Semiconductor laser element

Abstract

To increase the coupling coefficient of a semiconductor laser element. [Solution] The semiconductor laser element 100 comprises a substrate 110 and a laminated structure 102 including an n-type semiconductor layer 122, an active layer 124, and a p-type semiconductor layer 126. The laminated structure 102 is provided with a current-constricting structure 141 and a diffraction grating 150 adjacent to the current-constricting structure 141. The diffraction grating 150 has a first portion 151 having a first refractive index n1 with a plurality of grooves 152 formed thereon, a second portion 153 having a second refractive index n2 formed to cover the surface of the plurality of grooves 152, and a third portion 154 having a third refractive index n3 different from the second refractive index n2, surrounded by the second portion 153 inside the grooves 152.

Description

[Technical Field]

[0001] This disclosure relates to semiconductor laser devices. [Background technology]

[0002] As a longitudinal single-mode laser, a distributed feedback laser diode (DFB-LD) is used (Patent Document 1, Non-Patent Document 1). Various forms of DFB-LDs have been proposed, among which is the transversely coupled DFB-LD. One form of the transversely coupled DFB-LD has a stacked structure of an N-type cladding layer, an active layer, and a P-type cladding layer, and a ridge (mesa structure) is formed in the P-type cladding layer as a current-constricting structure. A diffraction grating is then formed in the P-type cladding layer adjacent to the ridge. This diffraction grating consists of a periodic structure composed of two or more materials with different refractive indices. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 5023567 [Patent Document 2] Japanese Patent Publication No. 2000-340882 [Non-patent literature]

[0004] [Non-Patent Document 1] Applied Physics Express 17, 052004 [Overview of the project] [Problems that the invention aims to solve]

[0005] An important parameter of a DFB-LD is the coupling coefficient (κ), which represents the magnitude of the coupling between the diffraction grating and the propagating light. Generally, the larger the coupling coefficient, the smaller the oscillation threshold of the DFB-LD, which is advantageous for low-power operation. The magnitude of the coupling coefficient is determined, for example, by the difference in refractive index of the periodic structure with different refractive indices that make up the diffraction grating. In particular, in the case of transversely coupled DFB-LDs, when the semiconductor surface is passivated, the surface of the diffraction grating is also made of SiO2 or SiN (Si3N4 or SiN x It is covered with insulating materials such as (although it is sometimes written as such, these are considered synonymous).

[0006] In such transversely coupled DFB-LDs, the grooves of the diffraction grating are filled with insulating material. In this case, the refractive index difference of the periodic structure of the diffraction grating is determined by the refractive index n1 of the semiconductor material that forms the base (convex part) and the refractive index n2 of the insulating material that fills the grooves (concave part).

[0007] When GaN is selected as the semiconductor material and SiO2 as the insulating material, n1 ≈ 2.47 and n2 ≈ 1.49 are obtained. It was possible to realize a DFB-LD with good characteristics even with a diffraction grating made of this combination. However, in order to further improve the characteristics of the laser, for example, to reduce the threshold current, it was necessary to increase the coupling coefficient by further increasing the refractive index difference between the concave and convex parts.

[0008] This disclosure is made in such circumstances, and one exemplary objective of a certain aspect thereof is to provide a semiconductor laser element with an increased coupling coefficient. [Means for solving the problem]

[0009] Certain aspects of this disclosure relate to semiconductor laser elements such as distributed feedback type and distributed reflection type. The semiconductor laser element comprises a substrate and a laminated structure formed on the substrate, including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. The laminated structure has a current constriction structure and a diffraction grating including a plurality of grooves. The diffraction grating has a first portion having a first refractive index n1 with a plurality of grooves formed thereon, a second portion having a second refractive index n2 formed to cover the surface of the plurality of grooves, and a third portion having a third refractive index n3 different from the second refractive index n2, surrounded by the second portion inside the grooves.

