Semiconductor laser device and method for manufacturing semiconductor laser device

Abstract

The 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) comprises: a well layer (41), 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). The Al composition ratio of the P-side second barrier layer (43b) is higher than that of the P-side first barrier layer (43a), and the bandgap energy of the P-side second barrier layer (43b) is greater than that of the P-side first barrier layer (43a). 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 greater than that of the well layer (41) at the center of the resonator along the length direction.

Description

Technical Field

[0001] This disclosure relates to a semiconductor laser device and a method for manufacturing a semiconductor laser device. Background Technology

[0002] Semiconductor laser elements have attracted attention for various applications, such as light sources for image display devices like displays or projectors, light sources for automotive headlights, light sources for industrial or civilian lighting, and light sources for industrial equipment like laser welding equipment, thin film annealing equipment, and laser processing equipment.

[0003] Among these light sources, especially in semiconductor laser elements used in projectors, laser processing equipment, or laser welding equipment, it is desirable to have high output characteristics exceeding 1 watt. For example, in semiconductor laser elements with a wavelength of 915 nm used in the light source of a laser welding equipment, a high output characteristic of 25W or more is desirable.

[0004] Semiconductor laser elements include, 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 (e.g., Patent Document 1).

[0005] In semiconductor laser devices with oscillating laser wavelengths of 900nm to 980nm, the active layer of a quantum well structure with InGaAs in the well layer and AlGaAs in the barrier layer is widely used.

[0006] (Existing technical literature)

[0007] (Patent Documents)

[0008] Patent Document 1: Japanese Patent Application Publication No. 62-249496

[0009] To enable semiconductor laser elements to achieve watt-level high output, one could consider increasing the thermal saturation level or the COD (Catastrophic Optical Damage) level.

[0010] However, in order to improve the COD level, a window region is formed at the end face of the semiconductor laser element, and the well layer of the active layer is thickened to improve the thermal saturation level. This will degrade the temperature characteristics and reduce the long-term reliability, thus hindering the improvement of the COD level. Summary of the Invention

[0011] In order to solve the above-mentioned problems, this disclosure aims to provide a semiconductor laser device with an end-face window structure that, even if the well layer is thickened, can suppress the degradation of temperature characteristics and the reduction of long-term reliability while suppressing the impairment of the improvement effect of COD level, as well as a method for manufacturing the semiconductor laser device.

[0012] To address the aforementioned problems, one embodiment of the semiconductor laser device disclosed herein is a semiconductor laser device that emits laser light, 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 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, wherein the Al composition ratio of the P-side second barrier layer is higher than that of the P-side first barrier layer, and the bandgap energy of the P-side second barrier layer is greater than that of the P-side first 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 light is emitted is greater than the bandgap energy of the well layer at the center of the resonator along its length direction.

[0013] Through this disclosure, in a semiconductor laser device with an end-face window structure, even if the well layer is thickened, it is possible to suppress the degradation of temperature characteristics and the reduction of long-term reliability while preventing the improvement of COD level from being hindered. Attached Figure Description

[0014] Figure 1 This is a top view of the semiconductor laser device involved in the embodiment.

[0015] Figure 2A Is Figure 1 A cross-sectional view of the semiconductor laser device involved in the implementation of the IIA-IIA line.

[0016] Figure 2B Is Figure 1 A cross-sectional view of the semiconductor laser device involved in the implementation on the IIB-IIB line.

[0017] Figure 2C Is Figure 1 A cross-sectional view of the semiconductor laser device involved in the implementation of the IIC-IIC line.

[0018] Figure 3A This is a diagram illustrating the semiconductor layer stacking process in the manufacturing method of the semiconductor laser device according to the embodiments.

[0019] Figure 3BThis is a diagram illustrating the current injection region formation process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0020] Figure 3C This is a diagram illustrating the embedding process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0021] Figure 3D This is a diagram illustrating the window region formation process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0022] Figure 3E This is a diagram illustrating the trench forming process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0023] Figure 3F This is a diagram illustrating the insulating film formation process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0024] Figure 3G This is a diagram illustrating the P-side electrode formation process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0025] Figure 3H This is a diagram illustrating the N-side electrode formation process in the manufacturing method of the semiconductor laser device according to the embodiment.

[0026] Figure 4 Specific examples of the composition, film thickness, and impurity concentration of each semiconductor layer in the three embodiments of the semiconductor laser device involved in the implementation are shown.

[0027] Figure 5A The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device of Example 1 are shown.

[0028] Figure 5B The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device of Example 2 are shown.

[0029] Figure 5C The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device of Example 3 are shown.

[0030] Figure 5D The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device of Example 4 are shown.

[0031] Figure 5E The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device of Example 5 are shown.

[0032] Figure 6 This is a diagram used to illustrate the function and effect of the semiconductor laser device involved in the implementation method.

[0033] Figure 7A The dependence of optical confinement efficiency on the length of the Al component tilt region in the semiconductor laser device according to the embodiments is shown.

[0034] Figure 7B The dependence of waveguide loss on the length of the Al component tilt region is shown in the semiconductor laser device according to the embodiments.

[0035] Figure 8A The dependence of optical confinement efficiency on the concentration of P-type impurities is shown in the semiconductor laser device according to the embodiments.

[0036] Figure 8B The dependence of waveguide loss on P-type impurity concentration is shown in the semiconductor laser device according to the embodiments.

[0037] Figure 9 The film thicknesses of the N-side first barrier layer and the P-side first barrier layer in the semiconductor laser device involved in the embodiment are shown, and the relationship between waveguide loss and optical confinement efficiency is illustrated.

[0038] Figure 10 The film thicknesses of the N-side and P-side second barrier layers in the semiconductor laser device according to the embodiments are shown, and the relationship between waveguide loss and optical confinement efficiency is illustrated.

[0039] Figure 11A The dependence of the barrier of the P-type guide layer of the semiconductor laser device according to the embodiments on the concentration of P-type impurities is shown.

[0040] Figure 11B The dependence of the electron current density of the P-type guide layer of the semiconductor laser device according to the embodiments on the P-type impurity concentration is shown.

[0041] Figure 12A The dependence of the barrier of the P-type semiconductor layer of the semiconductor laser device according to the embodiments on the concentration of P-type impurities is shown.

[0042] Figure 12B The dependence of the electron current density of the P-type semiconductor layer of the semiconductor laser device involved in the embodiment on the P-type impurity concentration is shown.

[0043] Figure 13A The dependence of the barrier of the P-type semiconductor layer of the semiconductor laser device of Example 1 on the concentration of P-type impurities is shown.

[0044] Figure 13BThe dependence of the electron current density of the P-type semiconductor layer of the semiconductor laser device of Example 1 on the P-type impurity concentration is shown.

[0045] Figure 14A The barrier of the P-type guiding layer of the semiconductor laser device of Example 3 is shown to be dependent on the Al composition.

[0046] Figure 14B The dependence of the electron current density of the P-type guide layer of the semiconductor laser device of Example 3 on the Al composition is shown.

[0047] Figure 15A The diagram illustrates the dependence of hole current density at a position 100 nm from the N-side interface of the well layer on the N-type impurity concentration in the semiconductor laser device according to the embodiment.

[0048] Figure 15B The diagram illustrates the dependence of hole current density at the N-type cladding layer substrate-side interface on N-type impurity concentration in the semiconductor laser device according to the embodiments.

[0049] Figure 16A This illustrates a first example of the N-type impurity concentration distribution in an N-type semiconductor layer within the semiconductor laser device described in the embodiment.

[0050] Figure 16B This illustrates a second example of the N-type impurity concentration distribution in the N-type semiconductor layer of the semiconductor laser device according to the embodiment.

[0051] Figure 16C This illustrates a third example of the N-type impurity concentration distribution in the N-type semiconductor layer of the semiconductor laser device according to the embodiment.

[0052] Figure 16D The fourth example of the N-type impurity concentration distribution in the N-type semiconductor layer in the semiconductor laser device according to the embodiment is shown.

[0053] Figure 17 The dependence of heavy hole and light hole quantum levels on the Al composition of the trap layer is shown when the Al composition of the first barrier layer on the P side and the second barrier layer on the N side is 0.06.

[0054] Figure 18 The dependence of heavy hole and light hole quantum levels on the Al composition of the trap layer is shown when the Al composition of the first barrier layer on the P side and the second barrier layer on the N side is 0.12.

[0055] Figure 19The dependence of heavy hole and light hole quantum levels on the Al composition of the trap layer is shown when the Al composition of the first barrier layer on the P side and the second barrier layer on the N side is 0.18.

[0056] Figure 20 This is a top view of the semiconductor laser device involved in the variation example.

[0057] Figure 21A Is Figure 20 A cross-sectional view of the semiconductor laser device involved in the implementation of the XXIA-XXIA line.

[0058] Figure 21B Is Figure 20 A cross-sectional view of the semiconductor laser device involved in the implementation of the XXIB-XXIB line.

[0059] Figure 21C Is Figure 20 A cross-sectional view of the semiconductor laser device involved in the implementation of the XXIC-XXIC line.

[0060] Figure 22 The illustration shows the semiconductor laser device involved in the modified example mounted on the submount with the junction down.

[0061] Figure 23 This is a cross-sectional view of a semiconductor laser device involved in other variations. Detailed Implementation

[0062] (The process of obtaining one form of this disclosure)

[0063] Before describing the embodiments of this disclosure, the process of obtaining one form of this disclosure will first be described.

[0064] To enable semiconductor laser elements to achieve watt-level high output, one could consider, for example, increasing the thermal saturation level, increasing the COD level, or reducing the thermal resistance by increasing the resonator length.

[0065] Specifically, to increase the thermal saturation level, it is necessary to either thicken the well layer to increase the optical confinement factor of the well layer and reduce the oscillation threshold, or increase the Al composition of the barrier layer composed of AlGaAs to increase the energy band shift (ΔEc) of the conduction band and thus increase the barrier to suppress electron overflow, or increase the resonator length to become a long resonator to reduce the working carrier density.

[0066] Furthermore, to improve COD levels, a window region can be formed on the laser emission end face, i.e., the front end face, to 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 well layer in the end face through vacancy diffusion, impurity diffusion, or ion implantation.

[0067] However, to increase the optical confinement factor for the well layer, the well layer needs to be thickened, which makes it difficult to disorder the atomic arrangement of the barrier layer and the well layer, thus making it difficult to form the window region.

[0068] Therefore, it was considered that increasing the annealing temperature during the formation of the window region could promote the exchange of atoms between the well layer and the barrier layer, thereby causing the atomic arrangement to become disordered.

[0069] However, if the annealing temperature for forming the window region is increased, atomic exchanges also occur between the well layer and the barrier layer in the active layer of the gain region where a window region is not desired. As a result, the bandgap energy (Eg) in the gain region increases, the leakage current in the gain region increases, the temperature characteristics deteriorate, or vacancies introduced during crystal growth or dangling bonds on the surface of the growth layer easily diffuse, reducing the controllability of the oscillation wavelength and thus decreasing long-term reliability. Specifically, if the bandgap energy increases, the migration wavelength of the quantum well layer in the gain region becomes shorter.

[0070] Furthermore, if the annealing temperature during window formation is increased, the migration region formed at the boundary between the desired window region (window section) and the undesirable window region (gain section) tends to lengthen. Consequently, light absorption in the migration region hinders the improvement in COD level achieved through the window region.

[0071] As mentioned above, in order to improve the COD level, a window region is formed at the end face of the semiconductor laser element. Furthermore, in order to improve the thermal saturation level, the well layer of the active layer is thickened. This will cause the temperature characteristics to deteriorate or the long-term reliability to decrease, thus hindering the effect of improving the COD level.

[0072] In order to solve the aforementioned problems, this disclosure aims to provide a semiconductor laser device with an end-face window structure that, even when the well layer is thickened, can suppress the degradation of temperature characteristics and the reduction of long-term reliability while suppressing the hindrance to the improvement of COD level, as well as a method for manufacturing the semiconductor device.

[0073] Furthermore, if the resonator length is increased in order to reduce thermal resistance, it will be easily affected by changes in the band structure due to the installation strain when installing semiconductor laser elements, which will also lead to a decrease in polarization ratio.

[0074] Therefore, another object of this disclosure is to provide a semiconductor laser device that can suppress the decrease in polarization ratio even when the resonator length is increased, and a method for manufacturing the semiconductor laser device.

[0075] The embodiments of this disclosure will now be described with reference to the accompanying drawings. Furthermore, the embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, constituent elements, and the arrangement and connection methods of the constituent elements shown in the following embodiments are all examples and are not intended to limit the scope of this disclosure.

[0076] Furthermore, these figures are schematic diagrams, not rigorous illustrations. Therefore, the scales and other parameters of each figure do not necessarily need to be consistent. In addition, in each figure, substantially identical components are given the same symbols, and repetitive descriptions are omitted or simplified.

[0077] Furthermore, in this specification, the terms "above" and "below" do not refer to the absolute spatial orientation of upward (vertically above) and downward (vertically below), but rather to the relative positional relationship defined by the stacking order in a layered structure. Moreover, the terms "above" and "below" apply not only to situations where two constituent elements are arranged with gaps between them, or where other constituent elements exist between them, but also to situations where two constituent elements are arranged in a state of contact with each other.

[0078] (Implementation Method)

[0079] [Layer Structure of Semiconductor Laser Devices]

[0080] First, using Figure 1 , Figure 2A , Figure 2B as well as Figure 2C The layer configuration of the semiconductor laser device 1 according to the embodiment will be described. Figure 1 This is a top view of the semiconductor laser device 1 according to the embodiment. Figure 2A Is Figure 1 A cross-sectional view of the semiconductor laser device 1 with line IIA-IIA. Figure 2B Is Figure 1 A cross-sectional view of the semiconductor laser device 1 of the IIB-IIB line. Figure 2C Is Figure 1 A cross-sectional view of the semiconductor laser device 1 with an IIC-IIC line. Additionally, Figure 2A A cross-section of the gain section of the semiconductor laser device 1 is shown. Figure 2B A cross-section of the end face of the semiconductor laser device 1 on the front end face 1a side is shown.

[0081] Semiconductor laser device 1 is a semiconductor laser element that emits laser light, comprising a substrate and a semiconductor stack (semiconductor stack structure) composed of multiple semiconductor layers disposed on the substrate. Specifically, as shown... Figures 1-2C As shown, the semiconductor laser device 1 includes: an N-type cladding layer 20 disposed above a substrate 10, an active layer 40 disposed above the N-type cladding layer 20, and a P-type cladding layer 60 disposed above the active layer 40. These layers are semiconductor layers constituting a semiconductor stack.

[0082] As a semiconductor layer constituting a semiconductor stack, the semiconductor laser device 1 further includes: an N-type guiding layer 30 disposed between the N-type cladding layer 20 and the active layer 40, a P-type guiding layer 50 disposed between the active layer 40 and the P-type cladding layer 60, a P-type contact layer 70 disposed above the P-type cladding layer 60, and a current blocking layer 80.

[0083] Furthermore, the semiconductor laser device 1 includes: a P-side electrode 91 and an N-side electrode 92 connected to a semiconductor laminate, and an insulating film 100 covering at least a portion of the semiconductor laminate.

[0084] The semiconductor laser device 1 described in this embodiment is a semiconductor laser element that emits laser light with a wavelength of 900 nm to 980 nm. For example, the semiconductor stack in the semiconductor laser device 1 is made of a III-V compound semiconductor, which is made of an AlGaInAs-type material. As an example, the semiconductor laser device 1 emits laser light in the 915 nm wavelength band. Furthermore, although it will be described in detail later, the semiconductor laser device 1 has an end-face window structure in which a window region 120 is formed in the semiconductor stack.

[0085] The constituent elements of the semiconductor laser device 1 according to this embodiment will be described in detail below.

[0086] Substrate 10 is a planar substrate with all its main surfaces being flat. Substrate 10 is a semiconductor substrate such as a GaAs substrate or an insulating substrate such as a sapphire substrate. In this embodiment, substrate 10 is an n-type GaAs substrate. Additionally, a buffer layer may be formed between substrate 10 and the N-type cladding layer 20. The buffer layer, for example, is an n-type GaAs layer stacked on substrate 10.

[0087] An N-type cladding layer 20 is formed above the substrate 10. If a buffer layer is formed on the substrate 10, the N-type cladding layer 20 is formed on the buffer layer. The N-type cladding layer 20 is an N-type semiconductor layer intentionally doped with impurities, such as an n-type AlGaAs layer. The impurities doped in the N-type cladding layer 20 are, for example, silicon (Si).

[0088] An N-type guiding layer 30 is disposed between the N-type cladding layer 20 and the N-side second barrier layer 42b of the active layer 40. Specifically, the N-type guiding layer 30 is formed on the N-type cladding layer 20. The N-type guiding layer 30 is an N-type semiconductor layer intentionally doped with impurities, such as an n-type AlGaAs layer. The impurities doped in the N-type guiding layer 30 are, for example, silicon (Si).

[0089] The active layer 40 is a semiconductor layer including a light-emitting layer, located between the N-type cladding layer 20 and the P-type cladding layer 60. Specifically, the active layer 40 is located between the N-type guiding layer 30 and the P-type guiding layer 50. In this embodiment, the active layer 40 is formed on the N-type guiding layer 30.

[0090] 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.

[0091] The trap layer 41 is located between the first barrier layer 42a on the N side and the first barrier layer 43a on the P side, and is in contact with the first barrier layer 42a on the N side and the first barrier layer 43a on the P side. Specifically, the trap layer 41 is formed on the first barrier layer 42a on the N side.

[0092] Well layer 41 is, for example, a single quantum well structure comprising a single quantum well layer. Well layer 41 is, for example, an undoped GaInAs layer. Alternatively, well layer 41 is not limited to a single quantum well structure and can also be a multiple quantum well structure comprising multiple quantum well layers. In this embodiment, well layer 41 is relatively thick, for example, 6 nm or more.

[0093] The first barrier layer 42a and the second barrier layer 42b on the N side are located between the N-type cladding layer 20 and the well layer 41, and are arranged in this order from the well layer 41 to the N-type cladding layer 20. Specifically, the first barrier layer 42a and the second barrier layer 42b on the N side are located between the N-type guiding layer 30 and the well layer 41.

[0094] The first barrier layer 42a on the N-side is formed on the second barrier layer 42b on the N-side. In this embodiment, the first barrier layer 42a on the N-side is an N-type semiconductor layer that is intentionally doped with impurities, such as an n-type AlGaAs layer. The impurities doped in the first barrier layer 42a on the N-side are, for example, silicon (Si).

[0095] In addition to doped regions, the N-side first barrier layer 42a can also have undoped regions. In this case, the N-side first barrier layer 42a can have an undoped region located closer to the well layer 41 and a doped region located farther from the well layer 41. The film thickness of the undoped region of the N-side first barrier layer 42a can be 5 nm or more. If the N-side first barrier layer 42a near the well layer 41 is doped with impurities, although the series resistance of the semiconductor laser device will decrease, free carrier loss will occur, thereby increasing the waveguide loss. If the film thickness of the undoped region is too thick, the series resistance of the semiconductor laser device will increase. Therefore, in order to suppress the increase in series resistance while suppressing the increase in free carrier loss caused by impurity doping, the film thickness of the undoped region can be 5 nm or more and 40 nm or less. Even if the doping concentration of impurities in the N-type guide layer 30 varies in a manner that gradually increases from the well layer 41 toward the direction away from the well layer 41, the increase in waveguide loss can be suppressed even if the film thickness of the undoped region is set to a maximum of 20 nm or less.

[0096] A second N-side barrier layer 42b, located below the first N-side barrier layer 42a, is formed on the N-type guiding layer 30. In this embodiment, the second N-side barrier layer 42b is an N-type semiconductor layer intentionally doped with impurities, such as an n-type AlGaAs layer. The impurities doped in the second N-side barrier layer 42b are, for example, silicon (Si).

[0097] The first barrier layer 43a and the second barrier layer 43b on the P side are located between the well layer 41 and the P-type cladding layer 60, and are arranged in this order from the well layer 41 toward the P-type cladding layer 60. Specifically, the first barrier layer 43a and the second barrier layer 43b on the P side are located between the well layer 41 and the P-type guiding layer 50.

