Semiconductor laser device and method for manufacturing the same

Abstract

A semiconductor laser device (1) comprises an N-type cladding layer (20), an active layer (40), and a P-type cladding layer (60). The active layer (40) includes a well layer (41), a P-side first barrier layer (43a) disposed over the well layer (41), and a P-side second barrier layer (43b) disposed over the P-side first barrier layer (43a). The P-side second barrier layer (43b) has an Al composition ratio higher than an Al composition ratio of the P-side first barrier layer (43a). The P-side second barrier layer (43b) has a bandgap energy greater than a bandgap energy of the P-side first barrier layer (43a). The semiconductor laser device (1) has a window mirror structure in which a bandgap energy of the well layer (41) in the vicinity of a front end face (1a) is greater than a bandgap energy of the well layer (41) in a central portion of a resonator in the length direction thereof.

Description

Technical Field

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

Background Art

[0002] Semiconductor laser elements are attracting attention as light sources for various applications, such as light sources for image display devices such as displays and projectors, light sources for in-vehicle headlamps, light sources for industrial and household lighting, or light sources for industrial equipment such as laser welding devices, thin film annealing devices, and laser processing devices.

[0003] Among them, semiconductor laser elements used as light sources for projectors, laser processing devices, or laser welding devices are required to have high output characteristics with an optical output significantly exceeding 1 watt. For example, semiconductor laser elements in the wavelength 915 nm band used as light sources for laser welding devices are required to have high output characteristics of 25 W or more.

[0004] A semiconductor laser element includes, for example, a substrate, an N-type cladding layer disposed above the substrate, an active layer disposed above the N-type cladding layer and having a well layer and a barrier layer, and a P-type cladding layer disposed above the active layer (for example, Patent Document 1).

[0005] In semiconductor laser elements with an oscillation laser wavelength of 900 nm to 980 nm, an active layer having a quantum well structure with an InGaAs well layer and an AlGaAs barrier layer is widely used.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In order to increase the output power of a semiconductor laser element to the watt level, it is conceivable to improve the thermal saturation level or the COD (Catastrophic Optical Damage) level.

[0008] However, if a window region is formed in the end face portion of the semiconductor laser element to improve the COD level, and further, the well layer of the active layer is thickened to improve the thermal saturation level, the temperature characteristics deteriorate, the long-term reliability decreases, or the effect of improving the COD level is inhibited.

[0009] The present disclosure solves such problems, and in a semiconductor laser device having an end face window structure, even if the well layer is thickened, it suppresses deterioration of temperature characteristics and reduction of long-term reliability, and suppresses inhibition of the effect of improving the COD level. An object is to provide a semiconductor laser device and a method for manufacturing the same.

Means for Solving the Problems

[0010] In order to solve the above problems, one aspect of the semiconductor laser device according to the present disclosure is a semiconductor laser device that emits laser light, including a substrate, an N-type cladding layer disposed above the substrate, an active layer disposed above the N-type cladding layer, and a P-type cladding layer disposed above the active layer. The active layer has a well layer, a P-side first barrier layer disposed above the well layer, and a P-side second barrier layer disposed above the P-side first barrier layer. The Al composition ratio of the P-side second barrier layer is higher than the Al composition ratio of the P-side first barrier layer, and the bandgap energy of the P-side second barrier layer is larger than the bandgap energy of the P-side first barrier layer. The semiconductor laser device has an end face window structure in which the bandgap energy of the well layer near the end face from which the laser light is emitted is larger than the bandgap energy of the well layer at the center in the resonator length direction.

Effects of the Invention

[0011] According to the present disclosure, in a semiconductor laser device having an end face window structure, even if the well layer is thickened, it is possible to suppress the deterioration of temperature characteristics and the decrease in long-term reliability, and to suppress the inhibition of the effect of improving the COD level.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0013] (Process for obtaining an aspect of the present disclosure) First, prior to the description of the embodiment of the present disclosure, the process for obtaining an aspect of the present disclosure will be described.

[0014] In order to increase the output power of the semiconductor laser element to the watt level, it is conceivable to improve the thermal saturation level, improve the COD level, or reduce the thermal resistance by increasing the resonator length.

[0015] Specifically, in order to improve the thermal saturation level, it is conceivable to increase the light confinement coefficient in the well layer by thickening the well layer to reduce the oscillation threshold, increase the Al composition of the barrier layer made of AlGaAs to increase the conduction band offset (ΔEc) to increase the potential barrier and suppress the generation of electron overflow, or reduce the operating carrier density by increasing the resonator length to increase the resonator length.

[0016] In addition, in order to improve the COD level, it is conceivable to form a window region in the end face portion on the front end face side which is the light emitting end face of the laser light, and give the semiconductor laser element an end face window structure. The end face window structure can be formed by disordering the atomic arrangement of the barrier layer and the well layer in the end face portion by means of hole diffusion, impurity diffusion, ion implantation or the like.

[0017] However, if the well layer is thickened in an attempt to increase the optical confinement factor in the well layer, it becomes difficult to disorder the atomic arrangements of the barrier layer and the well layer, and it becomes difficult to form the window region.

[0018] Therefore, it is conceivable to promote the interatomic exchange between the well layer and the barrier layer to disorder the atomic arrangement by increasing the annealing temperature when forming the window region.

[0019] However, if the annealing temperature when forming the window region is increased, atomic exchange will also occur between the well layer and the barrier layer in the active layer in the gain section where the formation of the window region is not intended. As a result, the bandgap energy (Eg) in the gain section increases, the leakage current in the gain section increases and the temperature characteristics deteriorate, or the holes introduced during crystal growth or the holes on the surface of the growth layer due to the dangling bonds on the surface of the growth layer are likely to diffuse, resulting in a decrease in the oscillation wavelength controllability and a decrease in the long-term reliability. Specifically, when the bandgap energy increases, the transition wavelength of the quantum well layer in the gain section shifts to a shorter wavelength.

[0020] Furthermore, if the annealing temperature when forming the window region is increased, the transition region formed at the boundary between the region where the formation of the window region is intended (window section) and the region where the formation of the window region is not intended (gain section) is likely to become longer. As a result, the effect of improving the COD level by the window region is inhibited by the light absorption in the transition region.

[0021] Thus, when a window region is formed on the end face portion of the semiconductor laser element to improve the COD level, and further, the well layer of the active layer is thickened to improve the thermal saturation level, there are problems such as deterioration of the temperature characteristics, a decrease in the long-term reliability, and inhibition of the effect of improving the COD level.

[0022] The present disclosure has been made to solve such problems, and in a semiconductor laser device having an end face window structure, even if the well layer is thickened, it is possible to suppress deterioration of temperature characteristics and reduction of long-term reliability, and to suppress inhibition of the effect of improving the COD level. An object is to provide a semiconductor laser device and a method for manufacturing the same.

[0023] In addition, when the resonator length is increased to reduce the thermal resistance, the semiconductor laser element is likely to be affected by a change in the band structure due to mounting strain when the semiconductor laser element is mounted, so there is also a problem that the polarization ratio is likely to decrease.

[0024] Therefore, another object of the present disclosure is to provide a semiconductor laser device and a method for manufacturing the same that can suppress a decrease in the polarization ratio even when the resonator length is increased.

[0025] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below shows a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, and the arrangement positions and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0026] In addition, each drawing is a schematic diagram and is not necessarily drawn precisely. Therefore, the scales and the like in each drawing do not necessarily match. In each drawing, the same reference numerals are given to substantially the same configurations, and overlapping descriptions are omitted or simplified.

[0027] In this specification, the terms “upper” and “lower” do not indicate the upward direction (vertically upward) and the downward direction (vertically downward) in an absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. Further, the terms “upper” and “lower” are applied not only when two components are arranged at intervals and another component exists between the two components, but also when the two components are arranged in contact with each other.

[0028] (Embodiment) [Layer Structure of Semiconductor Laser Device] First, the layer structure of the semiconductor laser device 1 according to the embodiment will be described with reference to FIGS. 1, 2A, 2B, and 2C. FIG. 1 is a top view of the semiconductor laser device 1 according to the embodiment. FIG. 2A is a cross-sectional view of the semiconductor laser device 1 taken along the line IIA-IIA in FIG. 1, FIG. 2B is a cross-sectional view of the semiconductor laser device 1 taken along the line IIB-IIB in FIG. 1, and FIG. 2C is a cross-sectional view of the semiconductor laser device 1 taken along the line IIC-IIC in FIG. 1. Note that FIG. 2A shows a cross-section of the gain section of the semiconductor laser device 1, and FIG. 2B shows a cross-section of the end face portion on the front end face 1a side of the semiconductor laser device 1.

[0029] The semiconductor laser device 1 is a semiconductor laser element that emits laser light, and includes a substrate and a semiconductor laminate (semiconductor laminate structure) composed of a plurality of semiconductor layers disposed above the substrate. Specifically, as shown in FIGS. 1 to 2C, the semiconductor laser device 1 includes an N-type clad layer 20 disposed above the substrate 10, an active layer 40 disposed above the N-type clad layer 20, and a P-type clad layer 60 disposed above the active layer 40 as semiconductor layers constituting the semiconductor laminate.

[0030] The semiconductor laser device 1 further includes an N-type guide layer 30 disposed between the N-type clad layer 20 and the active layer 40, a P-type guide layer 50 disposed between the active layer 40 and the P-type clad layer 60, a P-type contact layer 70 disposed above the P-type clad layer 60, and a current blocking layer 80 as semiconductor layers constituting the semiconductor laminate.

[0031] The semiconductor laser device 1 further includes a P-side electrode 91 and an N-side electrode 92 connected to the semiconductor laminate, and an insulating film 100 covering at least a part of the semiconductor laminate.

[0032] The semiconductor laser device 1 according to this embodiment is a semiconductor laser element that emits laser light with a wavelength in the range of 900 nm to 980 nm. For example, the semiconductor laminate in the semiconductor laser device 1 is composed of a III-V group compound semiconductor made of an AlGaInAs-based material. As an example, the semiconductor laser device 1 emits laser light in the 915 nm band. Further, although details will be described later, the semiconductor laser device 1 has an end face window structure in which a window region 120 is formed in the semiconductor laminate.

[0033] Hereinafter, each component of the semiconductor laser device 1 according to this embodiment will be described in detail.

[0034] The substrate 10 is a planar substrate whose main surface is uniformly flat. The substrate 10 is a semiconductor substrate such as a GaAs substrate or an insulating substrate such as a sapphire substrate. In this embodiment, the substrate 10 is an n-type GaAs substrate. Note that a buffer layer may be formed between the substrate 10 and the N-type clad layer 20. The buffer layer is, for example, an n-type GaAs layer and is laminated on the substrate 10.

[0035] The N-type clad layer 20 is formed above the substrate 10. When a buffer layer is formed on the substrate 10, the N-type clad layer 20 is formed on the buffer layer. The N-type clad layer 20 is an N-type semiconductor layer in which impurities are intentionally doped, and is, for example, an n-type AlGaAs layer. The impurity doped into the N-type clad layer 20 is, for example, silicon (Si).

[0036] The N-type guide layer 30 is disposed between the N-type clad layer 20 and the N-side second barrier layer 42b of the active layer 40. Specifically, the N-type guide layer 30 is formed on the N-type clad layer 20. The N-type guide layer 30 is an N-type semiconductor layer in which impurities are intentionally doped, and is, for example, an n-type AlGaAs layer. The impurity doped into the N-type guide layer 30 is, for example, silicon (Si).

[0037] The active layer 40 is a semiconductor layer including a light-emitting layer, and is located between the N-type clad layer 20 and the P-type clad layer 60. Specifically, the active layer 40 is located between the N-type guide layer 30 and the P-type guide layer 50. In the present embodiment, the active layer 40 is formed on the N-type guide layer 30.

[0038] The active layer 40 includes a well layer 41, an N-side first barrier layer 42a disposed below the well layer 41, an N-side second barrier layer 42b disposed below the N-side first barrier layer 42a, a P-side first barrier layer 43a disposed above the well layer 41, and a P-side second barrier layer 43b disposed above the P-side first barrier layer 43a.

[0039] The well layer 41 is located between the N-side first barrier layer 42a and the P-side first barrier layer 43a, and is in contact with the N-side first barrier layer 42a and the P-side first barrier layer 43a. Specifically, the well layer 41 is formed on the N-side first barrier layer 42a.

[0040] The well layer 41 (quantum well layer) has, for example, a single quantum well structure including a single quantum well layer. The well layer 41 is, for example, an undoped GaInAs layer. Note that the well layer 41 is not limited to a single quantum well structure, and may have a multiple quantum well structure including a plurality of quantum well layers. In the present embodiment, the thickness of the well layer 41 is increased, and is, for example, 6 nm or more.

[0041] The N-side first barrier layer 42a and the N-side second barrier layer 42b are located between the N-type clad layer 20 and the well layer 41, and are arranged in this order from the well layer 41 toward the N-type clad layer 20. Specifically, the N-side first barrier layer 42a and the N-side second barrier layer 42b are located between the N-type guide layer 30 and the well layer 41.

[0042] The N-side first barrier layer 42a is formed on the N-side second barrier layer 42b. In the present embodiment, the N-side first barrier layer 42a is an N-type semiconductor layer intentionally doped with impurities, for example, an n-type AlGaAs layer. The impurities doped into the N-side first barrier layer 42a are, for example, silicon (Si).

[0043] The N-side first barrier layer 42a may have an undoped region where no impurities are doped, in addition to the doped region doped with impurities. In this case, the N-side first barrier layer 42a preferably has an undoped region in the region closer to the well layer 41 and a doped region on the side farther from the well layer 41. The film thickness of the undoped region of the N-side first barrier layer 42a is preferably 5 nm or more. Doping impurities into the N-side first barrier layer 42a near the well layer 41 reduces the series resistance of the semiconductor laser device, but free carrier loss occurs and the waveguide loss increases. If the film thickness of the undoped region becomes too thick, the series resistance of the semiconductor laser device increases. Therefore, in order to suppress the increase in the series resistance and suppress the increase in the free carrier loss due to the doping of impurities, the film thickness of the undoped region may be 5 nm or more and 40 nm or less. When the doping concentration of the impurities in the N-type guide layer 30 changes so as to gradually increase in the direction away from the well layer 41, the increase in the waveguide loss can be suppressed even if the film thickness of this undoped region is 20 nm or less at maximum.

[0044] The N-side second barrier layer 42b located under the N-side first barrier layer 42a is formed on the N-type guide layer 30. In the present embodiment, the N-side second barrier layer 42b is an N-type semiconductor layer intentionally doped with impurities, for example, an n-type AlGaAs layer. The impurities doped into the N-side second barrier layer 42b are, for example, silicon (Si).

[0045] The P-side first barrier layer 43a and the P-side second barrier layer 43b are located between the well layer 41 and the P-type clad layer 60, and are arranged in this order from the well layer 41 toward the P-type clad layer 60. Specifically, the P-side first barrier layer 43a and the P-side second barrier layer 43b are located between the well layer 41 and the P-type guide layer 50.

[0046] The P-side first barrier layer 43a is formed on the well layer 41. In the present embodiment, the P-side first barrier layer 43a is a P-type semiconductor layer in which impurities are intentionally doped, for example, a P-type AlGaAs layer. The impurity doped into the P-side first barrier layer 43a is, for example, carbon (C).

[0047] The P-side first barrier layer 43a may have an undoped region where no impurities are doped, in addition to the doped region where impurities are doped. In this case, the P-side first barrier layer 43a preferably has an undoped region in the region closer to the well layer 41 and a doped region on the side farther from the well layer 41. The film thickness of the undoped region of the P-side first barrier layer 43a is preferably 5 nm or more. Doping impurities into the P-side first barrier layer 43a near the well layer 41 reduces the series resistance of the semiconductor laser device, but free carrier loss occurs and the waveguide loss increases. If the film thickness of the undoped region becomes too thick, the series resistance of the semiconductor laser device increases. Therefore, in order to suppress the increase in the series resistance and suppress the increase in the free carrier loss due to the doping of impurities, the film thickness of the undoped region may be 5 nm or more and 40 nm or less. When the doping concentration of the impurities in the P-type guide layer changes so as to gradually increase in the direction away from the well layer 41, even if the film thickness of this undoped region is 20 nm or less at maximum, an increase in the waveguide loss can be suppressed.

[0048] The P-side second barrier layer 43b is formed on the P-side first barrier layer 43a. In the present embodiment, the P-side second barrier layer 43b is a P-type semiconductor layer in which impurities are intentionally doped, for example, a P-type AlGaAs layer. The impurity doped into the P-side second barrier layer 43b is, for example, carbon (C).

[0049] The P-type guide layer 50 is disposed between the P-side second barrier layer 43b of the active layer 40 and the P-type clad layer 60. Specifically, the P-type guide layer 50 is formed on the P-side second barrier layer 43b. The P-type guide layer 50 is a P-type semiconductor layer intentionally doped with impurities, for example, a P-type AlGaAs layer. The impurity doped into the P-type guide layer 50 is, for example, carbon (C).

[0050] The P-type clad layer 60 is formed on the P-type guide layer 50. The P-type clad layer 60 is a P-type semiconductor layer intentionally doped with impurities, for example, a P-type AlGaAs layer. C is doped as an impurity. The impurity doped into the P-type clad layer 60 is, for example, carbon (C).

[0051] The P-type contact layer 70 is formed on the P-type clad layer 60. The P-type contact layer 70 is formed between the P-type clad layer 60 and the P-side electrode 91. The P-type contact layer 70 is a P-type semiconductor layer intentionally doped with impurities, for example, a P-type GaAs layer.

[0052] In the present embodiment, the P-type contact layer 70 is a laminated film in which a first contact layer 71 and a second contact layer 72 are laminated in order from the P-type clad layer 60 side. As an example, the first contact layer 71 is a P-type GaAs layer with a film thickness of 0.2 μm. The second contact layer 72 is a P-type GaAs layer with a film thickness of 1 μm and is formed on the first contact layer 71 and on the current blocking layer 80 so as to fill the opening 80a of the current blocking layer 80.

[0053] The current blocking layer 80 is provided inside the P-type contact layer 70. Specifically, the current blocking layer 80 is formed on the first contact layer 71 of the P-type contact layer 70. In the present embodiment, the current blocking layer 80 is composed of a P-type semiconductor layer intentionally doped with impurities. Specifically, the current blocking layer 80 is an n-type GaAs layer doped with silicon (Si) as an impurity.

[0054] The current blocking layer 80 has an opening 80a for defining a current injection region. The opening 80a of the current blocking layer 80 extends linearly along the resonator length direction of the semiconductor laser device 1. The opening 80a of the current blocking layer 80 exists in the gain section of the semiconductor laser device 1 but does not exist in the end face section of the semiconductor laser device 1. Therefore, as shown in FIG. 2A, in the gain section of the semiconductor laser device 1, the current blocking layer 80 does not cover the central portion of the first contact layer 71. On the other hand, as shown in FIG. 2B, in the end face section of the semiconductor laser device 1, since the opening 80a of the current blocking layer 80 is not formed, the current blocking layer 80 covers the entire first contact layer 71.

[0055] Thus, by providing the N-type current blocking layer 80 inside the P-type contact layer 70, current confinement is performed by the current blocking layer 80, and an effective refractive index step is formed in the horizontal direction of the active layer 40 due to the heat generation in the first contact layer 71 serving as the current injection region. Thereby, horizontal optical confinement can be achieved.

[0056] The P-side electrode 91 is disposed on the P-type cladding layer 60 side and is connected to the P-type contact layer 70. Specifically, the P-side electrode 91 is formed on the P-type contact layer 70. The P-side electrode 91 contains, for example, at least one metal among Pt, Ti, Cr, Ni, Mo, and Au.

