Semiconductor laser device and method for manufacturing a semiconductor laser device

Abstract

To provide a semiconductor laser device and the like capable of preventing inhibition of an improvement effect on a COD level while suppressing deterioration of temperature characteristics and reduction in long-term reliability even when a well layer is made thicker.SOLUTION: A semiconductor laser device (1) comprises an N-type cladding layer (20), an active layer (40), and a P-type cladding layer (60). The active layer (40) includes a well layer (41), a P-side first barrier layer (43a) disposed over the well layer (41), and a P-side second barrier layer (43b) disposed over the P-side first barrier layer (43a). The P-side second barrier layer (43b) has an Al composition ratio higher than an Al composition ratio of the P-side first barrier layer (43a). The P-side second barrier layer (43b) has a bandgap energy greater than a bandgap energy of the P-side first barrier layer (43a). The semiconductor laser device further includes a P-type guide layer (50) and a P-side high AI composition layer (45). A bandgap energy of the P-type guide layer (50) is greater than a bandgap energy of the P-side second barrier layer (43b).SELECTED DRAWING: Figure 2A

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 are attracting attention as light sources for a variety of applications, including light sources for image display devices such as displays and projectors, light sources for automotive headlamps, light sources for industrial and consumer lighting, and light sources for industrial equipment such as laser welding equipment, thin-film annealing equipment, and laser processing equipment.

[0003] In particular, semiconductor laser elements used as light sources for projectors, laser processing equipment, or laser welding equipment are required to have high output characteristics that significantly exceed 1 watt. For example, semiconductor laser elements in the 915 nm wavelength band used as light sources for laser welding equipment are required to have high output characteristics of 25 W or more.

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

[0005] In semiconductor laser devices with an oscillation laser wavelength of 900 nm to 980 nm, an active layer with a quantum well structure, where the well layer is InGaAs and the barrier layer is AlGaAs, is widely used. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 62-249496 [Overview of the project] [Problems that the invention aims to solve]

[0007] To increase the power output of semiconductor laser elements to the watt range, possible approaches include improving the thermal saturation level and improving the COD (Catastrophic Optical Damage: end-face fracture) level.

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

[0009] This disclosure aims to solve these problems and to provide a semiconductor laser apparatus and a method for manufacturing the same that can suppress the improvement of the COD level while suppressing the deterioration of temperature characteristics and the decrease in long-term reliability, even when the well layer is thickened. [Means for solving the problem]

[0010] To solve the above problems, one embodiment of a semiconductor laser apparatus according to the present disclosure is a semiconductor laser apparatus 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, and the Al composition ratio of the P-side second barrier layer is the Al composition ratio of the P-side first barrier layer The ratio is higher than the band gap energy of the P-side second barrier layer, and the band gap energy of the P-side first barrier layer is greater than the band gap energy of the P-side first barrier layer. Furthermore, a P-type guide layer is provided between the P-side second barrier layer and the P-type cladding layer, and a P-side high-Al composition layer with a higher Al composition than the P-side first barrier layer is provided between the well layer and the P-side first barrier layer, the band gap energy of the P-type guide layer is greater than the band gap energy of the P-side second barrier layer, and the P-side high-Al composition layer is doped with P-type impurities. [Effects of the Invention]

[0011] According to this disclosure, even if the well layer is thickened, it is possible to suppress the deterioration of temperature characteristics and the decrease in long-term reliability while preventing the improvement of the COD level from being hindered. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a top view of a semiconductor laser device according to an embodiment. [Figure 2A] Figure 2A is a cross-sectional view of a semiconductor laser apparatus according to an embodiment along the line IIA-IIA in Figure 1. [Figure 2B] Figure 2B is a cross-sectional view of a semiconductor laser apparatus according to an embodiment of the line IIB-IIB in Figure 1. [Figure 2C] Figure 2C is a cross-sectional view of a semiconductor laser apparatus according to the embodiment in the IIC-IIC line shown in Figure 1. [Figure 3A] Figure 3A is a diagram illustrating the semiconductor layer stacking process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3B] Figure 3B is a diagram illustrating the current injection region formation process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3C] Figure 3C is a diagram illustrating the embedding process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3D] Figure 3D is a diagram illustrating the window region formation process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3E] Figure 3E is a diagram illustrating the groove formation process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3F] Figure 3F is a diagram illustrating the insulating film formation process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3G] Figure 3G is a diagram illustrating the P-side electrode formation process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 3H]Figure 3H is a diagram illustrating the N-side electrode formation process in the manufacturing method of a semiconductor laser device according to an embodiment. [Figure 4] Figure 4 shows specific examples of the composition, film thickness, and impurity concentration of each semiconductor layer in three embodiments, Example 1, Example 2, and Example 3, of the semiconductor laser apparatus according to the embodiment. [Figure 5A] Figure 5A shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device of Example 1. [Figure 5B] Figure 5B shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device of Example 2. [Figure 5C] Figure 5C shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device of Example 3. [Figure 5D] Figure 5D shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser apparatus of Example 4. [Figure 5E] Figure 5E shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser device of Example 5. [Figure 6] Figure 6 is a diagram illustrating the operation and effects of a semiconductor laser device according to an embodiment. [Figure 7A] Figure 7A shows the dependence of the optical confinement rate on the length of the Al composition gradient region in a semiconductor laser device according to the embodiment. [Figure 7B] Figure 7B shows the dependence of waveguide loss on the length of the Al composition gradient region in a semiconductor laser device according to the embodiment. [Figure 8A] Figure 8A shows the dependence of the light confinement rate on the P-type impurity concentration in a semiconductor laser device according to the embodiment. [Figure 8B] Figure 8B shows the dependence of waveguide loss on the P-type impurity concentration in a semiconductor laser device according to the embodiment. [Figure 9]Figure 9 shows the relationship between the optical confinement rate and waveguide loss for the film thickness of the N-side first barrier layer and the P-side first barrier layer in a semiconductor laser device according to the embodiment. [Figure 10] Figure 10 shows the relationship between the wavelength loss and the optical confinement rate for the film thickness of the N-side second barrier layer and the P-side second barrier layer in a semiconductor laser device according to the embodiment. [Figure 11A] Figure 11A is a diagram showing the dependence of the potential barrier of the P-type guide layer of a semiconductor laser apparatus according to an embodiment on the concentration of P-type impurities. [Figure 11B] Figure 11B is a diagram showing the dependence of the electron current density on the P-type impurity concentration in the P-type guide layer of a semiconductor laser apparatus according to an embodiment. [Figure 12A] Figure 12A is a diagram showing the dependence of the potential barrier of the P-type semiconductor layer of a semiconductor laser apparatus according to the embodiment on the concentration of P-type impurities. [Figure 12B] Figure 12B is a diagram showing the dependence of the electron current density on the P-type impurity concentration in the P-type semiconductor layer of a semiconductor laser device according to an embodiment. [Figure 13A] Figure 13A shows the dependence of the potential barrier on the P-type impurity concentration for the P-type semiconductor layer of the semiconductor laser apparatus of Example 1. [Figure 13B] Figure 13B shows the dependence of the electron current density on the P-type impurity concentration in the P-type semiconductor layer of the semiconductor laser apparatus of Example 1. [Figure 14A] Figure 14A shows the dependence of the Al composition of the potential barrier for the P-type guide layer of the semiconductor laser apparatus in Example 3. [Figure 14B] Figure 14B shows the dependence of the electron current density on the Al composition of the P-type guide layer of the semiconductor laser apparatus of Example 3. [Figure 15A] Figure 15A shows the dependence of the hole current density at a position 100 nm from the N-side interface of the well layer on the concentration of N-type impurities in a semiconductor laser device according to an embodiment. [Figure 15B]Figure 15B shows the dependence of the hole current density at the N-type cladding layer substrate interface on the semiconductor laser apparatus according to the embodiment on the N-type cladding layer interface. [Figure 16A] Figure 16A shows a first example of the N-type impurity concentration distribution in the N-type semiconductor layer of a semiconductor laser device according to an embodiment. [Figure 16B] Figure 16B shows a second example of the N-type impurity concentration distribution in the N-type semiconductor layer in a semiconductor laser device according to the embodiment. [Figure 16C] Figure 16C shows a third example of the N-type impurity concentration distribution in the N-type semiconductor layer in a semiconductor laser device according to an embodiment. [Figure 16D] Figure 16D shows a fourth example of the N-type impurity concentration distribution in the N-type semiconductor layer in a semiconductor laser device according to an embodiment. [Figure 17] Figure 17 shows the dependence of the heavy hole and light hole quantum level energies on the Al composition of the well layer 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. [Figure 18] Figure 18 shows the dependence of the heavy hole and light hole quantum level energies on the Al composition of the well layer 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. [Figure 19] Figure 19 shows the dependence of the heavy hole and light hole quantum level energies on the Al composition of the well layer 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. [Figure 20] Figure 20 is a top view of a modified semiconductor laser device. [Figure 21A] Figure 21A is a cross-sectional view of a semiconductor laser apparatus according to an embodiment of the XXIA-XXIA line shown in Figure 20. [Figure 21B] Figure 21B is a cross-sectional view of a semiconductor laser apparatus according to an embodiment of the XXIB-XXIB line in Figure 20. [Figure 21C]Figure 21C is a cross-sectional view of a semiconductor laser apparatus according to an embodiment of the XXIC-XXIC line shown in Figure 20. [Figure 22] Figure 22 shows the semiconductor laser device according to the modified example when mounted on a submount with a junction down configuration. [Figure 23] Figure 23 is a cross-sectional view of a semiconductor laser device relating to another modification. [Modes for carrying out the invention]

[0013] (The circumstances that led to obtaining one aspect of this disclosure) First, before describing the embodiments of this disclosure, we will explain the circumstances that led to obtaining one aspect of this disclosure.

[0014] To increase the power output of semiconductor laser elements to the watt level, possible methods include improving the thermal saturation level, improving the COD level, and reducing thermal resistance by increasing the resonator length.

[0015] Specifically, to improve the thermal saturation level, one could increase the optical confinement coefficient in the well layer by increasing the thickness of the well layer, thereby lowering the oscillation threshold; increase the Al composition of the barrier layer made of AlGaAs to increase the conduction band offset (ΔEc), thereby raising the potential barrier and suppressing the occurrence of electron overflow; or increase the resonator length to reduce the operating carrier density.

[0016] Furthermore, to improve the COD level, it is conceivable to create a window region on the front end face, which is the laser beam emission end face, and to give the semiconductor laser element an end-face window structure. The end-face window structure can be formed by disrupting the atomic arrangement of the barrier layer and well layer at the end face through methods such as vacancy diffusion, impurity diffusion, or ion implantation.

[0017] However, if the well layer is thickened in an attempt to increase the light confinement coefficient within the well layer, it becomes more difficult to disorder the atomic arrangement of the barrier layer and the well layer, making it difficult to form a window region.

[0018] Therefore, it is conceivable that increasing the annealing temperature when forming the window region would promote the exchange of atoms between the well layer and the barrier layer, thereby disordering the atomic arrangement.

[0019] However, increasing the annealing temperature when forming the window region can cause atomic exchange to occur between the well layer and the barrier layer in the active layer in the gain region, where window region formation is not intended. As a result, the band gap energy (Eg) in the gain region increases, leading to increased leakage current in the gain region, degrading the temperature characteristics, and making vacancies on the surface of the grown layer, caused by vacancies introduced during crystal growth or dangling bonds on the surface of the grown layer, more likely to diffuse, reducing oscillation wavelength controllability and decreasing long-term reliability. Specifically, an increase in band gap energy shortens the transition wavelength of the quantum well layer in the gain region.

[0020] Furthermore, increasing the annealing temperature when forming the window region tends to lengthen the transition region formed at the boundary between the region where the window region is intended to be formed (window area) and the region where the window region is not intended to be formed (gain area). As a result, light absorption in the transition region inhibits the COD level improvement effect of the window region.

[0021] Thus, when a window region is formed on the edge of a semiconductor laser element to improve the COD level, and the well layer of the active layer is thickened to further improve the thermal saturation level, there are challenges such as deterioration of temperature characteristics, reduced long-term reliability, and inhibition of the COD level improvement effect.

[0022] This disclosure is made to solve these problems and aims to provide a semiconductor laser device and a method for manufacturing the same that can suppress the inhibition of the COD level improvement effect while suppressing the deterioration of temperature characteristics and the decrease in long-term reliability, even when the well layer is thickened in a semiconductor laser device having an end-face window structure.

[0023] Furthermore, increasing the resonator length to reduce thermal resistance makes the device more susceptible to changes in band structure due to mounting distortion when semiconductor laser elements are mounted, which can lead to a decrease in polarization ratio.

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

[0025] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, components, and their arrangement and connection configurations shown in the following embodiments are examples only and are not intended to limit this disclosure.

[0026] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, the scale and other aspects may not necessarily be consistent across all figures. In addition, the same reference numerals are used for substantially identical components in each figure, and redundant explanations are omitted or simplified.

[0027] Furthermore, in this specification, the terms "upper" and "lower" do not refer to upward (vertically upward) and downward (vertically downward) directions in absolute spatial perception, but rather are used as terms defined by the relative positional relationship based on the stacking order in a stacked configuration. Moreover, the terms "upper" and "lower" apply not only when two components are spaced apart and another component exists between them, but also when two components are placed in contact with each other.

[0028] (Embodiment) [Layer configuration of semiconductor laser devices] First, the layer configuration of the semiconductor laser device 1 according to the embodiment will be explained using Figures 1, 2A, 2B, and 2C. Figure 1 is a top view of the semiconductor laser device 1 according to the embodiment. Figure 2A is a cross-sectional view of the semiconductor laser device 1 along the line IIA-IIA in Figure 1, Figure 2B is a cross-sectional view of the semiconductor laser device 1 along the line IIB-IIB in Figure 1, and Figure 2C is a cross-sectional view of the semiconductor laser device 1 along the line IIC-IIC in Figure 1. Note that Figure 2A shows a cross-section of the gain section of the semiconductor laser device 1, and Figure 2B shows a cross-section of the end face on the front end face 1a side of the semiconductor laser device 1.

[0029] The semiconductor laser device 1 is a semiconductor laser element that emits laser light and comprises a substrate and a semiconductor stack (semiconductor stack structure) consisting of a plurality of semiconductor layers arranged above the substrate. Specifically, as shown in Figures 1 to 2C, the semiconductor laser device 1 comprises an N-type cladding layer 20 arranged above the substrate 10, an active layer 40 arranged above the N-type cladding layer 20, and a P-type cladding layer 60 arranged above the active layer 40 as semiconductor layers constituting the semiconductor stack.