[0098] A first barrier layer 43a on the P-side is formed on the well layer 41. In this embodiment, the first barrier layer 43a on the P-side is a P-type semiconductor layer that is intentionally doped with impurities, such as a P-type AlGaAs layer. The impurities doped in the first barrier layer 43a on the P-side are, for example, carbon (C).

[0099] In addition to doped regions, the P-side first barrier layer 43a can also have undoped regions. In this case, the P-side first barrier layer 43a can have an undoped region located closer to the well layer 41 and a doped region located farther from the well layer 41. The film thickness of the undoped region of the P-side first barrier layer 43a can be 5 nm or more. If the P-side first barrier layer 43a near the well layer 41 is doped with impurities, although the series resistance of the semiconductor laser device will decrease, free carrier loss will occur, and waveguide loss will increase. If the film thickness of the undoped region is too thick, the series resistance of the semiconductor laser device will increase. Therefore, in order to suppress the increase in series resistance while suppressing the increase in free carrier loss caused by impurity doping, the film thickness of the undoped region can be 5 nm or more but less than 40 nm. Even if the doping concentration of impurities in the P-type guide layer varies in a manner that gradually increases from the well layer 41 toward a direction away from the well layer 41, the increase in waveguide loss can be suppressed even if the film thickness of the undoped region is set to a maximum of 20 nm or less.

[0100] A second barrier layer 43b on the P-side is formed on the first barrier layer 43a on the P-side. In this embodiment, the second barrier layer 43b on the P-side is a P-type semiconductor layer that is intentionally doped with impurities, such as a P-type AlGaAs layer. The impurities doped in the second barrier layer 43b on the P-side are, for example, carbon (C).

[0101] A P-type guiding layer 50 is disposed between the P-side second barrier layer 43b and the P-type cladding layer 60 of the active layer 40. Specifically, the P-type guiding layer 50 is formed on the P-side second barrier layer 43b. The P-type guiding layer 50 is a P-type semiconductor layer intentionally doped with impurities, such as a P-type AlGaAs layer. The impurities doped in the P-type guiding layer 50 are, for example, carbon (C).

[0102] A p-type cladding layer 60 is formed on the p-type guiding layer 50. The p-type cladding layer 60 is a p-type semiconductor layer that is intentionally doped with impurities, such as a p-type AlGaAs layer. C is used as the impurity. The impurity doped in the p-type cladding layer 60 is, for example, carbon (C).

[0103] A P-type contact layer 70 is formed on the P-type cladding layer 60. The P-type contact layer 70 is formed between the P-type cladding layer 60 and the P-side electrode 91. The P-type contact layer 70 is a P-type semiconductor layer that is intentionally doped with impurities, such as a P-type GaAs layer.

[0104] In this embodiment, the P-type contact layer 70 is a laminated film consisting of a first contact layer 71 and a second contact layer 72, sequentially stacked starting from the P-type overlay layer 60 side. As an example, the first contact layer 71 is a P-type GaAs layer with a thickness of 0.2 μm. Furthermore, the second contact layer 72 is a P-type GaAs layer with a thickness of 1 μm, formed on both the first contact layer 71 and the current blocking layer 80 in a manner that allows the opening 80a of the current blocking layer 80 to be filled.

[0105] A current blocking layer 80 is disposed 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 this embodiment, the current blocking layer 80 is composed of a P-type semiconductor layer that is intentionally doped with impurities. Specifically, the current blocking layer 80 is an n-type GaAs layer doped with silicon (Si) as an impurity.

[0106] The current blocking layer 80 has an opening 80a for defining the current injection region. The opening 80a of the current blocking layer 80 extends in a straight line along the length direction of the resonator of the semiconductor laser device 1. Although the opening 80a of the current blocking layer 80 exists in the gain section of the semiconductor laser device 1, it does not exist in the end section of the semiconductor laser device 1. Therefore, as... Figure 2A As shown, 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. And as... Figure 2B As shown, at the end face of the semiconductor laser device 1, since there is no opening 80a of the current blocking layer 80, the current blocking layer 80 covers the entire first contact layer 71.

[0107] In this way, by providing an N-type current blocking layer 80 inside the P-type contact layer 70, the current is limited by the current blocking layer 80. Due to the heat generated by the first contact layer 71, which becomes the current injection region, an effective refractive index step is formed in the horizontal direction of the active layer 40. Accordingly, light can be confined in the horizontal direction.

[0108] The P-side electrode 91 is disposed on one side of the P-type cladding layer 60 and 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 includes, for example, at least one of the following metals: Pt, Ti, Cr, Ni, Mo, and Au.

[0109] 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. These layers are stacked on the P-type contact layer 70 in the order of the first P-electrode layer 91a, the plating layer 91b, and the second P-electrode layer 91c. Furthermore, the first P-electrode layer 91a and the second P-electrode layer 91c are further composed of multilayer films, such as a Ti / Pt / Au three-layer structure. The plating layer 91b is a gold-plated film.

[0110] And, as Figure 2A As shown, the gain section of the semiconductor laser device 1 contains three layers: a first P electrode layer 91a, a plating layer 91b, and a second P electrode layer 91c. Figure 2B As shown, there is no plating layer 91b on the end face of the semiconductor laser device 1, but there are two layers: the first P electrode layer 91a and the second P electrode layer 91c.

[0111] The N-side electrode 92 is disposed on one side of the N-type cladding layer 20. In this embodiment, the N-side electrode 92 is formed on the bottom surface of the substrate 10 (i.e., the back surface of the substrate 10). The N-side electrode 92 includes, for example, AuGe film, Ni film, Au film, Ti film, Pt film and Au film sequentially stacked on one side of the substrate 10.

[0112] The insulating film 100 is a dielectric film that covers at least the sides of the active layer 40. In this embodiment, the insulating film 100 covers a pair of sides of the semiconductor laminate. Specifically, the insulating film 100 covers the sides of the N-type cladding layer 20, the N-type guiding layer 30, the active layer 40, the P-type guiding layer 50, the P-type cladding layer 60, the P-type contact layer 70, and the current blocking layer 80. The insulating film 100 is made of, for example, an insulating film such as SiN or SiO2, and functions as a current blocking film.

[0113] In this embodiment, a pair of side surfaces of the semiconductor stack are inclined surfaces, and the insulating film 100 at least covers the inclined surfaces. Furthermore, the inclined surfaces of the semiconductor stack are formed at least on the side surfaces of the active layer 40. Because the side surfaces of the active layer 40 are inclined, it is possible to reduce the amount of diffuse light returning from the central portion of the active layer 40 in the width direction to the side surfaces. Therefore, it is possible to suppress the conflict between the laser oscillating in the active layer 40 and the diffuse light, thereby stabilizing the laser drive operation.

[0114] Furthermore, the insulating film 100 has an opening 100a. The opening 100a of the insulating film 100 extends in a straight line along the length direction of the resonator of the semiconductor laser device 1. Although the opening 100a of the insulating film 100 exists in the gain portion of the semiconductor laser device 1, it does not exist in the end portion of the semiconductor laser device 1. Therefore, as... Figure 2AAs shown, in the gain section of the semiconductor laser device 1, the insulating film 100 only covers the end of the P-type contact layer 70. Furthermore, as... Figure 2B As shown, since there is no opening 100a of insulating film 100 formed at the end face of semiconductor laser device 1, insulating film 100 covers the entire P-type contact layer 70.

[0115] like Figure 1 as well as Figure 2C As shown, the semiconductor laser device 1 has a front end face 1a (light emission end face) and a rear end face 1b. The front end face 1a is the end face of the front end of the emitted laser, and the rear end face 1b is the end face of the rear end opposite to the front end face 1a.

[0116] The semiconductor stack of the semiconductor laser device 1 includes an optical waveguide with a front facet 1a and a rear facet 1b serving as resonator mirrors. Therefore, the front facet 1a and the rear facet 1b are the resonator end faces, and the resonator length of the semiconductor laser device 1 is the distance between the front facet 1a and the rear facet 1b. In this embodiment, the resonator length of the semiconductor laser device 1 is 2 mm or more, and can be longer, 4 mm or more. Alternatively, the resonator length of the semiconductor laser device 1 can be less than 2 mm.

[0117] 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 face 1a and the rear face 1b. That is, the position of the end of the current injection region in the length direction of the resonator is further inside than the front face 1a and the rear face 1b.

[0118] Furthermore, in the semiconductor laser device 1, a first end-face coating film 111 is formed on the front end face 1a of the semiconductor stack, and a second end-face coating film 112 is formed on the rear end face 1b of the semiconductor stack. Both the first end-face coating film 111 and the second end-face coating film 112 are reflective films composed of dielectric multilayer films. 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%.

[0119] Furthermore, the reflectivity of the first end-face coating film 111 and the second end-face coating film 112 is not limited by this. For example, when the semiconductor laser device 1 is used in a semiconductor laser module composed of an external resonator, the reflectivity of the first end-face coating film 111 can be 0.2% or less. Accordingly, problems such as knotting caused by the conflict between the laser oscillation mode of the semiconductor laser device 1 and the laser oscillation mode of the external resonator can be suppressed.

[0120] Furthermore, in this embodiment, the semiconductor stack in the semiconductor laser device 1 has end-face window structures at both ends along the length of the resonator. Specifically, window regions 120 are formed in the non-injection regions near the two end faces of the optical waveguide in the active layer 40, and in a region at a predetermined distance from the front end face 1a. The window regions 120 are formed on the end face of the semiconductor stack on the front end face 1a side. Alternatively, the same window region may be formed on the end face of the semiconductor stack on the rear end face 1b side. The window region on the rear end face 1b side is not necessarily required.

[0121] Here, the peak energy of photoluminescence in the region of the active layer 40 where the window region 120 is not formed is set as Eg1, and the peak energy of photoluminescence in the region of the active layer 40 where the window region 120 is formed is set as Eg2. If the difference between Eg1 and Eg2 is set as ΔEg, the window region 120 can be formed, for example, in a manner where ΔEg = Eg2 - Eg1 = 100 meV. That is, the bandgap of the active layer 40 in the region near the front end face 1a and the region near the rear end face 1b is larger than the bandgap of the active layer 40 in the region other than the region near the front end face 1a and the region near the rear end face 1b. Specifically, the bandgap energy of the well layer 41 near the front end face 1a and the region near the rear end face 1b is larger than the bandgap energy of the well layer 41 in the central part of the resonator along the length direction.

[0122] Furthermore, the window formation method for forming the window region 120 includes the general impurity diffusion method and the vacancy diffusion method; in this embodiment, the vacancy diffusion method is used. This is because, in ultra-high output semiconductor laser devices with each emitter exceeding 10W, reducing light absorption by minimizing losses is crucial. In other words, if the window region is formed using the impurity diffusion method, light absorption increases due to the influence of impurities, making it difficult to reduce light absorption loss. However, since the vacancy diffusion method is free of impurities, it eliminates light absorption loss caused by impurity introduction. By forming the window region using the vacancy diffusion method, the window region 120 is formed on the front end face 1a side as an end-face window structure. The same window region is also formed on the rear end face 1b side.

[0123] Furthermore, the vacancy diffusion method can form a window region by performing rapid high-temperature processing. For example, during high-temperature processing, after forming a protective film for generating Ga vacancies on the semiconductor layer in the region where the window region is formed, a very high temperature of 800°C to 950°C (near the crystal growth temperature) is applied to diffuse the Ga vacancies. This allows the quantum well structure of the active layer 40 to be disordered through the interdiffusion of vacancies and group III elements, thereby forming a window (transparency). This increases the band gap of the active layer 40, allowing the disordered region of the quantum well structure to be used as a window region. Moreover, outside the window region, a protective film for suppressing the generation of Ga vacancies is formed during high-temperature processing, thereby suppressing the disordering of the quantum well structure.

[0124] As described above, by having an end-face window structure, the resonator end face of the semiconductor laser device 1 can be made transparent, thereby reducing light absorption near the front end face 1a. Accordingly, COD can be suppressed at the front end face 1a.

[0125] [Manufacturing Method of Semiconductor Laser Devices]

[0126] Next, using Figures 3A to 3H The manufacturing method of the semiconductor laser device 1 according to the embodiment will be described. Figures 3A to 3H This is a diagram illustrating each step in the manufacturing method of the semiconductor laser device 1 according to the embodiment. Additionally, in Figures 3B to 3H In the diagram, the top figure shows a cross-section corresponding to the region where current is injected, i.e., the current injection region, while the bottom figure shows a cross-section corresponding to the region where no current is injected, i.e., the current non-injection region.

[0127] like Figure 3A As shown, a substrate 10 is first prepared, and multiple semiconductor layers are stacked on the substrate 10. The process of stacking multiple semiconductor layers includes at least the following steps: placing an N-type cladding layer 20 on top of the substrate 10, placing an active layer 40 on top of the N-type cladding layer 20, and placing a P-type cladding layer 60 on top of the active layer 40.

[0128] Specifically, on the n-GaAs wafer, i.e. the substrate 10, the N-type cladding layer 20, the N-type guiding layer 30, the active layer 40, the P-type guiding layer 50, the P-type cladding layer 60, the first contact layer 71 of the P-type contact layer 70, and the current blocking layer 80 are stacked sequentially by crystal growth using the metal-organic chemical vapor deposition (MOCVD) crystal growth technology.

[0129] As the active layer 40, the N-side second barrier layer 42b, the N-side first barrier layer 42a, the well layer 41, the P-side first barrier layer 43a, and the P-side second barrier layer 43b are sequentially crystal grown on the N-type guiding layer 30 to form a stack.

[0130] Then as Figure 3B As shown, an opening 80a for defining the current injection region is formed in the current blocking layer 80. Specifically, a mask made of SiO2 or the like is formed on the first contact layer 71 using photolithography in a predetermined pattern. Afterward, the current blocking layer 80 is etched using wet etching until the first contact layer 71 is exposed, forming the opening 80a in the portion of the current blocking layer 80 corresponding to the current injection region. Furthermore, no opening 80a is formed in the current blocking layer 80 in the non-current injection region of the end face of the semiconductor laser device 1. Additionally, a sulfuric acid-based etching solution is suitable for etching the current blocking layer 80. For example, an etching solution with a sulfuric acid:hydrogen peroxide solution:water ratio of 1:1:40 can be used.

[0131] Then as Figure 3C As shown, after removing the mask used to form the opening 80a in the current blocking layer 80 with a fluorine-based etchant, the second contact layer 72 of the P-type contact layer 70 is crystal grown using MOCVD crystal growth technology. Specifically, the second contact layer 72 is crystal grown on the current blocking layer 80 and on the first contact layer 71 exposed from the opening 80a in the current injection region, in a manner that fills the opening 80a in the current blocking layer 80.

[0132] Then as Figure 3D As shown, a window region 120 is formed at a portion corresponding to the end face of the resonator along its length in a semiconductor stack of multiple semiconductor layers. Specifically, the window region 120 is formed at a portion corresponding to the end face on one side of the front face 1a of the semiconductor stack. In this embodiment, the window region 120 is formed near the front face 1a of a portion of the P-type contact layer 70, P-type cladding layer 60, P-type guiding layer 50, active layer 40, N-type guiding layer 30, N-type cladding layer 20, and a portion of the substrate 10. Furthermore, although the window region 120 is formed by vacancy diffusion, it is not limited to this method.

[0133] Then as Figure 3EAs shown, a groove 130 with an inclined surface is formed on the side of the semiconductor stack. Specifically, a mask made of SiO2 or the like is formed on the P-type contact layer 70 using photolithography with a predetermined pattern. After that, wet etching is performed from the P-type contact layer 70 to the middle of the N-type cladding layer 20, thereby forming the groove 130 with an inclined surface on the side of the semiconductor stack. The groove 130 is a separation groove for the monolithization of the semiconductor laser device 1, and extends along the length of the resonator when viewed from above.

[0134] Furthermore, the etching solution used in forming tank 130 can be a sulfuric acid-based etching solution, for example. In this case, an etching solution with a ratio of sulfuric acid:hydrogen peroxide solution:water = 1:1:10 can be used. Moreover, the etching solution is not limited to sulfuric acid-based etching solutions; organic acid-based etching solutions or ammonia-based etching solutions can also be used.

[0135] Furthermore, the trench 130 is formed by isotropic wet etching. Accordingly, inclined surfaces are formed on the sides of the multiple semiconductor layers, thereby enabling the formation of a necked structure (i.e., an overhang shape) in the multiple semiconductor layers. The inclination angle of the sides of the trench 130 varies according to the Al composition ratio of the Al component in the AlGaAs material constituting each of the multiple semiconductor layers. In this case, by increasing the Al composition of the AlGaAs material, the etching rate can be accelerated. Therefore, in order to form a structure with... Figure 3E The inclined side profile shown allows for the highest Al composition ratio in the P-type cladding layer 60, thereby maximizing the lateral (horizontal) etching rate among the multiple semiconductor layers. Consequently, the narrowest portion (the narrowest portion in the horizontal direction) of the multiple semiconductor layers can be formed near the P-type cladding layer 60.

[0136] Next, as Figure 3F As shown, after removing the mask used to form the trench 130 using a fluorine-based etchant, a SiN film is deposited as an insulating film 100 on the entire surface of the substrate 10. Then, using photolithography and etching techniques, the portion of the insulating film 100 corresponding to the current injection region is removed to form the opening 100a. Conversely, the portion of the insulating film 100 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.

[0137] The etching of the insulating film 100 can be performed using wet etching with a fluoride-based etching solution or dry etching using reactive ion etching (RIE). Furthermore, while the insulating film 100 is made of SiN, it is not limited to this method and can also be made of SiO2 or other materials.

[0138] Next, as Figure 3GAs shown, a P-side electrode 91 is formed on a semiconductor stack. In this embodiment, the P-side electrode 91 is formed on the P-type contact layer 70 in the order of a first P-electrode layer 91a, a plating layer 91b, and a second P-electrode layer 91c.

[0139] Specifically, a first P electrode layer 91a, consisting of a Ti film, a Pt film, and an Au film, is formed as a base electrode by electron beam evaporation. Following this, a gold-plated layer 91b is formed by electroplating. Then, the portion of the layer 91b corresponding to the non-current injection region is selectively etched away using photolithography and a stripping technique. In this case, an iodine solution can be used as the etching solution for etching the gold-plated layer 91b. In this embodiment, an iodine solution with a ratio of iodine:potassium iodide:water = 288.8 g:490 g:3500 g is used, and etching is further performed in a bubbling state to stabilize the etching process. Afterward, a second P electrode layer 91c, consisting of a Ti film, a Pt film, and an Au film, is formed on the layer 91b by electron beam evaporation. Thus, the first P electrode layer 91a and the second P electrode layer 91c can be formed over almost the entire length of the resonator, while the Au coating 91b is not formed in the non-current injection region.

[0140] Next, as Figure 3H As shown, an N-side electrode 92 is formed on the lower surface of the substrate 10. Specifically, starting from one side of the substrate 10, films are formed in the order of AuGe film, Ni film, Au film, Ti film, Pt film, and Au film to form the N-side electrode 92.

[0141] Although not illustrated, the substrate 10, on which the semiconductor laminate is formed, is cut or cleaved with a cutter to separate it into rod-shaped pieces. Then, the groove 130 is further used as a shearing section for shearing, thereby separating the chip. Based on this, a monolithic semiconductor laser device 1 can be manufactured.

[0142] [Composition and band structure of semiconductor layers]

[0143] Next, a specific example of the semiconductor laser device 1 according to this embodiment will be described.

[0144] Figure 4 Specific examples of the composition, film thickness, and impurity concentration of each semiconductor layer in the three embodiments of the semiconductor laser device 1 described above, namely Embodiment 1, Embodiment 2, and Embodiment 3, are shown.

[0145] In this embodiment, the semiconductor layer of the semiconductor stack in the semiconductor laser device 1 is composed of a III-V compound semiconductor made of AlGaInAs type material, with the Al component and In component designated as X and Y, respectively. X Ga 1-X-Y In Y The composition formula of As (0 < X ​​< 1, 0 < Y < 1) is used to represent it.

