Semiconductor laser element

Abstract

To provide a semiconductor laser element having a good optical confinement.SOLUTION: A semiconductor laser element includes: an n-side cladding layer; a p-side cladding layer; and an active layer provided between the n-side cladding layer and the p-side cladding layer. The n-side cladding layer includes: a semiconductor part made of a nitride semiconductor; and a low refractive index part made of a medium other than the nitride semiconductor having a lower refractive index than the semiconductor part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor laser device. [Background technology]

[0002] Semiconductor laser elements oscillate at a wavelength determined by the bandgap energy of the active layer, and output coherent light with consistent phase and direction. Semiconductor laser elements using nitride semiconductors can oscillate over a wide wavelength range from ultraviolet to red depending on the material design, and can be widely used as light sources for optical communications, optical recording and playback, sensing, projectors, etc. When guiding light in a semiconductor laser element in a direction perpendicular to the stacking direction, the active layer is sandwiched between cladding layers with a lower refractive index than the active layer, confining the light near the active layer.

[0003] As an example of a surface-emitting laser, a configuration using a photonic crystal in an optical guide layer adjacent to an active layer is known (see, for example, Patent Document 1). A light-emitting device is known in which a low refractive index portion is provided in the p-side cladding layer to reduce light absorption in the p-side electrode on the opposite side of the substrate side of the laminate (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 155710 [Patent Document 2] Japanese Patent Application Publication No. 2019-83232 Summary of the Invention [Problem to be solved by the invention]

[0005] In semiconductor laser devices using nitride semiconductors, when the cladding layer confines light near the active layer, the choice of cladding material is limited. While it is possible to increase the refractive index difference with the core by changing the composition ratio of the semiconductor material in the cladding layer, the change in refractive index when the composition ratio of the cladding layer is changed by a few percent to 10% is, for example, about 5%. Due to the wavelength dependence of the refractive index, the refractive index change due to the mixed crystal becomes smaller as the oscillation wavelength becomes longer, especially in the visible light range, and the choice of material becomes increasingly limited. On the other hand, when a semiconductor layer with a composition ratio different from that of the substrate by 10% or more is grown to a thickness of several hundred nanometers while maintaining crystal quality, cracks may occur.

[0006] One aspect of the present disclosure provides a semiconductor laser device with good optical confinement. [Means for solving the problem]

[0007] In one embodiment of the present disclosure, the semiconductor laser device comprises: an n-side cladding layer; a p-side cladding layer; an active layer provided between the n-side cladding layer and the p-side cladding layer; The n-side cladding layer has a semiconductor portion made of a nitride semiconductor and a low refractive index portion made of a medium other than a nitride semiconductor and having a refractive index lower than that of the semiconductor portion. [Effects of the Invention]

[0008] A semiconductor laser device with good optical confinement is realized. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view perpendicular to the waveguide direction of a semiconductor laser element according to an embodiment. [Figure 2] 2 is a cross-sectional view taken along the waveguiding direction of a laminate of the semiconductor laser device of FIG. 1. FIG. [Figure 3] 1 is a cross-sectional view of a laminate used in the semiconductor laser device of the first embodiment. [Figure 4]FIG. 4 is a diagram showing the light intensity distribution of the semiconductor laser element of FIG. [Figure 5] 3 shows a spectrum when the semiconductor laser element of the first embodiment is oscillated in single mode. [Figure 6] 3 shows a spectrum when the semiconductor laser element of the first embodiment is oscillated in multimode. [Figure 7] FIG. 10 is a cross-sectional view of a laminate used in the semiconductor laser device of the second embodiment. [Figure 8] FIG. 8 is a diagram showing the light intensity distribution of the semiconductor laser element of FIG. [Figure 9] FIG. 10 is a cross-sectional view of a laminate used in the semiconductor laser device of the third embodiment. [Figure 10] FIG. 10 is a diagram showing the light intensity distribution of the semiconductor laser element of FIG. [Figure 11] FIG. 10 is a cross-sectional view of a laminate used in the semiconductor laser device of the fourth embodiment. [Figure 12] FIG. 12 is a diagram showing the light intensity distribution of the semiconductor laser element of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. The following description is intended to embody the technical concept of the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following description. In each drawing, components having the same function may be assigned the same reference numerals. For convenience, the embodiments may be shown separately in consideration of ease of explanation or understanding of the main points, but partial substitution or combination of configurations shown in different embodiments or examples is possible. In the embodiments shown later, differences from the previously shown embodiments will be mainly described, and overlapping descriptions of commonalities with the previously shown embodiments may be omitted. The size and positional relationship of components shown in each drawing may be exaggerated for clarity.

[0011] (Configuration of semiconductor laser element) Fig. 1 is a cross-sectional view perpendicular to the waveguiding direction of a semiconductor laser device 10 according to an embodiment, and Fig. 2 is a cross-sectional view along the waveguiding direction of a laminate 15 of the semiconductor laser device 10 of Fig. 1. The waveguiding direction is the direction along the cavity length in which light repeats. In the coordinate systems of Figs. 1 and 2, the waveguiding direction of the semiconductor laser device 10 is defined as the Y direction, the stacking direction of the semiconductor laser device 10 is defined as the Z direction, and the direction perpendicular to the Y and Z directions is defined as the X direction.

[0012] The semiconductor laser device 10 includes an n-side cladding layer 12, a p-side cladding layer 14, and an active layer 13 provided between the n-side cladding layer 12 and the p-side cladding layer 14. The n-side cladding layer 12 includes a semiconductor portion 121 made of a nitride semiconductor and a low-refractive-index portion 122 made of a medium other than a nitride semiconductor. The refractive index of the low-refractive-index portion 122 is lower than that of the semiconductor portion 121. By forming the n-side cladding layer 12 with the semiconductor portion 121 made of a nitride semiconductor and the low-refractive-index portion 122 made of a medium other than a nitride semiconductor that has a lower refractive index than a nitride semiconductor, the refractive index of the n-side cladding layer 12 as a whole is lowered, thereby improving light confinement in the active layer 13. The medium other than a nitride semiconductor may be, for example, a gas such as air, a solid or semi-solid oxide, a resin, or a polymer.

