Semiconductor laser and method for manufacturing the same

Abstract

We provide high-performance, highly reliable nitride semiconductor lasers. [Solution] The semiconductor laser 100 includes a semiconductor substrate 110 and a laminated structure 112. The laminated structure 112 includes an n-type semiconductor layer 120, an active layer 130, and a p-type semiconductor layer 140. The laminated structure 112 includes a resonator and a diffraction grating layer 160 having a periodic structure including porous portions 162 and non-porous portions 164 that are periodically repeated in the direction of the resonator.

Description

[Technical Field]

[0001] This disclosure relates to semiconductor lasers. [Background technology]

[0002] Nitride semiconductor DFB-LDs are expected to have applications in fields such as spectroscopic analysis, quantum computing, atomic clocks, underwater communications, and medicine.

[0003] In conventional embedded nitride semiconductor distributed feedback laser diodes (DFB-LDs), for example, a periodic structure is formed on the surface of the n-AlGaN cladding layer using electron beam exposure and dry etching, and a GaN guide layer is regrown using a method such as MOCVD (Metal Organic Chemical Vapor Deposition) to embed a diffraction grating with periodically changing refractive index, on which the remaining LD multilayer structure including the active layer is grown (Non-Patent Literature 1). Continuous oscillation at room temperature down to several tens of mV has been reported with nitride semiconductor DFB-LDs fabricated by this method.

[0004] However, in this structure, crystal defects such as dislocations and vacancies, as well as impurity contamination, are likely to occur near the regrowth interface between the diffraction grating formed on the n-AlGaN cladding layer and the n-GaN guide layer. This can easily degrade the quality of the active layer regrown on top of it, potentially negatively impacting the initial characteristics and reliability of the finished semiconductor laser.

[0005] On the other hand, a method has been proposed for fabricating a structure in which the refractive index periodically changes in the thickness direction of the substrate (Patent Document 1). In this method, the refractive index is controlled using a porous structure formed in a high-concentration n-type GaN crystal by photoelectrochemical etching. Furthermore, Patent Document 2 discloses that a GaN-based LED with high light extraction efficiency can be realized by forming a DBR (Distributed Bragg Reflector) layer consisting of a nanoporous periodic structure in an n-type layer on a sapphire substrate using the method described in Patent Document 1. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent 9206524B2 [Patent Document 2] U.S. Patent 10458038B2 [Non-patent literature]

[0007] [Non-Patent Document 1] Shinichi Nagahama et al., Laser Research, Vol. 36, Supplement, 2008, pp. S23-S24. [Overview of the project] [Problems that the invention aims to solve]

[0008] In the structure described in Non-Patent Document 1, the uneven structure formed on the surface of the AlGaN layer by dry etching, etc., is embedded by crystal growth. This raises concerns that crystal defects such as dislocations and vacancies, as well as impurity contamination, may occur at the interface between the n-AlGaN cladding layer and the regrowth layer, degrading the quality of the active layer and negatively affecting the initial characteristics and reliability of the laser.

[0009] This disclosure is made in the circumstances described herein, and one exemplary objective of a certain aspect thereof is to provide a high-performance, highly reliable embedded nitride semiconductor laser with low occurrence of crystal defects such as dislocations and vacancies and impurity contamination at the regrowth interface, and high crystal quality of the active layer. [Means for solving the problem]

[0010] A semiconductor laser according to one aspect of the present disclosure comprises a semiconductor substrate and a laminated structure stacked on the semiconductor substrate, including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. The laminated structure comprises a resonator and a diffraction grating layer having a periodic structure including porous and non-porous portions that are periodically repeated in the direction of the resonator.

[0011] In addition, combinations of the above components arbitrarily, and those obtained by mutually replacing components and expressions among methods, apparatuses, systems, etc. are also effective as aspects of the present invention or the present disclosure. Furthermore, the description of this item does not explain all the essential features of the present invention, and thus, sub-combinations of these described features can also be the present invention.

