layer. １９ cm －３ It is doped with Mg.

[0168] A ridge 710R is formed in the p-type cladding layer 710, similar to the p-type cladding layer 710 according to the first embodiment. Two grooves 710T and two protrusions 710P are formed in the p-type cladding layer 710, arranged along the ridge 710R and extending in the Y-axis direction. A groove 710T is formed between each of the two protrusions 710P and the ridge 710R.

[0169] The effects of nitride semiconductor laser device 700 according to this embodiment will be described with reference to Fig. 58. Fig. 58 is a diagram showing the relationship between each characteristic of nitride semiconductor laser device 700 according to this embodiment and the thickness Tcp of p-type cladding layer 710. Note that the combinations of thickness Tcp1 of the first p-type cladding layer and thickness Tcp2 of the second p-type cladding layer in each of the examples where thickness Tcp of p-type cladding layer 710 is 0.1 µm, 0.2 µm, 0.25 µm, 0.35 µm, and 0.45 µm are the same as the combinations shown in Fig. 5.

[0170] Nitride semiconductor laser device 700 according to the present embodiment provides the same effects as nitride semiconductor laser device 100 according to embodiment 1. For example, as shown in Fig. 58 , nitride semiconductor laser device 700 according to the present embodiment can suppress waveguide loss even when thickness Tcp of p-type cladding layer 710 is small.

[0171] Furthermore, in this embodiment, the Al composition ratio of the p-type cladding layer 710 can be reduced, thereby reducing the electrical resistance of the p-type cladding layer 710. Therefore, the operating voltage of the nitride semiconductor laser device 700 can be reduced. Furthermore, by reducing the Al composition ratio of the p-type cladding layer 710, a desired hole concentration can be easily obtained even if the impurity concentration (in this embodiment, the Mg concentration) is reduced. Therefore, free carrier loss due to impurities can be reduced, and therefore waveguide loss can be reduced.

[0172] Eighth Embodiment A nitride semiconductor laser device according to the eighth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from the nitride semiconductor laser device according to the third embodiment in the configuration of the active layer, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIGS. 59 and 60 , focusing on the differences from the nitride semiconductor laser device according to the third embodiment. FIG. 59 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser device 800 according to this embodiment. Like FIG. 2 , FIG. 59 shows a cross-section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 800. FIG. 60 is a schematic cross-sectional view showing the configuration of an active layer 805 included in nitride semiconductor laser device 800 according to this embodiment. FIG. 60 shows an enlarged view of only the cross-section of active layer 805 out of the cross-section shown in FIG. 59 .

[0173] 59 , a nitride semiconductor laser device 800 according to this embodiment includes a semiconductor stack 800S, a current blocking layer 112, a conductive oxide film 113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117. The semiconductor stack 800S includes a substrate 101, an n-type cladding layer 102, an n-side guide layer 304, an active layer 805, a p-side guide layer 306, an intermediate layer 108, an electron barrier layer 109, a p-type cladding layer 110, and a contact layer 111.

[0174] The active layer 805 according to this embodiment is a light-emitting layer disposed above the n-type cladding layer 102. In this embodiment, the active layer 805 is disposed above the n-side guide layer 304 and has a quantum well structure. As shown in Fig. 60 , the active layer 805 has a well layer 805b and barrier layers 805a and 805c. In this way, the active layer 805 has a single quantum well structure.

[0175] The barrier layer 805a is disposed above the n-side guide layer 304 and functions as a barrier of the quantum well structure. In this embodiment, the barrier layer 805a is an undoped In layer having a thickness of 7 nm. ０．０５ Ga ０．９５ This is the N layer.

[0176] The well layer 805b is disposed above the barrier layer 805a and functions as a well of the quantum well structure. The well layer 805b is disposed between the barrier layer 805a and the barrier layer 805c. In this embodiment, the well layer 805b is a 3 nm-thick undoped In ０．１８ Ga ０．８２ This is the N layer.

[0177] The barrier layer 805c is disposed above the well layer 805b and functions as a barrier for the quantum well structure. In this embodiment, the barrier layer 805c is an undoped In layer having a thickness of 5 nm. ０．０５ Ga ０．９５ This is the N layer.

[0178] The effects of nitride semiconductor laser device 800 according to this embodiment will be described with reference to Fig. 61. Fig. 61 is a diagram showing the relationship between each characteristic of nitride semiconductor laser device 800 according to this embodiment and thickness Tcp of p-type cladding layer 110.

[0179] Even when nitride semiconductor laser device 800 according to the present embodiment includes active layer 805 having a single quantum well structure, it is possible to achieve the same effects as the nitride semiconductor laser device according to embodiment 3. For example, as shown in Fig. 61 , in the nitride semiconductor laser device according to the present embodiment, waveguide loss can be suppressed even when thickness Tcp of p-type cladding layer 110 is small.

[0180] Ninth Embodiment A nitride semiconductor laser device according to the ninth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment in, for example, the oscillation wavelength band. Hereinafter, the nitride semiconductor laser device according to this embodiment will be described with reference to FIGS. 62 to 64 , focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment. FIG. 62 is a schematic cross-sectional view showing the overall configuration of nitride semiconductor laser device 900 according to this embodiment. Like FIG. 2 , FIG. 62 shows a cross-section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 900. FIG. 63 is a schematic cross-sectional view showing the configuration of an active layer 905 included in nitride semiconductor laser device 900 according to this embodiment. FIG. 63 shows an enlarged view of only the cross-section of active layer 905 out of the cross-section shown in FIG. 62 . FIG. 64 is a diagram showing the configuration of each layer included in nitride semiconductor laser device 900 according to this embodiment.

[0181] 62 , the nitride semiconductor laser device 900 includes a semiconductor stack 900S, a current blocking layer 112, a conductive oxide film 113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117. The semiconductor stack 900S includes a substrate 101, an underlayer 921, a buffer layer 922, an n-type cladding layer 902, an n-side guide layer 904, an active layer 905, a p-side guide layer 906, an intermediate layer 908, an electron barrier layer 109, a p-type cladding layer 910, and a contact layer 111.

[0182] The underlayer 921 is a semiconductor layer disposed between the substrate 101 and the n-type cladding layer 902. In this embodiment, the underlayer 921 is disposed between the substrate 101 and the buffer layer 922. In this embodiment, the underlayer 921 has a concentration of 1×10 １８ cm －３ Si-doped n-type Al with a thickness of 1500 nm ０．０１５ Ga ０．９８５ This is the N layer.

[0183] The buffer layer 922 is disposed between the substrate 101 and the n-type cladding layer 902 and is a semiconductor layer made of InGaN. In this embodiment, the buffer layer 922 has a concentration of 1×10 １８ cm －３ Si-doped n-type In ０．０４ Ga ０．９６ This is the N layer.

[0184] The nitride semiconductor laser device 900 according to the present embodiment includes the buffer layer 922, and therefore is capable of applying compressive strain to the semiconductor laminate 900S. This reduces tensile strain in the semiconductor laminate 900S, thereby suppressing breakage of the GaN wafer and the occurrence of cracks in the GaN wafer when semiconductor layers are stacked on the GaN wafer and processed.

[0185] The n-type cladding layer 902 is an n-type cladding layer disposed above the substrate 101. The n-type cladding layer 902 has a smaller refractive index than the active layer 905 and a larger band gap energy. In this embodiment, the n-type cladding layer 902 has a first n-type cladding layer 902a and a second n-type cladding layer 902b. As shown in FIG. 64, the first n-type cladding layer 902a is an n-type Al 1000 nm thick layer. ０．０８ Ga ０．９２ The first n-type cladding layer 902a contains an impurity of 1×10 １８ cm －３ The second n-type cladding layer 902b is disposed above the first n-type cladding layer 902a. As shown in FIG. 64, the second n-type cladding layer 902b is an n-type GaN layer with a thickness of 200 nm. The second n-type cladding layer 902b contains an impurity of 1×10 １８ cm －３ is doped with Si.

[0186] The n-side guide layer 904 is an optical guide layer disposed above the n-type cladding layer 902. The n-side guide layer 904 is disposed between the n-type cladding layer 902 and the active layer 905. The n-side guide layer 904 has a higher refractive index and a smaller band gap energy than the n-type cladding layer 902. In this embodiment, as shown in FIG. 64, the n-side guide layer 904 is an undoped InP layer having a thickness of 220 nm. ０．０３ Ga ０．９７ This is the N layer.

[0187] The active layer 905 is a light-emitting layer disposed above the n-type cladding layer 902. In this embodiment, the active layer 905 is disposed above the n-side guide layer 904 and has a quantum well structure. As shown in Fig. 63 , the active layer 905 has well layers 905b, 905d, and 905f, and barrier layers 905a, 905c, 905e, and 905g.

[0188] The barrier layer 905a is disposed above the n-side guide layer 904 and functions as a barrier of the quantum well structure. In this embodiment, as shown in Fig. 64, the barrier layer 905a is an undoped GaN layer with a thickness of 7 nm.

[0189] The well layer 905b is disposed above the barrier layer 905a and functions as a well of the quantum well structure. The well layer 905b is disposed between the barrier layer 905a and the barrier layer 905c. In this embodiment, as shown in FIG. 64, the well layer 905b is a 3 nm-thick undoped In ０．２５ Ga ０．７５ This is the N layer.

[0190] The barrier layer 905c is disposed above the well layer 905b and functions as a barrier for the quantum well structure. In this embodiment, as shown in Fig. 64, the barrier layer 905c is an undoped GaN layer with a thickness of 7 nm.

[0191] The well layer 905d is disposed above the barrier layer 905c and functions as a well of the quantum well structure. The well layer 905d is disposed between the barrier layer 905c and the barrier layer 905e. In this embodiment, as shown in FIG. 64, the well layer 905d is a 3-nm-thick undoped In ０．２５Ga ０．７５ This is the N layer.

[0192] The barrier layer 905e is disposed above the well layer 905d and functions as a barrier for the quantum well structure. In this embodiment, as shown in Fig. 64, the barrier layer 905e is an undoped GaN layer with a thickness of 5 nm.

[0193] The well layer 905f is disposed above the barrier layer 905e and functions as a well of the quantum well structure. The well layer 905f is disposed between the barrier layer 905e and the barrier layer 905g. In this embodiment, as shown in FIG. 64, the well layer 905f is a 3 nm-thick undoped In ０．２５ Ga ０．７５ This is the N layer.

[0194] The barrier layer 905g is disposed above the well layer 905f and functions as a barrier for the quantum well structure. In this embodiment, as shown in Fig. 64, the barrier layer 905g is an undoped GaN layer with a thickness of 5 nm.

[0195] The p-side guide layer 906 is an optical guide layer disposed above the active layer 905. The p-side guide layer 906 is disposed between the active layer 905 and the p-type cladding layer 910. The p-side guide layer 906 has a higher refractive index and a smaller band gap energy than the p-type cladding layer 910. In this embodiment, as shown in FIG. 64, the p-side guide layer 906 is an undoped InP layer having a thickness of 220 nm. Ｘｐｇ Ga １－Ｘｐｇ The p-side guide layer 906 is an In layer near the interface closer to the active layer 905. ０．０３ Ga ０．９７ The composition ratio of In monotonically decreases toward the p-type cladding layer 910, and the composition ratio near the interface closer to the p-type cladding layer 910 is expressed as GaN.

[0196] The intermediate layer 908 is a layer disposed above the active layer 905. In this embodiment, the intermediate layer 908 is disposed between the p-side guide layer 906 and the electron barrier layer 109, and reduces stress caused by the difference in lattice constant between the p-side guide layer 906 and the electron barrier layer 109. This makes it possible to suppress the occurrence of crystal defects in the nitride semiconductor laser device 900. In this embodiment, as shown in FIG. 64 , the intermediate layer 908 is an undoped GaN layer with a thickness of 200 nm.