[0010] Furthermore, any combination of the above components, or any substitution of components or expressions between methods, apparatus, systems, etc., are also valid as embodiments of the present invention or this disclosure. Moreover, the description in this section (means for solving the problem) does not describe all the indispensable features of the present invention, and therefore, subcombinations of these described features may also constitute the present invention. [Effects of the Invention]

[0011] According to a semiconductor laser element in one aspect of this disclosure, the coupling coefficient can be increased. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view of a distributed feedback semiconductor laser element (DFB-LD) according to an embodiment. [Figure 2] This is a cross-sectional view of the diffraction grating of a semiconductor laser element according to the embodiment, taken along the line A-A'. [Figure 3] This is a cross-sectional view of a semiconductor laser element according to Example 1. [Figure 4] This is a cross-sectional view of a semiconductor laser element according to Example 2. [Figure 5] This is a cross-sectional view of a semiconductor laser element according to Example 3. [Figure 6] This is a cross-sectional view of a semiconductor laser element according to Example 4. [Figure 7]This is a cross-sectional view of a semiconductor laser element according to Example 5. [Figure 8] Figure 7 illustrates an example of a method for manufacturing a diffraction grating. [Figure 9] This figure shows the dependence of the coupling coefficient and the average refractive index inside the grooves on the void occupancy rate in the diffraction grating shown in Figure 8. [Figure 10] This is a perspective view of the distributed Bragg reflective semiconductor laser element (DBR-LD) according to Example 6. [Figure 11] This is a perspective view of the Master Oscillator Power Amplifier (MOPA) laser according to Example 7. [Modes for carrying out the invention]

[0013] (Summary of the embodiment) This section outlines some exemplary embodiments of the present disclosure. This outline serves as a prelude to the detailed description that follows, or as a means of understanding the embodiments. This outline provides a simplified explanation of some concepts of one or more embodiments and does not limit the scope of the invention or disclosure. Furthermore, this outline is not a comprehensive overview of all possible embodiments and does not limit the essential components of the embodiments. For convenience, “one embodiment” may be used to refer to one embodiment (example or variation) or more embodiments (example or variation) disclosed herein.

[0014] A distributed feedback type semiconductor laser element according to one embodiment comprises a substrate and a laminated structure formed on the substrate, including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. The laminated structure includes a current-constricting structure and a diffraction grating with a plurality of grooves in a region adjacent to the current-constricting structure. The diffraction grating has a first portion having a first refractive index n1 with a plurality of grooves formed thereon, a second portion having a second refractive index n2 formed to cover the surface of the plurality of grooves, and a third portion having a third refractive index n3 different from the second refractive index n2, surrounded by the second portion within the grooves.

[0015] With this configuration, instead of completely filling the groove with the second part, the effective refractive index (average refractive index) inside the groove can be adjusted by forming a second and third part with different refractive indices inside the groove. This allows for a larger difference in refractive index between the recessed part inside the groove and the convex part of the first part, thereby increasing the coupling coefficient.

[0016] In one embodiment, the relationship between the first refractive index n1, the second refractive index n2, and the third refractive index n3 in the diffraction grating may be n1>n2>n3.

[0017] In one embodiment, the upper surface of the region where the diffraction grating is formed may be covered with a protective layer made of a different material from the first portion.

[0018] In one embodiment, the protective layer may be made of the same material as the second portion.

[0019] In one embodiment, the third portion may be a void.

[0020] In one embodiment, the width of the multiple grooves may be 100 nm or less. By depositing a second portion onto the first portion of such grooves using a CVD method, a structure having voids inside the grooves and its surface covered with a protective layer can be formed in a single process.

[0021] In one embodiment, the third portion may be an insulating material.

[0022] In one embodiment, the protective layer may be made of the same material as the third portion.

[0023] In one embodiment, the first part may be a semiconductor and the second part may be an insulating material.

[0024] In one embodiment, the insulating material may be an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr.

[0025] In one embodiment, the first portion may be a semiconductor layer of a second conductivity type.

[0026] In one embodiment, when 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1, the active layer is In x Al y Ga 1-x-y N, In x Al y Ga 1-x-y P, In x Al y Ga 1-x-y As, or In x Ga 1-x As y P 1-y and may be.

[0027] (Embodiment) Hereinafter, preferred embodiments will be described with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. Further, the embodiments are illustrative and not intended to limit the disclosure or the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure or the invention.

[0028] Also, the dimensions (thickness, length, width, etc.) of each member described in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of a plurality of members do not necessarily represent their size relationships, and on the drawing, even if a member A is drawn thicker than another member B, member A may be thinner than member B.

