Semiconductor laser element and method for producing semiconductor laser element

Abstract

A semiconductor laser element (100) emits laser light and comprises: a substrate (11); a semiconductor multilayer body (100S) that is disposed above the substrate (11) and contains a GaN-based semiconductor; and a contact electrode (41) that is in contact with the semiconductor multilayer body (100S) and contains Ag. The semiconductor multilayer body (100S) has an n-type semiconductor layer that is disposed above the substrate (11), an active layer (22) that is disposed above the n-type semiconductor layer, and a p-type semiconductor layer that is disposed above the active layer (22), and also has a bottom surface (30Rb) that is positioned at the upper end of the semiconductor multilayer body (100S) above the active layer (22), and a ridge (30R) that is adjacent to the bottom surface (30Rb), protrudes upward from the bottom surface (30Rb), and extends in the emission direction of the laser light. The contact electrode (41) is in contact with an upper surface (30Ru) and a side surface (30Rs) of the ridge (30R), and at least a part of the bottom surface (30Rb).

Description

Semiconductor laser element and method for manufacturing semiconductor laser element

[0001] The present disclosure relates to a semiconductor laser device and a method for manufacturing a semiconductor laser device.

[0002] Conventionally, semiconductor laser elements have been used as light sources for processing devices and the like. High efficiency is required for light sources. To improve the efficiency of semiconductor laser elements, for example, a technique is known in which a ridge (i.e., a ridge stripe) is formed in a semiconductor layer to confine current within the ridge (see, for example, Patent Document 1).

[0003] JP 2010-67763 A

[0004] In semiconductor laser devices, not only high efficiency but also high output power is required. As the output power of semiconductor laser devices increases, the amount of heat generated increases, so there is a demand for improved heat dissipation characteristics of semiconductor laser devices.

[0005] The present disclosure is intended to solve such problems, and has an object to provide a semiconductor laser element or the like that can improve heat dissipation characteristics.

[0006] In order to solve the above problems, one aspect of the semiconductor laser element according to the present disclosure is a semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate that is disposed above the substrate and contains a GaN-based semiconductor; and a contact electrode that is in contact with the semiconductor laminate and contains Ag, wherein the semiconductor laminate has an n-type semiconductor layer that is disposed above the substrate, an active layer that is disposed above the n-type semiconductor layer, and a p-type semiconductor layer that is disposed above the active layer, and has a bottom surface that is located at an upper end of the semiconductor laminate and is located above the active layer, and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, and the contact electrode is in contact with an upper surface and a side surface of the ridge and at least a part of the bottom surface.

[0007] In order to solve the above problems, one aspect of the semiconductor laser element according to the present disclosure is a semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor stack arranged above the substrate; a contact electrode in contact with the semiconductor stack and containing Ag; and a covering electrode arranged above the contact electrode and having a melting point higher than that of the contact electrode; the semiconductor stack has an n-type semiconductor layer arranged above the substrate, an active layer arranged above the n-type semiconductor layer, and a p-type semiconductor layer arranged above the active layer; and the semiconductor stack has a bottom surface that is located at an upper end of the semiconductor stack and above the active layer; and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, the contact electrode being in contact with an upper surface and a side surface of the ridge and at least a part of the bottom surface, and the covering electrode covering an edge of the contact electrode.

[0008] In order to solve the above problems, one aspect of the semiconductor laser element according to the present disclosure is a semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor stacked layer disposed above the substrate; a contact electrode in contact with the semiconductor stacked layer and containing Ag; and an n-side electrode disposed on a second main surface of the substrate that is on the back side of a first main surface on which the semiconductor stacked layer is disposed; the semiconductor stacked layer has an n-type semiconductor layer disposed above the substrate, an active layer disposed above the n-type semiconductor layer, and a p-type semiconductor layer disposed above the active layer, and has a bottom surface that is located at an upper end of the semiconductor stacked layer and above the active layer, and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in an emission direction of the laser light; the contact electrode is in contact with an upper surface and a side surface of the ridge and with at least a part of the bottom surface; and a dimension of the n-side electrode in at least one direction parallel to the second main surface is smaller than a dimension of the contact electrode in the at least one direction.

[0009] In order to solve the above problems, one aspect of the semiconductor laser element according to the present disclosure is a semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate disposed above the substrate; a contact electrode that is in contact with the semiconductor laminate and contains Ag; and an n-side electrode that is disposed on a second main surface of the substrate on the back side of a first main surface on which the semiconductor laminate is disposed; the semiconductor laminate has an n-type semiconductor layer disposed above the substrate, an active layer disposed above the n-type semiconductor layer, and a p-type semiconductor layer disposed above the active layer; The semiconductor device has a bottom surface located at the upper end of the conductor laminate and located above the active layer, a ridge adjacent to the bottom surface, protruding upward from the bottom surface, and extending in the emission direction of the laser light, and a protrusion adjacent to the bottom surface, protruding upward from the bottom surface, and extending in the emission direction of the laser light, and the contact electrode is in contact with the top surface and side surfaces of the ridge and at least a portion of the bottom surface, and the edge of the contact electrode is located between the ridge and the protrusion, and the protrusion protrudes upward beyond the edge of the contact electrode.

[0010] In order to solve the above-described problems, one aspect of the semiconductor laser element according to the present disclosure is a semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate that is disposed above the substrate and contains a GaN-based semiconductor; and a contact electrode that is in contact with the semiconductor laminate and contains Ag, the semiconductor laminate having an n-type semiconductor layer that is disposed above the substrate, an active layer that is disposed above the n-type semiconductor layer, and a p-type semiconductor layer that is disposed above the active layer, the semiconductor laminate having a bottom surface that is located at an upper end of the semiconductor laminate and is located above the active layer, and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, the contact electrode being in contact with an upper surface and a side surface of the ridge and with at least a part of the bottom surface, and an electrical contact resistance between the side surface of the ridge and the contact electrode is higher than the electrical contact resistance between the upper surface of the ridge and the contact electrode.

[0011] In order to solve the above-described problems, one aspect of a method for manufacturing a semiconductor laser element according to the present disclosure is a method for manufacturing a semiconductor laser element that emits laser light, the method including: a semiconductor laminate formation step of forming a semiconductor laminate above a substrate; and a contact electrode formation step of forming a contact electrode that is in contact with the semiconductor laminate and contains Ag, the semiconductor laminate formation step including an etching step of forming, by dry etching, a bottom surface located at an upper end of the semiconductor laminate, and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, and the contact electrode is in contact with an upper surface and a side surface of the ridge and at least a part of the bottom surface.

[0012] According to the present disclosure, it is possible to provide a semiconductor laser element or the like that can improve heat dissipation characteristics.

[0013] 1 is a schematic cross-sectional view showing an overall configuration of a semiconductor laser device according to a first embodiment. FIG. 2 is a schematic cross-sectional view showing a configuration of an active layer of the semiconductor laser device according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing a stacking step of a method for manufacturing a semiconductor laser device according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing an etching step of a method for manufacturing a semiconductor laser device according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing an insulating layer forming step of a method for manufacturing a semiconductor laser device according to the first embodiment. FIG. 6 is a schematic cross-sectional view showing a contact electrode forming step of a method for manufacturing a semiconductor laser device according to the first embodiment. FIG. 7 is a schematic cross-sectional view showing a covering electrode forming step of a method for manufacturing a semiconductor laser device according to the first embodiment. FIG. 8 is a graph showing the relationship between the refractive index and wavelength of various metals and dielectrics including Ag. FIG. 9 is a schematic diagram showing the distribution of the refractive index n(z) and light intensity I(z) in the stacking direction of a semiconductor laser device of a comparative example. FIG. 10 is a schematic cross-sectional view showing the distribution of the refractive index n(z) and light intensity I(z) in the stacking direction of a semiconductor laser device according to the first embodiment. 10 is a schematic cross-sectional view showing a fourth step of a method for forming an experimental element. It is a graph showing the relationship between the voltage and current applied between two electrodes of an experimental element. It is a schematic cross-sectional view for explaining a first step of a method for forming experimental elements of Types 1 and 2. It is a schematic cross-sectional view for explaining a second step of a method for forming experimental elements of Types 1 and 2. It is a schematic cross-sectional view for explaining a third step of a method for forming experimental elements of Types 1 and 2. It is a schematic cross-sectional view showing the configuration of an experimental element of Type 3. It is a graph showing the relationship between the voltage and current applied between two electrodes of each of experimental elements of Types 1 to 3. It is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to a second embodiment. It is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to a third embodiment. It is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to a fourth embodiment. It is a schematic cross-sectional view showing the configuration in the vicinity of a contact electrode of a semiconductor laser element according to a fifth embodiment. It is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to a sixth embodiment.10 is a schematic cross-sectional view showing the configuration of a contact electrode of a semiconductor laser element according to a sixth embodiment; FIG. 11 is a diagram showing the relationship between the film thickness of a translucent conductive film and the reflectivity of a stack including a translucent conductive film and a reflective metal film for light with a wavelength of 380 nm; FIG. 12 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser element according to a seventh embodiment; FIG. 13 is a diagram showing the relationship between the film thickness of a translucent conductive film and the reflectivity of a stack including a translucent conductive film and a reflective metal film for light with a wavelength of 450 nm; FIG. 14 is a diagram showing the relationship between the film thickness of a translucent conductive film and the reflectivity of a stack including a translucent conductive film and a reflective metal film for light with a wavelength of 630 nm; and FIG. 15 is a diagram showing the relationship between the film thickness of a translucent conductive film and the reflectivity of a stack including a translucent conductive film and a reflective metal film for light with a wavelength of 980 nm.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] Furthermore, in this specification, terms indicating the relationship between elements, such as vertical, terms indicating the shape of elements, such as plate-like, 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 a few percent.