[0013] The n-side cladding layer 12, the active layer 13, and the p-side cladding layer 14 form a laminate 15 that constitutes the optical waveguide of the semiconductor laser device 10. The Z direction from the n-side cladding layer 12 toward the p-side cladding layer 14 is the lamination direction of the semiconductor laser device 10. In this specification, the term "cladding layer" refers to a layer that has the optical function of confining light in the core. The n-side cladding layer 12 and the p-side cladding layer 14 have the optical confinement function for the active layer 13 and have a lower refractive index than the active layer 13. When the active layer 13 has a quantum well structure including well layers and barrier layers, the refractive index of the n-side cladding layer 12 and the p-side cladding layer 14 is lower than the refractive index of the well layer, which means that the n-side cladding layer 12 and the p-side cladding layer 14 have a lower refractive index than the active layer 13. When comparing the refractive index of the n-side cladding layer 12 having the low-refractive-index portion 122 with the refractive index of the active layer 13, the effective refractive index of the n-side cladding layer 12, taking into account the ratio of the low-refractive-index portion 122 to the semiconductor portion 121 in the waveguide direction, may be used as the refractive index of the n-side cladding layer 12. The refractive index of the semiconductor portion 121 may be lower than that of the active layer 13, and the n-side cladding layer 12 may be considered to have a lower refractive index than the active layer 13. The same applies when the p-side cladding layer has a low-refractive-index portion. Either or both of the n-side cladding layer 12 and the p-side cladding layer 14 may be formed of a material having a lower refractive index and a larger bandgap energy than the active layer 13, thereby providing carrier confinement as well as light confinement. In the example shown in FIGS. 1 and 2, for simplicity of explanation, the semiconductor layers constituting the stack 15 are illustrated as three layers: the n-side cladding layer 12, the active layer 13, and the p-side cladding layer 14. The stack 15 may include other layers such as a p-side contact layer, an n-side contact layer, a p-side optical guide layer, and an n-side optical guide layer.

[0014] The semiconductor laser device 10 is driven, for example, by current injection. The semiconductor laser device 10 has an electrode 16 (p-side electrode) electrically connected to the p-side cladding layer 14 and an electrode 17 (n-side electrode) electrically connected to the n-side cladding layer 12. The electrode 17 may be electrically connected to the n-side cladding layer 12 via another layer (e.g., an n-side contact layer or a conductive substrate) provided between the electrode 17 and the n-side cladding layer 12. In the example of FIG. 1, the electrode 17 is provided on the back surface of the conductive substrate 11. However, the substrate 11 may be removed and the electrode 17 may be provided on the back surface of an n-side contact layer provided as part of the n-side semiconductor. When the p-side cladding layer 14 is made of a semiconductor, the electrode 16 may be electrically connected to the electrode 16 via another layer (e.g., a p-side contact layer) provided between the electrode 16 and the p-side cladding layer 14. The p-side cladding layer 14 is not limited to a semiconductor material as long as it has a light confinement function for the active layer 13. It may also be a layer of a conductive oxide such as ITO, IZO, or IZTO. When the p-side cladding layer 14 is a layer of a conductive oxide, the p-side cladding layer 14 can also serve as a p-electrode.

[0015] In the example of FIG. 1, the laminate 15 is processed into the shape of a ridge 19, and the surface of the laminate 15 is covered with an insulating layer 18. In the portion of the laminate 15 where the thickness is increased by the ridge 19, the effective refractive index experienced by the light emitted by the active layer 13 increases, and the light is laterally confined in the vicinity of the active layer 13 directly below the ridge 19. The ridge 19 may be formed to a depth that does not reach the active layer 13, or may be formed by digging deeper than the active layer 13. The ridge 19 is not essential for the semiconductor laser device 10, and the ridge 19 may not be provided.

[0016] The laser light emitted by the semiconductor laser device 10 may be ultraviolet light or visible light. Among semiconductor laser devices using nitride semiconductors, those emitting blue laser light have the highest efficiency. To allow the semiconductor laser device to oscillate at wavelengths shorter than blue, the band gap energy of the active layer 13 is increased compared to that for blue oscillation. In this case, AlGaN, which has a relatively high Al composition ratio, may be used as the n-side cladding layer 12. However, the higher the Al composition ratio, the more difficult it becomes to grow a high-quality n-side cladding layer 12. By using the n-side cladding layer 12 of this embodiment, it is possible to achieve both a reduced refractive index and improved crystallinity. The semiconductor laser device 10 of this embodiment may be a semiconductor laser device emitting laser light in the ultraviolet range. The peak wavelength of the laser light emitted by the semiconductor laser device 10 may be 385 nm or less.

[0017] Furthermore, when the semiconductor laser device 10 oscillates at a wavelength longer than blue, the difference in refractive index due to differences in the composition ratio of the nitride semiconductor decreases as the wavelength increases due to wavelength dispersion. The active layer 13 includes, for example, an InGaN well layer. The oscillation wavelength increases as the In composition ratio of the well layer increases. However, the crystallinity of the nitride semiconductor tends to deteriorate as the In composition ratio increases. Therefore, improving the crystallinity of the n-side cladding layer 12, which also serves as a base layer for forming the active layer 13, is desirable. By using the n-side cladding layer 12 of this embodiment, it is possible to achieve both a reduced refractive index and improved crystallinity. The semiconductor laser device 10 of this embodiment may be a semiconductor laser device that oscillates green laser light or a semiconductor laser device that oscillates laser light with a longer wavelength. The peak wavelength of the laser light oscillated by the semiconductor laser device 10 may be 460 nm or longer.

[0018] In the n-side cladding layer 12, the semiconductor portion 121 made of a nitride semiconductor is, for example, Al x Ga 1-xN, and the Al composition ratio x is less than 0.04. The higher the Al composition ratio in AlGaN, the lower the refractive index. However, even if the Al composition ratio x is about 0.1 (10% in percentage), the refractive index difference with the active layer 13 (for example, the refractive index difference with the well layer) may not be sufficient. Also, the higher the Al composition ratio in AlGaN, the more difficult it is to grow AlGaN with high quality. In particular, when a GaN substrate is used as the substrate 11, the higher the Al composition ratio of AlGaN, the greater the difference in lattice constant with the substrate, so the higher the Al composition ratio, the more difficult it is to grow AlGaN with high quality. In the embodiment, the semiconductor portion 121 of the n-side cladding layer 12 is Al x Ga 1-x When the n-side cladding layer 12 is made of N, the refractive index of the n-side cladding layer 12 as a whole can be reduced by making the Al composition ratio x smaller than 0.04 and introducing the low refractive index portion 122 into the n-side cladding layer 12. This can improve the light confinement effect on the active layer 13. Furthermore, by improving the crystallinity of the n-side cladding layer 12 provided between the substrate 11 and the active layer 13, the crystallinity of the active layer 13 can be improved. The semiconductor laser device 10 can have a substrate. The semiconductor laser device 10 may have a substrate-less structure, which can be achieved by removing the substrate after growing the stack 15 on the substrate.

