Semiconductor laser element

Abstract

A semiconductor laser element (1) comprises: a semiconductor substrate (2) formed of GaAs; a plurality of laser structures (4); a tunnel junction layer (5); a first reflective film (8) disposed on first end surfaces (4a) of the plurality of laser structures (4); and a second reflective film (9) disposed on second end surfaces (4b) of the plurality of laser structures (4). The semiconductor laser element (1) includes: an n-type carrier block layer (46) disposed between an active region (41) and an n-type clad layer (44) and having a thickness smaller than the thickness of the n-type clad layer (44); and a p-type carrier block layer (47) disposed between the active region (41) and the p-type clad layer (45) and having a thickness smaller than the thickness of the p-type clad layer (45).

Description

Semiconductor laser element

[0001] This disclosure relates to semiconductor laser devices.

[0002] Patent Document 1 describes a stacked semiconductor laser structure. In this stacked semiconductor laser structure, a first laser structure unit and a second laser structure unit are stacked on a substrate made of GaAs, and a tunnel junction is provided between the first laser structure unit and the second laser structure unit. Each of the first and second laser structure units includes an active layer, a pair of guide layers sandwiching the active layer, and a pair of cladding layers sandwiching the pair of guide layers, and each cladding layer is made of AlGaAs.

[0003] Japanese Patent Publication No. 2010-225658

[0004] In the semiconductor laser structure described in Patent Document 1, multiple laser structure units, each containing an active layer, are stacked on a substrate to achieve high power output. In such a semiconductor laser structure, distortion occurs due to the difference in lattice constants (lattice mismatch) between the substrate formed of GaAs and the cladding layer formed of AlGaAs, and this distortion may increase as the number of stacked laser structure units increases. If this distortion increases, warping or other deformation may occur in the semiconductor laser structure, which may degrade the quality of the laser light output from the semiconductor laser structure.

[0005] Therefore, the purpose of this disclosure is to provide a semiconductor laser element that can improve the output of laser light while suppressing a deterioration in the quality of laser light.

[0006] A semiconductor laser element according to one aspect of the present disclosure comprises: [1] a semiconductor substrate formed of GaAs; a plurality of laser structures stacked on the semiconductor substrate along a first direction which is the thickness direction of the semiconductor substrate, with a second direction intersecting the first direction as the resonance direction; a tunnel junction layer disposed between two adjacent laser structures in the first direction; a first reflective film disposed on a first end face on one side of the plurality of laser structures in the second direction; and a second reflective film disposed on a second end face on the other side of the plurality of laser structures in the second direction, wherein each of the plurality of laser structures is made of a GaAs-based compound semiconductor. A semiconductor laser element comprising: an active region including a formed quantum well layer; a first cladding layer of a first conductivity type formed of AlGaAs, disposed on the semiconductor substrate side with respect to the active region; a second cladding layer of a second conductivity type formed of AlGaAs, disposed on the opposite side of the active region from the semiconductor substrate; a first carrier block layer of the first conductivity type disposed between the active region and the first cladding layer and having a thickness smaller than the thickness of the first cladding layer; and a second carrier block layer of the second conductivity type disposed between the active region and the second cladding layer and having a thickness smaller than the thickness of the second cladding layer.

[0007] In the above semiconductor laser element, a plurality of laser structures having the same resonance direction are stacked on a semiconductor substrate made of GaAs, with a tunnel junction layer placed between two adjacent laser structures, and a first reflective film and a second reflective film are placed on the first and second end faces of the plurality of laser structures in the resonance direction. With this configuration, light resonates between the first and second end faces of the plurality of laser structures, and amplified light is emitted from each of the plurality of laser structures. Therefore, the output of the laser light can be improved compared to when a single laser structure is used. In addition, in each laser structure, a first carrier block layer and a second carrier block layer are placed on both sides of the active region which includes a quantum well layer made of a GaAs-based compound semiconductor, and a first cladding layer and a second cladding layer made of AlGaAs are placed on both sides of the first and second carrier block layers. With this configuration, carriers are confined to the active region by the first and second carrier block layers, so the first cladding layer and the second cladding layer can be designed to have at least the function of confining the light generated in the active region. In other words, if the first and second carrier block layers are not positioned on both sides of the active region, the first and second cladding layers must be designed to have both carrier confinement and light confinement functions, but this is not necessary in this configuration. Furthermore, the first carrier block layer has a thickness smaller than the first cladding layer, and the second carrier block layer has a thickness smaller than the second cladding layer. With this configuration, the influence of the first and second carrier block layers on the light confinement function can be reduced, thus relaxing the design constraints on the first and second cladding layers. This makes it easier to design to mitigate lattice mismatch between the semiconductor substrate formed of GaAs and the first and second cladding layers, respectively, formed of AlGaAs. For example, it becomes easier to reduce the amount of Al in the first and second cladding layers, respectively, to mitigate lattice mismatch.As a result, it becomes possible to suppress the degradation of laser light quality caused by warping of the semiconductor laser element, etc. Therefore, with the above semiconductor laser element, it is possible to improve the output of the laser light while suppressing the degradation of the laser light quality.

[0008] One aspect of the semiconductor laser element of this disclosure is [2] "The first reflective film has a reflectance that decreases as the wavelength increases in the wavelength range of light in which each of the plurality of laser structures can oscillate, the reflectance of the first reflective film is R1, the reflectance of the second reflective film is R2, the distance between the first end face and the second end face is L, and the mirror loss is αm, such that αm = {1 / (2 × L)} × ln{1 / (R1 × R2)} holds, and the mirror loss is 15 [cm] at a predetermined wavelength included in the wavelength range. －１ The semiconductor laser element described in [1] may be the one described in [1]. With this semiconductor laser element, when the operating temperature of the semiconductor laser element rises, the central wavelength of the laser light does not shift to a wavelength longer than a predetermined wavelength, and the shape of the laser light spectrum is less likely to be disturbed (these are findings discovered by the present inventors). Therefore, it is possible to fix the central wavelength of the laser light to a specific wavelength and maintain the steepness of the laser light spectrum.

[0009] One aspect of the present disclosure may be the semiconductor laser element described in [2], wherein the reflectance of the second reflective film is substantially constant in the wavelength range. The semiconductor laser element makes it possible to easily adjust the reflectance of the second reflective film.

[0010] One aspect of the present disclosure is a semiconductor laser element according to any one of [1] to [3], wherein the composition ratio of Al in each of the first cladding layer and the second cladding layer is 0.3 or less. This semiconductor laser element can sufficiently mitigate lattice mismatch between the semiconductor substrate formed of GaAs and the first cladding layer and the second cladding layer, each formed of AlGaAs. As a result, it is possible to further suppress the deterioration of laser light quality caused by warping of the semiconductor laser element, etc.

[0011] One aspect of the present disclosure is a semiconductor laser element according to any one of [1] to [4], wherein the thickness of the first cladding layer is 500 nm or more, and the thickness of the second cladding layer is 500 nm or more. With this semiconductor laser element, the first cladding layer and the second cladding layer can sufficiently confine the light generated in the active region.

