Semiconductor laser

Abstract

This semiconductor laser comprises: an active layer (103) formed on a substrate (101); an n-type semiconductor layer (106) and a p-type semiconductor layer (107) which are formed in contact with the active layer (103); an n-type electrode (108) connected to the n-type semiconductor layer (106); and a p-type electrode (109) connected to the p-type semiconductor layer (107). The active layer (103) is sandwiched between a first semiconductor layer (104a) and a second semiconductor layer (104b) in the vertical direction when viewed from the substrate 101. Furthermore, a thermally conductive layer (110) formed on the second semiconductor layer (104b) in contact with the p-type electrode (109) and the second semiconductor layer (104b) is provided between the n-type electrode (108) and the p-type electrode (109).

Description

semiconductor laser

[0001] The present invention relates to a semiconductor laser.

[0002] With the explosive increase in communication traffic, there is a demand for optical transceivers that are faster, have larger capacities, consume less power, and are smaller and less expensive.

[0003] A thin-film laser (membrane laser) formed on a thin film of III-V compound semiconductor formed on a Si substrate has a semiconductor layer sandwiched between low-refractive-index materials (e.g., SiO2) on both the top and bottom, achieving high optical confinement in the active layer, thereby enabling low-threshold, i.e., low-power laser oscillation. Furthermore, membrane lasers have a lateral p-i-n structure, which reduces junction capacitance and enables high-speed modulation.

[0004] In addition, since the semiconductor layer of the membrane laser can be formed thin, it is possible to use the same Si optical waveguide and SiO x It is easy to match the effective refractive index with the optical waveguide, and the short taper length of the mode conversion section allows for low-loss optical connection with the above-mentioned optical waveguide. For this reason, membrane lasers have a high affinity for integration with compact, high-performance Si photonics circuits. With these characteristics, membrane lasers are attracting attention as key devices for the above-mentioned optical transceivers.

[0005] Generally, in semiconductor lasers, a current is injected into the active layer to cause laser oscillation, but Joule heat is generated as a result of the current injection. This Joule heat (self-heating) increases the temperature of the active layer, deteriorating the laser characteristics (e.g., optical output power and modulation speed).

[0006] In particular, in membrane lasers, the active layer is surrounded by a material with high thermal resistance (e.g., SiO2), so the temperature rise is more significant than in general semiconductor lasers, which has hindered the membrane laser from achieving even higher optical output and faster modulation operation.

[0007] Generally, a semiconductor laser or an optical circuit chip on which a semiconductor laser is integrated is housed in a metal housing and, if necessary, placed on a carrier via a TEC. The housing containing the optical circuit chip is cooled by natural or forced air cooling.

[0008] To prevent degradation of optical output and modulation speed due to self-heating of semiconductor lasers, a thermoelectric cooler (TEC) is used to maintain a constant chip temperature. However, the TEC consumes a lot of power, making it unsuitable for reducing the power consumption of optical transceivers. Furthermore, the greater the heat generated by the semiconductor laser, the greater the power consumption of the TEC. Furthermore, the heat generated by the TEC itself increases the temperature of the housing, placing stricter demands on the housing cooling performance.

[0009] From the above considerations, in applications where the fluctuation margin of the absolute value of the oscillation wavelength of a semiconductor laser is large, a configuration that does not use a TEC is desirable, and for this purpose, it is important to reduce the amount of self-heating of the semiconductor laser.

[0010] S. Yamaoka et al., "Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate", Nature Photonics, vol. 15, pp. 28-35, 2021.

[0011] Conventionally, as shown in Non-Patent Document 1, by forming a membrane laser on a SiC substrate with low thermal resistance, it is possible to suppress the deterioration of characteristics due to self-heating and realize high-speed, low-power operation. However, the refractive index of SiC is about n = 2.6 in the communication wavelength band, and it is difficult to use an optical waveguide with a low refractive index (e.g., SiO x Furthermore, because a SiC substrate is used, there was also the issue that it could not be integrated with a Si photonics circuit.

[0012] The present invention has been made to solve the above problems, and aims to suppress performance degradation due to laser self-heating while allowing integration with optical waveguides made of low refractive index materials and Si photonics circuits.