[0019] The n-side cladding layer 12 may be formed of one or more layers. When the n-side cladding layer 12 includes multiple layers, it is sufficient that the low-refractive-index portion 122 is provided in at least one of the layers. The thickness of the layer in which the low-refractive-index portion 122 is provided is 50 nm or more, preferably 100 nm or more, and more preferably 500 nm or more. This makes it easier to provide the low-refractive-index portion 122 in the n-side cladding layer 12. Furthermore, the greater the thickness of the layer in which the low-refractive-index portion 122 is provided, the greater the height of the low-refractive-index portion 122 in the thickness direction can be, and the lower the refractive index of the n-side cladding layer 12 can be.

[0020] In a preferred configuration example, when the integrated optical intensity in the stacking direction of the semiconductor laser device 10 is taken as 100%, the optical intensity of the n-side cladding layer 12 is 5% or less. Even if the active layer 13 is sandwiched between the n-side cladding layer 12 and the p-side cladding layer 14 to confine light in the active layer 13, a small amount of light leaks in the vertical direction (Z direction). In the embodiment, the refractive index of the n-side cladding layer 12 is reduced by the low-refractive-index portions 122, thereby reducing the light leaking into the n-side cladding layer 12 and reducing the optical intensity in the n-side cladding layer 12. The n-side cladding layer 12 is preferably arranged so that the integrated optical intensity in the stacking direction of the semiconductor laser device 10 in the n-side cladding layer 12 is 5% or less of the total. This allows the n-side cladding layer 12 to function well as a cladding layer. The integrated optical intensity distribution of the n-side cladding layer 12 can be adjusted by the volume or area ratio of the low-refractive-index portions 122 in the cross section along the waveguide direction, the distance from the active layer 13, etc. By using the n-side cladding layer 12 provided with the low-refractive-index portions 122 as a cladding layer, a semiconductor laser device 10 with improved optical confinement can be obtained with a simple structure. A composite layer consisting of the n-side cladding layer 12 and one or more adjacent layers may also function as a cladding layer. In this case, the adjacent one or more layers may be, for example, an AlGaN layer having an Al composition ratio x greater than 0.04. When a composite layer consisting of the n-side cladding layer 12 and one or more adjacent layers functions as a cladding layer, the integrated optical intensity distribution of the n-side cladding layer 12 provided with the low-refractive-index portions 122 may be greater than 5%.

[0021] A layer having a refractive index lower than that of the active layer 13 may be disposed between the n-side cladding layer 12 and the active layer 13. This can further reduce the light intensity in the n-side cladding layer 12. An Al layer having an Al composition ratio y of 0.04 or more may be disposed between the low refractive index portion 122 of the n-side cladding layer 12 and the active layer 13. y Ga 1-y An N layer may be disposed. y Ga 1-y The thickness of the N layer is preferably smaller than the thickness of the n-side cladding layer 12. y Ga 1-yThe provision of the N layer can prevent the deterioration of the crystallinity of the active layer 13.

[0022] In the example of FIG. 2, the low-refractive-index portion 122 is a void. Using a void as the low-refractive-index portion 122 simplifies the manufacturing process. The void may be a hole, such as a cylindrical, polygonal, or elliptical cylinder, or a groove. The void formed in the nitride semiconductor portion 121 may be filled with air or other gas. The low-refractive-index portion 122 does not have to be a void. In this case, the void may be filled with an inorganic material having a lower refractive index than the semiconductor portion 121, or with a polymer or resin to form the low-refractive-index portion 122. Examples of inorganic materials having a lower refractive index than the nitride semiconductor portion 121 include SiO2, TiO2, ZrO2, Al2O3, SiN, and SiON. The provision of the low-refractive-index portion 122 reduces the refractive index of the n-side cladding layer 12 as a whole. The refractive index of the entire n-side cladding layer 12 is, for example, a weighted average of the refractive index of the semiconductor portion 121 and the refractive index of the low-refractive-index portion 122. The weighting coefficient can be determined, for example, by the volume ratio of the semiconductor portion 121 to the low refractive index portion 122, or the area ratio of the low refractive index portion 122 in the XY plane.

[0023] The distribution of the waveguiding direction (Y direction) of the low refractive index portions 122 is periodic in a plane perpendicular to the stacking direction (Z direction) of the semiconductor laser element 10. By making the distribution of the waveguiding direction of the low refractive index portions 122 periodic, it is possible to improve the optical confinement of the semiconductor laser element 10 and to provide wavelength selectivity. Alternatively, the distribution of the waveguiding direction of the low refractive index portions 122 may be random in a plane perpendicular to the stacking direction (Z direction) of the semiconductor laser element 10. In this case, it is possible to improve the optical confinement in the vertical direction of the semiconductor laser element 10 and to achieve high optical output power by performing multi-mode oscillation.

[0024] The low refractive index portions 122 have a periodic distribution in the waveguiding direction in the XY plane perpendicular to the lamination direction, and the period a of the low refractive index portions 122 is λ / (2×n eff), the semiconductor laser device 10 becomes a distributed feedback (DFB) laser and oscillates in a single mode at a single wavelength. Here, λ is the oscillation wavelength of the semiconductor laser device 10, n eff is the effective refractive index of the semiconductor laser element 10 sensed by light of wavelength λ. When the period a of the low refractive index portions 122 is λ / (2×n eff ), the oscillation wavelength λ coincides with the energy or wave number of the Brillouin Zone boundary.

[0025] The low refractive index portion 122 has a periodic distribution in a plane perpendicular to the stacking direction, and the period a is λ / (2×n eff ) is not necessarily an integer multiple. "Not an integer multiple" does not mean that there is an allowance for error, but rather that it is intentionally set to λ / (2×n eff This means that the period is designed by removing the integer multiple of λ / (2×n eff ), the gain width of the active layer 13 does not include the energy of the Brillouin zone boundary, or the upper end (high energy side) of the gain width is less than the energy of the first Brillouin zone. Here, the wavelength at which the peak intensity ratio of the gain curve is 10% is defined as the end of the gain width. The gain width can be identified by observing the emission spectrum of the semiconductor laser device 10. For example, the period a is λ / (2×n eff ) may be set to 0.05 times or more and 0.95 times or less. The period a may be set to λ / (2×n eff ), preferably, the period a is set to λ / (2×n eff ), the semiconductor laser element 10 can be made to oscillate in multiple longitudinal modes. A multi-longitudinal mode laser is suitable for applications that require productivity rather than precision, and can be used, for example, as a light source for a projector, laser processing, etc.