[0012] One aspect of the present disclosure is a semiconductor laser element according to any one of [1] to [5], wherein the distance between the quantum well layer and the first carrier block layer is 150 nm or less, and the distance between the quantum well layer and the second carrier block layer is 150 nm or less. With this semiconductor laser element, the first carrier block layer and the second carrier block layer can sufficiently confine carriers in the active region. As a result, the energy of the carriers is concentrated to a specific energy, so the voltage applied to the semiconductor laser element to perform stimulated emission of light can be reduced. Therefore, stimulated emission of light can be easily performed.

[0013] One aspect of the present disclosure is a semiconductor laser element according to any one of [1] to [6], wherein the thickness of the first carrier block layer is 20 nm or less, and the thickness of the second carrier block layer is 20 nm or less. With this semiconductor laser element, the influence of the first carrier block layer and the second carrier block layer on the light confinement function can be reduced. Therefore, the design constraints of the first cladding layer and the second cladding layer can be sufficiently relaxed.

[0014] One aspect of the present disclosure is a semiconductor laser element according to any one of [1] to [7], wherein the thickness of the first carrier block layer is 1 / 10 or less of the thickness of the first cladding layer, and the thickness of the second carrier block layer is 1 / 10 or less of the thickness of the second cladding layer. With this semiconductor laser element, the influence of the first carrier block layer and the second carrier block layer on the light confinement function can be reduced. Therefore, the design constraints of the first cladding layer and the second cladding layer can be sufficiently relaxed.

[0015] A semiconductor laser element according to one aspect of the present disclosure may be [9] "a semiconductor laser element according to any one of [1] to [8], wherein one of the first carrier block layer and the second carrier block layer is a Te-doped n-type carrier block layer, and the other of the first carrier block layer and the second carrier block layer is a C-doped p-type carrier block layer." With this semiconductor laser element, the diffusion coefficients of the dopants Te and C are relatively small, so the diffusion of Te and C is suppressed. This makes it possible to suppress Te and C from adversely affecting the active region.

[0016] One aspect of the present disclosure is a semiconductor laser element according to any one of [1] to [9], wherein the quantum well layer is formed of InGaAs, AlInGaAs, or InGaAsP. According to this semiconductor laser element, a quantum well layer suitable for realizing a desired laser light wavelength can be formed.

[0017] A semiconductor laser element in one aspect of the present disclosure may be

[11] "a semiconductor laser element according to any one of [1] to

[10] , wherein each of the plurality of laser structures further comprises a first guide layer of a first conductivity type disposed between the first cladding layer and the first carrier block layer, and a second guide layer of a second conductivity type disposed between the second cladding layer and the second carrier block layer." With this semiconductor laser element, light generated in the active region can be suitably confined in the first guide layer and the second guide layer.

[0018] According to this disclosure, it is possible to provide a semiconductor laser element that can improve the output of laser light while suppressing a degradation in the quality of laser light.

[0019] Figure 1 is a perspective view of a semiconductor laser element according to one embodiment. Figure 2 is a cross-sectional view of the semiconductor laser element along the line II-II shown in Figure 1. Figure 3 is a schematic diagram showing the stacked structure of the semiconductor laser element shown in Figure 1. Figure 4 is a cross-sectional view of the stacked structure of the semiconductor laser element shown in Figure 1. Figure 5(a) is a graph showing the reflectance of the first reflective film, and Figure 5(b) is a graph showing the reflectance of the second reflective film. Figure 6(a) is a graph showing the product of the reflectance of the first reflective film and the reflectance of the second reflective film in the case of a short resonator, and Figure 6(b) is a graph showing the product of the reflectance of the first reflective film and the reflectance of the second reflective film in the case of a long resonator. Figure 7(a) is a graph showing the laser light spectrum when an SCH structure is used, and Figure 7(b) is a graph showing the laser light spectrum when a DCH structure is used. Figure 8(a) is a graph showing the relationship between the gain spectrum, reflectance spectrum, and effective gain spectrum of the material in an SCH structure, and Figure 8(b) is a graph showing the relationship between the gain spectrum, reflectance spectrum, and effective gain spectrum of the material in a DCH structure. Figure 9(a) is a graph showing the experimental results of the laser light output when a 3-stage stacked SCH structure is used, Figure 9(b) is a graph showing the experimental results of the laser light output when a 5-stage stacked SCH structure is used, and Figure 9(c) is a graph showing the experimental results of the laser light output when a 5-stage stacked DCH structure is used. Figure 10(a) is a graph showing the experimental results of the output ratio of the laser light when a 3-stage stacked SCH structure is used, with the device temperature at 25°C as the reference, Figure 10(b) is a graph showing the experimental results of the output ratio of the laser light when a 5-stage stacked SCH structure is used, and Figure 10(c) is a graph showing the experimental results of the output ratio of the laser light when a 5-stage stacked DCH structure is used.

[0020] Embodiments of this disclosure will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0021] As shown in Figures 1 and 2, the semiconductor laser element 1 comprises a semiconductor substrate 2, a plurality of stacked structures LS1, LS2, and LS3, an insulating film 10, a cathode electrode 11, and an anode electrode 12. The semiconductor laser element 1 is a pulsed laser diode used in LiDAR (Light Detection and Ranging), etc. Hereinafter, the thickness direction of the semiconductor substrate 2 will be referred to as the first direction D1, the direction perpendicular to the first direction D1 will be referred to as the second direction D2, and the direction perpendicular to the first direction D1 and the second direction D2 will be referred to as the third direction D3. When simply referred to as "thickness," it means the thickness in the first direction D1.

[0022] The shape of the semiconductor laser element 1 is, for example, a rectangular parallelepiped with the second direction D2 as the longitudinal direction. As an example, the length of the semiconductor laser element 1 in the second direction D2 is 500 μm to 1500 μm, the thickness of the semiconductor laser element 1 is 100 μm to 200 μm, and the width of the semiconductor laser element 1 in the third direction D3 is 300 μm to 600 μm.

[0023] The semiconductor substrate 2 is formed of GaAs. The semiconductor substrate 2 is doped with Si. The Si concentration in the semiconductor substrate 2 is, for example, 1.5 × 10⁻⁶. １８ cm －３ That is the case.

[0024] Each of the stacked structures LS1, LS2, and LS3 is arranged on the surface 2a of the semiconductor substrate 2 and extends along the second direction D2. Stacked structure LS1 is located between stacked structures LS2 and LS3 in the third direction D3. A pair of trenches TR are formed between stacked structures LS1 and LS2, and between stacked structures LS1 and LS3. Each trench TR extends along the second direction D2. The cross-sectional shape of each stacked structure LS1, LS2, and LS3 is, for example, trapezoidal. The width (emission width) of stacked structure LS1 in the third direction D3 is, for example, 50 μm to 300 μm. Multiple stacked structures LS1, LS2, and LS3 are formed on the semiconductor substrate 2 by an epitaxial growth method. Each of the stacked structures LS1, LS2, and LS3 has the same stacked structure as the others. Stacked structure LS1 emits laser light as described later.