[0197] The p-type cladding layer 910 is a p-type cladding layer disposed above the active layer 905. In this embodiment, the p-type cladding layer 910 is disposed between the electron barrier layer 109 and the contact layer 111. The p-type cladding layer 910 is a layer having a lower refractive index than the active layer 905 and a higher band gap energy. In this embodiment, as shown in FIG. 64 , the p-type cladding layer 910 has a first p-type cladding layer 910 a and a second p-type cladding layer 910 b disposed above the first p-type cladding layer 910 a. The first p-type cladding layer 910 a is a p-type Al layer having a thickness Tcp1 [nm]. ０．０４ Ga ０．９６ The first p-type cladding layer 910a contains an impurity of 2×10 １８ cm －３ The second p-type cladding layer 910b is doped with p-type Al with a thickness of Tcp2 [nm]. ０．０４ Ga ０．９６ The second p-type cladding layer 910b contains an impurity of 1×10 １９ cm －３ As described above, the impurity concentration of the first p-type cladding layer 910a is lower than the impurity concentration of the second p-type cladding layer 910b.

[0198] Here, the thickness Tcp (=Tcp1+Tcp2) of the p-type cladding layer 910 will be described with reference to Fig. 65. Fig. 65 is a diagram showing configuration examples of the thickness Tcp of the p-type cladding layer 910, the thickness Tcp1 of the first p-type cladding layer 910a, and the thickness Tcp2 of the second p-type cladding layer 910b according to this embodiment. As shown in Fig. 65, in this embodiment, studies were conducted on examples in which the thickness Tcp of the p-type cladding layer 910 was 0.1 µm, 0.2 µm, 0.25 µm, and 0.30 µm. The results of the study will be described later.

[0199] As shown in FIG. 62 , a ridge 910R is formed in the p-type cladding layer 910. The p-type cladding layer 910 also has two grooves 910T and two protrusions 910P formed along the ridge 910R and extending in the Y-axis direction. A groove 910T is formed between each of the two protrusions 910P and the ridge 910R. In this embodiment, the ridge width W is approximately 30 μm. As shown in FIG. 62 , the film thickness of the p-type cladding layer 910 at the bottom end of the ridge 910R (i.e., the distance between the bottom end of the ridge 910R and the interface between the p-type cladding layer 910 and the electron barrier layer 109) is designated dc. In this embodiment, the distance dc is 40 nm.

[0200] The effects of nitride semiconductor laser device 900 according to this embodiment will be described with reference to Fig. 66. Fig. 66 is a diagram showing the relationship between each characteristic of nitride semiconductor laser device 900 according to this embodiment and thickness Tcp of p-type cladding layer 910.

[0201] The nitride semiconductor laser device 900 emitting light in the 530 nm wavelength band as in the present embodiment also achieves the same effects as the nitride semiconductor laser device 100 according to the first embodiment. Specifically, as shown in FIG. 66 , in addition to the effect of suppressing waveguide loss, the nitride semiconductor laser device 900 according to the present embodiment also achieves the effects of lowering the oscillation threshold and improving the slope efficiency. In a nitride semiconductor laser device emitting light in the 530 nm wavelength band, such as the nitride semiconductor laser device 900 according to the present embodiment, the refractive index of the active layer 905 is small, resulting in a reduced optical confinement factor in the active layer 905. This tendency is particularly pronounced when the barrier layers 905a, 905c, 905e, and 905g made of GaN are used as in the present embodiment. In such a nitride semiconductor laser device 900, the above-described effects are particularly effective. When each barrier layer contains In, the refractive index of the active layer 905 increases, suppressing the spread of the optical intensity distribution in the vertical direction (Z-axis direction), thereby further increasing the optical confinement factor and further reducing the waveguide loss.

[0202] Furthermore, by using barrier layers 905a, 905c, 905e, and 905g made of GaN as in this embodiment, it is possible to realize nitride semiconductor laser element 900 having good crystallinity even when well layers 905b, 905d, and 905f having a high In composition ratio (25%) are used.

[0203] In addition, in this embodiment, the thickness of the p-side guide layer 906 is equal to the thickness of the n-side guide layer 904, but the thickness of the p-side guide layer 906 may be greater than the thickness of the n-side guide layer 904. This reduces the light intensity distribution in the p-type cladding layer 910, thereby increasing the optical confinement factor and reducing waveguide loss.

[0204] Tenth Embodiment A nitride semiconductor laser device according to a tenth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from the nitride semiconductor laser device 900 according to the ninth embodiment in the depth of the grooves formed in the p-type cladding layer, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 67 , focusing on the differences from the nitride semiconductor laser device 900 according to the ninth embodiment. FIG. 67 is a schematic cross-sectional view showing the overall configuration of a nitride semiconductor laser device 1000 according to this embodiment. Like FIG. 2 , FIG. 67 shows a cross section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 1000.

[0205] 67 , the nitride semiconductor laser device 1000 includes a semiconductor stack 1000S, a current blocking layer 112, a conductive oxide film 113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117. The semiconductor stack 1000S includes a substrate 101, an underlayer 921, a buffer layer 922, an n-type cladding layer 902, an n-side guide layer 904, an active layer 905, a p-side guide layer 906, an intermediate layer 908, an electron barrier layer 109, a p-type cladding layer 1010, and a contact layer 111.

[0206] The p-type cladding layer 1010 according to this embodiment has a first p-type cladding layer and a second p-type cladding layer disposed above the first p-type cladding layer, similar to the p-type cladding layer 910 according to the ninth embodiment. The first p-type cladding layer is a p-type Al ０．０４ Ga ０．９６ The first p-type cladding layer contains an impurity of 2×10 １８ cm －３ The second p-type cladding layer is a p-type Al layer having a thickness of Tcp2 [nm]. ０．０４ Ga ０．９６ The second p-type cladding layer is an N layer. １９ cm －３ It is doped with Mg.

[0207] As shown in FIG. 67 , a ridge 1010R is formed in the p-type cladding layer 1010. Furthermore, two grooves 1010T and two protrusions 1010P are formed in the p-type cladding layer 1010, which are arranged along the ridge 1010R and extend in the Y-axis direction. A groove 1010T is formed between each of the two protrusions 1010P and the ridge 1010R. In this embodiment, the ridge width W is approximately 45 μm. Furthermore, as shown in FIG. 67 , the lower end of the ridge 1010R is located below the p-type cladding layer 1010. In this embodiment, the lower end of the ridge 1010R is located in the intermediate layer 908, and the distance dc1 from the lower interface of the electron barrier layer 109 to the lower end of the ridge 1010R is 40 nm.

[0208] The effects of nitride semiconductor laser device 1000 according to this embodiment will be described with reference to Fig. 68. Fig. 68 is a diagram showing the relationship between each characteristic of nitride semiconductor laser device 1000 according to this embodiment and thickness Tcp of p-type cladding layer 1010.

[0209] Nitride semiconductor laser device 1000 according to this embodiment also exhibits the same effects as those of nitride semiconductor laser device 900 according to the ninth embodiment, as shown in FIG.

[0210] Furthermore, in this embodiment, by forming the ridge 1010R up to the intermediate layer 908 made of GaN below the p-type cladding layer 1010, the effective refractive index difference ΔN can be made larger than that of the nitride semiconductor laser device 900 according to the ninth embodiment. In particular, when the ridge width is 30 μm or less, in order to prevent a kink from occurring in the IL characteristics of the nitride semiconductor laser device 1000, it is necessary to increase the effective refractive index difference ΔN and thereby increase the number of operable higher-order transverse modes. When the intermediate layer 908 made of GaN and having a thickness of 10 nm or more is disposed below and in contact with the electron barrier layer 109 and the ridge 1010R is formed so that the lower end of the ridge 1010R is located in the intermediate layer 908, fluctuations in the refractive index due to manufacturing errors can be suppressed in the GaN layer constituting the intermediate layer 908, and therefore the magnitude of the effective refractive index difference ΔN can be stabilized at a desired value.

[0211] Eleventh Embodiment A nitride semiconductor laser device according to Eleventh Embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment in, for example, the oscillation wavelength band. Hereinafter, the nitride semiconductor laser device according to this embodiment will be described with reference to FIGS. 69 to 71 , focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment. FIG. 69 is a schematic cross-sectional view showing the overall configuration of nitride semiconductor laser device 1100 according to this embodiment. Like FIG. 2 , FIG. 69 shows a cross-section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 1100. FIG. 70 is a schematic cross-sectional view showing the configuration of active layer 1105 included in nitride semiconductor laser device 1100 according to this embodiment. FIG. 70 shows an enlarged view of only the cross-section of active layer 1105 of the cross-section shown in FIG. 69 . FIG. 71 is a diagram showing the configuration of each layer included in nitride semiconductor laser device 1100 according to this embodiment.

[0212] 69 , the nitride semiconductor laser device 1100 according to the present embodiment has an oscillation wavelength in the 375 nm band. As shown in FIG. 69 , the nitride semiconductor laser device 1100 includes a semiconductor stack 1100S, a current blocking layer 112, a conductive oxide film 1113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117. The semiconductor stack 1000S includes a substrate 101, an n-type cladding layer 1102, an n-side guide layer 1104, an active layer 1105, an electron barrier layer 109, a p-type cladding layer 1110, and a contact layer 111.

[0213] The n-type cladding layer 1102 is an n-type cladding layer disposed above the substrate 101. The n-type cladding layer 1102 has a smaller refractive index than the active layer 1105 and a larger band gap energy. In this embodiment, the n-type cladding layer 1102 is a layer having an n-type Al 2 O 3 layer with a thickness of 650 nm, as shown in FIG. Ｘｎｃ Ga １－Ｘｎｃ The n-type cladding layer 1102 contains an impurity of 1×10 １８ cm －３In this embodiment, the Al composition ratio Xnc of the n-type cladding layer 1102 is larger than the Al composition ratio Xpc of the p-type cladding layer 1110. The Al composition ratio Xnc of the n-type cladding layer 1102 is, for example, 0.07.

[0214] The n-side guide layer 1104 is an optical guide layer disposed above the n-type cladding layer 1102. The n-side guide layer 1104 is disposed between the n-type cladding layer 1102 and the active layer 1105. The n-side guide layer 1104 has a refractive index higher than that of the n-type cladding layer 1102 and a band gap energy lower than that of the n-type cladding layer 1102. In this embodiment, as shown in FIG. 71 , the n-side guide layer 1104 has a concentration of 1×10 １８ cm －３ Si-doped n-type Al with a thickness of 127 nm ０．０３ Ga ０．９７ A first n-side guide layer 1104a made of an N layer and an undoped Al layer having a thickness of 60 nm arranged above the first n-side guide layer 1104a. ０．０３ Ga ０．９７ and a second n-side guide layer 1104b made of an N layer.

[0215] The active layer 1105 is a light-emitting layer disposed above the n-type cladding layer 1102. In this embodiment, the active layer 1105 is disposed above the n-side guide layer 1104 and has a quantum well structure. As shown in FIG. 70 , the active layer 1105 has a well layer 1105 b and barrier layers 1105 a and 1105 c. In this way, the active layer 1105 has a single quantum well structure.

[0216] The barrier layer 1105a is disposed above the n-side guide layer 1104 and functions as a barrier for the quantum well structure. In this embodiment, as shown in FIG. 71, the barrier layer 1105a is a 12 nm-thick undoped Al ０．０４ Ga ０．９６ This is the N layer.

[0217] The well layer 1105b is disposed above the barrier layer 1105a and functions as a well of the quantum well structure. The well layer 1105b is disposed between the barrier layer 1105a and the barrier layer 1105c. In this embodiment, as shown in FIG. 71, the well layer 1105b is an undoped In layer having a thickness of 17.5 nm. ０．０１ Ga ０．９９ This is the N layer.

[0218] The barrier layer 1105c is disposed above the well layer 1105b and functions as a barrier for the quantum well structure. In this embodiment, as shown in FIG. 71, the barrier layer 1105c is made of an undoped AlN layer having a thickness of 12 nm. ０．０４ Ga ０．９６ This is the N layer.