[0057] In this embodiment, the P-side electrode 91 is composed of multiple layers. Specifically, the P-side electrode 91 is composed of three layers: a first P-electrode layer 91a, a plating layer 91b, and a second P-electrode layer 91c. The first P-electrode layer 91a, the plating layer 91b, and the second P-electrode layer 91c are stacked in this order on the P-type contact layer 70. Also, the first P-electrode layer 91a and the second P-electrode layer 91c are each further composed of multiple films, for example, each having a three-layer structure of Ti / Pt / Au. The plating layer 91b is an Au plating film.

[0058] Also, as shown in FIG. 2A, there are three layers, namely the first P-electrode layer 91a, the plating layer 91b, and the second P-electrode layer 91c, in the gain section of the semiconductor laser device 1. However, as shown in FIG. 2B, in the end face portion of the semiconductor laser device 1, the plating layer 91b does not exist, and there are two layers, namely the first P-electrode layer 91a and the second P-electrode layer 91c.

[0059] The N-side electrode 92 is disposed on the N-type clad layer 20 side. In this embodiment, the N-side electrode 92 is formed on the lower surface of the substrate 10 (that is, the main surface on the back side of the substrate 10). The N-side electrode 92 includes, for example, an AuGe film, a Ni film, an Au film, a Ti film, a Pt film, and an Au film stacked in this order from the substrate 10 side.

[0060] The insulating film 100 is a dielectric film that covers at least the side surface of the active layer 40. In this embodiment, the insulating film 100 covers a pair of side surfaces of the semiconductor laminate. Specifically, the insulating film 100 covers the side surfaces of the N-type clad layer 20, the N-type guide layer 30, the active layer 40, the P-type guide layer 50, the P-type clad layer 60, the P-type contact layer 70, and the current blocking layer 80. The insulating film 100 is composed of, for example, an insulating film such as SiN or SiO2 and functions as a current blocking film.

[0061] In the present embodiment, a pair of side surfaces of the semiconductor laminate are inclined inclined surfaces, and the insulating film 100 covers at least the inclined surfaces. Further, the inclined surfaces of the semiconductor laminate are formed at least on the side surfaces of the active layer 40. By inclining the side surfaces of the active layer 40, it is possible to reduce the stray light that travels from the central portion in the width direction of the active layer 40 toward the side surfaces from returning to the central portion again. Therefore, since the competition between the laser light oscillating in the active layer 40 and the stray light can be suppressed, the laser driving operation is stabilized.

[0062] Further, the insulating film 100 has an opening 100a. The opening 100a of the insulating film {100} extends linearly along the resonator length direction of the semiconductor laser device 1. The opening 100a of the insulating film 100 exists in the gain section of the semiconductor laser device 1, but does not exist in the end face section of the semiconductor laser device 1. Therefore, as shown in FIG. 2A, in the gain section of the semiconductor laser device 1, the insulating film 100 covers only the end of the P-type contact layer 70. On the other hand, as shown in FIG. 2B, in the end face section of the semiconductor laser device 1, since the opening 100a of the insulating film 100 is not formed, the insulating film 100 covers the entire P-type contact layer 70.

[0063] As shown in FIGS. 1 and 2C, the semiconductor laser device 1 has a front end face 1a (light emitting end face), which is the end face on the front side from which laser light is emitted, and a rear end face 1b, which is the end face on the rear side opposite to the front end face 1a.

[0064] The semiconductor laminate of the semiconductor laser device 1 includes an optical waveguide having the front end face 1a and the rear end face 1b as resonator reflection mirrors. Therefore, the front end face 1a and the rear end face 1b become resonator end faces, and the resonator length of the semiconductor laser device 1 is the distance between the front end face 1a and the rear end face 1b. In the present embodiment, the resonator length of the semiconductor laser device 1 is as long as 2 mm or more, and may be further 4 mm or more. Note that the resonator length of the semiconductor laser device 1 may be less than 2 mm.

[0065] The width of the current injection region into the optical waveguide is defined by the opening 80a of the current blocking layer 80. The opening 80a of the current blocking layer 80 is formed inside the front end face 1a and the rear end face 1b. That is, the ends of the current injection region in the resonator length direction are located inside the front end face 1a and the rear end face 1b.

[0066] In the semiconductor laser device 1, a first end face coating film 111 is formed on the front end face 1a of the semiconductor laminate, and a second end face coating film 112 is formed on the rear end face 1b of the semiconductor laminate. The first end face coating film 111 and the second end face coating film 112 are reflection films composed of a dielectric multilayer film. For example, the first end face coating film 111 is a multilayer film of Al2O3 and Ta2O5, and the second end face coating film 112 is a multilayer film of Al2O3, SiO2, and Ta2O5. As an example, the reflectivity of the first end face coating film 111 is 2%, and the reflectivity of the second end face coating film 112 is 95%.

[0067] Note that the reflectivities of the first end face coating film 111 and the second end face coating film 112 are not limited to this. For example, when the semiconductor laser device 1 is used in a semiconductor laser module configured with an external resonator, the reflectivity of the first end face coating film 111 may be 0.2% or less. Thereby, problems such as kink generation due to competition between the laser oscillation mode in the semiconductor laser device 1 and the laser oscillation mode in the external resonator can be suppressed.

[0068] In the present embodiment, the semiconductor laminate in the semiconductor laser device 1 has an end face window structure at both ends in the resonator length direction. Specifically, in the current non-injection regions near both end faces of the optical waveguide in the active layer 40, a window region 120 is formed in a region having a predetermined length from the front end face 1a. The window region 120 is formed in the end face portion on the front end face 1a side of the semiconductor laminate. Note that a similar window region may also be formed in the end face portion on the rear end face 1b side of the semiconductor laminate. The window region on the rear end face 1b side does not necessarily have to be formed.

[0069] Here, let the peak energy of photoluminescence in the region where the window region 120 is not formed in the active layer 40 be Eg1, the peak energy of photoluminescence in the region where the window region 120 is formed in the active layer 40 be Eg2, and the difference between Eg1 and Eg2 be ΔEg. For example, the window region 120 is formed such that ΔEg = Eg2 - Eg1 = 100 meV. That is, the bandgap of the active layer 40 in the regions near the front end face 1a and the rear end face 1b is made larger than the bandgap of the active layer 40 in the regions other than near the front end face 1a and the rear end face 1b. Specifically, the bandgap energy of the well layer 41 near the front end face 1a and the rear end face 1b is larger than the bandgap energy of the well layer 41 at the center in the resonator length direction.

[0070] Also, there are generally an impurity diffusion method and a hole diffusion method for forming the window region 120. In this embodiment, the window is formed by the hole diffusion method. This is because in a semiconductor laser device with an ultra-high output exceeding 10 W per emitter, reducing the amount of light absorption due to low loss is important. That is, when the window region is formed by the impurity diffusion method, light absorption increases due to impurities, making it difficult to reduce the light absorption loss. However, since the hole diffusion method is impurity-free, forming the window region by the hole diffusion method can eliminate the light absorption loss caused by impurity introduction. By forming the window region by the hole diffusion method, as an end face window structure, the window region 120 is formed on the front end face 1a side. Also, a similar window region is formed on the rear end face 1b side.

[0071] Note that the pore diffusion method can form a window region by performing rapid high-temperature processing. For example, after forming a protective film that generates Ga pores during high-temperature processing on the semiconductor layer in the region where the window region is to be formed, by exposing it to a very high temperature of 800°C to 950°C near the crystal growth temperature to diffuse the Ga pores, the quantum well structure of the active layer 40 can be disordered by the mutual diffusion of the pores and group III elements to achieve windowing (transparency). As a result, the bandgap of the active layer 40 can be increased, and the region where the quantum well structure is disordered can function as a window region. Also, in regions other than the window region, by forming a protective film that suppresses the generation of Ga pores during high-temperature processing, the disordering of the quantum well structure can be suppressed.

[0072] In this way, since the semiconductor laser device 1 has an end window structure, the resonator end face of the semiconductor laser device 1 can be made transparent to reduce light absorption near the front end face 1a. Thereby, the occurrence of COD at the front end face 1a can be suppressed.

[0073] [Manufacturing Method of Semiconductor Laser Device] Next, with reference to FIGS. 3A to 3H, the manufacturing method of the semiconductor laser device 1 according to the embodiment will be described. FIGS. 3A to 3H are diagrams for explaining each step in the manufacturing method of the semiconductor laser device 1 according to the embodiment. In FIGS. 3B to 3H, the upper figure shows a cross-section of the portion corresponding to the current injection region where current is injected, and the lower figure shows a cross-section of the portion corresponding to the current non-injection region where current is not injected.

[0074] As shown in FIG. 3A, first, a substrate 10 is prepared, and a plurality of semiconductor layers are stacked on the substrate 10. The step of stacking a plurality of semiconductor layers includes at least the step of disposing an N-type cladding layer 20 above the substrate 10, the step of disposing an active layer 40 above the N-type cladding layer 20, and the step of disposing a P-type cladding layer 60 above the active layer 40.

[0075] Specifically, on a substrate 10 which is an n-GaAs wafer, an N-type cladding layer 20, an N-type guiding layer 30, an active layer 40, a P-type guiding layer 50, a P-type cladding layer 60, a first contact layer 71 of a P-type contact layer 70, and a current blocking layer 80 are sequentially grown by crystal growth technology by metalorganic chemical vapor deposition (MOCVD) to be laminated.

[0076] As the active layer 40, on the N-type guiding layer 30, an N-side second barrier layer 42b, an N-side first barrier layer 42a, a well layer 41, a P-side first barrier layer 43a, and a P-side second barrier layer 43b are sequentially grown by crystal growth technology to be laminated.

[0077] Next, as shown in FIG. 3B, an opening 80a for defining a current injection region is formed in the current blocking layer 80. Specifically, on the first contact layer 71, a mask made of SiO2 or the like is formed in a predetermined pattern by photolithography technology, and then, by wet etching technology, the current blocking layer 80 is etched until the first contact layer 71 is exposed, thereby forming the opening 80a in the current blocking layer 80 in the portion corresponding to the current injection region. On the other hand, in the current non-injection region at the end face portion of the semiconductor laser device 1, the opening 80a is not formed in the current blocking layer 80. Note that, as the etching solution for etching the current blocking layer 80, a sulfuric acid-based etching solution is preferably used. For example, an etching solution of sulfuric acid: hydrogen peroxide water: water = 1:1:40 can be used. [[ID=IO]]

[0078] Next, as shown in FIG. 3C, after removing the mask when forming the opening 80a in the current blocking layer 80 with a hydrofluoric acid-based etching solution, the second contact layer 72 of the P-type contact layer 70 is grown by crystal growth technology by the MOCVD method. Specifically, the second contact layer 72 is grown on the current blocking layer 80 and on the first contact layer 71 exposed from the opening 80a of the current blocking layer 80 so as to fill the opening 80a in the current blocking layer 80 in the current injection region.

[0079] Next, as shown in FIG. 3D, a window region 120 is formed in a portion corresponding to the end face portion in the resonator length direction in the semiconductor laminate of a plurality of semiconductor layers. Specifically, the window region 120 is formed in a portion corresponding to the end face portion on the front end face 1a side of the semiconductor laminate. In the present embodiment, the window region 120 is formed in a portion corresponding to the vicinity of the front end face 1a in a part of the P-type contact layer 70, the P-type clad layer 60, the P-type guide layer 50, the active layer 40, the N-type guide layer 30, the N-type clad layer 20, and the substrate 10. Note that the window region 120 is formed by a hole diffusion method, but is not limited thereto.

[0080] Next, as shown in FIG. 3E, a groove 130 having an inclined surface is formed on the side surface of the semiconductor laminate. Specifically, a mask made of SiO2 or the like is formed in a predetermined pattern on the P-type contact layer 70 by photolithography technology, and then, by wet etching technology, etching is performed from the P-type contact layer 70 to the middle of the N-type clad layer 20, whereby an inclined groove 130 can be formed on the side surface of the semiconductor laminate. The groove 130 is a separation groove when the semiconductor laser device 1 is separated into individual pieces, and extends in the resonator length direction in a top view.

[0081] Note that, as the etching solution for forming the groove 130, for example, a sulfuric acid-based etching solution can be used. In this case, an etching solution of sulfuric acid: hydrogen peroxide water: water = 1:1:10 can be used. Further, the etching solution is not limited to a sulfuric acid-based etching solution, and an organic acid-based etching solution or an ammonia-based etching solution may be used.

[0082] Further, the groove 130 is formed by isotropic wet etching. Thereby, inclined surfaces can be formed on the side surfaces of the plurality of semiconductor layers, and a constriction structure (i.e., an overhang structure) can be formed in the plurality of semiconductor layers. The inclination angle of the side surface of the groove 130 varies with the composition ratio of the Al composition of the AlGaAs material of each layer constituting the plurality of semiconductor layers. In this case, by increasing the Al composition of the AlGaAs material, the etching rate can be increased. Therefore, in order to form side surfaces having an inclination as shown in FIG. 3E in the plurality of semiconductor layers, by making the composition ratio of the Al composition of the P-type clad layer 60 the highest, the lateral (horizontal) etching rate in the plurality of semiconductor layers can be made the fastest. Thereby, the narrowest portion (the narrowest portion in the horizontal direction) of the plurality of semiconductor layers can be formed near the P-type clad layer 60.

[0083] Next, as shown in FIG. 3F, after removing the mask when forming the groove 130 with a hydrofluoric acid-based etching solution, a SiN film is deposited as the insulating film 100 on the entire surface of the substrate 10, and then, using photolithography technology and etching technology, the insulating film 100 in the portion corresponding to the current injection region is removed to form the opening 100a. Note that the insulating film 100 in the portion corresponding to the non-current injection region is not removed, and the opening 100a is not formed in the portion corresponding to the non-current injection region.

[0084] As the etching of the insulating film 100, wet etching using a hydrofluoric acid-based etching solution or dry etching by reactive ion etching (RIE) can be used. Further, the insulating film 100 is a SiN film, but is not limited thereto, and may be a SiO2 film or the like.

[0085] Next, as shown in FIG. 3G, a P-side electrode 91 is formed on the semiconductor laminate. In the present embodiment, on the P-type contact layer 70, as the P-side electrode 91, a first P electrode layer 91a, a plating layer 91b, and a second P electrode layer 91c are formed in this order.

[0086] Specifically, a first P electrode layer 91a made of a stacked film of a Ti film, a Pt film, and an Au film is formed as a base electrode by an electron beam evaporation method, and then, an electroplated layer 91b made of an Au plating film is formed by an electroplating method. Then, using photolithography technology and lift-off technology, the electroplated layer 91b in the portion corresponding to the current non-injection region is selectively etched and removed. In this case, an iodine solution can be used as the etching solution for etching the electroplated layer 91b made of an Au plating film. In the present embodiment, an iodine solution of iodine: potassium iodide: water = 288.8 g: 490 g: 3500 g is used, and further, in order to stabilize the etching, the etching is performed in a bubbling state. Then, a second P electrode layer 91c made of a stacked film of a Ti film, a Pt film, and an Au film is formed on the electroplated layer 91b by an electron beam evaporation method. In this way, the first P electrode layer 91a and the second P electrode layer 91c are formed over substantially the entire length in the resonator length direction, but the Au electroplated layer 91b is not formed in the current non-injection region.

[0087] Next, as shown in FIG. 3H, an N-side electrode 92 is formed on the lower surface of the substrate 10. Specifically, the N-side electrode 92 is formed by sequentially depositing an AuGe film, a Ni film, an Au film, a Ti film, a Pt film, and an Au film from the substrate 10 side.

[0088] Thereafter, although not shown, the substrate 10 on which the semiconductor laminate is formed is separated into bars by dicing or cleavage using a blade or the like, and then, further, chip separation is performed by cutting with the groove 130 as a cutting portion. Thereby, the individual semiconductor laser device 1 can be manufactured.

[0089] [Composition and Band Structure of Semiconductor Layer] Next, a specific example of the semiconductor laser device 1 according to the present embodiment will be described.

[0090] FIG. 4 is a diagram showing specific examples of the composition, film thickness, and impurity concentration of each semiconductor layer in three examples, Example 1, Example 2, and Example 3, of the semiconductor laser device 1 according to the above embodiment.

[0091] In each semiconductor layer of the semiconductor laminate in the semiconductor laser device 1 according to the present embodiment, the semiconductor layer is composed of a III-V compound semiconductor made of an AlGaInAs-based material. With the Al composition and the In composition being X and Y respectively, Al X Ga 1-X-Y In Y As (0 < X < 1, 0 < Y < 1).

[0092] In FIG. 4, the Al composition and the In composition of the N-type clad layer 20 are X NC and Y NC respectively, the Al composition and the In composition of the N-type guide layer 30 are X NG and Y NG respectively, the Al composition and the In composition of the N-side second barrier layer 42b in the active layer 40 are X NB2 and Y NB2 respectively, the Al composition and the In composition of the N-side first barrier layer 42a in the active layer 40 are X NB1 and Y NB1 respectively, the Al composition and the In composition of the well layer 41 in the active layer 40 are X W and Y W respectively, the Al composition and the In composition of the P-side first barrier layer 43a in the active layer 40 are X PB1 and Y PB1 respectively, the Al composition and the In composition of the P-side second barrier layer 43b in the active layer 40 are X PB2 and Y PB2 respectively, the Al composition and the In composition of the P-type guide layer 50 are X PG and Y PG respectively, the Al composition and the In composition of the P-type clad layer 60 are X PC and Y PC respectively. Note that FIG. 4 shows the conditions for obtaining a laser beam in the 915 nm wavelength band.

[0093] As shown in FIG. 4, in the semiconductor laser device 1 according to the present embodiment, in the active layer 40, the Al composition ratio of the N-side second barrier layer 42b is higher than that of the N-side first barrier layer 42a, and the Al composition ratio of the P-side second barrier layer 43b is higher than that of the P-side first barrier layer 43a.

[0094] In the semiconductor laser device 1 according to the present embodiment, the Al composition changes in the interface region between the N-type clad layer 20 and the N-type guide layer 30 and in the interface region between the P-type guide layer 50 and the P-type clad layer 60. Specifically, the Al composition in at least the interface region between the N-type clad layer 20 and the N-type guide layer 30 gradually increases as it moves away from the well layer 41. Similarly, the Al composition in at least the interface region between the P-type guide layer 50 and the P-type clad layer 60 gradually increases as it moves away from the well layer 41.

[0095] Next, the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser devices 1 of Examples 1 to 3 shown in FIG. 4 will be described with reference to FIGS. 5A to 5C.

[0096] FIG. 5A is a diagram showing the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device 1 of Example 1.

[0097] FIG. 5B is a diagram showing the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device 1 of Example 2.

[0098] FIG. 5C is a diagram showing the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device 1 of Example 3.

[0099] In FIGS. 5A to 5C, D NB1 represents the length of the undoped region in the N-side first barrier layer 42a, and D PB1 represents the length of the undoped region in the P-side first barrier layer 43a.

[0100] As shown in FIGS. 5A to 5C, in the semiconductor laser device 1 according to the present embodiment, in any of Examples 1 to 3, the concentrations of impurities doped in the N-type clad layer 20, the N-type guide layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a increase stepwise as they are farther from the well layer 41. That is, as they are farther from the well layer 41, the impurity concentrations increase stepwise in the order of the N-side first barrier layer 42a, the N-side second barrier layer 42b, the N-type guide layer 30, and the N-type clad layer 20. Further, in the present embodiment, the impurity concentration is constant in each of the N-side first barrier layer 42a, the N-side second barrier layer 42b, the N-type guide layer 30, and the N-type clad layer 20.

[0101] Note that the concentrations of impurities doped in the N-type clad layer 20, the N-type guide layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a may increase gradually (i.e., increase with a gradient) rather than stepwise as they are farther from the well layer 41.