[0146] exist Figure 4 In this context, the Al and In components of the N-type coating layer 20 are designated as X. NC and Y NC The Al and In components of the N-type guiding layer 30 are set as X. NG and Y NG Let the Al and In components of the second barrier layer 42b on the N side of the active layer 40 be set as X. NB2 and Y NB2 Let the Al and In components of the first barrier layer 42a on the N side of the active layer 40 be X. NB1 and Y NB1 Let the Al and In components of the well layer 41 in the active layer 40 be set as X. W and Y W Let the Al and In components of the first barrier layer 43a on the P side of the active layer 40 be X. PB1 and Y PB1 Let the Al and In components of the second barrier layer 43b on the P side of the active layer 40 be set as X. PB2 and Y PB2 The Al and In components of the P-type guiding layer 50 are set as X. PG and Y PG Let the Al and In components of the P-type coating layer 60 be set as X. PC and Y PC Additionally, in Figure 4 The conditions for obtaining laser light in the 915nm wavelength band are shown in the figure.

[0147] like Figure 4 As shown, in the semiconductor laser device 1 of this embodiment, in the active layer 40, the Al composition ratio of the second barrier layer 42b on the N side is higher than that of the first barrier layer 42a on the N side, and the Al composition ratio of the second barrier layer 43b on the P side is higher than that of the first barrier layer 43a on the P side.

[0148] Furthermore, in the semiconductor laser device 1 of this embodiment, the Al composition changes in the interface regions of the N-type cladding layer 20 and the N-type guiding layer 30, and in the interface regions of the P-type guiding layer 50 and the P-type cladding layer 60. Specifically, at least in the interface region of the N-type cladding layer 20 and the N-type guiding layer 30, the Al composition gradually increases with distance from the well layer 41. Similarly, at least in the interface region of the P-type guiding layer 50 and the P-type cladding layer 60, the Al composition gradually increases with distance from the well layer 41.

[0149] Next, using Figures 5A to 5C right Figure 4 The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser devices 1 of Examples 1 to 3 shown will be described.

[0150] Figure 5A The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device 1 of Embodiment 1 are shown.

[0151] Figure 5B The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device 1 of Embodiment 2 are shown.

[0152] Figure 5C The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device 1 of Embodiment 3 are shown.

[0153] In addition Figures 5A to 5C In the middle, D NB1 D represents the length of the undoped region in the first barrier layer 42a on the N side. PB1 This represents the length of the undoped region in the first barrier layer 43a on the P side.

[0154] like Figures 5A to 5C As shown, in the semiconductor laser device 1 of this embodiment, regardless of which of Embodiments 1 to 3, the concentration of impurities doped in the N-type cladding layer 20, the N-type guiding layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a increases stepwise with distance from the well layer 41. That is, with distance from the well layer 41, the impurity concentration increases stepwise in the order of the N-side first barrier layer 42a, the N-side second barrier layer 42b, the N-type guiding layer 30, and the N-type cladding layer 20. Furthermore, in this embodiment, the impurity concentration remains constant in each of the N-side first barrier layer 42a, the N-side second barrier layer 42b, the N-type guiding layer 30, and the N-type cladding layer 20.

[0155] Furthermore, the concentration of impurities doped in the N-type cladding layer 20, the N-type guiding layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a does not increase in a stepwise manner, but rather gradually increases as the distance from the well layer 41 increases (i.e., increases at an angle).

[0156] Furthermore, the impurity concentration at the interface between the P-type cladding layer 60 and the P-type guiding layer 50 remains unchanged at 2 × 10⁻⁶. 18 cm -3 The impurity concentration of the P-type cladding layer 60 can increase stepwise or continuously in the direction away from the well layer 41. In the region of the P-type cladding layer 60 away from the well layer 41, the intensity of the waveguide light distribution in the vertical direction is attenuated, so the impurity concentration can be increased for doping. In this region, due to the low light distribution intensity, the free carrier absorption loss caused by impurities occurs less, and the resistance value decreases by increasing the impurity concentration, thus preventing an increase in waveguide loss and reducing the series resistance of the semiconductor laser device. Specifically, the impurity concentration on the well layer 41 side is set to 2 × 10⁻⁶. 18 cm -3 The impurity concentration of the part farthest from the well layer 41 is set to 5 × 10⁻⁶. 18 cm -3 The concentration of P-type impurities in the P-type cladding layer 60 can be gradually increased, or it can be increased in a stepwise manner by increasing the impurity concentration away from the well layer 41. Here, when the Al composition of the P-type cladding layer 60 is more than twice that of the P-type guiding layer 50, due to the large difference in refractive index between the P-type cladding layer 60 and the P-type guiding layer 50, the light distribution intensity in the direction perpendicular to the substrate normal decreases sharply from the P-type guiding layer 50 towards the P-type cladding layer 60. In this case, in order to suppress the increase in waveguide loss caused by free carrier loss due to impurity doping, and to reduce the series resistance of the semiconductor laser device, the impurity concentration can be continuously increased from the well layer 41 towards the P-type cladding layer 60. Thus, in regions with high light distribution intensity, the low impurity concentration suppresses the increase in waveguide loss, while in regions with low light distribution intensity, the high impurity concentration achieves both a reduction in the series resistance of the semiconductor laser device and suppression of the increase in waveguide loss.

[0157] Furthermore, the concentrations of impurities doped in the P-type guide layer 50, the second P-side barrier layer 43b, and the first P-side barrier layer 43a gradually increase (i.e., increase at an angle) as they move away from the well layer 41. In the structures shown in Examples 1 to 3, the P-type impurity concentration increases from 2 × 10⁻⁶ to 10⁻⁶. 17 cm -3 Become 5×10 17 cm -3 In this manner, the impurity concentration continuously increases. Furthermore, the impurity concentration at the interface region between the P-type coating layer 60 and the P-type guide layer 50 increases from 5 × 10⁻⁶. 17 cm -3 Become 2×1018 cm -3 The waveguide loss increases continuously in a certain manner. In this case, the increase in waveguide loss caused by free carrier absorption loss due to impurity doping can be suppressed in the interface region between the P-type cladding layer 60 and the P-type guiding layer 50.

[0158] And, as Figures 5A to 5C As shown, the N-side first barrier layer 42a has an undoped region (without impurities) located on the side closer to the well layer 41, and a doped region (doped with impurities) located on the side 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.

[0159] Furthermore, regarding the N-side second barrier layer 42b, the entire region is doped with impurities. That is, impurities are intentionally doped throughout 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.

[0160] Similarly, the P-side first barrier layer 43a has an undoped region (without impurities) located on the side closer to the well layer 41, and a doped region (doped with impurities) located on the side farther from the well layer 41. In this embodiment, the thickness of the undoped region of the P-side first barrier layer 43a is 5 nm.

[0161] Furthermore, regarding the second barrier layer 43b on the P-side, it is doped with impurities throughout the entire region. That is, impurities are intentionally doped throughout the entire second barrier layer 43b on the P-side in the thickness direction.

[0162] Regarding the bandgap energy in each embodiment, as follows: Figures 5A to 5C As shown, in the N-side semiconductor region of the active layer 40, the bandgap energy of the second barrier layer 42b on the N-side is greater than the bandgap energy of the first barrier layer 42a on the N-side. Similarly, in the P-side semiconductor region of the active layer 40, the bandgap energy of the second barrier layer 43b on the P-side is greater than the bandgap energy of the first barrier layer 43a on the P-side.

[0163] Furthermore, the band gap energy of the P-type cladding layer 60 is greater than that of the N-type cladding layer 20.

[0164] Furthermore, as described above, the semiconductor laser device 1 has an end-face window structure in which the 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 greater than the bandgap energy of the well layer 41 at the center of the resonator in the longitudinal direction of the semiconductor laser device 1.

[0165] In addition, Figure 5AAlthough the bandgap energy of the second barrier layer 42b on the N side remains unchanged, it is not limited by this. For example... Figure 5B As shown, the bandgap energy of the second barrier layer 42b on the N side can gradually increase as it moves away from the well layer 41. Accordingly, the formation of heterojunction spikes or notches in the conduction band or valence band formed at the interface between the first barrier layer 42a and the second barrier layer 42b on the N side can be suppressed, thereby reducing the operating voltage.

[0166] Similarly, in Figure 5A Although the bandgap energy of the second barrier layer 43b on the P-side remains unchanged, it is not limited by this. For example, the bandgap energy of the second barrier layer 43b on the P-side can gradually increase as it moves away from the well layer 41. Accordingly, the formation of heterojunction spikes or notches in the conduction band or valence band formed at the interface between the first barrier layer 43a and the second barrier layer 43b on the P-side can be suppressed, thereby reducing the operating voltage.

[0167] Furthermore, in Figure 5A as well as Figure 5B In this context, although the bandgap energy of the P-type guiding layer 50 is the same as that of the N-type guiding layer 30, it is not a limitation. That is, the compositions of the N-type guiding layer 30 and the P-type guiding layer 50 can also be asymmetric. For example... Figure 5C As shown, when the bandgap energy of the P-type guiding layer 50 is greater than that of the N-type guiding layer 30, the electrons injected into the well layer 41 are excited by heat, thereby suppressing the occurrence of leakage current to the P-type guiding layer 50. Furthermore, since the N-type guiding layer 30 has a higher refractive index than the P-type guiding layer 50, the light distribution in the vertical direction relative to the substrate normal of the waveguide path can be biased towards the N-type layer. In this case, by controlling the Al composition difference between the N-type guiding layer 30 and the P-type guiding layer 50, the light distribution in the vertical direction can be precisely controlled. This allows for the excellent reproduction of a semiconductor laser device capable of high-temperature, high-output operation with both reduced waveguide loss and excellent temperature characteristics. If the Al composition difference between the N-type guiding layer 30 and the P-type guiding layer 50 is too large, the light distribution in the vertical direction will be excessively biased towards the N-type layer, resulting in a decrease in the optical confinement factor for the well layer 41 and an increase in the oscillation threshold current. Therefore, regarding the difference in Al composition between the N-type guiding layer 30 and the P-type guiding layer 50, the Al composition of the P-type guiding layer 50 can be relatively increased, so that the difference is less than 0.05.

[0168] Furthermore, when the bandgap energy of the P-type guiding layer 50 is smaller than that of the N-type guiding layer 30, by making the refractive index of the N-type guiding layer 30 lower than that of the P-type guiding layer 50, the light distribution in the vertical direction relative to the substrate normal direction of the waveguide can be biased towards the P side. This results in a high optical confinement factor for the well layer 41, enabling a semiconductor laser device that can reduce the oscillation threshold current while achieving excellent temperature characteristics and high-temperature, high-output operation. Regarding the Al composition difference between the N-type guiding layer 30 and the P-type guiding layer 50, if the N-type guiding layer 30 is too large, the light distribution in the vertical direction will be excessively biased towards the P-type layer, leading to increased waveguide loss, increased oscillation threshold current, and decreased tilting efficiency. Therefore, the Al composition difference between the N-type guiding layer 30 and the P-type guiding layer 50 can be relatively increased, keeping the difference below 0.04.

[0169] And in Figure 5A as well as Figure 5B While the maximum bandgap energy of the P-side second barrier layer 43b is the same as that of the N-side second barrier layer 42b, it is not a limitation. For example, the maximum bandgap energy of the P-side second barrier layer 43b can be greater than that of the N-side second barrier layer 42b. Accordingly, electrons injected into the well layer 41 are excited by heat, thereby suppressing the occurrence of current leakage to the P-type guiding layer 50. Furthermore, since the N-type guiding layer 30 has a higher refractive index than the P-type guiding layer 50, the light distribution in the waveguide path perpendicular to the substrate normal direction can be biased towards the N-type layer. In this case, by controlling the Al composition of the N-side second barrier layer 42b, the N-type guiding layer 30, the P-side second barrier layer 43b, and the P-type guiding layer 50, the light distribution in the vertical direction can be precisely controlled. Thus, a semiconductor laser device capable of high-temperature, high-output operation with excellent temperature characteristics can be reproduced well. In the difference between the maximum value of the Al component in the second barrier layer 43b on the P-side and the maximum value of the Al component in the second barrier layer 42b on the N-side, if the Al component of the second barrier layer 43b on the P-side is too large, the light distribution in the vertical direction will be too biased towards the N-type layer, which will lead to a decrease in the optical confinement factor for the well layer 41 and an increase in the oscillation threshold current. Therefore, regarding the difference between the maximum value of the Al component in the second barrier layer 43b on the P-side and the maximum value of the Al component in the second barrier layer 42b on the N-side, the maximum value of the Al component in the second barrier layer 43b on the P-side can be relatively increased, and the difference should be less than 0.05.

[0170] Furthermore, the maximum value of the bandgap energy of the second barrier layer 43b on the P-side can be smaller than the maximum value of the bandgap energy of the second barrier layer 42b on the N-side. In this case, the bandgap energy of the P-type guiding layer 50 is smaller than the bandgap energy of the N-type guiding layer 30. When the bandgap energy of the P-type guiding layer 50 is smaller than that of the N-type guiding layer 30, by making the refractive index of the N-type guiding layer 30 lower than that of the P-type guiding layer 50, the light distribution in the direction perpendicular to the substrate normal can be biased towards the P-side. In this way, a high optical confinement factor for the well layer 41 can be obtained, thereby obtaining a semiconductor laser device that can reduce the oscillation threshold current and perform high-temperature, high-output operation with excellent temperature characteristics. In the Al composition difference between the N-type guiding layer 30 and the P-type guiding layer 50, if the N-type guiding layer 30 is too large, the light distribution in the vertical direction will be biased too much towards the P-type layer, resulting in increased waveguide loss, increased oscillation threshold current, and decreased tilting efficiency. Therefore, regarding the difference in Al composition between the N-type guiding layer 30 and the P-type guiding layer 50, the Al composition of the N-type guiding layer 30 can be relatively increased, and the difference can be kept below 0.04. That is, regarding the difference in Al composition 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, the Al composition of the N-side second barrier layer 42b can be relatively increased, and the difference can be kept below 0.04.

[0171] In addition Figure 5A In this context, although the P-type guiding layer 50 and the second barrier layer 43b on the P side have the same bandgap energy, they are not limited by this. For example... Figure 5D As shown, the bandgap energy of the P-type guiding layer 50 can be greater than the bandgap energy of the second barrier layer 43b on the P side. With this configuration, electrons injected into the well layer 41 are excited by heat during high-temperature, high-output operation, thereby suppressing the occurrence of electron current leakage to the P-type guiding layer 50. In this way, a semiconductor laser device suitable for high-temperature, high-output operation can be obtained.

[0172] Furthermore, by making the bandgap energy of the second barrier layer 43b on the P side greater than that of the second barrier layer 42b on the N side, the electrons injected into the well layer 41 are excited by heat during high-temperature, high-output operation, thereby suppressing the occurrence of electron current leaking to the P-type guiding layer 50. In this way, a semiconductor laser device suitable for high-temperature, high-output operation can be obtained.

[0173] Furthermore, the bandgap energies of the first barrier layer 42a and the second barrier layer 42b on the N-side can be the same, and the bandgap energy of the N-type guiding layer 30 can also be higher than that of the second barrier layer 42b on the N-side. With this configuration, the refractive indices of the second barrier layer 42b and the first barrier layer 42a on the N-side become higher than that of the N-type guiding layer 30, thereby increasing the optical confinement factor for the well layer 41. This reduces the oscillation threshold current and leakage current during high-temperature, high-output operation, resulting in a semiconductor laser device suitable for high-temperature, high-output operation.

[0174] Furthermore, although the bandgap energies of the first P-side barrier layer 43a and the second P-side barrier layer 43b are the same, the bandgap energy of the P-type guiding layer 50 can also be higher than that of the second P-side barrier layer 43b. With this configuration, the refractive indices of the second P-side barrier layer 43b and the first P-side barrier layer 43a become higher than that of the P-type guiding layer 50, thereby increasing the optical confinement factor for the well layer 41.

[0175] This reduces the oscillation threshold current and leakage current during high-temperature, high-output operation, thus enabling the development of semiconductor laser devices suitable for high-temperature, high-output operation.

[0176] Figure 5E The impurity concentration distribution and band structure of the semiconductor stack in the semiconductor laser device of Embodiment 5 are shown. The semiconductor laser device of Embodiment 5 is based on the structure of the semiconductor laser device shown in Embodiment 1, but includes an N-side high-Al content layer 44 with a higher Al content than the N-side first barrier layer 42a between the N-side first barrier layer 42a and the well layer 41, and a P-side high-Al content layer 45 with a higher Al content than the P-side first barrier layer 43a between the P-side first barrier layer 43a and the well layer 41. Furthermore, Figure 5E Although the illustrated embodiment 5 has both the N-side high Al composition layer 44 and the P-side high Al composition layer 45, it may also have only one of them.

[0177] Based on this configuration, when the window is formed by vacancy diffusion and impurity diffusion, and the window is formed by thermal annealing or ion implantation, the increase in 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, leads to an increase in the band gap in the well layer 41 of the window due to the exchange of atoms between the two layers. Therefore, the difference in band gap energy between the window and the gain region is easily increased. Accordingly, even if the thickness of the well layer 41 is increased, the window region 120 can be easily formed.

[0178] 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 resulting from the exchange of atoms with the well layer 41 will be reduced, and the increase in band gap energy of the well layer 41 in the window region 120 generated by the thermal annealing process during window formation will also be reduced. 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, the refractive index of the N-side high-Al composition layer 44 will be lower than that of the N-side first barrier layer 42a, and the refractive index of the P-side high-Al composition layer 45 will be lower than that of the P-side first barrier layer 43a, thus reducing the optical confinement factor for the well layer 41. Furthermore, since the band gap energy of the N-side high Al composition layer 44 is greater 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 greater than that of the P-side first barrier layer 43a, the N-side high Al composition layer 44 will hinder electron injection into the well layer 41, and the P-side high Al composition layer 45 will hinder hole injection into the well layer 41, thus increasing the operating voltage.

[0179] Therefore, the thickness of the N-side high Al composition layer 44 and the P-side high Al composition layer 45 can be more than 3 nm and less than 10 nm.

[0180] Furthermore, if the Al composition of the N-side high Al composition layer 44 and the P-side high Al composition layer 45 is too small, the disordering effect of the quantum well structure generated by the exchange of atoms 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, will be reduced, and the increase in band gap energy of the well layer 41 in the window region 120 generated by the thermal annealing process during window formation will also be reduced. Conversely, if the Al composition is 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, thus reducing the optical confinement factor for the well layer 41. Furthermore, since the band gap energy of the N-side high Al composition layer 44 is greater 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 greater than that of the P-side first barrier layer 43a, the N-side high Al composition layer 44 hinders electron injection into the well layer 41, and the P-side high Al composition layer 45 hinders hole injection into the well layer 41, thereby increasing the operating voltage.

[0181] Therefore, the Al composition of the N-side high Al composition layer 44 and the P-side high Al composition layer 45 can be above 0.27 and below 0.35.

[0182] By having an N-side high Al composition layer 44 and a P-side high Al composition layer 45, even if the thickness of the well layer 41 is increased, the bandgap energy of the well layer 41 in the window region 120 can be easily increased, thereby easily obtaining a semiconductor laser device with high COD levels that is suitable for high-temperature operation.

[0183] Furthermore, in Figure 5E While the illustrated structure shows an example where the N-side high Al composition layer 44 and the P-side high Al composition layer 45 are undoped, the series resistance of the semiconductor laser device can also be reduced by doping the N-side high Al composition layer 44 with N-type impurities and the P-side high Al composition layer 45 with P-type impurities. Furthermore, doping the N-side high Al composition layer 44 with N-type impurities lowers the valence band potential energy, thereby suppressing leakage of hole current injected into the well layer 41. Conversely, doping the P-side high Al composition layer 45 with P-type impurities increases the conduction band potential energy, thus suppressing leakage of electron current injected into the well layer 41. This suppresses leakage current when the semiconductor laser device operates at high temperature and high output, resulting in a semiconductor laser device with excellent temperature characteristics. To achieve both reduced series resistance and improved temperature characteristics of the semiconductor laser device, the N-side high Al composition layer 44 can be doped with 1×10⁻⁶ impurities. 17 cm -3 Up to 1×10 18 cm -3 N-type impurities in the range of 1×10⁻⁶ are doped in the high Al composition layer 45 on the P-side. 17 cm -3 Up to 5×10 17 cm -3 P-type impurities within the range.