[0029] FIG. 1 is a perspective view of a distributed feedback semiconductor laser device (DFB-LD) 100 according to an embodiment. The semiconductor laser device 100 includes a substrate 110 and a stacked structure 120 formed on the substrate 110.

[0030] When the active layer is In x Al y Ga 1-x-yIn the case of N(0≦x≦1, 0≦y≦1, 0≦x+y≦1), the substrate 110 is In x Al y Ga 1-x-y It can have a composition of N. Also, the active layer may be In x Al y Ga 1-x-y P(0≦x≦1, 0≦y≦1, 0≦x+y≦1), In x Al y Ga 1-x-y As(0≦x≦1, 0≦y≦1, 0≦x+y≦1), or In x Ga 1-x As y P 1-y In the case of (0≦x≦1, 0≦y≦1), the substrate 110 is GaAs. To generate a 444nm blue laser beam, the material of the substrate 110 can be GaN(x=y=0). Furthermore, the substrate 110 is not limited to this, as long as it has equivalent effects, for example, a Si substrate or a sapphire substrate may also be used.

[0031] The n-type semiconductor layer 122, the active layer 124, and the p-type semiconductor layer 126 are sequentially formed on the n-type substrate 110 by epitaxial growth, constituting a stacked structure 120.

[0032] The n-type semiconductor layer 122 may include an n-type cladding layer and an n-type guide layer. For example, the material of the n-type cladding layer is n-Al 0.05 Ga 0.95 The material is N, and the n-type guide layer material is n-GaN.

[0033] An active layer (light-emitting layer) 124 having a quantum well structure is formed on the n-type semiconductor layer 122. When the oscillation wavelength is 444 nm, the material of the quantum well structure is In as the barrier layer. 0.01 Ga 0.99 N as a well layer 0.15 Ga 0.85 You can choose N.

[0034] To suppress the diffusion of impurities from the n-type semiconductor layer 122 to the active layer 124, an undoped nitride guide layer (not shown) is placed between them. 0.02Ga 0.98 N can be inserted.

[0035] The p-type semiconductor layer 126 may include a carrier block (electron block EB) layer, a p-type guide layer, a p-type cladding layer, and a contact layer. For example, the material of the carrier block layer may be p-Al 0.15 Ga 0.85 The material is N, and the p-type guide layer material is p-In 0.02 Ga 0.98 The material is N, and the p-type cladding layer is p-Al 0.04 Ga 0.96 The material is N, and the contact layer material is p-GaN.

[0036] To suppress the diffusion of impurities from the p-type semiconductor layer 126 to the active layer 124, an undoped nitride guide layer (not shown) can be inserted between them.

[0037] Ridge regions (also called mesa regions) 142 are formed as current-constricting structures 141 in the p-type semiconductor layer 126 (p-type cladding layer). The height of the ridge regions 142 can be several hundred nm, and the width of the ridge regions 142 (mesa width) can be several microns. For example, the height may be 500 nm and the width 2 μm.

[0038] The coupling coefficient κ also changes with the mesa width; the narrower the mesa width, the larger the coupling coefficient κ becomes. However, when the mesa width is less than 1 μm, lateral confinement weakens, and the laser characteristics begin to deteriorate. On the other hand, when the mesa width exceeds 3 μm, the laser changes from lateral single-mode to lateral multi-mode. Therefore, in order to obtain a high coupling coefficient κ in lateral single-mode, it is preferable that the mesa width Wm be 1 μm ≤ Wm ≤ 3 μm.

[0039] The p-type semiconductor layer 126 having a ridge portion 142, together with the active layer 124 and the n-type semiconductor layer 122, forms a ridge-type waveguide 144. The ridge-type waveguide 144 extends in the first direction (z-axis direction in the figure).

[0040] The n-side electrode 171 is formed on the back surface of the substrate 110, and the p-side electrode 172 is formed on the upper surface of the ridge portion 142.

[0041] Diffraction gratings 150_1 and 150_2 are formed on both sides of the mesa adjacent to the ridge-type waveguide 144 in the second direction (x-axis direction). Each of the diffraction gratings 150_1 and 150_2 has a plurality of grooves 152 formed in the p-type semiconductor layer 126 adjacent to the mesa. The plurality of grooves 152 are adjacent in the first direction, and each groove extends in the second direction.