Advantages of the Invention

[0012] According to the present disclosure, a high-performance and highly reliable embedded nitride semiconductor laser can be provided.

Brief Description of the Drawings

[0013] [Figure 1] It is a perspective view of a semiconductor laser according to Embodiment 1. [Figure 2] It is a diagram for explaining a method of manufacturing the semiconductor laser of FIG. 1. [Figure 3] It is a diagram for explaining a manufacturing method according to Modification 1. [Figure 4] It is a diagram for explaining a manufacturing method according to Modification 2. [Figure 5] It is a perspective view of a semiconductor laser according to Modification 3. [Figure 6] It is a diagram for explaining a method of manufacturing the semiconductor laser of FIG. 5. [Figure 7] It is a perspective view of a semiconductor laser according to Modification 4. [Figure 8] It is a diagram for explaining a method of manufacturing the semiconductor laser of FIG. 7. [Figure 9] It is a perspective view of MOPA-LD.

Modes for Carrying Out the Invention

[0014] (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.

[0015] A semiconductor laser according to one embodiment comprises a semiconductor substrate and a laminated structure stacked on the semiconductor substrate, including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. The laminated structure comprises a resonator and a diffraction grating layer including a periodic structure with porous and non-porous portions that are periodically repeated in the direction of the resonator.

[0016] In this configuration, the diffraction grating layer can be formed by periodically porousizing it in the direction of the resonator using photoelectrochemical etching. Conventional methods, which require the formation of a rough structure by dry etching and crystal growth inside the recesses, result in crystal defects and impurity contamination near the interface between the diffraction grating layer and adjacent layers. Forming the diffraction grating by porosity suppresses crystal defects and impurity contamination near the interface, resulting in a high-performance, highly reliable embedded nitride semiconductor DFB-LD.

[0017] The term "porous" refers to a portion of a material that has numerous pores formed within it. In contrast, the term "non-porous" refers to a portion of a material that does not have pores, or has negligible pores. For example, in a diffraction grating formed by a combination of two-beam interference exposure and photoelectrochemical etching, in a cross-section along the optical waveguide direction, the portion corresponding to the bright areas of the interference fringes may have a relatively large specific surface area (porous portion), while the portion corresponding to the dark areas of the interference fringes may have a relatively small specific surface area (non-porous portion). For example, the ratio of the specific surface areas of the porous portion to the non-porous portion may be 1000:1 or greater.

[0018] In one embodiment, the impurity concentration of the diffraction grating layer may be higher than the impurity concentration of the layer formed in contact with the diffraction grating layer.

[0019] In one embodiment, the impurity concentration of the diffraction grating layer may be higher than the impurity concentration of the layer formed in contact with the diffraction grating layer.

[0020] In one embodiment, the bandgap energy of the diffraction grating layer may be smaller than the bandgap energy of the layer formed in contact with the diffraction grating layer.

[0021] In one embodiment, the bandgap energy of the diffraction grating layer may be smaller than the bandgap energy of the layer formed in contact with the diffraction grating layer.

[0022] In one embodiment, the periodic structure may have different porous densities directly below the resonator and in other parts.

[0023] In one embodiment, the periodic structure may have a lower porous density directly below the resonator than the porous density of other parts.

[0024] In one embodiment, the resonator may be formed in the ridge growth section.

[0025] In one embodiment of the method for manufacturing a semiconductor laser, a two-beam interference exposure method is used in the step of forming the periodic structure described above.

[0026] In one embodiment of the semiconductor laser manufacturing method, an epitaxial wafer is prepared in which a low-concentration n-type AlGaN layer is formed on a high-concentration n-type AlGaN layer. While irradiating the wafer with light for a diffraction grating pattern using a two-beam interference lithography method or the like in an electrolyte such as KOH (potassium hydroxide), only the n-type AlGaN layer is periodically porousd by photoelectrochemical etching to create a periodic refractive index structure, i.e., a diffraction grating structure. At this time, the low-concentration n-type AlGaN layer is not etched, and a flat and clean crystal surface is maintained. Specific examples of electrolytes include KOH (potassium hydroxide) and K2S2O8 (potassium peroxodisulfate).