[0018] First Embodiment A semiconductor laser device according to a first embodiment will be described.

[0019] [1-1. Overall Configuration] First, the overall configuration of the semiconductor laser device according to this embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 100 according to this embodiment. FIG. 1 shows a cross section perpendicular to the emission direction of laser light emitted by the semiconductor laser device 100. FIG. 1 also shows some of the electric field lines Le formed when current is applied to the semiconductor laser device 100, indicated by dashed arrows. FIG. 2 is a schematic cross-sectional view showing the configuration of the active layer 22 of the semiconductor laser device 100 according to this embodiment. FIG. 2 shows an enlarged view of only the cross section of the active layer 22 among the cross sections shown in FIG. 1. 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 the semiconductor laser device 100 is parallel to the Z-axis, and the emission direction of laser light is parallel to the Y-axis.

[0020] 1, the semiconductor laser device 100 includes a semiconductor stack 100S, and emits laser light from an end face located at an end in the Y-axis direction perpendicular to the stacking direction (i.e., the Z-axis direction) of the semiconductor stack 100S. The oscillation wavelength (i.e., the wavelength of the laser light) of the semiconductor laser device 100 according to this embodiment is 350 nm or more and 420 nm or less. In this embodiment, the semiconductor laser device 100 has two end faces that form a resonator.

[0021] 1 , the semiconductor laser device 100 includes a substrate 11, a semiconductor stack 100S, and a contact electrode 41. In this embodiment, the semiconductor laser device 100 further includes a covering electrode 42, an n-side electrode 51, and an insulating layer 60.

[0022] The substrate 11 is a plate-like member that serves as a base for the semiconductor laser device 100. The substrate 11 has a first main surface 11a and a second main surface 11b on the back side of the first main surface 11a. In this embodiment, the substrate 11 is an n-type GaN substrate.

[0023] The semiconductor laminate 100S is a laminate disposed above the substrate 11. The semiconductor laminate 100S is disposed on the first main surface 11a of the substrate 11. In this embodiment, the semiconductor laminate 100S includes a GaN-based semiconductor. The semiconductor laminate 100S has an n-type semiconductor layer, an active layer 22, and a p-type semiconductor layer. It has an n-type cladding layer 12, the active layer 22, a p-type cladding layer 32, and a contact layer 33. In this embodiment, the semiconductor laminate 100S further has an n-type guide layer 13, an n-side guide layer 21, a p-side guide layer 23, and an electron barrier layer 31.

[0024] The n-type cladding layer 12 is an example of an n-type semiconductor layer disposed above the substrate 11. In this embodiment, the n-type cladding layer 12 is disposed on the first main surface 11a of the substrate 11. The n-type cladding layer 12 has a smaller refractive index than the active layer 22 and a larger band gap energy. In this embodiment, the n-type cladding layer 12 is made of a nitride semiconductor containing Al. More specifically, the n-type cladding layer 12 is an n-type AlGaN layer. The n-type cladding layer 12 is doped with Si as an impurity.

[0025] The n-type guide layer 13 is an example of an n-type semiconductor layer disposed above the substrate 11. In this embodiment, the n-type guide layer 13 is an n-type optical guide layer disposed above the n-type cladding layer 12. The n-type guide layer 13 is disposed between the n-type cladding layer 12 and the active layer 22. In this embodiment, the n-type guide layer 13 is disposed between the n-type cladding layer 12 and the n-side guide layer 21. The n-type guide layer 13 has a higher refractive index and a smaller band gap energy than the n-type cladding layer 12. In this embodiment, the n-type guide layer 13 is an n-type GaN layer. The n-type guide layer 13 is doped with Si as an impurity.

[0026] The n-side guide layer 21 is an undoped optical guide layer disposed above the n-type cladding layer 12. The n-side guide layer 21 is disposed between the n-type cladding layer 12 and the active layer 22. In this embodiment, the n-side guide layer 21 is disposed between the n-type guide layer 13 and the active layer 22. The n-side guide layer 21 has a higher refractive index and a smaller band gap energy than the n-type cladding layer 12. In this embodiment, the n-side guide layer 21 is an undoped InGaN layer.

[0027] The active layer 22 is a light-emitting layer disposed above the n-type cladding layer 12. In this embodiment, the active layer 22 is disposed above the n-side guide layer 21 and has a quantum well structure. The active layer 22 has one or more well layers and a plurality of barrier layers. In this embodiment, the active layer 22 has well layers 22b and 22d and barrier layers 22a, 22c, and 22e, as shown in FIG. 2 .

[0028] The barrier layer 22a is disposed above the n-side guide layer 21 and functions as a barrier of the quantum well structure. In this embodiment, the barrier layer 22a is an undoped InGaN layer.

[0029] The well layer 22b is disposed between the barrier layers 22a and 22c and functions as a well in the quantum well structure. The bandgap energy of the well layer 22b is smaller than the bandgap energies of the barrier layers 22a and 22c. In this embodiment, the well layer 22b is an undoped InGaN layer.

[0030] The barrier layer 22c is disposed above the well layer 22b and functions as a barrier of the quantum well structure. In this embodiment, the barrier layer 22c is an undoped InGaN layer.

[0031] The well layer 22d is disposed between the barrier layers 22c and 22e and functions as a well in the quantum well structure. The bandgap energy of the well layer 22d is smaller than the bandgap energies of the barrier layers 22c and 22e. In this embodiment, the well layer 22d is an undoped InGaN layer.

[0032] The barrier layer 22e is disposed above the well layer 22d and functions as a barrier of the quantum well structure. In this embodiment, the barrier layer 22e is an undoped InGaN layer.

[0033] In this embodiment, the active layer 22 has a multiple quantum well structure including two well layers 22b and 22d, but the active layer 22 may have a multiple quantum well structure including three or more well layers, or a single quantum well structure including one well layer.

[0034] The p-side guide layer 23 is an undoped optical guide layer disposed above the active layer 22. The p-side guide layer 23 is disposed between the active layer 22 and the p-type cladding layer 32. In this embodiment, the p-side guide layer 23 is disposed between the active layer 22 and the electron barrier layer 31. The p-side guide layer 23 has a higher refractive index and a smaller band gap energy than the p-type cladding layer 32. In this embodiment, the p-side guide layer 23 is an undoped InGaN layer.

[0035] The electron barrier layer 31 is an example of a p-type semiconductor layer disposed above the active layer 22. In this embodiment, the electron barrier layer 31 is disposed between the p-side guide layer 23 and the p-type cladding layer 32. The band gap energy of the electron barrier layer 31 is larger than the band gap energy of the p-type cladding layer 32. In this embodiment, the electron barrier layer 31 is a p-type AlGaN layer. The electron barrier layer 31 is doped with Mg as an impurity. The electron barrier layer 31 having such a configuration can prevent electrons injected from the n-type cladding layer 12 from leaking from the active layer 22 to the p-type cladding layer 32.

[0036] The p-type cladding layer 32 is an example of a p-type semiconductor layer disposed above the active layer 22. In this embodiment, the p-type cladding layer 32 is disposed between the electron barrier layer 31 and the contact layer 33. The p-type cladding layer 32 has a smaller refractive index and a larger band gap energy than the active layer 22. In this embodiment, the p-type cladding layer 32 is a p-type AlGaN layer. The p-type cladding layer 32 is doped with Mg as an impurity.

[0037] The contact layer 33 is an example of a p-type semiconductor layer disposed above the active layer 22. In this embodiment, the contact layer 33 is disposed above the p-type cladding layer 32. In this embodiment, the contact layer 33 is a p-type GaN layer, and is in contact with the contact electrode 41. The contact layer 33 is doped with Mg as an impurity.

[0038] The semiconductor laminate 100S has a bottom surface 30Rb located at the upper end of the semiconductor laminate 100S and above the active layer 22, and a ridge 30R adjacent to the bottom surface 30Rb, protruding upward from the bottom surface 30Rb, and extending in the emission direction of the laser light. The ridge 30R has a top surface 30Ru, which is the upper end surface, and a side surface 30Rs, which is the surface located at the end in the X-axis direction. In this embodiment, the ridge 30R is formed in the p-type cladding layer 32 and the contact layer 33. The bottom surface 30Rb is located in the p-type cladding layer 32. The top surface 30Ru of the ridge 30R is the upper surface of the contact layer 33.

[0039] The electrical resistance of the side surface 30Rs of the ridge 30R is higher than the electrical resistance of the top surface 30Ru of the ridge 30R. That is, the ridge 30R has a high-resistance layer including the side surface 30Rs and a low-resistance layer including the top surface 30Ru and having a lower electrical resistance than the high-resistance layer.