[0219] The p-type cladding layer 1110 is a p-type cladding layer disposed above the active layer 1105. In this embodiment, the p-type cladding layer 1110 is disposed between the electron barrier layer 109 and the contact layer 111. The p-type cladding layer 1110 is a layer having a lower refractive index than the active layer 1105 and a higher band gap energy. In this embodiment, as shown in FIG. 71 , the p-type cladding layer 1110 has a first p-type cladding layer 1110a and a second p-type cladding layer 1110b disposed above the first p-type cladding layer 1110a. The first p-type cladding layer 1110a is a p-type Al layer having a thickness Tcp1 [nm]. ０．０３ Ga ０．９７ The first p-type cladding layer 1110a contains an impurity of 1×10 １８ cm －３ The second p-type cladding layer 1110b is doped with p-type Al with a thickness of Tcp2 [nm]. ０．０３ Ga ０．９７ The second p-type cladding layer 1110b contains an impurity of 1×10 １９ cm －３As described above, the impurity concentration of the first p-type cladding layer 1110a is lower than the impurity concentration of the second p-type cladding layer 1110b. As with the p-type cladding layer 910 according to the ninth embodiment, the thicknesses Tcp (=Tcp1+Tcp2) of the p-type cladding layer 1110 were examined for each of the thickness examples shown in FIG. 65. The results of the examination will be described later.

[0220] As shown in Fig. 69, a ridge 1110R is formed in the p-type cladding layer 1110. Furthermore, two grooves 1110T and two protrusions 1110P are formed in the p-type cladding layer 1110, which are arranged along the ridge 1110R and extend in the Y-axis direction. A groove 1110T is formed between each of the two protrusions 1110P and the ridge 1110R. In this embodiment, the ridge width W is about 20 µm.

[0221] The conductive oxide film 1113 is disposed above the p-type cladding layer 1110 and is a film that is transparent to light having the oscillation wavelength of the nitride semiconductor laser device 1100. In this embodiment, the conductive oxide film 1113 is disposed on the upper surface 1110Ru of the ridge 1110R and is in contact with the contact layer 111. The conductive oxide film 1113 has a uniform film thickness in the X-axis direction in FIG. 69 . In this embodiment, the conductive oxide film 1113 is NiO with a film thickness of 200 nm. Using NiO as the conductive oxide film 1113 can reduce absorption loss of light in the 375 nm wavelength band in the conductive oxide film 1113. The film thickness of the conductive oxide film 1113 may be 0.3 nm or more and 300 nm or less. The conductive oxide film 1113 has the function of increasing adhesion between the metal electrode 114 and the semiconductor stack 1100S. By making the thickness of the conductive oxide film 1113 0.3 nm or more, it is possible to reliably improve the adhesion between the metal electrode 114 and the semiconductor stack 1100S. Furthermore, when the conductive oxide film 1113 has a thickness sufficient to refract light, the conductive oxide film 1113 functions as a cladding layer and can be used to control the light intensity distribution in the stacking direction. In other words, when the conductive oxide film 1113 has a sufficient thickness, the conductive oxide film 1113 functions as a cladding layer and can reduce the intensity of laser light at the conductive oxide film 1113. The thickness of the conductive oxide film 1113 may be 300 nm or less. This reduces free carrier loss in the conductive oxide film 1113. Therefore, it is possible to suppress attenuation of spontaneous emission light that passes through the conductive oxide film 1113. Therefore, it is possible to suppress attenuation of spontaneous emission light that is reflected by the metal electrode 114 and fed back to the active layer 1105. The conductive oxide film 1113 may also be a conductive oxide containing at least one of Ag and Ga.

[0222] The effects of the nitride semiconductor laser device according to the present embodiment will be described with reference to Figures 72 and 73, in comparison with the nitride semiconductor laser device according to Comparative Example 3. Figures 72 and 73 are diagrams showing the relationship between the characteristics of the nitride semiconductor laser device according to Comparative Example 3 and the present embodiment and the thickness Tcp of p-type cladding layer 1110, respectively.

[0223] The nitride semiconductor laser element of Comparative Example 3 differs from nitride semiconductor laser element 1100 of the present embodiment in that it does not have conductive oxide film 1113 of the present embodiment and that it has a metal electrode made of Pd instead of metal electrode 114, but is the same in other respects.

[0224] According to nitride semiconductor laser device 1100 of the present embodiment, the same effects as those of nitride semiconductor laser device 100 of the first embodiment are achieved.

[0225] When the oscillation wavelength is 375 nm, as in the nitride semiconductor laser device 1100 according to this embodiment, the refractive index of the substrate 101 made of GaN is greater than the effective refractive index for light in the guided mode. Therefore, when the light in the guided mode reaches the substrate 101, the light propagates within the substrate 101. This light propagating within the substrate 101 cannot be used as output light from the nitride semiconductor laser device 1100. Therefore, in this embodiment, the Al composition ratio Xpc of the p-type cladding layer 1110 is made smaller than the Al composition ratio Xnc of the n-type cladding layer 1102, thereby making the refractive index of the p-type cladding layer 1110 greater than the refractive index of the n-type cladding layer 1102. While this can suppress light propagation within the substrate 101, it can also increase the optical intensity near the metal electrodes. Therefore, the nitride semiconductor laser device according to Comparative Example 3 has high waveguide loss. On the other hand, the nitride semiconductor laser device 1100 according to this embodiment includes a conductive oxide film 1113 disposed above the p-type cladding layer 1110 and having a refractive index smaller than that of the p-type cladding layer 1110, and therefore can confine light below the p-type cladding layer 1110. Therefore, as shown in Fig. 73, this embodiment can reduce waveguide loss. Furthermore, by using NiO, which has a large bandgap energy (approximately 4 eV), as the conductive oxide film 1113, the light absorption loss in the conductive oxide film 1113 can be further reduced.

[0226] Twelfth Embodiment A nitride semiconductor laser device according to a twelfth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment in that it includes an adhesion layer disposed between conductive oxide film 113 and metal electrode 114, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 74 , focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment. FIG. 74 is a schematic cross-sectional view showing the overall configuration of nitride semiconductor laser device 1200 according to this embodiment. Like FIG. 2 , FIG. 74 shows a cross section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 1200.

[0227] As shown in FIG. 74 , the nitride semiconductor laser element 1200 according to this embodiment includes a semiconductor stack 100S, a current blocking layer 112, a conductive oxide film 113, an adhesion layer 1231, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117.

[0228] The adhesion layer 1231 may be, for example, a metal layer disposed between the conductive oxide film 113 and the metal electrode 114. In this embodiment, the adhesion layer 1231 is made of a metal having a higher ionization tendency than the metal electrode 114 and has an average film thickness of 0.3 nm or more and 5 nm or less. Here, if the average film thickness of the adhesion layer 1231 is 0.3 nm or more and 1 nm or less, it may not be possible to form the adhesion layer 1231 with a uniform film thickness. For example, if the film thickness of the adhesion layer 1231 is 0.3 nm or more and 1 nm or less, the adhesion layer 1231 may have a mesh-like shape or an island-like (or dot-like) shape in plan view. In this way, if the film thickness of the adhesion layer 1231 is 0.3 nm or more and 1 nm or less and the film thickness of the adhesion layer 1231 is non-uniform, the average film thickness of the adhesion layer 1231 is defined as the average value of the film thickness at each position on the adhesion layer 1231.

[0229] When the metal electrode 114 is made of Ag, the adhesion layer 1231 may be made of, for example, Ni, Ti, or Al. A part of the adhesion layer 1231 made of Ni, Ti, Al, or the like combines with oxygen contained in the conductive oxide film 113 to form an oxide having light-transmitting properties (i.e., a band gap energy greater than the energy corresponding to light), thereby suppressing loss in the adhesion layer 1231. The adhesion layer 1231 may also be a conductive oxide containing at least one of Ag and In.

[0230] The effect of the adhesion layer 1231 according to this embodiment will be described. Generally, the bond between a metal and an oxygen atom is an ionic bond, and the bonding force between a metal with a high ionization tendency and an oxygen atom is strong. For this reason, by disposing the adhesion layer 1231 made of a metal with a higher ionization tendency than the metal electrode 114 between the conductive oxide film 113 containing oxygen atoms and the metal electrode 114, the adhesion force between the conductive oxide film 113 and the adhesion layer 1231 and between the conductive oxide film 113 and the metal electrode 114 can be increased. Therefore, peeling of the metal electrode 114 can be suppressed.

[0231] The adhesion of the adhesion layer 1231 was confirmed by a peeling test. The peeling test involved attaching adhesive tape to the metal electrode 114 and then peeling it off. When the metal electrode 114 was formed directly on the conductive oxide film 113, the metal electrode 114 peeled off when adhesive tape was attached to the metal electrode 114 and then peeled off. In contrast, when an adhesion layer 1231 having a thickness of 0.3 nm or more was disposed between the conductive oxide film 113 and the metal electrode 114, the metal electrode 114 did not peel off when adhesive tape was attached to the metal electrode 114 and then peeled off. This confirmed that the adhesion layer 1231 having a thickness of 0.3 nm or more disposed between the conductive oxide film 113 and the metal electrode 114 has the effect of increasing the adhesion between the conductive oxide film 113 and the adhesion layer 1231 and the metal electrode 114.

[0232] Next, the effects of providing the adhesion layer 1231 on increasing the amount of feedback of spontaneously emitted light by the metal electrode 114 and reducing absorption loss will be described with reference to FIGS. 75 to 77 . FIG. 75 is a graph showing the relationship between the film thickness (Al film thickness) of the adhesion layer 1231 made of Al and the reflectance of the laminated film made of the conductive oxide film 113, the adhesion layer 1231, and the metal electrode 114 with respect to the nitride semiconductor layer. FIG. 75 shows the reflectance for light with wavelengths of 425 nm, 450 nm, and 550 nm. FIG. 76 is a diagram for explaining the reflectance shown in FIG. 75 . FIG. 77 is a graph showing the relationship between the film thickness of the adhesion layer 1231 and the waveguide loss of the nitride semiconductor laser device 1200. FIG. 77 shows the waveguide loss when Al, Pd, and Rh are used as the adhesion layer 1231. FIG. 77 shows the waveguide loss when the thickness of the p-type cladding layer 110 is 0.1 μm.

[0233] The reflectance shown in Figure 75 will be explained using Figure 76. As shown in Figure 76, in a laminate in which a 200 nm thick ITO layer, an Al layer, and a 200 nm thick Ag layer are sequentially stacked on a GaN layer, the reflectance Pr / Pi is defined using the power Pi of light incident from the GaN layer to the ITO layer and the power Pr of reflected light propagating from the ITO layer into the GaN layer. Here, the angle of incidence of light from the GaN layer to the ITO layer is perpendicular (i.e., 90°) to the interface between the GaN layer and the ITO layer. In other words, the incident direction of light is the normal direction to the interface between the GaN layer and the ITO layer. The reflected light includes light reflected at the interface between the GaN layer and the ITO layer, light reflected at the interface between the ITO layer and the Al layer and returning to the GaN layer, light reflected at the interface between the Al layer and the Ag layer and returning to the GaN layer, and light reflected at the top surface of the Ag layer (the end surface of the Ag layer opposite to the end surface in contact with the Al layer) and returning to the GaN layer.

[0234] As shown in FIG. 75, if the thickness of the adhesion layer 1231 is 5 nm or less, the reflectance of the conductive oxide film 113, the adhesion layer 1231, and the metal electrode 114 for light having a wavelength of 425 nm or more and 550 nm or less can be made 75% or more, and the effect of feeding back spontaneous emission light can be fully achieved.

[0235] The total film thickness of the adhesion layer 1231 and the metal electrode 114 may be 100 nm or more. This makes it possible to suppress light from passing through the adhesion layer 1231 and the metal electrode 114. The total film thickness of the adhesion layer 1231 and the metal electrode 114 may be 200 nm or more. This makes it possible to further suppress light from passing through the adhesion layer 1231 and the metal electrode 114.

[0236] 77, the increase in waveguide loss caused by the adhesion layer 1231 having a thickness of 30 nm or less is suppressed to about 5% or less. In particular, when the adhesion layer 1231 is made of Al, there is almost no increase in waveguide loss.

[0237] As described above, by using the adhesion layer 1231 made of a metal with a higher ionization tendency than the metal electrode 114 and having a film thickness of 0.3 nm or more and 5 nm or less, it is possible to increase the adhesion between the conductive oxide film 113 and the metal electrode 114 while ensuring the effects of increasing the feedback amount of spontaneous emission light, thereby reducing the oscillation threshold, and reducing absorption loss.