[0030] The semiconductor laser apparatus 1 further comprises, as semiconductor layers constituting the semiconductor stack, an N-type guide layer 30 disposed between the N-type cladding layer 20 and the active layer 40, a P-type guide 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.

[0031] 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 that covers at least a portion of the semiconductor laminate.

[0032] The semiconductor laser device 1 according to this embodiment is a semiconductor laser element that emits laser light with a wavelength of 900 nm to 980 nm. For example, the semiconductor laminate in the semiconductor laser device 1 is composed of a III-V compound semiconductor made of AlGaInAs-based material. As an example, the semiconductor laser device 1 emits laser light in the 915 nm wavelength band. Furthermore, as 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 laminate.

[0033] The following describes in detail each component of the semiconductor laser device 1 according to this embodiment.

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

[0035] The N-type cladding layer 20 is formed on top of the substrate 10. If a buffer layer is formed on the substrate 10, the N-type cladding layer 20 is formed on top of the buffer layer. The N-type cladding layer 20 is an N-type semiconductor layer that is intentionally doped with impurities, for example, an n-type AlGaAs layer. The impurities doped into the N-type cladding layer 20 are, for example, silicon (Si).

[0036] The N-type guide layer 30 is positioned between the N-type cladding layer 20 and the N-side second barrier layer 42b of the active layer 40. Specifically, the N-type guide layer 30 is formed on top of the N-type cladding layer 20. The N-type guide layer 30 is an N-type semiconductor layer that has been intentionally doped with impurities, for example, an n-type AlGaAs layer. The impurities doped into the N-type guide layer 30 are, for example, silicon (Si).

[0037] The active layer 40 is a semiconductor layer including an emissive layer, and is 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 guide layer 30 and the P-type guide layer 50. In this embodiment, the active layer 40 is formed on the N-type guide layer 30.

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

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

[0040] The well layer 41 (well layer) is, for example, a single quantum well structure containing a single quantum well layer. The well layer 41 is, for example, an undoped GaInAs layer. Note that the well layer 41 is not limited to a single quantum well structure, but may also be a multiple quantum well structure containing multiple quantum well layers. In this embodiment, the thickness of the well layer 41 is thick, for example, 6 nm or more.

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

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

[0043] The N-side first barrier layer 42a may have an undoped region in addition to the doped region where impurities are doped. In this case, it is preferable that the N-side first barrier layer 42a has an undoped region in the region closer to the well layer 41 and a doped region on the side farther from the well layer 41. The film thickness of the undoped region of the N-side first barrier layer 42a should be 5 nm or more. Doping the N-side first barrier layer 42a near the well layer 41 reduces the series resistance of the semiconductor laser device, but free carrier loss occurs and waveguide loss increases. If the film thickness of the undoped region becomes too thick, the series resistance of the semiconductor laser device increases. Therefore, in order to suppress the increase in series resistance while suppressing the increase in free carrier loss due to impurity doping, the film thickness of the undoped region should be 5 nm or more and 40 nm or less. If the impurity doping concentration in the N-type guide layer 30 gradually increases away from the well layer 41, the increase in waveguide loss can be suppressed even if the film thickness of this undoped region is limited to a maximum of 20 nm or less.

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

[0045] The first P-side barrier layer 43a and the second P-side barrier layer 43b 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 P-side barrier layer 43a and the second P-side barrier layer 43b are located between the well layer 41 and the P-type guide layer 50.

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

[0047] The P-side first barrier layer 43a may have an undoped region in addition to the doped region where impurities are doped. In this case, it is preferable that the P-side first barrier layer 43a has an undoped region in the region closer to the well layer 41 and a doped region on the side farther from the well layer 41. The film thickness of the undoped region of the P-side first barrier layer 43a should be 5 nm or more. Doping the P-side first barrier layer 43a near the well layer 41 reduces the series resistance of the semiconductor laser device, but free carrier loss occurs and waveguide loss increases. If the film thickness of the undoped region becomes too thick, the series resistance of the semiconductor laser device increases. Therefore, in order to suppress the increase in series resistance while suppressing the increase in free carrier loss due to impurity doping, the film thickness of the undoped region should be 5 nm or more and 40 nm or less. If the impurity doping concentration in the P-type guide layer gradually increases away from the well layer 41, the increase in waveguide loss can be suppressed even if the film thickness of this undoped region is limited to 20 nm or less.

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

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

[0050] The P-type cladding layer 60 is formed on the P-type guide layer 50. The P-type cladding layer 60 is a P-type semiconductor layer that is intentionally doped with impurities, for example, a P-type AlGaAs layer. Carbon (C) is used as the impurity for doping. For example, carbon (C) is used as the impurity for doping the P-type cladding layer 60.

[0051] The P-type contact layer 70 is formed on top of 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 has been intentionally doped with impurities, for example, a P-type GaAs layer.

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

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

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

[0055] In this way, by providing an N-type current-blocking layer 80 inside the P-type contact layer 70, the current-blocking layer 80 confines the current, and the heat generated in the first contact layer 71, which becomes the current injection region, forms an effective refractive index step in the horizontal direction of the active layer 40. This enables optical confinement in the horizontal direction.

[0056] The P-side electrode 91 is positioned on the P-type cladding layer 60 side 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 contains, for example, at least one of the following metals: Pt, Ti, Cr, Ni, Mo, and Au.

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

[0058] Furthermore, as shown in Figure 2A, the gain section of the semiconductor laser device 1 has three layers: a first P electrode layer 91a, a plating layer 91b, and a second P electrode layer 91c. However, as shown in Figure 2B, the end face of the semiconductor laser device 1 does not have a plating layer 91b, and only two layers exist: the first P electrode layer 91a and the second P electrode layer 91c.

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

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

[0061] In this embodiment, a pair of sides of the semiconductor laminate are inclined surfaces, and the insulating film 100 covers at least these inclined surfaces. Furthermore, the inclined surfaces of the semiconductor laminate are formed on at least the sides of the active layer 40. The inclination of the sides of the active layer 40 reduces the likelihood of stray light traveling from the center of the active layer 40 in the width direction to the sides and then returning to the center. Therefore, competition between the laser light oscillating in the active layer 40 and stray light can be suppressed, thereby stabilizing the laser driving operation.

[0062] Furthermore, the insulating film 100 has an opening 100a. The opening 100a of the insulating film 100 extends linearly along the resonator length direction of the semiconductor laser device 1. The opening 100a of the insulating film 100 is present in the gain portion of the semiconductor laser device 1, but not at the end face portion of the semiconductor laser device 1. Therefore, as shown in Figure 2A, in the gain portion of the semiconductor laser device 1, the insulating film 100 only covers the edges of the P-type contact layer 70. On the other hand, as shown in Figure 2B, since the opening 100a of the insulating film 100 is not formed at the end face portion of the semiconductor laser device 1, the insulating film 100 covers the entire P-type contact layer 70.

[0063] As shown in Figures 1 and 2C, the semiconductor laser device 1 has a front end surface 1a (light emission end surface), which is the front end surface from which the laser light is emitted, and a rear end surface 1b, which is the rear end surface opposite to the front end surface 1a.

[0064] The semiconductor laminate of the semiconductor laser device 1 includes an optical waveguide with a front end surface 1a and a rear end surface 1b serving as resonator reflection mirrors. Therefore, the front end surface 1a and the rear end surface 1b become the resonator end surfaces, and the resonator length of the semiconductor laser device 1 is the distance between the front end surface 1a and the rear end surface 1b. In this embodiment, the resonator length of the semiconductor laser device 1 is long, at least 2 mm, and may be 4 mm or longer. However, the resonator length of the semiconductor laser device 1 may also be less than 2 mm.

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

[0066] Furthermore, in the semiconductor laser device 1, a first end-face coating film 111 is formed on the front end surface 1a of the semiconductor laminate, and a second end-face coating film 112 is formed on the rear end surface 1b of the semiconductor laminate. 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%.

[0067] The reflectivity of the first end-face coating film 111 and the second end-face coating film 112 is not limited to these values. For example, when the semiconductor laser device 1 is used in a semiconductor laser module configured with an external resonator, the reflectivity of the first end-face coating film 111 may be 0.2% or less. This helps to suppress problems such as kink generation caused by competition between the laser oscillation mode in the semiconductor laser device 1 and the laser oscillation mode in the external resonator.

[0068] Furthermore, in this embodiment, the semiconductor laminate in the semiconductor laser device 1 has end-face window structures at both ends in the resonator length direction. Specifically, in the current-non-injection region near both end faces of the optical waveguide in the active layer 40, a window region 120 is formed in a region of a predetermined length from the front end face 1a. The window region 120 is formed on the end face portion on the front end face 1a side of the semiconductor laminate. A similar window region may also be formed on the end face portion on the rear end face 1b side of the semiconductor laminate. The window region on the rear end face 1b side is not necessarily required.

[0069] Here, let Eg1 be the peak photoluminescence energy of the region in the active layer 40 where the window region 120 is not formed, and Eg2 be the peak photoluminescence energy of the region in the active layer 40 where the window region 120 is formed. If ΔEg is the difference between Eg1 and Eg2, then the window region 120 is formed such that, for example, ΔEg = Eg2 - Eg1 = 100 meV. In other words, the band gap of the active layer 40 in the regions near the front end surface 1a and the rear end surface 1b is made larger than the band gap of the active layer 40 in regions other than those near the front end surface 1a and the rear end surface 1b. Specifically, the band gap energy of the well layer 41 near the front end surface 1a and the rear end surface 1b is larger than the band gap energy of the well layer 41 in the central part in the direction of the resonator length.

[0070] Furthermore, while there are generally two methods for forming the window region 120, the impurity diffusion method and the vacancy diffusion method, in this embodiment, the window is formed by the vacancy diffusion method. This is because, in ultra-high-power semiconductor laser devices exceeding 10W per emitter, reducing light absorption by reducing losses is crucial. In other words, if the window region is formed by the impurity diffusion method, the impurities increase light absorption, making it difficult to reduce light absorption loss. However, since the vacancy diffusion method is impurity-free, forming the window region using the vacancy diffusion method eliminates light absorption loss caused by the introduction of impurities. By forming the window region using the vacancy diffusion method, the window region 120 is formed on the front end surface 1a side as an end-face window structure. A similar window region is also formed on the rear end surface 1b side.

[0071] Furthermore, the vacancy diffusion method can form a window region by applying rapid high-temperature treatment. For example, by forming a protective film that generates Ga vacancies during high-temperature treatment on the semiconductor layer of the region where the window region is to be formed, and then exposing it to extremely high temperatures of 800°C to 950°C near the crystal growth temperature to diffuse the Ga vacancies, the quantum well structure of the active layer 40 can be disordered and windowed (made transparent) through interdiffusion between the vacancies and group III elements. As a result, the band gap of the active layer 40 can be increased, and the region with the disordered quantum well structure can function as a window region. In addition, in regions other than the window region, the disordering of the quantum well structure can be suppressed by forming a protective film that suppresses the generation of Ga vacancies during high-temperature treatment.

[0072] Thus, by having an end-face window structure in the semiconductor laser device 1, the end face of the resonator of the semiconductor laser device 1 can be made transparent, reducing light absorption near the front end face 1a. This suppresses the generation of COD at the front end face 1a.

[0073] [Manufacturing method for semiconductor laser devices] Next, the manufacturing method of the semiconductor laser apparatus 1 according to the embodiment will be explained using Figures 3A to 3H. Figures 3A to 3H are diagrams illustrating each step in the manufacturing method of the semiconductor laser apparatus 1 according to the embodiment. In Figures 3B to 3H, the upper figure shows a cross-section of the part corresponding to the current injection region, which is the region where current is injected, and the lower figure shows a cross-section of the part corresponding to the non-current injection region, which is the region where current is not injected.

[0074] As shown in Figure 3A, first, a substrate 10 is prepared, and multiple semiconductor layers are stacked on the substrate 10. The process of stacking multiple semiconductor layers includes at least the steps of 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.

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

[0076] The active layer 40 is constructed by sequentially growing crystals on the N-type guide layer 30, consisting of an N-side second barrier layer 42b, an N-side first barrier layer 42a, a well layer 41, a P-side first barrier layer 43a, and a P-side second barrier layer 43b.

[0077] Next, as shown in Figure 3B, an opening 80a is formed in the current blocking layer 80 to define the current injection region. Specifically, a mask made of SiO2 or the like is formed on the first contact layer 71 in a predetermined pattern using photolithography, and then the current blocking layer 80 is etched using wet etching until the first contact layer 71 is exposed, thereby forming an opening 80a in the portion of the current blocking layer 80 corresponding to the current injection region. On the other hand, in the non-current injection region at the end face of the semiconductor laser device 1, no opening 80a is formed in the current blocking layer 80. A sulfuric acid-based etching solution is preferably used to etch the current blocking layer 80. For example, an etching solution with sulfuric acid:hydrogen peroxide:water = 1:1:40 can be used.

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

[0079] Next, as shown in Figure 3D, a window region 120 is formed in the portion of the semiconductor stack of multiple semiconductor layers that corresponds to the end face in the resonator length direction. Specifically, the window region 120 is formed in the portion of the semiconductor stack that corresponds to the end face on the front end face 1a side. In this embodiment, the window region 120 is formed in the P-type contact layer 70, P-type cladding layer 60, P-type guide layer 50, active layer 40, N-type guide layer 30, N-type cladding layer 20, and a portion of the substrate 10 that corresponds to the vicinity of the front end face 1a. Note that the window region 120 was formed by pore diffusion, but is not limited to this method.

[0080] Next, as shown in Figure 3E, grooves 130 having an inclined surface are formed on the side surface of the semiconductor laminate. Specifically, a mask made of SiO2 or the like is formed in a predetermined pattern on the P-type contact layer 70 using photolithography technology, and then, by etching from the P-type contact layer 70 to partway up the N-type cladding layer 20 using wet etching technology, inclined grooves 130 can be formed on the side surface of the semiconductor laminate. The grooves 130 are separation grooves when the semiconductor laser device 1 is separated into individual parts, and in a top view, they extend in the direction of the resonator length.

[0081] Furthermore, when forming the groove 130, an etching solution such as a sulfuric acid-based etching solution can be used. In this case, an etching solution with a ratio of sulfuric acid:hydrogen peroxide:water = 1:1:10 can be used. In addition, the etching solution is not limited to a sulfuric acid-based etching solution; an organic acid-based etching solution or an ammonia-based etching solution may also be used.