[0040] The width of the ridge 30R (i.e., the dimension in the X-axis direction) is not particularly limited, but is 100 μm or less in this embodiment. The width of the ridge 30R may be 1 μm or more.

[0041] In this embodiment, the semiconductor stack 100S has recesses 100T located at each end in the X-axis direction. The recesses 100T are portions recessed downward relative to the bottom surface 30Rb. In this embodiment, the lower ends of the recesses 100T are located in the n-type cladding layer 12.

[0042] The insulating layer 60 is an electrical insulating layer that covers the recess 100T of the semiconductor laminate 100S. In this embodiment, the insulating layer 60 continuously covers the recess 100T and a part of the bottom surface 30Rb. The insulating layer 60 is made of, for example, SiO ２ It is a layer.

[0043] The recess 100T and the insulating layer 60 are formed to prevent electrical short-circuiting when the semiconductor laser element 100 is mounted on a heat dissipation member such as a submount. For example, when the top surface of the semiconductor laser element 100, i.e., the covering electrode 42, is bonded to a heat dissipation member using solder, a portion of the solder may rise and come into contact with the side surface of the semiconductor laser element 100 (i.e., the end surface in the X-axis direction). Therefore, by keeping the n-type layer as far away from the bonding surface as possible and covering the side surface with the insulating layer 60, electrical short-circuiting can be avoided even if the solder comes into contact with the side surface. In this embodiment, the lower end of the recess 100T is located in the n-type cladding layer 12, but it may be located further down. For example, the lower end of the recess 100T may be located on the substrate 11.

[0044] The contact electrode 41 is a conductive member containing Ag and is in contact with the semiconductor laminate 100S. The contact electrode 41 is in contact with the top surface 30Ru and side surface 30Rs of the ridge 30R, and at least a portion of the bottom surface 30Rb. In this embodiment, the contact electrode 41 continuously covers a portion of the bottom surface 30Rb located on one side of the ridge 30R in the X-axis direction, the ridge 30R (i.e., the side surface 30Rs and top surface 30Ru), and a portion of the bottom surface 30Rb located on the other side of the ridge 30R in the X-axis direction. Note that the contact electrode 41 does not necessarily have to be formed continuously as described above. For example, the contact electrode 41 may be interrupted near the boundary between the top surface 30Ru and side surface 30Rs of the ridge 30R.

[0045] The film thickness at a position facing the side surface 30Rs of the contact electrode 41 (i.e., the dimension in a direction perpendicular to the side surface 30Rs) may be smaller than each of the film thickness at a position facing the top surface 30Ru of the contact electrode 41 (i.e., the dimension in a direction perpendicular to the top surface 30Ru) and the film thickness at a position facing the bottom surface 30Rb (i.e., the dimension in a direction perpendicular to the bottom surface 30Rb).

[0046] In this embodiment, the electrical contact resistance between the side surface 30Rs of the ridge 30R and the contact electrode 41 is higher than the electrical contact resistance between the upper surface 30Ru of the ridge 30R and the contact electrode 41.

[0047] In this embodiment, the contact electrode 41 is made of Ag. That is, the entire contact electrode 41 is made of Ag. The thickness of the contact electrode 41 is not particularly limited. In this embodiment, the thickness of the contact electrode 41 disposed on the upper surface 30Ru of the ridge 30R is 50 nm or more.

[0048] The covering electrode 42 is disposed above the contact electrode 41 and has a higher melting point than the contact electrode 41. The covering electrode 42 may be disposed above the contact electrode 41 and has a lower ionization tendency than the contact electrode 41. In this embodiment, the covering electrode 42 covers the edge 41e of the contact electrode 41. In other words, the edge 41e of the contact electrode 41 is not exposed from the covering electrode 42. The covering electrode 42 may have a Ti layer and an Au layer stacked in this order from the contact electrode 41 side.

[0049] The film thickness at a position facing the side surface 30Rs of the covering electrode 42 may be smaller than the film thickness at a position facing the top surface 30Ru of the covering electrode 42 and the film thickness at a position facing the bottom surface 30Rb.

[0050] The n-side electrode 51 is an electrode disposed on the second main surface 11b of the substrate 11. In the present embodiment, the dimension of the n-side electrode 51 in the X-axis direction is larger than the dimension of the contact electrode 41 in the X-axis direction. The configuration of the n-side electrode 51 is not particularly limited, and the n-side electrode 51 may be, for example, a single-layer film or a multilayer film formed of at least one of Cr, Ti, Ni, Pd, Pt, and Au. In the present embodiment, the n-side electrode 51 has a Ti layer, a Pt layer, and an Au layer stacked in this order from the second main surface 11b.

[0051] [1-2. Manufacturing Method of Semiconductor Laser Device] A manufacturing method of the semiconductor laser device 100 according to this embodiment will be described with reference to Fig. 1 and Fig. 3 to Fig. 7. Fig. 3 to Fig. 7 are schematic cross-sectional views showing each step of the manufacturing method of the semiconductor laser device 100 according to this embodiment. Fig. 3 to Fig. 7 show cross sections at the same positions as the cross section shown in Fig. 1.

[0052] First, a semiconductor stack 100S is formed above a substrate 11 (semiconductor stack formation process). As shown in FIG. 3, each semiconductor layer constituting the semiconductor stack 100S is stacked on a first main surface 11a of the substrate 11 (stacking process). In this embodiment, an n-type cladding layer 12, an n-type guide layer 13, an n-side guide layer 21, an active layer 22, a p-side guide layer 23, an electron barrier layer 31, a p-type cladding layer 32, and a contact layer 33 are stacked in this order on the first main surface 11a. The semiconductor stack 100S is stacked using, for example, a metal organic chemical vapor deposition (MOCVD) method. 4, a bottom surface 30Rb located at the upper end of the semiconductor laminate 100S and a ridge 30R adjacent to the bottom surface 30Rb, protruding upward from the bottom surface 30Rb, and extending in the direction of emission of the laser light are formed by dry etching (etching step). More specifically, a SiO 2 film is formed by photolithography in a region corresponding to the top surface 30Ru of the ridge 30R. ２ and the like, and Cl is applied to the area not covered by the mask. ２ , BCl ３ The ridge 30R is formed by dry etching using a mask such as HF. The mask is removed by wet etching using HF or the like. In this embodiment, the recess 100T is also formed in the etching process.

[0053] 5, an insulating layer 60 is formed (insulating layer forming step). The insulating layer 60 is formed by, for example, a low-pressure CVD (Chemical Vapor Deposition) method. The insulating layer 60 may also be formed by, for example, an atmospheric pressure CVD method.

[0054] 6, a contact electrode 41 containing Ag is formed in contact with the semiconductor stack 100S (contact electrode formation process). Here, the contact electrode 41 is in contact with the top surface 30Ru and side surface 30Rs of the ridge 30R, and at least a portion of the bottom surface 30Rb. The contact electrode 41 is formed using, for example, electron beam evaporation.

[0055] 7, a covering electrode 42 is formed above the contact electrode 41 (covering electrode forming step). The covering electrode 42 is formed by using, for example, electron beam evaporation.

[0056] 1, an n-side electrode 51 is formed on the second main surface 11b of the substrate 11 (n-side electrode forming step). The n-side electrode 51 is formed by, for example, electron beam evaporation.

[0057] Through the above steps, the semiconductor laser device 100 according to this embodiment is manufactured.

[0058] [1-3. Effects] The effects of the semiconductor laser device 100 according to this embodiment and the method for manufacturing the same will be described.

[0059] First, the effect of the contact electrode 41 of the semiconductor laser device 100 according to this embodiment will be described.

[0060] As described above, the contact electrode 41 according to this embodiment contains Ag. The refractive index of Ag will now be described with reference to FIG. 8 . FIG. 8 is a graph showing the relationship between the refractive index and wavelength of various metals and dielectrics containing Ag. Note that the refractive indexes in FIG. 8 and those described below all refer to the real part of the complex refractive index.

[0061] As shown in FIG. 8 , Ag has a refractive index significantly lower than other metals and dielectrics in the wavelength band of 200 nm to 800 nm, particularly in the wavelength band of 320 nm to 800 nm. The effect of contact electrode 41 containing Ag with such a low refractive index will be described using FIGS. 9 and 10 , comparing it with a comparative example. FIGS. 9 and 10 are schematic diagrams showing the distribution of refractive index n(z) and light intensity I(z) in the stacking direction (z-axis direction) of semiconductor laser devices according to the comparative example and the present embodiment, respectively. FIGS. 9 and 10 show the refractive index n(z) and light intensity I(z) at position z on the z-axis shown in each figure.

[0062] 9 differs from the semiconductor laser device 100 according to the present embodiment in the configurations of the p-type cladding layer 932, contact electrode 941, and insulating layer 960, but is otherwise identical in configuration. The (maximum) thickness of the p-type cladding layer 932 of the comparative example is greater than the (maximum) thickness of the p-type cladding layer 32 according to the present embodiment. The contact electrode 941 of the comparative example is made of Pd. The insulating layer 960 of the comparative example covers the side surfaces and the end of the top surface of the ridge.

[0063] 9 , the comparative semiconductor laser device 900 has a high refractive index of the contact electrode 941. Therefore, in order to sufficiently suppress the light intensity at the contact electrode 941 and reduce the waveguide loss due to light absorption at the contact electrode 941, it is necessary to increase the thickness of the p-type cladding layer 932.