[0026] As will be described later, a low-refractive-index portion may be provided in the p-side cladding layer 14 in addition to the n-side cladding layer 12. In this case, the p-side cladding layer 14 has a second semiconductor portion made of a nitride semiconductor and a second low-refractive-index portion made of a material other than a nitride semiconductor and having a lower refractive index than the second semiconductor portion. This configuration reduces the refractive indexes of both the p-side cladding layer 14 and the n-side cladding layer 12, thereby more effectively confining light near the active layer 13. The second low-refractive-index portion provided in the p-side cladding layer 14 may be a hole or groove that is circular, polygonal, semicircular, elliptical, or the like in a planar view from the Z direction. The inside of the hole or groove may be filled with a gas such as air, or with an inorganic material or resin having a refractive index lower than that of the nitride semiconductor of the p-side cladding layer 14.

[0027] The second low-refractive-index portions of the p-side cladding layer 14 may be arranged periodically or randomly in the waveguide direction in the XY plane perpendicular to the stacking direction. The low-refractive-index portions 122 of the n-side cladding layer 12 may be arranged periodically with a first period in the XY plane, and the second low-refractive-index portions of the p-side cladding layer 14 may be arranged periodically with a second period, where the first period and the second period may be different. By making the first period and the second period different, the arrangement of the low-refractive-index portions becomes random throughout the semiconductor laser device 10, allowing multimode oscillation. The period in the waveguide direction of the low-refractive-index portions 122 of the n-side cladding layer 12 and the period in the waveguide direction of the low-refractive-index portions of the p-side cladding layer 14 may be the same. In this case, the semiconductor laser device operates as a DFB laser.

[0028] As shown in FIG. 2, the semiconductor laser device 10 has end faces 101 and 102 that are perpendicular to the waveguide direction (Y direction). The term "perpendicular to" the waveguide direction means that the end faces 101 and 102 do not need to be at an angle of exactly 90° with respect to the longitudinal axis of the resonator; they may be inclined by approximately ±5°. The end faces 101 and 102 may be reflective surfaces formed by cleavage. Light generated in the active layer 13 travels back and forth between the end faces 101 and 102, where it is amplified and oscillates by stimulated emission. When light is emitted from the end face 101, as indicated by the white arrow in the figure, a highly reflective metal or dielectric multilayer mirror may be formed on the end face 102 opposite the end face 101. The mirror has a reflectivity of 95% or higher, preferably 98% or higher, and more preferably close to 100%. This allows for efficient optical amplification and oscillation.

[0029] (Fabrication process of semiconductor laser element) The semiconductor laser device 10 shown in FIGS. 1 and 2 can be fabricated, for example, by the following process.

[0030] (n-side cladding layer) An n-side cladding layer 12 is formed on a substrate 11. A nitride semiconductor substrate such as GaN is used as the substrate 11. When a GaN substrate having a +c plane ((0001) plane) as its primary surface is used, the n-side cladding layer 12 can be grown on the +c plane in the c-axis direction. When the +c plane is referred to as the "primary surface," it may have an off-angle of ±1° or less relative to the primary surface. The n-side cladding layer 12 is provided as a single-layer or multi-layer semiconductor portion 121 made of a nitride semiconductor such as GaN, InGaN, or AlGaN. Of the nitride semiconductor layers constituting the semiconductor portion 121, a layer located at the interface with the substrate may be grown as a buffer layer.

[0031] The semiconductor portion 121 is, for example, Al x Ga 1-x During or after the growth of the nitride semiconductor layer, n-type impurities such as Si, Ge, Sn, S, Ti, Zr, and O are added at a concentration of 5×10 17 cm -3 That's it, 5 x 10 20 cm -3 Add at the following concentrations:

[0032] (low refractive index part) After forming the nitride semiconductor layer of the n-side cladding layer 12, a mask for forming holes or grooves is formed by known photolithography and etching. Instead of photolithography, a mask pattern for etching may be formed by electron beam lithography or nanoimprinting. The etching of the holes or grooves may be performed by either a dry process or a wet process, but when the pattern of the low refractive index portions 122 is fine, it is preferable to use dry etching such as reactive ion etching (RIE).

[0033] When the holes or grooves formed in the n-side cladding layer 12 are used as voids for the low-refractive-index portions 122, the mask used to form the holes or grooves is removed, and a nitride semiconductor is grown on the surface of the semiconductor portion 121 by metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), or the like. By controlling the growth conditions for MOCVD or HVPE, a nitride semiconductor layer such as GaN can be grown laterally from the surface of the semiconductor portion 121. An n-type impurity may be added during growth of this nitride semiconductor layer to form part of the n-side cladding layer 12. Alternatively, a separate substrate on which the p-side cladding layer 14 and the active layer 13 are formed may be prepared, and the active layer 13 may be bonded to the n-side cladding layer 12. The bonding between the semiconductor portion 121 of the n-side cladding layer 12 with the holes or grooves formed and the active layer 13 formed on the separate substrate may be surface-activated bonding between nitride semiconductors.

[0034] The holes or grooves formed in the n-side cladding layer 12 may be filled with a low refractive index material such as SiO2. In this case, the mask used to form the holes or grooves may be left in place without being removed. After filling the holes or grooves with the low refractive index material, the surface is planarized until the semiconductor portion 121 of the nitride semiconductor is exposed, and a nitride semiconductor such as GaN is grown by MOCVD, HVPE, or the like. By controlling the growth conditions, the nitride semiconductor can also be grown laterally.

[0035] (active layer) The active layer 13 is grown on the n-side cladding layer 12. The active layer 13 is formed, for example, with a quantum well structure. The active layer 13 includes, for example, InGaN well layers. The quantum well structure may be a single quantum well structure or a multiple quantum well structure. In the case of a multiple quantum well structure, a barrier layer having a bandgap energy higher than that of the well layers is disposed between two or more well layers. The barrier layer located at the interface between the n-side cladding layer 12 and the active layer 13 may be used as an n-side optical guiding layer. Similarly, the uppermost barrier layer of the active layer 13 may be used as a p-side optical guiding layer. In this case, the n-side optical guiding layer, the active layer 13, and the p-side optical guiding layer form a waveguide core. The active layer 13 may be formed with a quantum well structure including GaN well layers or AlGaN well layers. In this case, even if the semiconductor portion 121 is made of GaN or AlGaN, the difference in bandgap energy between the semiconductor portion 121 and the well layers constituting the active layer 13 can be increased by providing a low-refractive-index portion 122. This improves the optical confinement efficiency.