[0013] a first cladding layer formed on a substrate; an active layer made of a compound semiconductor formed on the first cladding layer; first and second semiconductor layers made of undoped compound semiconductor formed on the substrate above and below the active layer; an n-type semiconductor layer and a p-type semiconductor layer formed on the first cladding layer in contact with the active layer and sandwiching a stacked structure made of the first semiconductor layer, active layer, and second semiconductor layer; an n-type electrode connected to the n-type semiconductor layer; a p-type electrode connected to the p-type semiconductor layer; a resonator formed on the substrate; a thermal conduction layer formed on the second semiconductor layer in contact with the p-type electrode and the second semiconductor layer, between the n-type electrode and the p-type electrode; and a second cladding layer formed on the thermal conduction layer.

[0014] As described above, according to the present invention, a thermal conduction layer is formed on the second semiconductor layer between the n-type electrode and the p-type electrode, in contact with the p-type electrode and the second semiconductor layer. This makes it possible to suppress performance degradation due to self-heating of the laser, while allowing integration with an optical waveguide made of a low refractive index material or a Si photonics circuit.

[0015] FIG. 1 is a cross-sectional view showing the configuration of a semiconductor laser according to a first embodiment of the present invention. FIG. 2 is a plan view showing a partial configuration of the semiconductor laser according to the first embodiment of the present invention. FIG. 3A is a distribution diagram showing the results of heat conduction analysis of a conventional semiconductor laser calculated using a heat conduction simulator. FIG. 3B is a distribution diagram showing the results of heat conduction analysis of a conventional semiconductor laser calculated using a heat conduction simulator. FIG. 3C is a distribution diagram showing the results of heat conduction analysis of a semiconductor laser according to an embodiment calculated using a heat conduction simulator. FIG. 3D is a distribution diagram showing the results of heat conduction analysis of a semiconductor laser according to an embodiment calculated using a heat conduction simulator. FIG. 4 is a cross-sectional view showing the configuration of another semiconductor laser according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view showing the configuration of a semiconductor laser according to a second embodiment of the present invention. FIG. 6 is a plan view showing a partial configuration of a semiconductor laser according to the second embodiment of the present invention. FIG. 7A is a characteristic diagram showing the threshold gain of a DFB laser using a complex-coupled diffraction grating. FIG. 7B is a characteristic diagram showing the calculation results of the oscillation spectrum in the fundamental mode of a DFB laser using a complex-coupled diffraction grating.

[0016] A semiconductor laser according to an embodiment of the present invention will now be described.

[0017] First Embodiment First, a semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS.

[0018] First, a semiconductor laser according to a first embodiment of the present invention will be described with reference to Fig. 1. This semiconductor laser includes an active layer 103 formed on a substrate 101, an n-type semiconductor layer 106 and a p-type semiconductor layer 107 formed in contact with the active layer 103, an n-type electrode 108 connected to the n-type semiconductor layer 106, and a p-type electrode 109 connected to the p-type semiconductor layer 107. In this configuration, a current is injected into the active layer 103 in a direction parallel to the plane of the substrate 101. This semiconductor laser is a so-called membrane laser.

[0019] A first cladding layer 102 is formed on a substrate 101, and an active layer 103 is formed thereon. The active layer 103 is sandwiched between a first semiconductor layer 104a and a second semiconductor layer 104b in the vertical direction when viewed from the substrate 101. The stacked structure of the first semiconductor layer 104a, the active layer 103, and the second semiconductor layer 104b is sandwiched between an n-type semiconductor layer 106 and a p-type semiconductor layer 107. The n-type semiconductor layer 106 and the p-type semiconductor layer 107 are formed to sandwich the active layer 103 in a direction parallel to the plane of the substrate 101.

[0020] In this example, an active layer 103 is formed on and in contact with a first semiconductor layer 104a, and a second semiconductor layer 104b is formed on and in contact with the active layer 103. The first semiconductor layer 104a and the second semiconductor layer 104b can be made of compound semiconductors having a lower refractive index and a larger band gap than the active layer 103. With this configuration, a buried heterostructure can be formed by the first semiconductor layer 104a, the active layer 103, and the second semiconductor layer 104b. In addition, an n-type semiconductor layer 106 and a p-type semiconductor layer 107 are formed on the sides of the stacked structure of the first semiconductor layer 104a, the active layer 103, and the second semiconductor layer 104b.