[0184] The N-side high Al composition layer 44 and the P-side high Al composition layer 45 can be either AlGaAs or AlGaInAs layers. If AlGaInAs is used in the P-side high Al composition layer 45, the valence band potential energy of the first barrier layer 43a on the P-side can be reduced, and the conduction band potential energy can be increased. This allows for the easy formation of the window region 120 while suppressing electron leakage from the well layer 41 to the P-type layer side.

[0185] In particular, when AlGaInAs is used for both the N-side high Al composition layer 44 and the P-side high Al composition layer 45, the potential energy difference in the valence band between the P-side first barrier layer 43a and the P-side high Al composition layer 45 can be reduced by setting the Al composition to 0.3% to 0.45% and the In composition to 0.05% to 0.15%. Furthermore, by including In in the N-side high Al composition layer 44, the band gap energy of the N-side high Al composition layer 44 is reduced, thereby reducing the potential energy difference in the conduction band between the N-side first barrier layer 42a and the N-side high Al composition layer 44. Thus, compared to AlGaAs layers with the same Al composition, the injection of electrons and holes into the well layer 41 becomes easier, and the operating voltage is reduced. Furthermore, due to the increased Al composition difference between the well layer 41 and the N-side high Al composition layer 44 and the P-side high Al composition layer 45, during the formation of the window region 120, the thermal annealing process or ion implantation process during window formation can easily lead to disordering of the group III atom arrangement through atomic exchange. This increases the bandgap energy difference between the window region and the gain region. Therefore, a semiconductor laser device with a high COD level can be obtained.

[0186] Furthermore, if an AlGaInAs layer with an In composition of 0.02 or less is used in the N-type guiding layer 30, it is possible to suppress the occurrence of lattice defects in the N-type guiding layer 30 and slightly increase its refractive index. This allows light to be more easily concentrated in the N-type guiding layer 30 in the vertical direction, thereby improving the controllability of the light distribution shape biased towards the N-type layer. In this case, the N-type guiding layer 30 can also be formed by a superlattice of InGaAs and AlGaAs.

[0187] [The function and effects of semiconductor laser devices]

[0188] Next, using Figure 6 The function and effects of the semiconductor laser device 1 involved in this embodiment will be explained. Figure 6 This diagram illustrates the function and effects of the semiconductor laser device 1 according to the embodiment. Figure 6 The diagram shows the band structure before and after annealing in a semiconductor laser device with an end-face window structure, in the region where a window area is desired (window portion) and the region where a window area is not desired (gain portion).

[0189] exist Figure 6 In this context, "this embodiment" refers to the semiconductor laser device 1 described in this embodiment.

[0190] And in Figure 6In this context, "Comparative Example" refers to the semiconductor laser device of the comparative example. The semiconductor laser device of the comparative example has an active layer between an N-side barrier layer composed of AlGaAs and a P-side barrier layer composed of AlGaAs, and a well layer composed of InGaAs is formed in the active layer. In order to achieve high output, the Al composition of the barrier layer is increased, thereby resulting in a configuration with improved thermal saturation level.

[0191] In semiconductor laser devices, a window region is formed near the end face to achieve high output and increase the COD level. The window region can be formed by disrupting the atomic arrangement of the barrier layer and well layer at the end face through vacancy diffusion and other methods.

[0192] In semiconductor laser devices with end-face window structures, to further achieve high output, it is advisable to thicken the well layer to increase the optical confinement factor. However, if the well layer is thickened, it becomes difficult to disorder the atomic arrangement of both the barrier layer and the well layer, thus hindering the formation of the window region. Therefore, it is considered to promote the exchange of atoms between the well layer and the barrier layer by increasing the annealing temperature during window formation, thereby disordering the atomic arrangement.

[0193] In this case, such as Figure 6 As shown, in the window region where the window area is to be formed, the band gap energy (Eg) after annealing can be increased. W1 The band gap energy (Eg) compared to that before annealing W0 Therefore, even if the trap layer thickens, a window region can still be formed.

[0194] However, if the annealing temperature for forming the window region is increased, atomic exchange will occur between the well layer and the barrier layer in the active layer of the gain region where it is undesirable to form a window region. Thus, even in the gain region, the bandgap energy (Eg) will become the annealed bandgap energy. G1 The band gap energy (Eg) compared to that before annealing G0 This means that the bandgap energy increases not only in the window region but also in the gain region. Consequently, the leakage current in the gain region increases, the temperature characteristics deteriorate, and due to the influence of vacancies introduced during crystal growth or dangling bonds on the surface of the growth layer, vacancies on the surface of the growth layer are prone to diffusion, thereby reducing the controllability of the oscillation wavelength or reducing long-term reliability.

[0195] In this embodiment, the semiconductor laser device 1, as described above, forms a P-side first barrier layer 43a and a P-side second barrier layer 43b on one side of the well layer 41, and the Al composition is changed in at least two stages. Specifically, the Al composition ratio of the P-side second barrier layer 43b is relatively increased relative to 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 on the side closer to the well layer 41 is low, and the Al composition of the P-side second barrier layer 43b on the side farther from the well layer 41 is high. Furthermore, in this embodiment, the bandgap energy of the P-side second barrier layer 43b is higher than that of the P-side first barrier layer 43a.

[0196] Accordingly, Figure 6 As shown in the "This Embodiment", even if the well layer is thickened and the annealing temperature is increased when forming the window region, the bandgap energy (Eg) after annealing can be increased at the window portion where the desired window region is formed. W1 The band gap energy (Eg) compared to that before annealing W0 The gain is large, and it is undesirable to form a window region in the gain region, so that the bandgap energy (Eg) after annealing is large. G1 ) and the band gap energy before annealing (Eg G0 () are of the same degree.

[0197] In other words, the gain portion can suppress both the change in bandgap energy before and after annealing and the increase in bandgap energy, while the window portion can increase the bandgap energy. Therefore, the window portion can promote the transparency of the semiconductor stack including the active layer 40, and the gain portion can suppress the transparency of the semiconductor stack including the active layer 40.

[0198] Thus, in the semiconductor laser device 1 according to this embodiment, since a first barrier layer 43a on the P-side with low Al composition and high refractive index is used, the optical confinement factor of the well layer 41 is increased, and the working carrier density is reduced. Furthermore, when the well layer is thickened, since the window region is formed by increasing the bandgap energy of the window portion, even if the annealing temperature during window region formation is increased, the low Al composition of the first barrier layer 43a on the P-side means that the bandgap energy of the well layer 41 in the gain region is less susceptible to changes caused by impurity diffusion, thereby suppressing wavelength changes in the well layer 41 in the gain region due to the increase in bandgap energy. This suppresses the reduction in long-term reliability. Moreover, it not only suppresses the obstruction of the COD level improvement effect but also suppresses the reduction in tilt efficiency or temperature characteristics.

[0199] Therefore, with the semiconductor laser device 1 according to this embodiment, even if the well layer 41 is thickened, the degradation of temperature characteristics and the reduction of long-term reliability can be suppressed, and the improvement effect of COD level can be suppressed.

[0200] Furthermore, in the semiconductor laser device 1 according to this embodiment, the bandgap energy of the P-type cladding layer 60 is greater than that of the N-type cladding layer 20.

[0201] Accordingly, since the refractive index of the P-type cladding layer 60 is smaller than that of the N-type cladding layer 20, the light distribution in the vertical direction of the substrate is biased towards the N-type cladding layer, which can reduce waveguide loss in the optical waveguide. Therefore, a semiconductor laser device 1 with high efficiency light emission can be realized.

[0202] Furthermore, when the semiconductor laser device 1 is mounted with the junction facing downwards (i.e., when the P-side electrode 91 side, which is furthest from the substrate 10, is mounted to the base), the P-type cladding layer 60 is easily affected by mounting strain. Moreover, due to the high Al content, the lattice mismatch strain with the substrate 10 increases, thus amplifying the effect of mounting strain. Consequently, birefringence occurs, and the light distribution transmitted through the optical waveguide diffuses more into the P-type cladding layer 60 compared to the N-type cladding layer 20 side, resulting in a reduced polarization ratio.

[0203] At this point, by making the bandgap energy of the P-type cladding layer 60 greater than that of the N-type cladding layer 20, the light distribution in the vertical direction of the substrate is biased towards the N-type cladding layer, thereby reducing the proportion of light distribution present in the P-type cladding layer 60. Accordingly, the reduction in polarization ratio can be suppressed.

[0204] Furthermore, in the semiconductor laser device 1 according to this embodiment, the thickness of the well layer 41 is 6 nm or more.

[0205] By making the thickness of the well layer 41 greater than 6 nm, the optical confinement factor of the well layer 41 can be significantly increased, thereby reducing the working carrier density and improving the thermal saturation level. This, in turn, improves the temperature characteristics.

[0206] Furthermore, when the light distribution is biased towards the N-type cladding layer 20, the optical confinement factor of the well layer 41 decreases, the oscillation threshold current increases, or the operating current increases. This can lead to leakage current and a decrease in thermal saturation level. However, by setting the thickness of the well layer 41 to 6 nm or more, the impact of the decrease in the optical confinement factor of the well layer 41 can be mitigated even if the light distribution is biased towards the N-type cladding layer 20.

[0207] Furthermore, in the semiconductor laser device 1 according to this embodiment, the well layer 41 is made of Al X Ga1-X-Y In y The composition of semiconductor materials represented by the composition formula of As (0 < X ​​< 1, 0 < Y < 1).

[0208] With this configuration, the compressive strain of the well layer 41 increases, which increases the energy between the heavy holes (HH1) and light holes (LH1) of the first energy level. Accordingly, the number of light holes (LH number) required for the TM mode is reduced. Furthermore, the number of light hole energy levels (LH level number) formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a can be set to 1. Therefore, the polarization ratio can be increased.

[0209] Among AlAs, GaAs, and InAs, InAs has the largest lattice constant and the smallest band gap energy. In this case, when using a semiconductor material with a quaternary composition of AlGaInAs as the well layer and barrier layer of the active layer to obtain the desired band gap energy, the compressibility strain increases due to the increased In content compared to obtaining the desired band gap with InGaAs or AlGaAs.

[0210] Therefore, in the semiconductor laser device using AlGaInAs in the well layer and barrier layer as shown in this embodiment, vacancies or impurities are diffused at the front end of the emitted laser to form an end-face window structure. In this case, since the strain energy of the well layer is reduced, the In atoms in the well layer are more likely to exchange with Al atoms or Ga atoms present in the lattice positions of group III in the stacking direction, thereby making it easier to increase the band gap energy (Eg) of the well layer.

[0211] In this way, the band gap energy of the well layer near the laser emission end face, i.e. the front end face with high optical density, is easy to increase. Even if the band gap energy near the front end face decreases due to heat generation, the well layer near the front end face can easily maintain a state of low light absorption.

[0212] Therefore, as shown in the semiconductor laser device 1 of this embodiment, by forming the well layer 41 with AlGaInAs, it is possible to suppress the occurrence of COD caused by the absorption of laser light near the front end face 1a.

[0213] Furthermore, as shown in this embodiment, the window region 120 is formed by vacancy diffusion, which, compared to the case where the window region 120 is formed by impurity diffusion, can suppress the occurrence of free carrier losses due to the presence of impurities. Accordingly, the reduction in tilt efficiency can be suppressed.

[0214] Furthermore, in the semiconductor laser device 1 according to this embodiment, the bandgap energy of the second barrier layer 43b on the P side gradually increases as it moves away from the well layer 41.

[0215] This configuration increases the average refractive index of the second barrier layer 43b on the P-side. Consequently, the optical confinement factor for the well layer 41 is significantly increased, resulting in a decrease in the working carrier density and thus an improvement in the thermal saturation level. Therefore, the temperature characteristics are improved.

[0216] Furthermore, by gradually increasing the bandgap energy of the second barrier layer 43b on the P-side away from the well layer 41, the series resistance of the semiconductor laser device 1 can be reduced. Therefore, a low-voltage driven semiconductor laser device 1 can be realized.

[0217] Furthermore, in the semiconductor laser device 1 of this embodiment, the first barrier layer 43a on the P side includes an undoped region without any doped impurities, and the film thickness of the undoped region can be 5 nm or more.

[0218] Accordingly, since the doping of impurities begins from the middle of the first barrier layer 43a on the P-side, the series resistance of the semiconductor laser device 1 can be reduced. Furthermore, since the electron barrier of the first barrier layer 43a on the P-side is increased, electron leakage can be suppressed. If the undoped region is too thick, the series resistance of the semiconductor laser device will increase; therefore, the undoped region can be 40 nm or less.

[0219] Furthermore, in the semiconductor laser device 1 according to this embodiment, the entire region of the second barrier layer 43b on the P side is doped with impurities, the first barrier layer 43a on the P side has an undoped region without impurities located on the side close to the well layer 41, and a doped region with impurities located on the side far from the well layer 41.

[0220] Accordingly, since the doping begins from the middle of the first barrier layer 43a on the P side, the series resistance of the semiconductor laser device 1 can be reduced. Furthermore, since the electron barriers of the first barrier layer 43a and the second barrier layer 43b on the P side are increased, electron leakage can be suppressed.

[0221] Furthermore, in the semiconductor laser device 1 according to this embodiment, the concentration of impurities doped in the second barrier layer 43b on the P side gradually increases as the distance from the well layer 41 increases.

[0222] With this configuration, the electronic barrier of the second barrier layer 43b on the P side is increased, which can suppress both current leakage and the increase in waveguide loss, thereby simultaneously reducing the series resistance of the semiconductor laser device.

[0223] Furthermore, the semiconductor laser device 1 according to this embodiment further includes a P-type guiding layer 50 located between the second barrier layer 43b on the P side and the P-type cladding layer 60.

[0224] Thus, by providing the P-type guiding layer 50, the optical confinement factor for the well layer 41 can be further increased. Consequently, the working carrier density is further reduced, thereby further improving the thermal saturation level. Therefore, the temperature characteristics can be further improved.

[0225] Furthermore, in the semiconductor laser device 1 according to this embodiment, regarding the Al composition of the P-type guiding layer 50 and the P-type cladding layer 60, the Al composition in the interface region of the P-type guiding layer 50 and the P-type cladding layer 60 gradually increases as one moves away from the well layer 41.

[0226] This configuration allows for an increased bandgap energy tilt in the interface region between the P-type guiding layer 50 and the P-type cladding layer 60. Consequently, the occurrence of heterojunction spikes or notches in the valence band at the interface between the P-type guiding layer 50 and the P-type cladding layer 60 can be suppressed, hole conductivity is improved, and thus the series resistance of the semiconductor laser device can be reduced.

[0227] 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 with increasing distance from the well layer 41, a high optical confinement factor can be obtained. This will be explained using... Figure 7A as well as Figure 7B To explain. Figure 7A The dependence of the light confinement efficiency on the length of the Al component tilt region in the semiconductor laser device 1 according to this embodiment is shown. Figure 7B The dependence of waveguide loss on the length of the Al component tilt region in this semiconductor laser device 1 is shown. Additionally, in Figure 7A as well as Figure 7B In the process, the length of the tilted region of the Al component is the length of the region where the Al component tilts and increases at the interface between the P-type guiding layer 50 and the P-type coating layer 60.

[0228] like Figure 7A As shown, by increasing the length of the tilted region of the Al component, the light confinement efficiency can be improved, which can lead to a reduction in the operating threshold current and an increase in the maximum light output. Furthermore, as... Figure 7B As shown, if the length of the Al component tilt region is too long, the resistivity increases, and the waveguide loss increases. Therefore, the length of the Al component tilt region is preferably less than 200 nm. Furthermore, as described above, from the viewpoint of suppressing the occurrence of spikes in the valence band at the interface between the P-type guiding layer 50 and the P-type cladding layer 60, the length of the Al component tilt region can be greater than 20 nm.

[0229] Furthermore, in the semiconductor laser device 1 according to this embodiment, the concentration of impurities doped in the P-type guide layer 50 gradually increases with increasing distance from the well layer 41. That is, the concentration of impurities doped in the P-type guide layer 50 increases at an angle.

[0230] With this configuration, the electronic barrier of the P-type guiding layer 50 is increased, which can suppress both current leakage and the increase of waveguide loss, and at the same time reduce the series resistance of the semiconductor laser device.

[0231] Here, to achieve a tilted concentration of P-type impurities in the P-side semiconductor layer, the following method is used: Figure 8A as well as Figure 8B Let me explain. Figure 8A The dependence of the optical confinement efficiency on the concentration of P-type impurities in the semiconductor laser device 1 according to the embodiment is shown. Figure 8B The dependence of waveguide loss on P-type impurity concentration in this semiconductor laser device 1 is shown. Figure 8A as well as Figure 8B The diagram shows simulation results of four samples taken in the semiconductor laser device 1 according to this embodiment, with variations in the Al composition and thickness of the first P-side barrier layer 43a and the second P-side barrier layer 43b. Figure 8A as well as Figure 8B In the above, sample 1 uses a first barrier layer 43a on the P-side with an Al composition of 0.12 and a thickness of 30 nm, and a second barrier layer 43b on the P-side with an Al composition that gradually increases from 0.12 to 0.24 and a thickness of 15 nm. Sample 2 uses a first barrier layer 43a on the P-side with an Al composition of 0.12 and a thickness of 15 nm, and a second barrier layer 43b on the P-side with an Al composition that gradually increases from 0.12 to 0.24 and a thickness of 15 nm. The conditions used in sampling 3 are: a first barrier layer 43a on the P side with an Al composition of 0.18 and a thickness of 30 nm, and a second barrier layer 43b on the P side with an Al composition that increases from 0.12 to 0.24 and a thickness of 15 nm; the conditions used in sampling 4 are: a first barrier layer 43a on the P side with an Al composition of 0.18 and a thickness of 15 nm, and a second barrier layer 43b on the P side with an Al composition that increases from 0.12 to 0.24 and a thickness of 15 nm.

[0232] from Figure 8A As can be seen, although the concentration of p-type impurities is almost independent of the optical confinement efficiency, reducing the Al composition of the first barrier layer 43a on the p-side significantly increases the optical confinement efficiency when the thickness of the first barrier layer 43a on the p-side is increased. Furthermore, as... Figure 8B As shown, if the concentration of P-type impurities is too high, the waveguide loss will increase. Therefore, the concentration of P-type impurities should not be too high.

[0233] Furthermore, in the semiconductor laser device 1 according to this embodiment, the active layer 40 further comprises: 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. Therefore, 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 band gap energy of the N-side second barrier layer 42b is greater than that of the N-side first barrier layer 42a.

[0234] With this configuration, by increasing the annealing temperature when thickening the well layer to form the window region, the wavelength change of the well layer 41 in the gain region due to the increase in bandgap energy can be suppressed not only in the P-side region of the well layer 41 but also in the N-side region. Furthermore, the bandgap energy can be increased in the window region, thereby increasing the wavelength change. Accordingly, the degradation of temperature characteristics and the reduction in long-term reliability can be further controlled, thereby further suppressing the hindrance to the improvement of COD level.

[0235] Furthermore, in the semiconductor laser device 1 according to this embodiment, the bandgap energy of the second barrier layer 42b on the N side gradually increases as it moves away from the well layer 41.

[0236] Based on this configuration, the average refractive index of the second barrier layer 42b on the N side can be increased. Consequently, the optical confinement factor for the well layer 41 can be significantly increased, thereby further reducing the working carrier density and further improving the thermal saturation level. Therefore, temperature characteristics can be further improved.

[0237] Furthermore, by making the bandgap energy of the second barrier layer 42b on the N side gradually increase as it moves away from the well layer 41, the series resistance of the semiconductor laser device 1 can be reduced.