[0082] Furthermore, the grooves 130 are formed by isotropic wet etching. This allows for the formation of inclined surfaces on the sides of multiple semiconductor layers, thereby creating a constricted structure (i.e., an overhang structure) in the multiple semiconductor layers. The inclination angle of the sides of the grooves 130 changes depending on the composition ratio of the Al composition of the AlGaAs material in each of the multiple semiconductor layers. In this case, increasing the Al composition of the AlGaAs material can increase the etching rate. Therefore, in order to form sides with inclinations as shown in Figure 3E in multiple semiconductor layers, the etching rate in the lateral direction (horizontal direction) can be made fastest in the multiple semiconductor layers by making the composition ratio of the Al composition of the P-type cladding layer 60 the highest. This allows for the formation of the narrowest part (the narrowest part in the horizontal direction) of the multiple semiconductor layers near the P-type cladding layer 60.

[0083] Next, as shown in Figure 3F, after removing the mask used to form the groove 130 with a hydrofluoric acid-based etching solution, a SiN film is deposited as an insulating film 100 over the entire surface of the substrate 10. Subsequently, an opening 100a is formed by removing the insulating film 100 in the areas corresponding to the current injection regions using photolithography and etching techniques. Note that the insulating film 100 in the areas corresponding to the non-current injection regions is not removed, and no opening 100a is formed in the areas corresponding to the non-current injection regions.

[0084] For etching the insulating film 100, wet etching using a hydrofluoric acid-based etching solution or dry etching by reactive ion etching (RIE) can be used. Furthermore, although the insulating film 100 is described as a SiN film, it is not limited to this and may be an SiO2 film or the like.

[0085] Next, as shown in Figure 3G, the P-side electrode 91 is formed on the semiconductor laminate. 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.

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

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

[0088] Subsequently, although not shown in the diagram, the substrate 10 on which the semiconductor laminate is formed is separated into bar shapes by dicing or cleaving using a blade, and then chip separation is performed by cutting along the grooves 130. This makes it possible to produce individual semiconductor laser devices 1.

[0089] [Composition and band structure of semiconductor layers] Next, a specific example of the semiconductor laser apparatus 1 according to this embodiment will be described.

[0090] Figure 4 shows specific examples of the composition, film thickness, and impurity concentration of each semiconductor layer in three examples, Example 1, Example 2, and Example 3, for the semiconductor laser apparatus 1 according to the above embodiment.

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

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

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

[0094] Furthermore, in the semiconductor laser apparatus 1 of this embodiment, the Al composition changes in the interface region between the N-type cladding layer 20 and the N-type guide layer 30, and in the interface region between the P-type guide layer 50 and the P-type cladding layer 60. Specifically, the Al composition in at least the interface region between the N-type cladding layer 20 and the N-type guide layer 30 gradually increases as it moves away from the well layer 41. Similarly, the Al composition in at least the interface region between the P-type guide layer 50 and the P-type cladding layer 60 gradually increases as it moves away from the well layer 41.

[0095] Next, the impurity concentration profiles and band structures of the semiconductor laminates in the semiconductor laser apparatus 1 of Examples 1 to 3 shown in Figure 4 will be explained using Figures 5A to 5C.

[0096] Figure 5A shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser apparatus 1 of Example 1.

[0097] Figure 5B shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser apparatus 1 of Example 2.

[0098] Figure 5C shows the impurity concentration profile and band structure of the semiconductor laminate in the semiconductor laser apparatus 1 of Example 3.

[0099] Note that in Figures 5A to 5C, D NB1 This indicates the length of the undoped region in the N-side first barrier layer 42a, and D PB1 This indicates the length of the undoped region in the P-side first barrier layer 43a.

[0100] As shown in Figures 5A to 5C, in the semiconductor laser apparatus 1 of this embodiment, in all of Examples 1 to 3, the concentration of impurities doped into the N-type cladding layer 20, N-type guide layer 30, N-side second barrier layer 42b, and N-side first barrier layer 42a increases in a stepwise manner as you move away from the well layer 41. In other words, as you move away from the well layer 41, the concentration of impurities increases in a stepwise manner in the order of N-side first barrier layer 42a, N-side second barrier layer 42b, N-type guide layer 30, and N-type cladding layer 20. Furthermore, in this embodiment, the impurity concentration is constant in each of the N-side first barrier layer 42a, N-side second barrier layer 42b, N-type guide layer 30, and N-type cladding layer 20.

[0101] Furthermore, the concentrations of impurities doped into the N-type cladding layer 20, the N-type guide layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a may not be stepwise, but rather gradually increase (i.e., increase in a gradient) as they move away from the well layer 41.

[0102] On the other hand, the impurity concentration doped in the interface region between the P-type cladding layer 60 and the P-type guide layer 50 is 2 × 10⁻⁶. 18 cm -3 The concentration of impurities in the P-type cladding layer 60 is kept constant. The impurity concentration of the P-type cladding layer 60 may be increased stepwise or continuously as it moves away from the well layer 41. In the region of the P-type cladding layer 60 far from the well layer 41, the optical distribution intensity in the direction perpendicular to the guided light is attenuated, so the impurity concentration may be increased to dope it. In this region, because the optical distribution intensity is small, the occurrence of free carrier absorption loss due to impurities is small, and as the resistance value decreases with increasing the impurity concentration, the series resistance of the semiconductor laser device can be reduced without increasing waveguide loss. Specifically, the P-type impurity concentration of the P-type cladding layer 60 is 2 × 10⁻⁶ times the impurity concentration on the well layer 41 side. 18 cm -3 The impurity concentration in the part furthest from the well layer 41 is set to 5 × 10⁻⁶. 18 cm -3The impurity concentration may be gradually increased so that it becomes as described above, or it may be increased in steps so that the impurity concentration increases in the direction away from the well layer 41. Here, if the Al composition of the P-type cladding layer 60 is more than twice that of the Al composition of the P-type guide layer 50, the light distribution intensity in the direction perpendicular to the substrate normal direction will attenuate rapidly from the P-type guide layer 50 toward the P-type cladding layer 60 because of the large difference in refractive index between the P-type cladding layer 60 and the P-type guide layer 50. In this case, in order to reduce the series resistance of the semiconductor laser device while suppressing the increase in waveguide loss due to the generation of free carrier loss caused by impurity doping, it is good to continuously increase the impurity concentration from the well layer 41 toward the P-type cladding layer 60. This is because in the region with high light distribution intensity, the increase in waveguide loss is suppressed because the impurity concentration is low, and in the region with low light distribution intensity, the increase in waveguide loss is suppressed while obtaining the effect of reducing the series resistance of the semiconductor laser device because the impurity concentration is high.

[0103] Furthermore, the concentrations of impurities doped into the P-type guide layer 50, the P-side second barrier layer 43b, and the P-side first barrier layer 43a gradually increase (i.e., increase in a gradient) as they move away from the well layer 41. In the structures shown in Examples 1 to 3, the P-type impurity concentration is 2 × 10⁻⁶. 17 cm -3 From 5x10 17 cm -3 The impurity concentration is continuously increased to achieve this result. Furthermore, the impurity concentration doped in the interface region between the P-type cladding layer 60 and the P-type guide layer 50 is 5 × 10 17 cm -3 From 2 x 10 18 cm -3 The doping ratio may be increased continuously. In this case, the increase in waveguide loss due to free carrier absorption loss caused by impurity doping in the interface region between the P-type cladding layer 60 and the P-type guide layer 50 can be suppressed.

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

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

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

[0107] On the other hand, the P-side second barrier layer 43b is doped with impurities throughout its entire region. In other words, the entire P-side second barrier layer 43b is intentionally doped with impurities in the thickness direction.

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

[0109] Furthermore, the band gap energy of the P-type cladding layer 60 is greater than that of the N-type cladding layer 20.

[0110] Furthermore, as described above, the semiconductor laser device 1 has an end-face window structure in which a window region 120 is formed. Specifically, the semiconductor laser device 1 has an end-face window structure in which the bandgap energy of the well layer 41 near the front end surface 1a is greater than the bandgap energy of the well layer 41 in the central part in the resonator length direction of the semiconductor laser device 1.

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

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

[0113] Furthermore, in Figures 5A and 5B, the bandgap energy of the P-type guide layer 50 was the same as that of the N-type guide layer 30, but this is not limited to this. In other words, the composition of the N-type guide layer 30 and the P-type guide layer 50 may be asymmetrical. For example, as shown in Figure 5C, if the bandgap energy of the P-type guide layer 50 is greater than that of the N-type guide layer 30, the generation of current that leaks into the P-type guide layer 50 due to the excitation of electrons injected into the well layer 41 by heat can be suppressed. Also, since the refractive index of the N-type guide layer 30 is higher than that of the P-type guide layer 50, the vertical optical distribution in the direction of the substrate normal of the waveguide can be made closer to the N-type layer. In this case, the vertical optical distribution can be precisely controlled by controlling the difference in Al composition between the N-type guide layer 30 and the P-type guide layer 50. As a result, a semiconductor laser device capable of high-temperature, high-power operation with better temperature characteristics can be reproducibly obtained while reducing waveguide losses. If the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 is too large for the P-type guide layer 50, the vertical light distribution will shift too much towards the N-type layer, reducing the optical confinement coefficient in the well layer 41 and leading to an increase in the oscillation threshold current. Therefore, the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 should be such that the Al composition of the P-type guide layer 50 is relatively larger, and the difference should be 0.05 or less.

[0114] Furthermore, if 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 becomes lower than that of the P-type guide layer 50, which allows the vertical optical distribution in the direction normal to the substrate of the waveguide to be shifted towards the P-type. As a result, a high optical confinement coefficient in the well layer 41 can be obtained, and a semiconductor laser device capable of high-temperature, high-power operation with good temperature characteristics can be obtained while reducing the oscillation threshold current. If the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 is too large for the N-type guide layer 30, the vertical optical distribution will be shifted too much towards the P-type layer, increasing waveguide losses and leading to an increase in the oscillation threshold current and a decrease in slope efficiency. For this reason, the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 should be such that the Al composition of the N-type guide layer 30 is relatively large, and the difference should be 0.04 or less.

[0115] Furthermore, in Figures 5A and 5B, the maximum bandgap energy of the P-side second barrier layer 43b was the same as the maximum bandgap energy of the N-side second barrier layer 42b, but this is not limited to this. For example, the maximum bandgap energy of the P-side second barrier layer 43b may be greater than the maximum bandgap energy of the N-side second barrier layer 42b. This suppresses the generation of current that leaks into the P-type guide layer 50 due to the thermal excitation of electrons injected into the well layer 41. Also, since the refractive index of the N-type guide layer 30 is higher than that of the P-type guide layer 50, the vertical optical distribution in the direction of the substrate normal of the waveguide can be made closer to the N-type layer. In this case, the vertical optical distribution can be precisely controlled by controlling the Al composition of the N-side second barrier layer 42b, the N-type guide layer 30, the P-side second barrier layer 43b, and the P-type guide layer 50. As a result, a semiconductor laser device capable of high-temperature, high-power operation with superior temperature characteristics can be reproducibly obtained. If the Al composition of the P-side second barrier layer 43b becomes too large in the Al composition difference between the maximum Al composition of the P-side second barrier layer 43b and the maximum Al composition of the N-side second barrier layer 42b, the vertical light distribution will shift too much towards the N-type layer, reducing the optical confinement coefficient to the well layer 41 and leading to an increase in the oscillation threshold current. Therefore, the Al composition difference between the maximum Al composition of the P-side second barrier layer 43b and the maximum Al composition of the N-side second barrier layer 42b should be such that the maximum Al composition of the P-side second barrier layer 43b is relatively large, while the difference remains 0.05 or less.

[0116] Furthermore, the maximum bandgap energy of the P-side second barrier layer 43b may be smaller than the maximum bandgap energy of the N-side second barrier layer 42b. In this case, the bandgap energy of the P-type guide layer 50 will be smaller than the bandgap energy of the N-type guide layer 30. When the bandgap energy of the P-type guide layer 50 is smaller than that of the N-type guide layer 30, the refractive index of the N-type guide layer 30 will be lower than that of the P-type guide layer 50, thereby shifting the vertical optical distribution in the direction of the substrate normal of the waveguide towards the P-side. As a result, a high optical confinement coefficient in the well layer 41 can be obtained, and a semiconductor laser device capable of high-temperature, high-power operation with good temperature characteristics can be obtained while reducing the oscillation threshold current. If the Al composition difference between the N-type guide layer 30 and the P-type guide layer 50 is too large for the N-type guide layer 30, the vertical optical distribution will be too close to the P-type layer, increasing waveguide loss and leading to an increase in oscillation threshold current and a decrease in slope efficiency. Therefore, the difference in Al composition between the N-type guide layer 30 and the P-type guide layer 50 should be such that the Al composition of the N-type guide layer 30 is relatively larger, and the difference should be 0.04 or less. In other words, 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 should be such that the Al composition of the N-side second barrier layer 42b is relatively larger, and the difference should be 0.04 or less.

[0117] In Figure 5A, the bandgap energies of the P-type guide layer 50 and the P-side second barrier layer 43b were the same, but this is not limited to this. For example, as shown in Figure 5D, the bandgap energy of the P-type guide layer 50 may be greater than the bandgap energy of the P-side second barrier layer 43b. This configuration makes it possible to suppress the generation of electron currents that leak into the P-type guide layer 50 when electrons injected into the well layer 41 are excited by heat during high-temperature, high-power operation. As a result, a semiconductor laser device with excellent high-temperature, high-power operation capabilities can be obtained.

[0118] Furthermore, by making the bandgap energy of the P-side second barrier layer 43b greater than that of the N-side second barrier layer 42b, it becomes possible to suppress the generation of electron currents that leak into the P-type guide layer 50 when electrons injected into the well layer 41 are excited by heat during high-temperature, high-power operation. As a result, a semiconductor laser device with excellent high-temperature, high-power operation capabilities can be obtained.

[0119] Furthermore, the bandgap energies of the N-side first barrier layer 42a and the N-side second barrier layer 42b may be the same, but the bandgap energy of the N-type guide layer 30 only needs to be greater than or equal to the bandgap energy of the N-side second barrier layer 42b. With this configuration, the refractive indices of the N-side second barrier layer 42b and the N-side first barrier layer 42a become greater than or equal to the refractive index of the N-type guide layer 30, thereby increasing the optical confinement coefficient to the well layer 41. As a result, the oscillation threshold and leakage current during high-temperature, high-power operation are reduced, and a semiconductor laser device with excellent high-temperature, high-power operation capabilities can be obtained.

[0120] Furthermore, the band gap energies of the P-side first barrier layer 43a and the P-side second barrier layer 43b may be the same, but the band gap energy of the P-type guide layer 50 must be greater than or equal to the band gap energy of the P-side second barrier layer 43b. With this configuration, the refractive indices of the P-side second barrier layer 43b and the P-side first barrier layer 43a become greater than or equal to the refractive index of the P-type guide layer 50, thereby increasing the optical confinement coefficient to the well layer 41.

[0121] As a result, the oscillation threshold and leakage current during high-temperature, high-power operation are reduced, making it possible to obtain a semiconductor laser device that excels in high-temperature, high-power operation.