[0238] In nitride semiconductor laser device 100 according to the first embodiment, metal electrode 114 made of Al may be used. This makes it possible to increase the adhesion between conductive oxide film 113 and metal electrode 114 without using adhesion layer 1231.

[0239] Furthermore, adhesion layer 1231 according to the present embodiment can also be applied to nitride semiconductor laser elements other than nitride semiconductor laser element 1200 according to the present embodiment. An application example of adhesion layer 1231 will be described below with reference to FIG. 78 . FIG. 78 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser element 1200a according to an application example of adhesion layer 1231. As with FIG. 2 , FIG. 78 shows only a portion of nitride semiconductor laser element 1200a, including ridge 110R, in a cross section perpendicular to the main emission direction (Y-axis direction) of light (laser light).

[0240] 78 , nitride semiconductor laser device 1200a according to this application example differs from nitride semiconductor laser device 100 according to the first embodiment in that it includes metal electrode 1214 instead of metal electrode 114 and in that it includes adhesion layer 1231 disposed between conductive oxide film 113 and metal electrode 1214, but is the same in other respects. That is, nitride semiconductor laser device 1200a according to this application example includes n-type cladding layer 102, active layer 105 disposed above n-type cladding layer 102, p-type cladding layer 110 disposed above active layer 105 and having ridge 110R formed thereon, and conductive oxide film 113 disposed above p-type cladding layer 110 and transparent to light having the oscillation wavelength of nitride semiconductor laser device 1200a. The nitride semiconductor laser device 1200a according to this application example further includes a metal electrode 1214 that is disposed above the conductive oxide film 113 and contains a metal that has high reflectivity for light of the oscillation wavelength, and an adhesion layer 1231 that is disposed between the conductive oxide film 113 and the metal electrode 1214. The adhesion layer 1231 has a higher ionization tendency than the metal electrode 1214.

[0241] 78 , the adhesion layer 1231 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side portion 112s of the current blocking layer 112 that faces the side surface 113s of the conductive oxide film 113. In other words, the adhesion layer 1231 continuously covers the upper surface 113u of the conductive oxide film 113 and at least a portion of the side portion 112s. As shown in FIG. 78 , the adhesion layer 1231 may continuously cover the side portion 112s of the current blocking layer 112 and at least a portion of the bottom portion 112b disposed in the groove 110T. Note that the adhesion layer 1231 may cover the entire upper surface of the semiconductor stack 100S.

[0242] As shown in FIG. 78 , the metal electrode 1214 is disposed on the adhesion layer 1231. Like the adhesion layer 1231, the metal electrode 1214 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side portion 112s of the current blocking layer 112 that faces the side surface 113s of the conductive oxide film 113. In other words, the metal electrode 1214 continuously covers the upper surface 113u of the conductive oxide film 113 and at least a portion of the side portion 112s. As shown in FIG. 78 , the metal electrode 1214 may continuously cover the side portion 112s of the current blocking layer 112 and at least a portion of the bottom portion 112b disposed in the groove 110T. Note that the metal electrode 1214 may cover the entire upper surface of the semiconductor stack 100S.

[0243] The metal electrode 1214 included in the nitride semiconductor laser device 1200a according to this application example is made of, for example, Pd. The metal electrode 1214 made of Pd has a lower ionization tendency than the metal electrode 114 made of Ag, and therefore has poorer adhesion to the conductive oxide film 113 than the metal electrode 114 made of Ag. Therefore, by disposing an adhesion layer 1231 having a higher ionization tendency than the metal electrode 1214 between the conductive oxide film 113 and the metal electrode 1214, it is possible to increase the adhesion between the conductive oxide film 113 and the adhesion layer 1231 and between the conductive oxide film 113 and the metal electrode 1214. This makes it possible to suppress peeling of the metal electrode 1214.

[0244] When the metal electrode 1214 is made of Pd, the adhesion layer 1231 may be made of, for example, Ni, Ti, Al, Zn, Ga, In, or Sn. A part of the adhesion layer 1231 made of Ni, Ti, Al, Zn, Ga, In, Sn, or the like bonds with oxygen contained in the conductive oxide film 113 to form a light-transmitting oxide, thereby suppressing loss in the adhesion layer 1231. Therefore, the nitride semiconductor laser device 1200a according to this application example can achieve high efficiency.

[0245] Such metal electrode 1214 can also reflect the spontaneously emitted light with high reflectivity, thereby providing the effect of feeding back the spontaneously emitted light to active layer 105. Accordingly, the oscillation threshold value of nitride semiconductor laser device 1200a can be reduced.

[0246] Furthermore, in the nitride semiconductor laser device 1200a according to this application example, similar to the structural example shown in FIG. 43 , the conductive oxide film 113 may have a concave side surface 113s. The metal electrode 1214 may have a side portion 1214s disposed at a position facing the concave side surface 113s. The surface of the side portion 1214s of the metal electrode 1214 facing the conductive oxide film 113 has a convex region facing the conductive oxide film 113. Such a side portion 1214s functions as a convex reflection surface along the side surface 113s for the spontaneously emitted light. Therefore, the spontaneously emitted light is fed back almost uniformly over a wide range of the active layer 105. This makes it possible to uniformize the gain of the laser light in the active layer 105, thereby preventing the gain of a specific higher-order transverse mode from being selectively increased. This prevents amplification of the higher-order transverse mode, thereby preventing degradation of the linearity of the IL characteristics of the nitride semiconductor laser device 1200a. In this way, nitride semiconductor laser device 1200a including conductive oxide film 113 having concave side surfaces 113s can stabilize the optical output.

[0247] Furthermore, the metal electrode 1214 made of Pd has the function of absorbing hydrogen atoms (H) contained in the contact layer 111. This increases the activation rate of the impurity (Mg) in the contact layer 111. Therefore, the electrical resistance in the contact layer 111 can be reduced.

[0248] Thirteenth Embodiment A nitride semiconductor laser device according to thirteenth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment in that it includes a hydrogen absorption layer disposed between conductive oxide film 113 and metal electrode 114, but is the same in other respects. The nitride semiconductor laser device according to this embodiment will be described below with reference to FIG. 79 , focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment. FIG. 79 is a schematic cross-sectional view showing the overall configuration of nitride semiconductor laser device 1300 according to this embodiment. Like FIG. 2 , FIG. 79 shows a cross section perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 1300.

[0249] As shown in FIG. 79 , the nitride semiconductor laser element 1300 according to this embodiment includes a semiconductor stack 100S, a current blocking layer 112, a conductive oxide film 113, a hydrogen absorbing layer 1332, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117.

[0250] The hydrogen absorption layer 1332 is a metal layer disposed between the conductive oxide film 113 and the metal electrode 114. The hydrogen absorption layer 1332 has a function of absorbing hydrogen atoms. The material constituting the hydrogen absorption layer 1332 is not particularly limited as long as it has a function of absorbing hydrogen atoms. In this embodiment, the hydrogen absorption layer 1332 is made of Pd and has an average film thickness of 0.3 nm or more and 5 nm or less. Here, if the average film thickness of the hydrogen absorption layer 1332 is 0.3 nm or more and 1 nm or less, it may not be possible to form the hydrogen absorption layer 1332 with a uniform film thickness, as with the adhesion layer 1231 in embodiment 12. If the film thickness of the hydrogen absorption layer 1332 is 0.3 nm or more and 1 nm or less and the film thickness of the adhesion layer 1231 is non-uniform, the average film thickness of the hydrogen absorption layer 1332 is defined as the average film thickness value at each position on the hydrogen absorption layer 1332.

[0251] By providing the hydrogen absorption layer 1332, the nitride semiconductor laser device 1300 can absorb hydrogen atoms contained in the contact layer 111. This can increase the activation rate of the impurity (Mg) in the contact layer 111. Therefore, the electrical resistance in the contact layer 111 can be reduced.

[0252] Next, the influence of the hydrogen absorption layer 1332 on the effect of increasing the amount of spontaneously emitted light feedback by the metal electrode 114 will be described with reference to FIGS. 80 and 81 . FIG. 80 is a graph showing the relationship between the film thickness (Pd film thickness) of the hydrogen absorption layer 1332 made of Pd and the reflectance of the stacked film made of the conductive oxide film 113, the hydrogen absorption layer 1332, and the metal electrode 114 to the nitride semiconductor layer. FIG. 80 shows the reflectance for light with wavelengths of 425 nm, 450 nm, and 550 nm. FIG. 81 is a diagram for explaining the reflectance shown in FIG. 80 .

[0253] The reflectance shown in FIG. 80 will be explained using FIG. 81 . As shown in FIG. 81 , in a laminate in which a 200-nm-thick ITO layer, a Pd layer, and a 200-nm-thick Ag layer are sequentially stacked on a GaN layer, the reflectance Pr / Pi is defined using the power Pi of light incident from the GaN layer to the ITO layer and the power Pr of reflected light propagating from the ITO layer toward the GaN layer. Here, the angle of incidence of light from the GaN layer to the ITO layer is perpendicular to the interface between the GaN layer and the ITO layer. In other words, the direction of incidence of light is the normal direction to the interface between the GaN layer and the ITO layer. Furthermore, the power Pr of reflected light propagating from the ITO layer toward the GaN layer is calculated taking into account multiple reflections within the multiple layers consisting of the ITO layer, the Pd layer, and the Ag layer.

[0254] 80 , if the film thickness of the hydrogen absorption layer 1332 is 5 nm or less, the reflectance of the conductive oxide film 113, the hydrogen absorption layer 1332, and the metal electrode 114 for light having a wavelength of 425 nm or more and 550 nm or less can be made 55% or more, and the reflectance can be increased compared to when a single layer film made of Pd is used instead of the hydrogen absorption layer 1332 and the metal electrode 114. Therefore, in this embodiment, the amount of feedback of spontaneously emitted light can be increased. Accordingly, the oscillation threshold value of the nitride semiconductor laser device 1300 can be reduced.

[0255] As described above, by disposing the hydrogen absorption layer 1332 between the conductive oxide film 113 and the metal electrode 114, it is possible to reduce the electrical resistance in the contact layer 111 while ensuring the effect of increasing the amount of feedback of spontaneous emission light and the associated effect of reducing the oscillation threshold.

[0256] Furthermore, the structure of nitride semiconductor laser device 1300 according to the present embodiment is not limited to the structure shown in Fig. 79. Another structural example of nitride semiconductor laser device 1300 according to the present embodiment will be described below with reference to Fig. 82. Fig. 82 is a schematic cross-sectional view showing another structural example of nitride semiconductor laser device 1300 according to the present embodiment. Fig. 82 shows only a portion of nitride semiconductor laser device 1300, including ridge 110R, in a cross section perpendicular to the main emission direction (Y-axis direction) of light (laser light).

[0257] 82 , in this structural example of the nitride semiconductor laser device 1300, the hydrogen absorption layer 1332 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side portion 112s of the current blocking layer 112 that faces the side surface 113s of the conductive oxide film 113. In other words, the hydrogen absorption layer 1332 continuously covers the upper surface 113u of the conductive oxide film 113 and at least a portion of the side portion 112s. As shown in FIG. 82 , the hydrogen absorption layer 1332 may continuously cover the side portion 112s of the current blocking layer 112 and at least a portion of the bottom portion 112b disposed in the groove 110T. Note that the hydrogen absorption layer 1332 may cover the entire upper surface of the semiconductor stack 100S.

[0258] As shown in FIG. 82 , the metal electrode 114 is disposed on the hydrogen absorption layer 1332. Similar to the hydrogen absorption layer 1332, the metal electrode 114 continuously covers the upper surface 110Ru of the ridge 110R and at least a portion of the side portion 112s of the current blocking layer 112 that faces the side surface 113s of the conductive oxide film 113. In other words, the metal electrode 114 continuously covers the upper surface 113u of the conductive oxide film 113 and at least a portion of the side portion 112s. As shown in FIG. 82 , the metal electrode 114 may continuously cover the side portion 112s of the current blocking layer 112 and at least a portion of the bottom portion 112b disposed in the trench 110T. Note that the metal electrode 114 may cover the entire upper surface of the semiconductor stack 100S.