[0238] Furthermore, in the semiconductor laser device 1 according to this embodiment, the entire region of the second barrier layer 42b on the N side is doped with impurities, the first barrier layer 42a on the N side has an undoped region located on the side close to the well layer 41 that is not doped with impurities, and a doped region located on the side far from the well layer 41 that is doped with impurities.

[0239] Accordingly, since impurity doping begins midway through the first barrier layer 42a on the N-side, the series resistance of the semiconductor laser device can be reduced. Furthermore, since the electron barriers of both the first barrier layer 42a and the second barrier layer 42b on the N-side are increased, electron leakage can be suppressed. Moreover, by making the interface of the well layer 41 in the first barrier layer 42a an undoped region, the reduction in gain of the well layer 41 can be suppressed.

[0240] Furthermore, in the semiconductor laser device 1 according to this embodiment, the bandgap energy of the second barrier layer 43b on the P side is greater than the bandgap energy of the second barrier layer 42b on the N side.

[0241] Therefore, it can both suppress the increase of working voltage and effectively suppress the occurrence of electron leakage.

[0242] Furthermore, the semiconductor laser device 1 according to this embodiment further includes an N-type guiding layer 30 located between the second barrier layer 42b on the N side and the N-type cladding layer 20.

[0243] In this way, by setting the N-type guiding layer 30, the optical confinement factor for the well layer 41 can be further increased. Accordingly, the working carrier density can be further reduced, and the thermal saturation level can be further improved. Therefore, the temperature characteristics can be further improved.

[0244] Furthermore, in the semiconductor laser device 1 according to this embodiment, the Al composition of the N-type guiding layer 30 and the N-type cladding layer 20, at least in the interface region of the N-type guiding layer 30 and the N-type cladding layer 20, gradually increases as it moves away from the well layer 41.

[0245] This configuration allows for an increased bandgap energy tilt in the interface region between the N-type guiding layer 30 and the N-type cladding layer 20. Consequently, it suppresses the occurrence of spikes in the valence band at the interface between the N-type guiding layer 30 and the N-type cladding layer 20, and improves hole conductivity, thereby reducing the series resistance of the semiconductor laser device.

[0246] Furthermore, in the semiconductor laser device 1 according to this embodiment, the concentration of impurities doped in the N-type cladding layer 20, the N-type guiding layer 30, the N-side second barrier layer 42b and the N-side first barrier layer 42a gradually increases or increases in a stepwise manner as the distance from the well layer 41 increases.

[0247] This configuration reduces both the series resistance of the semiconductor laser device and the waveguide loss, and enables efficient laser oscillation with high tilt efficiency while reducing the operating voltage.

[0248] Furthermore, in the semiconductor laser device 1 according to this embodiment, the active layer 40 may have 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 band gap energy of the N-side second barrier layer 42b is greater than that of the N-side first barrier layer 42a. An N-type guiding layer 30 is provided between the N-side second barrier layer 42b and the N-type cladding layer 20, and the band gap energy of the P-type guiding layer 50 is different from that of the N-type guiding layer 30.

[0249] With this configuration, when the band gap energy of the P-type guiding layer 50 is greater than that of the N-type guiding layer 30, the electron barrier is increased, thereby suppressing electron leakage.

[0250] Furthermore, since the bandgap energy of the P-type guide layer 50 is smaller than that of the N-type guide layer 30, the refractive index of the N-type guide layer 30 is lower than that of the P-type guide layer 50, resulting in weaker optical confinement of the N-type guide layer 30. Therefore, a high optical confinement factor for the well layer 41 can be obtained.

[0251] Furthermore, in the semiconductor laser device 1 according to this embodiment, between the well layer 41 and the N-type cladding layer 20, an N-side first barrier layer 42a and an N-side second barrier layer 42b are sequentially provided in the direction from the well layer 41 toward the N-type cladding layer 20. 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 band gap energy of the N-side second barrier layer 42b is greater than that of the N-side first barrier layer 42a. The band gap energy of the N-side second barrier layer 42b gradually increases as it moves away from the well layer 41. The maximum value of the band gap energy of the P-side second barrier layer 43b is greater than that of the N-side second barrier layer 42b.

[0252] This configuration increases the electron potential barrier, thereby suppressing electron leakage.

[0253] Here, the film thicknesses of the N-side first barrier layer 42a, N-side second barrier layer 42b, P-side first barrier layer 43a, and P-side second barrier layer 43b in the active layer 40 will be determined using... Figure 9 as well as Figure 10 To explain. Figure 9 The relationship between film thickness, optical confinement efficiency and waveguide loss is shown for the N-side first barrier layer 42a and the P-side first barrier layer 43a. Figure 10 The relationship between optical confinement efficiency and waveguide loss is shown for the film thickness of the second barrier layer 42b on the N side and the second barrier layer 43b on the P side. Additionally, in Figure 9 as well as Figure 10The simulation results show the film thickness variations in 5nm increments within the 15nm–40nm range. Furthermore, in... Figure 9 as well as Figure 10 Using a film thickness of 15nm as a baseline, curves were used to connect various points.

[0254] from Figure 9 As can be seen, by making the thickness of the first barrier layer 42a on the N side greater than the thickness of the first barrier layer 43a on the P side, waveguide loss can be reduced and optical confinement efficiency can be improved. That is, among the first barrier layer 42a, the second barrier layer 42b on the N side, the first barrier layer 43a on the P side, and the second barrier layer 43b on the P side, the thickness of the first barrier layer 42a on the N side and the first barrier layer 43a on the P side closer to the well layer 41 can be greater than the thickness of the first barrier layer 43a on the P side.

[0255] Additionally from Figure 10 As can be seen from the diagram, among the N-side first barrier layer 42a, N-side second barrier layer 42b, P-side first barrier layer 43a, and P-side second barrier layer 43b, the N-side second barrier layer 42b and P-side second barrier layer 43b on the side furthest from the well layer 41 may have a film thickness of P-side second barrier layer 43b that is thicker than that of N-side second barrier layer 42b. Specifically, by making the film thickness of P-side second barrier layer 43b greater than that of N-side second barrier layer 42b, both waveguide loss and optical confinement efficiency can be reduced.

[0256] Here, holes have lower mobility than electrons, and the activation ratio of impurities is also lower. Therefore, in order to reduce the series resistance of the semiconductor laser device and lower the rise voltage of the PN junction, the impurity concentration in the P-type semiconductor layer needs to be higher than that in the N-type semiconductor layer to increase the hole carrier density. Consequently, the impact of free carrier losses occurring in the optical waveguide propagation on the P-type semiconductor layer is greater than that on the N-type semiconductor layer, requiring precise control of the P-type impurity doping distribution.

[0257] Therefore, the inventors have investigated the impurity concentration in the P-type semiconductor layer for the semiconductor laser device 1 in this embodiment. The following will utilize... Figures 11A to 16B The results of this study will be explained. Additionally, in Figures 11A to 16B China and Israel Figure 8A as well as Figure 8B The discussion is based on the four sampling methods described in the text: sampling 1, sampling 2, sampling 3, and sampling 4.

[0258] First, using Figure 11A as well as Figure 11B The effect of impurity doping on the P-type guide layer 50 is explained. Figure 11A The diagram illustrates the dependence of the potential barrier (ΔEg) on ​​the concentration of the P-type impurity in the P-type guide layer 50, the first P-side barrier layer 43a, and the second P-side barrier layer 43b, in the semiconductor laser device 1 according to this embodiment, when the P-type guide layer 50 is doped with a P-type impurity and the first P-side barrier layer 43a and the second P-side barrier layer 43b are not doped with a P-type impurity (undoped). Figure 11B The dependence of the electron current density on the concentration of P-type impurities in the P-type guiding layer 50 is shown.

[0259] Specifically, for the first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side, the Al composition is set to 0.12 and 0.18, respectively, and the thickness is set to 15 nm and 30 nm, respectively. Furthermore, for the second barrier layer 43b on the P-side and the second barrier layer 42b on the N-side, the Al composition is set to slope from 0.12 to 0.24 and from 0.18 to 0.24, respectively, and the thickness is set to 15 nm. Therefore, both the first barrier layer 43a and the second barrier layer 43b on the P-side are set to be completely undoped. Furthermore, for the first barrier layer 42a on the N-side, the region of 5 nm starting from the well layer 41 is set to be undoped, and the region located at a distance of 5 nm or more from the well layer 41 is set to be doped with 1 × 10⁻⁶. 17 cm -3 Impurities. Furthermore, for the N-side second barrier layer 42b, 1.4 × 10⁻⁶ impurities were doped throughout the entire region. 17 cm -3 Impurities. Furthermore, for the N-type guide layer 30, 1.4 × 10⁻⁶ impurities were doped. 17 cm -3 Impurities. Additionally, for the N-type cladding layer 20, doping with 1.4 × 10⁻⁶ particles is carried out in stages, starting from the side closest to the well layer 41 and moving towards the side furthest away. 17 cm -3 2×10 17 cm -3 6×10 17 cm -3 2×10 18 cm -3 To increase the concentration of impurities.

[0260] In this structure, it is known that if the concentration of P-type impurities in the 0.2 μm thick P-type guiding layer 50 is increased from 1 × 10⁻⁶, the P-type impurity concentration will be reduced from 1 × 10⁻⁶. 17 cm -3 Increase to 5×10 17 cm -3 If so Figure 11A as well as Figure 11BAs shown, the potential barrier (ΔEg) increases from 0.215 eV to over 0.25 eV. At the same time, the electron current flowing in the P-type guiding layer 50 decreases, which has the effect of suppressing reactive current. Furthermore, if the P-type impurity concentration in the P-type guiding layer 50 is increased, it is possible to suppress the electron current from flowing across the well layer 41 into the P-side semiconductor layer.

[0261] In addition, if the concentration of P-type impurities in the P-type guiding layer 50 is increased, the barrier increases and the series resistance of the semiconductor laser device decreases, but the waveguide loss increases and the luminous efficiency (tilt efficiency) decreases.

[0262] Therefore, regarding the concentration of P-type impurities in the P-type guide layer 50, the average concentration of P-type impurities throughout the P-type guide layer 50 is controlled at 2 × 10⁻⁶. 17 cm -3 Up to 4×10 17 cm -3 This reduces waveguide loss, series resistance of semiconductor laser devices, and electronic current leakage, thereby increasing the potential barrier.

[0263] Furthermore, since the refractive index of the first barrier layer 43a on the P-side is higher than that of the second barrier layer 43b on the P-side, increasing the thickness of the first barrier layer 43a on the P-side can increase the optical confinement factor for the well layer 41. Especially in optical waveguides where the light distribution is biased towards the N-type semiconductor layer, the optical confinement factor for the well layer 41 tends to decrease; therefore, increasing the thickness of the first barrier layer 43a on the P-side is effective in suppressing the decrease in the optical confinement factor. However, the electron current flowing through the well layer 41 into the P-type guiding layer 50 increases when the thickness of the first barrier layer 43a on the P-side increases. Therefore, the thickness of the first barrier layer 43a on the P-side can be between 10 nm and 30 nm.

[0264] Next, regarding the impurity doping effects of the first barrier layer 43a on the P-side, the second barrier layer 43b on the P-side, and the P-type guide layer 50, the following will be utilized... Figure 12A as well as Figure 12B To explain. Figure 12A This paper illustrates the dependence of the potential barrier (ΔEg) on ​​the concentration of P-type impurities in the semiconductor laser device 1 according to this embodiment, when a certain amount of P-type impurities are doped in the P-type guiding layer 50, the first P-side barrier layer 43a, and the second P-side barrier layer 43b. Figure 12B The dependence of the electron current density on the concentration of P-type impurities is shown.

[0265] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al composition is set to 0.12 and 0.18, and the thickness is set to 15 nm and 30 nm, respectively. In this case, for the P-side first barrier layer 43a, a 5 nm region starting from the well layer 41 side is designated as an undoped region. Furthermore, for the N-side first barrier layer 42a, a 5 nm region starting from the well layer 41 side is designated as an undoped region, and a 1×10⁻⁶ doped region is placed in a region located at a distance of more than 5 nm from the well layer 41. 17 cm -3 The N-type impurities. Furthermore, for the P-side second barrier layer 43b and the N-side second barrier layer 42b, the Al composition was set to slope from 0.12 to 0.24 and from 0.18 to 0.24, respectively, and the thickness was set to 15 nm. In this case, for the N-side second barrier layer 42b, 1 × 10⁻⁶ impurities were doped throughout the entire region. 17 cm -3 The N-type impurities. Furthermore, for the N-type guide layer 30, 1×10⁻⁶ impurities were doped. 17 cm -3 Impurities. Furthermore, for the N-type cladding layer 20, doping with 1.4 × 10⁻⁶ particles is performed in multiple stages, from the side closest to the well layer 41 towards the side furthest away. 17 cm -3 2×10 17 cm -3 6×10 17 cm -3 2×10 18 cm -3 The impurities increase the concentration of impurities.

[0266] In this structure, it can be seen that if the concentration of P-type impurities in the first P-side barrier layer 43a, the second P-side barrier layer 43b, and the P-type guiding layer 50 (film thickness 0.2 μm) is increased from 1 × 10⁻⁶, the P-type impurity concentration will be reduced from 1 × 10⁻⁶. 17 cm -3 Increase to 5× 17 cm -3 If so Figure 12A as well as Figure 12B As shown, the potential barrier (ΔEg) increases from 0.216 eV to 0.254 eV, and the electron current flowing into the P-type guiding layer 50 decreases, thereby suppressing reactive current. Furthermore, while increasing the P-type impurity concentration in the P-type guiding layer 50 increases the potential barrier and decreases the series resistance of the semiconductor laser device, it also increases waveguide loss and reduces luminous efficiency (tilt efficiency).

[0267] Therefore, similarly, for the P-type impurity concentration doped in the P-type guide layer 50, the average P-type impurity concentration for the entire P-type guide layer 50 is controlled at 2 × 10⁻⁶. 17 cm-3 Up to 4×10 17 cm -3 This reduces waveguide loss, series resistance of semiconductor laser devices, and electronic current leakage, thereby increasing the potential barrier.

[0268] Furthermore, by doping the P-side first barrier layer 43a, P-side second barrier layer 43b, and P-type guide layer 50 with P-type impurity concentration, compared to the case where the P-side first barrier layer 43a, P-side second barrier layer 43b, and P-type guide layer 50 are not doped with P-type impurity concentration, the electron current flowing through the well layer 41 into the P-type semiconductor layer can be reduced, thereby reducing leakage current. At the same time, the barrier increase effect is also greater.

[0269] Furthermore, since the refractive index of the first P-side barrier layer 43a is higher than that of the second P-side barrier layer 43b, increasing the thickness of the first P-side barrier layer 43a can increase the optical confinement factor for the well layer 41. Especially in optical waveguides where the light distribution is biased towards the N-type semiconductor layer, the optical confinement factor for the well layer 41 tends to decrease. Increasing the thickness of the first P-side barrier layer 43a is effective in suppressing the decrease in the optical confinement factor. However, the electron current flowing through the well layer 41 into the P-type guide layer 50 will increase due to the increased thickness of the first P-side barrier layer 43a, but the increase in electron current leakage is reduced by about 10% compared to the case where the first P-side barrier layer 43a, the second P-side barrier layer 43b, and the P-type guide layer 50 are not doped with P-type impurities. Therefore, compared with the case where no P-type impurity concentration is doped in the first barrier layer 43a, the second barrier layer 43b on the P side and the P-type guide layer 50, the film thickness of the first barrier layer 43a on the P side can be increased by about 10%, so it can be above 15nm and below 40nm.

[0270] Here, in Figure 12A as well as Figure 12B Although the concentration of P-type impurities in the first P-side barrier layer 43a, the second P-side barrier layer 43b, and the P-type guide layer 50 is not tilted, if the concentration of P-type impurities in the first P-side barrier layer 43a, the second P-side barrier layer 43b, and the P-type guide layer 50 is tilted, then it becomes... Figure 13A as well as Figure 13B The results are shown. Figure 13A It shows in Figure 5A The dependence of the potential barrier (ΔEg) on ​​the concentration of P-type impurities in the impurity doping distribution of the semiconductor laser device 1 in Example 1. Figure 13B The dependence of the electron current density on the concentration of P-type impurities is shown.

[0271] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al composition is set to 0.12 and 0.18, respectively, and the thickness is set to 15 nm and 30 nm, respectively. In this case, for the P-side first barrier layer 43a, a 5 nm region starting from the well layer 41 side is designated as an undoped region. Furthermore, for the N-side first barrier layer 42a, a 5 nm region starting from the well layer 41 side is designated as an undoped region, and a 1×10⁻⁶ doped region is placed in the area located at a distance of more than 5 nm from the well layer 41. 17 cm -3 The N-type impurities. Furthermore, for the P-side second barrier layer 43b and the N-side second barrier layer 42b, the Al composition was set to slope from 0.12 to 0.24 and from 0.18 to 0.24, respectively, with a thickness of 15 nm. In this case, for the N-side second barrier layer 42b, 1 × 10⁻⁶ impurities were doped throughout the entire region. 17 cm -3 The N-type impurities. Furthermore, 1×10⁻⁶ impurities were doped into the N-type guide layer 30. 17 cm -3 Impurities. Additionally, for the N-type cladding layer 20, doping with 1.4 × 10⁻⁶ particles is performed in stages, from the side closest to the well layer 41 towards the side furthest away. 17 cm -3 2×10 17 cm -3 6×10 17 cm -3 2×10 18 cm -3 The impurities increase the concentration of impurities.

[0272] In this structure, the impurity concentration at the starting doping position P1 of the P-type impurity in the first barrier layer 43a on the P side is set to 1 × 10⁻⁶. 17 cm -3 The P-type impurity concentration at position P2 of the P-type guide layer 50 on the side furthest from the well layer 41 is set to be 1 × 10⁻⁶. 17 cm -3 The tilt is increased to 1×10 18 cm -3 ,like Figure 13A as well as Figure 13B As shown, when the thickness of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is 15 nm, the barrier (ΔEg) increases from 0.216 eV to 0.254 eV. When the thickness of the second barrier layer 43b on the P side and the second barrier layer 42b on the N side is 30 nm, the barrier (ΔEg) increases from 0.215 eV to 0.234 eV.

[0273] Furthermore, increasing the P-type impurity concentration at position P2 reduces the electron current flowing into the P-type guiding layer 50, thereby suppressing reactive current. In this case, increasing the P-type impurity concentration at position P2 increases the potential barrier and decreases the series resistance of the semiconductor laser device. Moreover, due to the tilted P-type impurity concentration in the P-type guiding layer 50, increasing the P-type impurity concentration at position P2 can suppress the increase in waveguide loss.

[0274] Therefore, by controlling the concentration of P-type impurities doped in the P-type guide layer 50, the average concentration of P-type impurities across the entire P-type guide layer 50 is set to 2 × 10⁻⁶. 17 cm -3 Up to 4×10 17 cm -3 This allows for a reduction in waveguide loss, series resistance of semiconductor laser devices, and electronic current leakage, thereby increasing the potential barrier.

[0275] Furthermore, by tilting the impurity concentration in the first barrier layer 43a, the second barrier layer 43b on the P side, and the P-type guide layer 50, P-type impurities can be doped, thereby reducing leakage current.

[0276] Furthermore, since the refractive index of the first barrier layer 43a on the P-side is higher than that of the second barrier layer 43b on the P-side, increasing the thickness of the first barrier layer 43a on the P-side can increase the optical confinement factor for the well layer 41. Especially in optical waveguides where the light distribution is biased towards the N-type semiconductor layer, the optical confinement factor for the well layer 41 decreases. Therefore, increasing the thickness of the first barrier layer 43a on the P-side is effective in suppressing the decrease in the optical confinement factor. However, if the thickness of the first barrier layer 43a on the P-side is too thick, the optical confinement for the well layer 41 can easily increase, thus increasing the likelihood of COD (Cyclic Optical Depletion). Specifically, the thickness of the first barrier layer 43a on the P-side is preferably 15 nm to 50 nm. In this way, in optical waveguides where the light distribution is biased towards the N-type semiconductor layer, both COD can be suppressed and the optical confinement for the well layer 41 can be increased, thereby reducing the oscillation threshold current.