[0102] On the other hand, the impurity concentration doped in the interface region between the P-type clad layer 60 and the P-type guide layer 50 is constant at 2×10 18 cm -3 . The impurity concentration of the P-type clad layer 60 may be increased stepwise or continuously in the direction away from the well layer 41. In the region of the P-type clad layer 60 far from the well layer 41, since the light distribution intensity in the vertical direction of the guided light is attenuated, the impurity concentration may be increased for doping. In this region, since the light distribution intensity is small, the generation of free carrier absorption loss due to impurities is small, and since the resistance value decreases due to the increase in the impurity concentration, the series resistance of the semiconductor laser device can be reduced without causing an increase in the waveguide loss. Specifically, the P-type impurity concentration of the P-type clad layer 60 is 2×10 18 cm -3 on the well layer 41 side, and the impurity concentration at the portion farthest from the well layer 41 is 5×10 18 cm -3It may be gradually increased so as to become, or may be increased stepwise so that the impurity concentration becomes higher in the direction away from the well layer 41. Here, when the Al composition of the P-type clad layer 60 is twice or more that of the P-type guide layer 50, the light distribution intensity in the direction perpendicular to the substrate normal direction is such that the refractive index difference between the P-type clad layer 60 and the P-type guide layer 50 is large. Therefore, it rapidly attenuates from the P-type guide layer 50 toward the P-type clad layer 60. In this case, in order to suppress an increase in waveguide loss due to the generation of free carrier loss by impurity doping and reduce the series resistance of the semiconductor laser device, it is preferable to continuously increase the impurity concentration from the well layer 41 toward the P-type clad layer 60. By doing so, since the impurity concentration is low in the region where the light distribution intensity is large, an increase in waveguide loss is suppressed, and in the region where the light distribution intensity is small, since the impurity concentration is high, an increase in waveguide loss is also suppressed while obtaining the effect of reducing the series resistance of the semiconductor laser device.

[0103] Also, the concentration of the impurity doped in the P-type guide layer 50, the P-side second barrier layer 43b, and the P-side first barrier layer 43a gradually increases as it moves away from the well layer 41 (that is, the inclination increases). In the structures shown in Example 1 to Example 3, the P-type impurity concentration is 2×10 17 cm -3 to 5×10 17 cm -3 and the impurity concentration is continuously increased. Also, the impurity concentration doped in the interface region between the P-type clad layer 60 and the P-type guide layer 50 may be continuously increased from 5×10 17 cm -3 to 2×10 18 cm -3 In this case, an increase in waveguide loss due to free carrier absorption loss generated by impurity doping in the interface region between the P-type clad layer 60 and the P-type guide layer 50 can be suppressed.

[0104] Also, as shown in FIGS. 5A to 5C, the N-side first barrier layer 42a has an undoped region where impurities are not doped in the region closer to the well layer 41, and has a doped region where impurities are doped in the region farther from the well layer 41. In this embodiment, the film thickness of the undoped region of the N-side first barrier layer 42a is 5 nm.

[0105] On the other hand, for the N-side second barrier layer 42b, impurities are doped in the entire region. That is, impurities are intentionally doped in the entire N-side second barrier layer 42b in the thickness direction. The impurity concentration of the N-side second barrier layer 42b is the same as the impurity concentration of the doped region of the N-side first barrier layer 42a.

[0106] Similarly, the P-side first barrier layer 43a has an undoped region where impurities are not doped in the region closer to the well layer 41, and has a doped region where impurities are doped in the region farther from the well layer 41. In this embodiment, the film thickness of the undoped region of the P-side first barrier layer 43a is 5 nm.

[0107] On the other hand, for the P-side second barrier layer 43b, impurities are doped in the entire region. That is, impurities are intentionally doped in the entire P-side second barrier layer 43b in the thickness direction.

[0108] Regarding the bandgap energy in each embodiment, as shown in FIGS. 5A to 5C, in the N-side semiconductor region of the active layer 40, the bandgap energy of the N-side second barrier layer 42b is larger than the bandgap energy of the N-side first barrier layer 42a. Similarly, in the P-side semiconductor region of the active layer 40, the bandgap energy of the P-side second barrier layer 43b is larger than the bandgap energy of the P-side first barrier layer 43a.

[0109] Also, the bandgap energy of the P-type clad layer 60 is larger than the bandgap energy of the N-type clad layer 20.

[0110] Also, as described above, the semiconductor laser device 1 has an end face window structure in which a window region 120 is formed. Specifically, the semiconductor laser device 1 has an end face window structure in which the bandgap energy of the well layer 41 near the front end face 1a is larger than the bandgap energy of the well layer 41 at the center in the resonator length direction of the semiconductor laser device 1.

[0111] In addition, in FIG. 5A, the bandgap energy of the N-side second barrier layer 42b was constant, but it is not limited to this. For example, as shown in FIG. 5B, the bandgap energy of the N-side second barrier layer 42b may gradually increase as it moves away from the well layer 41. Thereby, formation of hetero-structure spikes and notches in the conduction band and valence band formed at the interface between the N-side first barrier layer 42a and the N-side second barrier layer 42b can be suppressed, and the operating voltage can be reduced.

[0112] Similarly, in FIG. 5A, the bandgap energy of the P-side second barrier layer 43b was constant, but it is not limited to this. For example, the bandgap energy of the P-side second barrier layer 43b may gradually increase as it moves away from the well layer 41. Thereby, formation of hetero-structure spikes and notches in the conduction band and valence band formed at the interface between the P-side first barrier layer 43a and the P-side second barrier layer 43b can be suppressed, and the operating voltage can be reduced.

[0113] Also, in FIGS. 5A and 5B, the bandgap energy of the P-type guide layer 50 was the same as that of the N-type guide layer 30, but it is not limited to this. That is, the compositions of the N-type guide layer 30 and the P-type guide layer 50 may be asymmetric. For example, as shown in FIG. 5C, when the bandgap energy of the P-type guide layer 50 is larger than that of the N-type guide layer 30, the generation of current in which electrons injected into the well layer 41 are excited by heat and leak into the P-type guide layer 50 can be suppressed. Further, since the N-type guide layer 30 has a higher refractive index than the P-type guide layer 50, the vertical light distribution in the direction perpendicular to the substrate normal direction of the waveguide can be made closer to the N-type layer. In this case, the vertical light distribution can be precisely controlled by controlling the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50. As a result, a semiconductor laser device capable of high-temperature high-output operation with better temperature characteristics while reducing waveguide loss can be obtained with good reproducibility. In the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50, if the P-type guide layer 50 becomes too large, the vertical light distribution becomes too close to the N-type layer, the light confinement factor in the well layer 41 decreases, and the oscillation threshold current value increases. Therefore, the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 may be such that the Al composition of the P-type guide layer 50 is relatively increased and the difference is 0.05 or less.

[0114] Also, when the bandgap energy of the P-type guide layer 50 is smaller than the bandgap energy of the N-type guide layer 30, the refractive index of the N-type guide layer 30 becomes lower than the refractive index of the P-type guide layer 50, so that the vertical light distribution in the substrate normal direction of the waveguide can be shifted toward the P side. As a result, a high light confinement factor in the well layer 41 can be obtained, and a semiconductor laser device capable of excellent high-temperature high-output operation with good temperature characteristics while reducing the oscillation threshold current can be obtained. In the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50, if the N-type guide layer 30 becomes too large, the vertical light distribution will shift too much toward the P-type layer, increasing the waveguide loss and causing an increase in the oscillation threshold current and a decrease in the slope efficiency. Therefore, the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 may be such that the Al composition of the N-type guide layer 30 is relatively increased and the difference is 0.04 or less.

[0115] Also, in FIGS. 5A and 5B, the maximum value of the bandgap energy of the P-side second barrier layer 43b was the same as the maximum value of the bandgap energy of the N-side second barrier layer 42b, but it is not limited to this. For example, the maximum value of the bandgap energy of the P-side second barrier layer 43b may be larger than the maximum value of the bandgap energy of the N-side second barrier layer 42b. Thereby, it is possible to suppress the generation of a current in which electrons injected into the well layer 41 are excited by heat and leak to the P-type guide layer 50. Further, since the N-type guide layer 30 has a higher refractive index than the P-type guide layer 50, the vertical light distribution in the direction perpendicular to the substrate normal direction of the waveguide can be made closer to the N-type layer. In this case, the vertical light distribution can be precisely controlled by controlling the Al composition of the N-side second barrier layer 42b, the N-type guide layer 30, the P-side second barrier layer 43b, and the P-type guide layer 50. As a result, a semiconductor laser device capable of high-temperature high-output operation with excellent temperature characteristics can be obtained with good reproducibility. In the Al composition difference between the maximum value of the Al composition of the P-side second barrier layer 43b and the maximum value of the Al composition of the N-side second barrier layer 42b, if the Al composition of the P-side second barrier layer 43b becomes too large, the vertical light distribution becomes too close to the N-type layer, the light confinement factor in the well layer 41 decreases, and the oscillation threshold current value increases. Therefore, the Al composition difference between the maximum value of the Al composition of the P-side second barrier layer 43b and the maximum value of the Al composition of the N-side second barrier layer 42b may be such that the maximum value of the Al composition of the P-side second barrier layer 43b is relatively large and the difference is 0.05 or less.

[0116] Also, the maximum value of the bandgap energy of the P-side second barrier layer 43b may be smaller than the maximum value of the bandgap energy of the N-side second barrier layer 42b. In this case, the bandgap energy of the P-type guide layer 50 becomes smaller than the bandgap energy of the N-type guide layer 30. When the bandgap energy of the P-type guide layer 50 is smaller than the bandgap energy of the N-type guide layer 30, the refractive index of the N-type guide layer 30 becomes lower than the refractive index of the P-type guide layer 50, so that the vertical light distribution in the direction perpendicular to the substrate normal direction of the waveguide can be shifted toward the P side. As a result, a high light confinement factor for the well layer 41 can be obtained, and a semiconductor laser device capable of excellent high-temperature high-output operation with reduced oscillation threshold current and good temperature characteristics can be obtained. In the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50, if the N-type guide layer 30 becomes too large, the vertical light distribution shifts too much toward the P-type layer, increasing the waveguide loss and causing an increase in the oscillation threshold current and a decrease in the slope efficiency. Therefore, the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 may be such that the Al composition of the N-type guide layer 30 is relatively increased and the difference is 0.04 or less. That is, the Al composition difference between the maximum value of the Al composition of the N-side second barrier layer 42b and the maximum value of the Al composition of the P-side second barrier layer 43b may be such that the Al composition of the N-side second barrier layer 42b is relatively increased and the difference is 0.04 or less.

[0117] Note that in FIG. 5A, the bandgap energies of the P-type guide layer 50 and the P-side second barrier layer 43b were the same, but this is not restrictive. For example, as shown in FIG. 5D, the bandgap energy of the P-type guide layer 50 may be larger than the bandgap energy of the P-side second barrier layer 43b. With this configuration, it becomes possible to suppress the generation of an electron current in which electrons injected into the well layer 41 are excited by heat and leak into the P-type guide layer 50 during high-temperature high-output operation. As a result, a semiconductor laser device excellent in high-temperature high-output operation can be obtained.

[0118] Also, by making the bandgap energy of the P-side second barrier layer 43b larger than the bandgap energy of the N-side second barrier layer 42b, it becomes possible to suppress the generation of an electron current in which electrons injected into the well layer 41 are excited by heat and leak to the P-type guide layer 50 during high-temperature high-output operation. As a result, a semiconductor laser device excellent in high-temperature high-output operation can be obtained.

[0119] Also, the bandgap energies of the N-side first barrier layer 42a and the N-side second barrier layer 42b may be the same, but the bandgap energy of the N-type guide layer 30 may be equal to or higher than the bandgap energy of the N-side second barrier layer 42b. With this configuration, the refractive indices of the N-side second barrier layer 42b and the N-side first barrier layer 42a become equal to or higher than the refractive index of the N-type guide layer 30, and the optical confinement factor for the well layer 41 can be increased. As a result, the oscillation threshold and the leakage current during high-temperature high-output operation are reduced, and a semiconductor laser device excellent in high-temperature high-output operation can be obtained.

[0120] Also, the bandgap energies of the P-side first barrier layer 43a and the P-side second barrier layer 43b may be the same, but the bandgap energy of the P-type guide layer 50 may be equal to or higher than the bandgap energy of the P-side second barrier layer 43b. With this configuration, the refractive indices of the P-side second barrier layer 43b and the P-side first barrier layer 43a become equal to or higher than the refractive index of the P-type guide layer 50, and the optical confinement factor for the well layer 41 can be increased.

[0121] As a result, the oscillation threshold and the leakage current during high-temperature high-output operation are reduced, and a semiconductor laser device excellent in high-temperature high-output operation can be obtained.

[0122] Fig. 5E shows the impurity concentration profile and band structure of a semiconductor laminate in a semiconductor laser device according to Example 5, which has both an N-side high Al composition layer 44 with an Al composition higher than that of the N-side first barrier layer 42a and a P-side high Al composition layer 45 with an Al composition higher than that of the P-side first barrier layer 43a, between the N-side first barrier layer 42a and the well layer 41, and between the P-side first barrier layer 43a and the well layer 41, in the structure of the semiconductor laser device shown in Example 1. Note that Example 5 shown in Fig. 5E has both the N-side high Al composition layer 44 and the P-side high Al composition layer 45, but it may have only one of them.

[0123] With this structure, in the case of forming a window portion by hole diffusion or impurity diffusion, during the thermal annealing process or window formation by ion implantation, the Al composition difference between the well layer 41 and the N-side high Al composition layer 44, and between the well layer 41 and the P-side high Al composition layer 45 becomes large. Therefore, due to the mutual exchange of atoms between the two layers, the band gap in the well layer 41 of the window portion is likely to increase, making it easier to increase the difference in band gap energy between the window portion and the gain portion. As a result, even if the well layer 41 is thick, the window region 120 can be formed more easily.

[0124] If the thicknesses of the N-side high Al composition layer 44 and the P-side high Al composition layer 45 are too thin, the disordering effect of the quantum well structure due to the mutual exchange of atoms with the well layer 41 decreases, and the effect of increasing the band gap energy of the well layer 41 in the window region 120 by the window formation thermal annealing process decreases. Conversely, if the thicknesses of the N-side high Al composition layer 44 and the P-side high Al composition layer 45 are too thick, since the refractive index of the N-side high Al composition layer 44 is lower than that of the N-side first barrier layer 42a, and the refractive index of the P-side high Al composition layer 45 is lower than that of the P-side first barrier layer 43a, the light confinement coefficient to the well layer 41 decreases. Furthermore, since the band gap energy of the N-side high Al composition layer 44 is larger than that of the N-side first barrier layer 42a, and the band gap energy of the P-side high Al composition layer 45 is larger than that of the P-side first barrier layer 43a, the N-side high Al composition layer 44 inhibits the injection of electrons into the well layer 41, and the P-side high Al composition layer 45 inhibits the injection of holes into the well layer 41, resulting in an increase in the operating voltage.

[0125] Therefore, the thicknesses of the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 may be 3 nm or more and 10 nm The following or more.

[0126] Also, if the Al composition of the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 becomes too small, the disordering effect of the quantum well structure due to the atomic exchange between the well layer 41 and the N-side high-Al composition layer 44 and between the well layer 41 and the P-side high-Al composition layer 45 decreases, and the increasing effect of the bandgap energy of the well layer 41 in the window region 120 by the thermal annealing process for window formation decreases. Conversely, if the Al composition becomes too large, the refractive index of the N-side high-Al composition layer 44 is lower than that of the N-side first barrier layer 42a, and the refractive index of the P-side high-Al composition layer 45 is lower than that of the P-side first barrier layer 43a. Therefore, the light confinement factor in the well layer 41 decreases. Furthermore, since the bandgap energy of the N-side high-Al composition layer 44 is larger than that of the N-side first barrier layer 42a, and the bandgap energy of the P-side high-Al composition layer 45 is larger than that of the P-side first barrier layer 43a, the N-side high-Al composition layer 44 inhibits the injection of electrons into the well layer 41, and the P-side high-Al composition layer 45 inhibits the injection of holes into the well layer 41, resulting in an increase in the operating voltage.

[0127] Therefore, the Al composition of the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 may be 0.27 or more and 0.35 or less.

[0128] By providing the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45, it becomes easy to increase the bandgap energy of the well layer 41 in the window region 120 even when the thickness of the well layer 41 is increased, and a semiconductor laser device with excellent high-temperature operating characteristics and a high COD level can be easily obtained.

[0129] In addition, in the structure shown in FIG. 5E, although an example in which the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 are not doped with impurities is shown, by doping the N-side high-Al composition layer 44 with an N-type impurity and doping the P-side high-Al composition layer 45 with a P-type impurity, the series resistance of the semiconductor laser device can be reduced. Further, if the N-side high-Al composition layer 44 is doped with an N-type impurity, the leakage of the hole current injected into the well layer 41 can be suppressed because the potential energy of the valence band decreases. Also, if the P-side high-Al composition layer 45 is doped with a P-type impurity, the leakage of the electron current injected into the well layer 41 can be suppressed because the potential energy of the conduction band increases. As a result, when the semiconductor laser device is operated at high temperature and high output, the generation of leakage current can be suppressed, and a semiconductor laser device with excellent temperature characteristics can be obtained. In order to reduce the series resistance and improve the temperature characteristics of the semiconductor laser device, the N-side high-Al composition layer 44 may be doped with an N-type impurity in the range of 1×10 17 cm -3 to 1×10 18 cm -3 and the P-side high-Al composition layer 45 may be doped with a P-type impurity in the range of 1×10 17 cm -3 to 5×10 17 cm -3 .

[0130] The N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 may be AlGaAs layers or AlGaInAs layers. When AlGaInAs is used for the P-side high-Al composition layer 45, it is possible to reduce the potential energy of the valence band of the P-side first barrier layer 43a and increase the potential energy of the conduction band, suppressing the generation of electrons leaking from the well layer 41 to the P-type layer side and easily forming the window region 120.

[0131] In particular, when the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 are made of AlGaInAs, by setting the Al composition to 0.3 or more and 0.45 or less, and the In composition to 0.05 or more and 0.15 or less, the difference in potential energy of the valence band between the P-side first barrier layer 43a and the P-side high-Al composition layer 45 can be reduced. Furthermore, by including In in the N-side high-Al composition layer 44, the bandgap energy of the N-side high-Al composition layer 44 becomes smaller, so that the difference in potential energy of the conduction band between the N-side first barrier layer 42a and the N-side high-Al composition layer 44 can be reduced. As a result, the injection of electrons and holes into the well layer 41 becomes easier and the operating voltage is reduced compared to the case where an AlGaAs layer having the same Al composition is used. Also, since the difference in Al composition between the well layer 41 and the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 becomes larger, during the window formation thermal annealing process or the ion implantation process for forming the window region 120, the disordering of the group III atom arrangement due to atomic exchange is likely to occur, and the difference in bandgap energy between the window portion and the gain portion is likely to become larger. Therefore, a semiconductor laser device with a high COD level can be obtained.

[0132] Also, when the N-type guide layer 30 is an AlGaInAs layer containing In with an In composition of 0.02 or less, it becomes possible to slightly increase the refractive index of the N-type guide layer 30 while suppressing the generation of lattice defects in the N-type guide layer 30, and since it becomes easier to collect light in the N-type guide layer 30 in the vertical direction light distribution, the controllability of the light distribution shape closer to the N-type layer can be improved. In this case, the N-type guide layer 30 may be formed from a superlattice of InGaAs and AlGaAs.

[0133] [Operation and effects of semiconductor laser device] Next, the operation and effects of the semiconductor laser device 1 according to the present embodiment will be described with reference to FIG. 6. FIG. 6 is a diagram for explaining the operation and effects of the semiconductor laser device 1 according to the embodiment. In FIG. 6, in a semiconductor laser device having an end face window structure, the band structures before and after annealing in a region where the formation of the window region is intended (window portion) and a region where the formation of the window region is not intended (gain portion) are shown.