[0259] The hydrogen absorption layer 1332 and the metal electrode 114 having the above-described structure can also reflect the spontaneously emitted light with high reflectivity, thereby achieving the effect of feeding back the spontaneously emitted light to the active layer 105. Accordingly, the oscillation threshold value of the nitride semiconductor laser device 1300 can be reduced.

[0260] Furthermore, in the nitride semiconductor laser device 1300 according to this structural example, similar to the structural example shown in FIG. 43 , the conductive oxide film 113 may have a concave side surface 113s. The metal electrode 114 may have a side portion 114s disposed at a position facing the concave side surface 113s. The surface of the side portion 114s of the metal electrode 114 facing the conductive oxide film 113 has a convex region facing the conductive oxide film 113. Such a side portion 114s functions as a convex reflection surface along the side surface 113s for the spontaneously emitted light. Therefore, the spontaneously emitted light is fed back almost uniformly over a wide range of the active layer 105. This makes it possible to uniformize the gain of the laser light in the active layer 105, thereby preventing the gain of a specific higher-order transverse mode from being selectively increased. This prevents amplification of the higher-order transverse mode, thereby preventing degradation of the linearity of the IL characteristics of the nitride semiconductor laser device 1300. In this way, in nitride semiconductor laser device 1300 including conductive oxide film 113 having concave side surfaces 113s, the optical output can be stabilized.

[0261] Fourteenth Embodiment A nitride semiconductor laser device according to a fourteenth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment mainly in the configuration of the current blocking layer. The nitride semiconductor laser device according to this embodiment will be described below, focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment shown in FIG.

[0262] [14-1. Overall Configuration] The overall configuration of the nitride semiconductor laser element according to the present embodiment will be described with reference to FIGS. 83 to 85 . FIG. 83 is a schematic plan view showing the overall configuration of nitride semiconductor laser element 1400 according to the present embodiment. FIGS. 84 and 85 are schematic cross-sectional views showing the overall configuration of nitride semiconductor laser element 1400 according to the present embodiment. FIG. 84 shows a cross section taken along line 84-84 in FIG. 83 . FIG. 85 shows a cross section taken along line 85-85 in FIG. 83 . For simplification of the drawings, FIGS. 83 to 85 omit illustration of substrate 101, barrier electrode 115, cover electrode 116, and n-side electrode 117 of nitride semiconductor laser element 1400, as in FIG. 44 and the like.

[0263] As shown in FIGS. 84 and 85 , the nitride semiconductor laser device 1400 according to this embodiment includes an n-type cladding layer 102, an n-side guide layer 104, an active layer 105, a p-side guide layer 106, an intermediate layer 108, an electron barrier layer 109, a p-type cladding layer 110, a contact layer 111, a current blocking layer 1412, a conductive oxide film 113, and a metal electrode 114.

[0264] The current blocking layer 1412 according to this embodiment is disposed above the p-type cladding layer 110 and is an electrically insulating layer that is transparent to light from the active layer 105. The current blocking layer 1412 covers the side surface of the ridge 110R. The current blocking layer 1412 has a side portion 1412s that faces the side surface 113s of the conductive oxide film 113.

[0265] The current blocking layer 1412 according to this embodiment has a plurality of openings 1412a located above the upper surface 110Ru of the ridge 110R. In this embodiment, the current blocking layer 1412 covers the region located above the upper surface 110Ru except for the plurality of openings 1412a. The plurality of openings 1412a are arranged in the resonance direction (i.e., the Y-axis direction) of the laser light emitted by the nitride semiconductor laser element. The current blocking layer 1412 is disposed in the region between two adjacent openings 1412a. The current blocking layer 1412 is made of, for example, SiO ２ The region of the current blocking layer 1412 other than the plurality of openings 1412a may include, for example, a 230 nm thick SiO ２ It may be a layer.

[0266] In this embodiment, the ridge width W (the width of the lower end of the ridge 110R, in other words, the maximum width of the ridge 110R) is 50 μm, and the shape of each of the multiple openings 1412a in a plan view (see FIG. 83) is a square with a side length of 20 μm. Note that the shape of each of the multiple openings 1412a is not limited to this. The shape of each of the multiple openings 1412a in a plan view may be rectangular, circular, elliptical, polygonal, or the like. Furthermore, in the example shown in FIG. 83, the multiple openings 1412a are arranged in a line in the resonance direction, but the arrangement of the multiple openings 1412a is not limited to this. The multiple openings 1412a may be arranged in multiple lines or in a staggered arrangement.

[0267] 84 , metal electrode 114 is electrically connected to conductive oxide film 113 through a plurality of openings 1412 a. Note that, similar to nitride semiconductor laser device 1200 according to embodiment 12, nitride semiconductor laser device 1400 according to this embodiment may have adhesion layer 1231 disposed between metal electrode 114 and conductive oxide film 113. In this case, metal electrode 114 is electrically connected to conductive oxide film 113 through adhesion layer 1231. Adhesion layer 1231 may also be disposed between current blocking layer 1412 and metal electrode 114. As adhesion layer 1231, for example, Al with a film thickness of 1 nm may be used.

[0268] [14-2. Effects] The effects of nitride semiconductor laser device 1400 according to this embodiment will be described.

[0269] As described above, the current blocking layer 1412 according to this embodiment is made of SiO ２85 ) and has a plurality of openings 1412a located above the top surface 110Ru of the ridge 110R. That is, compared to the nitride semiconductor laser device 100 according to the first embodiment, the nitride semiconductor laser device 1400 according to this embodiment has a larger area in which the current blocking layer 1412 is located above the top surface 110Ru. Thus, the current blocking layer 1412 located above the top surface 110Ru can increase the amount of feedback to the active layer 105 of spontaneously emitted light (see the dashed arrows in FIG. 85 ) propagating from the active layer 105 toward the top surface 110Ru. Furthermore, as shown in FIG. 85 , when the conductive oxide film 113 has inclined side surfaces 113s, the reflectance near the side surfaces 113s can be increased. Furthermore, since the current blocking layer 1412 has a plurality of openings 1412a, current can be sufficiently diffused within the ridge 110R from the plurality of openings 1412a via the conductive oxide film 113. Therefore, an increase in the operating voltage of nitride semiconductor laser device 1400 can be suppressed.

[0270] This effect will be described with reference to Figs. 86 to 89. Fig. 86 is a schematic diagram showing the configuration of an experimental stack used in an experiment for evaluating nitride semiconductor laser device 1400 according to this embodiment. Fig. 87 is a graph showing the relationship between the angle of incidence of light on the experimental stack and the reflectance. Fig. 87 shows the relationship between the angle of incidence of light on the experimental stack and the reflectance. ２ When the thickness t of the layer is 0 (i.e., when the experimental laminate does not contain SiO ２ The reflectivity of the SiO layer (without the SiO layer) is shown by the dashed line. ２ The reflectance when the layer thickness t is 230 nm is shown by the solid line. ２ 89 is a graph showing the relationship between the layer thickness t and the average reflectance of the SiO ２ FIG. 10 is a diagram showing the relationship between layer thickness t and average reflectance.

[0271] In order to evaluate the effect of nitride semiconductor laser device 1400 according to this embodiment, an experimental stack as shown in Fig. 86 was prepared. The experimental stack is a stack that simulates contact layer 111 and the structure above it of nitride semiconductor laser device 1400 according to this embodiment. The experimental stack consists of a GaN layer with a thickness of 800 nm, an ITO layer with a thickness of 200 nm disposed on the GaN layer, and an SiO ２ layer and the SiO ２ The experimental stack had a GaN layer, an ITO layer, and a SiO layer, and an Al layer with a thickness of 1 nm disposed on the GaN layer, an Ag layer with a thickness of 100 nm disposed on the Al layer. ２ The Al layer, the Al layer, and the Ag layer are layers that respectively imitate the contact layer 111, the conductive oxide film 113, the current blocking layer 1412, the adhesion layer 1231, and the metal electrode 114 of the nitride semiconductor laser device 1400 according to this embodiment.

[0272] The reflectance (Pr / Pi) of the experimental laminate was measured by irradiating light of power Pi having a wavelength of 450 nm onto the lower surface (lower surface of the GaN layer) of the experimental laminate at an incident angle θi and measuring the power Pr of the reflected light reflected at an exit angle θr. ２ The reflectance was measured under each condition while changing the layer thickness t from 0 nm to 280 nm. Figures 88 and 89 show the average reflectance, which is the average of the reflectance corresponding to each case where the incident angle θi is from 0° to 90°.

[0273] As shown in FIG. 87, the experimental laminate was made of SiO 3 simulating the current blocking layer 1412. ２ Compared to the case without a layer (thickness t = 0 nm), the experimental stack had a 230 nm thick SiO ２ The experimental stack had a 230 nm thick SiO ２ When the layer is provided, the reflectance is particularly high when the incident angle θi is in the range of 0° to 25° and in the range of 30° to 50°.

[0274] 88 and 89, when the film thickness t is 150 nm or more (280 nm or less), the average reflectance is higher than when the film thickness t is 0 nm. The average reflectance is maximum when the film thickness t is 230 nm.

[0275] As described above, the experimental laminate was formed by using SiO ２ By providing the layer, the reflectivity of the experimental stack can be increased. Therefore, by disposing the current blocking layer 1412 between the conductive oxide film 113 and the metal electrode 114 above the upper surface 110Ru of the ridge 110R, the amount of feedback of spontaneously emitted light from above the upper surface 110Ru can be increased. As a result, the quantum efficiency of the nitride semiconductor laser device 1400 can be increased. By increasing the quantum efficiency, it is possible to reduce the oscillation threshold of the nitride semiconductor laser device 1400 and improve the slope efficiency. In this way, the nitride semiconductor laser device 1400 according to this embodiment can achieve high efficiency.

[0276] The current blocking layer 1412 disposed above the upper surface 110Ru may have a thickness of 150 nm or more. This makes it possible to more reliably increase the average reflectance, as shown in FIGS. 88 and 89 . The current blocking layer 1412 disposed above the upper surface 110Ru may have a thickness t of 280 nm or less. This makes it possible to more reliably increase the average reflectance. The current blocking layer 1412 disposed above the upper surface 110Ru may have a thickness t of 200 nm or more and 250 nm or less. This makes it possible to further increase the average reflectance.

[0277] [14-3. Other Configuration Examples of Current Blocking Layer] Other configuration examples of the current blocking layer 1412 according to this embodiment will be described.

[0278] The current blocking layer 1412 may be, for example, a DBR (Distributed Bragg Reflector) layer. Specifically, the current blocking layer 1412 has one or more first layers made of an electrically insulating material having optical transparency, and one or more second layers made of an electrically insulating material having optical transparency different from the one or more first layers, and the one or more first layers and the one or more second layers may be alternately stacked. The one or more first layers and the one or more second layers have mutually different refractive indices. The refractive index of the first layer may be set to n １ and the refractive index of the second layer is n ２ For example, the thickness of the first layer is 1 / (4n １ ) times the oscillation wavelength λ, and the thickness of the second layer is 1 / (4n ２ ) times the oscillation wavelength λ. ｓ ) times the SiO ２ As the second layer, for example, a layer having a film thickness of 1 / (4n) of the oscillation wavelength λ can be used. ｔ ) times Ta ２ O ５ layers can be used, where n ｓ is SiO ２ represents the refractive index of ｔ Is Ta ２ O ５ The electrically insulating material constituting the first layer is, for example, Ga ２ O ３ , MgF ２ , Al ２ O ３ The electrically insulating material constituting the second layer may be, for example, TiO ２ , Nb ２ O ５ , ZrO ２ , AlN, SiN, AlON, etc.