[0064] In contrast, in the semiconductor laser device 100 according to this embodiment, as shown in FIG. 10 , the refractive index of the contact electrode 41 is significantly lower than that of the contact electrode 941 of the comparative example. Therefore, the optical intensity at the contact electrode 41 can be sufficiently suppressed. Therefore, in the semiconductor laser device 100 according to this embodiment, the thickness of the p-type cladding layer 32 can be reduced. Thus, in this embodiment, even in a configuration in which the distance from the active layer 22, which is the light-emitting layer, to the contact electrode 41 is shorter than the distance from the active layer 22 to the contact electrode 941 in the comparative example, the optical intensity at the contact electrode 41 can be sufficiently suppressed. Therefore, the waveguide loss associated with optical absorption at the contact electrode 41 can be reduced. For example, the distance between the well layer 22d closest to the contact electrode 41 and the top surface 30Ru of the ridge 30R may be 100 nm or more and 550 nm or less. Thus, even when the distance from the active layer 22 to the contact electrode 41 is small, the waveguide loss associated with optical absorption at the contact electrode 41 can be reduced. Furthermore, by setting the distance from the active layer 22 to the contact electrode 41 to 550 nm or less, it is possible to reduce the electrical resistance (series resistance) of the semiconductor laser device 100. Therefore, it is possible to improve the efficiency of the semiconductor laser device 100.

[0065] The contact electrode 41 disposed on the upper surface 30Ru of the ridge 30R may have a thickness of 50 nm or more. This allows the contact electrode 41 to more reliably confine light below the contact electrode 41. Furthermore, the spread of light above the contact electrode 41 can be suppressed.

[0066] The contact electrode 41 also has the function of reflecting spontaneously emitted light from the active layer 22. Because spontaneously emitted light is emitted in an unspecified direction, most of it does not contribute to the oscillation and amplification of laser light. In other words, most of the spontaneously emitted light is lost without being effectively utilized. The semiconductor laser device 100 according to this embodiment includes the contact electrode 41 with high reflectivity. This makes it possible to increase the proportion of spontaneously emitted light that is reflected by the contact electrode 41 out of the spontaneously emitted light that is incident on the contact electrode 41. At least a portion of the spontaneously emitted light reflected by the contact electrode 41 returns to the active layer 22. Therefore, by increasing the proportion of spontaneously emitted light that is reflected by the contact electrode 41 out of the spontaneously emitted light that is incident on the contact electrode 41, it is possible to increase the amount of spontaneously emitted light that is reabsorbed in the active layer 22. This increases the quantum efficiency of the semiconductor laser device 100. This allows the semiconductor laser device 100 to have high efficiency.

[0067] Next, the electrical resistance between the contact electrode 41 and the semiconductor stack 100S according to this embodiment (in other words, the electrical contact resistance between the contact electrode 41 and the semiconductor stack 100S) will be described. First, the effect of using dry etching in the etching step of forming the ridge 30R in the semiconductor stack 100S, that is, the effect of the etching step according to this embodiment, will be described. In order to explain the effect of using dry etching, first, an experimental element for measuring the electrical resistance of an etched surface formed by dry etching and an etched surface formed by wet etching will be described with reference to FIGS. 11 to 14. FIGS. 11 to 14 are schematic cross-sectional views showing each step of a method for forming an experimental element.

[0068] As shown in FIG. 11 , similarly to the semiconductor laser device 100 according to this embodiment, an n-type cladding layer 12, an n-type guide layer 13, an n-side guide layer 21, an active layer 22, a p-side guide layer 23, an electron barrier layer 31, a p-type cladding layer 32, and a contact layer 33 are laminated in this order on a substrate 11.

[0069] Subsequently, as shown in FIG. 12, SiO ２ An insulating layer 961 made of the above is formed by CVD.

[0070] Subsequently, as shown in FIG. ３ The insulating layer 961 is removed by dry etching using HCl or wet etching using HF to expose the contact layer 33 .

[0071] 14, two electrodes 942a and 942b are formed on the contact layer 33. The distance De between the two electrodes 942a and 942b is 14 μm. Each of the two electrodes 942a and 942b has a Pd layer and a Pt layer stacked in this order on the contact layer 33.

[0072] The electrical resistance between the two electrodes 942a, 942b of the experimental element formed by the above-described method will be described with reference to Fig. 15. Fig. 15 is a graph showing the relationship between the voltage and current applied between the two electrodes 942a, 942b of the experimental element. Fig. 15 shows the relationship for both the experimental element formed by dry etching and the experimental element formed by wet etching.

[0073] 15, when dry etching is used, the current flowing between the two electrodes 942a and 942b is smaller than when wet etching is used. In other words, the electrical resistance of the etched surface formed by dry etching is significantly higher than the electrical resistance of the etched surface formed by wet etching. This is presumably because the etched surface is damaged by ions, which are the etchant, during dry etching (i.e., the crystallinity is reduced).

[0074] As described above, the electrical resistance of the etched surface formed by dry etching is significantly higher than the electrical resistance of the etched surface formed by wet etching. Therefore, the electrical resistance of the bottom surface 30Rb of the semiconductor stack 100S according to this embodiment and the side surface 30Rs of the ridge 30R, which are etched surfaces formed by dry etching, is significantly higher than the electrical resistance of the top surface 30Ru of the ridge 30R. Therefore, when a voltage is applied between the contact electrode 41 and the n-side electrode 51 of the semiconductor laser device 100 according to this embodiment, in the region covered by the contact electrode 41, a current flows substantially only from the top surface 30Ru of the ridge 30R toward the n-side electrode 51, and no current flows from the bottom surface 30Rb or the side surface 30Rs of the ridge 30R. Therefore, in the semiconductor laser device 100 according to this embodiment, current confinement to the ridge 30R is possible without disposing a dielectric layer (i.e., an electrical insulating layer) on the bottom surface 30Rb or the side surface 30Rs of the ridge 30R. Furthermore, in the etching process according to this embodiment, the ridge 30R is formed by dry etching, which allows the formation of the ridge 30R and the increase in resistance of the bottom surface 30Rb and the side surface 30Rs of the ridge 30R to be performed simultaneously.

[0075] The electrical resistances of the bottom surface 30Rb and the top surface 30Ru and side surface 30Rs of the ridge 30R correspond to the carrier concentration. That is, as the carrier concentration of the semiconductor layer increases, the electrical resistance of the semiconductor layer decreases. In this embodiment, the carrier concentration of the bottom surface 30Rb and side surface 30Rs of the ridge 30R is lower than the carrier concentration of the top surface 30Ru of the ridge 30R. The carrier distribution in the semiconductor layer can be measured and visualized using, for example, scanning microwave microscopy (SMM), scanning capacitance microscopy (SCM), or the like.

[0076] Furthermore, in a configuration in which the contact electrode 41 is in contact with the top surface 30Ru and the side surface 30Rs of the ridge 30R and at least a part of the bottom surface 30Rb, as in the present embodiment, the thermal resistance between the ridge 30R and the contact electrode 41 can be significantly reduced compared to a case in which a dielectric layer is disposed between the contact electrode 41 and the side surface 30Rs of the ridge 30R. Therefore, the semiconductor laser device 100 according to the present embodiment can have improved heat dissipation characteristics compared to a semiconductor laser device in which a dielectric layer is disposed between the contact electrode 41 and the side surface 30Rs of the ridge 30R. Furthermore, in the present embodiment, the semiconductor laser device 100 and its manufacturing method can be simplified by not disposing a dielectric layer between the contact electrode 41 and the side surface 30Rs of the ridge 30R.

[0077] Furthermore, as described above, the contact electrode 41 has a SiO ２ The contact electrode 41 having such a low refractive index is in contact with the side surface 30Rs of the ridge 30R, thereby enabling light to be confined within the ridge 30R in the width direction (i.e., the X-axis direction in FIG. 1 , etc.).

[0078] Furthermore, the width of the ridge 30R of the semiconductor laser device 100 according to this embodiment may be 100 μm or less.

[0079] Because current is confined in the ridge 30R, the amount of heat generated in the ridge 30R, such as Joule heat, is greater than in other regions. If the width of the ridge 30R, which generates a large amount of heat, is small, problems such as a decrease in efficiency due to heat generation and damage to the semiconductor laser device 100 caused by heat generation may occur. When the width of the ridge 30R is small in this way, the effect of improving the heat dissipation characteristics by the contact electrode 41 of the semiconductor laser device 100 according to this embodiment becomes even more pronounced, and the occurrence of the above problems can be suppressed.

[0080] Next, the effect of annealing on the electrical resistance of the etched surface after dry etching will be described. To investigate the effect of annealing, experiments were conducted using experimental elements of types 1 to 3. The method of forming the experimental elements used in this experiment will be described with reference to FIGS. 16 to 19. FIGS. 16 to 18 are schematic cross-sectional views illustrating the steps of the method of forming the experimental elements of types 1 and 2. FIG. 19 is a schematic cross-sectional view showing the configuration of the experimental element of type 3.