[0042] A protective layer 160 is formed on the p-type semiconductor layer 126. The material of the protective layer 160 is an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr.

[0043] Figure 2 is a cross-sectional view of the diffraction grating 150 of the semiconductor laser element 100 according to the embodiment, taken along the line A-A'.

[0044] The diffraction grating 150 includes a first part 151, a second part 153, and a third part 154.

[0045] The first portion 151 has a first refractive index n1 and corresponds to the convex portion of the periodic structure of the diffraction grating 150. In this embodiment, the first portion 151 is a p-type semiconductor layer 126. The first portion 151 has a plurality of grooves 152 that correspond to the concave portions of the periodic structure.

[0046] The second portion 153 is formed to cover the surface of the groove 152. It has a second refractive index n2 that is different from the first refractive index n1.

[0047] The third portion 154 has a third refractive index n3 that is different from the first refractive index n1 and the second refractive index n2. The third portion 154 is formed inside the groove 152, surrounded by the second portion 153.

[0048] In one embodiment, n1 > n2 > n3.

[0049] The above describes the configuration of the semiconductor laser element 100. The advantages of the semiconductor laser element 100 become clear when compared with other technologies.

[0050] In the comparative technique, the interior of the groove 152 is filled with the same single insulating material (with a refractive index of n2) as the protective layer 160, which is an insulating film. The coupling coefficient of the periodic structure of the diffraction grating 150 correlates with the refractive index difference between the convex and concave parts. In the comparative technique, the refractive index of the convex part is the refractive index n1 of the first part 151, and the refractive index of the concave part is the refractive index n2 of the second part 153. Therefore, the refractive index of the first part 151 is determined by the material of the p-type semiconductor layer 126, and the material of the second part 153 is determined by the material of the protective layer 160, which is an insulating film, leaving no freedom of selection. Although it is possible to obtain a DFB-LD with good characteristics even with the configuration of the comparative technique, it was difficult to increase the refractive index difference in order to further increase the coupling coefficient.

[0051] In the embodiment shown in Figure 2, the refractive index of the convex portion is the refractive index n1 of the first portion 151, which is determined by the material of the p-type semiconductor layer 126, as in the comparative technology. On the other hand, the effective refractive index n2' inside the concave portion, i.e., the groove 152, is determined by the refractive index n2 of the second portion 153 and the refractive index n3 of the third portion 154. Therefore, compared to the comparative technology, there is a greater degree of design freedom, and the difference between the refractive index n1 of the convex portion and the effective refractive index n2' of the concave portion can be made larger. As a result, a higher coupling efficiency can be achieved than in the comparative technology.

[0052] This disclosure extends to various devices and methods as understood in the cross-sectional view of Figure 2 or derived from the above description, and is not limited to any particular configuration. More specific configuration examples and embodiments are described below, not to narrow the scope of this disclosure, but to aid in understanding and clarifying the essence and operation of this disclosure and the present invention.

[0053] Figure 3 is a cross-sectional view of a semiconductor laser element 100A according to Example 1. In this example, the surface of the diffraction grating 150 is covered with a protective layer 160. The protective layer 160 is an insulating film made of a different material from the first part 151. The material of the protective layer 160 is an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr, such as SiO2 or SiN(Si3N4 or SiN x (Although these are sometimes written as, these are considered synonymous) is preferable. Also, the material of the second part 153 is, for example, SiN, and the material of the third part 154 is, for example, SiO2.

[0054] Figure 4 is a cross-sectional view of a semiconductor laser element 100B according to Example 2. In this example, the material of the third portion 154 is the same as the material of the protective layer 160, and they are formed integrally. For example, the material of the second portion 153 is SiN, and the materials of the third portion 154 and the protective layer 160 are SiO2.

[0055] Figure 5 is a cross-sectional view of a semiconductor laser element 100C according to Example 3. In this example, the material of the second portion 153 is the same as the material of the protective layer 160, and they are formed integrally. For example, the material of the second portion 153 and the protective layer 160 is SiN, and the material of the third portion 154 is SiO2.