[0277] exist Figure 13A as well as Figure 13B In this context, the Al composition of the N-type guiding layer 30 and the P-type guiding layer 50 is symmetrical. If the Al composition of the N-type guiding layer 30 and the P-type guiding layer 50 is made asymmetrical, then it becomes... Figure 14A as well as Figure 14B The results are shown. Specifically, in Figure 14A as well as Figure 14B In this process, the Al composition of the P-type guiding layer 50 is made larger than that of the N-type guiding layer 30 so that the band gap energy of the P-type guiding layer 50 is greater than that of the N-type guiding layer 30. Additionally, Figure 14A Showing the target Figure 5C The barrier of the P-type guiding layer 50 of the semiconductor laser device 1 in Embodiment 3 is dependent on the Al composition. Figure 14B The dependence of the electron current density of the P-type guiding layer 50 of the semiconductor laser device 1 on the Al composition is shown.

[0278] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al composition is set to 0.12 and 0.18, and the thickness is set to 15 nm and 30 nm, respectively. In this case, for the P-side first barrier layer 43a, a 5 nm region starting from the well layer 41 is designated as an undoped region. Furthermore, for the N-side first barrier layer 42a, a 5 nm region starting from the well layer 41 is designated as an undoped region, and a 1×10⁻⁶ doped region is formed in the region 5 nm or more away from the well layer 41. 17 cm -3 The N-type impurities. Furthermore, regarding the N-side second barrier layer 42b, the Al composition is set to a gradient from 0.12 to 0.24 and from 0.18 to 0.24, with a thickness of 15 nm. Regarding the P-side second barrier layer 43b, the Al composition is set to a gradient from 0.12 to X pg and from 0.18 to X pg, with a thickness of 15 nm. In this case, regarding the N-side second barrier layer 42b, 1 × 10⁻⁶ impurities are doped throughout the entire region. 17 cm -3 The N-type impurities are added. Furthermore, the Al composition of the N-type guiding layer 30 is set to 0.24, and the Al composition of the P-type guiding layer 50 is set to X pg. Additionally, regarding the N-type coating layer 20, it is doped with 1.4 × 10⁻⁶ impurities in multiple stages, from the side closest to the well layer 41 towards the side furthest away. 17 cm -3 2×10 17 cm -3 6×10 17 cm -3 2×10 18 cm -3 The impurities increase the concentration of impurities.

[0279] In this structure, the impurity concentration at the starting doping position P1 of the P-type impurity in the first barrier layer 43a on the P side is set to 1 × 10⁻⁶. 17 cm -3 The P-type impurity concentration at position P2 of the P-type guide layer 50 on the side furthest from the well layer 41 is set to 5 × 10⁻⁶. 18 cm -3 The tilt is increased in this way to dope P-type impurities.

[0280] Here, if we change XPG from 0.24 to 0.3, then as follows: Figure 14A as well as Figure 14B As shown, when the thickness of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is 15 nm, the barrier (ΔEg) increases from 0.235 eV to 0.32 eV. When the thickness of the second barrier layer 43b on the P side and the second barrier layer 42b on the N side is 30 nm, the barrier (ΔEg) increases from 0.25 eV to 0.315 eV.

[0281] Furthermore, increasing the P-type impurity concentration at position P2 reduces the electron current flowing into the P-type guiding layer 50, thereby suppressing reactive current. Increasing the P-type impurity concentration at position P2 increases the potential barrier and decreases the series resistance of the semiconductor laser device. Moreover, due to the tilted P-type impurity concentration in the P-type guiding layer 50, even increasing the P-type impurity concentration at position P2 can suppress the increase in waveguide loss.

[0282] Furthermore, it can be seen that if the Al composition of the P-type guiding layer 50 increases, the electron current flowing into the P-type guiding layer 50 through the well layer 41 decreases sharply. The average P-type impurity concentration of the P-type guiding layer 50 is 3 × 10⁻⁶. 17 cm -3 On the left and right sides, impurities are doped by reducing the concentration of P-type impurities on the side closer to the well layer 41. Therefore, the series resistance can be reduced and the increase of the potential barrier can be suppressed with low waveguide loss.

[0283] Furthermore, the aforementioned effects can be achieved by increasing the Al composition of the P-type guiding layer 50 relative to the Al composition of the N-type guiding layer 30. Specifically, if the Al composition of the P-type guiding layer 50 is 0.02 greater than that of the N-type guiding layer 30, the barrier increases by 0.03 eV, thereby reducing the electron current leaking into the P-type guiding layer 50 to approximately 50% or less. Moreover, if the Al composition of the P-type guiding layer 50 is 0.27 greater than that of the N-type guiding layer, the barrier can be increased to 0.27 eV or more; if the Al composition of the P-type guiding layer 50 is 0.29 greater than that of the N-type guiding layer, the barrier can be increased to 0.3 eV or more.

[0284] Furthermore, by setting the well layer thickness to 8 nm or more, and making the Al composition of the P-type cladding layer 60 greater than that of the N-type cladding layer 20, and the Al composition of the P-type guiding layer 50 greater than that of the N-type guiding layer 30, it is possible to bias the light distribution towards the N-type semiconductor layer while increasing the optical confinement factor for the well layer 41, thereby reducing light leakage into the P-type cladding layer 60. This improves the thermal saturation level, resulting in good temperature characteristics and enabling a semiconductor laser device with a high polarization ratio.

[0285] Next, regarding the effect of N-type impurity concentration on hole leakage current, the following was investigated: Figure 15A , Figure 15B , Figure 16A as well as Figure 16B Let me explain. Figure 15A The diagram illustrates the dependence of hole current density at a position 100 nm from the N-side interface of the well layer 41 on the N-type impurity concentration in the semiconductor laser device 1 according to this embodiment. Figure 15B This illustrates the dependence of the hole current density at the N-type cladding layer substrate-side interface on the N-type impurity concentration in the semiconductor laser device 1 according to this embodiment. Furthermore, Figure 16A An example of the N-type impurity concentration distribution in the N-type semiconductor layer of the semiconductor laser device 1 according to this embodiment is shown. Figure 16B This illustrates another example of the N-type impurity concentration distribution in an N-type semiconductor layer.

[0286] In this structure, the impurity concentration at the starting doping position P1 of the P-type impurity in the first barrier layer 43a on the P side is set to 1 × 10⁻⁶. 17 cm -3 The P-type impurity concentration at position P2 of the P-type guide layer 50 on the side furthest from the well layer 41 is set to be 1 × 10⁻⁶. 17 cm -3 The tilt is increased to 1×10 18 cm -3 This is how p-type impurities are doped. Furthermore, 2 × 10⁶ impurities are doped into the p-type coating layer 60. 18 cm -3 P-type impurities.

[0287] Increasing the P-type impurity concentration at position P2 reduces the electron current flowing into the P-type guiding layer 50, thereby suppressing reactive current. Furthermore, increasing the P-type impurity concentration at position P2 increases the potential barrier and decreases the series resistance of the semiconductor laser device. Also, because the P-type impurity concentration is tilted in the P-type guiding layer 50, increasing the P-type impurity concentration at position P2 can suppress the increase in waveguide loss.

[0288] Therefore, by controlling the concentration of P-type impurities in the P-type guide layer 50 to an average value of 2 × 10⁻⁶ for the entire P-type guide layer 50, the overall P-type impurity concentration is achieved. 17 cm -3 With 4×10 17 cm -3 This reduces waveguide loss, series resistance of semiconductor laser devices, and electronic current leakage, thereby increasing the potential barrier.

[0289] Furthermore, since the N-type impurities in the N-type semiconductor layer are doped in a manner that the light distribution in the vertical direction is biased towards the N-type semiconductor layer, the N-type impurity concentration increases in the direction away from the well layer 41. Figure 16A The situation shown is as follows: 5 × 10⁻⁶ doping is performed in the N-type guide layer 30 and the following region. 16 cm -3 The N-type impurity, the aforementioned region refers to the area extending from a distance of 5 nm or more from the well-off layer 41 of the first barrier layer 42a on the N side towards the substrate 10 and up to the N-type guide layer 30; for the N-type cladding layer 20, it is doped in stages with a doping density of 7 × 10⁻⁶ nm from the side closer to the well-off layer 41 to the side farther away. 16 cm -3 (0.25μm), 1×10 17 cm -3 (0.25μm), 3×10 17 cm -3 (0.5μm), 1×10 18 cm -3 (2 μm) to increase the impurity concentration. Furthermore, when doping N-type impurities in stages, in adjacent regions of the N-type cladding layer 20 with different impurity concentrations, the region farthest from the well layer 41 has the thickest film thickness. In other regions, the film thickness of the region closer to the well layer 41 is less than the film thickness of the region farther from the well layer 41. This is because in the region with the highest impurity concentration on the side of the N-type cladding layer 20 farthest from the well layer 41, the intensity of the light distribution in the vertical direction is attenuated. Even if the impurity concentration is increased, the effect on free carrier loss is not significant, thus avoiding an increase in waveguide loss, thereby achieving the effect of reducing the series resistance of the semiconductor laser device.

[0290] Furthermore, the rate of change of the intensity of the light distribution in the vertical direction and the rate of attenuation of this intensity in the N-type cladding layer 20 increases the closer it is to the well layer 41. Accordingly, since the increase in waveguide loss caused by the increase in impurity concentration can be avoided, the film thickness of each region with a fixed concentration when the impurity concentration is increased in multiple stages in the region where the light distribution in the vertical direction is not sufficiently attenuated is preferably made thinner in the region closer to the well layer 41.

[0291] Based on the N-type layer impurity concentration distribution, and setting each concentration to 1x, 1.2x, 1.5x, 2x, and 3x, then in Figure 15A The calculated hole current density at a position of 100 nm on the N-side interface of the off-well layer 41 is shown. Figure 15B The calculated hole current density at the interface of the N-type cladding substrate is shown.

[0292] from Figure 15A as well as Figure 15B As can be seen from this, when the N-type impurity concentration is increased, the hole current density decreases, and the hole current flowing into the N-type semiconductor layer through the well layer 41 decreases.

[0293] Furthermore, by increasing the N-type impurity concentration, the series resistance of the semiconductor laser device is reduced, thereby decreasing the operating current of the semiconductor laser device. Moreover, by maximizing the light distribution in the N-type guiding layer 30, the light distribution is biased towards the N-type semiconductor layer, thus making the N-type impurity concentration in the N-type guiding layer 30 the lowest compared to the N-type impurities in other N-type semiconductor layers, thereby reducing waveguide loss. Accordingly, by making the doping distribution of the N-type impurity concentration... Figure 16A The state shown enables the simultaneous reduction of series resistance and waveguide loss in semiconductor laser devices.

[0294] In addition, the doping distribution of N-type impurities can be not only Figure 16A The step-like changes shown can be... Figure 16B As shown by the solid line, the N-type impurity concentration on the substrate 10 side continuously increases. Furthermore, as... Figure 16B As shown by the dashed line, in the N-type guiding layer 30, the N-type impurity concentration at the location with the highest light distribution intensity is reduced, and the N-type impurity concentration increases continuously or stepwise from that location toward the substrate 10, thereby further reducing waveguide loss. Alternatively, it can be done as follows... Figure 16B As shown by the single-dotted line, the concentration of N-type impurities exhibits a nonlinear change.

[0295] And it can also be like this Figure 16C As shown, the impurity concentration in the first barrier layer 42a on the N side is increased, so that the impurity concentration in the second barrier layer 42b on the N side is lower than that in the first barrier layer 42a on the N side, and the N-type impurity concentration is increased in stages from the well layer 41 to the substrate 10.

[0296] In this case, the impurity concentration in the first barrier layer on the N side can be 5 × 10⁻⁶. 17 cm -3 Up to 1×10 18 cm -3Accordingly, the valence band potential of the first barrier layer 42a on the N-side decreases, and the holes injected into the well layer 41 can suppress the leakage of hole current to the N-type layer side, thereby further improving the high-temperature, high-output operation of the semiconductor laser device. Furthermore, although the N-type impurity concentration of the second barrier layer 42b on the N-side can be the same as that of the first barrier layer 42a on the N-side, and increased relative to the N-type guide layer 30, the increase in waveguide loss will result in increased N-type impurity concentration in the second barrier layer 42b on the N-side. Therefore, even increasing the N-type impurity concentration in the region within 10 nm of the interface between the second barrier layer 42b and the first barrier layer 42a on the N-side can suppress hole current leakage.

[0297] Furthermore, if the doping concentration of the first barrier layer 42a on the N side is increased, when the window region is formed by vacancy diffusion or ion implantation, even if the temperature of the thermal annealing process in the window formation is reduced, due to the presence of N-type impurities, atomic exchange easily occurs between them and the well layer 41, thereby achieving the effect of easily increasing the band gap energy of the well layer 41 in the window region.

[0298] Furthermore, the doping of N-type impurities in the N-type guiding layer 30 can be as follows: Figure 16D Therefore, the increase is phased from near the interface with the N-type cladding layer 20 toward the substrate 10. In an optical waveguide where the N-type light distribution is biased toward the N-type semiconductor layer, since the region with the highest light intensity in the light distribution perpendicular to the substrate normal direction is the region on the well layer 41 side of the N-type guide layer 30, as long as there is a region with the lowest N-type impurity concentration on the well layer 41 side of the N-type guide layer 30, the increase in waveguide loss can be suppressed.

[0299] exist Figures 16A to 16D In the example shown, the minimum N-type impurity concentration in the N-type guiding layer 30 is 5 × 10⁻⁶. 16 cm -3 Above, 3×10 17 cm -3 The following results in suppression of increased waveguide loss, suppression of hole current generation, and suppression of increased series resistance in the semiconductor laser device. Furthermore, even if the N-type impurity concentration on the substrate 10 side of the N-type cladding layer 20 is increased, the increase in waveguide loss is relatively small because the proportion of light distribution in the N-type cladding layer 20 in the region extending 1 μm or more from the interface between the N-type guide layer 30 and the N-type cladding layer 20 towards the substrate 10 is small. Therefore, to reduce the series resistance of the semiconductor laser device, it is preferable to increase the N-type impurity concentration in the N-type cladding layer 20 in the region extending 1 μm or more from the interface between the N-type guide layer 30 and the N-type cladding layer 20 towards the substrate 10 to a level that does not reduce mobility; for example, it could be 1 × 10⁻⁶. 18cm -3 Above, 3×10 18 cm -3 the following.

[0300] Furthermore, the N-type impurity concentration of the first barrier layer 42a on the N side can be such that... Figure 16C as well as Figure 16D As shown, the concentration of N-type impurities in the second barrier layer 42b, the N-type guiding layer 30, and the N-type coating layer 20 is increased as shown. Figure 16B The changes occur continuously as shown. Furthermore, even if the region near the well layer 41 where the N-type impurity concentration is increased includes a portion of the N-side second barrier layer 42b in addition to the N-side first barrier layer 42a, as long as the film thickness in this region is less than 10 nm, the increase in waveguide loss can be suppressed to a small extent, while the series resistance of the semiconductor laser device can be reduced, thereby further suppressing hole current leakage.

[0301] Next, the quantum well structure of the well layer 41 of the active layer 40 is discussed. The following utilizes... Figures 17-19 The results of this study will be explained. Figures 17-19 The dependence of heavy hole and light hole quantum levels on the Al composition of the trap layer is shown.

[0302] Figure 17 As shown, with the Al composition set to 0.06, the first barrier layer 43a on the P side and the first barrier layer 42a on the N side are considered as Al 0.06 Ga 0.94 As, with a thickness of 15 nm, the second barrier layer 43b on the P side and the second barrier layer 42b on the N side are considered as Al. 0.24 Ga 0.76 As, with a thickness of 15 nm, and the well layer 41 is considered as Al X Ga 1-X-Y In Y As, under such conditions, calculations were performed on the relative potential energies of the heavy hole (HH) and light hole (LH) levels formed in the well layer 41, with the thickness set to 6 nm, 8.5 nm, 12 nm, and 15 nm, respectively, showing their dependence on the Al composition. Here, the electronic energy level, HH energy level, and LH energy level are denoted as En, HHn, and LHn, respectively. Furthermore, n is a natural number, and the substrate energy level is 1. In this calculation, to obtain the same oscillation wavelength as 915 nm, the energy difference between E1 and H1 was set to a fixed value (1.35 eV). Additionally, in... Figure 17 The diagram shows the relationship 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. Furthermore, the lattice mismatch with the GaAs substrate in the well layer 41 having each Al composition is indicated by dashed lines.

[0303] Here, the relationship between the potential energy relative to the electron energy level is the opposite of the relationship between the potential energy relative to the hole energy level. Figure 17 In the calculation results shown, when comparing the potential energy between different energy levels, the energy level with the largest relative potential energy (i.e., located at the top of the line graph) is interpreted as having the lowest potential energy relative to the hole.

[0304] like Figure 17 As shown, with a well layer 41 thickness of 6 nm, two energy levels HH with relatively lower potential energy than L1 are formed. Therefore, when holes are injected into the well layer 41, they are filled in the order of H1, H2, and L1, starting from the lowest potential energy.

[0305] Here, if the Al composition of the well layer 41 is continuously increased, the compressive strain of the well layer 41 increases, the energy level of HH changes towards the direction with lower potential energy relative to holes, and the energy level of LH changes towards the direction with higher potential energy relative to holes. It can be seen from the above that increasing the Al composition of the well layer 41 increases the compressive strain, thereby increasing the energy difference between H1 and L1. Accordingly, in HH, holes are more likely to exist in H1 where the hole potential energy is the lowest, while in LH, holes are less likely to exist in L1 where the hole potential energy is the highest. It can be seen from the above that increasing the Al composition of the well layer 41 and increasing 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 normal to the substrate in oscillating laser light, an increase in the number of holes in LH will lead to a decrease in the polarization ratio (TE / (TE+TM)). Therefore, it can be concluded that increasing the Al composition of the well layer 41 and increasing the compressive strain can improve the polarization ratio.

[0306] Furthermore, if the thickness of the well layer 41 is 6 nm, the HH energy level, which has a lower potential energy than the LH, is formed into two energy levels. Therefore, holes can preferentially exist in the HH energy level, thereby obtaining a laser with a high TE mode component and a high polarization ratio.

[0307] In the case where the thickness of well layer 41 is 8.5 nm, if the Al composition of well layer 41 is set to 0.08 or higher, the energy level of LH is higher than the hole potential energy compared to the valence band energy of the first barrier layer. Therefore, no LH quantum level is formed within the quantum well formed by the first barrier layer 43a on the P side, the first barrier layer 42a on the N side, and well layer 41. Instead, a quantum level is formed with the second barrier layer 43b on the P side and the second barrier layer 42b on the N side as 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 further decreases, and the effect of increasing the polarization ratio increases. This state... Figure 17 The various line graphs are represented by the thick dashed line L1. For example... Figure 17 As shown, if the thickness of the well layer 41 is set to 8.5 nm or more, then when the Al composition of the well layer 41 is 0.04 or more, LH will not form in the first barrier layer 43a on the P side and the first barrier layer 42a on the N side. Furthermore, the thicker the well layer 41 is, the less likely LH will form in the first barrier layer 43a on the P side and the first barrier layer 42a on the N side, given the low lattice mismatch of the well layer 41. It can also be seen that when the well layer 41 is thick, the number of HH energy levels with lower hole potential than L1 increases, and the number of holes existing in L1 is more likely to decrease.

[0308] like Figure 17 As shown, if the thickness of the well layer 41 is set to 8.5 nm or more, then when the Al composition of the well layer 41 is 0.04 or more, there are 3 HH energy levels with hole potential energy lower than L1, which can reduce the number of LH energy levels and effectively increase the polarization ratio.