[0134] In FIG. 6, "this embodiment" refers to the semiconductor laser device 1 according to the above-described embodiment.

[0135] Also, in FIG. 6, "comparative example" refers to the semiconductor laser device of the comparative example. The semiconductor laser device of the comparative example has an active layer in which a well layer made of InGaAs is formed between an N-side barrier layer made of AlGaAs and a P-side barrier layer made of AlGaAs, and is configured to increase the Al composition of the barrier layer to improve the thermal saturation level in order to achieve higher output.

[0136] In a semiconductor laser device, in order to achieve higher output, a window region is formed near the end face to improve the COD level. The window region can be formed by disordering the atomic arrangement of the barrier layer and the well layer in the end face portion by means of hole diffusion or the like.

[0137] In a semiconductor laser device having an end-face window structure, in order to further increase the output, it is conceivable to thicken the well layer to increase the optical confinement factor. However, when the well layer is thickened, it becomes difficult to disorder the atomic arrangement of the barrier layer and the well layer, and it becomes difficult to form the window region. Therefore, it is conceivable to promote the mutual exchange of atoms between the well layer and the barrier layer by increasing the annealing temperature when forming the window region to disorder the atomic arrangement.

[0138] In this case, as shown in FIG. 6, in the window portion intended for forming the window region, the bandgap energy (Eg W1 ) after annealing can be made larger than the bandgap energy (Eg W0 ) before annealing. Thereby, even if the well layer is thick, the window region can be formed.

[0139] However, when the annealing temperature when forming the window region is increased, atomic exchange also occurs between the well layer and the barrier layer in the active layer in the gain portion where the formation of the window region is not intended. As a result, also in the gain portion, the bandgap energy (EgG1 ) becomes larger than the bandgap energy (E gG0 ) before annealing. That is, not only in the window portion but also in the gain portion, the bandgap energy increases. As a result, the leakage current in the gain portion increases, deteriorating the temperature characteristics, or the vacancies introduced during crystal growth or the vacancies on the surface of the growth layer due to dangling bonds on the surface of the growth layer easily diffuse, reducing the oscillation wavelength controllability and deteriorating the long-term reliability.

[0140] On the other hand, in the semiconductor laser device 1 according to the present embodiment, as described above, the P-side first barrier layer 43a and the P-side second barrier layer 43b are formed on one side of the well layer 41, and the Al composition is changed in at least two steps. Specifically, the Al composition ratio of the P-side second barrier layer 43b is made relatively higher than the Al composition ratio of the P-side first barrier layer 43a. That is, the Al composition of the P-side first barrier layer 43a closer to the well layer 41 is lowered, and the Al composition of the P-side second barrier layer 43b farther from the well layer 41 is increased. Further, in the semiconductor laser device 1 according to the present embodiment, the bandgap energy of the P-side second barrier layer 43b is made higher than the bandgap energy of the P-side first barrier layer 43a.

[0141] Thereby, even if the annealing temperature is increased when forming the window region by thickening the well layer, as shown in "This Embodiment" of FIG. 6, in the window portion intended for forming the window region, the bandgap energy (Eg W1 ) after annealing is made larger than the bandgap energy (Eg W0 ) before annealing, while in the gain portion not intended for forming the window region, the bandgap energy (Eg G1 ) after annealing can be made approximately the same as the bandgap energy (Eg G0 ) before annealing.

[0142] That is, in the gain section, the change in the bandgap energy before and after annealing is suppressed to suppress the increase in the bandgap energy, while in the window section, the bandgap energy can be increased. Therefore, in the window section, the transparency of the semiconductor laminate including the active layer 40 can be promoted, while in the gain section, the transparency of the semiconductor laminate including the active layer 40 can be suppressed.

[0143] Thus, according to the semiconductor laser device 1 according to the present embodiment, since the P-side first barrier layer 43a having a low Al composition and a high refractive index is used, the optical confinement factor in the well layer 41 increases and the operating carrier density decreases. Further, even if the annealing temperature when forming the window region is increased to increase the bandgap energy of the window region by thickening the well layer, since the Al composition of the P-side first barrier layer 43a is low, the bandgap energy of the well layer 41 in the gain section is hardly affected by the change due to impurity diffusion, and the wavelength change of the well layer 41 in the gain section due to the increase in the bandgap energy can be suppressed. As a result, a decrease in long-term reliability can be suppressed. Also, it is possible to suppress the inhibition of the effect of improving the CCOD level, and it is also possible to suppress a decrease in the slope efficiency and a decrease in the temperature characteristics.

[0144] Therefore, according to the semiconductor laser device 1 according to the present embodiment, in a semiconductor laser device having an end face window structure, even if the well layer 41 is thickened, it is possible to suppress deterioration of the temperature characteristics and a decrease in long-term reliability, and to suppress the inhibition of the effect of improving the COD level.

[0145] Further, in the semiconductor laser device 1 according to the present embodiment, the bandgap energy of the P-type clad layer 60 is larger than the bandgap energy of the N-type clad layer 20.

[0146] As a result, the refractive index of the P-type cladding layer 60 becomes smaller than that of the N-type cladding layer 20, so that the light distribution in the substrate vertical direction becomes closer to the N-type cladding layer, and the waveguide loss in the optical waveguide can be reduced. Therefore, the semiconductor laser device 1 that emits light with high efficiency can be realized.

[0147] Furthermore, when the semiconductor laser device 1 is mounted in a junction-down manner (that is, when the P-side electrode 91 side far from the substrate 10 is mounted on the submount), the P-type cladding layer 60 is likely to be affected by mounting strain. Moreover, due to the high Al composition, the lattice mismatch strain with the substrate 10 is large and the influence of mounting strain becomes large. For this reason, birefringence occurs, and if the light distribution propagating through the optical waveguide oozes more greatly into the P-type cladding layer 60 than the N-type cladding layer 20 side, the polarization ratio decreases.

[0148] At this time, by making the bandgap energy of the P-type cladding layer 60 larger than the bandgap energy of the N-type cladding layer 20, the light distribution in the substrate vertical direction becomes closer to the N-type cladding layer, and the proportion of the light distribution existing in the P-type cladding layer 60 can be reduced. Thereby, it is also possible to suppress a decrease in the polarization ratio.

[0149] In the semiconductor laser device 1 according to the present embodiment, the thickness of the well layer 41 is 6 nm or more.

[0150] In this way, by setting the thickness of the well layer 41 to 6 nm or more, the light confinement factor for the well layer 41 can be greatly increased, so that the operating carrier density can be reduced and the thermal saturation level can be improved. Therefore, the temperature characteristics can be improved.

[0151] Furthermore, when the light distribution is closer to the N-type cladding layer 20, the light confinement factor in the well layer 41 decreases, the oscillation threshold increases, the operating current value increases, leading to the generation of leakage current and a decrease in the thermal saturation level. However, by setting the thickness of the well layer 41 to 6 nm or more, even when the light distribution is closer to the N-type cladding layer 20, the influence of the decrease in the light confinement factor in the well layer 41 can be reduced.

[0152] Also, in the semiconductor laser device 1 according to the present embodiment, the well layer 41 is made of a semiconductor material represented by the composition formula of Al X Ga 1-X-Y In y As (0 < X < 1, 0 < Y < 1).

[0153] With this configuration, the compressive strain in the well layer 41 increases, and the energy between the levels of the heavy hole (HH1) in the first level and the light heavy hole (LH1) in the first level can be increased. As a result, the number of light heavy holes (LH number) contributing to the TM mode decreases. Moreover, it becomes possible to set the number of levels of the light hole (LH number of levels) formed by the P-side first barrier layer 43a and the N-side first barrier layer 42a to one level. Therefore, the polarization ratio can be increased.

[0154] Here, among AlAs, GaAs, and InAs, InAs has the largest lattice constant and the smallest bandgap energy. In this case, when obtaining a desired bandgap energy using a semiconductor material having a quaternary composition of AlGaInAs for the well layer and the barrier layer of the active layer, compared with the case of obtaining a desired bandgap with InGaAs or AlGaAs, the compressive strain becomes larger because the In content increases.

[0155] Therefore, in a semiconductor laser device in which AlGaInAs is used for the well layer and the barrier layer as in this embodiment, when holes or impurities are diffused on the front end face from which the laser light is emitted to form an end face window structure, in order to reduce the strain energy of the well layer, the In atoms in the well layer are more likely to exchange with Al atoms or Ga atoms existing at the lattice positions of group III with respect to the stacking direction, and the bandgap energy (Eg) of the well layer is likely to increase.

[0156] As a result, since the bandgap energy of the well layer in the vicinity of the front end face where the optical density of the laser light emission end face is high easily increases, even if the bandgap energy in the vicinity of the front end face decreases due to heat generation, it is possible to easily maintain a state where the light absorption in the well layer in the vicinity of the front end face is small.

[0157] Therefore, by configuring the well layer 41 with AlGaInAs as in the semiconductor laser device 1 according to this embodiment, it is possible to suppress the occurrence of COD in which the vicinity of the front end face 1a is melted and destroyed by the absorption of laser light.

[0158] Furthermore, by forming the window region 120 by hole diffusion as in this embodiment, it is possible to suppress the occurrence of free carrier loss due to the presence of impurities as compared with the case where the window region 120 is formed by impurity diffusion. Thereby, a decrease in slope efficiency can be suppressed.

[0159] Also, in the semiconductor laser device 1 according to this embodiment, the bandgap energy of the P-side second barrier layer 43b gradually increases as it is separated from the well layer 41.

[0160] With this configuration, the average refractive index of the P-side second barrier layer 43b can be increased. Thereby, the light confinement factor to the well layer 41 can be greatly increased, so that the operating carrier density can be reduced and the thermal saturation level can be improved. Therefore, the temperature characteristics can be improved.

[0161] Moreover, by gradually increasing the bandgap energy of the P-side second barrier layer 43b as it moves away from the well layer 41, the series resistance of the semiconductor laser device 1 can be reduced. Therefore, a semiconductor laser device 1 that can be driven at a low voltage can be realized.

[0162] Also, in the semiconductor laser device 1 according to the present embodiment, the P-side first barrier layer 43a includes an undoped region where no impurities are doped, and the film thickness of the undoped region is preferably 5 nm or more.

[0163] As a result, impurity doping starts from the middle of the P-side first barrier layer 43a, so that the series resistance of the semiconductor laser device 1 can be reduced. Furthermore, since the electron potential barrier of the P-side first barrier layer 43a increases, leakage electrons can be suppressed. This undoped region is preferably 40 nm or less because if it becomes too thick, the series resistance of the semiconductor laser device increases.

[0164] Also, in the semiconductor laser device 1 according to the present embodiment, impurities are doped in the entire region of the P-side second barrier layer 43b, and the P-side first barrier layer 43a has an undoped region where no impurities are doped in the region closer to the well layer 41 and a doped region where impurities are doped in the region farther from the well layer 41.

[0165] As a result, impurity doping starts from the middle of the P-side first barrier layer 43a, so that the series resistance of the semiconductor laser device 1 can be reduced. Also, since the electron potential barriers of each of the P-side first barrier layer 43a and the P-side second barrier layer 43b increase, leakage electrons can also be suppressed.

[0166] Also, in the semiconductor laser device 1 according to the present embodiment, the concentration of the impurities doped in the P-side second barrier layer 43b gradually increases as it moves away from the well layer 41.

[0167] With this configuration, since the electron potential barrier of the P-side second barrier layer 43b increases, it is possible to simultaneously achieve suppression of current leakage and reduction of the series resistance of the semiconductor laser device while suppressing an increase in waveguide loss.

[0168] Further, the semiconductor laser device 1 according to the present embodiment further includes a P-type guide layer 50 between the P-side second barrier layer 43b and the P-type clad layer 60.

[0169] Thus, by providing the P-type guide layer 50, the light confinement factor in the well layer 41 can be further increased. As a result, the operating carrier density can be further reduced, and the thermal saturation level can be further improved. Therefore, the temperature characteristics can be further improved.

[0170] Also, in the semiconductor laser device 1 according to the present embodiment, the Al composition in at least the interface region between the P-type guide layer 50 and the P-type clad layer 60 gradually increases as it moves away from the well layer 41.

[0171] With this configuration, the bandgap energy in the interface region between the P-type guide layer 50 and the P-type clad layer 60 can be increased with a gradient. As a result, the generation of heterojunction spikes and notches in the valence band at the interface between the P-type guide layer 50 and the P-type clad layer 60 can be suppressed, the conductivity of holes can be improved, and the series resistance of the semiconductor laser device can be reduced.

[0172] Furthermore, by gradually increasing the Al composition in the interface region between the P-type guide layer 50 and the P-type cladding layer 60 as the distance from the well layer 41 increases, a high light confinement ratio can also be obtained. This point will be described with reference to FIGS. 7A and 7B. FIG. 7A shows the dependence of the light confinement ratio on the length of the Al composition gradient region in the semiconductor laser device 1 according to the present embodiment. FIG. 7B shows the dependence of the waveguide loss on the length of the Al composition gradient region in the semiconductor laser device 1. In FIGS. 7A and 7B, the length of the Al composition gradient region is the length of the region where the Al composition gradually increases and slopes in the interface region between the P-type guide layer 50 and the P-type cladding layer 60.

[0173] As shown in FIG. 7A, by increasing the length of the Al composition gradient region, the light confinement ratio can be improved, so that the operating threshold current can be reduced and the maximum optical output can be improved. On the other hand, as shown in FIG. 7B, if the length of the Al composition gradient region is made too long, the resistance component increases and the waveguide loss increases. Therefore, it is desirable that the length of the Al composition gradient region be 200 nm or less. As described above, from the viewpoint of suppressing the generation of spikes in the valence band at the interface between the P-type guide layer 50 and the P-type cladding layer 60, the length of the Al composition gradient region is preferably 20 nm or more.

[0174] In the semiconductor laser device 1 according to the present embodiment, the concentration of the impurity doped in the P-type guide layer 50 gradually increases as the distance from the well layer 41 increases. That is, the concentration of the impurity doped in the P-type guide layer 50 increases in a gradient manner.

[0175] With this configuration, since the electron potential barrier of the P-type guide layer 50 increases, it is possible to simultaneously realize suppression of current leakage and reduction of the series resistance of the semiconductor laser device while suppressing an increase in waveguide loss.

[0176] Here, with reference to FIGS. 8A and 8B, the case of providing a gradient in the P-type impurity concentration of the P-side semiconductor layer will be described. FIG. 8A shows the dependence of the optical confinement factor on the P-type impurity concentration in the semiconductor laser device 1 according to the embodiment. FIG. 8B shows the dependence of the waveguide loss on the P-type impurity concentration in the semiconductor laser device 1. In FIGS. 8A and 8B, the simulation results of four samples are shown when the Al composition and thickness of the P-side first barrier layer 43a and the P-side second barrier layer 43b in the semiconductor laser device 1 according to the present embodiment are changed. In FIGS. 8A and 8B, Sample 1 is a case where the P-side first barrier layer 43a with an Al composition of 0.12 and a thickness of 30 nm and the P-side second barrier layer 43b with an Al composition increasing linearly from 0.12 to 0.24 and a thickness of 15 nm are used. Sample 2 is a case where the P-side first barrier layer 43a with an Al composition of 0.12 and a thickness of 15 nm and the P-side second barrier layer 43b with an Al composition increasing linearly from 0.12 to 0.24 and a thickness of 15 nm are used. Sample 3 is a case where the P-side first barrier layer 43a with an Al composition of 0.18 and a thickness of 30 nm and the P-side second barrier layer 43b with an Al composition increasing linearly from 0.12 to 0.24 and a thickness of 15 nm are used. Sample 4 is a case where the P-side first barrier layer 43a with an Al composition of 0.18 and a thickness of 15 nm and the P-side second barrier layer 43b with an Al composition increasing linearly from 0.12 to 0.24 and a thickness of 15 nm are used.

[0177] As shown in FIG. 8A, although the P-type impurity concentration hardly depends on the optical confinement factor, it can be seen that reducing the Al composition of the P-side first barrier layer 43a has a greater effect of increasing the optical confinement factor when the thickness of the P-side first barrier layer 43a is increased. On the other hand, as shown in FIG. 8B, if the P-type impurity concentration is made too high, the waveguide loss increases, so it is better not to make the P-type impurity concentration too high.

[0178] In the semiconductor laser device 1 according to the present embodiment, the active layer 40 further includes an N-side first barrier layer 42a disposed below the well layer 41 and an N-side second barrier layer 42b disposed below the N-side first barrier layer 42a. The Al composition ratio of the N-side second barrier layer 42b is higher than that of the N-side first barrier layer 42a, and the bandgap energy of the N-side second barrier layer 42b is larger than that of the N-side first barrier layer 42a.

[0179] With this configuration, when the annealing temperature is increased when forming the window region by thickening the well layer, not only in the P-side region but also in the N-side region of the well layer 41, while suppressing the wavelength change of the well layer 41 in the gain section due to the increase in the bandgap energy, the bandgap energy can be increased in the window section to increase the wavelength change. As a result, it is possible to further suppress the deterioration of the temperature characteristics and the decrease in the long-term reliability, and further suppress the inhibition of the COD level improvement effect.

[0180] In the semiconductor laser device 1 according to the present embodiment, the bandgap energy of the N-side second barrier layer 42b gradually increases as it moves away from the well layer 41.

[0181] With this configuration, the average refractive index of the N-side second barrier layer 42b can be increased. As a result, the optical confinement factor for the well layer 41 can be further increased, so that the operating carrier density can be further reduced and the thermal saturation level can be further improved. Therefore, the temperature characteristics can be further improved.

[0182] Moreover, by gradually increasing the bandgap energy of the N-side second barrier layer 42b as it moves away from the well layer 41, the series resistance of the semiconductor laser device 1 can be reduced.

[0183] In the semiconductor laser device 1 according to the present embodiment, the entire region of the N-side second barrier layer 42b is doped with impurities. The N-side first barrier layer 42a has an undoped region where impurities are not doped in the region closer to the well layer 41, and has a doped region where impurities are doped in the region farther from the well layer 41.

[0184] As a result, since the doping of impurities starts from the middle of the N-side first barrier layer 42a, the series resistance of the semiconductor laser device can be reduced. In addition, since the electron potential barriers of each of the N-side first barrier layer 42a and the N-side second barrier layer 42b increase, leakage electrons can also be suppressed. Moreover, by making the interface between the N-side first barrier layer 42a and the well layer 41 an undoped region, a decrease in the gain of the well layer 41 can also be suppressed.

[0185] In the semiconductor laser device 1 according to the present embodiment, the bandgap energy of the P-side second barrier layer 43b is larger than the bandgap energy of the N-side second barrier layer 42b.

[0186] Thereby, while suppressing an increase in the operating voltage, generation of leakage electrons can be effectively suppressed.

[0187] The semiconductor laser device 1 according to the present embodiment further includes an N-type guide layer 30 between the N-side second barrier layer 42b and the N-type clad layer 20.

[0188] In this way, by providing the N-type guide layer 30, the optical confinement factor for the well layer 41 can be further increased. As a result, the operating carrier density can be further reduced, and the thermal saturation level can be further improved. Therefore, the temperature characteristics can be further improved.

[0189] In the semiconductor laser device 1 according to the present embodiment, the Al composition in at least the interface region between the N-type guide layer 30 and the N-type cladding layer 20 gradually increases as it moves away from the well layer 41.

[0190] With this configuration, the bandgap energy in the interface region between the N-type guide layer 30 and the N-type cladding layer 20 can be increased with a gradient. As a result, the generation of spikes in the valence band at the interface between the N-type guide layer 30 and the N-type cladding layer 20 can be suppressed, the conductivity of holes can be improved, and the series resistance of the semiconductor laser device can be reduced.

[0191] In the semiconductor laser device 1 according to the present embodiment, the concentration of impurities doped in the N-type cladding layer 20, the N-type guide layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a may gradually increase or increase stepwise as it moves away from the well layer 41.