[0036] (p-side cladding layer) A p-side cladding layer 14 is grown on the active layer 13. The p-side cladding layer 14 is a nitride semiconductor having a lower refractive index than the well layer included in the active layer 13, and is formed of, for example, AlGaN. In order to increase the refractive index difference between the active layer 13 and the well layer, the Al composition ratio of the p-side cladding layer 14 may be set, for example, in the range of more than 0 and not more than 0.2. The p-type impurity may be 1×10 19 cm -3 More than 1×10 21 cm -3 The following Mg is added: After growing the p-side cladding layer 14, the p-side cladding layer 14 may be processed into the shape of the ridge 19 shown in FIG.

[0037] (electrodes and mirrors) The surface of the p-side cladding layer 14 is covered with an insulating layer 18, and an opening is formed where the electrode is to be formed, forming the p-side electrode 16. The p-side electrode 16 is formed by a known appropriate method, such as sputtering, vacuum deposition, or lift-off. The p-side electrode 16 may be formed of a multilayer film of metals such as Ni / Au. An n-side electrode 17 is formed on the back surface of the substrate 11. In this case, the substrate 11 is a conductive substrate in which an n-type impurity such as Si is added to a GaN substrate. The substrate 11 may be thinned or removed, and the n-side electrode 17 may be formed on the back surface of the n-side contact layer formed as part of the n-side cladding layer 12. The n-side electrode 17 may be formed of a multilayer film of metals such as Ti / Al. The insulating layer 18 may cover the side surface of the laminate 15 constituting the waveguide. A mirror may be formed on the end face 102 of the semiconductor laser device 10 in the waveguide direction, using a highly reflective metal film or a dielectric multilayer film. The mirror may be formed by a physical growth method such as vacuum deposition or sputtering, or a chemical vapor deposition (CVD) method. The end face 101 of the semiconductor laser device 10 in the light emission direction may be a reflective surface obtained by cleavage.

[0038] Various samples of semiconductor laser devices will be fabricated and their optical characteristics will be examined below.

[0039] (First embodiment) FIG. 3 is a cross-sectional view of a laminate 15A used in the semiconductor laser device 10A of the first embodiment. This cross section may be along the waveguide direction or perpendicular to the waveguide direction. The semiconductor laser device 10A has an n-side cladding layer 120A. The n-side cladding layer 120A includes a semiconductor portion 121 made of a nitride semiconductor and a low-refractive-index portion 122 made of a material other than a nitride semiconductor and having a lower refractive index than the semiconductor portion 121. The semiconductor portion 121 is formed of GaN containing n-type impurities (referred to as "n-GaN"). The low-refractive-index portion 122 is an air gap. An n-GaN layer 123 is provided below the n-side cladding layer 120A, and an n-GaN layer 124 is provided on the n-side cladding layer 120A. A GaN substrate may be provided below the n-GaN layer 123. The semiconductor portion 121 of the n-side cladding layer 120A may be grown continuously from the n-GaN layer 123. The thickness of the n-side cladding layer 120A is 500 nm, and the thickness of the n-GaN layer 124 is 60 nm. In the figure, the thickness of the low refractive index portion 122 is set to be equal to the thickness of the n-side cladding layer 120A, but the thickness of the low refractive index portion 122 may be smaller than the thickness of the n-side cladding layer 120A.

[0040] On the n-GaN layer 124, there are arranged an InGaN layer 131 having a thickness of 100 nm, an InGaN layer 133 having a thickness of 200 nm, and an active layer 132 having a thickness of 10 nm provided between the InGaN layers 131 and 133. The active layer 132 and the InGaN layers 131 and 133 sandwiching the active layer 132 from above and below may form a waveguide core. The InGaN layers 131 and 133 may be used as optical guiding layers. The active layer 132 includes an InGaN well layer and a GaN barrier layer.

[0041] The semiconductor device includes, on the InGaN layer 133, a 120-nm-thick GaN layer 141, a 130-nm-thick AlGaN layer 142, a 10-nm-thick p-type impurity-doped AlGaN (referred to as "p-AlGaN") layer 143, a 100-nm-thick p-AlGaN layer 144, and a 20-nm-thick p-GaN layer 145, in this order. The GaN layer 141 and the AlGaN layer 142 may function as part of an optical guide layer. The p-AlGaN layer 143 can be used as an electron blocking layer. The p-AlGaN layer 144 functions as a p-side cladding layer. The Al composition ratio of the p-AlGaN layer 144 is higher than that of the AlGaN layer 142, and the Al composition ratio of the p-AlGaN layer 143 is higher than that of the p-AlGaN layer 144. The uppermost p-GaN layer 145 can be used as a p-side contact layer.

[0042] FIG. 4 shows the light intensity distribution of the semiconductor laser device 10A of FIG. 3. The horizontal axis represents the depth position from the surface of the p-GaN layer 145, and the vertical axis represents the relative light intensity normalized to 1. The peak position coincides with the position of the active layer 132. The shaded area indicates the position of the n-side cladding layer 120A having the low-refractive-index portions 122. The porosity of the low-refractive-index portions 122 is 10%. Here, the porosity refers to the area ratio occupied by the low-refractive-index portions 122 in a plane perpendicular to the stacking direction. The light intensity distribution of the n-side cladding layer 120A with respect to the integrated light intensity of the semiconductor laser device 10A is 2.2%. It can be seen that the provision of the low-refractive-index portions 122 reduces light leakage from the active layer 132 to the outside of the n-side cladding layer 120A, thereby effectively achieving light confinement.

[0043] Fig. 5 shows the spectrum when the semiconductor laser device 10A of the first embodiment is oscillated in single mode, and Fig. 6 shows the spectrum when the semiconductor laser device 10A is oscillated in multimode. Two types of samples of the semiconductor laser device 10A are fabricated using the layer structure of Fig. 3 by changing the period in the waveguiding direction of the low refractive index portions 122 of the n-side cladding layer 120A. Sample I has a period a1 in the waveguiding direction of the low refractive index portions 122 of λ / 2n eff In sample II, the period a2 of the low refractive index portions 122 in the waveguiding direction satisfies an integer multiple of λ / 2n effThe design oscillation wavelength λ of the semiconductor laser element 10A is 445 nm, and the effective refractive index n eff is 2.47.