[0122] Figure 5E shows the impurity concentration profile and band structure of the semiconductor laminate in Example 5, a semiconductor laser device in which, in addition to the structure of the semiconductor laser device shown in Example 1, a high Al composition N-side layer 44 with a higher Al composition than the first barrier layer 42a is placed between the first barrier layer 42a and the well layer 41, and a high Al composition P-side layer 45 with a higher Al composition than the first barrier layer 43a is placed between the first barrier layer 43a and the well layer 41. Although Example 5 shown in Figure 5E includes both the high Al composition N-side layer 44 and the high Al composition P-side layer 45, it may also include only one of them.

[0123] This structure allows for greater Al composition differences 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, during thermal annealing processes or ion implantation to form windows by vacancy diffusion or impurity diffusion. This leads to greater atomic exchange between the two layers, which in turn increases the band gap in the well layer 41 of the window region, thus making it easier to increase the difference in band gap energy between the window region and the gain region. As a result, the window region 120 can be formed more easily, even with a thicker well layer 41.

[0124] If the thicknesses of the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 become too thin, the disordering effect of the quantum well structure due to the exchange of atoms with the well layer 41 decreases, and the increase effect of the window-forming thermal annealing process on the band gap energy of the well layer 41 in the window region 120 decreases. Conversely, if the thicknesses of the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 become too thick, 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, so the optical confinement coefficient to the well layer 41 decreases. Furthermore, the N-side high-Al composition layer 44 has a larger band gap energy than the N-side first barrier layer 42a, and the P-side high-Al composition layer 45 has a larger band gap energy than the P-side first barrier layer 43a. As a result, the N-side high-Al composition layer 44 inhibits electron injection into the well layer 41, and the P-side high-Al composition layer 45 inhibits hole injection into the well layer 41, thus increasing the operating voltage.

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

[0126] Furthermore, if the Al composition of the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 becomes too small, the disordering effect of the quantum well structure due to the mutual 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 decreases, and the increase effect of the window-forming thermal annealing process on the band gap energy of the well layer 41 in the window region 120 decreases. Conversely, if the Al composition becomes too large, the refractive index of the N-side high-Al composition layer 44 is lower than that of the N-side first barrier layer 42a, and the refractive index of the P-side high-Al composition layer 45 is lower than that of the P-side first barrier layer 43a, so the optical confinement coefficient to the well layer 41 decreases. Furthermore, the N-side high-Al composition layer 44 has a larger band gap energy than the N-side first barrier layer 42a, and the P-side high-Al composition layer 45 has a larger band gap energy than the P-side first barrier layer 43a. As a result, the N-side high-Al composition layer 44 inhibits electron injection into the well layer 41, and the P-side high-Al composition layer 45 inhibits hole injection into the well layer 41, thus increasing the operating voltage.

[0127] Therefore, the Al composition of the N-side high Al composition layer 44 and the P-side high Al composition layer 45 should be 0.27 or higher and 0.35 or lower, respectively.

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

[0129] Furthermore, while the structure shown in Figure 5E does not show an example where the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 are not doped with impurities, the series resistance of the semiconductor laser device can 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. Moreover, doping the N-side high-Al composition layer 44 with N-type impurities reduces the potential energy of the valence band, thereby suppressing leakage of hole current injected into the well layer 41. Similarly, doping the P-side high-Al composition layer 45 with P-type impurities increases the potential energy of the conduction band, thereby suppressing leakage of electron current injected into the well layer 41. As a result, the generation of leakage current can be suppressed when the semiconductor laser device is operated at high temperature and high power, and a semiconductor laser device with excellent temperature characteristics can be obtained. In order to achieve reduced series resistance and improved temperature characteristics of the semiconductor laser device, doping the N-side high-Al composition layer 44 with N-type impurities at a rate of 1 × 10⁻¹⁶ 17 cm -3 From 1 x 10 18 cm -3 Doping within the specified range is sufficient, and P-type impurities should be added to the P-side high-Al composition layer 45 by 1 × 10 17 cm -3 From 5x10 17 cm -3 Doping is acceptable within that range.

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

[0131] In particular, when the N-side high-Al composition layer 44 and the P-side high-Al composition layer 45 are made of AlGaInAs, the difference in valence band potential energy 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 or higher and 0.45 or lower, and the In composition to 0.05 or higher and 0.15 or lower. 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 difference in conduction band potential energy between the N-side first barrier layer 42a and the N-side high-Al composition layer 44. As a result, the injection of electrons and holes into the well layer 41 becomes easier compared to when an AlGaAs layer with the same Al composition is used, and the operating voltage is reduced. Furthermore, because the 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 becomes large, disorder of the group III atomic arrangement due to atomic exchange is more likely to occur during the window formation thermal annealing process and ion implantation process for forming the window region 120, and the difference in band gap energy between the window region and the gain region tends to increase. As a result, a semiconductor laser device with a high COD level can be obtained.

[0132] Furthermore, if the N-type guide layer 30 is an AlGaInAs layer containing In with an In composition of 0.02 or less, it becomes possible to slightly increase the refractive index of the N-type guide layer 30 while suppressing the occurrence of lattice defects in the N-type guide layer 30. This makes it easier to concentrate light on the N-type guide layer 30 in the vertical light distribution, thereby improving the controllability of the light distribution shape near the N-type layer. In this case, the N-type guide layer 30 may be formed from a superlattice of InGaAs and AlGaAs.

[0133] [Operation and Effects of Semiconductor Laser Devices] Next, the operation and effects of the semiconductor laser apparatus 1 according to this embodiment will be explained using Figure 6. Figure 6 is a diagram for explaining the operation and effects of the semiconductor laser apparatus 1 according to this embodiment. In Figure 6, the band structure before and after annealing is shown in the region where a window region is intended to be formed (window portion) and the region where a window region is not intended to be formed (gain portion) in a semiconductor laser apparatus having an end-face window structure.

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

[0135] Furthermore, in Figure 6, "Comparative Example" refers to the comparative semiconductor laser device. The comparative semiconductor laser device has an active layer in which a well layer made of InGaAs is formed between an N-side barrier layer made of AlGaAs and a P-side barrier layer also made of AlGaAs. In order to achieve higher power output, the Al composition of the barrier layers is increased to improve the thermal saturation level.

[0136] In semiconductor laser devices, a window region is formed near the end face to improve the COD level in order to increase power output. 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 or the like.

[0137] In semiconductor laser devices with an end-face window structure, increasing the well layer thickness to increase the optical confinement coefficient is conceivable in order to achieve even higher output. However, increasing the well layer thickness makes it more difficult to disorder the atomic arrangement of the barrier layer and the well layer, making it difficult to form a window region. Therefore, it is conceivable to increase the annealing temperature when forming the window region to promote the mutual exchange of atoms between the well layer and the barrier layer, thereby disordering the atomic arrangement.

[0138] In this case, as shown in Figure 6, in the window region intended to form a window area, the band gap energy (Eg) after annealing is W1 ) is the band gap energy (Eg) before annealing. W0 This allows for a larger size than ). This makes it possible to form a window region even if the well layer is thick.

[0139] However, if the annealing temperature is increased when forming the window region, atomic exchange will occur between the well layer and the barrier layer in the active layer in the gain region, where window region formation is not intended. As a result, even in the gain region, the band gap energy (Eg) after annealing will also be affected.G1 ) is the band gap energy (E) before annealing. gG0 This becomes larger than the window section. In other words, the bandgap energy increases not only in the window section but also in the gain section. As a result, leakage current in the gain section increases, degrading the temperature characteristics, and vacancies introduced during crystal growth or vacancies on the surface of the growth layer caused by dangling bonds on the surface of the growth layer become more easily diffused, reducing the controllability of the oscillation wavelength and decreasing long-term reliability.

[0140] In contrast, in the semiconductor laser device 1 of this embodiment, as described above, a P-side first barrier layer 43a and a P-side second barrier layer 43b are formed on one side of the well layer 41, and the structure is designed to change the Al composition in at least two stages. Specifically, the Al composition ratio of the P-side second barrier layer 43b is made relatively higher than that of the P-side first barrier layer 43a. In other words, the Al composition of the P-side first barrier layer 43a on the side closer to the well layer 41 is made lower, and the Al composition of the P-side second barrier layer 43b on the side further from the well layer 41 is made higher. Furthermore, in the semiconductor laser device 1 of this embodiment, the band gap energy of the P-side second barrier layer 43b is made higher than that of the P-side first barrier layer 43a.

[0141] As a result, even if the annealing temperature is increased when the well layer is thickened to form the window region, as shown in "This Embodiment" in Figure 6, the band gap energy (Eg) after annealing is maintained in the window portion intended for the formation of the window region. W1 ) the band gap energy (Eg) before annealing W0 While making it larger than ), in the gain section where the formation of a window region is not intended, the band gap energy after annealing (Eg G1 ) the band gap energy (Eg) before annealing G0 It can be made to the same extent as ).

[0142] In other words, in the gain region, the change in band gap energy before and after annealing is suppressed, thereby suppressing the increase in band gap energy, while in the window region, the band gap energy can be increased. Therefore, in the window region, the transparency of the semiconductor laminate including the active layer 40 can be promoted, while in the gain region, the transparency of the semiconductor laminate including the active layer 40 can be suppressed.

[0143] Thus, according to the semiconductor laser apparatus 1 of this embodiment, since a P-side first barrier layer 43a with a low Al composition and high refractive index is used, the optical confinement coefficient in the well layer 41 increases, and the operating carrier density decreases. Furthermore, even if the annealing temperature for forming the window region is increased in order to increase the band gap energy of the window region when the well layer is thickened, the low Al composition of the P-side first barrier layer 43a makes it less susceptible to changes in the band gap energy of the well layer 41 in the gain region due to impurity diffusion, and the wavelength change of the well layer 41 in the gain region due to the increase in band gap energy can be suppressed. As a result, a decrease in long-term reliability can be suppressed. In addition, the effect of improving the CCOD level can be suppressed, and a decrease in slope efficiency or a decrease in temperature characteristics can also be suppressed.

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

[0145] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the band gap energy of the P-type cladding layer 60 is greater than the band gap energy of the N-type cladding layer 20.

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

[0147] Furthermore, the P-type cladding layer 60 becomes more susceptible to mounting distortion when the semiconductor laser device 1 is mounted in a junction-down configuration (i.e., when the P-side electrode 91, which is farther from the substrate 10, is mounted in a submount). Moreover, the high Al composition results in large lattice misalignment distortion with the substrate 10, which amplifies the effects of mounting distortion. As a result, birefringence occurs, and the light distribution propagating through the optical waveguide spills more towards the P-type cladding layer 60 than towards the N-type cladding layer 20, causing a decrease in polarization ratio.

[0148] In this case, 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 perpendicular to the substrate becomes closer to the N-type cladding layer, and the proportion of the light distribution present in the P-type cladding layer 60 can be reduced. This also suppresses a decrease in the polarization ratio.

[0149] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the thickness of the well layer 41 is 6 nm or more.

[0150] Thus, by making the thickness of the well layer 41 6 nm or more, the optical confinement coefficient in the well layer 41 can be greatly increased, which reduces the operating carrier density and improves the thermal saturation level. Therefore, the temperature characteristics can be improved.

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

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

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

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

[0155] Therefore, in a semiconductor laser device using AlGaInAs for the well layer and barrier layer, as in this embodiment, when a window structure is formed on the front end surface from which the laser light is emitted by diffusing vacancies or impurities, the In atoms in the well layer are more likely to exchange with Al atoms and Ga atoms located at group III lattice positions relative to the stacking direction, thereby reducing the strain energy of the well layer and increasing the band gap energy (Eg) of the well layer.

[0156] As a result, the band gap energy of the well layer near the front end surface, which is the laser beam emission end surface and has a high light density, easily increases. Therefore, even if the band gap energy near the front end surface decreases due to heat generation, the well layer near the front end surface can easily maintain a state of low light absorption.

[0157] Therefore, as in the semiconductor laser apparatus 1 according to this embodiment, by constructing the well layer 41 with AlGaInAs, it is possible to suppress the occurrence of COD, in which the area near the front end surface 1a melts and breaks down due to the absorption of laser light.

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

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

[0160] This configuration allows for an increase in the average refractive index of the P-side second barrier layer 43b. This significantly increases the optical confinement coefficient in the well layer 41, thereby reducing the operating carrier density and improving the thermal saturation level. Consequently, the temperature characteristics can be improved.

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

[0162] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the P-side first barrier layer 43a includes an undoped region that is not doped with impurities, and the thickness of the undoped region is preferably 5 nm or more.

[0163] As a result, impurity doping begins partway through the first barrier layer 43a on the P side, which reduces the series resistance of the semiconductor laser device 1. Furthermore, the electron potential barrier of the first barrier layer 43a on the P side increases, which suppresses leakage electrons. This undoped region should ideally be 40 nm or less, as excessive thickness would increase the series resistance of the semiconductor laser device.

[0164] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the entire area of ​​the P-side second barrier layer 43b is doped with impurities, and the P-side first barrier layer 43a has an undoped region where impurities are not doped in the area closer to the well layer 41, and a doped region where impurities are doped in the area further away from the well layer 41.

[0165] As a result, impurity doping begins partway through the first barrier layer 43a on the P side, which reduces the series resistance of the semiconductor laser device 1. In addition, the electron potential barriers of the first barrier layer 43a and the second barrier layer 43b on the P side are increased, which also suppresses leakage electrons.

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

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

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

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

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

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

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

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

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

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

[0176] Here, the process of creating a gradient in the P-type impurity concentration of the P-side semiconductor layer will be explained using Figures 8A and 8B. Figure 8A shows the dependence of the optical confinement rate on the P-type impurity concentration in the semiconductor laser apparatus 1 according to this embodiment. Figure 8B shows the dependence of the waveguide loss on the P-type impurity concentration in the same semiconductor laser apparatus 1. Figures 8A and 8B show the simulation results of four samples in the semiconductor laser apparatus 1 according to this embodiment, when the Al composition and thickness of the P-side first barrier layer 43a and the P-side second barrier layer 43b are changed. In Figures 8A and 8B, Sample 1 uses a first P-side barrier layer 43a with an Al composition of 0.12 and a thickness of 30 nm, and a second P-side barrier layer 43b with an Al composition that increases in a gradual manner from 0.12 to 0.24 and a thickness of 15 nm. Sample 2 uses a first P-side barrier layer 43a with an Al composition of 0.12 and a thickness of 15 nm, and a second P-side barrier layer 43b with an Al composition that increases in a gradual manner from 0.12 to 0.24 and a thickness of 15 nm. In this case, Sample 3 uses a first P-side barrier layer 43a with an Al composition of 0.18 and a thickness of 30 nm, and a second P-side barrier layer 43b with an Al composition that increases in a gradual manner from 0.12 to 0.24 and a thickness of 15 nm, while Sample 4 uses a first P-side barrier layer 43a with an Al composition of 0.18 and a thickness of 15 nm, and a second P-side barrier layer 43b with an Al composition that increases in a gradual manner from 0.12 to 0.24 and a thickness of 15 nm.