[0021] Furthermore, a thermal conduction layer 110 is provided between the n-type electrode 108 and the p-type electrode 109, and is formed on the second semiconductor layer 104b in contact with the p-type electrode 109 and the second semiconductor layer 104b. In the first embodiment, the thermal conduction layer 110 is formed in contact with the first semiconductor layer 104a and the second semiconductor layer 104b. In addition, a second clad layer 111 is formed on the thermal conduction layer 110 between the n-type electrode 108 and the p-type electrode 109.

[0022] This semiconductor laser also includes a resonator formed on the substrate 101. For example, the active layer 103 extends a predetermined length in the light propagation direction. A resonator can be configured as a distributed feedback (DFB) laser by using a diffraction grating 105 formed in a region that couples with the mode field of the active layer 103 configured in this manner. In this example, the diffraction grating 105 is formed on the second semiconductor layer 104b. A resonator can also be configured as a distributed Bragg reflector (DBR) laser by using a diffraction grating structure (not shown) formed on an extension of the optical waveguide formed by the active layer 103.

[0023] The substrate 101 may be made of, for example, silicon, and the first cladding layer 102 may be made of, for example, SiO2. The first cladding layer 102 may be made of, for example, SiO2, which is silica with an adjusted Si and O composition. x The second cladding layer 111 can be made of, for example, SiO2, SiN, etc.

[0024] The active layer 103 can be made of a compound semiconductor such as InGaAsP, InGaAs, or InGaAlAs, and can have a multiple quantum well (MQW) structure in which the above-mentioned compound semiconductors are stacked with different compositions.

[0025] The first semiconductor layer 104a and the second semiconductor layer 104b can be made of, for example, undoped InP (i-InP). Alternatively, the first semiconductor layer 104a and the second semiconductor layer 104b can be made of InGaAsP, InGaAlAs, or the like, which has a larger band gap than the active layer 103. By forming a buried heterostructure with this configuration, it becomes possible to efficiently inject light and carriers into the active layer 103.

[0026] The n-type semiconductor layer 106 contains 1×10 18 cm -3 The p-type semiconductor layer 107 is made of n-type InP (n-InP) doped to a degree of 1×10 18 cm -3The n-type semiconductor layer 106 and the p-type semiconductor layer 107 may be made of p-type InP (p-InP) doped to a certain extent. In order to reduce electrical resistance, a contact layer made of InGaAsP or the like may be formed on the n-type semiconductor layer 106 and the p-type semiconductor layer 107, and an n-type electrode 108 and a p-type electrode 109 may be formed on the contact layer.

[0027] The thermal conduction layer 110 can be made of any of AlN, Al2O3, SiC, and BeO.

[0028] For example, the thermal conduction layer 110 can be made of AlN, a highly thermoelectric material, and have a thickness of about 100 nm, and can be formed in contact with the n-type electrode 108 and the p-type electrode 109, which are made of Au and have a thickness of 6 μm.

[0029] According to the first embodiment, as shown by the arrows in FIG. 2, heat generated by self-heating of the semiconductor laser moves to n-type electrode 108 and p-type electrode 109 via thermal conduction layer 110 .

[0030] Next, the results of a thermal conduction analysis of a semiconductor laser calculated using a general thermal conduction simulator will be described with reference to Figures 3A, 3B, 3C, and 3D. In Figures 3A, 3B, 3C, and 3D, the lower figures show a calculation model. In the calculation model, a heat source was placed in the p-type semiconductor layer 107, which has a relatively high electrical resistance, between the p-type electrode 109 and the active layer 103. The heat quantity per unit length was assumed to be 500 mW / 1 mm. The ambient temperature was also assumed to be 300 K. The active layer 103 had a multiple quantum well structure, and the n-type semiconductor layer 106 and the p-type semiconductor layer 107 were made of InP. The thermal conduction layer 110 was made of AlN. The n-type electrode 108 and the p-type electrode 109 were made of Au. Each cladding layer was made of SiO2.

[0031] 3A shows the analysis results for a conventional semiconductor laser in which the thicknesses of n-type electrode 108 and p-type electrode 109 are 1 μm, and FIG. 3B shows the analysis results for a conventional semiconductor laser in which the thicknesses of n-type electrode 108 and p-type electrode 109 are 6 μm.