[0044] The period a1 in the waveguiding direction of the low refractive index portion 122 of sample I is a1=λ / 2n eff 5, the semiconductor laser device 10A has a period a1 and an effective refractive index n eff On the other hand, the period a2 in the waveguiding direction of the low refractive index portion 122 of sample II is set to λ / 2n eff The period a2 is set to 83 nm, which is not an integer multiple of λ / 2n. eff At this time, as shown in Fig. 6, the semiconductor laser device 10A oscillates in multiple longitudinal modes on the shorter wavelength side than the design wavelength.

[0045] In this way, the low refractive index portions 122 provided in the n-side cladding layer 120A are periodically arranged in the waveguiding direction, and the period a is set to λ / 2n eff or λ / 2n eff Depending on whether the configuration is such that it is not an integer multiple of , it is possible to oscillate in a longitudinal single mode or longitudinal multimode.

[0046] (Second embodiment) FIG. 7 is a cross-sectional view of a laminate 25 used in a semiconductor laser device 20 according to a second embodiment. In the second embodiment, low-refractive-index portions are provided in the n-side cladding layer and the p-side cladding layer. The semiconductor laser device 20 includes an n-side cladding layer 220, a p-side cladding layer 240, and an active layer 232 provided between the n-side cladding layer 220 and the p-side cladding layer 240. The n-side cladding layer 220 includes a semiconductor portion 221 made of a nitride semiconductor and a low-refractive-index portion 222 made of a material other than a nitride semiconductor and having a lower refractive index than the semiconductor portion 221. The semiconductor portion 221 is made of n-GaN. The low-refractive-index portion 222 is an air gap. An n-GaN layer 223 is provided below the n-side cladding layer 220, and an n-GaN layer 224 is provided above the n-side cladding layer 220. The n-side cladding layer 220 has a thickness of 500 nm, and the n-GaN layer 224 has a thickness of 200 nm. In the figure, the thickness of the low refractive index portion 222 is set to be equal to the thickness of the n-side cladding layer 220 , but the thickness of the low refractive index portion 222 may be set to be smaller than the thickness of the n-side cladding layer 220 .

[0047] On the n-GaN layer 224, there are arranged an InGaN layer 231 having a thickness of 30 nm, an InGaN layer 233 having a thickness of 30 nm, and an active layer 232 having a thickness of 10 nm provided between the InGaN layers 231 and 233. The active layer 232 and the InGaN layers 231 and 233 sandwiching the active layer 232 from above and below may form a waveguide core. The InGaN layers 231 and 233 may be used as optical guiding layers. The active layer 232 includes an InGaN well layer and a GaN barrier layer.

[0048] The active layer 232 includes a 200-nm-thick GaN layer 241, a 10-nm-thick p-AlGaN layer 242, and a 250-nm-thick p-side cladding layer 240, arranged in this order on the InGaN layer 233. The p-side cladding layer 240 is formed of a semiconductor portion 243 made of p-GaN and a low-refractive-index portion 244 having a lower refractive index than the semiconductor portion 243. In this example, the low-refractive-index portion 244 is an air gap. The GaN layer 241 may be an optical guide layer. The p-AlGaN layer 242 may be used as an electron blocking layer. The p-side cladding layer 240 functions as a cladding layer to further ensure optical confinement for the active layer 232. In the figure, the low-refractive-index portion 244 is equal to the thickness of the p-side cladding layer 240; however, the low-refractive-index portion 244 may be thinner than the thickness of the p-side cladding layer 240. A p-side contact layer may be provided on the p-side cladding layer 240.

[0049] 8 is a diagram showing the light intensity distribution of the semiconductor laser device 20 of FIG. 7. The horizontal axis represents the depth position from the surface of the p-side cladding layer 240, and the vertical axis represents the relative light intensity normalized to 1 at the peak. The position of the peak coincides with the position of the active layer 232. The porosity of the p-side cladding layer 240 is 16%, and the light intensity in the p-side cladding layer 240 is low at 1.3% of the integrated light intensity of the entire semiconductor laser device 20. The porosity of the n-side cladding layer 220 is 16%, and the light intensity in the n-side cladding layer 220 is low at 1.6% of the integrated light intensity of the entire semiconductor laser device 20. It can be seen that the provision of the p-side cladding layer 240 effectively confines light in the vicinity of the active layer 232.

[0050] The semiconductor laser device 20 oscillates in either a single longitudinal mode or a multi-longitudinal mode by adjusting the arrangement of the low refractive index portion 244 of the p-side cladding layer 240 and the low refractive index portion 222 of the n-side cladding layer 220. (a) The period a1 in the waveguiding direction of the low refractive index portion 222 and the period a2 in the waveguiding direction of the low refractive index portion 244 are both λ / 2n eff If the integral multiple of the above is satisfied, single longitudinal mode oscillation occurs. (b) The low refractive index portions 222 and 244 are arranged at the same period in the waveguiding direction, but the period a is λ / 2n effIf the wavelength is not an integer multiple of , longitudinal multimode oscillation occurs. (c) When the low refractive index portions 222 and 244 are arranged at different periods in the waveguiding direction, the semiconductor laser device 20 as a whole becomes non-periodic, and longitudinal multimode oscillation occurs. (d) When either or both of the low refractive index portions 222 and 244 are randomly arranged in the waveguiding direction, longitudinal multimode oscillation occurs.

[0051] In either case, by adjusting the proportion of the low refractive index section 222 in the n-side cladding layer 220 and the proportion of the low refractive index section 244 in the p-side cladding layer 240, the refractive index difference with the active layer 232 (well layer) can be adjusted, and light can be effectively confined in the vicinity of the active layer 232.