[0192] With this configuration, while reducing the series resistance of the semiconductor laser device, the waveguide loss can be reduced, the operating voltage can be reduced, and high-efficiency laser oscillation with a high slope efficiency can be realized.

[0193] In the semiconductor laser device 1 according to the present embodiment, the active layer 40 has an N-side first barrier layer 42a disposed below the well layer 41 and an N-side second barrier layer 42b disposed below the N-side first barrier layer 42a. The Al composition ratio of the N-side second barrier layer 42b is higher than that of the N-side first barrier layer 42a, the bandgap energy of the N-side second barrier layer 42b is larger than that of the N-side first barrier layer 42a, an N-type guide layer 30 is provided between the N-side second barrier layer 42b and the N-type cladding layer 20, and the bandgap energy of the P-type guide layer 50 is preferably different from that of the N-type guide layer 30.

[0194] With this configuration, when the bandgap energy of the P-type guide layer 50 is larger than the bandgap energy of the N-type guide layer 30, the electron potential barrier increases, and the generation of leakage electrons can be suppressed.

[0195] Also, when the bandgap energy of the P-type guide layer 50 is smaller than the bandgap energy of the N-type guide layer 30, the refractive index of the N-type guide layer 30 becomes lower than that of the P-type guide layer 50, and the optical confinement in the N-type guide layer 30 becomes weaker, so that a high optical confinement factor for the well layer 41 can be obtained.

[0196] In addition, in the semiconductor laser device 1 according to the present embodiment, an N-side first barrier layer 42a and an N-side second barrier layer 42b are provided between the well layer 41 and the N-type clad layer 20 and face from the well layer 41 toward the N-type clad layer 20. The Al composition ratio of the N-side second barrier layer 42b is higher than the Al composition ratio of the N-side first barrier layer 42a, the bandgap energy of the N-side second barrier layer 42b is larger than the bandgap energy of the N-side first barrier layer 42a, the bandgap energy of the N-side second barrier layer 42b gradually increases as it moves away from the well layer 41, and the maximum value of the bandgap energy of the P-side second barrier layer 43b is preferably larger than the maximum value of the bandgap energy of the N-side second barrier layer 42b.

[0197] With this configuration, the electron potential barrier increases, and the generation of leakage electrons can be suppressed.

[0198] Here, regarding the film thicknesses of the N-side first barrier layer 42a, the N-side second barrier layer 42b, the P-side first barrier layer 43a, and the P-side second barrier layer 43b in the active layer 40, they will be described with reference to FIGS. 9 and 10. FIG. 9 shows the relationship between the waveguide loss and the light confinement ratio with respect to the film thicknesses of the N-side first barrier layer 42a and the P-side first barrier layer 43a. FIG. 10 shows the relationship between the waveguide loss and the light confinement ratio with respect to the film thicknesses of the N-side second barrier layer 42b and the P-side second barrier layer 43b. Note that FIGS. 9 and 10 show the simulation results when the film thickness is changed at 5 nm intervals in the range of 15 nm to 40 nm. Also, in FIGS. 9 and 10, each point is plotted with the film thickness of 15 nm as a reference.

[0199] As shown in FIG. 9, it can be seen that by making the film thickness of the N-side first barrier layer 42a larger than that of the P-side first barrier layer 43a, the waveguide loss can be reduced and the light confinement efficiency can be increased. That is, among the N-side first barrier layer 42a, the N-side second barrier layer 42b, the P-side first barrier layer 43a, and the P-side second barrier layer 43b, for the N-side first barrier layer 42a and the P-side first barrier layer 43a closer to the well layer 41, the film thickness of the N-side first barrier layer 42a is preferably larger than that of the P-side first barrier layer 43a.

[0200] On the other hand, as shown in FIG. 10, it can be seen that for the N-side second barrier layer 42b and the P-side second barrier layer 43b farther from the well layer 41 among the N-side first barrier layer 42a, the N-side second barrier layer 42b, the P-side first barrier layer 43a, and the P-side second barrier layer 43b, the film thickness of the P-side second barrier layer 43b is preferably larger than that of the N-side second barrier layer 42b. Specifically, it can be seen that by making the film thickness of the P-side second barrier layer 43b larger than that of the N-side second barrier layer 42b, the waveguide loss can be reduced and the light confinement efficiency can be increased.

[0201] Here, holes have a lower mobility than electrons and also a lower impurity activation rate. Therefore, in order to reduce the series resistance of the semiconductor laser device and also reduce the turn-on voltage of the PN junction, it is necessary to increase the impurity concentration doped in the P-type semiconductor layer to be higher than the impurity concentration doped in the N-type semiconductor layer, in order to increase the carrier density of holes. For this reason, the free carrier loss occurring in the optical distribution propagating through the optical waveguide has a greater influence in the P-type semiconductor layer than in the N-type semiconductor layer, and it is necessary to precisely control the doping profile of the P-type impurity.

[0202] Therefore, the inventors examined the impurity concentration doped in the P-type semiconductor layer in the semiconductor laser device 1 in this embodiment. Hereinafter, the examination results will be described with reference to FIGS. 11A to 16B. In FIGS. 11A to 16B, the examination was based on the four samples of Sample 1, Sample 2, Sample 3, and Sample 4 described in FIGS. 8A and 8B.

[0203] First, the impurity doping effect of the P-type guide layer 50 will be described with reference to FIGS. 11A and 11B. FIG. 11A shows the dependence of the potential barrier (ΔEg) on the P-type impurity concentration of the P-type guide layer 50 when the P-type guide layer 50 in the semiconductor laser device 1 according to this embodiment is doped with P-type impurities, and the P-side first barrier layer 43a and the P-side second barrier layer 43b are not doped with P-type impurities (undoped). FIG. 11B shows the dependence of the electron current density on the P-type impurity concentration of the P-type guide layer 50 at that time.

[0204] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al composition was set to 0.12 and 0.18, and the thicknesses were set to 15 nm and 30 nm. For the P-side second barrier layer 43b and the N-side second barrier layer 42b, there were cases of compositional gradients from 0.12 to 0.24 and from 0.18 to 0.24 for the Al composition, and the thickness was set to 15 nm. For both the P-side first barrier layer 43a and the P-side second barrier layer 43b, the entire region was undoped. For the N-side first barrier layer 42a, a 5-nm region on the well layer 41 side was an undoped region, and impurities of 1×10 17 cm -3 were doped in the region at a distance of 5 nm or more from the well layer 41. For the N-side second barrier layer 42b, impurities of 1.4×10 17 cm -3 were doped in the entire region. For the N-type guide layer 30, impurities of 1.4×10 17 cm -3 were doped. For the N-type cladding layer 20, impurities were doped in multiple stages of 1.4×10 17 cm -3 , 2×10 17 cm -3 , 6×10 17 cm -3 , 2×10 18 cm -3 from the side closer to the well layer 41 towards the farther side to increase the impurity concentration.

[0205] In this structure, when the P-type impurity concentration of the P-type guide layer 50 with a film thickness of 0.2 μm is increased from 1×10 17 cm -3 to 5×10 17 cm -3 , as shown in FIGS. 11A and 11B, it can be seen that the potential barrier (ΔEg) increases from 0.215 eV to 0.25 eV or more, and the electron current flowing through the P-type guide layer 50 decreases, having an effect of suppressing the idle current. Also, when the P-type impurity concentration of the P-type guide layer 50 is increased, the electron current flowing into the P-side semiconductor layer beyond the well layer 41 can be suppressed.

[0206] On one hand, when increasing the P-type impurity concentration of the P-type guide layer 50, although the potential barrier increases and the series resistance of the semiconductor laser device decreases, the waveguide loss increases and the light emission efficiency (slope efficiency) decreases.

[0207] Therefore, the P-type impurity concentration for doping the P-type guide layer 50 is such that the average value of the P-type impurity concentration throughout the P-type guide layer 50 is 2×10 17 cm -3 to 4×10 17 cm -3 By controlling it to be in this range, the waveguide loss, the series resistance of the semiconductor laser device, and the leakage electron current can be reduced, and the potential barrier can be increased.

[0208] Note that since the refractive index of the P-side first barrier layer 43a is higher than that of the P-side second barrier layer 43b, increasing the film thickness of the P-side first barrier layer 43a increases the light confinement coefficient to the well layer 41. In particular, in an optical waveguide where the light distribution is closer to the N-type semiconductor layer, the light confinement coefficient to the well layer 41 tends to be small. Therefore, in order to suppress the decrease in the light confinement coefficient, it is effective to increase the film thickness of the P-side first barrier layer 43a. However, the electron current flowing through the P-type guide layer 50 beyond the well layer 41 increases as the film thickness of the P-side first barrier layer 43a increases. Therefore, the film thickness of the P-side first barrier layer 43a is preferably 10 nm or more and 30 nm or less.

[0209] Next, the impurity doping effects of the P-side first barrier layer 43a and the P-side second barrier layer 43b and the P-type guide layer 50 will be described with reference to FIGS. 12A and 12B. FIG. 12A shows the dependence of the potential barrier (ΔEg) on the P-type impurity concentration when a certain P-type impurity is doped into any of the P-type guide layer 50, the P-side first barrier layer 43a, and the P-side second barrier layer 43b in the semiconductor laser device 1 according to the present embodiment. FIG. 12B shows the dependence of the electron current density on the P-type impurity concentration at that time.

[0210] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al composition was set to 0.12 and 0.18, and the thicknesses were set to 15 nm and 30 nm. In this case, for the P-side first barrier layer 43a, a 5-nm region on the well layer 41 side was set as an undoped region. On the other hand, for the N-side first barrier layer 42a, a 5-nm region on the well layer 41 side was set as an undoped region, and a region at a distance of 5 nm or more from the well layer 41 was doped with N-type impurities of 1×10 17 cm -3 . Also, for the P-side second barrier layer 43b and the N-side second barrier layer 42b, cases where the Al composition had a compositional gradient from 0.12 to 0.24 and from 0.18 to 0.24 were considered, and the thickness was set to 15 nm. In this case, for the N-side second barrier layer 42b, the entire region was doped with N-type impurities of 1×10 17 cm -3 . Also, for the N-type guide layer 30, it was doped with impurities of 1×10 17 cm -3 . Note that for the N-type cladding layer 20, from the side closer to the well layer 41 to the side farther away, 1.4×10 17 cm -3 , 2×10 17 cm -3 , 6×10 17 cm -3 , 2×10 18 cm -3 and the impurity concentration was increased by doping impurities in multiple stages.

[0211] In this structure, the P-type impurity concentrations of the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50 (film thickness 0.2 μm) were from 1×10 17 cm -3 to 5× 17 cm -3When it is increased to, as shown in FIGS. 12A and 12B, the potential barrier (ΔEg) increases from 0.216 eV to 0.254 eV, and it can be seen that the electron current flowing through the P-type guide layer 50 decreases, having the effect of suppressing the leakage current. On the other hand, when the P-type impurity concentration of the P-type guide layer 50 is increased, although the potential barrier becomes larger and the series resistance of the semiconductor laser device becomes smaller, the waveguide loss becomes larger and the emission efficiency (slope efficiency) decreases.

[0212] Therefore, also in this case, the P-type impurity concentration doped into the P-type guide layer 50 is such that the average value of the P-type impurity concentration throughout the P-type guide layer 50 is 2×10 17 cm -3 to 4×10 17 cm -3 By controlling so as to be in the range, the waveguide loss, the series resistance of the semiconductor laser device, and the leakage electron current can be reduced, and the potential barrier can be increased.

[0213] Also, by doping the P-type impurity concentration into the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50, compared with the case where the P-type impurity concentration is not doped into the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50, the electron current flowing to the P-type semiconductor layer side beyond the well layer 41 can be made smaller to reduce the leakage current, and the effect of increasing the potential barrier also becomes larger.

[0214] Note that since the refractive index of the P-side first barrier layer 43a is higher than that of the P-side second barrier layer 43b, increasing the film thickness of the P-side first barrier layer 43a increases the light confinement factor in the well layer 41. In particular, in an optical waveguide where the light distribution is closer to the N-type semiconductor layer, the light confinement factor in the well layer 41 tends to be small. Therefore, in order to suppress a decrease in the light confinement factor, it is effective to increase the film thickness of the P-side first barrier layer 43a. However, the electron current flowing through the P-type guide layer 50 beyond the well layer 41 increases as the film thickness of the P-side first barrier layer 43a increases, but the increase in the leakage electron current is about 10% smaller than the case where the P-type impurity concentration is not doped in the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50. Therefore, the film thickness of the P-side first barrier layer 43a can be made about 10% thicker than the case where the P-type impurity concentration is not doped in the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50, and it is preferably 15 nm or more and 40 nm or less.

[0215] Here, in FIGS. 12A and 12B, the P-type impurity concentration doped in the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50 does not have a gradient. However, if a gradient is provided in the P-type impurity concentration doped in the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50, the results shown in FIGS. 13A and 13B are obtained. FIG. 13A shows the dependence of the potential barrier (ΔEg) on the P-type impurity concentration in the impurity doping profile of the semiconductor laser device 1 of Example 1 shown in FIG. 5A when impurities are doped. FIG. 13B shows the dependence of the electron current density on the P-type impurity concentration at that time.

[0216] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al compositions were 0.12 and 0.18, and the thicknesses were 15 nm and 30 nm. In this case, for the P-side first barrier layer 43a, a 5 nm region on the well layer 41 side was an undoped region. On the other hand, for the N-side first barrier layer 42a, a 5 nm region on the well layer 41 side was an undoped region, and in a region at a distance of 5 nm or more from the well layer 41, 1×10 17cm -3 was doped with N-type impurities. For the P-side second barrier layer 43b and the N-side second barrier layer 42b, the Al composition was changed with a composition gradient from 0.12 to 0.24 and from 0.18 to 0.24, and the thickness was set to 15 nm. In this case, for the N-side second barrier layer 42b, N-type impurities of 1×10 17 cm -3 were doped. For the N-type guide layer 30, impurities of 1×10 17 cm -3 were doped. For the N-type cladding layer 20, impurities were doped in multiple steps of 1.4×10 17 cm -3 , 2×10 17 cm -3 , 6×10 17 cm -3 , 2×10 18 cm -3 from the side closer to the well layer 41 to the side farther away to increase the impurity concentration.

[0217] In this structure, when the impurity concentration at the impurity doping start position P1 in the P-side first barrier layer 43a is 1×10 17 cm -3 and the P-type impurity concentration at the position P2 of the P-type guide layer 50 on the side away from the well layer 41 is doped with P-type impurities so as to increase gradually from 1×10 17 cm -3 to 1×10 18 cm -3 as shown in FIGS. 13A and 13B, when the thicknesses of the P-side first barrier layer 43a and the N-side first barrier layer 42a are 15 nm, the potential barrier (ΔEg) increases from 0.216 eV to 0.254 eV, and when the thicknesses of the P-side second barrier layer 43b and the N-side second barrier layer 42b are 30 nm, the potential barrier (ΔEg) increases from 0.215 eV to 0.234 eV.

[0218] In addition, when the P-type impurity concentration at the position P2 is increased, the electron current flowing through the P-type guide layer 50 decreases, and the leakage current can be suppressed. Here, when the P-type impurity concentration at the position P2 is increased, the potential barrier increases, and the series resistance of the semiconductor laser device also decreases. Further, since the P-type impurity concentration in the P-type guide layer 50 is inclined, even if the P-type impurity concentration at the position P2 is increased, an increase in waveguide loss is suppressed.

[0219] Therefore, by controlling the P-type impurity concentration doped into the P-type guide layer 50 so that the average value of the P-type impurity concentration throughout the P-type guide layer 50 is between 2×10 17 cm -3 and 4×10 17 cm -3 , the waveguide loss, the series resistance of the semiconductor laser device, and the leakage electron current can be reduced, and the potential barrier can be increased.

[0220] In addition, by doping the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50 with a gradient in impurity concentration, the leakage current can be reduced.

[0221] Note that since the refractive index of the P-side first barrier layer 43a is higher than that of the P-side second barrier layer 43b, increasing the film thickness of the P-side first barrier layer 43a increases the light confinement coefficient to the well layer 41. In particular, in an optical waveguide where the light distribution is closer to the N-type semiconductor layer, the light confinement coefficient to the well layer 41 tends to be small. Therefore, in order to suppress a decrease in the light confinement coefficient, it is effective to increase the film thickness of the P-side first barrier layer 43a. However, if the film thickness of the P-side first barrier layer 43a is made too thick, light confinement to the well layer 41 becomes large and COD is likely to occur. Specifically, the film thickness of the P-side first barrier layer 43a is preferably 15 nm or more and 50 nm or less. As a result, in an optical waveguide where the light distribution is closer to the N-type semiconductor layer, it is possible to increase the light confinement to the well layer 41 while suppressing the occurrence of COD and reduce the oscillation threshold current value.

[0222] Here, in FIGS. 13A and 13B, the Al compositions of the N-type guide layer 30 and the P-type guide layer 50 were symmetric, but when the Al compositions of the N-type guide layer 30 and the P-type guide layer 50 are made asymmetric, the results shown in FIGS. 14A and 14B are obtained. Specifically, in FIGS. 14A and 14B, the Al composition of the P-type guide layer 50 is made larger than that of the N-type guide layer 30 so that the bandgap energy of the P-type guide layer 50 becomes larger than the bandgap energy of the N-type guide layer 30. Note that FIG. 14A shows the dependence of the Al composition of the potential barrier for the P-type guide layer 50 of the semiconductor laser device 1 shown in FIG. 5C. FIG. 14B shows the dependence of the Al composition of the electron current density for the P-type guide layer 50 of the semiconductor laser device 1.

[0223] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al compositions were 0.12 and 0.18, and the thicknesses were 15 nm and 30 nm, respectively. In this case, for the P-side first barrier layer 43a, a 5-nm region on the well layer 41 side was an undoped region. On the other hand, for the N-side first barrier layer 42a, a 5-nm region on the well layer 41 side was an undoped region, and a region at a distance of 5 nm or more from the well layer 41 was doped with N-type impurities of 1×10 17 cm -3 . Also, for the N-side second barrier layer 42b, there were cases where the Al composition had a compositional gradient from 0.12 to 0.24 and from 0.18 to 0.24, and the thickness was 15 nm. For the P-side second barrier layer 43b, there were cases where the Al composition had a compositional gradient from 0.12 to Xpg and from 0.18 to Xpg, and the thickness was 15 nm. In this case, for the N-side second barrier layer 42b, the entire region was doped with N-type impurities of 1×10 17 cm -3 . Also, the Al composition of the N-type guide layer 30 was 0.24, and the Al composition of the P-type guide layer 50 was Xpg. Note that for the N-type clad layer 20, from the side closer to the well layer 41 toward the farther side, 1.4×10 17 cm -3 , 2×10 17 cm -3 , 6×10 17cm -3 , 2 × 10 18 cm -3 The impurity concentration was increased by doping impurities in multiple stages.

[0224] In this structure, the impurity concentration at the doping start position P1 of the P-type impurity in the P-side first barrier layer 43a is set to 1×10 17 cm -3 The P-type impurity concentration at the position P2 of the P-type guide layer 50 on the side away from the well layer 41 is set to 5×10 18 cm -3 The P-type impurities are doped so that the doping rate increases gradually from

[0225] Here, when Xpg is changed from 0.24 to 0.3, as shown in Figures 14A and 14B, when the thicknesses of the P-side first barrier layer 43a and the N-side first barrier layer 42a are 15 nm, the potential barrier (ΔEg) increases from 0.235 eV to 0.32 eV, and when the thicknesses of the P-side second barrier layer 43b and the N-side second barrier layer 42b are 30 nm, the potential barrier (ΔEg) increases from 0.25 eV to 0.315 eV.