[0056] Figure 6 is a cross-sectional view of the semiconductor laser element 100D according to Example 4. In this example, as in Example 3 (Figure 5), the second portion 153 and the protective layer 160 are made of the same material. The difference from Figure 5 is that the third portion 154 is covered by the protective layer 160.

[0057] Figure 7 is a cross-sectional view of the semiconductor laser element 100E according to Example 5. In this example, as in Example 4 (Figure 6), the second portion 153 and the protective layer 160 are made of the same material. The difference from Figure 6 is that the third portion 154 is a void, formed of air, vacuum, or a gas such as nitrogen or oxygen. In this case, n3=1, which allows the refractive index of the recessed portion of the periodic structure to be lowest, thereby increasing the refractive index difference between the recessed and convex portions.

[0058] Figure 8 illustrates an example of a method for manufacturing the diffraction grating shown in Figure 7. First, a laminated structure 120 is formed on a substrate 110, and a current-constricting structure 141 is formed on the p-type semiconductor layer 126. Figure 8 shows the first portion 151 before the formation of the diffraction grating 150 (S100).

[0059] Grooves 152 are formed in the first portion 151 at a predetermined pitch by etching (S102). Subsequently, insulating materials that will become the protective layer 160 and the second portion 153 are deposited on the first portion 151 with the uneven surface formed by CVD (Chemical Vapor Deposition) (S104).

[0060] As deposition continues, a large amount of insulating material is deposited at the corners of the protrusions of the periodic structure, i.e., at the shallowest parts of the grooves 152 (S106). Finally, on the surface of the first part 151, the insulating materials connect to each other across the grooves 152, forming a protective layer 160, and a void is formed inside the first part 151 surrounded by the protective layer 160 and the second part 153 (S108). This void becomes the third part 154.

[0061] In order to form the third portion 154 using the manufacturing method shown in Figure 8, the width of the groove 152 is important, and by making it 100 nm or less, the void shown in S108 of Figure 8 can be formed.

[0062] Figure 9 shows the dependence (simulation result) of the coupling coefficient and the average refractive index inside the recess of the groove 152 on the void occupancy rate in the diffraction grating 150 shown in Figure 8. The horizontal axis represents the void occupancy rate, i.e., the ratio of the void (third part 154) to the groove 152. The left vertical axis represents κL, i.e., the product of the coupling coefficient κ and the resonator length L, and the right vertical axis represents the average refractive index. The material of the first part 151 is GaN, and its refractive index is approximately 2.47 (hereinafter referred to as ~2.47). The material of the protective layer 160 and the second part 153 is SiO2, and its refractive index is ~1.5. L = 1000 μm.

[0063] As the air gap increases, the difference between the refractive index n1 (~2.47) of the GaN in the convex part of the periodic structure and the average refractive index inside the concave part of groove 152 increases, and κL increases. In other words, the oscillation threshold of the DFB-LD can be reduced.

[0064] Figure 10 is a perspective view of a distributed Bragg reflective semiconductor laser element (DBR-LD) 200 according to an embodiment. The semiconductor laser element 200 comprises a substrate 210 and a laminated structure 220 formed on the substrate 210.

[0065] The active layer is In x Al y Ga 1-x-y In the case of N(0≦x≦1, 0≦y≦1, 0≦x+y≦1), substrate 210 is In x Al y Ga 1-x-y It can have a composition of N. Also, the active layer is In x Al y Ga 1-x-y P(0≦x≦1, 0≦y≦1, 0≦x+y≦1), In x Al y Ga 1-x-y As(0≦x≦1, 0≦y≦1, 0≦x+y≦1), or In x Ga 1-x As y P 1-y In the case of (0≦x≦1, 0≦y≦1), substrate 210 is GaAs. To generate a 510nm green laser beam, the material of substrate 210 can be GaN(x=y=0). Furthermore, substrate 210 is not limited to this, as long as it has equivalent effects, for example, a Si substrate or a sapphire substrate may also be used.

[0066] The n-type semiconductor layer 222, the active layer 224, and the p-type semiconductor layer 226 are sequentially formed on the n-type substrate 210 by epitaxial growth, constituting a stacked structure 220.