[0279] The effects of this configuration example will be described using FIGS. 90 to 93. FIG. 90 is a schematic diagram showing the configuration of an experimental stack used in an experiment to evaluate this configuration example. FIG. 91 is a graph showing the relationship between the angle of incidence of light on the experimental stack and reflectance. In FIG. 91, the reflectance when the experimental stack does not include a DBR layer is shown by a dashed line, and the reflectance when the experimental stack includes a DBR layer is shown by a solid line. FIG. 92 is a graph showing the relationship between the number of DBR pairs in the experimental stack and the average reflectance. FIG. 93 is a diagram showing the relationship between the DBR configuration (number of DBR pairs) and the average reflectance in the experimental stack.

[0280] In order to evaluate the effect of this configuration example, an experimental stack as shown in FIG. 90 was prepared. The experimental stack is a stack that simulates the contact layer 111 and the structure above it of the nitride semiconductor laser device 1400 according to this embodiment. The experimental stack comprises a GaN layer with a thickness of 800 nm, an ITO layer with a thickness of 200 nm disposed on the GaN layer, and a DBR layer (with a thickness λ / (4n s ) SiO ２ Each of the layers and one or more film thicknesses λ / (4n t ) Ta ２ O ５ The experimental stack included a GaN layer, an ITO layer, a DBR layer, an Al layer having a thickness of 1 nm, and an Ag layer having a thickness of 100 nm, which were arranged on the Al layer. The GaN layer, the ITO layer, the DBR layer, the Al layer, and the Ag layer of the experimental stack were layers that resembled contact layer 111, conductive oxide film 113, current blocking layer 1412, adhesion layer 1231, and metal electrode 114, respectively, of nitride semiconductor laser device 1400 according to the present embodiment.

[0281] The reflectance (Pr / Pi) of the experimental laminate was measured by irradiating light of power Pi having a wavelength of 450 nm onto the lower surface (lower surface of the GaN layer) of the experimental laminate at an incident angle θi and measuring the power Pr of the reflected light reflected at an exit angle θr. Here, the incident angle θi was changed from 0° to 90°, and the number of pairs of the DBR layer was changed to 0, 1, 3, 5, and 10 pairs, and the reflectance was measured under each condition. Here, the state in which the number of pairs is n pairs means that when n≧1, one Ta layer is used.２ O ５ On top of the layer, SiO ２ Layer and Ta ２ O ５ 92 and 93 show the average reflectance, which is the average of the reflectance corresponding to each case where the incident angle θi is from 0° to 90°.

[0282] The solid curve in Fig. 91 shows the reflectivity when the number of pairs of DBR layers in the experimental stack is 10. As shown in Fig. 91, the experimental stack having the DBR layer has a higher reflectivity in the range of incident angle θi from 0° to 15° and from 40° to 50° compared to the experimental stack not having the DBR layer simulating current blocking layer 1412.

[0283] 92 and 93, when the number of pairs of DBR layers in the experimental stack is 1 or more, the average reflectance is higher than when there is no DBR layer. When the number of pairs of DBR layers is 5 or more, the average reflectance is even higher.

[0284] As described above, the experimental stack has a DBR layer, which can increase the reflectivity of the experimental stack. Therefore, by disposing the current blocking layer 1412 made of a DBR layer between the conductive oxide film 113 and the metal electrode 114 above the upper surface 110Ru of the ridge 110R, the amount of feedback of spontaneously emitted light from above the upper surface 110Ru can be increased. As a result, the quantum efficiency of the nitride semiconductor laser device 1400 can be increased. The increased quantum efficiency can reduce the oscillation threshold of the nitride semiconductor laser device 1400 and improve the slope efficiency. Thus, the nitride semiconductor laser device 1400 according to this embodiment can achieve high efficiency.

[0285] Furthermore, a current blocking layer 1412 is formed of SiO ２ The current blocking layer 1412 may be, for example, a SiO 2 layer having a thickness of 150 nm or more. ２ layer and the SiO ２The DBR layer may have one or more pairs of a first layer and a second layer, similar to the above-described DBR layer. ２ The layer has a thickness of 1 / (4n s ) times larger than the SiO ２ Since the reflectance of the SiO 2 layer and the DBR layer differs in dependence on the incident angle, this configuration ２ The layer and the DBR layer complement each other to improve the reflectivity, and the average reflectivity can be further improved, thereby further increasing the amount of feedback of spontaneously emitted light.

[0286] Fifteenth Embodiment A nitride semiconductor laser device according to a fifteenth embodiment will be described. The nitride semiconductor laser device according to this embodiment differs from nitride semiconductor laser device 100 according to the first embodiment mainly in the configuration of the active layer. The nitride semiconductor laser device according to this embodiment will be described below, focusing on the differences from nitride semiconductor laser device 100 according to the first embodiment.

[0287] [15-1. Overall Configuration] The overall configuration of nitride semiconductor laser device 1500 according to the present embodiment will be described with reference to FIGS. 94 and 95 . FIG. 94 is a schematic cross-sectional view showing the overall configuration of nitride semiconductor laser device 1500 according to the present embodiment. FIG. 95 is a schematic cross-sectional view showing the configuration of active layer 1505 included in nitride semiconductor laser device 1500 according to the present embodiment. FIG. 95 shows an enlarged view of only the cross-section of active layer 1505 out of the cross-section shown in FIG. 94 . Like FIG. 2 , FIGS. 94 and 95 show cross-sections perpendicular to the main emission direction (Y-axis direction) of light (laser light) from nitride semiconductor laser device 1500.

[0288] As shown in FIG. 94, the nitride semiconductor laser element 1500 according to this embodiment includes a semiconductor stack 1500S, a current blocking layer 112, a conductive oxide film 113, a metal electrode 114, a barrier electrode 115, a cover electrode 116, and an n-side electrode 117.

[0289] The semiconductor laminate 1500S has a substrate 101, an n-type cladding layer 1502, an n-side guide layer 1504, an active layer 1505, a p-side guide layer 1506, an intermediate layer 1508, an electron barrier layer 1509, a p-type cladding layer 1510, and a contact layer 1511.

[0290] The n-type cladding layer 1502 may include a first n-type cladding layer 1502 a and a second n-type cladding layer 1502 b disposed above the first n-type cladding layer 1502 a. The n-side guiding layer 1504 may include a first n-side guiding layer 1504 a and a second n-side guiding layer 1504 b disposed above the first n-side guiding layer 1504 a.

[0291] As shown in FIG. 95 , the active layer 1505 includes 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 an example of a first barrier layer. The barrier layer 105c is an example of a second barrier layer disposed above the well layer 1505b. The well layer 1505b includes a region in which the bandgap energy increases with increasing distance from the barrier layer 1505a. In this region of the well layer 1505b, the bandgap energy may increase continuously or stepwise with increasing distance from the barrier layer 1505a.

[0292] The detailed configuration of each layer of the semiconductor laminate 1500S according to this embodiment will be described later.

[0293] The semiconductor stack 1500S according to this embodiment may not include at least one of the guide layers, the intermediate layer 1508, and the other layers shown in Fig. 94. Furthermore, the p-type cladding layer 1510 may include a first p-type cladding layer 1510a and a second p-type cladding layer 1510b disposed above the first p-type cladding layer 1510a, as shown in Fig. 96, which will be described later.

[0294] [15-2. Structural Example 1] Structural Example 1 of nitride semiconductor laser device 1500 according to the present embodiment will be described with reference to FIG. 96. FIG. 96 is a diagram showing the configuration of each layer included in Structural Example 1 of nitride semiconductor laser device 1500 according to the present embodiment. Structural Example 1 of nitride semiconductor laser device 1500 emits laser light in the ultraviolet range. Specifically, Structural Example 1 of nitride semiconductor laser device 1500 emits laser light in the 375 nm band.

[0295] As shown in FIG. 96, the well layer 1505b according to Configuration Example 1 is an In layer having a thickness of 17.5 nm. Ｘｗｉ Ga １－Ｘｗｉ The In composition ratio Xwi of the well layer 1505b is an N layer (0≦Xwi≦0.01), and the In composition ratio Xwi of the well layer 1505b decreases continuously with increasing distance from the barrier layer 1505a. Accordingly, the band gap energy of the well layer 1505b increases continuously with increasing distance from the barrier layer 1505a.

[0296] [15-3. Effects of Configuration Example 1] The effects of Configuration Example 1 of the nitride semiconductor laser device 1500 will be described in comparison with Comparative Example A (and Comparative Example B, which will be described later). The nitride semiconductor laser device of Comparative Example A has an In ０．０１ Ga ０．９９ Comparative Example A is a structural example of nitride semiconductor laser device 100 according to the first embodiment, and differs from Structural Example 1 in that it has well layer 9505b, which is an N layer, but is the same in other respects.

[0297] In nitride semiconductor laser devices that emit laser light in the ultraviolet range, such as those in Configuration Example 1 and Comparative Example A, a cladding layer having a high Al composition ratio is essential. This increases tensile strain in the semiconductor laminate, which makes it easy for cracks to occur in the wafer that is the base material of the substrate 101 during the manufacture of the nitride semiconductor laser device. To prevent cracks in the wafer, it is necessary to make the Al composition ratio of the n-type cladding layer as small as possible while also making the film thickness thin.

[0298] As described above, since the Al composition ratio of the cladding layers of a nitride semiconductor laser device that emits laser light in the ultraviolet region cannot be increased, it is difficult to sufficiently increase the optical confinement coefficient in the well layer, which increases the oscillation threshold carrier density.

[0299] The problems that arise when the carrier density in the well layer 9505b of Comparative Example A increases will be described using FIGS. 97 to 100. FIGS. 97 and 98 are graphs showing the wave functions of ground-level electrons and heavy holes (HH), respectively, in the well layer 9505b of Comparative Example A when the carrier density is low. FIGS. 99 and 100 are graphs showing the wave functions of electrons and HH, respectively, in the well layer 9505b of Comparative Example A when the carrier density is high. In FIGS. 97 and 99, the potential distribution of the conduction band of the well layer 9505b is shown by a dashed line, and the ground-state level of electrons is shown by a dotted line. In FIGS. 98 and 100, the potential distribution of the valence band of the well layer 9505b is shown by a dashed line, and the ground-state level of HH is shown by a dotted line. 97 to 100, the vertical axis on the left side represents the potential, and the vertical axis on the right side represents the amplitude of the wave function.

[0300] In general, in a semiconductor laser device, electrons and holes are injected into a well layer in an active layer and emit light through radiative recombination. Electrons are injected into the well layer from the n-type layer side, and holes are injected from the p-type layer side. Here, quantum levels of electrons are formed in the conduction band of the well layer due to the quantum effect. Holes include heavy holes (HH) with large effective masses and light holes (LH) with small effective masses, so HH and LH quantum levels are formed in the valence band. Various quantum levels are formed, ranging from the ground state energy level to possible higher energy levels, depending on the band structure formed by the well layer and barrier layer.

[0301] Depending on the Fermi energies of electrons and holes relative to the operating current value of the semiconductor laser element, electrons, HH, and LH are dispersed and present at each energy level.

[0302] Among the quantum levels, a high proportion of electrons exist in the ground level, which has the lowest quantization energy and is closest to the conduction band, and a high proportion of holes exist in the ground level, HH, which has the lowest quantization energy and is closest to the valence band.

[0303] 97 and 98 , in Comparative Example A, when the amount of current injected into the active layer is small, i.e., when the carrier density is low, the piezoelectric field of the well layer 9505b causes a gradient in the potential of the conduction band and the valence band of the well layer 9505b. Along with this gradient in potential, the amplitude of the electron wave function becomes larger near the end of the well layer 9505b closer to the barrier layer 1505c, and the amplitude of the heavy hole wave function becomes larger near the end of the well layer 9505b closer to the barrier layer 1505a. Thus, when the carrier density is low, the position where the amplitude of the electron wave function is maximized and the position where the amplitude of the heavy hole wave function is maximized are relatively far apart. That is, the correlation coefficient between the electron wave function and the heavy hole wave function is small.

[0304] Here, if the position in the stacking direction is represented by the value of the z-axis parallel to the stacking direction, the wave function of the electron ground level is represented by φe(z), and the wave function of the heavy hole ground level is represented by φh(z), the correlation coefficient is given by the magnitude of the correlation between the wave functions of the electron and heavy hole ground levels, as expressed by the following equation (1):

[0305] |∫φe(z)φh * (z)dz| (1)

[0306] where |∫φe(z)φe * (z)dz|=1, |∫φh(z)φh * φe(z) and φh(z) are normalized so that (z)dz|=1.