[0025] The insulating film 10 is arranged across the surfaces of each laminated structure LS1, LS2, and LS3 and the bottom surface of each trench TR. The insulating film 10 is formed of an electrically insulating material such as SiN. The thickness of the insulating film 10 is, for example, 100 nm to 200 nm.

[0026] The cathode electrode 11 is located on the back surface 2b (the surface opposite to the front surface 2a) of the semiconductor substrate 2. The cathode electrode 11 is made of a metallic material. For example, the cathode electrode 11 is an AuGe / Ni / Au film, in which case the thickness of the AuGe film is 120 nm, the thickness of the Ni film is 15 nm, and the thickness of the Au film is 500 nm.

[0027] The anode electrode 12 is positioned on the top surface LS1a of the laminated structure LS1. The anode electrode 12 is positioned in an opening 10a formed in the insulating film 10, and its surface is exposed from the insulating film 10. The anode electrode 12 is made of a metallic material. For example, the anode electrode 12 is a Ti / Pt / Au film, in which case the thickness of the Ti film is 50 nm, the thickness of the Pt film is 100 nm, and the thickness of the Au film is 1000 nm.

[0028] As shown in Figures 3 and 4, the laminated structure LS1 includes an n-type buffer layer 3, a plurality of laser structures 4, a plurality of tunnel junction layers 5, a p-type graded layer 6, and a p-type contact layer 7.

[0029] As an example, the stacked structure LS1 is configured as a three-stage stack type having three laser structures 4 and two tunnel junction layers 5. In the three-stage stack type, an n-type buffer layer 3, one laser structure 4, one tunnel junction layer 5, one laser structure 4, one tunnel junction layer 5, one laser structure 4, a p-type graded layer 6, and a p-type contact layer 7 are stacked in this order on the surface 2a of the semiconductor substrate 2 along the first direction D1. The total thickness of one laser structure 4 and one tunnel junction layer 5 is, for example, 4 μm to 6 μm. Therefore, in the three-stage stack type, the total thickness of the multiple laser structures 4 and multiple tunnel junction layers 5 is, for example, 12 μm to 18 μm.

[0030] The n-type buffer layer 3 is a layer for ensuring the flatness of crystal growth. The n-type buffer layer 3 is disposed on the surface 2a of the semiconductor substrate 2. The n-type buffer layer 3 includes a first layer 31 disposed on the surface 2a and a second layer 32 disposed on the side opposite to the semiconductor substrate 2 with respect to the first layer 31. The first layer 31 is formed of GaAs. The first layer 31 is doped with Si (or Te). The concentration of Si (or Te) in the first layer 31 is, for example, 0.8×10 １８ cm －３ to 2.0×10 １８ cm －３ . The thickness of the first layer 31 is, for example, 300 nm. The second layer 32 is formed of Al ０．２～０．３ GaAs, or a graded layer in which the Al composition continuously increases from GaAs to Al ０．３ GaAs. The second layer 32 is doped with Te. The concentration of Te in the second layer 32 is, for example, 1.5×10 １８ cm －３ . The thickness of the second layer 32 is, for example, 100 nm.

[0031] Each laser structure 4 has a completely separated confinement structure (DCH: Decoupled Confinement Heterostructure) with the second direction D2 as the resonance direction. Each laser structure 4 includes a first end face 4a on one side in the second direction D2 and a second end face 4b on the other side in the second direction D2. In the present embodiment, the light resonated by each laser structure 4 is emitted from the first end face 4a as laser light L0. Each laser structure 4 includes an active region 41, an n-type guide layer (first guide layer of the first conductivity type) 42, a p-type guide layer (second guide layer of the second conductivity type) 43, an n-type clad layer (first clad layer of the first conductivity type) 44, a p-type clad layer (second clad layer of the second conductivity type) 45, an n-type carrier blocking layer (first carrier blocking layer of the first conductivity type) 46, and a p-type carrier blocking layer (second carrier blocking layer of the second conductivity type) 47.

[0032] The n-type cladding layer 44 is positioned on the semiconductor substrate 2 side relative to the active region 41 and is in contact with the n-type buffer layer 3. The p-type cladding layer 45 is positioned on the opposite side of the active region 41 from the semiconductor substrate 2 and is in contact with the tunnel junction layer 5. The n-type carrier block layer 46 is positioned between the active region 41 and the n-type cladding layer 44. The p-type carrier block layer 47 is positioned between the active region 41 and the p-type cladding layer 45. The n-type guide layer 42 is positioned between the n-type cladding layer 44 and the n-type carrier block layer 46. The p-type guide layer 43 is positioned between the p-type cladding layer 45 and the p-type carrier block layer 47. In other words, the n-type cladding layer 44, n-type guide layer 42, n-type carrier block layer 46, active region 41, p-type carrier block layer 47, p-type guide layer 43, and p-type cladding layer 45 are stacked in this order on the n-type buffer layer 3 along the first direction D1.

[0033] The active region 41 is a region having a multiple quantum well structure including two quantum well layers. The active region 41 includes a first quantum well layer 411, a second quantum well layer 412, a first barrier layer 413, a second barrier layer 414, and a third barrier layer 415. In the active region 41, the first quantum well layer 411 and the second quantum well layer 412, as well as the first barrier layer 413, the second barrier layer 414, and the third barrier layer 415 are arranged alternately. Specifically, the first barrier layer 413 is located on the semiconductor substrate 2 side relative to the second barrier layer 414. The third barrier layer 415 is located on the side opposite to the semiconductor substrate 2 relative to the second barrier layer 414. The first quantum well layer 411 is located between the first barrier layer 413 and the second barrier layer 414. The second quantum well layer 412 is located between the second barrier layer 414 and the third barrier layer 415. Each layer in the active region 41 is an undoped layer. An "undoped layer" is defined as a layer in which the concentration of impurities (e.g., C) is 5.0 × 10⁻⁶. １６ cm －３ It means less than.

[0034] Each of the first quantum well layer 411 and the second quantum well layer 412 is, for example, In ０．１It is formed of GaAs. The thickness of the first quantum well layer 411 and the second quantum well layer 412 is, for example, 6 nm to 10 nm. As an example, the first quantum well layer 411 and the second quantum well layer 412 each emit light with a wavelength of 850 nm to 950 nm.

[0035] Each of the first barrier layer 413, the second barrier layer 414, and the third barrier layer 415 is, for example, Al ０．１８～０．２５ It is formed of GaAs. For example, the thickness of the first barrier layer 413 is 50 nm to 70 nm, the thickness of the second barrier layer 414 is 6 nm to 10 nm, and the thickness of the third barrier layer 415 is 30 nm to 50 nm.

[0036] The n-type guide layer 42 is, for example, Al ０．１８～０．２５ It is formed of GaAs. The n-type guide layer 42 is doped with Te. The concentration of Te in the n-type guide layer 42 is, for example, 1.0 × 10⁻⁶. １７ cm －３ ~5.0 x 10 １７ cm －３ The thickness of the n-type guide layer 42 is 1000 nm or less. The refractive index of the n-type guide layer 42 is greater than that of the n-type cladding layer 44.