[0081] In forming the experimental elements of Type 1 and Type 2, first, as shown in Fig. 16, a p-type cladding layer 32 and a contact layer 33 are laminated on a sapphire substrate 91. Then, as shown in Fig. 17, the contact layer 33 and a part of the p-type cladding layer 32 are laminated with CHF ３ 18, two electrodes 41a and 41b are formed on the etched surface of the p-type cladding layer 32. Each of the two electrodes 41a and 41b is made of Ag.

[0082] Here, in the Type 1 experimental element, annealing is performed before dry etching to electrically activate the p-type impurities, but no annealing is performed after dry etching. On the other hand, in the Type 2 experimental element, annealing is not performed before dry etching, but is performed after dry etching and before electrode formation.

[0083] 19, the Type 3 experimental element includes a p-type cladding layer 32, a contact layer 33, and two electrodes 41a and 41b disposed on a sapphire substrate 91. In forming the Type 3 experimental element, the p-type cladding layer 32 and the contact layer 33 are stacked and then annealed. Then, the two electrodes 41a and 41b are formed on the contact layer 33.

[0084] The electrical resistance of the surface on which the two electrodes 41a, 41b of each of the experimental elements of types 1 to 3 formed as described above will be described with reference to Fig. 20. Fig. 20 is a graph showing the relationship between the voltage and current applied between the two electrodes 41a, 41b of each of the experimental elements of types 1 to 3.

[0085] 20 , the Type 1 and Type 2 experimental elements have significantly less current than the Type 3 experimental element. That is, the electrical resistance of the etched surface of each of the Type 1 and Type 2 experimental elements is higher than the electrical resistance of the top surface of the contact layer 33 of the Type 3 experimental element. In particular, the Type 1 experimental element has almost zero current when the applied voltage is 5 V or less. Generally, since the voltage applied to the semiconductor laser element 100 (i.e., the operating voltage) is 5 V or less, substantially no current flows from the contact electrode 41 to the bottom surface 30Rb of the semiconductor laser element 100 and the side surface 30Rs of the ridge 30R, which are dry-etched surfaces similar to the Type 1 etched surface.

[0086] 20, comparing the experimental results of the Type 1 and Type 2 experimental elements, the Type 2 experimental element has a higher current than the Type 1 experimental element. In other words, the etched surface of the Type 2 experimental element has a lower electrical resistance than the etched surface of the Type 1 experimental element. This is presumably because the crystallinity of the etched surface of the Type 2 experimental element was enhanced (i.e., restored) by annealing after dry etching. Thus, annealing the etched surface after dry etching can reduce the electrical resistance of the etched surface. Therefore, in manufacturing the semiconductor laser element 100, it is better not to perform annealing after forming the side surface 30Rs of the ridge 30R by dry etching.

[0087] Next, the effect of the covering electrode 42 of the semiconductor laser device 100 according to this embodiment will be described with reference to Fig. 1. As shown in Fig. 1, when the dimension W41 in the X-axis direction of the contact electrode 41 (and the dimension W42 in the X-axis direction of the covering electrode 42) is smaller than the dimension W51 in the X-axis direction of the n-side electrode 51, an electric field is generated in the direction indicated by the electric field line Le in Fig. 1 while the semiconductor laser device 100 is energized. In other words, an electric field is generated in the direction away from the ridge 30R in the X-axis direction. Here, since Ag is a metal that is relatively susceptible to migration, the Ag contained in the contact electrode 41 is oxidized by the electric field. ＋There is a risk that the ions will move away from the ridge 30R in the X-axis direction. ＋ As the ions move away from the ridge 30R, Ag ＋ The ions can move to the side surfaces of the active layer 22 (that is, the end surfaces located at the ends in the X-axis direction of the active layer 22) and short-circuit the p-type semiconductor layer and the n-type semiconductor layer.

[0088] However, in the semiconductor laser device 100 according to this embodiment, the covering electrode 42, which has a melting point higher than that of Ag, covers the edge 41e of the contact electrode 41. The metal ions contained in such covering electrode 42 are ＋ Therefore, the covering electrode 42 prevents Ag contained in the contact electrode 41 from migrating. ＋ This can prevent ions from moving away from the ridge 30 R. Therefore, the occurrence of a short circuit between the p-type semiconductor layer and the n-type semiconductor layer in the semiconductor laser device 100 can be prevented.

[0089] The oscillation wavelength of the semiconductor laser device 100 according to this embodiment may be 350 nm or more and 420 nm or less.

[0090] The semiconductor laser device 100 according to this embodiment includes the contact electrode 41 containing Ag, which has low optical absorption even in the wavelength band of 350 nm or more and 420 nm or less. Therefore, the semiconductor laser device 100 according to this embodiment can suppress waveguide loss even in this wavelength band.

[0091] (Embodiment 2) A semiconductor laser device according to embodiment 2 will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 100 according to embodiment 1 in the configuration of the n-side electrode, but is the same in other configurations. The semiconductor laser device according to this embodiment will be described below with reference to FIG. 21 , focusing on the differences from the semiconductor laser device 100 according to embodiment 1. FIG. 21 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 200 according to this embodiment. FIG. 21 shows a cross section perpendicular to the emission direction of laser light emitted by the semiconductor laser device 200. In FIG. 21 , some of the electric field lines Le formed when current is applied to the semiconductor laser device 200 are indicated by dashed arrows.

[0092] As shown in FIG. 21, the semiconductor laser device 200 according to this embodiment includes a substrate 11, a semiconductor stack 100S, a contact electrode 41, a covering electrode 42, an insulating layer 60, and an n-side electrode 251.

[0093] The n-side electrode 251 according to this embodiment is an electrode disposed on the second main surface 11b of the substrate 11. In this embodiment, the dimension W251 of the n-side electrode 251 in the X-axis direction is smaller than the dimension W41 of the contact electrode 41 in the X-axis direction.

[0094] In this way, the dimension of the n-side electrode 251 in the X-axis direction is smaller than the dimension of the contact electrode 41 in the X-axis direction, and therefore, as shown by the electric field line Le in FIG. 21 , the electric field formed between the contact electrode 41 and the n-side electrode 251 does not have a component in the direction away from the ridge 30R in the X-axis direction. ＋ This can prevent ions from migrating in the X-axis direction away from the ridge 30R, thereby preventing short circuits between the p-type and n-type semiconductor layers in the semiconductor laser device 200.

[0095] Furthermore, when the covering electrode 42 covers the edge 41e of the contact electrode 41 as in the semiconductor laser device 200 according to the present embodiment, the dimension W251 in the X-axis direction of the n-side electrode 251 may be smaller than the dimension W42 in the X-axis direction of the covering electrode 42. This can prevent the electric field formed between the contact electrode 41 and the n-side electrode 251 from having a component directed away from the ridge 30R in the X-axis direction. This can prevent the occurrence of a short circuit between the p-type semiconductor layer and the n-type semiconductor layer in the semiconductor laser device 200.

[0096] Although the above has described the dimensions of each electrode in the X-axis direction, the same can be said for the dimensions of each electrode in other directions parallel to the second main surface 11b of the substrate 11. Therefore, the dimension of the n-side electrode 251 in at least one direction parallel to the second main surface 11b may be smaller than the dimension of the contact electrode 41 or the covering electrode 42 in that at least one direction.

[0097] (Third Embodiment) A semiconductor laser device according to the third embodiment will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 200 according to the second embodiment in the configuration of the semiconductor laminate and the like, but is the same in other configurations. The semiconductor laser device according to this embodiment will be described below with reference to FIG. 22 , focusing on the differences from the semiconductor laser device 200 according to the second embodiment. FIG. 22 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 300 according to this embodiment. FIG. 22 shows a cross section perpendicular to the emission direction of laser light emitted by the semiconductor laser device 300. In FIG. 22 , some of the electric field lines Le formed when the semiconductor laser device 300 is energized are indicated by dashed arrows.

[0098] As shown in FIG. 22, the semiconductor laser device 300 according to this embodiment includes a substrate 11, a semiconductor stack 300S, a contact electrode 41, a covering electrode 342, an insulating layer 360, and an n-side electrode 351.

[0099] As shown in FIG. 22 , the semiconductor stack 300S according to this embodiment includes an n-type cladding layer 12, an n-type guide layer 13, an n-side guide layer 21, an active layer 22, a p-side guide layer 23, an electron barrier layer 31, a p-type cladding layer 332, and a contact layer 333. Similar to the semiconductor stack 100S according to the first embodiment, the semiconductor stack 300S includes a bottom surface 30Rb located at the upper end of the semiconductor stack 300S and a ridge 30R adjacent to the bottom surface 30Rb, protruding upward from the bottom surface 30Rb, and extending in the direction of emission of the laser light. The semiconductor stack 300S according to this embodiment further includes a protrusion 30P adjacent to the bottom surface 30Rb, protruding upward from the bottom surface 30Rb, and extending in the direction of emission of the laser light. The semiconductor stack 300S according to this embodiment includes two protrusions 30P. A ridge 30R is located between the two protruding portions 30P. A bottom surface 30Rb is located between the ridge 30R and the protruding portion 30P. The protruding portion 30P has a top surface 30Pu, which is the surface at the top end, and a side surface 30Ps, which is the surface located at the end in the X-axis direction. The ridge 30R and the protruding portion 30P are formed in the p-type cladding layer 332 and the contact layer 333. The top surface 30Pu is located in the contact layer 333.