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

[0178] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the active layer 40 further includes an N-side first barrier layer 42a disposed below the well layer 41 and an N-side second barrier layer 42b disposed below the N-side first barrier layer 42a. The Al composition ratio of the N-side second barrier layer 42b is higher than that of the N-side first barrier layer 42a, and the band gap energy of the N-side second barrier layer 42b is greater than that of the N-side first barrier layer 42a.

[0179] With this configuration, when the annealing temperature is increased when the well layer is thickened to form the window region, the wavelength change of the well layer 41 in the gain region due to the increase in band gap energy can be suppressed not only in the P-side region of the well layer 41 but also in the N-side region, while the band gap energy can be increased in the window region, thereby increasing the wavelength change. This further suppresses the deterioration of temperature characteristics and the decrease in long-term reliability, while further suppressing the inhibition of the COD level improvement effect.

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

[0181] This configuration allows for an increase in the average refractive index of the N-side second barrier layer 42b. This further increases the optical confinement coefficient in the well layer 41, thereby further reducing the operating carrier density and improving the thermal saturation level. Consequently, the temperature characteristics can be further improved.

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

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

[0184] As a result, impurity doping begins partway through the N-side first barrier layer 42a, which reduces the series resistance of the semiconductor laser device. In addition, the electron potential barriers of the N-side first barrier layer 42a and the N-side second barrier layer 42b are increased, which can suppress leakage electrons. Moreover, by making the interface between the N-side first barrier layer 42a and the well layer 41 an undoped region, the decrease in the gain of the well layer 41 can be suppressed.

[0185] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the band gap energy of the P-side second barrier layer 43b is greater than the band gap energy of the N-side second barrier layer 42b.

[0186] This effectively suppresses leakage electron generation while preventing an increase in operating voltage.

[0187] Furthermore, the semiconductor laser apparatus 1 according to this embodiment further includes an N-type guide layer 30 between the N-side second barrier layer 42b and the N-type cladding layer 20.

[0188] In this way, by providing the N-type guide layer 30, the optical confinement coefficient in the well layer 41 can be further increased. This further reduces the operating carrier density and improves the thermal saturation level. Therefore, the temperature characteristics can be further improved.

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

[0190] This configuration allows for a gradient increase in the band gap energy at the interface between the N-type guide layer 30 and the N-type cladding layer 20. This suppresses the generation of spikes in the valence band at the interface between the N-type guide layer 30 and the N-type cladding layer 20, improving hole conductivity and reducing the series resistance of the semiconductor laser device.

[0191] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the concentrations of impurities doped into the N-type cladding layer 20, the N-type guide layer 30, the N-side second barrier layer 42b, and the N-side first barrier layer 42a should gradually increase or increase in steps as they move away from the well layer 41.

[0192] This configuration allows for reduced series resistance and waveguide losses in the semiconductor laser device, enabling a reduction in operating voltage and achieving highly efficient laser oscillation due to high slope efficiency.

[0193] Furthermore, in the semiconductor laser apparatus 1 according to this embodiment, the active layer 40 has an N-side first barrier layer 42a disposed below the well layer 41 and an N-side second barrier layer 42b disposed below the N-side first barrier layer 42a, the Al composition ratio of the N-side second barrier layer 42b is higher than that of the N-side first barrier layer 42a, the 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 guide 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 guide layer 50 is different from that of the N-type guide layer 30.

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

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

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

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

[0198] Here, 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 explained using Figures 9 and 10. Figure 9 shows the relationship between the optical confinement rate and waveguide loss for the film thickness of the N-side first barrier layer 42a and the P-side first barrier layer 43a. Figure 10 shows the relationship between the optical confinement rate and waveguide loss for the film thickness of the N-side second barrier layer 42b and the P-side second barrier layer 43b. Figures 9 and 10 show the simulation results when the film thickness is changed in 5 nm increments in the range of 15 nm to 40 nm. Also, in Figures 9 and 10, each point is plotted with the film thickness at 15 nm as the reference point.

[0199] As shown in Figure 9, it can be seen that by making the thickness of the N-side first barrier layer 42a greater than the thickness of the P-side first barrier layer 43a, waveguide loss can be reduced and the optical confinement efficiency can be increased. In other words, 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, for the N-side first barrier layer 42a and P-side first barrier layer 43a on the side closer to the well layer 41, the thickness of the N-side first barrier layer 42a should be greater than the thickness of the P-side first barrier layer 43a.

[0200] On the other hand, as shown in Figure 10, 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, it can be seen that for the N-side second barrier layer 42b and P-side second barrier layer 43b that are farther from the well layer 41, the film thickness of the P-side second barrier layer 43b should be thicker than the film thickness of the N-side second barrier layer 42b. Specifically, it can be seen that by making the film thickness of the P-side second barrier layer 43b greater than that of the N-side second barrier layer 42b, waveguide loss can be reduced and the optical confinement efficiency can be increased.

[0201] Here, holes have lower mobility than electrons, and the activation rate of impurities is also lower. Therefore, in order to reduce the series resistance of a semiconductor laser device and to reduce the rise voltage of the PN junction, it is necessary to increase the impurity concentration doping the P-type semiconductor layer to be greater than that doping the N-type semiconductor layer, thereby increasing the hole carrier density. For this reason, the free carrier loss occurring in the light distribution propagating through the optical waveguide is more affected by the P-type semiconductor layer than by the N-type semiconductor layer, and the doping profile of P-type impurities needs to be precisely controlled.

[0202] Therefore, the inventors investigated the impurity concentration to dope the P-type semiconductor layer in the semiconductor laser apparatus 1 of this embodiment. The results of this investigation will be explained below with reference to Figures 11A to 16B. In Figures 11A to 16B, the investigation was based on the four samples, Sample 1, Sample 2, Sample 3, and Sample 4, which were explained in Figures 8A and 8B.

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

[0204] Specifically, for the P-side first barrier layer 43a and the N-side first barrier layer 42a, the Al composition was set to 0.12 and 0.18, and the thickness was set to 15 nm and 30 nm. For the P-side second barrier layer 43b and the N-side second barrier layer 42b, the Al composition was set to either a composition gradient from 0.12 to 0.24 or a composition gradient from 0.18 to 0.24, and the thickness was set to 15 nm. Furthermore, the entire region of both the P-side first barrier layer 43a and the P-side second barrier layer 43b was undoped. In addition, for the N-side first barrier layer 42a, the region 5 nm from the well layer 41 was set to an undoped region, and the region at a distance of 5 nm or more from the well layer 41 contained 1 × 10⁻¹⁴ 17 cm -3 The impurities were doped into the N-side second barrier layer 42b. 17 cm -3 The impurities were doped into the N-type guide layer 30. 17 cm -3 The impurities were doped into the N-type cladding layer 20, from the side closer to the well layer 41 to the side further away, at a rate of 1.4 × 10⁻⁶. 17 cm -3 , 2×10 17 cm -3 , 6×10 17 cm -3 , 2×10 18 cm -3 The impurity concentration was increased by doping the product with impurities in multiple stages.

[0205] In this structure, the P-type impurity concentration of the P-type guide layer 50 with a thickness of 0.2 μm is 1 × 10⁻¹⁰ 17 cm -3 From 5x10 17 cm -3 As the concentration of P-type impurities is increased, as shown in Figures 11A and 11B, the potential barrier (ΔEg) increases from 0.215 eV to 0.25 eV or higher, and the electron current flowing through the P-type guide layer 50 decreases, which has the effect of suppressing reactive current. Furthermore, increasing the concentration of P-type impurities in the P-type guide layer 50 can suppress the electron current flowing beyond the well layer 41 to the P-side semiconductor layer.

[0206] On the other hand, increasing the concentration of P-type impurities in the P-type guide layer 50 increases the potential barrier, which reduces the series resistance of the semiconductor laser device, but also increases waveguide loss, which lowers the luminous efficiency (slope efficiency).

[0207] Therefore, the concentration of P-type impurities to dope the P-type guide layer 50 is the average concentration of P-type impurities in the entire P-type guide layer 50, which is 2 × 10⁻⁶. 17 cm -3 From 4x10 17 cm -3 By controlling the parameters to fall within a certain range, waveguide losses, series resistance and leakage electron current of semiconductor laser devices can be reduced, and the potential barrier can be increased.

[0208] Furthermore, since the P-side first barrier layer 43a has a higher refractive index than the P-side second barrier layer 43b, increasing the thickness of the P-side first barrier layer 43a increases the optical confinement coefficient to the well layer 41. In particular, in optical waveguides where the light distribution is closer to the N-type semiconductor layer, the optical confinement coefficient to the well layer 41 tends to be small, so increasing the thickness of the P-side first barrier layer 43a is effective in suppressing the decrease in the optical confinement coefficient. However, the electron current flowing through the P-type guide layer 50 beyond the well layer 41 increases as the thickness of the P-side first barrier layer 43a increases. Therefore, the thickness of the P-side first barrier layer 43a should be between 10 nm and 30 nm.

[0209] Next, the impurity doping effect of the P-side first barrier layer 43a and the P-side second barrier layer 43b and the P-type guide layer 50 will be explained using Figures 12A and 12B. Figure 12A shows the dependence of the potential barrier (ΔEg) on ​​the P-type impurity concentration when the P-type guide layer 50, the P-side first barrier layer 43a, and the P-side second barrier layer 43b are doped with a constant amount of P-type impurity in the semiconductor laser apparatus 1 according to this embodiment. Figure 12B shows the dependence of the electron current density on the P-type impurity concentration at that time.

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

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

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

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

[0214] Furthermore, since the P-side first barrier layer 43a has a higher refractive index than the P-side second barrier layer 43b, increasing the thickness of the P-side first barrier layer 43a increases the optical confinement coefficient to the well layer 41. In particular, in optical waveguides where the light distribution is closer to the N-type semiconductor layer, the optical confinement coefficient to the well layer 41 tends to be small, so increasing the thickness of the P-side first barrier layer 43a is effective in suppressing the decrease in the optical confinement coefficient. However, although the electron current flowing through the P-type guide layer 50 beyond the well layer 41 increases as the thickness of the P-side first barrier layer 43a increases, the increase in leakage electron current is about 10% smaller compared to when the P-type impurity concentration is not doped into the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50. Therefore, the film thickness of the P-side first barrier layer 43a can be increased by about 10% compared to the case where the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50 are not doped with P-type impurities, and it is preferable to set the thickness to 15 nm or more and 40 nm or less.

[0215] Here, in Figures 12A and 12B, there was no gradient in the concentration of P-type impurities doped into the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50. However, when a gradient is introduced in the concentration of P-type impurities doped into the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50, the results shown in Figures 13A and 13B are obtained. Figure 13A shows the dependence of the potential barrier (ΔEg) on ​​the concentration of P-type impurities when the semiconductor laser apparatus 1 of Example 1 shown in Figure 5A is doped with impurities using the impurity doping profile. Figure 13B shows the dependence of the electron current density on the concentration of P-type impurities at that time.

[0216] Specifically, the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a was set to 0.12 and 0.18, and the thicknesses were set to 15 nm and 30 nm. In this case, for the P-side first barrier layer 43a, the 5 nm region on the well layer 41 side was set as an undoped region. On the other hand, for the N-side first barrier layer 42a, the 5 nm region on the well layer 41 side was set as an undoped region, and the region at a distance of 5 nm or more from the well layer 41 contained 1 × 10⁻¹⁴ 17cm -3 The material was doped with N-type impurities. Furthermore, for the P-side second barrier layer 43b and the N-side second barrier layer 42b, the Al composition was graded from 0.12 to 0.24 and from 0.18 to 0.24, with a thickness of 15 nm. In this case, the N-side second barrier layer 42b had 1 × 10⁻¹⁶ impurities throughout its entire region. 17 cm -3 The N-type impurities were doped into the N-type guide layer 30. 17 cm -3 The impurities were doped into the N-type cladding layer 20, from the side closer to the well layer 41 to the side further away, at a rate of 1.4 × 10⁻⁶. 17 cm -3 , 2×10 17 cm -3 , 6×10 17 cm -3 , 2×10 18 cm -3 The impurity concentration was increased by doping the product with impurities in multiple stages.

[0217] In this structure, the impurity concentration at the doping start position P1 of the P-type impurity in the P-side first barrier layer 43a is 1 × 10⁻⁶. 17 cm -3 Assuming the P-type impurity concentration at position P2 of the P-type guide layer 50 on the side away from the well layer 41 is 1 × 10⁻⁶ 17 cm -3 From 1 x 10 18 cm -3 When doping with P-type impurities to increase in a gradient, as shown in Figures 13A and 13B, if the thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a is 15 nm, the potential barrier (ΔEg) increases from 0.216 eV to 0.254 eV, and if the thickness of the P-side second barrier layer 43b and the N-side second barrier layer 42b is 30 nm, the potential barrier (ΔEg) increases from 0.215 eV to 0.234 eV.

[0218] Furthermore, increasing the P-type impurity concentration at position P2 reduces the electron current flowing through the P-type guide layer 50, thereby suppressing reactive current. Here, increasing the P-type impurity concentration at position P2 increases the potential barrier, and thus reduces the series resistance of the semiconductor laser device. Also, because the P-type impurity concentration is gradient in the P-type guide layer 50, increasing the P-type impurity concentration at position P2 suppresses an increase in waveguide loss.

[0219] Therefore, the concentration of P-type impurities to dope the P-type guide layer 50 is the average concentration of P-type impurities in the entire P-type guide layer 50, which is 2 × 10⁻⁶. 17 cm -3 From 4x10 17 cm -3 By controlling the parameters to fall within a certain range, waveguide losses, series resistance and leakage electron current of semiconductor laser devices can be reduced, and the potential barrier can be increased.

[0220] Furthermore, leakage current can be reduced by doping the P-type impurities in the P-side first barrier layer 43a, the P-side second barrier layer 43b, and the P-type guide layer 50 in such a gradient that the impurity concentration is graded.

[0221] Furthermore, since the P-side first barrier layer 43a has a higher refractive index than the P-side second barrier layer 43b, increasing the thickness of the P-side first barrier layer 43a increases the optical confinement coefficient in the well layer 41. In particular, in optical waveguides where the light distribution is closer to the N-type semiconductor layer, the optical confinement coefficient in the well layer 41 tends to be small, so increasing the thickness of the P-side first barrier layer 43a is effective in suppressing the decrease in the optical confinement coefficient. However, if the thickness of the P-side first barrier layer 43a is made too thick, optical confinement in the well layer 41 increases, making COD more likely to occur. Specifically, the thickness of the P-side first barrier layer 43a should be between 15 nm and 50 nm. As a result, in optical waveguides where the light distribution is closer to the N-type semiconductor layer, it is possible to increase optical confinement in the well layer 41 while suppressing the occurrence of COD, and to reduce the oscillation threshold current value.