[0067] The n-type semiconductor layer 222 may include an n-type cladding layer and an n-type guide layer. For example, the material of the n-type cladding layer may be n-Al 0.08 Ga0.92 The material is N, and the n-type guide layer material is n-GaN.

[0068] An active layer (light-emitting layer) 224 having a quantum well structure is formed on the n-type semiconductor layer 222. When the oscillation wavelength is 510 nm, the material for the quantum well structure is GaN as the barrier layer and In as the well layer. 0.3 Ga 0.7 You can choose N.

[0069] To suppress the diffusion of impurities from the n-type semiconductor layer 222 to the active layer 224, an undoped nitride guide layer (not shown) is placed between them. 0.02 Ga 0.98 N can be inserted.

[0070] The p-type semiconductor layer 226 may include a carrier block (electron block) layer, a p-type guide layer, a p-type cladding layer, and a contact layer. For example, the material of the carrier block layer may be p-Al 0.15 Ga 0.85 The material for the p-type guide layer is N, the material for the p-type cladding layer is p-GaN, and the material for the p-type cladding layer is p-Al 0.04 Ga 0.96 The material is N, and the contact layer material is p-GaN.

[0071] To suppress the diffusion of impurities from the p-type semiconductor layer 226 to the active layer 224, an undoped nitride guide layer (not shown) can be inserted between them.

[0072] Ridge regions (also called mesa regions) 242 are formed as current-constricting structures 241 in the p-type semiconductor layer 226 (p-type cladding layer). The height of the ridge regions 242 can be several hundred nm, and the width of the ridge regions 242 (mesa width) can be several microns. For example, the height may be 500 nm and the width 2 μm.

[0073] The p-type semiconductor layer 226 having a ridge portion 242, together with the active layer 224 and the n-type semiconductor layer 222, forms a ridge-type waveguide 244. The ridge-type waveguide 244 extends in the first direction (z-axis direction in the figure).

[0074] The n-side electrode 271 is formed on the back surface of the substrate 110, and the p-side electrode 272 is formed on the upper surface of the ridge portion 242.

[0075] Near both end faces of the ridge portion 242, DBR mirrors 250_1 and 250_2 are formed in a second direction (x-axis direction) relative to the ridge-type waveguide 244. Each of the DBR mirrors 250_1 and 250_2 has a plurality of grooves 252 formed in the ridge portion 242, and the length in the first direction (DBR region length) is L DBR1 =200μm, L DBR2 = 400 μm. Multiple grooves 252 are adjacent in the first direction, and each groove extends in the second direction.

[0076] A protective layer 260 is formed on the p-type semiconductor layer 226. The material of the protective layer 260 is an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr.

[0077] The cross-sectional view of the DBR mirror 250 of the semiconductor laser element 200 according to this embodiment, with respect to the plane Syz perpendicular to the x-axis, is the same as in Figure 7.

[0078] In this embodiment, similar to Embodiment 4 (Figure 6), the second portion of the diffraction grating 250 (not shown, corresponding to the second portion 153 in Figure 6) and the protective layer 260 are made of the same material. The difference from Figure 6 is that the third portion of the diffraction grating 250 (not shown, corresponding to 154 in Figure 6) is a void, formed from air, vacuum, or a gas such as nitrogen or oxygen. In this case, n3=1, which allows the refractive index of the recesses in the periodic structure to be lowest, thereby increasing the refractive index difference between the recesses and convex parts.

[0079] As the void size increases, the difference between the refractive index n1 (~2.47) of the GaN in the convex part of the periodic structure and the average refractive index inside the concave part of groove 252 becomes larger, and even with the same DBR region length, the κL is greater compared to when there is no void. DBR1 and κL DBR2increases. In other words, the reflectivity of the DBR mirror 150B can be increased, and the oscillation threshold can be decreased.

[0080] FIG. 11 is a perspective view of a MOPA (Master Oscillator Power Amplifier) laser 300 according to an embodiment. The semiconductor laser element 300 includes a substrate 310 and a stacked structure 320 formed on the substrate 310, and has a length L for oscillating longitudinal single-mode light DFB in a DFB region 380 and a length L taper for amplifying longitudinal single-mode light in a tapered region 382.