[0226] Furthermore, increasing the P-type impurity concentration at the position P2 reduces the electron current flowing through the P-type guide layer 50, thereby suppressing the reactive current. Here, increasing the P-type impurity concentration at the position P2 increases the potential barrier, thereby reducing the series resistance of the semiconductor laser device. Furthermore, because the P-type impurity concentration is graded in the P-type guide layer 50, increasing the P-type impurity concentration at the position P2 suppresses an increase in waveguide loss.

[0227] It is also found that as the Al composition of the P-type guide layer 50 increases, the electron current flowing through the well layer 41 into the P-type guide layer 50 decreases rapidly. The average value of the P-type impurity concentration in the P-type guide layer 50 is 3×10 17 cm -3To such an extent, impurities are doped so that the P-type impurity concentration on the side closer to the well layer 41 becomes smaller. Therefore, in a state where waveguide loss is small, series resistance can be reduced and an increase in the potential barrier can be suppressed.

[0228] Also, by making the Al composition of the P-type guide layer 50 relatively higher than the Al composition of the N-type guide layer 30, the above-described effects can be obtained. Specifically, if the Al composition of the P-type guide layer 50 is made 0.02 larger than the Al composition of the N-type guide layer 30, the potential barrier becomes 0.03 eV larger, and the electron current leaking into the P-type guide layer 50 can also be reduced to about 50% or less. Further, if the Al composition of the P-type guide layer 50 is made 0.27, which is 0.03 larger than the Al composition of the N-type guide layer, the potential barrier can increase to a size of 0.27 eV or more. If the Al composition of the P-type guide layer 50 is made 0.29, which is 0.05 larger than the Al composition of the N-type guide layer, the potential barrier can increase to a size of 0.3 eV or more.

[0229] Furthermore, by setting the well layer thickness to 8 nm or more, making the Al composition of the P-type clad layer 60 larger than the Al composition of the N-type clad layer 20, and making the Al composition of the P-type guide layer 50 larger than the Al composition of the N-type guide layer 30, while increasing the optical confinement factor to the well layer 41, the light distribution can be made closer to the N-type semiconductor layer, and the leakage of the light distribution into the P-type clad layer 60 can be reduced. As a result, a semiconductor laser device with a high thermal saturation level, good temperature characteristics, and a high polarization ratio can be obtained.

[0230] Next, the influence of the N-type impurity concentration on the hole leakage current will be described with reference to FIGS. 15A, 15B, 16A, and 16B. FIG. 15A shows the dependence of the hole current density on the N-type impurity concentration at a position 100 nm from the N-side interface of the well layer 41 in the semiconductor laser device 1 according to the present embodiment. FIG. 15B shows the dependence of the hole current density on the N-type impurity concentration at the position of the N-type clad layer substrate-side interface in the semiconductor laser device 1 according to the present embodiment. Further, FIG. 16A shows an example of the N-type impurity concentration distribution in the N-type semiconductor layer in the semiconductor laser device 1 according to the present embodiment, and FIG. 16B shows another example of the N-type impurity concentration distribution in the N-type semiconductor layer.

[0231] In this structure, the impurity concentration at the doping start position P1 of the P-type impurity in the P-side first barrier layer 43a is 1×10 17 cm -3 and the P-type impurity is doped so that the P-type impurity concentration at the position P2 of the P-type guide layer 50 on the side away from the well layer 41 increases in a gradient manner from 1×10 17 cm -3 to 1×10 18 cm -3 Further, the P-type clad layer 60 is doped with 2×10 18 cm -3 of P-type impurities.

[0232] When the P-type impurity concentration at the position P2 is increased, the electron current flowing through the P-type guide layer 50 decreases, and the idle current can be suppressed. Here, when the P-type impurity concentration at the position P2 is increased, the potential barrier increases, and the series resistance of the semiconductor laser device also decreases. Further, since the P-type impurity concentration is gradient in the P-type guide layer 50, an increase in the waveguide loss is suppressed even when the P-type impurity concentration at the position P2 is increased.

[0233] Therefore, the P-type impurity concentration doped into the P-type guide layer 50 is such that the average value of the P-type impurity concentration over the entire P-type guide layer 50 is from 2×10 17 cm -3 to 4×10 17 cm -3By controlling so as to be between, waveguide loss, the series resistance of the semiconductor laser device, and leakage electron current can be reduced, and the potential barrier can be increased.

[0234] Further, since the N-type impurities in the N-type semiconductor layer are doped so that the light distribution in the vertical direction becomes closer to the N-type semiconductor layer, doping is performed so that the N-type impurity concentration increases in a direction away from the well layer 41. In the case shown in FIG. 16A, in the region from a distance of 5 nm or more from the well layer 41 of the N-type guide layer 30 and the N-side first barrier layer 42a to the N-type guide layer 30 toward the substrate 10 side, N-type impurities are 5×10 16 cm -3 are doped, and for the N-type cladding layer 20, from the side closer to the well layer 41 toward the side farther away, 7×10 16 cm -3 (0.25 μm), 1×10 17 cm -3 (0.25 μm), 3×10 17 cm -3 (0.5 μm), 1×10 18 cm -3 (2 μm) and the impurity concentration is increased by doping in multiple steps. When doping N-type impurities in multiple steps, in the N-type cladding layer 20, in adjacent regions having different impurity concentrations, the film thickness of the region farthest from the well layer 41 is the thickest, and in other regions, the film thickness of the region closer to the well layer 41 is less than or equal to the film thickness of the region farther from the well layer. This is because in the region having the highest impurity concentration on the side farthest from the well layer 41 in the N-type cladding layer 20, the light distribution intensity in the vertical direction is attenuated, and even if the impurity concentration is increased, the influence of free carrier loss is small, so it does not lead to an increase in waveguide loss and the effect of reducing the series resistance of the semiconductor laser device can be obtained.

[0235] In addition, the vertical light distribution intensity in the N-type cladding layer 20 and the change rate of the attenuation of the intensity are larger closer to the well layer 41. From this, in order to avoid an increase in waveguide loss due to an increase in impurity concentration, when increasing the impurity concentration in multiple steps in a region where the vertical light distribution is not sufficiently attenuated, the film thickness of each concentration constant region should be made thinner on the side closer to the well layer 41.

[0236] Based on this N-type layer impurity concentration profile, with each concentration being 1 times, 1.2 times, 1.5 times, 2 times, and 3 times, in FIG. 15A, the calculation results of the hole current density at a position 100 nm from the N-side interface of the well layer 41 are shown, and in FIG. 15B, the calculation results of the hole current density at the position of the N-type cladding layer substrate-side interface are shown.

[0237] As shown in FIGS. 15A and 15B, it can be seen that increasing the N-type impurity concentration results in a lower hole current density and a reduction in the hole current leaking into the N-type semiconductor layer beyond the well layer 41.

[0238] In addition, by increasing the N-type impurity concentration, the series resistance of the semiconductor laser device can be reduced, so the operating current of the semiconductor laser device can also be reduced. Also, since the light distribution is made closer to the N-type semiconductor layer so that the ratio of the existence of the light distribution is the largest in the N-type guide layer 30, by making the N-type impurity concentration of the N-type guide layer 30 the lowest compared to the N-type impurities of other N-type semiconductor layers, the waveguide loss can be reduced. From this, by making the doping profile of the N-type impurity concentration into the pattern shown in FIG. 16A, it is possible to simultaneously achieve a reduction in the series resistance and a reduction in the waveguide loss of the semiconductor laser device.

[0239] Note that the doping profile of the N-type impurity may be changed not only in a stepwise manner as shown in FIG. 16A, but also such that the N-type impurity concentration on the substrate 10 side increases continuously as shown by the solid line in FIG. 16B. Further, as shown by the dashed line in FIG. 16B, in the N-type guide layer 30, the N-type impurity concentration at the position where the light distribution intensity is highest is lowered, and the N-type impurity concentration is increased continuously or stepwise from that position toward the substrate 10 side, whereby the waveguide loss can be further reduced. Note that, as shown by the dash-dotted line in FIG. 16B, the N-type impurity concentration may be changed non-linearly.

[0240] Also, as shown in FIG. 16C, the impurity concentration doped in the N-side first barrier layer 42a may be increased, the impurity concentration of the N-side second barrier layer 42b may be made lower than the doping concentration of the N-side first barrier layer 42a, and the N-type impurity concentration may be increased stepwise from the well layer 41 toward the substrate 10.

[0241] In this case, the impurity concentration doped in the N-side first barrier layer may be from 5×10 17 cm -3 to 1×10 18 cm -3 This can lower the potential of the valence band of the N-side first barrier layer 42a and suppress the leakage of the hole current in which the holes injected into the well layer 41 leak to the N-type layer side, and can further enhance the high-temperature high-output operation of the semiconductor laser device. Further, the N-type impurity concentration of the N-side second barrier layer 42b may be increased relative to the N-type impurity concentration of the N-type guide layer 30 in the same manner as the impurity concentration of the N-side first barrier layer 42a. However, since this is accompanied by an increase in the waveguide loss, even if the N-type impurity concentration in the region within a distance of 10 nm or less from the vicinity of the interface between the N-side second barrier layer 42b and the N-side first barrier layer 42a is increased in the N-side second barrier layer 42b, the leakage of the hole current can be suppressed.

[0242] Furthermore, when increasing the doping concentration of the N-side first barrier layer 42a, in the case of forming a window region by hole diffusion or ion implantation, even if the temperature of the thermal annealing process for forming the window portion is lowered, via N-type impurities, atomic exchange is likely to occur with the well layer 41, and the effect that the bandgap energy of the well layer 41 in the window portion is likely to increase can be obtained.

[0243] Also, the doping of N-type impurities into the N-type guide layer 30 may be gradually increased toward the substrate 10 side step by step from the vicinity of the interface with the N-type cladding layer 20 as shown in FIG. 16D. In an optical waveguide in which the N-type light distribution is closer to the N-type semiconductor layer, since the portion with the highest light intensity in the vertical light distribution in the substrate normal direction is in the region on the well layer 41 side in the N-type guide layer 30, in the N-type guide layer 30, if there is a minimum concentration region of the N-type impurity concentration in the region on the well layer 41 side in the N-type guide layer 30, an increase in waveguide loss can be suppressed.

[0244] In the examples shown in FIGS. 16A to 16D, the minimum value of the N-type impurity concentration in the N-type guide layer 30 is 5×10 16 cm -3 or more and 3×10 17 cm -3 or less. In this case, all the effects of suppressing an increase in waveguide loss, suppressing the generation of hole leakage current, and suppressing an increase in the series resistance of the semiconductor laser device can be obtained. Also, even if the N-type impurity concentration on the substrate 10 side of the N-type cladding layer 20 is increased, since the ratio of the light distribution existing in the N-type cladding layer 20 in the region of 1 μm or more from the interface between the N-type guide layer 30 and the N-type cladding layer 20 toward the substrate 10 side is small, the increase in waveguide loss is small. Therefore, for reducing the series resistance of the semiconductor laser device, the N-type impurity concentration of the N-type cladding layer 20 in the region of 1 μm or more from the interface between the N-type guide layer 30 and the N-type cladding layer 20 toward the substrate 10 side is preferably high to such an extent that the mobility does not decrease. For example, it is preferably 1×10 18 cm -3 or more and 3×10 18 cm -3 or less.

[0245] Also, while increasing the N-type impurity concentration of the N-side first barrier layer 42a as shown in FIGS. 16C and 16D, the N-type impurity concentrations of the N-side second barrier layer 42b, the N-type guide layer 30, and the N-type clad layer 20 may be continuously changed as shown in FIG. 16B. Further, the region where the N-type impurity concentration is increased in the vicinity of the well layer 41 may include not only the N-side first barrier layer 42a but also a part of the N-side second barrier layer 42b. If the film thickness of that region is 10 nm or less, while suppressing an increase in waveguide loss to a small extent, the series resistance of the semiconductor laser device can be reduced, and the leakage of the hole current can be further suppressed.

[0246] Next, the quantum well structure of the well layer 41 of the active layer 40 was examined. Hereinafter, the examination results will be described with reference to FIGS. 17 to 19. FIGS. 17 to 19 are diagrams showing the dependence of the Al composition of the well layer on the heavy hole and light hole quantum level energies.

[0247] FIG. 17 shows that with an Al composition of 0.06, the P-side first barrier layer 43a and the N-side 1 barrier layer 42 a are made of Al 0.06 Ga 0.94 As with a thickness of 15 nm, and the P-side second barrier layer 43b and the N-side second barrier layer 42b are made of Al 0.24 Ga 0.76 As with a thickness of 15 nm, and the well layer 41 is made of Al X Ga 1-X-Y In YWhen As is used, the calculation results of the Al composition dependence of the relative potential energies of the heavy hole (HH) and light hole (LH) levels formed in the well layer 41 are shown when the thickness of the well layer 41 is 6 nm, 8.5 nm, 12 nm, and 15 nm. Here, the electron level, HH level, and LH level are represented as En, HHn, and LHn, respectively. Also, n is a natural number, and the ground level is taken as 1. In this calculation, in order to obtain the same oscillation wavelength of 915 nm, the energy difference between E1 - H1 is kept constant (1.35 eV). Note that in Fig. 17, the relational expression between the In composition Y and the Al composition X for obtaining the same oscillation wavelength is shown when the Al composition X of the well layer 41 is changed. Also, the misalignment with the GaAs substrate in the well layer 41 having each Al composition is shown by a dashed line.

[0248] Here, the magnitude relationship of the potential energy with respect to the electron level is opposite to that with respect to the hole level. In the calculation results shown in Fig. 17, when the potential energies between the levels are relatively compared, the level with the highest relative potential energy (i.e., located at the top of the graph) is interpreted as having the lowest potential for holes.

[0249] As shown in Fig. 17, when the thickness of the well layer 41 is 6 nm, two levels of HH with relatively lower potential energy than L1 are formed. Therefore, when holes are injected into the well layer 41, the holes are filled in the order of H1, H2, L1 from the lowest potential energy.

[0250] Here, when the Al composition of the well layer 41 is increased, the compressive strain of the well layer 41 increases. Therefore, the energy level of HH changes in the direction where the potential energy with respect to holes is low, and the energy level of LH changes in the direction where the potential energy with respect to holes is high. From this, the greater the Al composition of the well layer 41 is increased to enhance the compressive strain, the greater the energy difference between H1 and L1 becomes. Holes are more likely to exist in H1 where the hole potential energy is the smallest among HH, and conversely, holes are less likely to exist in L1 where the hole potential energy is the largest among LH. From this, increasing the Al composition of the well layer 41 to enhance the compressive strain results in an increase in the number of holes in HH and a decrease in the number of holes in LH. Since LH contributes to the generation of TM mode light whose polarization direction is in the substrate normal direction in the oscillated laser light, an increase in the number of holes in LH leads to a decrease in the polarization ratio (TE / (TE + TM)). Therefore, it can be understood that increasing the Al composition of the well layer 41 to enhance the compressive strain can increase the polarization ratio.

[0251] Also, if the thickness of the well layer 41 is 6 nm, two energy levels of HH with a potential energy lower than the potential energy of LH are formed. Therefore, holes can preferentially exist in the energy levels of HH, and laser light with a high polarization ratio and a large TE mode component can be obtained.

[0252] In the case where the thickness of the well layer 41 is 8.5 nm, when the Al composition of the well layer 41 is 0.08 or more, the energy level of the heavy hole (HH) is higher than the energy level of the valence band of the first barrier layer in terms of the hole potential energy, and no quantum level of the light hole (LH) is formed in the quantum well formed by the P-side first barrier layer 43a, the N-side first barrier layer 42a, and the well layer 41. Instead, a quantum level is formed with the P-side second barrier layer 43b and the N-side second barrier layer 42b as the barrier layers. In this case, since the density of states of the quantum level is inversely proportional to the thickness of the quantum well structure, the density of states of LH1 becomes even smaller, and the effect of increasing the polarization ratio increases. This state is indicated by the thick dashed line of L1 in each graph of FIG. 17. As shown in FIG. 17, when the thickness of the well layer 41 is 8.5 nm or more, no LH is formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a when the Al composition of the well layer 41 is 0.04 or more. Also, it can be seen that as the well layer 41 becomes thicker, with a lower lattice mismatch in the well layer 41, no LH is formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a. Further, it can be seen that the thicker the well layer 41, the larger the number of HH levels with a hole potential energy lower than that of L1, and the number of holes existing in L1 is likely to decrease.

[0253] As shown in FIG. 17, when the thickness of the well layer 41 is 8.5 nm or more, when the Al composition of the well layer 41 is 0.04 or more, the number of HH levels with a hole potential energy lower than that of L1 becomes 3 levels, and the number of LHs existing in the LH level can be reduced, which is effective for increasing the polarization ratio.

[0254] Also, when the thickness of the well layer 41 is 12 nm or more, when the Al composition of the well layer 41 is 0.0 or more, the number of HH levels with a hole potential energy lower than that of L1 becomes 3 levels, and the number of LHs existing in the LH level can be reduced, which is effective for increasing the polarization ratio.

[0255] Note that since the well layer 41 has a high refractive index, the light confinement coefficient for the well layer 41 becomes larger as the film thickness increases, and the threshold carrier density required for laser oscillation is reduced. Therefore, the number of holes existing in L1 is further reduced, and the polarization ratio increases.

[0256] The P-side first barrier layer 43a and the N-side first barrier layer 42a also have a low Al composition, and have a higher refractive index than the P-side second barrier layer 43b, the N-side second barrier layer 42b, the N-type guide layer 30, the N-type cladding layer 20, the P-type guide layer 50, and the P-type cladding layer 60. Therefore, the film thicknesses of the P-side first barrier layer 43a and the N-side first barrier layer 42a should be thicker to increase the light confinement coefficient to the well layer 41 and reduce the threshold carrier density required for laser oscillation. As a result, the number of holes present in L1 is further reduced and the polarization ratio is increased. For example, if the total film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a is 20 nm or more, it is effective in increasing the light confinement coefficient. However, if the total film thickness is made too thick, the light confinement coefficient to the well layer 41 becomes large, resulting in a decrease in the COD level. Therefore, the total thickness may be 80 nm or less.

[0257] Also, FIG. 18 shows the P-side first barrier layer 43a and the N-side first barrier layer 42a with an Al composition of 0.12 as Al 0.12 Ga 0.88 As, with a thickness of 15 nm, and also the P-side second barrier layer 43b and the N-side second barrier layer 42b as Al 0.24 Ga 0.76 As, with a thickness of 15 nm, and also the well layer 41 as Al X Ga 1-X-Y In Y As. When the thickness of the well layer is 6 nm, 8.5 nm, 12 nm, and 15 nm, the calculation results of the Al composition dependence of the relative potential energies of the heavy hole (HH) and light hole (LH) levels formed in the well layer 41 are shown. Here, similar to FIG. 17, the electron level, HH level, and LH level are represented as En, HHn, and LHn. Also, n is a natural number, and the ground level is 1. In this calculation as well, in order to obtain the same oscillation wavelength of 915 nm, the energy difference between E1-H1 is kept constant (1.35 eV). Note that FIG. 18 shows the relational expression between the In composition Y and the Al composition X for obtaining the same oscillation wavelength when the Al composition X of the well layer 41 is changed. Also, the misalignment with the GaAs substrate in the well layer 41 having each Al composition is indicated by a dashed line.

[0258] As shown in FIG. 18, when the thickness of the well layer 41 is 6 nm, two levels of HH having a relatively lower potential energy than L1 are formed. Therefore, when holes are injected into the well layer 41 as described above, the holes are filled in the order of H1, H2, and L1 from the lowest potential energy.