[0037] The p-type guide layer 43 is, for example, Al ０．１８～０．２５ It is formed of GaAs. The p-type guide layer 43 is doped with carbon. The concentration of carbon in the p-type guide layer 43 is, for example, 1.0 × 10⁻⁶. １７ cm －３ ~5.0 x 10 １７ cm －３ The thickness of the p-type guide layer 43 is, for example, 1000 nm or less. The refractive index of the p-type guide layer 43 is greater than the refractive index of the p-type cladding layer 45.

[0038] The n-type cladding layer 44 has the function of confining light generated in the active region 41. The n-type cladding layer 44 is made of Al ０．２～０．３ It is formed of GaAs. The composition ratio of Al in the n-type cladding layer 44 is, for example, 0.3 or less. The n-type cladding layer 44 is doped with Te. The concentration of Te in the n-type cladding layer 44 is, for example, 1.0 × 10⁻⁶.１８ cm －３ ~3.0 x 10 １８ cm －３ The thickness of the n-type cladding layer 44 may be 500 nm or more, or it may be between 800 nm and 2000 nm.

[0039] The p-type cladding layer 45 has the function of confining light generated in the active region 41. The p-type cladding layer 45 is made of Al ０．２～０．３ It is formed of GaAs. The composition ratio of Al in the p-type cladding layer 45 is, for example, 0.3 or less. The p-type cladding layer 45 is doped with C. The concentration of C in the p-type cladding layer 45 is, for example, 1.0 × 10⁻⁶. １８ cm －３ ~3.0 x 10 １８ cm －３ The thickness of the p-type cladding layer 45 may be 500 nm or more, or it may be between 800 nm and 2000 nm.

[0040] The n-type carrier block layer 46 has the function of confining carriers in the active region 41. The n-type carrier block layer 46 is made of, for example, Al ０．２５～１ It is formed by GaAs. The n-type carrier block layer 46 is doped with Te. The concentration of Te in the n-type carrier block layer 46 is, for example, 1.0 × 10⁻⁶. １８ cm －３ ~5.0 x 10 １８ cm －３ The thickness of the n-type carrier block layer 46 may be 20 nm or less, or 10 nm to 20 nm. The thickness of the n-type carrier block layer 46 is smaller than the thickness of the n-type cladding layer 44. For example, the thickness of the n-type carrier block layer 46 is 1 / 10 or less of the thickness of the n-type cladding layer 44. The band gap (band gap) of the n-type carrier block layer 46 is larger than the band gaps of the n-type cladding layer 44, n-type guide layer 42, active region 41, p-type guide layer 43, and p-type cladding layer 45.

[0041] The n-type carrier block layer 46 corresponds to the first doped layer when viewed from the undoped active region 41 and is located near the quantum well layer. For example, the distance between the quantum well layer and the n-type carrier block layer 46 in the first direction D1 is 150 nm or less. When multiple quantum well layers are arranged as in this embodiment, this distance is the distance between the n-type carrier block layer 46 and the quantum well layer closest to the n-type carrier block layer 46 among the multiple quantum well layers. In this embodiment, this distance is the distance T1 between the n-type carrier block layer 46 and the first quantum well layer 411, and corresponds to the thickness of the first barrier layer 413.

[0042] The p-type carrier block layer 47 has the function of confining carriers in the active region 41. The p-type carrier block layer 47 is, for example, Al ０．２５～１ It is formed by GaAs. The p-type carrier block layer 47 is doped with carbon. The concentration of carbon in the p-type carrier block layer 47 is, for example, 1.0 × 10⁻⁶. １８ cm －３ ~5.0 x 10 １８ cm －３ The thickness of the p-type carrier block layer 47 may be 20 nm or less, or 10 nm to 20 nm. The thickness of the p-type carrier block layer 47 is smaller than the thickness of the p-type cladding layer 45. For example, the thickness of the p-type carrier block layer 47 is 1 / 10 or less of the thickness of the p-type cladding layer 45. The band gap (band gap) of the p-type carrier block layer 47 is larger than the band gaps of the n-type cladding layer 44, n-type guide layer 42, active region 41, p-type guide layer 43, and p-type cladding layer 45.

[0043] The p-type carrier block layer 47 corresponds to the first doped layer when viewed from the undoped active region 41 and is located near the quantum well layer. For example, the distance between the quantum well layer and the p-type carrier block layer 47 in the first direction D1 is 150 nm or less. When multiple quantum well layers are arranged as in this embodiment, this distance is the distance between the p-type carrier block layer 47 and the quantum well layer closest to the p-type carrier block layer 47 among the multiple quantum well layers. In this embodiment, this distance is the distance T2 between the p-type carrier block layer 47 and the second quantum well layer 412, and corresponds to the thickness of the third barrier layer 415.

[0044] Each tunnel junction layer 5 is positioned between two adjacent laser structures 4 in a first direction D1. The tunnel junction layer 5 tunnel-bonds the p-type cladding layer 45 of the laser structure 4, which is positioned on the semiconductor substrate 2 side relative to the tunnel junction layer 5, to the n-type cladding layer 44 of the laser structure 4, which is positioned on the opposite side of the tunnel junction layer 5 from the semiconductor substrate 2. When a voltage is applied between the cathode electrode 11 and the anode electrode 12 to generate light in the active region 41, the tunneling effect in the tunnel junction layer 5 allows a current to flow with low resistance from the n-type cladding layer 44 of one laser structure 4 to the p-type cladding layer 45 of the other laser structure 4. The tunnel junction layer 5 includes a first layer 51, a second layer 52, a third layer 53, and a fourth layer 54. The first layer 51, second layer 52, third layer 53, and fourth layer 54 are stacked in this order on the p-type cladding layer 45 of the laser structure 4 along the first direction D1.

[0045] The first layer 51 is formed of, for example, GaAs. The first layer 51 is doped with C. The concentration of C in the first layer 51 is, for example, 1.0 × 10⁻⁶ １８ cm －３ ~3.0 x 10 １８ cm －３ The thickness of the first layer 51 is, for example, 50 nm.

[0046] The second layer 52 is formed by, for example, GaAs. The second layer 52 is doped with C. The concentration of C in the second layer 52 is, for example, 5.0 × 10⁻⁶. １９ cm －３ ~10.0 x 10 １９ cm －３ The thickness of the second layer 52 is, for example, 30 nm to 100 nm.

[0047] The third layer 53 is formed, for example, by GaAs. The third layer 53 is doped with Te. The concentration of Te in the third layer 53 is 5.0 × 10⁻⁶. １９ cm －３ ~10.0 x 10 １９ cm －３ The thickness of the third layer 53 is, for example, 30 nm to 100 nm.

[0048] The fourth layer 54 is, for example, Al ０．２～０．３ It is formed by GaAs. The fourth layer 54 is doped with Te. The concentration of Te in the fourth layer 54 is, for example, 1.0 × 10⁻⁶ １８ cm －３ ~3.0 x 10 １８ cm －３ The thickness of the fourth layer 54 is, for example, 50 nm.