[0081] When the active layer is In x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x + y≦1), the substrate 310 can have a composition of In x Al y Ga 1-x-y N. Also, when the active layer is In x Al y Ga 1-x-y P (0≦x≦1, 0≦y≦1, 0≦x + y≦1), In x Al y Ga 1-x-y As (0≦x≦1, 0≦y≦1, 0≦x + y≦1), or In x Ga 1-x As y P 1-y (0≦x≦1, 0≦y≦1), the substrate 110 is GaAs. To generate blue-violet laser light of 405 nm, the material of the substrate 310 can be GaN (x = y = 0). Also, the substrate 310 is not limited to this as long as it is a substrate having an equivalent effect, and for example, a Si substrate or a sapphire substrate may be used.

[0082] The n-type semiconductor layer 322, the active layer 324, and the p-type semiconductor layer 326 are sequentially formed on the n-type substrate 310 by epitaxial growth to form the stacked structure 320.

[0083] The n-type semiconductor layer 322 may include an n-type cladding layer and an n-type guiding layer. For example, the material of the n-type cladding layer is n-Al 0.03 Ga 0.97 N, and the material of the n-type guiding layer is n-GaN.

[0084] An active layer (light-emitting layer) 324 having a quantum well structure is formed on the n-type semiconductor layer 322. When the oscillation wavelength is 405 nm, for the material of the quantum well structure, In 0.02 Ga 0.98 N can be selected as the barrier layer, and In 0.08 Ga 0.92 N can be selected as the well layer.

[0085] In order to suppress the diffusion of impurities from the n-type semiconductor layer 322 to the active layer 324, an undoped nitride guiding layer (not shown) In 0.02 Ga 0.98 N can be inserted therebetween.

[0086] <G The p-type semiconductor layer 326 may include a carrier blocking (electron blocking) layer, a p-type guiding layer, a p-type cladding layer, and a contact layer. For example, the material of the carrier blocking layer is p-Al 0.15 Ga 0.85 N, the material of the p-type guiding layer is p-In 0.02 Ga 0.98 N, the material of the p-type cladding layer is p-Al 0.04 Ga 0.96 N, and the material of the contact layer is p-GaN.

[0087] In order to suppress the diffusion of impurities from the p-type semiconductor layer 326 to the active layer 124, an undoped nitride guiding layer (not shown) In 0.02 Ga 0.98 N can be inserted therebetween.

[0088] Ridge portions (also called mesa portions) 342 are formed as current-constricting structures 341 in the p-type semiconductor layer 326 (p-type cladding layer). The height of the ridge portion 342_1 in the DFB region can be several hundred nm, and the width of the ridge portion 342 (mesa width) can be several microns. For example, it may be 500 nm in height and 2 μm in width. The height of the ridge portion 342_2 in the tapered region may also be 500 nm. The width of the ridge portion 342 in the tapered region may widen in a tapered shape from the DFB region side toward the tapered region end face of the semiconductor laser element 300, from 2 μm to 10 μm in width.

[0089] The p-type semiconductor layer 326, having ridge portions 342 (342_1, 342_2), together with the active layer 324 and the n-type semiconductor layer 322, forms a ridge-type waveguide 344. The ridge-type waveguide 344 extends in the first direction (z-axis direction in the figure).

[0090] The n-side electrode 371 is formed on the back surface of the substrate 310, and the p-side electrode 372 is formed on the upper surface of the ridge portion 342.

[0091] Diffraction gratings 350_1 and 350_2 are formed on both sides of the mesa adjacent to the ridge-type waveguide 344 in the second direction (x-axis direction) of the DFB region 380. Each of the diffraction gratings 350_1 and 350_2 has a plurality of grooves 352 formed in the p-type semiconductor layer 326 adjacent to the mesa. The plurality of grooves 352 are adjacent in the first direction, and each groove extends in the second direction.

[0092] A protective layer 360 is formed on the p-type semiconductor layer 326. The material of the protective layer 360 is an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr.

[0093] The cross-sectional view of the diffraction grating 350 of the semiconductor laser element 300 according to this embodiment, in a plane Syz perpendicular to the x-axis, is the same as in Figure 7.