[0032] 3C shows the analysis results when the thicknesses of n-type electrode 108 and p-type electrode 109 are set to 6 μm in the semiconductor laser according to the embodiment, and FIG. 3D shows the analysis results when the thicknesses of n-type electrode 108 and p-type electrode 109 are set to 1 μm in the semiconductor laser according to the embodiment.

[0033] In the conventional structure, as shown in FIGS. 3A and 3B , the active layer 103 is surrounded by cladding layers and semiconductor layers, which are made of low thermal conductivity materials. Therefore, the heat generated from the heat source tends to be trapped in the heat source area, resulting in a significant temperature rise in the active layer 103.

[0034] On the other hand, according to the embodiment, as shown in Figure 2(c), heat generated from the heat source flows to the thermal conduction layer 110 via the thermal conduction layer 110, thereby suppressing the temperature rise of the active layer 103. It can also be seen that the effect of improving heat dissipation is significant by providing the thermal conduction layer 110 and thickening the electrodes. For example, while the maximum temperature rise in the conventional structure is 63K, according to the embodiment, it is suppressed to 16K.

[0035] In the above calculation, the temperature of the external atmosphere is assumed to be 300K. However, even if the temperature of the external atmosphere is assumed to be 400K, the amount of temperature rise due to self-heating of the semiconductor laser remains the same as above.

[0036] As described above, according to the first embodiment, the heat generated by the semiconductor laser is efficiently diffused and prevented from building up, thereby suppressing performance degradation and enabling the semiconductor laser to achieve even higher output power and faster modulation operation.

[0037] As shown in Reference 1, AlN is also used as a low-loss optical waveguide core material, and optical loss does not increase even if AlN is placed on top of a membrane laser as the heat conduction layer 110. Furthermore, since the refractive index of AlN is about 2 and the thickness is a thin film of about 100 nm, it does not significantly reduce the optical confinement in the active layer 103.

[0038] According to the first embodiment, the thermal conduction layer 110 is disposed on the active layer 103 (second semiconductor layer 104b) of the semiconductor laser, and the other configurations are the same as those of the conventional laser. Therefore, for example, as shown in Reference 2 or FIG. 4, a core 112 is embedded in the first cladding layer 102 and formed along the active layer 103, and an optical waveguide formed by the core 112 can be provided. The core 112 is disposed in a region that couples with the mode field of the active layer 103.

[0039] According to this configuration, laser light oscillated in the active layer 103 can be coupled to the optical waveguide formed by the core 112. With this configuration, the semiconductor laser according to the first embodiment can be integrated with a Si optical waveguide or a silicon photonics circuit (not shown) that is optically connected to the optical waveguide formed by the core 112, and can be used as a light source for these. Furthermore, by forming an optical waveguide having a supermode using the active layer 103 and the core 112, it is possible to enhance light confinement in the core 112 and reduce internal loss.

[0040] The first cladding layer 102 can be made of, for example, SiO2 as in the conventional case. x Integration with low refractive index waveguides such as optical waveguides is also possible.

[0041] Second Embodiment Next, a semiconductor laser according to a second embodiment of the present invention will be described with reference to FIGS.

[0042] This semiconductor laser includes an active layer 103 formed on a substrate 101, an n-type semiconductor layer 106 and a p-type semiconductor layer 107 formed in contact with the active layer 103, an n-type electrode 108 connected to the n-type semiconductor layer 106, and a p-type electrode 109 connected to the p-type semiconductor layer 107. In this configuration, a current is injected into the active layer 103 in a direction parallel to the plane of the substrate 101.

[0043] A first cladding layer 102 is formed on a substrate 101, and an active layer 103 is formed thereon. The active layer 103 is sandwiched between a first semiconductor layer 104a and a second semiconductor layer 104b in the vertical direction when viewed from the substrate 101. The stacked structure of the first semiconductor layer 104a, the active layer 103, and the second semiconductor layer 104b is sandwiched between an n-type semiconductor layer 106 and a p-type semiconductor layer 107. The n-type semiconductor layer 106 and the p-type semiconductor layer 107 are formed to sandwich the active layer 103 in a direction parallel to the plane of the substrate 101.