[0307] 99 and 100, in Comparative Example A, when the amount of current injected into the active layer is large, that is, when the carrier density is high, the piezoelectric field of the well layer 9505b is screened by the electrons and heavy holes in the well layer 9505b. In other words, when the carrier density increases, the electrons and heavy holes are distributed so as to cancel out the electric field due to the piezoelectric polarization charges, and the potential gradient in the well layer 9505b becomes smaller.

[0308] In this case, what acts most to cancel out the influence of the piezoelectric field generated in the well layer 9505b is the distribution of ground-level electrons in the conduction band, which is closest to the conduction field potential and most susceptible to the influence of the conduction field potential gradient, and in the valence band, it is the distribution of ground-level HHs, which is closest to the valence field potential and most susceptible to the influence of the valence field potential gradient.

[0309] Here, the distribution shapes of the ground level electrons and HH can be expressed by the distribution shapes of the ground level electron wave function and the HH wave function. Therefore, the degree of screening of the piezoelectric effect can be estimated by the correlation coefficient of the ground level wave functions of the electrons and HH.

[0310] When the degree of screening of the piezoelectric effect is large and the potential gradient of the conduction band and valence band of the well layer 9505b is small, the correlation coefficient of the wave functions of the electrons and the ground level of HH becomes large.

[0311] Therefore, in the present disclosure, the degree of screening of the piezoelectric effect is expressed by the correlation coefficient between the ground level wave function of the electron and the ground level wave function of HH in the hole.

[0312] As the correlation coefficient increases, the spontaneous emission rate in the well layer 9505b increases, shortening the radiative recombination time of electrons and heavy holes in the ground-level wave functions of electrons and HH. As a result, the carrier density required for laser oscillation increases, and the oscillation threshold increases. The increase in the oscillation threshold increases the effect of leakage current, lowering the thermal saturation level in the current-light output characteristics. The correlation coefficient increases with an increase in the amount of current injection, and the oscillation threshold also tends to increase accordingly.

[0313] In contrast, in Configuration Example 1, the bandgap energy of the well layer 1505b continuously increases with increasing distance from the barrier layer 1505a, thereby suppressing increases in the correlation coefficient and oscillation threshold. This effect will be described with reference to FIGS. 101 to 108 in comparison with Comparative Example B. FIGS. 101 and 102 are graphs showing the distribution of bandgap energy with respect to the stacking direction position of each well layer in Configuration Example 1 and Comparative Example B, respectively. FIGS. 101 and 102 also show the distribution of bandgap energy of a portion of each barrier layer. FIGS. 103 and 104 are graphs showing the wave functions of ground-level electrons and HH in the well layer 1505b of Configuration Example 1, respectively. FIGS. 105 and 106 are graphs showing the wave functions of ground-level electrons and HH in the well layer 9505b of Comparative Example B, respectively. In Figures 103 and 105, the distribution of the conduction band potential of each well layer is shown by a broken line, and the ground state level of electrons is shown by a dotted line. In Figures 104 and 106, the distribution of the valence band potential of each well layer is shown by a broken line, and the ground state level of HH is shown by a dotted line. In Figures 103 to 106, the surface current density of each nitride semiconductor laser element is 13,000 A / cm. ２ 103 to 106, the vertical axis on the left side represents potential, and the vertical axis on the right side represents the amplitude of the wave function. Fig. 107 is a graph showing the relationship between the surface current density and the correlation coefficient in each of the nitride semiconductor laser elements of Configuration Example 1 and Comparative Example B. Fig. 108 is a graph showing the relationship between the current and the correlation coefficient in each of the nitride semiconductor laser elements of Configuration Example 1 and Comparative Example B.

[0314] As described above, the well layer 1505b of the first configuration example is an In layer having a thickness of 17.5 nm. Ｘｗｉ Ga １－ＸｗｉThe In composition ratio Xwi of the well layer 1505b is an N layer (0≦Xwi≦0.01), and the In composition ratio Xwi of the well layer 1505b continuously decreases with increasing distance from the barrier layer 1505a. The band gap energy of such well layer 1505b increases with increasing distance from the barrier layer 1505a in the stacking direction, as shown in FIG.

[0315] On the other hand, Comparative Example B differs from Structural Example 1 in the configuration of the well layer 9505b, but the other configurations are the same. ０．００５ Ga ０．９９５ N layer. Comparative Example B of the nitride semiconductor laser element is one configuration example of the nitride semiconductor laser element 100 according to the first embodiment. The band gap energy of such well layer 9505b is constant with respect to the position in the stacking direction, as shown in FIG.

[0316] In Comparative Example B having such a well layer 9505b, when the carrier density is high, the piezoelectric effect is screened as shown in Figures 105 and 106. As a result, the peak of the wave function of electrons at the ground level and the peak of the wave function of HH at the ground level are closer to each other in the stacking direction, and the respective peaks become gentler.

[0317] In contrast, in Configuration Example 1 having the well layer 1505b, as shown in Figures 103 and 104, even when the carrier density is high (when the surface current density is large), the potentials of the conduction band and the valence band are inclined with respect to the stacking direction. As a result, as shown in Figure 104, the peak position of the ground level HH wave function is closer to the barrier layer 1505a and has a steeper peak than in Comparative Example B. Also, as shown in Figure 103, the peak position of the ground level electron wave function is farther from the barrier layer 1505a in the stacking direction than the peak position of the ground level HH wave function, and the ground level electron wave function has a steeper peak than in Comparative Example B.

[0318] 107 and 108 , in Configuration Example 1, when the injected surface current density and current are large, the correlation coefficient between the ground level wave functions of electrons and HH is smaller than that of Comparative Example B. Specifically, the correlation coefficient in Configuration Example 1 is maintained at 0.8 or less even when the injected surface current density and current are large. In the example shown in FIGS. 107 and 108 , the correlation coefficient is maintained at 0.7 or less. As a result, in Configuration Example 1, an increase in the oscillation threshold carrier density can be suppressed, and therefore an increase in the oscillation threshold and leakage current can be suppressed. Therefore, a nitride semiconductor laser device 1500 having excellent temperature characteristics and capable of high-output operation can be realized.

[0319] Furthermore, in Configuration Example 1, as in the above-described embodiments, the metal electrode 114 reflects spontaneously emitted light from the active layer 1505 and feeds it back to the active layer 1505, thereby reducing the oscillation threshold. This reduces the oscillation threshold carrier density in the well layer 1505b. Furthermore, by disposing the conductive oxide film 113, which has a low refractive index, above the p-type cladding layer 1510, the optical confinement factor in the active layer 1505 can be increased without increasing waveguide loss, thereby reducing the oscillation threshold and operating current value.

[0320] As a result, screening of the piezoelectric effect caused by carriers injected into the well layer 1505b is less likely to occur, and an increase in the correlation coefficient between the wave functions of electrons and HH can be further suppressed, thereby providing a semiconductor laser device with a small operating current and a high thermal saturation level.

[0321] [15-4. Structural Example 2 and Its Effects] Structural Example 2 of nitride semiconductor laser element 1500 according to the present embodiment and its effects will be described. First, the overall configuration of Structural Example 2 of nitride semiconductor laser element 1500 will be described with reference to FIG. 109. FIG. 109 is a diagram showing the configuration of each layer included in Structural Example 2 of nitride semiconductor laser element 1500 according to the present embodiment. Structural Example 2 of nitride semiconductor laser element 1500 emits laser light in the ultraviolet range. Specifically, Structural Example 2 of nitride semiconductor laser element 1500 emits laser light in the 365 nm band.

[0322] As shown in FIG. 109, the well layer 1505b according to Configuration Example 2 is made of an Al Ｘｗａ Ga １－Ｘｗａ The Al composition ratio X of the well layer 1505b increases continuously with increasing distance from the barrier layer 1505a, and the band gap energy of the well layer 1505b also increases continuously with increasing distance from the barrier layer 1505a.

[0323] The effects of nitride semiconductor laser device 1500 of Configuration Example 2 will be described with reference to Fig. 110 and Fig. 111 in comparison with Comparative Example C. Fig. 110 is a graph showing the relationship between the surface current density and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 2 and Comparative Example C. Fig. 111 is a graph showing the relationship between the current and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 2 and Comparative Example C.

[0324] The nitride semiconductor laser element of Comparative Example C has an Al ０．０１ Ga ０．９９ Comparative Example C differs from Configuration Example 2 in that it has well layer 9505b, which is an N layer, but is the same in other respects. Comparative Example C is a configuration example of nitride semiconductor laser device 100 according to embodiment 1. The bandgap energy of such well layer 9505b is constant with respect to the position in the stacking direction, similar to the bandgap energy of well layer 9505b of Comparative Example B shown in FIG.

[0325] In Comparative Example C having such a well layer 9505b, similar to Comparative Example B, when the carrier density is high, the piezoelectric effect is screened and the correlation coefficient becomes large as shown in FIGS.

[0326] In contrast, in Configuration Example 2 having well layer 1505b, an increase in the correlation coefficient associated with screening of the piezoelectric effect can be suppressed, similar to Configuration Example 1, even when the carrier density is high. Specifically, the correlation coefficient in Configuration Example 2 is maintained at 0.8 or less even when the injected surface current density and current are large. In the examples shown in FIGS. 110 and 111, the correlation coefficient is maintained at 0.5 or less. As a result, in Configuration Example 2, an increase in the oscillation threshold carrier density can be suppressed, and therefore an increase in the oscillation threshold and leakage current can be suppressed. Therefore, a nitride semiconductor laser device 1500 having excellent temperature characteristics and capable of high-output operation can be realized.

[0327] Furthermore, in Configuration Example 2, as in Configuration Example 1, the metal electrode 114 provides the effect of feeding back spontaneously emitted light to the active layer 1505, and the conductive oxide film 113, which has a low refractive index, provides the effect of increasing the optical confinement factor in the active layer 1505 without increasing waveguide loss. As a result, screening of the piezoelectric effect caused by carriers injected into the well layer 1505b is less likely to occur, and an increase in the correlation coefficient between the electron and HH wave functions can be further suppressed. Therefore, a semiconductor laser device with a small operating current and a high thermal saturation level can be obtained.

[0328] [15-5. Structural Example 3 and Its Effects] Structural Example 3 of nitride semiconductor laser device 1500 according to the present embodiment and its effects will be described. First, the overall configuration of Structural Example 3 of nitride semiconductor laser device 1500 will be described with reference to FIG. 112. FIG. 112 is a diagram showing the configuration of each layer included in Structural Example 3 of nitride semiconductor laser device 1500 according to the present embodiment. Structural Example 3 of nitride semiconductor laser device 1500 emits blue (or purple) laser light. Specifically, Structural Example 3 of nitride semiconductor laser device 1500 emits laser light in the 445 nm band.

[0329] As shown in FIG. 112, the well layer 1505b according to Configuration Example 3 is an In layer having a thickness of 4.5 nm. Ｘｗｉ Ga １－ＸｗｉThe In composition ratio Xwi of the well layer 1505b is an N layer (0.16≦Xwi≦0.2), and the In composition ratio Xwi of the well layer 1505b continuously decreases with increasing distance from the barrier layer 1505a. Accordingly, the band gap energy of the well layer 1505b continuously increases with increasing distance from the barrier layer 1505a.

[0330] The effects of nitride semiconductor laser device 1500 of Configuration Example 3 will be described with reference to Fig. 113 and Fig. 114 in comparison with Comparative Example D. Fig. 113 is a graph showing the relationship between the surface current density and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 3 and Comparative Example D. Fig. 114 is a graph showing the relationship between the current and the correlation coefficient in each of the nitride semiconductor laser devices of Configuration Example 3 and Comparative Example D.