[0100] In this embodiment, the edge 41 e of the contact electrode 41 is located between the ridge 30 R and the protruding portion 30 P, and the protruding portion 30 P protrudes upward beyond the edge 41 e of the contact electrode 41 .

[0101] In this embodiment, the semiconductor stack 300S has recesses 300T located at each end in the X-axis direction. The recesses 300T are portions recessed downward relative to the upper surface 30Pu of the protrusion 30P. In this embodiment, the lower ends of the recesses 300T are located in the n-type cladding layer 12.

[0102] The covering electrode 342 according to the present embodiment is disposed above the contact electrode 41, similar to the covering electrode 42 according to the first embodiment. In the present embodiment, the covering electrode 342 is disposed above the top surface 30Ru and side surface 30Rs of the ridge 30R, the bottom surface 30Rb, the side surface 30Ps of the protrusion 30P on the ridge 30R side, and a portion of the top surface 30Pu. In other words, the covering electrode 342 continuously covers from the top surface 30Pu of one protrusion 30P to the top surface 30Pu of the other protrusion 30P. The covering electrode 342 is also disposed above a portion of the insulating layer 360.

[0103] The insulating layer 360 according to this embodiment is an electrical insulating layer that covers the recess 300T of the semiconductor stack 300S. In this embodiment, the insulating layer 360 continuously covers the recess 300T, the protrusion 30P, and a part of the bottom surface 30Rb.

[0104] The effects of the semiconductor laser device 300 according to this embodiment will be described. As described above, in this embodiment, the edge 41e of the contact electrode 41 is located between the ridge 30R and the protrusion 30P, and the protrusion 30P protrudes upward from the edge 41e of the contact electrode 41. Here, as shown by the electric field lines Le in FIG. 22, there is no upward electric field component between the contact electrode 41 and the n-side electrode 351. Therefore, the Ag contained in the contact electrode 41 ＋ Ions are prevented from migrating to the upper surface 30Pu of the protrusion 30P and from migrating beyond the protrusion 30P to the side surface of the active layer 22. Therefore, it is possible to prevent short circuits from occurring between the p-type semiconductor layer and the n-type semiconductor layer in the semiconductor laser element 300.

[0105] In this embodiment, the dimension W351 in the X-axis direction of the n-side electrode 351 is larger than the dimension W41 in the X-axis direction of the contact electrode 41, but is smaller than the dimension W342 in the X-axis direction of the covering electrode 342. This makes it possible to prevent the formation of an electric field in a direction away from the ridge 30R in the X-axis direction. ＋ This can prevent ions from moving in a direction away from the ridge 30R.

[0106] Although the above has described the dimensions of each electrode in the X-axis direction, the same can be said for the dimensions of each electrode in other directions parallel to the second main surface 11b of the substrate 11. Therefore, the dimension of the n-side electrode 351 in at least one direction parallel to the second main surface 11b may be smaller than the dimension of the contact electrode 41 or the covering electrode 342 in that at least one direction.

[0107] (Fourth Embodiment) A semiconductor laser device according to the fourth embodiment will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 300 according to the third embodiment in the configuration of the n-side electrode, but is the same in other configurations. The semiconductor laser device according to this embodiment will be described below with reference to FIG. 23 , focusing on the differences from the semiconductor laser device 300 according to the third embodiment. FIG. 23 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 400 according to this embodiment. FIG. 23 shows a cross section perpendicular to the emission direction of laser light emitted by the semiconductor laser device 400. In FIG. 23 , some of the electric field lines Le formed when the semiconductor laser device 400 is energized are indicated by dashed arrows.

[0108] As shown in FIG. 23, the semiconductor laser device 400 according to this embodiment includes a substrate 11, a semiconductor stack 300S, a contact electrode 41, a covering electrode 342, an insulating layer 360, and an n-side electrode 451.

[0109] The n-side electrode 451 according to this embodiment is an electrode disposed on the second main surface 11b of the substrate 11. In this embodiment, the dimension W451 in the X-axis direction of the n-side electrode 451 is larger than the dimension W41 in the X-axis direction of the contact electrode 41 and the dimension W342 in the X-axis direction of the covering electrode 342.

[0110] 23, an electric field component is generated in a direction away from the ridge 30R in the X-axis direction. However, since the protrusion 30P is formed in the semiconductor laminate 300S, the Ag of the contact electrode 41 ＋In this embodiment, the edge 41e of the contact electrode 41 is covered with the covering electrode 342. Therefore, the Ag of the contact electrode 41 is prevented from moving in a direction away from the ridge 30R. ＋ This makes it possible to more reliably prevent ions from moving in a direction away from the ridge 30R.

[0111] Fifth Embodiment A semiconductor laser device according to a fifth embodiment will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 100 according to the first embodiment in the configuration of the contact electrodes, but is the same in other configurations. The semiconductor laser device according to this embodiment will be described below with reference to FIG. 24, focusing on the differences from the semiconductor laser device 100 according to the first embodiment. FIG. 24 is a schematic cross-sectional view showing the configuration in the vicinity of a contact electrode 541 of a semiconductor laser device 500 according to this embodiment. FIG. 24 shows a cross section perpendicular to the emission direction of laser light emitted by the semiconductor laser device 500.

[0112] As described above, the semiconductor laser device 500 according to this embodiment differs from the semiconductor laser device 100 according to the first embodiment in the configuration of the contact electrode 541, but is the same in other configurations.

[0113] The contact electrode 541 according to the present embodiment includes an Ag layer 541b made of Ag, and a contact metal layer 541a disposed between the Ag layer 541b and the upper surface 30Ru of the ridge 30R and in contact with the upper surface 30Ru of the ridge 30R. The contact metal layer 541a includes at least one of Ti, Al, Cr, Ni, Pd, and Pt, and the thickness of the contact metal layer 541a is 1 nm or less.

[0114] In this way, since the contact electrode 541 has the contact metal layer 541a, it is possible to reduce the contact resistance between the contact electrode 541 and the upper surface 30Ru of the ridge 30R. Furthermore, since the thickness of the contact metal layer 541a is 1 nm or less, it is possible to reduce the waveguide loss due to the contact metal layer 541a.

[0115] Sixth Embodiment A semiconductor laser device according to the sixth embodiment will be described. The semiconductor laser device according to the sixth embodiment differs from the semiconductor laser device 100 according to the first embodiment in the configuration of the contact electrodes, but is otherwise identical in configuration. The semiconductor laser device according to the sixth embodiment will be described below with reference to FIGS. 25 and 26 , focusing on the differences from the semiconductor laser device 100 according to the first embodiment. FIG. 25 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 600 according to the sixth embodiment. FIG. 26 is a schematic cross-sectional view showing the configuration of a contact electrode 641 of the semiconductor laser device 600 according to the sixth embodiment. FIG. 26 shows a cross-section of a portion of the contact electrode 641. FIGS. 25 and 26 show cross-sections perpendicular to the emission direction of laser light emitted by the semiconductor laser device 600.

[0116] As shown in FIG. 25, the semiconductor laser device 600 according to this embodiment includes a substrate 11, a semiconductor laminate 100S, a contact electrode 641, a covering electrode 42, an insulating layer 60, and an n-side electrode 51.

[0117] 26, the contact electrode 641 according to this embodiment has a light-transmitting conductive film 641a and a reflective metal film 641b. Also in this embodiment, the dimension W51 in the X-axis direction of the n-side electrode 51 is smaller than the dimension W641 in the X-axis direction of the contact electrode 641.

[0118] The translucent conductive film 641a is a translucent conductive film disposed between the reflective metal film 641b and the semiconductor stack 100S. The translucent conductive film 641a contacts the top surface 30Ru and the side surface 30Rs of the ridge 30R and at least a part of the bottom surface 30Rb. In this embodiment, the translucent conductive film 641a includes at least one of ITO, GZO, AZO, IGZO, and nickel oxide, for example. The film thickness of the translucent conductive film 641a is, for example, 0.1 nm or more and 400 nm or less.

[0119] The reflective metal film 641b is a metal layer disposed above the translucent conductive film 641a. In the present embodiment, the reflective metal film 641b covers the entire upper surface of the translucent conductive film 641a. The main component of the reflective metal film 641b may be Ag.

[0120] In this embodiment, similarly to the first embodiment, the covering electrode 42 covers the edge 641 e of the contact electrode 641 .

[0121] The semiconductor laser device 600 according to this embodiment also exhibits the same effects as those of embodiment 1. Here, the effect of reflecting spontaneous emission light by the contact electrode 641 of the semiconductor laser device 600 according to this embodiment will be described with reference to FIG.

[0122] FIG. 27 is a diagram showing the relationship between the film thickness of the translucent conductive film 641a and the reflectance of a stack including the translucent conductive film 641a and the reflective metal film 641b for light with a wavelength of 380 nm. A stack in which the translucent conductive film 641a and the reflective metal film 641b are stacked in this order on a semiconductor layer made of AlGaN is used as a model for calculating the reflectance shown in FIG. 27. The reflectance shown in FIG. 27 is calculated based on the complex refractive index of the semiconductor layer, the complex refractive index and film thickness of the translucent conductive film 641a, and the complex refractive index and film thickness of the reflective metal film 641b. In calculating the reflectance, the complex refractive index of ITO is used as the complex refractive index of the translucent conductive film 641a. Moreover, the complex refractive index of each of Ag, Cu, and Au is used as the complex refractive index of the reflective metal film 641b.