[0044] In this example, an active layer 103 is formed on and in contact with a first semiconductor layer 104a, and a second semiconductor layer 104b is formed on and in contact with the active layer 103. The first semiconductor layer 104a and the second semiconductor layer 104b can be made of compound semiconductors having a lower refractive index and a larger band gap than the active layer 103. With this configuration, a buried heterostructure can be formed by the first semiconductor layer 104a, the active layer 103, and the second semiconductor layer 104b. In addition, an n-type semiconductor layer 106 and a p-type semiconductor layer 107 are formed on the sides of the stacked structure of the first semiconductor layer 104a, the active layer 103, and the second semiconductor layer 104b.

[0045] Furthermore, a thermal conduction layer 110a is provided between the n-type electrode 108 and the p-type electrode 109, and is formed on the second semiconductor layer 104b in contact with the p-type electrode 109 and the second semiconductor layer 104b. In the second embodiment, the thermal conduction layer 110a extends from the p-type electrode 109 side to the n-type electrode 108 side and is composed of a plurality of ridges equally spaced in the light propagation direction, and is formed in a comb-like shape when viewed from the normal direction to the plane of the substrate 101. In the second embodiment, the thermal conduction layer 110a is made of a metal such as Au and can have a thickness of approximately 100 nm. In addition, a second cladding layer 111 is formed on the thermal conduction layer 110a between the n-type electrode 108 and the p-type electrode 109. The thermal conduction layer 110a is insulated and separated from the n-type semiconductor layer 106.

[0046] This semiconductor laser also includes a resonator formed on the substrate 101. In the second embodiment, the resonator is made up of a comb-shaped thermal conduction layer 110a consisting of a plurality of ridges. In the second embodiment, the comb-shaped thermal conduction layer 110a has ridges arranged at a period that forms a diffraction grating formed in a region that couples with the mode field of the active layer 103. The thermal conduction layer 110a configured in this manner can form a resonator, and can be used as a distributed feedback (DFB) laser.

[0047] The substrate 101 may be made of, for example, silicon, and the first cladding layer 102 may be made of, for example, SiO2. The first cladding layer 102 may be made of, for example, SiO2, which is silica with an adjusted Si and O composition. x The second cladding layer 111 can be made of, for example, SiO2, SiN, etc.

[0048] The active layer 103 can be made of a compound semiconductor such as InGaAsP, InGaAs, or InGaAlAs, and can have a multiple quantum well (MQW) structure in which the above-mentioned compound semiconductors are stacked with different compositions.

[0049] The first semiconductor layer 104a and the second semiconductor layer 104b can be made of, for example, undoped InP (i-InP). Alternatively, the first semiconductor layer 104a and the second semiconductor layer 104b can be made of InGaAsP, InGaAlAs, or the like, which has a larger band gap than the active layer 103. By forming a buried heterostructure with this configuration, it becomes possible to efficiently inject light and carriers into the active layer 103.

[0050] The n-type semiconductor layer 106 contains 1×10 18 cm -3 The p-type semiconductor layer 107 is made of n-type InP (n-InP) doped to a degree of 1×10 18 cm -3The n-type semiconductor layer 106 and the p-type semiconductor layer 107 may be made of p-type InP (p-InP) doped to a certain extent. In order to reduce electrical resistance, a contact layer made of InGaAsP or the like may be formed on the n-type semiconductor layer 106 and the p-type semiconductor layer 107, and an n-type electrode 108 and a p-type electrode 109 may be formed on the contact layer.

[0051] According to the second embodiment, as shown by the arrows in FIG. 6, heat generated by the self-heating of the semiconductor laser moves to p-type electrode 109 via thermal conduction layer 110a.

[0052] Generally, metals have a high optical loss coefficient. Therefore, when a metal structure is placed above the active layer, the light overlaps with the metal structure, significantly increasing the internal loss of the laser, resulting in degradation of characteristics such as a decrease in optical output and an increase in threshold current.

[0053] In the case of a distributed feedback grating, nodes and peaks of the standing wave occur at the period of the grating. In the thermal conduction layer 110a composed of multiple ridges, ideally, if the nodes of the standing wave occur in the ridged parts and the peaks occur in the non-ridged parts, overlap between light and metal is suppressed, thereby preventing a significant increase in optical loss. Furthermore, modes in which the peaks of the standing wave form ridges are suppressed due to the large optical loss. As a result, the mode at one end of the stop band is automatically selected without providing a phase shift to the grating, and single-mode oscillation can be achieved.