[0259] Here, as the Al composition of the well layer 41 increases, the compressive strain of the well layer 41 increases. Therefore, the energy level of HH changes in the direction where the potential energy for holes is low, and the energy level of LH changes in the direction where the potential energy for holes is low. From this, the greater the Al composition of the well layer 41 and the higher the compressive strain, the greater the energy difference between H1 and L1, and the easier it is for holes to exist in H1, which has the lowest hole potential energy among HH. Conversely, it becomes less likely for holes to exist in L1, which has the highest hole potential energy among LH. From this, increasing the Al composition of the well layer 41 and enhancing the compressive strain results in an increase in the number of holes in HH and a decrease in the number of holes in LH. Since LH contributes to the generation of TM mode light whose polarization direction is in the substrate normal direction in the oscillated laser light, an increase in the number of holes in LH leads to a decrease in the polarization ratio (TE / (TE + TM)). Therefore, it can be seen that increasing the Al composition of the well layer 41 and enhancing the compressive strain can increase the polarization ratio.

[0260] Also, if the film thickness of the well layer 41 is 6 nm, two levels of HH energy levels with a potential energy lower than that of LH are formed. Therefore, holes can preferentially exist in the HH energy levels, and laser light with a high polarization ratio and a large TE mode component can be obtained.

[0261] In the case of the thickness of the well layer 41 being 8.5 nm, when the Al composition of the well layer 41 is 0.08 or more, the energy level of the heavy hole (HH) is higher than the energy level of the valence band of the first barrier layer in terms of the hole potential energy, and no quantum level of the light hole (LH) is formed in the quantum well formed by the P-side first barrier layer 43a, the N-side first barrier layer 42a, and the well layer 41. Instead, a quantum level with the P-side second barrier layer 43b and the N-side second barrier layer 42b as the barrier layers is formed. In this case, since the density of states of the quantum level is inversely proportional to the thickness of the quantum well structure, the density of states of LH1 becomes even smaller, and the effect of increasing the polarization ratio increases. This state is shown by the thick dashed line of L1 or L2 in each graph of FIG. 17. As shown in FIG. 18, when the thickness of the well layer 41 is 8.5 nm or more, no LH is formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a with the Al composition of the well layer 41 being 0.08 or more. Also, it can be seen that as the well layer 41 becomes thicker, with a lower lattice mismatch in the well layer 41, no LH is formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a. Further, it can be seen that the thicker the well layer 41, the larger the number of HH levels with a hole potential energy lower than that of L1, and the number of holes existing in L1 is likely to decrease.

[0262] As shown in FIG. 18, when the thickness of the well layer 41 is 8.5 nm or more, with the Al composition of the well layer 41 being 0.02 or more, the number of HH levels with a hole potential energy lower than that of L1 becomes three levels, and the number of LHs existing in the LH level can be reduced, which is effective in increasing the polarization ratio.

[0263] Also, when the thickness of the well layer 41 is 12 nm or more, with the Al composition of the well layer 41 being 0.0 or more, the number of HH levels with a hole potential energy lower than that of L1 becomes three levels, and the number of LHs existing in the LH level can be reduced, which is effective in increasing the polarization ratio.

[0264] Note that since the well layer 41 has a high refractive index, the thicker the film thickness, the larger the light confinement coefficient to the well layer 41, and the threshold carrier density required for laser oscillation is reduced. Therefore, the number of holes existing in L1 is further reduced, and the polarization ratio increases.

[0265] The P-side first barrier layer 43a and the N-side first barrier layer 42a also have a low Al composition, and have a higher refractive index than the P-side second barrier layer 43b, the N-side second barrier layer 42b, the N-type guide layer 30, the N-type cladding layer 20, the P-type guide layer 50, and the P-type cladding layer 60. Therefore, the larger the film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a, the greater the light confinement coefficient to the well layer 41, and the lower the threshold carrier density required for laser oscillation. As a result, the number of holes present in L1 is further reduced and the polarization ratio is increased. For example, if the total film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a is set to 25 nm or more, it is effective in increasing the light confinement coefficient. However, if the total film thickness is made too large, the light confinement coefficient to the well layer 41 becomes large, resulting in a decrease in the COD level. Therefore, the total film thickness may be 90 nm or less.

[0266] Also, FIG. 19 shows the P-side first barrier layer 43a and the N-side first barrier layer 42a with an Al composition of 0.18 as Al 0.18 Ga 0.82 As, with a thickness of 15 nm, and also the P-side second barrier layer 43b and the N-side second barrier layer 42b as Al 0.24 Ga 0.76 As, with a thickness of 15 nm, and also the well layer 41 as Al X Ga 1-X-Y In Y As. When the thickness of the well layer is 6 nm, 8.5 nm, 12 nm, and 15 nm, the calculation results of the Al composition dependence of the relative potential energies of the heavy hole (HH) and light hole (LH) levels formed in the well layer 41 are shown. Here, similar to FIG. 17, the electron level, HH level, and LH level are represented as En, HHn, and LHn. Also, n is a natural number, and the ground level is 1. In this calculation as well, in order to obtain the same oscillation wavelength of 915 nm, the energy difference between E1 - H1 is kept constant (1.35 eV). Note that FIG. 19 shows the relational expression between the In composition Y and the Al composition X for obtaining the same oscillation wavelength when the Al composition X of the well layer 41 is changed. Also, the lattice mismatch with the GaAs substrate in the well layer 41 having each Al composition is shown by a dashed line.

[0267] As shown in Fig. 19, when the thickness of the well layer 41 is 6 nm, two levels of HH with relatively lower potential energy than L1 are formed. Therefore, when holes are injected into the well layer 41 as described above, the holes are filled in the order of H1, H2, and L1 from the lowest potential energy.

[0268] Here, as the Al composition of the well layer 41 increases, the compressive strain of the well layer 41 increases. Therefore, the energy levels of HH change in the direction of lower potential energy for holes, and the energy levels of LH change in the direction of lower potential energy for holes. From this, as described above, the greater the Al composition of the well layer 41 is increased to enhance the compressive strain, the greater the energy difference between H1 and L1 becomes, and holes are more likely to exist in H1 with the lowest hole potential energy in HH. Conversely, holes are less likely to exist in L1 with the highest hole potential energy in LH. From this, increasing the Al composition of the well layer 41 to enhance the compressive strain increases the number of holes in HH and decreases the number of holes in LH. Since LH contributes to the generation of TM mode light with the polarization direction in the substrate normal direction in the oscillated laser light, an increase in the number of holes in LH leads to a decrease in the polarization ratio (TE / (TE + TM)). Therefore, it can be seen that increasing the Al composition of the well layer 41 to enhance the compressive strain can increase the polarization ratio.

[0269] Also, if the film thickness of the well layer 41 is 6 nm, two levels of HH levels with potential energy lower than that of LH are formed. Therefore, holes can preferentially exist in the HH levels, and laser light with a high polarization ratio and a large TE mode component can be obtained.

[0270] As shown in Fig. 19, when the thickness of the well layer 41 is 8.5 nm or more, when the Al composition of the well layer 41 is 0.02 or more, the number of HH levels with hole potential energy lower than L1 becomes three levels, and the number of LHs existing in the LH levels can be reduced, which is effective in increasing the polarization ratio.

[0271] In addition, when the thickness of the well layer 41 is 12 nm or more, the number of HH levels with an Al composition of the well layer 41 of 0.0 or more and a hole potential energy lower than that of L1 becomes three levels, the number of LHs existing in the LH level can be reduced, which is effective in increasing the polarization ratio.

[0272] Since the well layer 41 has a high refractive index, the thicker the film thickness, the greater the optical confinement coefficient for the well layer 41, and the threshold carrier density required for laser oscillation is reduced. Therefore, the number of holes existing in L1 is further reduced and the polarization ratio is increased.

[0273] The P-side first barrier layer 43a and the N-side first barrier layer 42a also have a low Al composition and a higher refractive index than the P-side second barrier layer 43b, the N-side second barrier layer 42b, the N-type guide layer 30, the N-type cladding layer 20, the P-type guide layer 50, and the P-type cladding layer 60. Therefore, the thicker the film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a, the greater the optical confinement coefficient for the well layer 41, and the threshold carrier density required for laser oscillation is reduced. Therefore, the number of holes existing in L1 is further reduced and the polarization ratio is increased. For example, if the total film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a is 30 nm or more, it is effective in increasing the optical confinement coefficient. However, if the total film thickness is made too thick, the optical confinement coefficient for the well layer 41 becomes large, resulting in a decrease in the COD level. Therefore, the total thickness may be 100 nm or less.

[0274] As described above with reference to FIGS. 17 to 19, when the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a is set to 0.06 to 0.18 and the thickness of the well layer 41 is set to 6 nm to 15 nm, two or more HH levels with a potential energy lower than the potential energy of the LH are formed. Therefore, holes can preferentially exist in the HH level, and a laser beam with a high polarization ratio having a large TE mode component can be obtained.

[0275] In addition, when the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a is set to be from 0.06 to 0.18 and the thickness of the well layer 41 is set to be from 8.5 nm to 15 nm, the number of levels of HH having a potential energy lower than the hole potential energy of LH can be increased in a wider Al composition range of the well layer than in the case where the film thickness of the well layer 41 is 6 nm.

[0276] Further, when the thickness of the well layer 41 is 8.5 nm, even if InGaAs with an Al composition of 0.02 or more in the well layer 41 is used, or when the thickness of the well layer 41 is 12 nm, even if InGaAs with an Al composition of 0 in the well layer 41 is used as the well layer 41, the number of levels of HH having a potential energy lower than the hole potential energy can be made 3 or more, the number of LHs existing in L1 decreases, and the effect of increasing the polarization ratio can be obtained.

[0277] Note that when the thickness of the well layer 41 becomes thicker than 15 nm, the light confinement coefficient in the well layer 41 may increase and the COD level may decrease. Also, when forming a window region near the resonator end face, if the well layer 41 becomes too thick, the short-wavelength shift of the bandgap in the window region due to the group III atom exchange between the P-side first barrier layer 43a and the N-side first barrier layer 42a and the well layer 41 becomes small, and the COD generation suppression effect is reduced. Further, if the thickness of the well layer 41 becomes too thin, in the high-temperature annealing process during window formation, the short-wavelength shift of the bandgap of the well layer 41 in the gain section where the window region 120 is not formed easily occurs, and the temperature characteristics of the semiconductor laser device deteriorate. Therefore, the thickness of the well layer 41 is preferably set to be 6 nm or more and 15 nm or less.

[0278] In FIGS. 17 to 19, the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a made of AlGaAs is set to be from 0.06 to 0.18. However, if the Al compositions of the P-side first barrier layer 43a and the N-side first barrier layer 42a are increased too much, the optical confinement factor in the well layer 41 becomes small, and thus the temperature characteristics of the semiconductor laser device deteriorate. Therefore, the Al compositions of the P-side first barrier layer 43a and the N-side first barrier layer 42a are preferably 0.06 or more and 0.22 or less.

[0279] In addition, when the Al compositions of the N-side second barrier layer 42b and the P-side second barrier layer 43b made of AlGaAs are increased, leakage of electron current from the well layer 41 to the P-type layer side and leakage of hole current from the well layer 41 to the N-type layer side can be suppressed. Therefore, the Al composition is preferably 0.24 or more. However, if the Al compositions of the N-side second barrier layer 42b and the P-side second barrier layer 43b are increased too much, an increase in the operating voltage is caused. Therefore, the Al composition is preferably 0.32 or less.

[0280] In the semiconductor laser device 1 according to the present embodiment, the resonator length is long. Specifically, the resonator length of the semiconductor laser device 1 is 2 mm or more.

[0281] In this way, by increasing the resonator length of the semiconductor laser device 1, the thermal resistance of the semiconductor laser device 1 is reduced and the heat dissipation performance is improved. Thereby, the optical output at which thermal saturation occurs can be increased.

[0282] Note that if the resonator length of the semiconductor laser device 1 is increased too much, the mirror loss of the resonator may increase and the slope efficiency may decrease. However, in the present disclosure, since the optical distribution is made closer to the N-type semiconductor layer to reduce the waveguide loss, even if the resonator length of the semiconductor laser device 1 is increased, a decrease in the slope efficiency is suppressed, and the maximum optical output can be increased.

[0283] (Modification example) As described above, the semiconductor laser device and its manufacturing method according to the present disclosure have been described based on the embodiments. However, the present disclosure is not limited to the above-described embodiments.

[0284] For example, in the above embodiment, the current injection region was defined by providing the current blocking layer 80 having the opening 80a in the P-type contact layer 70, but it is not limited thereto. Specifically, like the semiconductor laser device 1A shown in FIGS. 20, 21A, 21B, and 21C, the current injection region may be defined by providing the ridge portion 200A. FIG. 20 is a top view of the semiconductor laser device 1A according to a modified example. FIG. 21A is a cross-sectional view of the semiconductor laser device 1A taken along line XXIA-XXIA of FIG. 20, FIG. 21B is a cross-sectional view of the semiconductor laser device 1A taken along line XXIB-XXIB of FIG. 20, and FIG. 21C is a cross-sectional view of the semiconductor laser device 1A taken along line XXIC-XXIC of FIG. 20. Note that FIG. 21A shows a cross-section of the gain portion of the semiconductor laser device 1A, and FIG. 21B shows a cross-section of the end face portion on the front end face 1a side of the semiconductor laser device 1A.

[0285] As shown in FIGS. 20 to 21C, the semiconductor laser device 1A in this modified example is a ridge stripe structure semiconductor laser element having a ridge portion 200A extending in the resonator length direction as an optical waveguide.

[0286] In the semiconductor laser device 1A, an insulating film 100A having an opening 100a corresponding to the ridge portion 200A is formed. The insulating film 100A is a dielectric film having a current blocking function. The insulating film 100A is composed of, for example, an insulating film such as SiO2.

[0287] Also, in this modified example, in order to form the ridge portion 200A, a pair of grooves having a depth of 0.2 μm are formed in the P-type contact layer 70, and the surface of the P-type contact layer 70 other than the ridge portion 200A serving as a current injection path is covered with the insulating film 100A. Thereby, the flowing current can be concentrated and made to flow through the ridge portion 200A. Note that the grooves for forming the ridge portion 200A may be formed not only in the P-type contact layer 70 but also in the P-type cladding layer 60.

[0288] In this modified example, the configuration other than the ridge portion 200A and the insulating film 100A is basically the same as that of the semiconductor laser device 1 in the above embodiment.

[0289] Therefore, the semiconductor laser device 1A according to this modified example also exhibits the same operational effects as the semiconductor laser device 1 according to the above embodiment.

[0290] In addition, it can be applied as a semiconductor laser device in various wavelength bands by combining the opening 80a in the above embodiment that defines the current injection region, the opening 100a in this modified example, the resonator length, and the well layer 41.

[0291] For example, by setting the input current to a semiconductor laser device with an opening width of about 90 μm or more and 300 μm or less and a resonator length of about 2000 μm or more and 6000 μm or less to about 15 A or more and 40 A or less, and the input voltage to about 1.7 V or more and 3 V or less, a semiconductor laser device can be realized that has a wavelength in the band of about 780 nm or more and 800 nm or less and emits laser light with an optical output of about 15 W or more and 30 W or less.

[0292] For example, by setting the input current to a semiconductor laser device with an opening width of about 90 μm or more and 300 μm or less and a resonator length of about 2000 μm or more and 6000 μm or less to about 15 A or more and 40 A or less, and the input voltage to about 1.6 V or more and 3 V or less, a semiconductor laser device can be realized that has a wavelength in the band of about 800 nm or more and 820 nm or less and emits laser light with an optical output of about 15 W or more and 30 W or less.

[0293] For example, by setting the input current to a semiconductor laser device with an opening width of about 90 μm or more and 300 μm or less and a resonator length of about 2000 μm or more and 6000 μm or less to about 15 A or more and 40 A or less, and the input voltage to about 1.5 V or more and 3 V or less, a semiconductor laser device can be realized that has a wavelength in the band of about 850 nm or more and 900 nm or less and emits laser light with an optical output of about 15 W or more and 30 W or less.

[0294] For example, by setting the input current to a semiconductor laser device having an aperture width of about 90 μm or more and 300 μm or less and a resonator length of about 2000 μm or more and 6000 μm or less to about 15 A or more and 50 A or less, and the input voltage to about 1.45 V or more and 3 V or less, a semiconductor laser device having optical characteristics of emitting laser light having a wavelength in a band of about 900 nm or more and 930 nm or less and an optical output of about 15 W or more and 40 W or less can be realized.

[0295] For example, by setting the input current to a semiconductor laser device having an aperture width of about 90 μm or more and 300 μm or less and a resonator length of about 2000 μm or more and 6000 μm or less to about 15 A or more and 50 A or less, and the input voltage to about 1.4 V or more and 3 V or less, a semiconductor laser device having optical characteristics of emitting laser light having a wavelength in a band of about 930 nm or more and 960 nm or less and an optical output of about 15 W or more and 40 W or less can be realized.

[0296] For example, by setting the input current to a semiconductor laser device having an aperture width of about 4 μm or more and 300 μm or less and a resonator length of about 2000 μm or more and 6000 μm or less to about 1 A or more and 50 A or less, and the input voltage to about 1.4 V or more and 3 V or less, a semiconductor laser device having optical characteristics of emitting laser light having a wavelength in a band of about 960 nm or more and 990 nm or less and an optical output of about 1 W or more and 40 W or less can be realized.

[0297] Further, in the semiconductor laser device 1A according to this modification, since it has the ridge portion 200A, it is possible to suppress characteristic deterioration and the like when the semiconductor laser device 1A is mounted on a submount or the like. This will be described below.

[0298] When the resonator length of the semiconductor laser device 1A is increased, the influence of the shear strain generated at the end in the width direction of the semiconductor laser device 1 on the optical waveguide when the semiconductor laser device 1 is mounted on the submount becomes large. In this case, when a shear stress that is asymmetric about the left and right is generated in the current injection region that becomes the optical waveguide, the polarization plane of the laser light propagating through the optical waveguide is inclined, resulting in an elliptical polarization wave and a decrease in the polarization ratio.

[0299] Therefore, as in the semiconductor laser device 1A according to this modification example, when a ridge portion 200A is provided and the optical waveguide is formed into a ridge type, when the semiconductor laser device 1A is mounted in a junction down manner, the shear stress generated in the ridge portion 200A and the shear stress generated at the end portion in the width direction of the semiconductor laser device cancel each other out, and the shear stress generated in the optical waveguide is reduced. As a result, it is possible to suppress the inclination of the polarization plane of the laser light propagating through the optical waveguide and the reduction of the polarization ratio.

[0300] This will be described in more detail with reference to FIG. 22. FIG. 22 is a diagram showing a state when the semiconductor laser device 1A according to this modification example is mounted on the submount 2 in a junction down manner.

[0301] As the submount 2, one having a larger coefficient of thermal expansion than the semiconductor laser device 1A is used. For example, the coefficients of thermal expansion of the semiconductor materials constituting the semiconductor laser device 1A are 5.35×10 -6 for GaAs, 3.4×10 -6 for AlAs, 4.33×10 -6 for InAs, 5.59×10 -6 for GaN, 4.15×10 -6 for AlN, and 2.85×10 -6 for InN. Therefore, as the submount 2, one containing a metal material or a ceramic material as a main constituent material is used. As the main constituent material of the submount 2, Cu (coefficient of thermal expansion 16.8×10 -6 ), Ti (coefficient of thermal expansion 8.4×10 -6 ), Pt (coefficient of thermal expansion 8.4×10 -6 ), Au (coefficient of thermal expansion 14.2×10 -6 ), Ni (coefficient of thermal expansion 13.4×10 -6 ), and SiC (coefficient of thermal expansion 6.6×10 -6 ) can be used.

[0302] In this case, as shown in FIG. 22, when the semiconductor laser device 1A is mounted on the submount 2 in a junction-down (face-down) manner, due to the difference in the thermal expansion coefficients between the semiconductor laser device 1A and the submount 2, a shear stress (σ1) generated at the end in the width direction of the semiconductor laser device 1 and a shear stress (σ2) generated at the ridge portion 200A are added to the active layer 40 of the semiconductor laser device 1A.