[0049] Each tunnel junction layer 5 is a layer formed by joining a p-type doping layer and an n-type doping layer, and has a depletion layer width of 15 nm or less. The materials of the p-type doping layer and the n-type doping layer are, for example, GaAs or InGaAs with an In composition of 5% or less. As an example, such a depletion layer width is achieved when the carrier concentrations of the p-type doping layer and the n-type doping layer are 2.0 × 10⁻⁶. １９ cm －３ This can be achieved by doing the above, and these will be 5.0 × 10 １９ cm －３ This can be reliably achieved. This ensures that the conditions for an appropriate band structure and a narrow depletion layer are met, resulting in tunnel current flow.

[0050] The p-type graded layer 6 is a layer for ensuring smooth crystal growth of the p-type contact layer 7. The p-type graded layer 6 is located on the p-type cladding layer 45 of the laser structure 4 furthest from the semiconductor substrate 2 among the multiple laser structures 4. The p-type graded layer 6 is formed of AlGaAs. However, in the p-type graded layer 6, the Al composition gradually decreases from the p-type cladding layer 45 toward the p-type contact layer 7, and at the point where it reaches the p-type contact layer 7, the Al composition is zero (i.e., GaAs). The p-type graded layer 6 is doped with carbon. The concentration of carbon in the p-type graded layer 6 is, for example, 1.0 × 10⁻⁶. １８ cm －３ ~2.0 x 10 １８ cm －３ The thickness of the p-type graded layer 6 is, for example, 100 nm.

[0051] The p-type contact layer 7 is located on the p-type graded layer 6. The anode electrode 12 is located on the p-type contact layer 7. The p-type contact layer 7 is formed of GaAs. The p-type contact layer 7 is doped with carbon. The concentration of carbon in the p-type contact layer 7 is, for example, 1.0 × 10⁻⁶. ２０ cm －３ The thickness of the p-type contact layer 7 is, for example, 200 nm.

[0052] The semiconductor laser element 1 further comprises a first reflective film 8 and a second reflective film 9. The first reflective film 8 is positioned on one end face in the second direction D2 of each of the n-type buffer layer 3, laser structure 4, tunnel junction layer 5, p-type graded layer 6, and p-type contact layer 7, and covers each end face. That is, the first reflective film 8 is positioned on the first end face 4a of each of the multiple laser structures 4, and covers each first end face 4a. The first reflective film 8 is formed continuously across the first end faces 4a of the multiple laser structures 4. The first reflective film 8 covers one portion (end face) of the outer edge of the insulating film 10 in the second direction D2, and one portion (end face) of the outer edge of the cathode electrode 11 in the second direction D2.

[0053] The first reflective film 8 is, for example, Al２ O ３ , Ta ２ O ５ , TiO ２ Or SiO ２ It is formed by laminating a plurality of layers formed by. As an example, the first reflective film 8 is six Al ２ O ３ layers and six Ta ２ O ５ layers are alternately laminated one by one. The first reflective film 8 is three Al ２ O ３ layers and three Ta ２ O ５ layers may be alternately laminated one by one. The first reflective film 8 has an Al ２ O ３ layer disposed on the first end face 4a, and four Ta ２ O ３ layers and four SiO ２ O ５ layers may be alternately laminated one by one on the first end face 4a with the Al ２ layer interposed therebetween. The first reflective film 8 has an Al ２ O ３ layer disposed on the first end face 4a, and three Ta ２ O ３ layers and three SiO ２ O ５ layers may be alternately laminated one by one on the first end face 4a with the Al ２ layer interposed therebetween.

[0054] As shown in Figure 5(a), the reflectance of the first reflective film 8 is wavelength-dependent. Specifically, the reflectance of the first reflective film 8 decreases as the wavelength increases within the wavelength range of light in which each laser structure 4 can oscillate. The "wavelength range of light in which the laser structure 4 can oscillate" means the wavelength range of light in which the laser structure 4 can oscillate within the operating temperature range of -40°C to 125°C, when a reflective film having substantially constant reflectance (flat reflectance without wavelength dependence) is placed on the first end face 4a and the second end face 4b instead of the first reflective film 8 and the second reflective film 9. "Substantially constant reflectance" means that the reflectance is within ±5% of the average value of the reflectance.

[0055] The second reflective film 9 is positioned on the other end face in the second direction D2 of each of the n-type buffer layer 3, laser structure 4, tunnel junction layer 5, p-type graded layer 6, and p-type contact layer 7, and covers each end face. That is, the second reflective film 9 is positioned on the second end face 4b of each of the multiple laser structures 4, and covers each second end face 4b. The second reflective film 9 is formed continuously across the second end faces 4b of the multiple laser structures 4. The second reflective film 9 covers the other end face of the outer edge of the insulating film 10 in the second direction D2, and the other end face of the outer edge of the cathode electrode 11 in the second direction D2.

[0056] The second reflective layer 9 is, for example, α-Si or Al ２ O ３ It is formed by stacking multiple layers formed by [the same process]. For example, the second reflective film 9 is made of three Al ２ O ３ It is formed by stacking layers and three α-Si layers alternately, one layer at a time.

[0057] As shown in Figure 5(b), the reflectance of the second reflective film 9 is not wavelength-dependent. Specifically, the reflectance of the second reflective film 9 is substantially constant within the wavelength range of light that each laser structure 4 can oscillate. "Substantially constant reflectance within the wavelength range of light that the laser structure 4 can oscillate" means that within the wavelength range of light that the laser structure 4 can oscillate, the reflectance is within ±5% of the average reflectance value.

[0058] When the reflectivity of the first reflective film 8 is R1, the reflectivity of the second reflective film 9 is R2, the distance between the first end face 4a and the second end face 4b in the second direction D2 (resonator length) is L, and the mirror loss is αm, then the equation αm = {1 / (2 × L)} × ln{1 / (R1 × R2)} holds true. The mirror loss αm is 10 to 20 cm at a predetermined wavelength included in the wavelength range of light that each laser structure 4 can oscillate. －１ Preferably 15 [cm] －１ Figure 6(a) shows the value of R1 × R2 when the distance L is relatively small (short resonator), and Figure 6(b) shows the value of R1 × R2 when the distance L is relatively large (long resonator). In Figure 6(a), αm = 15 [cm] at a predetermined wavelength λa. －１ The condition is satisfied, and in Figure 6(b), αm = 15 [cm] at a predetermined wavelength λb. －１ The following condition is met. In the case of a long resonator, the distance L is relatively large, but as shown in Figure 6(b), the value of R1 × R2 is small, so the mirror loss αm becomes large. Thus, the mirror loss αm depends on the distance L, and the optimal shape of R1 × R2 differs depending on the distance L.

[0059] In the semiconductor laser element 1, light is generated in the active region 41 when a voltage is applied between the cathode electrode 11 and the anode electrode 12. The light generated in the active region 41 is reflected by the first reflective film 8 and the second reflective film 9, and is amplified as it reciprocates between the first end face 4a and the second end face 4b along the second direction D2. The amplified light is emitted from the first end face 4a as laser light L0 along the second direction D2.