[0094] In this embodiment, similar to Embodiment 4 (Figure 6), the second portion of the diffraction grating 350 (not shown, corresponding to the second portion 153 in Figure 6) and the protective layer 360 are made of the same material. The difference from Figure 6 is that the third portion (not shown, corresponding to 154 in Figure 6) is a void, formed from air, vacuum, or a gas such as nitrogen or oxygen. In this case, n3=1, which allows the refractive index of the recesses in the periodic structure to be lowest, thereby increasing the refractive index difference between the recesses and convex parts.

[0095] As the gaps become larger, the difference between the refractive index n1 (~2.47) of the GaN in the convex parts of the periodic structure and the average refractive index inside the concave parts of the groove 352 increases, and κL DFB It can be seen that this becomes larger. In other words, the oscillation threshold of the DFB-LD can be reduced.

[0096] The embodiments merely illustrate the principles and applications of the present invention, and many modifications and changes in arrangement are permitted in the embodiments, without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0097] 100 Distributed feedback semiconductor laser element 110 circuit boards 120 Laminated structure 122 n-type semiconductor layer 124 Active layer 126 p-type semiconductor layer 141 Current confinement structure 142 Ridge section 144 Ridge Waveguides 150 Diffraction Gratings 151 Part 1 152 Groove 153 Part 2 154 Part 3 160 protective layer 200 Distributed Reflection Semiconductor Laser Element 210 circuit boards 220 Laminated structure 222 n-type semiconductor layer 224 Active layer 226 p-type semiconductor layer 241 Current confinement structure 242 Ridge section 244 Ridge Waveguide 250 DBR Mirror 252 Groove 260 protective layer 300 MOPA laser 310 circuit board 320 Laminated structure 322 n-type semiconductor layer 324 Active layer 326 p-type semiconductor layer 341 Current confinement structure 342 Ridge section 344 Ridge Waveguide 350 Diffraction Grating 352 Groove 360 protective layer 380 DFB area 382 Tapered Region

Claims

1. A semiconductor laser element, circuit board and A laminated structure comprising a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer formed on the substrate, Equipped with, The aforementioned laminated structure is formed with a current-constricting structure and a diffraction grating containing a plurality of grooves. The diffraction grating is The first refractive index n in which the plurality of grooves are formed １ A first part having, A second refractive index n is formed to cover the surface of the plurality of grooves. ２ A second part having, The second refractive index n, surrounded by the second portion inside the groove ２ The third refractive index n is different from the third refractive index n. ３ A third part having, A semiconductor laser element characterized by having the following features.

2. The first refractive index n in the diffraction grating １ , the second refractive index n ２ , the third refractive index n ３ are related such that n １ > n ２ > n ３ The semiconductor laser device according to claim 1, characterized in that this is the case.

3. The semiconductor laser element according to claim 1, characterized in that the upper surface of the region where the diffraction grating is formed is covered with a protective layer made of a different material from the first portion.

4. The semiconductor laser element according to claim 3, characterized in that the protective layer is made of the same material as the second portion.

5. The semiconductor laser element according to claim 3, characterized in that the third portion is a void.

6. The semiconductor laser element according to claim 5, characterized in that the width of the plurality of grooves is 100 nm or less.

7. The semiconductor laser element according to any one of claims 1 to 4, characterized in that the third part is an insulating material.

8. The semiconductor laser element according to claim 7, characterized in that the protective layer is made of the same material as the third portion.

9. The semiconductor laser element according to claim 7, characterized in that the insulating material is an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr.

10. The semiconductor laser element according to any one of claims 1 to 6, characterized in that the first part is a semiconductor and the second part is an insulating material.

11. The semiconductor laser element according to claim 10, characterized in that the insulating material is an oxide, nitride, or oxynitride containing at least one of Si, Ta, Al, Zn, Nb, Ti, Hf, or Zr.

12. The semiconductor laser element according to any one of claims 1 to 6, characterized in that the first portion is the second conductive semiconductor layer.

13. The active layer is defined as follows: In ｘ Al ｙ Ga １－ｘ－ｙ N, Individual ｘ Al ｙ Ga １－ｘ－ｙ P, In ｘ Al ｙ Ga １－ｘ―ｙ As, or In ｘ Ga １－ｘ As ｙ P １－ｙ A semiconductor laser element according to any one of claims 1 to 6, characterized in that it is the same as the above.

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