[0303] Here, when the average thermal expansion coefficient of the submount 2 (for example, when the submount is composed of a plurality of layers of materials, if the thermal expansion coefficient of each material is L(i) and the film thickness is Ti(i), it is ΣL(i)T(i) / ΣL(i)) is larger than the average thermal expansion coefficient of the semiconductor laser device 1A, a stress is generated in the semiconductor laser device 1A such that the submount 2 shrinks the semiconductor laser device 1A in the horizontal direction (the X direction in FIG. 22). Also, since the thermal expansion coefficient of the metal embedded in the grooves existing on both sides of the ridge portion 200A is larger than the thermal expansion coefficient of the semiconductor laser device 1A, a stress is generated in the semiconductor laser device 1A to widen the groove width. As a result, in the XY plane of the semiconductor laser device 1A, as shown in FIG. 22, shear stresses that are antisymmetric with respect to the center of the current injection region between the grooves are generated.

[0304] Specifically, in the active layer where the groove formed beside the ridge portion 200A and the X direction have the same position, since the shear stress (σ1L) generated at the left end in the width direction of the semiconductor laser device 1A and the shear stress (σ2L) generated at the groove on the left side of the ridge portion 200A, and the shear stress (σ1R) generated at the right end in the width direction of the semiconductor laser device 1A and the shear stress (σ2R) generated at the groove on the right side of the ridge portion 200A are in opposite directions respectively, the shear stresses cancel each other out and their magnitudes become smaller.

[0305] Also, since the light distribution of the light propagating through the optical waveguide spreads to the region of the groove in the horizontal direction, the influence of the shear stress received by the light distribution at the end of the light distribution is canceled by the shear stress of the groove and becomes smaller.

[0306] In addition, if the shear stresses on the left and right sides with respect to the center in the width direction of the ridge portion 200A are not completely antisymmetric, when birefringence occurs in the semiconductor laser device 1A due to the shear stress, the correlation integral of the optical distribution and the shear stress becomes non-zero, and thus the polarization plane will be inclined.

[0307] As described above, according to the semiconductor laser device 1A according to this modified example, when mounted on the submount 2, the shear stress generated at the end in the width direction of the semiconductor laser device 1A can be canceled by the shear stress due to the groove beside the ridge portion, so that the influence of the shear stress on the optical distribution can be reduced. Thereby, it is possible to suppress the inclination of the polarization plane of the laser light propagating through the optical waveguide and the decrease in the polarization ratio.

[0308] In order to reduce the influence of the shear stress generated at the end in the width direction of the ridge-type semiconductor laser device 1A on the laser light propagating through the optical waveguide, if the Al composition of the P-type cladding layer 60 is 0.8 or more, it is effective because the leakage of the optical distribution into the P-type cladding layer 60 can be reduced. If the Al composition is increased to 0.9 or more, the lattice mismatch with the GaAs substrate becomes large and the crystallinity may decrease due to the generation of lattice defects. Therefore, the Al composition may be 0.8 or more and 0.9 or less.

[0309] In addition, the width of the groove formed beside the ridge portion 200A is preferably 10 μm or more. Thereby, the shear stress outside the ridge portion 200A can be reduced. Specifically, if the width of the groove is too wide, the weight during mounting on the ridge portion 200A that becomes the current injection region will be concentrated. Therefore, the width of the groove is preferably 25 μm ± 15 μm. By making the groove have such a width, the rotation of the polarization plane due to the shear stress can be effectively suppressed.

[0310] Also, in this modified example, the semiconductor laser device 1A is mounted on the submount 2 by junction down, but it is not limited thereto. For example, the semiconductor laser device 1A may be mounted on a support substrate such as the submount 2 by junction up (face up).

[0311] In addition, when mounting the semiconductor laser device 1 in the above embodiment on a submount, the semiconductor laser device 1 may be mounted by either the junction-down or junction-up method.

[0312] (Other Modification Examples) For example, in the semiconductor laser device 1 in the above embodiment, although the case of using an AlGaInAs-based semiconductor material was exemplified, the present invention is not limited to this, and other semiconductor materials may be used.

[0313] Specifically, the semiconductor laser device may be composed of an AlGaInP-based semiconductor material. In this case, as shown in FIG. 23, the semiconductor laser device composed of an AlGaInP-based semiconductor material may have, for example, an N-type buffer layer 11, an N-type cladding layer 20, an N-type guide layer 30, an active layer 40, a P-type guide layer 50, a P-type cladding layer 60, an intermediate layer 64, a P-type contact layer 70, an insulating film 100A, and a P-side electrode 91 sequentially laminated on a substrate 10 which is an n-type GaAs substrate. The intermediate layer 64 has a structure in which a first intermediate layer 61, a second intermediate layer 62, and a third intermediate layer 63 are sequentially laminated.

[0314] As an example, the N-type buffer layer 11 is AlGaAs or GaAs (film thickness: 0.5 μm, Si impurity concentration: 3×10 17 cm -3 ). The N-type cladding layer 20 is (Al X Ga 1-X ) 0.5 In 0.5 P (film thickness: 3.6 μm, Al composition: 0.18, Si impurity concentration: 2×10 18 cm -3 , 6×10 17 cm -3 , 1.4×10 17 cm -3 of multiple stages), and the interface region between the N-type buffer layer 11 and the N-type cladding layer 20 is Al x Ga 1-x As with a film thickness of 75 nm, the Al composition continuously changes from 0 to 0.31, and the impurity concentration is 3×10 17 cm ―3It is. The N-type guide layer 30 is (Al X Ga 1-X ) 0.5 In 0.5 P (film thickness: 85 nm, Al composition: zero, 80 nm on the active layer 40 side: undoped, Si impurity concentration in the remaining part: 1×10 17 cm -3 ). The interface region between the N-type cladding layer 20 and the N-type guide layer 30 has a film thickness of 20 nm, and the Al composition continuously changes from 0.18 to 0.

[0315] Regarding the active layer 40, the N-side second barrier layer 42b is AlGaAs (film thickness: 6.5 nm, Al composition: 0.59, undoped), the N-side first barrier layer 42a is AlGaAs (film thickness: 3.5 nm, Al composition: 0.53, undoped), the well layer 41 is GaInAs (film thickness: 8.5 nm, In composition: 0.12), the P-side first barrier layer 43a is AlGaAs (film thickness: 3.5 nm, Al composition: 0.53, undoped), and the P-side second barrier layer 43b is AlGaAs (film thickness: 17.5 nm, Al composition: 0.59, undoped).

[0316] The P-type guide layer 50 is (Al X Ga 1-X ) 0.5 In 0.5 P (film thickness: 0.17 μm, Al composition: zero, 50 nm on the active layer 40 side: undoped, C impurity concentration in the remaining part: 5×10 17 cm -3 ). The P-type cladding layer 60 is (Al X Ga 1-X ) 0.5 In 0.5 P (film thickness: 0.6 μm, Al composition: 0.69, C impurity concentration: 5×10 17 cm -3 , 1.2×10 18 cm -3 multi-stage). The interface region between the P-type guide layer 50 and the P-type cladding layer 60 has a film thickness of 50 nm, the Al composition continuously changes from 0 to 0.69, and the C impurity concentration is: 5×10 17 cm -3 ).

[0317] Regarding the intermediate layer 64, the first intermediate layer 61 is (Al X Ga 1-X ) 0.5 In 0.5 P (film thickness: 0.2 μm, Al composition: 0.30, C impurity concentration: 1.2×10 18 cm -3 ), the second intermediate layer 62 is (Al X Ga 1-X ) 0.5 In 0.5 P (film thickness: 0.038 μm, Al composition: zero, C impurity concentration: 1.2×10 18 cm -3 ), and the third intermediate layer 63 is AlGaAs (film thickness: 0.05 μm, Al composition gradient: continuously changing from 0.52 to 0, C impurity concentration: 1.2×10 18 cm -3 ).

[0318] Note that the P-type contact layer 70 is GaAs (film thickness: 0.4 μm, C impurity concentration: 2×10 18 cm -3 ).

[0319] [[ID=4º]]Even for the semiconductor laser device according to this modified example configured as described above, the same effects as those in the above-described Embodiment 1 are achieved. For example, even if the well layer 41 is thickened, it is possible to suppress the deterioration of the temperature characteristics and the decrease in long-term reliability, and to suppress the inhibition of the effect of improving the COD level.

[0320] Furthermore, in the semiconductor laser device according to this modified example shown in FIG. 23, the following effects can also be obtained.

[0321] First, since the semiconductor laser device according to this modified example is composed of a semiconductor material of the AlGaInP system having a higher bandgap energy than the semiconductor material of the AlGaAs system, a high potential barrier can be obtained. As a result, carriers leaking from the active layer 40 to the P-type guide layer 50 can be suppressed, so that the slope efficiency can be improved and a semiconductor laser device that can be driven in high-temperature and high-output operation can be obtained.

[0322] Second, since impurities (Zn) are likely to diffuse, the impurity concentration required for window formation can be reduced. As a result, free carrier loss due to impurities can be reduced, so that the slope efficiency can be improved.

[0323] Third, since the N-type clad layer 20, the N-type guide layer 30, the P-type guide layer 50, the P-type clad layer 60, and the substrate 10 which is a GaAs substrate can be lattice-matched, warping of the semiconductor laser device (element) is reduced. And due to this reduction in warping, even when asymmetric strain occurs in the semiconductor laser device during junction down mounting, the generated asymmetric strain can be reduced. Therefore, the effect of the insulating film 100A which is a current blocking layer composed of an oxide film, that is, the effect of canceling the shear stress generated at the end of the semiconductor laser device with the shear stress due to the ridge shape can be enhanced.

[0324] Fourth, the drive voltage of the semiconductor laser device can be suppressed from rising by the intermediate layer 64. Specifically, since the Al composition is gradually reduced by the first intermediate layer 61 and the second intermediate layer 62 in the intermediate layer 64, the bandgap energy difference generated when AlGaInP and GaAs are joined can be minimized, and the rise in the drive voltage can be suppressed. Furthermore, by providing an inclined layer of the Al composition of AlGaAs by the third intermediate layer 63, the bandgap energy at the hetero interface can be smoothed, and the rise in the drive voltage can be suppressed.

[0325] Also, in the semiconductor laser device 1 in the above embodiment, a constriction structure is formed in a plurality of semiconductor layers constituting the semiconductor laminate, and the side surface of the semiconductor laminate is an inclined surface, but it is not limited to this.

[0326] In addition, forms obtained by applying various modifications conceivable by those skilled in the art to the above embodiments, and forms realized by arbitrarily combining the components and functions in the above embodiments without departing from the spirit of the present disclosure are also included in the present disclosure.

Industrial Applicability

[0327] The semiconductor laser device of the present disclosure can be applied to light sources for various uses, such as a light source for an image display device such as a display or a projector, a light source for an in-vehicle headlamp, a light source for industrial or household lighting, or a light source for industrial equipment such as a laser welding device, a thin film annealing device, or a laser processing device, as a high-power light source.

Explanation of Signs

[0328] 1, 1A Semiconductor laser device 1a Front end face 1b Rear end face 2 Submount 10 Substrate 11 N-type buffer layer 20 N-type cladding layer 30 N-type guide layer 40 Active layer 41 Well layer 42a N-side first barrier layer 42b N-side second barrier layer 43a P-side first barrier layer 43b P-side second barrier layer 44 N-side high Al composition layer 45 P-side high Al composition layer 50 P-type guide layer 60 P-type cladding layer 61 First intermediate layer 62 Second intermediate layer 63 Third intermediate layer 64 Intermediate layer 70 P-type contact layer 71 First contact layer 72 Second contact layer 80 Current blocking layer 80a Opening 91 P-side electrode 91a First P electrode layer 91b Plating layer 91c Second P electrode layer 92 N-side electrode 100, 100A Insulating film 100a Opening 111 First end face coating film 112 Second end face coating film 120 Window area 130 Groove 200A Ridge part

Claims

1. A semiconductor laser device that emits a laser beam, comprising a substrate, an N-type cladding layer disposed above the substrate, an active layer disposed above the N-type cladding layer, and a P-type cladding layer disposed above the active layer, wherein the active layer comprises a well layer, a P-side first barrier layer disposed above the well layer, and a P-side second barrier layer disposed above the P-side first barrier layer, wherein the Al composition ratio of the P-side second barrier layer is higher than the Al composition ratio of the P-side first barrier layer, and the bandgap energy of the P-side second barrier layer is greater than the bandgap energy of the P-side first barrier layer, further comprising a P-type guide layer between the P-side second barrier layer and the P-type cladding layer, and a P-side high-Al composition layer having a higher Al composition than the P-side first barrier layer between the well layer and the P-side first barrier layer, wherein the bandgap energy of the P-type guide layer is greater than the bandgap energy of the P-side second barrier layer, and the semiconductor laser device has an end face window structure in which the bandgap energy of the well layer near the end face from which the laser beam is emitted is greater than the bandgap energy of the well layer at the center in the resonator length direction. Semiconductor laser device.

2. The bandgap energy of the P-type cladding layer is greater than the bandgap energy of the N-type cladding layer. The semiconductor laser device according to claim 1.

3. The thickness of the well layer is 6 nm or more. The semiconductor laser device according to claim 1 or 2.

4. The well layer is Al Ｘ Ga １－Ｘ－Ｙ In ｙ and is composed of a semiconductor material represented by a composition formula of As (0 < X < 1, 0 < Y < 1). The semiconductor laser device according to any one of claims 1 to 3.

5. The bandgap energy of the P-side second barrier layer gradually increases as it moves away from the well layer. The semiconductor laser device according to any one of claims 1 to 4.

6. The P-side first barrier layer includes an undoped region where no impurities are doped, and the film thickness of the undoped region is 5 nm or more. The semiconductor laser device according to any one of claims 1 to 5.

7. Impurities are doped in the entire region of the P-side second barrier layer, and the P-side first barrier layer has an undoped region where no impurities are doped in the region close to the well layer, and a doped region where impurities are doped in the region far from the well layer. The semiconductor laser device according to any one of claims 1 to 6.

8. The concentration of the impurity doped in the P-side second barrier layer gradually increases as it moves away from the well layer. The semiconductor laser device according to any one of Claims 1 to 7.

9. The Al composition in at least the interface region between the P-type guide layer and the P-type clad layer gradually increases as it moves away from the well layer. The semiconductor laser device according to any one of Claims 1 to 8.

10. The concentration of the impurity doped in the P-type guide layer gradually increases as it moves away from the well layer. The semiconductor laser device according to any one of Claims 1 to 9.

11. The active layer further includes an N-side first barrier layer disposed below the well layer and an N-side second barrier layer disposed below the N-side first barrier layer. The Al composition ratio of the N-side second barrier layer is higher than that of the N-side first barrier layer. The bandgap energy of the N-side second barrier layer is larger than that of the N-side first barrier layer. The semiconductor laser device according to any one of Claims 1 to 10.

12. The active layer further includes an N-side first barrier layer disposed below the well layer and an N-side second barrier layer disposed below the N-side first barrier layer. The total film thickness of the P-side first barrier layer and the N-side first barrier layer is 20 nm or more and 80 nm or less. The semiconductor laser device according to any one of Claims 1 to 10.

13. The bandgap energy of the N-side second barrier layer gradually increases as it moves away from the well layer. The semiconductor laser device according to Claim 11 or 12.

14. The entire region of the N-side second barrier layer is doped with an impurity. The N-side first barrier layer has an undoped region where no impurity is doped in the region close to the well layer and a doped region where an impurity is doped in the region far from the well layer. The semiconductor laser device according to any one of Claims 11 to 13.

15. The bandgap energy of the P-side second barrier layer is larger than that of the N-side second barrier layer. The semiconductor laser device according to any one of Claims 11 to 14.

16. An N-side high Al composition layer having a higher Al composition than the N-side first barrier layer is provided between the well layer and the N-side first barrier layer. The semiconductor laser device according to any one of claims 11 to 15.

17. A semiconductor laser device that emits laser light, comprising: a substrate; an N-type clad layer disposed above the substrate; an active layer disposed above the N-type clad layer; a P-type clad layer disposed above the active layer, wherein the active layer has a well layer, a P-side first barrier layer disposed above the well layer, a P-side second barrier layer disposed above the P-side first barrier layer, an N-side first barrier layer disposed below the well layer, and an N-side second barrier layer disposed below the N-side first barrier layer, wherein the Al composition ratio of the P-side second barrier layer is higher than that of the P-side first barrier layer, the bandgap energy of the P-side second barrier layer is larger than the bandgap energy of the P-side first barrier layer, furthermore, a P-type guide layer is provided between the P-side second barrier layer and the P-type clad layer, and an N-side high Al composition layer having a higher Al composition than the N-side first barrier layer is provided between the well layer and the N-side first barrier layer, the bandgap energy of the P-type guide layer is larger than the bandgap energy of the P-side second barrier layer, the semiconductor laser device has an end face window structure in which the bandgap energy of the well layer near the end face from which the laser light is emitted is larger than the bandgap energy of the well layer at the center in the resonator length direction, the Al composition ratio of the N-side second barrier layer is higher than that of the N-side first barrier layer, the bandgap energy of the N-side second barrier layer is larger than the bandgap energy of the N-side first barrier layer semiconductor laser device.

18. Furthermore, an N-type guide layer is provided between the N-side second barrier layer and the N-type clad layer. The semiconductor laser device according to any one of claims 12 to 17.

19. The Al composition in at least the interface region between the N-type guide layer and the N-type clad layer gradually increases as the distance from the well layer increases. The semiconductor laser device according to claim 18.

20. The concentrations of impurities doped in the N-type clad layer, the N-type guide layer, the N-side second barrier layer, and the N-side first barrier layer gradually increase or increase stepwise as they are farther from the well layer. The semiconductor laser device according to claim 18 or 19.

21. The active layer has an N-side first barrier layer disposed below the well layer and an N-side second barrier layer disposed below the N-side first barrier layer. The Al composition ratio of the N-side second barrier layer is higher than the Al composition ratio of the N-side first barrier layer. The bandgap energy of the N-side second barrier layer is larger than the bandgap energy of the N-side first barrier layer. An N-type guide layer is provided between the N-side second barrier layer and the N-type clad layer. The bandgap energy of the P-type guide layer is different from the bandgap energy of the N-type guide layer. The semiconductor laser device according to any one of claims 1 to 11.

22. Located between the well layer and the N-type clad layer, and including an N-side first barrier layer and an N-side second barrier layer from the well layer toward the N-type clad layer. The Al composition ratio of the N-side second barrier layer is higher than the Al composition ratio of the N-side first barrier layer. The bandgap energy of the N-side second barrier layer is larger than the bandgap energy of the N-side first barrier layer. The bandgap energy of the N-side second barrier layer gradually increases as it is farther from the well layer. The maximum value of the bandgap energy of the P-side second barrier layer is larger than the maximum value of the bandgap energy of the N-side second barrier layer. The semiconductor laser device according to claim 5.

23. A method for manufacturing a semiconductor laser device that emits laser light, comprising: [[ID=])]]A step of disposing an N-type clad layer above a substrate; A step of disposing an active layer above the N-type clad layer; A step of disposing a P-type clad layer above the active layer, The active layer includes: A well layer; A P-side first barrier layer disposed above the well layer; A P-side second barrier layer disposed above the P-side first barrier layer, The Al composition ratio of the P-side second barrier layer is higher than the Al composition ratio of the P-side first barrier layer. Furthermore, a P-type guide layer is provided between the P-side second barrier layer and the P-type clad layer, and a P-side high-Al composition layer having a higher Al composition than the P-side first barrier layer is provided between the well layer and the P-side first barrier layer. The bandgap energy of the P-side second barrier layer is larger than the bandgap energy of the P-side first barrier layer. The semiconductor laser device has an end face window structure in which the bandgap energy of the well layer near the end face from which the laser light is emitted is larger than the bandgap energy of the well layer at the center in the resonator length direction. A method for manufacturing a semiconductor laser device.

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