[0331] The nitride semiconductor laser element of Comparative Example D has an In ０．１８ Ga ０．８２ Comparative Example D differs from Configuration Example 3 in that it has well layer 9505b, which is an N layer, but is the same in other respects. Comparative Example D is a configuration example of the nitride semiconductor laser device 100 according to the first embodiment. The bandgap energy of such well layer 9505b is constant with respect to the position in the stacking direction, similar to the bandgap energy of well layer 9505b of Comparative Example B shown in FIG.

[0332] In Comparative Example D having such a well layer 9505b, similarly to Comparative Example B, when the carrier density is high, the piezoelectric effect is screened and the correlation coefficient becomes large as shown in FIGS.

[0333] In contrast, in Configuration Example 3 having well layer 1505b, an increase in the correlation coefficient associated with screening of the piezoelectric effect can be suppressed, similar to Configuration Example 1, even when the carrier density is high. Specifically, the correlation coefficient in Configuration Example 3 is maintained at 0.8 or less even when the injected surface current density and current are large. In the examples shown in FIGS. 113 and 114, the correlation coefficient is maintained at 0.7 or less. As a result, in Configuration Example 3, an increase in the oscillation threshold carrier density can be suppressed, and therefore an increase in the oscillation threshold and leakage current can be suppressed. Therefore, a nitride semiconductor laser device 1500 having excellent temperature characteristics and capable of high-output operation can be realized.

[0334] Furthermore, in Configuration Example 3, as in Configuration Example 1, the metal electrode 114 provides the effect of feeding back spontaneously emitted light to the active layer 1505, and the conductive oxide film 113, which has a low refractive index, provides the effect of increasing the optical confinement factor in the active layer 1505 without increasing waveguide loss. As a result, screening of the piezoelectric effect caused by carriers injected into the well layer 1505b is less likely to occur, and an increase in the correlation coefficient between the electron and HH wave functions can be further suppressed. Therefore, a semiconductor laser device with a small operating current and a high thermal saturation level can be obtained.

[0335] Although the examples of Configuration Examples 1 to 3 show that the band gap energy of the well layer 1505b increases monotonically and continuously with increasing distance from the barrier layer 1505a, the well layer 1505b may include a region in which the band gap energy is constant in the stacking direction or a region in which the band gap energy increases discontinuously with increasing distance from the barrier layer 1505a. In the case of a discontinuous increase, if the discontinuously increasing energy is large, the electron wave function tends to bias toward a region of the well layer 1505b with small band gap energy close to the n-type layer. To suppress this bias of the electron wave function toward the region close to the n-type layer, the discontinuously increasing energy should be smaller than the difference between the band gap energy at the interface of the well layer 1505b on the p-type layer side and the band gap energy of the barrier layer 1505c on the p-type layer side.

[0336] (Modifications, etc.) Although the nitride 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.

[0337] For example, in each of the above embodiments, the nitride semiconductor laser element has a single ridge, but the nitride semiconductor laser element may have a plurality of ridges.

[0338] In addition, although the above-described embodiments have been described with reference to examples in which the metal electrode is made of Ag, an Ag alloy, Al, or Rh, the configuration of the metal electrode is not limited to the above examples, as long as it includes a metal having a higher reflectivity than Pd for light at the oscillation wavelength. For example, the metal electrode may include an Al layer and a Pd layer disposed above the Al layer. In this manner, the metal electrode may include a metal whose reflectivity for light at the oscillation wavelength is equal to or lower than that of Pd.

[0339] Furthermore, the nitride semiconductor laser elements according to the first to twelfth embodiments above include at least one of an underlayer, a buffer layer, an n-side guide layer, a p-side guide layer, an intermediate layer, an electron barrier layer, a current blocking layer, a barrier electrode, and a cover electrode, but do not necessarily need to include these components.

[0340] Although the p-type cladding layer has a uniform Al composition ratio, the configuration of each p-type cladding layer is not limited to this. For example, each p-type cladding layer may have a superlattice structure in which a plurality of AlGaN layers and a plurality of GaN layers are alternately stacked.

[0341] 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.

[0342] The nitride semiconductor laser device of the present disclosure can be applied to light sources for various applications, for example, as a high-output, highly efficient light source.

[0343] 100, 700, 800, 900, 1000, 1100, 1200, 1200a, 1300, 1400, 1500 Nitride semiconductor laser element 100F, 100R Facet 100S, 700S, 800S, 900S, 1000S, 1100S, 1500S Semiconductor laminate 101 Substrate 102, 702, 902, 1102, 1502 n-type cladding layer 102a, 702a, 902a, 1502a First n-type cladding layer 102b, 902b, 1502b Second n-type cladding layer 104, 204, 304, 404, 904, 1104, 1504 n-side guide layer 105, 305, 805, 905, 1105, 1505 Active layer 105a, 105c, 105e, 305a, 305c, 305e, 805a, 805c, 905a, 905c, 905e, 905g, 1105a, 1105c, 1505a, 1505c Barrier layer 105b, 105d, 805b, 905b, 905d, 905f, 1105b, 1505b, 9505b Well layer 106, 206, 306, 406, 506, 606, 906, 1506 P-side guide layer 108, 908, 1508 Intermediate layer 109, 1509 Electron barrier layer 110, 710, 910, 1010, 1110, 1510 p-type cladding layer 110a, 910a, 1110a, 1510a First p-type cladding layer 110b, 910b, 1110b, 1510b Second p-type cladding layer 110P, 710P, 910P, 1010P, 1110P Protruding portion 110R, 710R, 910R, 1010R, 1110R Ridge 110Ru, 113u, 1110Ru Top surface 110Rs, 113s Side surface 110T, 710T, 910T, 1010T, 1110T Groove 110Tu Bottom surface 111, 1511 Contact layer 112, 1412 Current blocking layer 112a, 1412a Opening 112b Bottom 112s, 114s, 1214s, 1412s Side 113, 1113 Conductive oxide film 114, 114c, 1214 Metal electrode 115 Barrier electrode 116 Cover electrode 117 N-side electrode 206a, 606a First p-side guide layer 206b, 606b Second p-side guide layer 921 Underlayer 922 Buffer layer 1104a, 1504a First n-side guide layer1104b, 1504b Second n-side guide layer 1231 Adhesion layer 1332 Hydrogen absorption layer Ep Light emitting point Msk Mask Mt Deposition film R0, R1 Resist Rb Lower layer Ru Upper layer St Susceptor Tg Target Wf Wafer

Claims

1. A nitride semiconductor laser element comprising: an n-type cladding layer; an active layer disposed above the n-type cladding layer; a p-type cladding layer disposed above the active layer and having a ridge formed thereon; a conductive oxide film disposed above the p-type cladding layer and transparent to light having an oscillation wavelength of the nitride semiconductor laser element; and a metal electrode disposed above the conductive oxide film and containing a metal having a higher reflectivity than Pd for light having the oscillation wavelength.

2. The nitride semiconductor laser element according to claim 1, wherein the conductive oxide film is disposed continuously on the upper surface of the ridge in the width direction of the ridge.

3. The nitride semiconductor laser element according to claim 1 or 2, wherein the metal electrode is made of Ag, an Ag alloy, Al, or Rh.

4. The nitride semiconductor laser element according to any one of claims 1 to 3, further comprising an adhesion layer disposed between said conductive oxide film and said metal electrode, said adhesion layer being made of a metal having a higher ionization tendency than said metal electrode.

5. The nitride semiconductor laser element according to claim 4, wherein the metal electrode is made of Ag, and the adhesion layer is made of Ni, Ti or Al.

6. The nitride semiconductor laser device according to any one of claims 1 to 5, comprising: an n-side guide layer disposed between the n-type cladding layer and the active layer; and a p-side guide layer disposed between the active layer and the p-type cladding layer, the p-side guide layer having a first p-side guide layer and a second p-side guide layer disposed above the first p-side guide layer, an average refractive index of the first p-side guide layer being equal to or greater than the average refractive index of the n-side guide layer, an average refractive index of the second p-side guide layer being less than the average refractive index of the n-side guide layer, and a film thickness of the p-side guide layer being equal to or greater than the film thickness of the n-side guide layer.

7. The nitride semiconductor laser element according to any one of claims 1 to 5, comprising: an n-side guide layer disposed between the n-type cladding layer and the active layer; and a p-side guide layer disposed between the active layer and the p-type cladding layer, wherein the refractive index of the p-side guide layer monotonically decreases with increasing distance from the active layer, the average refractive index of the p-side guide layer is equal to or less than the average refractive index of the n-side guide layer, and the film thickness of the p-side guide layer is equal to or greater than the film thickness of the n-side guide layer.

8. The nitride semiconductor laser element according to any one of claims 1 to 5, comprising: an n-side guide layer disposed between the n-type cladding layer and the active layer; and a p-side guide layer disposed between the active layer and the p-type cladding layer, wherein the refractive index of the n-side guide layer monotonically decreases with increasing distance from the active layer, the average refractive index of the p-side guide layer is not more than the average refractive index of the n-side guide layer, and the film thickness of the p-side guide layer is not less than the film thickness of the n-side guide layer.

9. The nitride semiconductor laser device according to any one of claims 1 to 8, wherein the average refractive index of said p-type cladding layer is greater than the average refractive index of said n-type cladding layer.

10. The nitride semiconductor laser element according to any one of claims 1 to 9, wherein each of the n-type cladding layer and the p-type cladding layer is made of a nitride semiconductor containing Al, and the Al composition ratio of the p-type cladding layer is smaller than the Al composition ratio of the n-type cladding layer.

11. The nitride semiconductor laser element according to claim 10, wherein the oscillation wavelength is in the 375 nm band.

12. The nitride semiconductor laser device according to any one of claims 1 to 11, wherein the active layer has a single quantum well structure.

13. The nitride semiconductor laser element according to any one of claims 1 to 12, wherein the p-type cladding layer has a thickness of 100 nm or more and 300 nm or less, the conductive oxide film has a thickness of 100 nm or more and 400 nm or less, and the metal electrode has a thickness of 100 nm or more and 300 nm or less.

14. The nitride semiconductor laser element according to any one of claims 1 to 13, further comprising an electrically insulating current blocking layer covering a side surface of the ridge, the current blocking layer covering at least a portion of the side surface of the conductive oxide film and having a smaller refractive index than the p-type cladding layer, and the metal electrode covering an upper surface of the ridge.

15. The nitride semiconductor laser element according to claim 14, wherein the current blocking layer continuously covers the side surfaces of the conductive oxide film and the ends of the upper surface of the conductive oxide film, and the metal electrode covers the upper surface of the ridge.

16. The nitride semiconductor laser element according to claim 15, wherein the metal electrode continuously covers an upper surface of the ridge and at least a part of a side of the current blocking layer facing the side surface of the conductive oxide film.

17. The nitride semiconductor laser element according to any one of claims 14 to 16, wherein the thickness of the conductive oxide film decreases toward the side surface of the ridge.

18. The nitride semiconductor laser element according to claim 17, wherein the conductive oxide film has a concave side surface, and the metal electrode has a side portion disposed in a position facing the side surface.

19. The nitride semiconductor laser element according to claim 17, wherein a surface of said metal electrode facing said conductive oxide film has a convex region facing said conductive oxide film.

20. An electrically insulating current blocking layer is provided covering the side surface of the ridge, and the current blocking layer is made of SiO ２ and having a plurality of openings located above an upper surface of the ridge, the plurality of openings being arranged in a resonance direction of laser light emitted by the nitride semiconductor laser element, and the metal electrode being electrically connected to the conductive oxide film via the plurality of openings.

21. The nitride semiconductor laser element according to any one of claims 1 to 13, further comprising an electrically insulating current blocking layer covering side surfaces of the ridge, the current blocking layer having an opening located above an upper surface of the ridge, the metal electrode being electrically connected to the conductive oxide film through the opening, the current blocking layer having one or more first layers made of an electrically insulating material having light transparency and one or more second layers made of an electrically insulating material having light transparency different from the one or more first layers, and each of the one or more first layers and each of the one or more second layers are stacked alternately.

22. The nitride semiconductor laser element according to any one of claims 1 to 21, wherein the active layer has a first barrier layer, a well layer disposed above the first barrier layer, and a second barrier layer disposed above the well layer, and the well layer includes a region in which band gap energy increases with increasing distance from the first barrier layer.

Images