[0123] 27, when the reflective metal film 641b is made of Ag, the reflectance can be particularly increased. Therefore, by making the reflective metal film 641b mainly composed of Ag, the reflectance of the contact electrode 641 for spontaneous emission light can be increased.

[0124] 27 also shows that the reflectance can be adjusted by adjusting the film thickness of the translucent conductive film 641a. For example, when the reflective metal film 641b is made of Ag, the reflectance of the stacked body becomes 80% or more by setting the film thickness of the translucent conductive film 641a to 15 nm or less. Furthermore, the reflectance of the stacked body becomes approximately 72% by setting the film thickness of the translucent conductive film 641a to approximately 95 nm.

[0125] In this way, the contact electrode 641 having the transparent conductive film 641a and the reflective metal film 641b can achieve a reflectivity for spontaneous emission light that is comparable to that of the contact electrode 41 made of Ag according to the first embodiment. Therefore, by increasing the proportion of spontaneous emission light incident on the contact electrode 641 that is reflected by the contact electrode 641, the amount of spontaneous emission light reabsorbed in the active layer 22 can be increased. This makes it possible to increase the quantum efficiency of the semiconductor laser device 600. Therefore, the efficiency of the semiconductor laser device 600 can be improved.

[0126] Furthermore, for example, if the translucent conductive film 641a is made of ITO, the surface of the Al-containing semiconductor layer is oxidized when the translucent conductive film 641a is formed on the semiconductor stack 100S. As a result, the electrical resistance between the p-type cladding layer 32, which is an Al-containing semiconductor layer, and the translucent conductive film 641a increases. Therefore, it is possible to further suppress the flow of current from the translucent conductive film 641a to the p-type cladding layer 32 exposed on the side surface of the ridge 30R.

[0127] Seventh Embodiment A semiconductor laser device according to a seventh embodiment will be described. The semiconductor laser device according to this embodiment differs from the semiconductor laser device 100 according to the sixth embodiment in the configurations of the insulating layer and the covering electrode, but is the same in other configurations. The semiconductor laser device according to this embodiment will be described below with reference to FIG. 28 , focusing on the differences from the semiconductor laser device 600 according to the sixth embodiment. FIG. 28 is a schematic cross-sectional view showing the overall configuration of a semiconductor laser device 700 according to this embodiment. FIG. 28 shows a cross section perpendicular to the emission direction of laser light emitted by the semiconductor laser device 700.

[0128] As shown in FIG. 28, the semiconductor laser device 700 according to this embodiment includes a substrate 11, a semiconductor stack 100S, a contact electrode 641, a covering electrode 742, an insulating layer 760, and an n-side electrode 51.

[0129] The insulating layer 760 according to this embodiment continuously covers the area from the bottom surface 30Rb to the upper surface of the contact electrode 641. The insulating layer 760 continuously covers the recess 100T, the bottom surface 30Rb, the side surface 30Rs of the ridge 30R, and a portion of the upper surface 30Ru of the ridge 30R. The insulating layer 760 covers a portion of the bottom surface 30Rb, the side surface 30Rs, and a portion of the upper surface 30Ru via the contact electrode 641. In this embodiment, the insulating layer 760 extends in the Y-axis direction (i.e., the emission direction of the laser light) above the end of the upper surface 30Ru in the X-axis direction (i.e., the width direction of the ridge 30R). In this manner, an opening 760a is formed in the insulating layer 760 at a position corresponding to the upper surface 30Ru. The opening 760a may be a slit extending along the ridge 30R. The opening 760a of the insulating layer 760 may be located above the upper surface 30Ru.

[0130] At least a portion of the insulating layer 760 is disposed between the contact electrode 641 and the covering electrode 742. More specifically, the insulating layer 760 is disposed between the contact electrode 641 and the covering electrode 742 at a position facing a portion of the bottom surface 30Rb, a portion of the side surface 30Rs, and a portion of the top surface 30Ru.

[0131] The covering electrode 742 according to the present embodiment differs from the covering electrode 42 according to the first embodiment in that it is disposed above the insulating layer 760. In the present embodiment, as in the first embodiment, the covering electrode 742 covers the edge 641e of the contact electrode 641. Also in the present embodiment, the dimension W51 in the X-axis direction of the n-side electrode 51 is smaller than the dimension W742 in the X-axis direction of the covering electrode 742.

[0132] The semiconductor laser device 700 according to this embodiment also provides the same effects as those of the semiconductor laser device 600 according to the sixth embodiment.

[0133] Furthermore, in this embodiment, the insulating layer 760 covers the upper surface of the semiconductor laminate 100S except for a portion of the upper surface 30Ru of the ridge 30R (i.e., the upper surface of the contact layer 33), thereby further preventing current from flowing outside the ridge 30R.

[0134] In this embodiment, the insulating layer 760 extends in the Y-axis direction above the end of the upper surface 30Ru in the X-axis direction, thereby preventing current from flowing to the end of the upper surface 30Ru in the X-axis direction, thereby further preventing current from flowing outside the ridge 30R.

[0135] Furthermore, in this embodiment, the opening 760a of the insulating layer 760 is located above the upper surface 30Ru of the ridge 30R, so that the current flowing to the opening 760a via the covering electrode 42 can be concentrated within the ridge 30R.

[0136] (Modifications, etc.) Although the semiconductor laser device and the manufacturing method thereof according to the present disclosure have been described above based on the respective embodiments, the present disclosure is not limited to the above-described respective embodiments.

[0137] For example, although the semiconductor laminate of the semiconductor laser element according to each of the above embodiments includes a GaN-based semiconductor, the configuration of the semiconductor laminate is not limited to this. For example, the semiconductor laminate may include a semiconductor other than a GaN-based semiconductor, such as a GaAs-based semiconductor. Furthermore, the oscillation wavelength of the semiconductor laser element may be in a wavelength band other than 350 nm or more and 420 nm or less.

[0138] Here, the effect of reflecting spontaneous emission light by the contact electrode 641 according to the sixth embodiment when the oscillation wavelength of the semiconductor laser element is in a wavelength band other than 350 nm or more and 420 nm or less will be described with reference to FIGS. 29 to 31.

[0139] 29, 30, and 31 are diagrams showing the relationship between the film thickness of the translucent conductive film 641a and the reflectivity of a stack including the translucent conductive film 641a and the reflective metal film 641b for light with wavelengths of 450 nm, 630 nm, and 980 nm, respectively. A stack in which the translucent conductive film 641a and the reflective metal film 641b are stacked in this order on a semiconductor layer made of AlGaN is used as a model for calculating the reflectivity shown in FIG. 30 and 31. A stack in which the translucent conductive film 641a and the reflective metal film 641b are stacked in this order on a semiconductor layer made of AlGaAs is used as a model for calculating the reflectivity shown in FIG. 29 to 31. The results of calculating the reflectivity using such a model and the same calculation method as in FIG. 27 are shown in FIGS. 29 to 31.

[0140] 29 to 31, when the reflective metal film 641b is made of Ag, the reflectance can be particularly increased. Therefore, by making the reflective metal film 641b mainly composed of Ag, the reflectance of the contact electrode 641 for spontaneously emitted light can be increased when the wavelength is 450 nm or more and 980 nm or less.

[0141] Furthermore, it can be seen from FIGS. 29 to 31 that the reflectance can be adjusted by adjusting the film thickness of the light-transmitting conductive film 641a.

[0142] 29, when the wavelength is 450 nm and the reflective metal film 641b is made of Ag, the reflectance of the stacked body becomes 80% or more by setting the thickness of the translucent conductive film 641a to 40 nm or less. Also, by setting the thickness of the translucent conductive film 641a to about 120 nm, the reflectance of the stacked body becomes about 70%.

[0143] 30 , when the wavelength is 630 nm and the reflective metal film 641b is made of Ag, the reflectance of the stacked body becomes 80% or more by setting the film thickness of the translucent conductive film 641a to 115 nm or less. Also, when the film thickness of the translucent conductive film 641a is set to about 165 nm, the reflectance of the stacked body becomes 80% or more.

[0144] 31 , when the wavelength is 980 nm and the reflective metal film 641b is made of Ag, the reflectance of the stack is 80% or more by setting the thickness of the translucent conductive film 641a to 155 nm or less. Also, when the thickness of the translucent conductive film 641a is set to about 375 nm, the reflectance of the stack is about 70%.

[0145] Thus, even in a wavelength band where the oscillation wavelength is 380 nm or more, the contact electrode 641 having the light-transmitting conductive film 641a and the reflective metal film 641b can achieve a reflectivity for spontaneous emission light that is comparable to that of the contact electrode 41 made of Ag according to the first embodiment. Therefore, by increasing the proportion of spontaneous emission light incident on the contact electrode 641 that is reflected by the contact electrode 641, the amount of spontaneous emission light reabsorbed in the active layer 22 can be increased. This makes it possible to increase the quantum efficiency of the semiconductor laser device 600. Therefore, the efficiency of the semiconductor laser device 600 can be improved.