[0309] Furthermore, if the thickness of the well layer 41 is set to 12 nm or more, and the Al composition of the well layer 41 is 0.0 or more, there are 3 HH energy levels with hole potential energy lower than L1, which can reduce the number of LH energy levels and effectively increase the polarization ratio.

[0310] In addition, due to the high refractive index of the well layer 41, the optical confinement factor of the well layer 41 increases with the thickness of the film, and the threshold carrier density required for laser oscillation decreases. Therefore, the number of holes in L1 is further reduced, and the polarization ratio increases.

[0311] Because the Al composition of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is also low, and their refractive indices are higher than those of the second barrier layer 43b on the P side, the second barrier layer 42b on the N side, the N-type guiding layer 30, the N-type cladding layer 20, the P-type guiding layer 50, and the P-type cladding layer 60, when the film thickness of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is thick, the optical confinement factor for the well layer 41 increases, the threshold carrier density required for laser oscillation decreases, and therefore the number of holes in L1 further decreases, increasing the polarization ratio. For example, when the total film thickness of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is set to 20 nm or more, the effect of increasing the optical confinement factor can be obtained. However, if the total film thickness is too thick, it leads to an increase in the optical confinement factor for the well layer 41 and a decrease in the COD level; therefore, the total film thickness can be below 80 nm.

[0312] and, Figure 18 It is shown that the Al composition is set to 0.12, and the first barrier layer 43a on the P side and the first barrier layer 42a on the N side are considered as Al. 0.12 Ga 0.88As, with a thickness of 15 nm, and considering the second barrier layer 43b on the P side and the second barrier layer 42b on the N side as Al 0.24 Ga 0.76 As, with a thickness of 15 nm, and the well layer 41 is considered as Al X Ga 1-X-Y In Y As, in this case, when the thickness of the well layer is set to 6 nm, 8.5 nm, 12 nm, and 15 nm, the calculation results show the dependence of the relative potential energy of the energy levels of heavy holes (HH) and light holes (LH) formed in the well layer 41 on the Al composition. Here, with Figure 17 Similarly, the electronic energy levels, HH level, and LH level are represented by En, HHn, and LHn, respectively. Furthermore, n is a natural number, and the ground level is set to 1. Even in this calculation, the energy difference between E1 and H1 is kept constant (1.35 eV) to obtain the same oscillation wavelength as 915 nm. Additionally, Figure 18 The relationship between the In composition Y and the Al composition X for obtaining the same oscillation wavelength is shown. Furthermore, the lattice mismatch with the GaAs substrate in the well layer 41 having each Al composition is indicated by dashed lines.

[0313] like Figure 18 As shown, with a well layer 41 thickness of 6 nm, two HH energy levels with relatively lower potential energy than L1 are formed. Therefore, similarly to the above, when holes are injected into the well layer 41, the holes are filled in the order of H1, H2, L1, starting from the side with the lowest potential energy.

[0314] Here, if the Al composition of the well layer 41 is continuously increased, the compressive strain of the well layer 41 increases. Therefore, the energy level of HH shifts towards the direction with lower potential energy relative to holes, and the energy level of LH shifts towards the direction with lower potential energy relative to holes. From the above, it can be seen that the greater the Al composition of the well layer 41, the greater the compressive strain, and the larger the energy difference between H1 and L1. In HH, holes tend to reside in H1, where the hole potential energy is the lowest; conversely, in LH, holes tend to reside in L1, where the hole potential energy is the highest. From the above, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain increases the number of holes in HH and decreases the number of holes in LH. In oscillating laser light, LH contributes to the generation of TM mode light with the polarization direction normal to the substrate. Therefore, 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 increase the compressive strain can improve the polarization ratio.

[0315] Furthermore, if the thickness of the well layer 41 is 6 nm, two HH energy levels with lower potential energy than LH are formed. Holes can preferentially exist in the HH energy levels, resulting in a higher TE mode component and thus enabling the production of lasers with a high polarization ratio.

[0316] In the case where the thickness of well layer 41 is 8.5 nm, if the Al composition of well layer 41 is set to 0.08 or higher, the hole potential energy of the LH level increases compared to the valence band energy of the first barrier layer. No LH quantum level is formed within the quantum well formed by the P-side first barrier layer 43a and the N-side first barrier layer 42a with 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 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 smaller, and the effect of increasing the polarization ratio is enhanced. This state is... Figure 17 The various line graphs are represented by thick dashed lines L1 or L2. From Figure 18 As shown, if the thickness of the well layer 41 is set to 8.5 nm or more, then when the Al composition of the well layer 41 is 0.08 or more, LH will not form in the first barrier layer 43a on the P side and the first barrier layer 42a on the N side. Furthermore, the thicker the well layer 41, the less likely LH will form in the first barrier layer 43a on the P side and the first barrier layer 42a on the N side, given the lower lattice mismatch of the well layer 41. It can also be seen that with a thicker well layer 41, there are more HH energy levels with hole potential energies lower than L1, making it easier to reduce the number of holes in L1.

[0317] like Figure 18 As shown, if the thickness of the well layer 41 is set to 8.5 nm or more, then when the Al composition of the well layer 41 is 0.02 or more, there are 3 HH energy levels with hole potential energy lower than L1, which can reduce the number of LH energy levels and is effective in increasing the polarization ratio.

[0318] Furthermore, if the thickness of the well layer 41 is set to 12 nm or more, then when the Al composition of the well layer 41 is 0.0 or more, there are 4 HH energy levels with hole potential energy lower than L1, which can reduce the number of LH energy levels present in LH energy levels and is effective in increasing the polarization ratio.

[0319] In addition, since the refractive index of the well layer 41 is high, when the film thickness is thick, the threshold carrier density required for laser oscillation is reduced due to the increase in the optical confinement factor for the well layer 41. Therefore, the number of holes present in L1 can be further reduced, thereby increasing the polarization ratio.

[0320] Since the first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side also have low Al content and high refractive index compared to the second barrier layer 43b on the P-side, the second barrier layer 42b on the N-side, the N-type guiding layer 30, the N-type cladding layer 20, the P-type guiding layer 50, and the P-type cladding layer 60, a thicker film thickness of the first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side increases the optical confinement factor for the well layer 41 and reduces the threshold carrier density required for laser oscillation, thereby further reducing the number of holes in L1 and increasing the polarization ratio. For example, if the combined film thickness of the first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side is set to 25 nm or more, it is effective in increasing the optical confinement factor. However, if the combined film thickness increases, the optical confinement factor for the well layer 41 increases and the COD level decreases; therefore, the combined film thickness can be below 90 nm.

[0321] and, Figure 19 It is shown that the Al composition is set to 0.18, and the first barrier layer 43a on the P side and the first barrier layer 42a on the N side are considered as Al. 0.18 Ga 0.82 As, with a thickness of 15 nm, and considering the second barrier layer 43b on the P side and the second barrier layer 42b on the N side as Al 0.24 Ga 0.76 As, with a thickness of 15 nm, and the well layer 41 is considered as Al X Ga 1-X-Y In Y In the case of As, the calculation results show the dependence of the relative potential energy of the energy levels of heavy holes (HH) and light holes (LH) formed in well layer 41 on Al composition when the thickness of the well layer is set to 6 nm, 8.5 nm, 12 nm, and 15 nm. Here, with Figure 17 Similarly, the electronic energy levels, HH level, and LH level are represented by En, HHn, and LHn, respectively. Furthermore, n is a natural number, and the ground level is 1. Even in this calculation, the energy difference between E1 and H1 is kept constant (1.35 eV) to obtain the same oscillation wavelength as 915 nm. Additionally, Figure 19 The relationship 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. Furthermore, the lattice mismatch with the GaAs substrate in the well layer 41 having each Al composition is indicated by dashed lines.

[0322] like Figure 19 As shown, with a well layer 41 thickness of 6 nm, two energy levels, HH, with a relative potential energy lower than L1, are formed. Therefore, similarly, when holes are injected into the well layer 41, they are filled in the order of H1, H2, and L1, starting from the side with the lowest potential energy.

[0323] Here, if the Al composition of the well layer 41 is increased, the compressive strain of the well layer 41 increases, and the energy levels of HH shift towards the direction with lower potential energy relative to holes, while the energy levels of LH shift towards the direction with lower potential energy relative to holes. From the above, it can be seen that, similarly, as the compressive strain of the well layer 41 increases, the energy difference between H1 and L1 increases. In HH, holes tend to exist in H1, where the hole potential energy is the lowest; conversely, in LH, holes are less likely to exist in L1, where the hole potential energy is the highest. From the above, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain increases the number of holes in HH and decreases the number of holes in LH. In oscillating laser light, since the generation of TM mode light with the polarization direction normal to the substrate contributes to the 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 increasing the compressive strain can improve the polarization ratio.

[0324] Furthermore, if the thickness of the well layer 41 is 6 nm, then an HH level with two lower potential energy levels than LH is formed. Holes can preferentially exist in the HH level, resulting in a higher TE mode component, thus enabling the production of lasers with a high polarization ratio.

[0325] like Figure 19 As shown, if the thickness of the well layer 41 is set to 8.5 nm or more, and the Al composition of the well layer 41 is 0.02 or more, there are 3 HH energy levels with hole potential energy lower than L1. Therefore, the number of LH energy levels can be reduced, which is effective in increasing the polarization ratio.

[0326] Furthermore, if the thickness of the well layer 41 is set to 12 nm or more, and the Al composition of the well layer 41 is 0.0 or more, there are 4 HH energy levels with hole potential energy lower than L1. Therefore, the number of LH energy levels can be reduced, which is effective in increasing the polarization ratio.

[0327] In addition, since the refractive index of the well layer 41 is high, the optical confinement factor of the well layer 41 increases when the film thickness is thick, and the threshold carrier density required for laser oscillation decreases. Therefore, the number of holes in L1 can be further reduced and the polarization ratio can be increased.

[0328] The first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side also have low Al composition and high refractive index compared to the second barrier layer 43b on the P-side, the second barrier layer 42b on the N-side, the N-type guiding layer 30, the N-type cladding layer 20, the P-type guiding layer 50, and the P-type cladding layer 60. Therefore, when the film thickness of the first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side is thick, the optical confinement factor for the well layer 41 increases, and the threshold carrier density required for laser oscillation decreases, thereby further reducing the number of holes in L1 and increasing the polarization ratio. For example, if the combined film thickness of the first barrier layer 43a on the P-side and the first barrier layer 42a on the N-side is 30 nm or more, it is effective in increasing the optical confinement factor. However, if the combined film thickness is too thick, it leads to an increase in the optical confinement factor for the well layer 41 and a decrease in the COD level. Therefore, the combined film thickness can be less than 100 nm.

[0329] As mentioned above Figures 17-19 As shown in the description, when the Al composition of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is set to 0.06 to 0.18 and the thickness of the well layer 41 is set to 6 nm to 15 nm, more than two HH energy levels with lower potential energy than LH are formed. Therefore, holes can preferentially exist in the HH energy level, and the TE mode component is more abundant, thereby obtaining laser with a high polarization ratio.

[0330] Furthermore, when the Al composition of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is set to 0.06 to 0.18 and the thickness of the well layer 41 is set to 8.5 nm to 15 nm, more HH energy levels with lower hole potential energy than LH can be formed in the Al composition range of the well layer with a film thickness greater than 6 nm.

[0331] Furthermore, when the thickness of the well layer 41 is 8.5 nm, using InGaAs with an Al composition of 0.02 or higher as the well layer 41, and when the thickness of the well layer 41 is 12 nm, even using InGaAs with an Al composition of 0 as the well layer 41, it is possible to set the number of HH energy levels with a potential energy lower than that of holes to be 3 or more, thereby reducing the number of LH levels in L1 and achieving an increase in polarization ratio.

[0332] Furthermore, if the thickness of the well layer 41 is greater than 15 nm, the optical confinement factor for the well layer 41 will increase, resulting in a decrease in the COD level. Also, when the window region is formed near the resonator end face, if the well layer 41 is too thick, the bandgap in the window region through the exchange of group III atoms between the P-side first barrier layer 43a and the N-side first barrier layer 42a and the well layer 41 will become shorter, reducing the COD suppression effect. Conversely, if the thickness of the well layer 41 is too thin, during the high-temperature annealing process during window formation, the bandgap of the well layer 41 without the formed window region 120 gain portion is prone to become shorter, reducing the temperature characteristics of the semiconductor laser device. Therefore, the thickness of the well layer 41 can be 6 nm or more and 15 nm or less.

[0333] And in Figures 17-19 In this design, the Al composition of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side, both composed of AlGaAs, is set to between 0.06 and 0.18. If the Al composition of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side is too large, the optical confinement factor for the well layer 41 will decrease, thereby reducing the temperature characteristics of the semiconductor laser device. Therefore, the Al composition of the first barrier layer 43a on the P side and the first barrier layer 42a on the N side can be between 0.06 and 0.22.

[0334] Furthermore, increasing the Al composition of the N-side second barrier layer 42b and the P-side second barrier layer 43b, both composed of AlGaAs, can suppress the leakage of electron current from the well layer 41 to the P-type layer side and the leakage of hole current from the well layer 41 to the N-type layer side. Therefore, the Al composition can be 0.24 or higher. However, if the Al composition of the N-side second barrier layer 42b and the P-side second barrier layer 43b is increased too much, it will lead to an increase in the operating voltage. Therefore, the Al composition is preferably 0.32 or lower.

[0335] Furthermore, in the semiconductor laser device 1 according to this embodiment, the resonator length is increased. Specifically, the resonator length of the semiconductor laser device 1 is 2 mm or more.

[0336] 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 is improved. Accordingly, the thermally saturated light output can be increased.

[0337] Furthermore, if the resonator length of the semiconductor laser device 1 is too long, there is a possibility that the mirror loss of the resonator will increase and the tilting efficiency will decrease. In this disclosure, since the light distribution is biased towards the N-type semiconductor layer, the waveguide loss is reduced. Therefore, even if the resonator length of the semiconductor laser device 1 is increased, the decrease in tilting efficiency can be suppressed and the maximum light output can be increased.

[0338] (Modified Example)

[0339] The semiconductor laser device and its manufacturing method involved in this disclosure have been described above based on the embodiments. This disclosure is not limited to the above embodiments.

[0340] For example, in the above embodiment, a current blocking layer 80 with an opening 80a is disposed within the P-type contact layer 70 to define the current injection region, but this is not a limitation. Specifically, as Figure 20 , Figure 21A , Figure 21B as well as Figure 21C As shown in the semiconductor laser device 1A, the current injection region can also be defined by setting the ridge portion 200A. Figure 20 This is a top view of the semiconductor laser device 1A involved in the modified example. Figure 21A yes Figure 20 A cross-sectional view of the semiconductor laser device 1A on the XXIA-XXIA line. Figure 21B yes Figure 20 A cross-sectional view of the semiconductor laser device 1A on the XXIB-XXIB line. Figure 21C yes Figure 20 A cross-sectional view of the semiconductor laser device 1A on the XXIC-XXIC line. Additionally, Figure 21A A cross-section of the gain section of the semiconductor laser device 1A is shown. Figure 21B A cross-section of the end face of the semiconductor laser device 1A on the front face 1a side is shown.

[0341] like Figures 20-21C As shown, the semiconductor laser device 1A in this modified example is a semiconductor laser element having a ridge structure with a ridge portion 200A extending in the resonator length direction as an optical waveguide.

[0342] In the semiconductor laser device 1A, an insulating film 100A is formed having an opening 100a corresponding to the ridge portion 200A. The insulating film 100A is a dielectric film with current blocking function. The insulating film 100A is, for example, made of an insulating film such as SiO2.

[0343] Furthermore, in this modified example, to form the ridge portion 200A, a pair of grooves with a depth of 0.2 μm are formed on the P-type contact layer 70, and the surface of the P-type contact layer 70 other than the ridge portion 200A, which serves as the current injection path, is covered by an insulating film 100A. Accordingly, the incoming current can be concentrated to flow through the ridge portion 200A. Additionally, the grooves for forming the ridge portion 200A can be formed not only on the P-type contact layer 70, but also on the P-type covering layer 60.

[0344] 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.

[0345] Therefore, even the semiconductor laser device 1A involved in this modification can achieve the same effect as the semiconductor laser device 1 involved in the above embodiment.

[0346] Furthermore, the opening 80a in the above embodiment that defines the current injection region, as well as the opening 100a or resonator length in this modified example, can be adapted to semiconductor laser devices of various wavelengths by combining the well layers 41.

[0347] For example, for a semiconductor laser device with an aperture width of approximately 90μm to 300μm and a resonator length of approximately 2000μm to 6000μm, by setting the input current to approximately 15A to 40A and the input voltage to approximately 1.7V to 3V, a semiconductor laser device with the following optical characteristics can be realized: having a wavelength in the band of approximately 780nm to 800nm ​​and an emitted light output of approximately 15W to 30W.

[0348] For example, for a semiconductor laser device with an aperture width of approximately 90μm to 300μm and a resonator length of approximately 2000μm to 6000μm, by setting the input current to approximately 15A to 40A and the input voltage to approximately 1.6V to 3V, a semiconductor laser device with the following optical characteristics can be realized: having a wavelength in the band of approximately 800nm ​​to 820nm and an emitted light output of approximately 15W to 30W.

[0349] For example, for a semiconductor laser device with an aperture width of approximately 90μm to 300μm and a resonator length of approximately 2000μm to 6000μm, by setting the input current to approximately 15A to 40A and the input voltage to approximately 1.5V to 3V, a semiconductor laser device with the following optical characteristics can be realized: having a wavelength in the band of approximately 850nm to 900nm and an emitted light output of approximately 15W to 30W.

[0350] For example, for a semiconductor laser device with an aperture width of approximately 90μm to 300μm and a resonator length of approximately 2000μm to 6000μm, by setting the input current to approximately 15A to 50A and the input voltage to approximately 1.45V to 3V, a semiconductor laser device with the following optical characteristics can be realized: a wavelength in the range of approximately 900nm to 930nm, and an output laser output of approximately 15W to 40W.

[0351] For example, for a semiconductor laser device with an aperture width of approximately 90μm to 300μm and a resonator length of approximately 2000μm to 6000μm, by setting the input current to approximately 15A to 50A and the input voltage to approximately 1.4V to 3V, a semiconductor laser device with the following optical characteristics can be realized: having a wavelength in the band of approximately 930nm to 960nm and an emitted light output of approximately 15W to 40W.

[0352] For example, for a semiconductor laser device with an aperture width of about 4μm to 300μm and a resonator length of about 2000μm to 6000μm, by setting the input current to about 1A to 50A and the input voltage to about 1.4V to 3V, a semiconductor laser device with the following optical characteristics can be realized. Here, the optical characteristics refer to having a wavelength in the band of about 960nm to 990nm and an output laser light of about 1W to 40W.

[0353] Furthermore, since the semiconductor laser device 1A according to this modified example has a ridge portion 200A, it is possible to suppress characteristic degradation when the semiconductor laser device 1A is mounted to a base or the like. This will be explained below.

[0354] If the resonator length of the semiconductor laser device 1A is increased, the shear strain generated at the end of the semiconductor laser device 1 in the width direction when it is mounted on the base will have a greater impact on the optical waveguide. In this case, if asymmetrical shear stress is generated in the current injection region that forms the optical waveguide, the polarization plane of the laser propagating in the optical waveguide will be tilted, resulting in an elliptically polarized wave and a decrease in the polarization ratio.

[0355] Therefore, as shown in the semiconductor laser device 1A of this modified example, by providing the ridge portion 200A, the optical waveguide becomes ridge-shaped. This allows the shear stress generated in the ridge portion 200A to cancel out the shear stress generated at the end of the semiconductor laser device in the width direction when the semiconductor laser device 1A is mounted junction-down, thereby reducing the shear stress in the optical waveguide. Accordingly, the tilting of the polarization plane of the laser propagating in the optical waveguide can be suppressed, and the polarization ratio is reduced.

[0356] This will be utilized Figure 22 Further details will be provided. Figure 22 The diagram shows the semiconductor laser device 1A involved in this modified example being mounted on the base 2 with the junction facing downwards.