[0060] Each of the stacked structures LS2 and LS3 has the same stacked structure as the stacked structure of the stacked structure LS1 described above. That is, each of the stacked structures LS2 and LS3 has an n-type buffer layer 3, a plurality of laser structures 4, a plurality of tunnel junction layers 5, a p-type graded layer 6, and a p-type contact layer 7. The plurality of stacked structures LS1, LS2, and LS3 are formed as follows. In the process of manufacturing the semiconductor laser element 1, an n-type buffer layer 3, one laser structure 4, one tunnel junction layer 5, one laser structure 4, one tunnel junction layer 5, one laser structure 4, a p-type graded layer 6, and a p-type contact layer 7 are stacked on the semiconductor substrate 2 in this order. After these layers are formed, a portion of these layers is removed by etching, thereby forming a pair of trenches TR and the plurality of stacked structures LS1, LS2, and LS3. [Operation and Effects]

[0061] In the semiconductor laser element 1, a plurality of laser structures 4 having the same resonance direction are stacked on a semiconductor substrate 2 made of GaAs, with a tunnel junction layer 5 placed between two adjacent laser structures 4. A first reflective film 8 and a second reflective film 9 are placed on the first end faces 4a and second end faces 4b of the plurality of laser structures 4 in the resonance direction. With this configuration, light resonates between the first end face 4a and the second end face 4b in the plurality of laser structures 4, and amplified light is emitted from each of the plurality of laser structures 4. Therefore, the output of the laser light L0 can be improved compared to when a single laser structure is used. In addition, in each laser structure 4, an n-type carrier block layer 46 and a p-type carrier block layer 47 are placed on both sides of the active region 41 which includes a first quantum well layer 411 and a second quantum well layer 412 made of InGaAs, and an n-type cladding layer 44 and a p-type cladding layer 45 made of AlGaAs are placed on both sides of the n-type carrier block layer 46 and the p-type carrier block layer 47. With this configuration, carriers are confined to the active region 41 by the n-type carrier block layer 46 and the p-type carrier block layer 47, so the n-type cladding layer 44 and the p-type cladding layer 45 can be designed to have at least the function of confining light generated in the active region 41. In other words, if the n-type carrier block layer 46 and the p-type carrier block layer 47 are not arranged on both sides of the active region 41, it is necessary to design the n-type cladding layer 44 and the p-type cladding layer 45 to have both the function of carrier confinement and light confinement, but this is not necessary with this configuration. Furthermore, the n-type carrier block layer 46 has a thickness smaller than the n-type cladding layer 44, and the p-type carrier block layer 47 has a thickness smaller than the p-type cladding layer 45. With this configuration, the influence of the n-type carrier block layer 46 and the p-type carrier block layer 47 on the light confinement function can be reduced, so the design constraints on the n-type cladding layer 44 and the p-type cladding layer 45 can be relaxed.This facilitates the design of a semiconductor substrate 2 formed of GaAs and the n-type cladding layer 44 and p-type cladding layer 45 formed of AlGaAs, respectively, to alleviate lattice mismatch. For example, it becomes easier to reduce the amount of Al in the n-type cladding layer 44 and p-type cladding layer 45 to alleviate lattice mismatch. As a result, it becomes possible to suppress the deterioration of the quality of the laser light L0 caused by warping of the semiconductor laser element 1, etc. Thus, with the above semiconductor laser element, it is possible to improve the output of the laser light L0 while suppressing the deterioration of the quality of the laser light L0.

[0062] The above actions and effects are supplemented below. When increasing the number of stacks to 3, 5, 6, or 7 stages in order to increase power output, there is a risk that the distortion caused by the difference in lattice constants (lattice mismatch) between the semiconductor substrate formed by GaAs and the cladding layer formed by AlGaAs will increase. In the conventionally used SCH (Separate confinement heterostructure) structure, there is no carrier block layer, and the concentration of Al in the cladding layer affects both carrier confinement and light confinement. Therefore, when the concentration of Al in the cladding layer is reduced to mitigate lattice mismatch, it becomes difficult to design a laser structure that can achieve both a height of potential barrier for carrier confinement and a suitable refractive index distribution for light confinement. In other words, the degree of design freedom is small. In contrast, in this embodiment, carrier confinement to the active region 41 is achieved by increasing the concentration of Al in the n-type carrier block layer 46 and the p-type carrier block layer 47. As a result, the n-type cladding layer 44 and the p-type cladding layer 45 can be designed considering only the light confinement function, without considering the carrier confinement function. Therefore, the semiconductor laser element 1 facilitates the design of mitigating lattice mismatch.

[0063] From the viewpoint of sufficiently minimizing the influence of the n-type carrier block layer 46 and the p-type carrier block layer 47 on the light confinement function, it is preferable that each of the n-type carrier block layer 46 and the p-type carrier block layer 47 is sufficiently thinner than the oscillation wavelength. For example, if the thickness of each of the n-type carrier block layer 46 and the p-type carrier block layer 47 is 1 / 10 or less of the oscillation wavelength, the influence on the light confinement function can be sufficiently minimized.

[0064] In the semiconductor laser element 1, the mirror loss αm is 15 cm at a predetermined wavelength included in the wavelength range of light that each laser structure 4 can oscillate. －１ This configuration allows the central wavelength of the laser light L0 to remain longer than a predetermined wavelength when the operating temperature of the semiconductor laser element 1 increases, and the shape of the laser light L0 spectrum is less likely to be distorted (these are findings discovered by the inventors). Therefore, it is possible to fix the central wavelength of the laser light L0 to a specific wavelength while maintaining the steepness of the laser light L0 spectrum.

[0065] The above effects and benefits are further supported by experimental results. Figure 7(a) shows the experimental results of the laser light spectrum at different operating temperatures when using the SCH structure. Figure 7(b) shows the experimental results of the laser light spectrum at different operating temperatures when using the DCH structure. In these SCH and DCH structures, as with the first reflective film 8 and second reflective film 9 described above, the reflectivity of one reflective film was wavelength-dependent, while the reflectivity of the other reflective film was flat. From the results in Figures 7(a) and (b), it can be seen that in both the SCH and DCH structures, the central wavelength of the laser light remains fixed even as the operating temperature increases.

[0066] In the SCH structure, as shown in Figure 7(a), the spectral shape becomes distorted as the operating temperature increases. In contrast, in the DCH structure, as shown in Figure 7(b), the spectral shape does not become distorted even when the operating temperature increases. The reason for this will be explained with reference to Figures 8(a) and (b). When the voltage applied to the semiconductor laser element is increased and the number of carriers injected into the active region increases, the gain spectrum of the material increases. In the case of a quantum well structure, the gain spectrum of the material becomes flat as the ground level saturates. In the DCH structure, the carrier confinement effect is high, and the ground level saturates more easily than in the SCH structure. Therefore, it is thought that the gain spectrum of the DCH structure material shown in Figure 8(b) is more likely to be flatter than the gain spectrum of the SCH structure material shown in Figure 8(a). Considering the effective gain spectrum obtained by multiplying the reflectance spectrum (the product of the reflectance of the first reflective layer and the reflectance of the second reflective layer) by the gain spectrum of the material, the SCH structure has multiple peaks in its effective gain spectrum, whereas the DCH structure has a single peak in its effective gain spectrum. Therefore, as shown in Figure 7(b), the steepness of the laser light spectrum is maintained in the DCH structure.