[0052] (Third embodiment) 9 is a cross-sectional view of a laminate 35 used in a semiconductor laser device 30 of the third embodiment. In the third embodiment, an Al layer having an Al composition ratio y of 0.04 or more is disposed adjacent to the n-side cladding layer. y Ga 1-yAn n-layer is provided. The semiconductor laser device 30 has an n-side cladding layer 320, a p-side cladding layer, and an active layer 332 provided between the n-side cladding layer 320 and the p-side cladding layer. The n-side cladding layer 320 has a semiconductor portion 321 made of a nitride semiconductor and a low-refractive-index portion 322 made of a material other than a nitride semiconductor and having a lower refractive index than the semiconductor portion 321. The n-side cladding layer 320 has a thickness of 500 nm. The semiconductor portion 321 is formed of n-GaN. The low-refractive-index portion 322 is an air gap. An n-AlGaN layer 324 having an Al composition ratio y of 0.045 and a thickness of 400 nm is provided below the n-side cladding layer 320, and an n-GaN layer 223 is provided below the n-AlGaN layer 324. A substrate may be provided below the n-GaN layer 323. The n-AlGaN layer 324 can be used as part of the n-side cladding layer by being provided together with the n-side cladding layer 320; however, without the n-side cladding layer 320, the n-AlGaN layer 324 alone does not function adequately as a cladding. The Al composition ratio y of the n-AlGaN layer 324 is 0.04 or higher, but the Al composition ratio y is so low that the n-AlGaN layer 324 alone does not function adequately as a cladding. An n-GaN layer 325 having a thickness of 250 nm is provided on the n-side cladding layer 320. In the figure, the thickness of the low-refractive-index portion 322 is set equal to that of the n-side cladding layer 320; however, the thickness of the low-refractive-index portion 322 may be smaller than that of the n-side cladding layer 320.

[0053] On the n-GaN layer 325, there are arranged an InGaN layer 331 having a thickness of 30 nm, an InGaN layer 333 having a thickness of 30 nm, and an active layer 332 having a thickness of 10 nm provided between the InGaN layers 331 and 333. The active layer 332 and the InGaN layers 331 and 333 sandwiching the active layer 332 from above and below may form a waveguide core. The InGaN layers 331 and 333 may be used as optical guiding layers. The active layer 332 includes an InGaN well layer and a GaN barrier layer.

[0054] The semiconductor device includes a 250-nm-thick GaN layer 341, a 10-nm-thick p-AlGaN layer 342, a 100-nm-thick p-AlGaN layer 343, and a 160-nm-thick p-GaN layer 344 on the InGaN layer 333, in this order. The GaN layer 341 may function as a part of the optical guide layer. The p-AlGaN layer 342 may be used as an electron blocking layer. The p-AlGaN layer 343 may function as a p-side cladding layer. The Al composition ratio of the p-AlGaN layer 342 is higher than that of the p-AlGaN layer 343. The uppermost p-GaN layer 344 may be used as a p-side contact layer.

[0055] FIG. 10 shows the optical intensity distribution of the semiconductor laser device 30 of FIG. 9 . The horizontal axis represents the depth position from the surface of the p-GaN layer 344, and the vertical axis represents the relative optical intensity normalized to 1. The peak position coincides with the position of the active layer 332. The porosity of the n-side cladding layer 320 is 2%, and the optical intensity in the n-side cladding layer 320 is 6.5% of the integrated optical intensity of the entire semiconductor laser device 30. When providing the low-refractive-index portion 322 with a small porosity, an AlGaN layer 324 may be provided adjacent to the n-side cladding layer 320 to enhance the optical confinement function. The Al composition ratio y and thickness of this AlGaN layer 324 are preferably low enough and / or thin enough that it would not function adequately as a cladding layer without the n-side cladding layer 320. This improves the crystallinity of the active layer 332.

[0056] The low refractive index portions 322 are formed periodically in the waveguiding direction, and the period a is λ / 2n eff By setting the value outside the integral multiple of , the semiconductor laser element 30 can oscillate in multiple modes.

[0057] (Fourth embodiment) 11 is a cross-sectional view of a laminate 45 used in a semiconductor laser device 40 of the fourth embodiment. In the fourth embodiment, an AlGaN layer 424 (Al y Ga 1-yN, y≧0.04). The semiconductor laser device 40 has an n-side cladding layer 420, a p-side cladding layer, and an active layer 432 provided between the n-side cladding layer 420 and the p-side cladding layer. The n-side cladding layer 420 has a semiconductor portion 421 made of a nitride semiconductor and a low-refractive-index portion 422 made of a material other than a nitride semiconductor and having a lower refractive index than the semiconductor portion 421. The n-side cladding layer 420 has a thickness of 400 nm. The semiconductor portion 421 is formed of n-GaN. The low-refractive-index portion 422 is an air gap. A 20-nm-thick n-AlGaN layer 424 having an Al composition ratio y of 0.07 is provided between the n-side cladding layer 420 and the active layer 432, and a 250-nm-thick n-GaN layer 425 is provided on the n-AlGaN layer 424. The Al composition ratio y of the n-AlGaN layer 424 is 0.04 or higher, but is low enough that the n-AlGaN layer 424 alone does not function adequately as a cladding layer without the n-side cladding layer 420. The thickness of the n-AlGaN layer 424 is also preferably thin enough that the n-AlGaN layer 424 does not function adequately as a cladding layer without the n-side cladding layer 420. This improves the crystal quality of the active layer 432. An n-GaN layer 423 may be provided below the n-side cladding layer 420. A substrate may be provided below the n-GaN layer 423. While the thickness of the low-refractive-index portion 422 is set equal to that of the n-side cladding layer 420 in the figure, the thickness of the low-refractive-index portion 422 may be smaller than that of the n-side cladding layer 420.

[0058] On the n-GaN layer 425, there are arranged an InGaN layer 431 having a thickness of 30 nm, an InGaN layer 433 having a thickness of 30 nm, and an active layer 432 having a thickness of 10 nm provided between the InGaN layers 431 and 433. The active layer 432 and the InGaN layers 431 and 433 sandwiching the active layer 432 from above and below may form a waveguide core. The InGaN layers 431 and 433 may be used as optical guiding layers. The active layer 432 includes an InGaN well layer and a GaN barrier layer.

[0059] The semiconductor device includes a 250-nm-thick GaN layer 441, a 10-nm-thick p-AlGaN layer 442, a 100-nm-thick p-AlGaN layer 443, and a 160-nm-thick p-GaN layer 444 on the InGaN layer 433, in this order. The GaN layer 441 may function as a part of the optical guide layer. The p-AlGaN layer 442 can be used as an electron blocking layer. The p-AlGaN layer 443 functions as a p-side cladding layer. The Al composition ratio of the p-AlGaN layer 442 is higher than that of the p-AlGaN layer 443. The uppermost p-GaN layer 444 can be used as a p-side contact layer.