[0357] The base 2 is made of a material with a larger coefficient of thermal expansion than that of the semiconductor laser device 1A. For example, the coefficient of thermal expansion of each semiconductor material constituting the semiconductor laser device 1A is 5.35 × 10⁻⁶ for GaAs. -6 AlAs is 3.4 × 10 -6 InAs is 4.33 × 10 -6 GaN is 5.59 × 10 -6 AlN is 4.15 × 10 -6 InN is 2.85 × 10 -6 Therefore, the base 2 is made primarily of metal or ceramic materials. Cu (with a coefficient of thermal expansion of 16.8 × 10⁻⁶) can be used as the main component material of the base 2. -6 Ti (thermal expansion coefficient 8.4 × 10⁻⁶) -6 Pt (thermal expansion coefficient 8.4 × 10⁻⁶) -6 Au (coefficient of thermal expansion 14.2 × 10⁻⁶) -6 Ni (thermal expansion coefficient 13.4 × 10⁻⁶) -6 SiC (thermal expansion coefficient 6.6 × 10⁻⁶) -6 ).

[0358] In this case, such as Figure 22 As shown, when the semiconductor laser device 1A is mounted to the base 2 with the junction facing down, due to the difference in the coefficients of thermal expansion between the semiconductor laser device 1A and the base 2, shear stress (σ1) is generated on the active layer 40 of the semiconductor laser device 1A at the end of the semiconductor laser device 1A in the width direction and shear stress (σ2) is generated on the ridge portion 200A.

[0359] Here, when the average coefficient of thermal expansion of the base 2 (for example, in the case where the base is composed of multiple layers of material, if the coefficient of thermal expansion of each material is set as L(i) and the film thickness is set as Ti(i), then it becomes ΣL(i)T(i) / ΣL(i)) is greater than the average coefficient of thermal expansion of the semiconductor laser device 1A, when the base 2 is in the horizontal direction of the semiconductor laser device 1A ( Figure 22 The semiconductor laser device 1A is stressed by shortening in the X direction. Furthermore, the coefficient of thermal expansion of the metal filled in the grooves on both sides of the ridge portion 200A is greater than that of the semiconductor laser device 1A; therefore, the width of the grooves increases, generating stress on the semiconductor laser device 1A. Thus, as... Figure 22 As shown, in the XY plane of semiconductor laser device 1A, an antisymmetric shear stress is generated relative to the center of the current injection region between the slots.

[0360] Specifically, the active layer with the groove formed on the side of the ridge portion 200A at the same position as the X direction has shear stress (σ1L) generated at the left end of the semiconductor laser device 1A in the width direction, shear stress (σ2L) generated in the groove on the left side of the ridge portion 200A, and shear stress (σ1R) generated at the right end of the semiconductor laser device 1A in the width direction and shear stress (σ2R) generated in the groove on the right side of the ridge portion 200A in the width direction, which are in opposite directions, so the shear stress cancels each other out and becomes smaller.

[0361] Furthermore, since the light distribution propagating in the optical waveguide extends horizontally into the region of the slot, the influence of the shear stress on the light distribution at the end of the light distribution is reduced by the shear stress of the slot.

[0362] Furthermore, if the shear stresses on the left and right sides are not perfectly antisymmetric relative to the center of the width direction of the ridge portion 200A, then when birefringence is generated in the semiconductor laser device 1A due to shear stress, the polarization plane is tilted because the integral of the light distribution with respect to the shear stress is not zero.

[0363] Thus, with the semiconductor laser device 1A involved in this modification, when mounted on the base 2, the shear stress generated at the end of the semiconductor laser device 1A in the width direction is offset by the shear stress generated by the groove on the side of the ridge portion, thereby reducing the influence of shear stress on the light distribution. Accordingly, by tilting the polarization plane of the laser propagating in the optical waveguide, the reduction in polarization ratio can be suppressed.

[0364] To reduce the impact of shear stress generated at the width-direction end of the ridge-type semiconductor laser device 1A on the laser propagating in the optical waveguide, setting the Al composition of the P-type cladding layer 60 to 0.8 or higher can reduce the leakage of light distribution into the P-type cladding layer 60. However, setting the Al composition to 0.9 or higher increases the lattice mismatch with the GaAs substrate, leading to lattice defects and reduced crystallinity. Therefore, the Al composition can be between 0.8 and 0.9.

[0365] Furthermore, the width of the groove formed on the side of the ridge portion 200A is preferably 10 μm or more. This reduces the external shear stress on the ridge portion 200A. Specifically, if the groove width is too wide, the weight during installation is concentrated on the ridge portion 200A, which becomes the current injection zone; therefore, a groove width of 25 μm ± 15 μm is desirable. By setting a groove of this width, the rotation of the polarization plane caused by shear stress can be effectively suppressed.

[0366] Furthermore, although the semiconductor laser device 1A is mounted to the base 2 with the junction facing downwards in this modified example, it is not limited to this. For example, the semiconductor laser device 1A can also be mounted to the support substrate such as the base 2 with the junction facing upwards (face facing upwards).

[0367] Furthermore, regarding the case of mounting the semiconductor laser device 1 in the above embodiment to the base, the semiconductor laser device 1 can be mounted using either a junction-down or junction-up method.

[0368] (Other variations)

[0369] For example, in the semiconductor laser device 1 of the above embodiment, although the example shows the use of AlGaInAs type semiconductor materials, it is not limited to this and other semiconductor materials may also be used.

[0370] Specifically, semiconductor laser devices can also be constructed from AlGaInP-type semiconductor materials. In this case, such as... Figure 23 As shown, a semiconductor laser device made of AlGaInP-type semiconductor materials can be configured, for example, by sequentially stacking an N-type buffer layer 11, 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, an intermediate layer 64, a P-type contact layer 70, an insulating film 100A, and a P-side electrode 91 on an n-type GaAs substrate, i.e., substrate 10. The intermediate layer 64 is composed of a first intermediate layer 61, a second intermediate layer 62, and a third intermediate layer 63 stacked sequentially.

[0371] As an example, the N-type buffer layer 11 is AlGaAs or GaAs (film thickness: 0.5 μm, Si impurity concentration: 3 × 10⁻⁶).17 cm -3 The N-type coating 20 is (Al) X Ga 1-X 0.5In0.5P (film thickness: 3.6μm, Al composition: 0.18, Si impurity concentration in multiple stages: 2×10⁻⁶) 18 cm -3 6×10 17 cm -3 1.4×10 17 cm -3 The interface region between the N-type buffer layer 11 and the N-type coating layer 20 is Al. x Ga 1-x As, film thickness 75 nm, Al composition continuously varying from 0 to 0.31, impurity concentration 3 × 10⁻⁶ 17 cm ―3 The N-type guiding layer 30 is (Al) X Ga 1-X 0.5In0.5P (film thickness: 85nm, Al composition: zero, active layer 40nm side 80nm: undoped, Si impurity concentration in the remaining portion: 1×10⁻⁶) 17 cm -3 The Al composition at the interface between the N-type coating layer 20 and the N-type guiding layer 30 changes continuously from 0.18 to 0 when the film thickness is 20 nm.

[0372] Regarding the active layer 40, the second barrier layer 42b on the N side is AlGaAs (film thickness: 6.5nm, Al composition: 0.59, undoped), the first barrier layer 42a on the N side is AlGaAs (film thickness: 3.5nm, Al composition: 0.53, undoped), the well layer 41 is GaInAs (film thickness: 8.5nm, In composition: 0.12), the first barrier layer 43a on the P side is AlGaAs (film thickness: 3.5nm, Al composition: 0.53, undoped), and the second barrier layer 43b on the P side is AlGaAs (film thickness: 17.5nm, Al composition: 0.59, undoped).

[0373] P-type guiding layer 50 is (Al) X Ga 1-X 0.5In0.5P (film thickness: 0.17μm, Al composition: zero, active layer 40nm side 50nm: undoped, C impurity concentration of the remaining portion: 5×10⁻⁶) 17 cm -3 ), P-type coating 60 is (Al X Ga 1-X 0.5In0.5P (Film thickness: 0.6μm, Al composition: 0.6g, C impurity concentration in multiple stages: 5×10⁻⁶) 17 cm -31.2×10 18 cm -3 At a film thickness of 50 nm, the interface region between the P-type guiding layer 50 and the P-type coating layer 60 exhibits a continuous Al composition ranging from 0 to 0.69, and a C impurity concentration of 5 × 10⁻⁶. 17 cm -3 .

[0374] Regarding intermediate layer 64, the first intermediate layer 61 is (Al) X Ga 1-X 0.5In0.5P (Film thickness: 0.2μm, Al composition: 0.30, C impurity concentration: 1.2×10⁻⁶) 18 cm -3 The second intermediate layer 62 is (Al) X Ga 1-X 0.5In0.5P (Film thickness: 0.038μm, Al composition: zero, C impurity concentration: 1.2×10⁻⁶) 18 cm -3 The third intermediate layer, 63, is AlGaAs (film thickness: 0.05 μm, Al composition tilt: continuously changing from 0.52 to 0, C impurity concentration: 1.2 × 10⁻⁶). 18 cm -3 ).

[0375] In addition, the P-type contact layer 70 is GaAs (film thickness: 0.4 μm, C impurity concentration: 2 × 10⁻⁶). 18 cm -3 ).

[0376] Even in semiconductor laser devices with this configuration, the same effects as in Embodiment 1 described above can be achieved. For example, even by thickening the well layer 41, it is possible to suppress the deterioration of temperature characteristics and the reduction in long-term reliability, and to prevent the improvement of COD levels from being hindered.

[0377] Further in Figure 23 The semiconductor laser device involved in this modified example can achieve the following effects.

[0378] The first effect is that, since the semiconductor laser device involved in this modification is constructed of AlGaInP-type semiconductor material, which has a higher bandgap energy than AlGaAs-type semiconductor materials, a high potential barrier can be obtained. Accordingly, a semiconductor laser device can be obtained that can suppress carriers leaking across the active layer 40 to the P-type guiding layer 50, thereby improving tilting efficiency and enabling high-temperature, high-output operation.

[0379] The second effect is that, because impurities (Zn) diffuse easily, the impurity concentration required for window formation can be reduced. This reduces free carrier losses caused by impurities, thereby improving tilting efficiency.

[0380] The third effect is that, since the N-type cladding layer 20, N-type guiding layer 30, P-type guiding layer 50, and P-type cladding layer 60 can be lattically matched with the GaAs substrate, i.e., substrate 10, warpage of the semiconductor laser device (element) can be reduced. Therefore, due to the reduced warpage, even when the semiconductor laser device experiences asymmetric strain during junction-down mounting, the asymmetric strain can be reduced, thereby improving the effect of the current-blocking layer, i.e., the insulating film 100A, composed of oxide film, in other words, improving the effect of offsetting the shear stress generated at the end of the semiconductor laser device by the shear stress generated by the ridge shape.

[0381] The fourth effect is that the intermediate layer 64 can suppress the rise in driving voltage of the semiconductor laser device. Specifically, the Al composition can be reduced in a stepwise manner through the first intermediate layer 61 and the second intermediate layer 62 in the intermediate layer 64, thus minimizing the bandgap energy difference generated when AlGaInP and GaAs are bonded, thereby suppressing the rise in driving voltage. Moreover, since the Al composition of AlGaAs is tilted through the third intermediate layer 63, the bandgap energy at the heterojunction interface can be smoothed, suppressing the rise in driving voltage.

[0382] Furthermore, in the semiconductor laser device 1 described above, a necking structure is formed in the multiple semiconductor layers constituting the semiconductor stack, making the side surface of the semiconductor stack an inclined surface, but it is not limited to this.

[0383] Furthermore, the forms obtained by performing various modifications that can be conceived by those skilled in the art on the above embodiments, as well as the forms achieved by arbitrarily combining the constituent elements and functions of the above embodiments without departing from the spirit of this disclosure, are all included in this disclosure.

[0384] The semiconductor laser device disclosed herein can be used as a high-output light source for various purposes, such as a light source for image display devices like monitors or projectors, a light source for automotive headlights, a light source for industrial or civilian lighting, or a light source for industrial equipment such as laser welding equipment, thin film annealing equipment, and laser processing equipment.

[0385] Symbol Explanation

[0386] 1.1A Semiconductor Laser Device

[0387] 1a Front end

[0388] 1b Back end face

[0389] 2. Submount

[0390] 10 Substrates

[0391] 11 N-type buffer layer

[0392] 20 N-type coating

[0393] 30 N-type guiding layer

[0394] 40 Active layer

[0395] 41. Well layer

[0396] 42a N-side first barrier layer

[0397] 42b N-side second barrier layer

[0398] 43a P-side first barrier layer

[0399] 43b P-side second barrier layer

[0400] 44 N-side high Al composition layer

[0401] 45 P-side high Al composition layer

[0402] 50 P-type guiding layer

[0403] 60 P-type coating

[0404] 61 First Intermediate Layer

[0405] 62 Second Intermediate Layer

[0406] 63 Third Intermediate Layer

[0407] 64 Intermediate Layer

[0408] 70 P-type contact layer

[0409] 71 First contact layer

[0410] 72 Second contact layer

[0411] 80 Current blocking layer

[0412] 80a Opening

[0413] 91 P-side electrode

[0414] 91a First P electrode layer

[0415] 91b coating

[0416] 91c 2P electrode layer

[0417] 92 N-side electrode

[0418] 100, 100A insulating film

[0419] 100a Opening

[0420] 111 First end face coating film

[0421] 112 Second end face coating film

[0422] 120 window area

[0423] 130 slots

[0424] 200A Ridge

Claims

1. A semiconductor laser device that emits laser light. The semiconductor laser device includes: Substrate; An N-type cladding layer is disposed above the substrate; an active layer configured above the N-type cladding layer; as well as A P-type coating layer is disposed above the active layer. The active layer has: trap layer; The first barrier layer on the P-side is disposed above the well layer; A high Al composition layer on the P-side is disposed between the well layer and the first barrier layer on the P-side. as well as The second barrier layer on the P-side is disposed above the first barrier layer on the P-side. The Al composition ratio of the second barrier layer on the P side is higher than that of the first barrier layer on the P side. The bandgap energy of the second barrier layer on the P side is greater than the bandgap energy of the first barrier layer on the P side. The semiconductor laser device further includes a P-type guiding layer located between the second barrier layer on the P-side and the P-type cladding layer. The bandgap energy of the P-type guiding layer is greater than the bandgap energy of the second barrier layer on the P side. 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 is emitted is greater than the bandgap energy of the well layer at the center of the resonator along its length. The high Al composition layer on the P side has a higher Al composition than the first barrier layer on the P side.

2. The semiconductor laser device as described in claim 1, The band gap energy of the P-type cladding layer is greater than that of the N-type cladding layer.

3. The semiconductor laser device as described in claim 1 or 2, The thickness of the well layer is 6 nm or more.

4. The semiconductor laser device as described in claim 1 or 2, The trap layer is made of Al X Ga 1-X-Y In y The composition of semiconductor materials represented by the As composition formula, wherein... 0 <X<1、0<Y<1。 5. The semiconductor laser device as described in claim 1 or 2, The bandgap energy of the second barrier layer on the P side gradually increases as it moves away from the well layer.

6. The semiconductor laser device as described in claim 1 or 2, The first barrier layer on the P side includes an undoped region without any doped impurities. The thickness of the undoped region is greater than 5 nm.

7. The semiconductor laser device as described in claim 1 or 2, The entire region of the second barrier layer on the P side is doped with impurities. The first barrier layer on the P side has: an undoped region located on the side closer to the well layer, and a doped region located on the side farther from the well layer.

8. The semiconductor laser device as described in claim 1 or 2, The concentration of impurities doped in the second barrier layer on the P side gradually increases with distance from the well layer.

9. The semiconductor laser device as described in claim 1, Regarding the Al composition of the P-type guiding layer and the P-type covering layer, the Al composition in the interface region of the P-type guiding layer and the P-type covering layer gradually increases with distance from the well layer.

10. The semiconductor laser device as claimed in claim 1, The concentration of impurities doped in the P-type guide layer gradually increases with distance from the well layer.

11. The semiconductor laser device as described in claim 1 or 2, The active layer further comprises 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 second barrier layer on the N side is higher than that of the first barrier layer on the N side. The bandgap energy of the second barrier layer on the N side is greater than that of the first barrier layer on the N side.

12. The semiconductor laser device as claimed in claim 11, The bandgap energy of the second barrier layer on the N side gradually increases as it moves away from the well layer.

13. The semiconductor laser device as claimed in claim 11, The entire region of the second barrier layer on the N side is doped with impurities. The first barrier layer on the N side has: an undoped region located on the side closer to the well layer, and a doped region located on the side farther from the well layer.

14. The semiconductor laser device as claimed in claim 11, The bandgap energy of the second barrier layer on the P side is greater than that of the second barrier layer on the N side.

15. The semiconductor laser device as claimed in claim 11, The semiconductor laser device includes an N-side high Al composition layer located between the well layer and the N-side first barrier layer, wherein the Al composition of the N-side high Al composition layer is higher than that of the N-side first barrier layer.

16. The semiconductor laser device as claimed in claim 11, The semiconductor laser device further includes an N-type guiding layer located between the second barrier layer on the N side and the N-type cladding layer.

17. The semiconductor laser device as claimed in claim 16, Regarding the Al composition of the N-type guiding layer and the N-type covering layer, the Al composition in the interface region of the N-type guiding layer and the N-type covering layer gradually increases with distance from the well layer.

18. The semiconductor laser device as claimed in claim 16 or 17, The concentration of impurities doped in the N-type cladding layer, the N-type guiding layer, the N-side second barrier layer, and the N-side first barrier layer gradually increases or increases stepwise as the distance from the well layer increases.

19. The semiconductor laser device as claimed in claim 1, 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 second barrier layer on the N side is higher than that of the first barrier layer on the N side. The bandgap energy of the second barrier layer on the N-side is greater than the bandgap energy of the first barrier layer on the N-side. The semiconductor laser device includes an N-type guiding layer located between the second barrier layer on the N-side and the N-type cladding layer. The bandgap energy of the P-type guiding layer is different from that of the N-type guiding layer.

20. The semiconductor laser device as claimed in claim 5, Between the well layer and the N-type cladding layer, an N-side first barrier layer and an N-side second barrier layer are provided in a direction from the well layer toward the N-type cladding layer. The Al composition ratio of the second barrier layer on the N side is higher than that of the first barrier layer on the N side. The bandgap energy of the second barrier layer on the N-side is greater than the bandgap energy of the first barrier layer on the N-side. The bandgap energy of the second barrier layer on the N side gradually increases with distance from the well layer. The maximum value of the bandgap energy of the second barrier layer on the P side is greater than the maximum value of the bandgap energy of the second barrier layer on the N side.

21. The semiconductor laser device as described in claim 1 or 2, The active layer further comprises 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 combined thickness of the first barrier layer on the P side and the first barrier layer on the N side is more than 20 nm and less than 80 nm.

22. A method for manufacturing a semiconductor laser device, which is a method for manufacturing a semiconductor laser device that emits laser light. The method for manufacturing the semiconductor laser device includes: The process of depositing an N-type cladding layer on top of a substrate; The process of depositing an active layer on top of the N-type coating layer; The process of depositing a P-type guiding layer above the active layer; and The process of depositing a P-type covering layer on top of the P-type guiding layer. The active layer has: trap layer; The first barrier layer on the P side is configured above the well layer; A high Al composition layer on the P-side is disposed between the well layer and the first barrier layer on the P-side. as well as The second barrier layer on the P-side is configured above the first barrier layer on the P-side. The Al composition ratio of the second barrier layer on the P side is higher than that of the first barrier layer on the P side. The bandgap energy of the second barrier layer on the P side is greater than the bandgap energy of the first barrier layer on the P side. The P-type guiding layer is located between the second barrier layer on the P-side and the P-type coating layer. The bandgap energy of the P-type guiding layer is greater than the bandgap energy of the second barrier layer on the P side. 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 is emitted is greater than the bandgap energy of the well layer at the center of the resonator along its length. The high Al composition layer on the P side has a higher Al composition than the first barrier layer on the P side.

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