[0054] 7A shows the threshold gain of a DFB laser using the above-described complex-coupled diffraction grating, and FIG. 7B shows the calculation results of the oscillation spectrum in the fundamental mode of a DFB laser using the above-described complex-coupled diffraction grating. As shown in FIGS. 7A and 7B, there is a large difference in the threshold gain between the long-wavelength side and the short-wavelength side. This is because the peaks of the standing waves in the long-wavelength side mode are ridges in the thermal conduction layer, resulting in large optical losses. On the other hand, the nodes of the standing waves in the short-wavelength side mode are ridges in the thermal conduction layer, resulting in reduced optical losses and a relatively low threshold gain. Furthermore, as can be seen from the calculation results of the spectrum in the fundamental mode, a single mode is achieved without any phase shift.

[0055] According to the second embodiment, since the thermal conduction layer 110a is provided as described above, it is expected that the heat generated by the semiconductor laser will be efficiently diffused, and that the heat generated will be prevented from building up. According to the second embodiment, the thermal conduction layer is made of a metal with a large optical loss, but by setting the arrangement period of the thermal conduction layer (each ridge of the layer) to a period that forms a distributed feedback diffraction grating, it is possible to improve heat dissipation without significantly increasing optical loss.

[0056] As described above, according to the embodiment of the present invention, a thermal conduction layer is formed on the second semiconductor layer between the n-type electrode and the p-type electrode, in contact with the p-type electrode and the second semiconductor layer. This makes it possible to suppress performance degradation due to self-heating of the laser in a state where it can be integrated with an optical waveguide made of a low refractive index material or a Si photonics circuit.

[0057] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0058] [Reference 1] DJ Blumenthal, "Photonic integration for UV to IR applications", APL Photonics, vol. 5, no. 2, 020903, 2020. [Reference 2] T. Aihara et al., "Membrane III-V / Si DFB Laser Using Uniform Grating and Width-Modulated Si Waveguide", Journal of Lightwave Technology , vol. 38, no. 11, pp. 2961-2967, 2020.

[0059] 101...Substrate, 102...1st クラッド layer, 103...active layer, 104a...1st semiconductor layer, 104b...2nd semiconductor layer, 105...folded lattice, 106...n-type semiconductor layer, 107...p-type semiconductor layer, 108...n-type electrode, 109...p-type electrode, 110...thermally conductive layer, 111...the second クラッド layer.

Claims

1. A semiconductor laser comprising: a first cladding layer formed on a substrate; an active layer made of a compound semiconductor formed on the first cladding layer; first and second semiconductor layers made of undoped compound semiconductor formed on top and bottom of the active layer on the substrate; an n-type semiconductor layer and a p-type semiconductor layer formed on top of the first cladding layer in contact with the active layer and sandwiching a stacked structure made of the first semiconductor layer, the active layer, and the second semiconductor layer; an n-type electrode connected to the n-type semiconductor layer; a p-type electrode connected to the p-type semiconductor layer; a resonator formed on the substrate; a thermal conduction layer formed on the second semiconductor layer between the n-type electrode and the p-type electrode and in contact with the p-type electrode and the second semiconductor layer; and a second cladding layer formed on the thermal conduction layer.

2. A semiconductor laser according to claim 1, wherein the heat conduction layer is formed in contact with the n-type electrode, the p-type electrode, and the second semiconductor layer, and is made of any one of AlN, Al2O3, SiC, and BeO.

3. A semiconductor laser according to claim 2, wherein the heat conduction layer is formed in contact with the first semiconductor layer and the second semiconductor layer.

4. A semiconductor laser according to claim 1, wherein the heat conduction layer is made up of a plurality of ridges extending from the p-type electrode side to the n-type electrode side and arranged at equal intervals in the light propagation direction, and the resonator is made up of the plurality of ridges.

5. A semiconductor laser according to claim 4, wherein the heat conduction layer is made of metal.

6. A semiconductor laser according to any one of claims 1 to 5, wherein the first semiconductor layer and the second semiconductor layer are made of a compound semiconductor having a smaller refractive index and a larger band gap than the active layer.

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