[0060] FIG. 12 shows the light intensity distribution of the semiconductor laser device 40 of FIG. 11. The horizontal axis represents the depth position from the surface of the p-GaN layer 444, and the vertical axis represents the relative light intensity normalized to 1 at the peak. The position of the peak coincides with the position of the active layer 432. The porosity of the n-side cladding layer 420 is 13%, and the light intensity in the n-side cladding layer 420 is 0.5% of the integrated light intensity of the entire semiconductor laser device 40. In FIG. 12, the solid line represents the light intensity distribution of the semiconductor laser device 40, and the dashed line represents the light intensity distribution of a semiconductor laser device of a reference example that is identical to the semiconductor laser device 40 except that it does not have the low-refractive-index portion 422. The semiconductor laser device of the reference example has the n-AlGaN layer 424 like the semiconductor laser device 40 of the embodiment. However, if an attempt is made to obtain cladding function using only the n-AlGaN layer 424 without the low-refractive-index portion 422, a sufficient light confinement effect cannot be obtained, as shown by the dashed line in FIG. 12. The provision of the low refractive index portion 422 achieves effective light confinement in the active layer 432. In the semiconductor laser device 40, it can be said that the n-side cladding layer 420 including the low refractive index portion 422 essentially functions as a cladding layer.

[0061] The low refractive index portions 422 are formed periodically in the waveguiding direction, and the period a is set to λ / 2n eff The semiconductor laser device 30 can be used as a DFB laser by forming the low refractive index portions 422 non-periodically in the waveguiding direction, or by setting the period a in the waveguiding direction to λ / 2n effBy setting the value outside the integral multiple of , the semiconductor laser element 30 can oscillate in multiple modes.

[0062] Embodiments of the present disclosure may include, for example, the following configurations. (Section 1) an n-side cladding layer; a p-side cladding layer; an active layer provided between the n-side cladding layer and the p-side cladding layer; and the n-side cladding layer has a semiconductor portion made of a nitride semiconductor and a low refractive index portion made of a medium other than a nitride semiconductor and having a refractive index lower than that of the semiconductor portion; Semiconductor laser element. (Section 2) The semiconductor portion of the n-side cladding layer is Al x Ga 1-x N, and the Al composition ratio x is less than 0.04; Item 1. The semiconductor laser device according to item 1. (Section 3) When the integrated light intensity in the stacking direction of the semiconductor laser element is taken as 100%, the light intensity of the n-side cladding layer is 5% or less. Item 1 or 2. The semiconductor laser device according to item 1 or 2. (Section 4) An Al composition ratio y of 0.04 or more is provided between the low refractive index portion and the active layer. y Ga 1-y having N layers, Item 4. The semiconductor laser device according to any one of items 1 to 3. (Section 5) The low refractive index portion is a gap. Item 5. The semiconductor laser device according to any one of items 1 to 4. (Section 6) the distribution of the waveguide direction of the low refractive index portion is periodic within a plane perpendicular to the stacking direction of the semiconductor laser element; Item 6. The semiconductor laser device according to any one of items 1 to 5. (Section 7) The oscillation wavelength of the semiconductor laser element is λ, and the effective refractive index of the semiconductor laser element at the oscillation wavelength is n effThen, the period of the low refractive index portion is λ / 2n eff is not an integer multiple of Item 7. The semiconductor laser device according to item 6. (Section 8) the distribution of the waveguide direction of the low refractive index portion is random within a plane perpendicular to the stacking direction of the semiconductor laser element; Item 6. The semiconductor laser device according to any one of items 1 to 5. (Section 9) the p-side cladding layer has a second semiconductor portion made of a nitride semiconductor and a second low refractive index portion made of a material other than a nitride semiconductor and having a refractive index lower than that of the second semiconductor portion; Item 6. The semiconductor laser device according to any one of items 1 to 5. (Section 10) the low refractive index portions of the n-side cladding layer are periodically provided with a first period, the second low refractive index portions of the p-side cladding layer are periodically provided with a second period; the first period and the second period are different; Item 10. The semiconductor laser device according to item 9. [Explanation of symbols]

[0063] 10, 10A, 20, 30, 40 Semiconductor laser element 11 Circuit Board 12, 120A, 220, 320, 420 n-side cladding layer 121, 221, 321, 421 Semiconductor Department 122, 222, 322, 422 Low refractive index section 13, 132, 232, 332, 432 active layer 14,240 p-side cladding layer 15, 15A, 25, 35, 45 laminate 243 Semiconductor Division (Second Semiconductor Division) 244 Low refractive index section (second low refractive index section) 343, 443 p-AlGaN layer (p-side cladding layer) 424 AlGaN layer (Al y Ga 1-y N,y≧0.04)

Claims

1. an n-side cladding layer; a p-side cladding layer; an active layer provided between the n-side cladding layer and the p-side cladding layer; and the n-side cladding layer has a semiconductor portion made of a nitride semiconductor and a low refractive index portion made of a medium other than a nitride semiconductor and having a refractive index lower than that of the semiconductor portion; Semiconductor laser element.

2. The semiconductor portion of the n-side cladding layer is Al ｘ Ga １－ｘ N, and the Al composition ratio x is less than 0.04; 2. The semiconductor laser device according to claim 1.

3. the optical intensity of the n-side cladding layer is 5% or less when the integrated optical intensity in the stacking direction of the semiconductor laser element is 100%; 2. The semiconductor laser device according to claim 1.

4. An Al composition ratio y of 0.04 or more is provided between the low refractive index portion and the active layer. ｙ Ga １－ｙ having N layers, 2. The semiconductor laser device according to claim 1.

5. The low refractive index portion is a gap.

2. The semiconductor laser device according to claim 1.

6. the distribution of the waveguide direction of the low refractive index portion is periodic within a plane perpendicular to the stacking direction of the semiconductor laser element; 2. The semiconductor laser device according to claim 1.

7. The oscillation wavelength of the semiconductor laser element is λ, and the effective refractive index of the semiconductor laser element at the oscillation wavelength is n eff Then, the period of the low refractive index portion is λ / 2n eff is not an integer multiple of 7. The semiconductor laser device according to claim 6.

8. the distribution of the waveguide direction of the low refractive index portion is random within a plane perpendicular to the stacking direction of the semiconductor laser element; 2. The semiconductor laser device according to claim 1.

9. the p-side cladding layer has a second semiconductor portion made of a nitride semiconductor and a second low refractive index portion made of a material other than a nitride semiconductor and having a refractive index lower than that of the second semiconductor portion; 6. The semiconductor laser device according to claim 1.

10. the low refractive index portions of the n-side cladding layer are periodically provided with a first period, the second low refractive index portions of the p-side cladding layer are periodically provided with a second period; the first period and the second period are different; 10. The semiconductor laser device according to claim 9.

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