[0222] Here, in Figures 13A and 13B, the Al compositions of the N-type guide layer 30 and the P-type guide layer 50 were symmetrical. However, if the Al compositions of the N-type guide layer 30 and the P-type guide layer 50 are made asymmetrical, the results shown in Figures 14A and 14B are obtained. Specifically, in Figures 14A and 14B, the Al composition of the P-type guide layer 50 is made greater than that of the N-type guide layer 30 so that the band gap energy of the P-type guide layer 50 is greater than that of the N-type guide layer 30. Figure 14A shows the dependence of the potential barrier on the Al composition of the P-type guide layer 50 of the semiconductor laser device 1 of Example 3 shown in Figure 5C. Figure 14B shows the dependence of the electron current density on the Al composition of the P-type guide layer 50 of the same semiconductor laser device 1.

[0223] Specifically, the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a was set to 0.12 and 0.18, and the thicknesses were set to 15 nm and 30 nm. In this case, for the P-side first barrier layer 43a, the 5 nm region on the well layer 41 side was set as an undoped region. On the other hand, for the N-side first barrier layer 42a, the 5 nm region on the well layer 41 side was set as an undoped region, and the region at a distance of 5 nm or more from the well layer 41 contained 1 × 10⁻¹⁴ 17 cm -3 The material was doped with N-type impurities. Furthermore, for the N-side second barrier layer 42b, the Al composition was graded from 0.12 to 0.24 and from 0.18 to 0.24, with a thickness of 15 nm. For the P-side second barrier layer 43b, the Al composition was graded from 0.12 to Xpg and from 0.18 to Xpg, with a thickness of 15 nm. In this case, the N-side second barrier layer 42b had 1 × 10⁻¹⁶ particles throughout its entire region. 17 cm -3 The material was doped with N-type impurities. Furthermore, the Al composition of the N-type guide layer 30 was set to 0.24, and the Al composition of the P-type guide layer 50 was set to Xpg. For the N-type cladding layer 20, the ratio from the side closer to the well layer 41 to the side further away was 1.4 × 10⁻⁶. 17 cm -3 , 2×10 17 cm -3 , 6×10 17cm -3 , 2×10 18 cm -3 The impurity concentration was increased by doping the product with impurities in multiple stages.

[0224] In this structure, the impurity concentration at the doping start position P1 of the P-type impurity in the P-side first barrier layer 43a is 1 × 10⁻⁶. 17 cm -3 The P-type impurity concentration at position P2 of the P-type guide layer 50, which is away from the well layer 41, is set to 5 × 10⁻⁶. 18 cm -3 P-type impurities are doped to increase the gradient.

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

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

[0227] Furthermore, it can be seen that as the Al composition of the P-type guide layer 50 increases, the electron current flowing from the well layer 41 to the P-type guide layer 50 decreases sharply. The average value of the P-type impurity concentration in the P-type guide layer 50 is 3 × 10⁻⁶. 17 cm -3The impurities are doped in such a way that the P-type impurity concentration on the side closer to the well layer 41 is small, thus reducing waveguide losses, reducing series resistance, and suppressing the increase in potential barrier.

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

[0229] Furthermore, by increasing the well layer thickness to 8 nm or more, making the Al composition of the P-type cladding layer 60 greater than that of the N-type cladding layer 20, and making the Al composition of the P-type guide layer 50 greater than that of the N-type guide layer 30, the optical confinement coefficient in the well layer 41 can be increased while shifting the optical distribution closer to the N-type semiconductor layer and reducing the leakage of the optical distribution into the P-type cladding layer 60. As a result, a semiconductor laser device with a high thermal saturation level, good temperature characteristics, and a high polarization ratio can be obtained.

[0230] Next, the effect of N-type impurity concentration on hole leakage current will be explained using Figures 15A, 15B, 16A, and 16B. Figure 15A shows the dependence of the hole current density on the N-type impurity concentration at a position 100 nm from the N-side interface of the well layer 41 in the semiconductor laser apparatus 1 according to this embodiment. Figure 15B shows the dependence of the hole current density on the N-type impurity concentration at the N-type cladding layer substrate-side interface in the semiconductor laser apparatus 1 according to this embodiment. Figure 16A shows an example of the N-type impurity concentration distribution in the N-type semiconductor layer in the semiconductor laser apparatus 1 according to this embodiment, and Figure 16B shows another example of the N-type impurity concentration distribution in the N-type semiconductor layer.

[0231] In this structure, the impurity concentration at the doping start position P1 of the P-type impurity in the P-side first barrier layer 43a is 1 × 10⁻⁶. 17 cm -3 Assuming the P-type impurity concentration at position P2 of the P-type guide layer 50 on the side away from the well layer 41 is 1 × 10⁻⁶ 17 cm -3 From 1 x 10 18 cm -3 P-type impurities are doped to increase the gradient. In addition, the P-type cladding layer 60 contains 2 × 10⁻¹⁶ impurities. 18 cm -3 It is doped with P-type impurities.

[0232] Increasing the P-type impurity concentration at position P2 reduces the electron current flowing through the P-type guide layer 50, thereby suppressing reactive current. Furthermore, increasing the P-type impurity concentration at position P2 increases the potential barrier, thus reducing the series resistance of the semiconductor laser device. Additionally, because the P-type impurity concentration is gradient in the P-type guide layer 50, increasing the P-type impurity concentration at position P2 suppresses an increase in waveguide loss.

[0233] Therefore, the concentration of P-type impurities to dope the P-type guide layer 50 is the average concentration of P-type impurities in the entire P-type guide layer 50, which is 2 × 10⁻⁶. 17 cm -3 From 4x10 17 cm -3By controlling the parameters to fall within a certain range, waveguide losses, series resistance and leakage electron current of semiconductor laser devices can be reduced, and the potential barrier can be increased.

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

[0235] Furthermore, the vertical light distribution intensity in the N-type cladding layer 20 and the rate of change in its intensity attenuation are greater the closer it is to the well layer 41. Therefore, in order to avoid an increase in waveguide loss due to an increase in impurity concentration, when increasing the impurity concentration in multiple steps in a region where the vertical light distribution is not sufficiently attenuated, it is better to make the film thickness in each constant concentration region thinner in the region closer to the well layer 41.

[0236] Based on this N-type layer impurity concentration profile, Figure 15A shows the calculated hole current density at a position 100 nm from the N-side interface of the well layer 41, and Figure 15B shows the calculated hole current density at the N-type cladding layer substrate side interface, with each concentration multiplied by 1, 1.2, 1.5, 2, and 3.

[0237] As shown in Figures 15A and 15B, it can be seen that increasing the N-type impurity concentration lowers the hole current density, reducing the hole current that leaks beyond the well layer 41 into the N-type semiconductor layer.

[0238] Furthermore, increasing the N-type impurity concentration reduces the series resistance of the semiconductor laser device, thereby reducing the operating current of the semiconductor laser device. In addition, since the optical distribution is positioned closer to the N-type semiconductor layer so that the proportion of optical distribution present is greatest in the N-type guide layer 30, waveguide loss can be reduced by making the N-type impurity concentration in the N-type guide layer 30 the lowest compared to the N-type impurities in other N-type semiconductor layers. Thus, by setting the doping profile of the N-type impurity concentration to the pattern shown in Figure 16A, it is possible to simultaneously reduce the series resistance and waveguide loss of the semiconductor laser device.

[0239] Furthermore, the doping profile of N-type impurities may be changed not only in a stepwise manner as shown in Figure 16A, but also so that the N-type impurity concentration on the substrate 10 side increases continuously, as shown by the solid line in Figure 16B. In addition, as shown by the dashed line in Figure 16B, waveguide loss can be further reduced by lowering the N-type impurity concentration at the position where the light distribution intensity is highest in the N-type guide layer 30, and then continuously or stepwise increasing the N-type impurity concentration from that position toward the substrate 10 side. Furthermore, as shown by the dashed line in Figure 16B, the N-type impurity concentration may be changed non-linearly.

[0240] Alternatively, as shown in Figure 16C, the impurity concentration doped into the N-side first barrier layer 42a may be increased, making the impurity concentration of the N-side second barrier layer 42b lower than that of the N-side first barrier layer 42a, thereby gradually increasing the N-type impurity concentration from the well layer 41 toward the substrate 10.

[0241] In this case, the impurity concentration to dope the N-side first barrier layer is 5 × 10⁻¹⁰ 17 cm -3 From 1 x 10 18 cm -3 This is sufficient. This reduces the potential of the valence band of the N-side first barrier layer 42a, making it possible to suppress hole current leakage from holes injected into the well layer 41 to the N-type layer side, thereby further improving the high-temperature, high-power operation of the semiconductor laser device. Alternatively, the N-type impurity concentration of the N-side second barrier layer 42b may be increased relative to the N-type impurity concentration of the N-type guide layer 30, similar to the impurity concentration of the N-side first barrier layer 42a, but this would result in increased waveguide loss. Therefore, even if the N-type impurity concentration in the N-side second barrier layer 42b is increased in a region within 10 nm of the interface between the N-side second barrier layer 42b and the N-side first barrier layer 42a, hole current leakage can still be suppressed.

[0242] Furthermore, by increasing the doping concentration of the N-side first barrier layer 42a, when forming a window region by vacancy diffusion or ion implantation, even if the temperature of the thermal annealing process for window formation is lowered, atomic exchange with the well layer 41 via N-type impurities becomes more likely, resulting in an effect where the band gap energy of the well layer 41 in the window region becomes larger.

[0243] Furthermore, the doping of N-type impurities into the N-type guide layer 30 may be increased stepwise from the vicinity of the interface with the N-type cladding layer 20 toward the substrate 10, as shown in Figure 16D. In an optical waveguide where the N-type light distribution is closer to the N-type semiconductor layer, the portion with the highest light intensity in the perpendicular light distribution in the direction of the substrate normal is in the region on the well layer 41 side of the N-type guide layer 30. Therefore, in the N-type guide layer 30, if the region with the lowest concentration of N-type impurities is in the region on the well layer 41 side of the N-type guide layer 30, the increase in waveguide loss can be suppressed.

[0244] In the example shown in Figures 16A to 16D, the minimum value of the N-type impurity concentration in the N-type guide layer 30 is 5 × 10⁻¹⁰ 16 cm -3 The above is 3 x 10 17 cm -3 The following conditions allow for the suppression of increased waveguide loss, suppression of hole leakage current generation, and suppression of increased series resistance of 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 small because the proportion of light distribution present in the N-type cladding layer 20 in the region of 1 μm or more from the interface between the N-type guide layer 30 and the N-type cladding layer 20 toward the substrate 10 is small. Therefore, in order to reduce the series resistance of the semiconductor laser device, the N-type impurity concentration in the N-type cladding layer 20 in the region of 1 μm or more from the interface between the N-type guide layer 30 and the N-type cladding layer 20 toward the substrate 10 should be high enough so as not to reduce mobility, for example, 1 × 10 18 cm -3 The above is 3 x 10 18 cm -3 The following would be preferable.

[0245] Furthermore, the N-type impurity concentration of the N-side first barrier layer 42a may be increased as shown in Figures 16C and 16D, while the N-type impurity concentrations of the N-side second barrier layer 42b, the N-type guide layer 30, and the N-type cladding layer 20 may be continuously varied as shown in Figure 16B. In addition, even if the region where the N-type impurity concentration is increased near the well layer 41 includes not only the N-side first barrier layer 42a but also a portion of the N-side second barrier layer 42b, as long as the film thickness of that region is 10 nm or less, it is possible to reduce the series resistance of the semiconductor laser device and further suppress hole current leakage while keeping the increase in waveguide loss to a minimum.

[0246] Next, the quantum well structure of the well layer 41 of the active layer 40 was investigated. The results of this investigation are explained below using Figures 17 to 19. Figures 17 to 19 show the dependence of the heavy hole and light hole quantum level energies on the Al composition of the well layer.

[0247] Figure 17 shows the P-side first barrier layer 43a and the N-side first barrier layer with an Al composition of 0.06. 1 Barrier layer 42 a Al 0.06 Ga 0.94 As, with a thickness of 15 nm, and the P-side second barrier layer 43b and the N-side second barrier layer 42b are made of Al 0.24 Ga 0.76 As, with a thickness of 15 nm, and the well layer 41 is made of Al X Ga 1-X-Y In YThis figure shows the calculation results of the dependence of the relative potential energy of the heavy hole (HH) and light hole (LH) levels formed in the well layer 41 on the Al composition, when the well layer thickness 41 is 6 nm, 8.5 nm, 12 nm, and 15 nm, assuming the Al composition is As. Here, the electronic level, HH level, and LH level are represented as En, HHn, and LHn, respectively. Also, n is a natural number, and the ground level is set to 1. In this calculation, the energy difference between E1 and H1 is kept constant (1.35 eV) in order to obtain the same oscillation wavelength of 915 nm. Figure 17 shows the relationship between the In composition Y and the Al composition X to obtain the same oscillation wavelength when the Al composition X of the well layer 41 is changed. Furthermore, the improper bonding between the well layer 41 with the GaAs substrate for each Al composition is shown by a dashed line.

[0248] Here, the relationship between the potential energies of electron levels and the potential energies of hole levels are inverse. In the calculation results shown in Figure 17, when comparing the potential energies between each level relatively, the level with the largest relative potential energy (i.e., located higher on the graph) is interpreted as having the lowest potential for holes.

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

[0250] Here, as the Al composition of the well layer 41 is increased, the compressive strain of the well layer 41 increases, causing the HH level to shift toward a lower potential energy for holes, and the LH level to shift toward a higher potential energy for holes. From this, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain increases the energy difference between H1 and L1, making it easier for holes to exist in H1, where the hole potential energy is smallest in HH, and conversely, making it harder for holes to exist in L1, where the hole potential energy is largeest in LH. From this, 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. Since LH contributes to the generation of TM mode light, where the polarization direction is toward the substrate normal direction in the oscillating laser light, an increase in the number of holes in LH leads to a decrease in the polarization ratio (TE / (TE+TM)). Therefore, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain can increase the polarization ratio.

[0251] Furthermore, if the well layer 41 has a thickness of 6 nm, two HH levels with a potential energy lower than that of LH are formed. As a result, holes can preferentially reside in the HH levels, and a laser beam with a high polarization ratio and a large TE mode component can be obtained.