[0067] Figure 9(a) shows the experimental results of laser beam output when using a 3-stage stacked SCH structure, Figure 9(b) shows the experimental results of laser beam output when using a 5-stage stacked SCH structure, and Figure 9(c) shows the experimental results of laser beam output when using a 5-stage stacked DCH structure. Figure 10(a) shows the experimental results of the laser beam output ratio when using a 3-stage stacked SCH structure, with the device temperature of 25°C as the reference, Figure 10(b) shows the experimental results of the laser beam output ratio when using a 5-stage stacked SCH structure, and Figure 10(c) shows the experimental results of the laser beam output ratio when using a 5-stage stacked DCH structure. The laser beam output ratio is the ratio of the laser beam output to the laser beam output when the operating temperature is 25°C. As shown in Figures 10(a) and (b), in the SCH structure, the output ratio decreases as the operating temperature increases. In contrast, as shown in Figure 10(c), the DCH structure exhibits relatively low reduction in the power ratio due to rising operating temperature. In the DCH structure, carrier confinement is sufficient even when the operating temperature rises, resulting in stable laser light output.

[0068] In the semiconductor laser element 1, the reflectivity of the second reflective film 9 is substantially constant within the wavelength range of light that each laser structure 4 can oscillate. This configuration makes it possible to easily adjust the reflectivity of the second reflective film 9.

[0069] In the semiconductor laser element 1, the composition ratio of Al in the n-type cladding layer 44 and the p-type cladding layer 45 is, for example, 0.3 or less. With this configuration, lattice mismatch between the semiconductor substrate 2 formed of GaAs and the n-type cladding layer 44 and the p-type cladding layer 45 formed of AlGaAs can be sufficiently mitigated. As a result, it becomes possible to further suppress the deterioration of laser light quality caused by warping of the semiconductor laser element 1, etc.

[0070] In the semiconductor laser element 1, the thickness of the n-type cladding layer 44 is, for example, 500 nm or more, and the thickness of the p-type cladding layer 45 is, for example, 500 nm or more. With this configuration, the light generated in the active region 41 can be sufficiently confined by the n-type cladding layer 44 and the p-type cladding layer 45.

[0071] In the semiconductor laser element 1, the distance T1 between the n-type carrier block layer 46 and the first quantum well layer 411 is, for example, 150 nm or less, and the distance T2 between the p-type carrier block layer 47 and the second quantum well layer 412 is, for example, 150 nm or less. With this configuration, the n-type carrier block layer 46 and the p-type carrier block layer 47 can sufficiently confine carriers in the active region 41. As a result, the energy of the carriers is concentrated to a specific energy, so the voltage applied to the semiconductor laser element 1 to generate light by stimulated emission can be reduced. Therefore, light oscillation by stimulated emission can be easily performed.

[0072] In the semiconductor laser element 1, the thickness of the n-type carrier block layer 46 is, for example, 20 nm or less, and the thickness of the p-type carrier block layer 47 is, for example, 20 nm or less. With this configuration, the influence of the n-type carrier block layer 46 and the p-type carrier block layer 47 on the light confinement function can be reduced. Therefore, the design constraints of the n-type cladding layer 44 and the p-type cladding layer 45 can be sufficiently relaxed.

[0073] In the semiconductor laser element 1, the thickness of the n-type carrier block layer 46 is, for example, 1 / 10 or less of the thickness of the n-type cladding layer 44, and the thickness of the p-type carrier block layer 47 is, for example, 1 / 10 or less of the thickness of the p-type cladding layer 45. With this configuration, the influence of the n-type carrier block layer 46 and the p-type carrier block layer 47 on the light confinement function can be reduced. Therefore, the design constraints on the n-type cladding layer 44 and the p-type cladding layer 45 can be sufficiently relaxed.

[0074] In the semiconductor laser element 1, the n-type carrier block layer 46 is an n-type carrier block layer doped with Te, and the p-type carrier block layer 47 is a p-type carrier block layer doped with C. With this configuration, the diffusion coefficients of the dopants Te and C are relatively small, so the diffusion of Te and C is suppressed. This makes it possible to suppress Te and C from adversely affecting the active region 41.

[0075] In the semiconductor laser element 1, the first quantum well layer 411 and the second quantum well layer 412 are each formed of InGaAs. This configuration allows for the formation of quantum well layers suitable for realizing the desired wavelength of laser light L0.

[0076] In the semiconductor laser element 1, each of the multiple laser structures 4 includes an n-type guide layer 42 disposed between an n-type cladding layer 44 and an n-type carrier block layer 46, and a p-type guide layer 43 disposed between a p-type cladding layer 45 and a p-type carrier block layer 47. With this configuration, the light generated in the active region 41 can be suitably confined in the n-type guide layer 42 and the p-type guide layer 43. [Modification]

[0077] This disclosure is not limited to the embodiments described above. The first quantum well layer 411 and the second quantum well layer 412 may each be formed of AlInGaAs or InGaAsP. That is, the first quantum well layer 411 and the second quantum well layer 412 may each be formed of a GaAs-based compound semiconductor. The number of quantum well layers in the active region 41 may be one or three or more. In other words, the number of quantum wells does not have to be two layers; it may be a single quantum well with one layer, or a multiple quantum well with three or more layers.

[0078] In the above embodiment, there were three laser structures 4 and two tunnel junction layers 5. However, the number of laser structures 4 can be n (where n is an integer greater than or equal to 2), and the number of tunnel junction layers 5 can be n-1.

[0079] In the above embodiment, the reflectance of the second reflective film 9 was substantially constant within the wavelength range of light from which each laser structure 4 can oscillate. However, the reflectance of the second reflective film 9 may be wavelength-dependent. For example, the reflectance of the second reflective film 9 may decrease as the wavelength increases within the wavelength range of light from which each laser structure 4 can oscillate. Neither the reflectance of the first reflective film 8 nor the reflectance of the second reflective film 9 is necessarily wavelength-dependent.

[0080] The composition ratio of Al in the n-type cladding layer 44 and the p-type cladding layer 45 may be 0.3 or more. The thickness of the n-type cladding layer 44 and the p-type cladding layer 45 may be 500 nm or less. Each laser structure 4 does not need to have an n-type guide layer 42 and a p-type guide layer 43.

[0081] The distance T1 between the n-type carrier block layer 46 and the first quantum well layer 411 may be 150 nm or more. The distance T2 between the p-type carrier block layer 47 and the second quantum well layer 412 may be 150 nm or more.