[0146] Furthermore, in the semiconductor laser elements according to the modifications of the sixth and seventh embodiments, the contact electrode 41 does not necessarily contain Ag. That is, the semiconductor laser element according to this modification emits laser light and includes a substrate 11, a semiconductor stack 100S disposed above the substrate 11 and including a GaN-based semiconductor, and a contact electrode 641 in contact with the semiconductor stack 100S. The semiconductor stack 100S includes an n-type semiconductor layer disposed above the substrate 11, an active layer 22 disposed above the n-type semiconductor layer, and a p-type semiconductor layer disposed above the active layer 22. The semiconductor stack 100S also includes a bottom surface 30Rb located at the upper end of the semiconductor stack 100S and above the active layer 22, and a ridge 30R adjacent to the bottom surface 30Rb, protruding upward from the bottom surface 30Rb, and extending in the emission direction of the laser light. The contact electrode 641 is in contact with the top surface 30Ru and side surface 30Rs of the ridge 30R, and at least a portion of the bottom surface 30Rb. The electrical contact resistance between the side surface 30Rs of the ridge 30R and the contact electrode 641 is higher than the electrical contact resistance between the top surface 30Ru of the ridge 30R and the contact electrode 641. The contact electrode 641 has a reflective metal film 641b and a translucent conductive film 641a disposed between the semiconductor stack 100S and the reflective metal film 641b. In this modification, the main component of the reflective metal film 641b may be, for example, Ag, Cu, or Au.

[0147] Furthermore, although the semiconductor laser device according to each of the above embodiments includes a covering electrode and an insulating layer, it does not necessarily have to include these components.

[0148] Furthermore, although the semiconductor laminate of the semiconductor laser device according to each of the above embodiments includes an n-type guide layer, an n-side guide layer, a p-side guide layer, and an electron barrier layer, it does not necessarily have to include these components.

[0149] 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.

[0150] For example, the contact electrode 541 according to the fifth embodiment may be used as a contact electrode according to other embodiments.

[0151] Furthermore, the contact electrode 641 according to the sixth embodiment may be used as a contact electrode according to other embodiments.

[0152] Furthermore, the configurations of the insulating layer 760 and the covering electrode 742 according to the seventh embodiment may be applied to the insulating layer and the covering electrode according to the other embodiments.

[0153] The semiconductor laser device of the present disclosure can be applied to light sources for various purposes, for example, as a high-output and highly efficient light source.

[0154] REFERENCE SIGNS LIST 11 substrate 11a first main surface 11b second main surface 12 n-type cladding layer 13 n-type guide layer 21 n-side guide layer 22 active layer 22a, 22c, 22e barrier layer 22b, 22d well layer 23 p-side guide layer 30P protrusion 30Ps, 30Rs side surface 30Pu, 30Ru top surface 30R ridge 30Rb bottom surface 31 electron barrier layer 32, 332, 932 p-type cladding layer 33, 333 contact layer 41, 541, 641, 941 contact electrode 41a, 41b, 942a, 942b electrode 41e, 641e edge 42, 342, 742 covering electrode 51, 251, 351, 451 n-side electrode 60, 360, 760, 960, 961 insulating layer 100, 200, 300, 400, 500, 600, 700, 900 semiconductor laser element 100S, 300S semiconductor laminate 100T, 300T recess 541a contact metal layer 541b Ag layer 641a light-transmitting conductive film 641b reflective metal film 760a opening

Claims

1. A semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate that is disposed above the substrate and includes a GaN-based semiconductor; and a contact electrode that is in contact with the semiconductor laminate and includes Ag, wherein the semiconductor laminate has an n-type semiconductor layer that is disposed above the substrate, an active layer that is disposed above the n-type semiconductor layer, and a p-type semiconductor layer that is disposed above the active layer, and has a bottom surface that is located at an upper end of the semiconductor laminate and is positioned above the active layer, and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, and the contact electrode is in contact with an upper surface and side surfaces of the ridge and at least a part of the bottom surface.

2. A semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate disposed above the substrate; a contact electrode that is in contact with the semiconductor laminate and contains Ag; and a covering electrode that is disposed above the contact electrode and has a melting point higher than that of the contact electrode, wherein the semiconductor laminate has: an n-type semiconductor layer disposed above the substrate; an active layer disposed above the n-type semiconductor layer; and a p-type semiconductor layer disposed above the active layer; and wherein the semiconductor laminate has: a bottom surface that is located at the upper end of the semiconductor laminate and is positioned above the active layer; and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, wherein the contact electrode is in contact with an upper surface and side surfaces of the ridge and at least a part of the bottom surface, and the covering electrode covers an edge of the contact electrode.

3. A semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate disposed above the substrate; a contact electrode containing Ag and in contact with the semiconductor laminate; and an n-side electrode disposed on a second main surface of the substrate on the back side of a first main surface on which the semiconductor laminate is disposed; the semiconductor laminate has an n-type semiconductor layer disposed above the substrate, an active layer disposed above the n-type semiconductor layer, and a p-type semiconductor layer disposed above the active layer, and has a bottom surface located at an upper end of the semiconductor laminate and positioned above the active layer, and a ridge adjacent to the bottom surface, protruding upward from the bottom surface, and extending in the emission direction of the laser light, the contact electrode being in contact with an upper surface and a side surface of the ridge and with at least a part of the bottom surface, and a dimension of the n-side electrode in at least one direction parallel to the second main surface is smaller than a dimension of the contact electrode in the at least one direction.

4. A semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate disposed above the substrate; a contact electrode containing Ag and in contact with the semiconductor laminate; and an n-side electrode disposed on a second main surface of the substrate on the back side of a first main surface on which the semiconductor laminate is disposed; the semiconductor laminate has an n-type semiconductor layer disposed above the substrate, an active layer disposed above the n-type semiconductor layer, and a p-type semiconductor layer disposed above the active layer, and has: a bottom surface located at the upper end of the semiconductor laminate and positioned above the active layer; a ridge adjacent to the bottom surface, protruding upward from the bottom surface, and extending in the emission direction of the laser light; and a protrusion adjacent to the bottom surface, protruding upward from the bottom surface, and extending in the emission direction of the laser light; the contact electrode is in contact with an upper surface and side surfaces of the ridge and at least a part of the bottom surface; an edge of the contact electrode is located between the ridge and the protrusion, and the protrusion protrudes upward beyond the edge of the contact electrode. Semiconductor laser element.

5. A semiconductor laser element that emits laser light, comprising: a substrate; a semiconductor laminate that is disposed above the substrate and contains a GaN-based semiconductor; and a contact electrode that is in contact with the semiconductor laminate and contains Ag, wherein the semiconductor laminate has an n-type semiconductor layer that is disposed above the substrate, an active layer that is disposed above the n-type semiconductor layer, and a p-type semiconductor layer that is disposed above the active layer, and has a bottom surface that is located at an upper end of the semiconductor laminate and is located above the active layer, and a ridge that is adjacent to the bottom surface, protrudes upward from the bottom surface, and extends in the emission direction of the laser light, wherein the contact electrode is in contact with an upper surface and side surfaces of the ridge and with at least a part of the bottom surface, and an electrical contact resistance between the side surfaces of the ridge and the contact electrode is higher than the electrical contact resistance between the upper surface of the ridge and the contact electrode.

6. A semiconductor laser device according to any one of claims 1, 3 to 5, further comprising a covering electrode disposed above said contact electrode and having a melting point higher than that of said contact electrode, said covering electrode covering the edge of said contact electrode.

7. The semiconductor laser device according to any one of claims 1 to 6, wherein the active layer has one or more well layers, and the distance between the top surface of the ridge and the well layer closest to the contact electrode among the one or more well layers is 550 nm or less.

8. The semiconductor laser device according to any one of claims 1 to 7, wherein the width of the ridge is 100 µm or less.

9. The semiconductor laser device according to any one of claims 1 to 8, wherein the contact electrode disposed on the upper surface of the ridge has a thickness of 50 nm or more.

10. The semiconductor laser device according to any one of claims 1 to 9, wherein the contact electrode comprises: an Ag layer made of Ag; and a contact metal layer disposed between the Ag layer and the upper surface of the ridge and in contact with the upper surface of the ridge; the contact metal layer contains at least one of Ti, Al, Cr, Ni, Pd, and Pt; and the thickness of the contact metal layer is 1 nm or less.

11. The semiconductor laser device according to any one of claims 1 to 9, wherein the contact electrode is made of Ag.

12. The semiconductor laser device according to any one of claims 1 to 11, wherein the oscillation wavelength of the semiconductor laser device is 350 nm or more and 420 nm or less.

13. A method for manufacturing a semiconductor laser element that emits laser light, comprising: a semiconductor laminate formation step of forming a semiconductor laminate above a substrate; and a contact electrode formation step of forming a contact electrode containing Ag in contact with the semiconductor laminate, wherein the semiconductor laminate formation step includes an etching step of forming, by dry etching, a bottom surface located at the upper end of the semiconductor laminate, and a ridge adjacent to the bottom surface, protruding upward from the bottom surface, and extending in the emission direction of the laser light, wherein the contact electrode is in contact with the top surface and side surfaces of the ridge and at least a part of the bottom surface.

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