[0252] In the case where the well layer 41 has a thickness of 8.5 nm, if the Al composition of the well layer 41 is 0.08 or higher, the hole potential energy of the LH level becomes higher than the energy of the valence band of the first barrier layer. As a result, the LH quantum level is not formed in the quantum well formed by the P-side first barrier layer 43a and N-side first barrier layer 42a and the well layer 41, and a quantum level is formed with the P-side second barrier layer 43b and N-side second barrier layer 42b as barrier layers. In this case, since the density of states of the quantum levels is inversely proportional to the thickness of the quantum well structure, the density of states of LH1 becomes even smaller, and the effect of increasing the polarization ratio increases. This state is shown by the thick dashed line L1 in each graph of Figure 17. As shown in Figure 17, when the thickness of the well layer 41 is 8.5 nm or more, LH is not formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a when the Al composition of the well layer 41 is 0.04 or more. Furthermore, it can be seen that the thicker the well layer 41, the less LH is formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a when the lattice disorder of the well layer 41 is low. In addition, it can be seen that the thicker the well layer 41, the more HH levels with lower potential energy than L1 are available, making it easier to reduce the number of holes present in L1.

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

[0254] Furthermore, if the thickness of the well layer 41 is 12 nm or more, the number of HH levels with an Al composition of 0.0 or higher and a hole potential energy lower than L1 becomes 3 levels, which reduces the number of LHs present in the LH level and is effective in increasing the polarization ratio.

[0255] Furthermore, because the well layer 41 has a high refractive index, a thicker film increases the optical confinement coefficient in the well layer 41, which reduces the threshold carrier density required for laser oscillation. This further reduces the number of holes present in L1 and increases the polarization ratio.

[0256] The P-side first barrier layer 43a and the N-side first barrier layer 42a also have a low Al composition and a higher refractive index than the P-side second barrier layer 43b, the N-side second barrier layer 42b, the N-type guide layer 30, the N-type cladding layer 20, the P-type guide layer 50, and the P-type cladding layer 60. Therefore, a thicker film thickness for the P-side first barrier layer 43a and the N-side first barrier layer 42a results in a larger optical confinement coefficient in the well layer 41, reducing the threshold carrier density required for laser oscillation. This further reduces the number of holes present in L1 and increases the polarization ratio. For example, increasing the total film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a to 20 nm or more is effective in increasing the optical confinement coefficient. However, making the total film thickness too thick will increase the optical confinement coefficient in the well layer 41 and lead to a decrease in the COD level, so the total thickness should be 80 nm or less.

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

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

[0259] Here, as the Al composition of the well layer 41 is increased, the compressive strain of the well layer 41 increases, causing the HH level to shift toward a lower potential energy for holes, and the LH level to shift toward a lower potential energy for holes. From this, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain increases the energy difference between H1 and L1, making it easier for holes to exist in H1, where the hole potential energy is smallest in HH, and conversely, making it harder for holes to exist in L1, where the hole potential energy is largeest in LH. From this, 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. Since LH contributes to the generation of TM mode light, where the polarization direction is in the direction of the substrate normal in the oscillating laser light, an increase in the number of holes in LH leads to a decrease in the polarization ratio (TE / (TE+TM)). Therefore, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain can increase the polarization ratio.

[0260] Furthermore, if the well layer 41 has a thickness of 6 nm, two HH levels with a potential energy lower than that of LH are formed. As a result, holes can preferentially reside in the HH levels, and a laser beam with a high polarization ratio and a large TE mode component can be obtained.

[0261] In the case where the well layer 41 has a thickness of 8.5 nm, if the Al composition of the well layer 41 is 0.08 or higher, the hole potential energy of the LH level becomes higher than the energy of the valence band of the first barrier layer. As a result, the LH quantum level is not formed in the quantum well formed by the P-side first barrier layer 43a and N-side first barrier layer 42a and the well layer 41, and a quantum level is formed with the P-side second barrier layer 43b and N-side second barrier layer 42b as barrier layers. In this case, since the density of states of the quantum levels is inversely proportional to the thickness of the quantum well structure, the density of states of LH1 becomes even smaller, and the effect of increasing the polarization ratio increases. This state is shown by the thick dashed lines L1 or L2 in each graph of Figure 17. As shown in Figure 18, when the thickness of the well layer 41 is 8.5 nm or more, LH is not formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a when the Al composition of the well layer 41 is 0.08 or more. Furthermore, it can be seen that the thicker the well layer 41, the less LH is formed in the P-side first barrier layer 43a and the N-side first barrier layer 42a when the lattice disorder of the well layer 41 is low. In addition, it can be seen that the thicker the well layer 41, the more HH levels with lower potential energy of holes than L1 are available, making it easier to reduce the number of holes present in L1.

[0262] As shown in Figure 18, when the thickness of the well layer 41 is 8.5 nm or more, the Al composition of the well layer 41 is 0.02 or more, and the number of HH levels with a hole potential energy lower than L1 becomes 3 levels. This reduces the number of LH levels present in the LH level, which is effective in increasing the polarization ratio.

[0263] Furthermore, if the thickness of the well layer 41 is increased to 12 nm or more, the Al composition of the well layer 41 will be 0.0 or higher, and the number of HH levels with lower hole potential energy than L1 will be 3. This reduces the number of LHs present in the LH level, which is effective in increasing the polarization ratio.

[0264] Furthermore, because the well layer 41 has a high refractive index, a thicker film increases the optical confinement coefficient in the well layer 41, which reduces the threshold carrier density required for laser oscillation. This further reduces the number of holes present in L1 and increases the polarization ratio.

[0265] The P-side first barrier layer 43a and the N-side first barrier layer 42a also have a low Al composition and a higher refractive index than the P-side second barrier layer 43b, the N-side second barrier layer 42b, the N-type guide layer 30, the N-type cladding layer 20, the P-type guide layer 50, and the P-type cladding layer 60. Therefore, a thicker film thickness for the P-side first barrier layer 43a and the N-side first barrier layer 42a results in a larger optical confinement coefficient in the well layer 41, reducing the threshold carrier density required for laser oscillation. This further reduces the number of holes present in L1 and increases the polarization ratio. For example, increasing the total film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a to 25 nm or more is effective in increasing the optical confinement coefficient. However, making the total film thickness too thick will increase the optical confinement coefficient in the well layer 41 and lead to a decrease in the COD level, so the total film thickness should be 90 nm or less.

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

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

[0268] Here, as the Al composition of the well layer 41 is increased, the compressive strain of the well layer 41 increases, causing the HH level to shift toward a lower potential energy for holes, and the LH level to shift toward a lower potential energy for holes. From this, as described above, the larger the Al composition of the well layer 41 and the higher the compressive strain, the larger the energy difference between H1 and L1 becomes, making it easier for holes to exist in H1, where the hole potential energy is smallest in HH, and conversely, making it harder for holes to exist in L1, where the hole potential energy is largeest in LH. From this, it can be seen that increasing the Al composition of the well layer 41 and increasing the compressive strain results in a larger number of holes in HH and a smaller number of holes in LH. Since LH contributes to the generation of TM mode light, where the polarization direction is in the direction of the substrate normal in the oscillating laser light, a large 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 increase the polarization ratio.

[0269] Furthermore, if the well layer 41 has a thickness of 6 nm, two HH levels with a potential energy lower than that of LH are formed. As a result, holes can preferentially reside in the HH levels, and a laser beam with a high polarization ratio and a large TE mode component can be obtained.

[0270] As shown in Figure 19, when the thickness of the well layer 41 is 8.5 nm or more, the Al composition of the well layer 41 is 0.02 or more, and the number of HH levels with a hole potential energy lower than L1 becomes 3 levels. This reduces the number of LHs present in the LH level, which is effective in increasing the polarization ratio.

[0271] Furthermore, if the thickness of the well layer 41 is 12 nm or more, the Al composition of the well layer 41 is 0.0 or higher, and the number of HH levels with a hole potential energy lower than L1 becomes 3 levels. This reduces the number of LHs present in the LH level, which is effective in increasing the polarization ratio.

[0272] Furthermore, because the well layer 41 has a high refractive index, a thicker film increases the optical confinement coefficient in the well layer 41, which reduces the threshold carrier density required for laser oscillation. This further reduces the number of holes present in L1 and increases the polarization ratio.

[0273] The P-side first barrier layer 43a and the N-side first barrier layer 42a also have a low Al composition and a higher refractive index than the P-side second barrier layer 43b, the N-side second barrier layer 42b, the N-type guide layer 30, the N-type cladding layer 20, the P-type guide layer 50, and the P-type cladding layer 60. Therefore, a thicker film thickness for the P-side first barrier layer 43a and the N-side first barrier layer 42a results in a larger optical confinement coefficient in the well layer 41, reducing the threshold carrier density required for laser oscillation. This further reduces the number of holes present in L1 and increases the polarization ratio. For example, increasing the total film thickness of the P-side first barrier layer 43a and the N-side first barrier layer 42a to 30 nm or more is effective in increasing the optical confinement coefficient. However, making the total film thickness too thick will increase the optical confinement coefficient in the well layer 41 and lead to a decrease in the COD level, so the total thickness should be 100 nm or less.

[0274] As explained above in Figures 17 to 19, by setting the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a from 0.06 to 0.18, and the thickness of the well layer 41 from 6 nm to 15 nm, two or more HH levels with a potential energy lower than the potential energy of LH are formed. As a result, holes can preferentially exist in the HH levels, and laser light with a high polarization ratio and a large TE mode component can be obtained.

[0275] Furthermore, by setting the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a to 0.06 to 0.18, and the thickness of the well layer 41 to 8.5 nm to 15 nm, it is possible to increase the number of HH levels having a potential energy lower than the hole potential energy of LH over a wider Al composition range of the well layer than when the thickness of the well layer 41 is 6 nm.

[0276] Furthermore, when the thickness of the well layer 41 is 8.5 nm, using InGaAs with an Al composition of 0.02 or higher for the well layer 41, and when the thickness of the well layer 41 is 12 nm, using InGaAs with an Al composition of 0 for the well layer 41, it is possible to have 3 or more HH levels with a potential energy lower than the hole potential energy, thereby reducing the number of LHs present in L1 and achieving the effect of increasing the polarization ratio.

[0277] Furthermore, if the thickness of the well layer 41 exceeds 15 nm, the optical confinement coefficient in the well layer 41 increases, which may reduce the COD level. Also, when forming a window region near the end face of the resonator, if the well layer 41 becomes too thick, the shortening of the band gap in the window region due to 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 becomes smaller, reducing the COD generation suppression effect. Moreover, if the thickness of the well layer 41 becomes too thin, the band gap of the well layer 41 in the gain region where the window region 120 is not formed is more likely to shorten during the high-temperature annealing process when forming the window, which degrades the temperature characteristics of the semiconductor laser device. For this reason, the thickness of the well layer 41 should be between 6 nm and 15 nm.

[0278] Furthermore, in Figures 17 to 19, the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a, which are made of AlGaAs, is set to 0.06 to 0.18. However, if the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a is made too high, the optical confinement coefficient in the well layer 41 decreases, which degrades the temperature characteristics of the semiconductor laser device. For this reason, the Al composition of the P-side first barrier layer 43a and the N-side first barrier layer 42a should be between 0.06 and 0.22.

[0279] Furthermore, increasing the Al composition of the N-side second barrier layer 42b and the P-side second barrier layer 43b, which are made of AlGaAs, can suppress electron current leakage from the well layer 41 to the P-type layer and hole current leakage from the well layer 41 to the N-type layer; therefore, an Al composition of 0.24 or higher is preferable. However, increasing the Al composition of the N-side second barrier layer 42b and the P-side second barrier layer 43b too much will lead to an increase in the operating voltage; therefore, an Al composition of 0.32 or lower is preferable.

[0280] Furthermore, the semiconductor laser device 1 according to this embodiment has a longer resonator length. Specifically, the resonator length of the semiconductor laser device 1 is 2 mm or more.

[0281] In this way, by increasing the resonator length of the semiconductor laser device 1, the thermal resistance of the semiconductor laser device 1 is reduced, and the heat dissipation is improved. This makes it possible to increase the optical output at which heat saturation occurs.

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

[0283] (modified version) The semiconductor laser apparatus and its manufacturing method described above have been explained based on embodiments, but this disclosure is not limited to the above embodiments.

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

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

[0286] 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 that has a current-blocking function. The insulating film 100A is composed of an insulating film such as SiO2.

[0287] Furthermore, in this modified example, a pair of grooves with a depth of 0.2 μm are formed in the P-type contact layer 70 to form the ridge portion 200A, 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 with an insulating film 100A. This allows the incoming current to be concentrated and flow through the ridge portion 200A. Note that the grooves for forming the ridge portion 200A may be formed not only in the P-type contact layer 70 but also in the P-type cladding layer 60.

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

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

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

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

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

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

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

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

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

[0297] 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 on a submount or the like. This point will be explained below.

[0298] Increasing the resonator length of the semiconductor laser device 1A increases the influence of shear strain generated at the widthwise ends of the semiconductor laser device 1 when it is mounted on a submount on the optical waveguide. In this case, if asymmetrical shear stress occurs in the current injection region that forms the optical waveguide, the polarization plane of the laser light propagating through the optical waveguide will tilt, resulting in elliptical polarization and a decrease in the polarization ratio.

[0299] Therefore, by providing a ridge portion 200A, as in the semiconductor laser device 1A according to this modified example, and making the optical waveguide a ridge type, when the semiconductor laser device 1A is mounted in a junction-down configuration, the shear stress generated in the ridge portion 200A and the shear stress generated at the widthwise ends of the semiconductor laser device cancel each other out, thereby reducing the shear stress generated in the optical waveguide. This makes it possible to suppress the tilting of the polarization plane of the laser light propagating through the optical waveguide and the resulting decrease in polarization ratio.

[0300] This will be explained in more detail using Figure 22. Figure 22 shows the semiconductor laser device 1A according to this modified example mounted on submount 2 in a junction-down configuration.

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

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

[0303] Here, if the average thermal expansion coefficient of submount 2 (for example, if the submount is composed of multiple layers of material, then ΣL(i)T(i) / ΣL(i) where L(i) is the thermal expansion coefficient of each material and Ti(i) is the film thickness) is greater than the average thermal expansion coefficient of semiconductor laser device 1A, then submount 2 will cause stress on semiconductor laser device 1A, causing it to shrink horizontally (in the X direction in Figure 22). Also, since the thermal expansion coefficient of the metal embedded in the grooves on both sides of the ridge portion 200A is greater than that of semiconductor laser device 1A, stress will be generated on semiconductor laser device 1A, causing the groove width to widen. As a result, in the XY plane of semiconductor laser device 1A, antisymmetric shear stress is generated with respect to the center of the current injection region between the grooves, as shown in Figure 22.