[0082] The thickness of the n-type carrier block layer 46 may be 20 nm or more. The thickness of the n-type carrier block layer 46 may be 1 / 10 or more of the thickness of the n-type cladding layer 44. The thickness of the p-type carrier block layer 47 may be 20 nm or more. The thickness of the p-type carrier block layer 47 may be 1 / 10 or more of the thickness of the p-type cladding layer 45.

[0083] The n-type carrier block layer 46 may be doped with n-type impurities other than Te. The p-type carrier block layer 47 may be doped with p-type impurities other than C. In the above embodiment, each laser structure 4 has the same configuration as the others, but each laser structure 4 may have different configurations as long as the wavelength ranges of the light emitted by each laser structure 4 overlap with each other.

[0084] The semiconductor laser element 1 may have other configurations, such as a configuration in which the n-type and p-type are reversed. For example, the n-type guide layer 42, the n-type cladding layer 44, and the n-type carrier block layer 46 may be a p-type guide layer, a p-type cladding layer, and a p-type carrier block layer, respectively. The p-type guide layer 43, the p-type cladding layer 45, and the p-type carrier block layer 47 may be an n-type guide layer, an n-type cladding layer, and an n-type carrier block layer, respectively.

[0085] The following disclosures can be extracted from the above embodiments. The quality of the laser light output from a semiconductor laser element (e.g., intensity distribution at the irradiation spot, spectral shape) is an important parameter in various applications. The following disclosures make it possible to improve the output of the laser light while suppressing a decrease in the quality of the laser light. The following disclosures also produce the above-mentioned effects and benefits described with reference to Figures 7 to 10.

[0086] A semiconductor laser element according to one aspect of the present disclosure comprises: a semiconductor substrate; a laser structure laminated on the semiconductor substrate along a first direction which is the thickness direction of the semiconductor substrate, with a second direction intersecting the first direction as the resonance direction; a first reflective film disposed on a first end face on one side of the laser structure in the second direction; and a second reflective film disposed on a second end face on the other side of the laser structure in the second direction, wherein the laser structure comprises: an active region including a quantum well layer; a first cladding layer of a first conductivity type disposed on the semiconductor substrate side with respect to the active region; a second cladding layer of a second conductivity type disposed on the opposite side of the semiconductor substrate with respect to the active region; and disposed between the active region and the first cladding layer. The laser structure includes a first carrier block layer of a first conductivity type having a thickness smaller than the thickness of the first cladding layer, and a second carrier block layer of a second conductivity type disposed between the active region and the second cladding layer, having a thickness smaller than the thickness of the second cladding layer, wherein the first reflective film has a reflectance that decreases as the wavelength increases in the wavelength range of light on which the laser structure can oscillate, the reflectance of the first reflective film is R1, the reflectance of the second reflective film is R2, the distance between the first end face and the second end face is L, and the mirror loss is αm, then αm = {1 / (2 × L)} × ln{1 / (R1 × R2)} holds, and the mirror loss is 15 [cm] at a predetermined wavelength included in the wavelength range. －１ It may also be a semiconductor laser element.

[0087] 1...Semiconductor laser element, 2...Semiconductor substrate, 4...Laser structure, 4a...First end face, 4b...Second end face, 5...Tunnel junction layer, 8...First reflective film, 9...Second reflective film, 41...Active region, 42...n-type guide layer, 43...p-type guide layer, 44...n-type cladding layer, 45...p-type cladding layer, 46...n-type carrier block layer, 47...p-type carrier block layer, 411...First quantum well layer, 412...Second quantum well layer, D1...First direction, D2...Second direction, L, T1, T2...Distance.

Claims

1. A semiconductor substrate formed of GaAs; a plurality of laser structures stacked on the semiconductor substrate along a first direction which is the thickness direction of the semiconductor substrate, with a second direction intersecting the first direction as the resonance direction; a tunnel junction layer disposed between two adjacent laser structures in the first direction; a first reflective film disposed on a first end face on one side of the plurality of laser structures in the second direction; and a second reflective film disposed on a second end face on the other side of the plurality of laser structures in the second direction, wherein each of the plurality of laser structures includes an active region including a quantum well layer formed of a GaAs-based compound semiconductor; a first cladding layer of a first conductivity type formed of AlGaAs, disposed on the semiconductor substrate side with respect to the active region; a second cladding layer of a second conductivity type formed of AlGaAs, disposed on the opposite side of the semiconductor substrate with respect to the active region; and a first carrier block layer of the first conductivity type disposed between the active region and the first cladding layer, having a thickness smaller than the thickness of the first cladding layer. A semiconductor laser element comprising: a second carrier block layer of a second conductivity type disposed between the active region and the second cladding layer, and having a thickness smaller than the thickness of the second cladding layer.

2. The first reflective film has a reflectivity that decreases as the wavelength increases within the wavelength range in which each of the plurality of laser structures can oscillate, and the reflectivity of the first reflective film is R1, the reflectivity of the second reflective film is R2, the distance between the first end face and the second end face is L, and the mirror loss is αm, then αm = {1 / (2 × L)} × ln{1 / (R1 × R2)} holds true, and the mirror loss is 15 [cm] at a predetermined wavelength included in the wavelength range. －１ The semiconductor laser element according to claim 1.

3. The semiconductor laser element according to claim 2, wherein the reflectance of the second reflective film is substantially constant in the wavelength range.

4. The semiconductor laser element according to any one of claims 1 to 3, wherein the composition ratio of Al in each of the first cladding layer and the second cladding layer is 0.3 or less.

5. The semiconductor laser element according to any one of claims 1 to 4, wherein the thickness of the first cladding layer is 500 nm or more, and the thickness of the second cladding layer is 500 nm or more.

6. The semiconductor laser element according to any one of claims 1 to 5, wherein the distance between the quantum well layer and the first carrier block layer is 150 nm or less, and the distance between the quantum well layer and the second carrier block layer is 150 nm or less.

7. The semiconductor laser element according to any one of claims 1 to 6, wherein the thickness of the first carrier block layer is 20 nm or less, and the thickness of the second carrier block layer is 20 nm or less.

8. The semiconductor laser element according to any one of claims 1 to 7, wherein the thickness of the first carrier block layer is 1 / 10 or less of the thickness of the first cladding layer, and the thickness of the second carrier block layer is 1 / 10 or less of the thickness of the second cladding layer.

9. The semiconductor laser element according to any one of claims 1 to 8, wherein one of the first carrier block layer and the second carrier block layer is a Te-doped n-type carrier block layer, and the other of the first carrier block layer and the second carrier block layer is a C-doped p-type carrier block layer.

10. The semiconductor laser element according to any one of claims 1 to 9, wherein the quantum well layer is formed of InGaAs, AlInGaAs, or InGaAsP.

11. The semiconductor laser element according to any one of claims 1 to 10, wherein each of the plurality of laser structures further comprises a first guide layer of the first conductivity type disposed between the first cladding layer and the first carrier block layer, and a second guide layer of the second conductivity type disposed between the second cladding layer and the second carrier block layer.

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