[0304] Specifically, in the active layer where the groove formed laterally to the ridge portion 200A is located at the same position in the X direction, the shear stress (σ1L) generated at the left end of the semiconductor laser device 1A in the width direction and the shear stress (σ2L) generated in the groove on the left side of the ridge portion 200A, and the shear stress (σ1R) generated at the right end of the semiconductor laser device 1A in the width direction and the shear stress (σ2R) generated in the groove on the right side of the ridge portion 200A, are in opposite directions. As a result, the shear stresses cancel each other out, and their magnitudes are reduced.

[0305] Furthermore, since the light distribution of light propagating through the optical waveguide extends horizontally to the groove region, the effect of shear stress on the light distribution at its edges is canceled out and reduced by the shear stress of the groove.

[0306] Furthermore, if the shear stresses on the left and right sides of the ridge section 200A are not perfectly antisymmetric with respect to the center in the width direction, then when birefringence occurs in the semiconductor laser device 1A due to the shear stress, the correlation integral between the light distribution and the shear stress will no longer be zero, causing the polarization plane to tilt.

[0307] Thus, according to the semiconductor laser device 1A of this modified example, when mounted on the submount 2, the shear stress generated at the widthwise end of the semiconductor laser device 1A can be canceled out by the shear stress caused by the lateral grooves of the ridge portion, thereby reducing the effect of shear stress on the light distribution. This makes it possible to suppress the tilting of the polarization plane of the laser light propagating through the optical waveguide and the resulting decrease in polarization ratio.

[0308] To reduce the influence of shear stress generated at the widthwise edges of the ridge-type semiconductor laser device 1A on the laser light propagating through the optical waveguide, it is effective to set the Al composition of the P-type cladding layer 60 to 0.8 or higher, as this reduces the leakage of the light distribution into the P-type cladding layer 60. Increasing the Al composition to 0.9 or higher may increase lattice misalignment with the GaAs substrate, potentially leading to a decrease in crystallinity due to the generation of lattice defects. Therefore, the Al composition should be between 0.8 and 0.9.

[0309] Furthermore, the width of the groove formed next to the ridge portion 200A should be 10 μm or more. This reduces the shear stress outside the ridge portion 200A. Specifically, if the groove width is too wide, the load during mounting will be concentrated on the ridge portion 200A, which is the current injection region, so the groove width should be 25 μm ± 15 μm. By using a groove of this width, the rotation of the polarization plane due to shear stress can be effectively suppressed.

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

[0311] Furthermore, even when the semiconductor laser device 1 in the above embodiment is mounted on a submount, the semiconductor laser device 1 may be mounted using either a junction-down or junction-up method.

[0312] (Other variations) For example, in the semiconductor laser apparatus 1 of the above embodiment, an example was given in which an AlGaInAs-based semiconductor material is used, but the invention is not limited to this, and other semiconductor materials may also be used.

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

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

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

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

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

[0318] The P-type contact layer 70 is made of GaAs (film thickness: 0.4 μm, C impurity concentration: 2 × 10⁻⁶). 18 cm -3 )

[0319] The semiconductor laser device according to this modified configuration also exhibits the same effects as the first embodiment described above. For example, even if the well layer 41 is thickened, it is possible to suppress the deterioration of temperature characteristics and the decrease in long-term reliability while preventing the improvement of the COD level from being hindered.

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

[0321] Firstly, since the semiconductor laser device according to this modification is composed of an AlGaInP-based semiconductor material with a higher bandgap energy than AlGaAs-based semiconductor materials, a high potential barrier can be obtained. As a result, carriers leaking beyond the active layer 40 into the P-type guide layer 50 can be suppressed, thereby improving slope efficiency and enabling the creation of a semiconductor laser device that can be driven at high temperatures and high power.

[0322] Secondly, since impurities (Zn) diffuse more easily, the impurity concentration required for window formation can be reduced. This reduces free carrier losses due to impurities, thereby improving slope efficiency.

[0323] Thirdly, the N-type cladding layer 20, N-type guide layer 30, P-type guide layer 50, and P-type cladding layer 60 can be lattice-matched with the GaAs substrate 10, thereby reducing the warpage of the semiconductor laser device (element). Furthermore, this reduction in warpage reduces the asymmetric strain that occurs in the semiconductor laser device during junction-down mounting, thereby enhancing the effect of the insulating film 100A, which is a current-blocking layer composed of an oxide film, that is, the effect of canceling out the shear stress generated at the edges of the semiconductor laser device with shear stress due to the ridge shape.

[0324] Fourth, the intermediate layer 64 can suppress an increase in the driving voltage of the semiconductor laser device. Specifically, since the Al composition is gradually reduced by the first intermediate layer 61 and the second intermediate layer 62 in the intermediate layer 64, the band gap energy difference that occurs when AlGaInP and GaAs are joined can be minimized, thereby suppressing an increase in the driving voltage. Furthermore, by providing a gradient layer of Al composition of AlGaAs with the third intermediate layer 63, the band gap energy of the heterointerface can be smoothed, thereby suppressing an increase in the driving voltage.

[0325] Furthermore, in the semiconductor laser apparatus 1 of the above embodiment, a constricted structure is formed in multiple semiconductor layers constituting the semiconductor laminate, making the side surface of the semiconductor laminate an inclined surface, but the invention is not limited to this.

[0326] Furthermore, this disclosure also includes forms that can be obtained by applying various modifications to each of the above embodiments that a person skilled in the art could conceive, as well as forms that can be realized by arbitrarily combining the components and functions of each of the above embodiments without departing from the spirit of this disclosure. [Industrial applicability]

[0327] The semiconductor laser device disclosed herein can be applied to a variety of light sources, such as a high-power light source for image display devices like displays and projectors, light sources for automotive headlamps, light sources for industrial and consumer lighting, or light sources for industrial equipment such as laser welding equipment, thin-film annealing equipment, and laser processing equipment. [Explanation of Symbols]

[0328] 1. 1A Semiconductor Laser Device 1a Front end surface 1b Rear end surface 2 Submount 10 circuit boards 11. N-type buffer layer 20 N-type cladding layer 30 N-type guide layer 40 Active layer 41 well layer 42a N-side first barrier layer 42b N-side second barrier layer 43a P-side first barrier layer 43b P-side second barrier layer 44 N side high Al composition layer 45 P side high Al composition layer 50 P-type guide layer 60 P-type cladding layer 61. First Meso-Marginal Layer 62. Second Meso-Marginal Layer 63 Third Meso-Marginal Layer 64 Middle Class 70 P-type contact layer 71. First Contact Layer 72 Second Contact Layer 80 Current Blocking Layer 80a opening 91 P side electrode 91a 1st P electrode layer 91b Plating layer 91c 2nd P electrode layer 92 N side electrode 100, 100A insulating film 100a opening 111 First end face coating film 112 Second end face coating film 120 window area 130 Groove 200A Ridge Section

Claims

1. A semiconductor laser device that emits laser light, circuit board and An N-type cladding layer is placed above the aforementioned substrate, An active layer positioned above the aforementioned N-type cladding layer, The active layer comprises a P-type cladding layer positioned above the active layer, The aforementioned active layer is The well-off class, A P-side first barrier layer is positioned above the aforementioned well layer, It has a second P-side barrier layer positioned above the first P-side barrier layer, The Al composition ratio of the P-side second barrier layer is higher than that of the P-side first barrier layer. The band gap energy of the P-side second barrier layer is greater than the band gap energy of the P-side first barrier layer. Furthermore, the P-type guide layer is provided between the P-side second barrier layer and the P-type cladding layer, and the P-side high-Al composition layer, which has a higher Al composition than the P-side first barrier layer, is provided between the well layer and the P-side first barrier layer. The band gap energy of the P-type guide layer is greater than the band gap energy of the P-side second barrier layer. The aforementioned P-side high-Al composition layer is doped with P-type impurities. Semiconductor laser device.

2. The band gap energy of the P-type cladding layer is greater than that of the N-type cladding layer. The semiconductor laser apparatus according to claim 1.

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

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

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

6. The P-side first barrier layer includes an undoped region that is not doped with impurities. The film thickness of the undoped region is 5 nm or more. A semiconductor laser apparatus according to any one of claims 1 to 5.

7. The entire region of the P-side second barrier layer is doped with impurities. The P-side first barrier layer has an undoped region in the area closer to the well layer where impurities are not doped, and a doped region in the area further away from the well layer where impurities are doped. A semiconductor laser apparatus according to any one of claims 1 to 6.

8. The concentration of impurities doped into the P-side second barrier layer gradually increases as it moves away from the well layer. A semiconductor laser apparatus according to any one of claims 1 to 7.

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

10. The concentration of impurities doped into the P-type guide layer gradually increases as it moves away from the well layer. A semiconductor laser apparatus according to any one of claims 1 to 9.

11. The active layer further comprises an N-side first barrier layer disposed below the well layer, and an N-side high-Al composition layer having a higher Al composition than the N-side first barrier layer, between the well layer and the N-side first barrier layer. The aforementioned N-side high-Al composition layer is doped with N-type impurities. A semiconductor laser apparatus according to any one of claims 1 to 10.

12. The active layer further comprises an N-side first barrier layer positioned below the well layer and an N-side second barrier layer positioned below the N-side first barrier layer. The Al composition ratio of the N-side second barrier layer is higher than that of the N-side first barrier layer. The band gap energy of the N-side second barrier layer is greater than the band gap energy of the N-side first barrier layer. A semiconductor laser apparatus according to any one of claims 1 to 10.

13. The active layer further comprises an N-side first barrier layer positioned below the well layer and an N-side second barrier layer positioned below the N-side first barrier layer. The total film thickness of the P-side first barrier layer and the N-side first barrier layer is 20 nm or more and 80 nm or less. A semiconductor laser apparatus according to any one of claims 1 to 10.

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

15. The entire region of the N-side second barrier layer is doped with impurities. The N-side first barrier layer has an undoped region in the area closer to the well layer where impurities are not doped, and a doped region in the area farther from the well layer where impurities are doped. A semiconductor laser apparatus according to any one of claims 12 to 14.

16. The band gap energy of the P-side second barrier layer is greater than the band gap energy of the N-side second barrier layer. A semiconductor laser apparatus according to any one of claims 12 to 15.

17. A semiconductor laser device that emits laser light, circuit board and An N-type cladding layer is placed above the aforementioned substrate, An active layer positioned above the aforementioned N-type cladding layer, The active layer comprises a P-type cladding layer positioned above the active layer, The aforementioned active layer is The well-off class, A P-side first barrier layer is positioned above the aforementioned well layer, A second barrier layer on the P side is positioned above the first barrier layer on the P side, An N-side first barrier layer is positioned below the well layer, It has an N-side second barrier layer positioned below the N-side first barrier layer, The Al composition ratio of the P-side second barrier layer is higher than that of the P-side first barrier layer. The band gap energy of the P-side second barrier layer is greater than the band gap energy of the P-side first barrier layer. Furthermore, the structure includes a P-type guide layer between the P-side second barrier layer and the P-type cladding layer, and an N-side high-Al composition layer with a higher Al composition than the N-side first barrier layer between the well layer and the N-side first barrier layer. The band gap energy of the P-type guide layer is greater than the band gap energy of the P-side second barrier layer. The aforementioned N-side high Al composition layer is doped with N-type impurities. The Al composition ratio of the N-side second barrier layer is higher than that of the N-side first barrier layer. The band gap energy of the N-side second barrier layer is greater than the band gap energy of the N-side first barrier layer. Semiconductor laser device.

18. The active layer has a P-side high-Al composition layer between the well layer and the P-side first barrier layer, with a higher Al composition than the P-side first barrier layer. The aforementioned P-side high-Al composition layer is doped with P-type impurities. The semiconductor laser apparatus according to claim 17.

19. Furthermore, an N-type guide layer is provided between the N-side second barrier layer and the N-type cladding layer. A semiconductor laser apparatus according to any one of claims 13 to 18.

20. The Al composition in at least the interface region between the N-type guide layer and the N-type cladding layer gradually increases as it moves away from the well layer. The semiconductor laser apparatus according to claim 19.

21. The concentrations of impurities doped into the N-type cladding layer, the N-type guide layer, the N-side second barrier layer, and the N-side first barrier layer gradually increase or increase stepwise as they move away from the well layer. The semiconductor laser apparatus according to claim 19 or 20.

22. The active layer comprises an N-side first barrier layer positioned below the well layer and an N-side second barrier layer positioned below the N-side first barrier layer. The Al composition ratio of the N-side second barrier layer is higher than that of the N-side first barrier layer. The band gap energy of the N-side second barrier layer is greater than the band gap energy of the N-side first barrier layer. An N-type guide layer is provided between the N-side second barrier layer and the N-type cladding layer. The band gap energy of the P-type guide layer is different from the band gap energy of the N-type guide layer. A semiconductor laser apparatus according to any one of claims 1, 3 to 11.

23. Located between the well layer and the N-type cladding layer, and comprising an N-side first barrier layer and an N-side second barrier layer extending from the well layer toward the N-type cladding layer, The Al composition ratio of the N-side second barrier layer is higher than that of the N-side first barrier layer. The band gap energy of the N-side second barrier layer is greater than the band gap energy of the N-side first barrier layer. The bandgap energy of the N-side second barrier layer gradually increases as it moves away from the well layer. The maximum band gap energy of the P-side second barrier layer is greater than the maximum band gap energy of the N-side second barrier layer. The semiconductor laser apparatus according to claim 6.

24. A method for manufacturing a semiconductor laser device that emits laser light, The process involves placing an N-type cladding layer on top of the substrate, The process involves placing an active layer above the aforementioned N-type cladding layer, The process includes placing a P-type cladding layer above the active layer, The aforementioned active layer is The well-off class, A P-side first barrier layer is positioned above the aforementioned well layer, It has a second P-side barrier layer positioned above the first P-side barrier layer, The Al composition ratio of the P-side second barrier layer is higher than that of the P-side first barrier layer. Furthermore, the P-type guide layer is provided between the P-side second barrier layer and the P-type cladding layer, and the P-side high-Al composition layer, which has a higher Al composition than the P-side first barrier layer, is provided between the well layer and the P-side first barrier layer. The band gap energy of the P-side second barrier layer is greater than the band gap energy of the P-side first barrier layer. The aforementioned P-side high-Al composition layer is doped with P-type impurities. A method for manufacturing a semiconductor laser device.

25. The active layer comprises an N-side first barrier layer positioned below the well layer, and an N-side high-Al composition layer having a higher Al composition than the N-side first barrier layer, between the well layer and the N-side first barrier layer. The aforementioned N-side high-Al composition layer is doped with N-type impurities. A method for manufacturing a semiconductor laser apparatus according to claim 24.

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