[0027] This allows for the growth of a multilayer LD structure including the active layer on the surface of a flat and clean low-concentration n-type AlGaN layer by regrowth using MOCVD or the like. This suppresses the occurrence of crystal defects and impurity contamination at the regrowth interface, resulting in a high crystal quality of the active layer and a high-performance, highly reliable embedded nitride semiconductor DFB-LD.

[0028] (Embodiment) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing will be denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. Furthermore, the embodiments are illustrative and not limiting to the disclosure or invention, and not all features or combinations thereof described in the embodiments are necessarily essential to the disclosure or invention.

[0029] Furthermore, the dimensions (thickness, length, width, etc.) of each component shown in the drawing may be enlarged or reduced as appropriate for ease of understanding. Moreover, the dimensions of multiple components do not necessarily represent their relative sizes; even if component A is depicted as thicker than component B in the drawing, component A may actually be thinner than component B.

[0030] (Embodiment 1) FIG. 1 is a perspective view of a semiconductor laser 100 according to Embodiment 1. The semiconductor laser 100 includes a substrate 110 and a stacked structure 112.

[0031] The substrate 110 is a nitride semiconductor and can have a composition of In x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x + y≦1). To generate blue laser light of 444 nm, the material of the substrate 110 can be GaN (x = y = 0). Also, the substrate 110 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.

[0032] The stacked structure 112 is formed on the substrate 110 by epitaxial growth and includes an n-type semiconductor layer 120, an active layer 130, and a p-type semiconductor layer 140. The n-type semiconductor layer 120 may include an n-type cladding layer 122 and an n-type guiding layer 124. For example, the material of the n-type cladding layer 122 is n-Al 0.05 Ga 0.95 N, and the material of the n-type guiding layer is n-GaN.

[0033] An active layer (light-emitting layer) 130 having a quantum well structure is formed on the n-type semiconductor layer 120. When the oscillation wavelength is 444 nm, for the material of the quantum well structure, In 0.01 Ga 0.99 N can be selected as the barrier layer, and In 0.15 Ga 0.85 N can be selected as the well layer.

[0034] In order to suppress the diffusion of impurities from the n-type semiconductor layer 120 to the active layer 130, an undoped nitride guiding layer (not shown) In 0.02 Ga 0.98 N can be inserted between them.

[0035] The p-type semiconductor layer 140 may also include an electron barrier layer (EBL) 142, a p-type guide layer 144, a p-type cladding layer 146, and a p-type contact layer 148. For example, the material of the electron barrier layer 142 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 140 to the active layer 130, an undoped nitride guide layer (not shown) can be inserted between them.

[0037] The p-type semiconductor layer 140 (p-type cladding layer 146) forms a ridge (also called a mesa) 150 as a current-constricted structure. The height of the ridge 150 can be several hundred nm, and the width of the ridge 150 (mesa width) can be several microns. For example, the height may be 500 nm and the width 2 μm.

[0038] The p-type cladding layer 146 having a ridge portion 150, together with the active layer 130 and the n-type cladding layer 122, forms a ridge waveguide type resonator. In the figure, the ridge waveguide type resonator extends in the z-axis direction, and the z-axis direction, that is, the direction of light guidance within the resonator, is called the resonator direction.

[0039] The laminated structure 112 includes a diffraction grating layer 160. The diffraction grating layer 160 includes porous portions 162 and non-porous portions 164 that are periodically repeated in the direction of the resonator.

[0040] In this embodiment, the diffraction grating layer 160 is formed within the n-type semiconductor layer 120, more specifically, within the n-type cladding layer 122.

[0041] The above describes the configuration of the semiconductor laser 100. As will be described later, the diffraction grating layer 160 can be formed by periodically porousizing it in the direction of the resonator using photoelectrochemical etching. This suppresses the occurrence of crystal defects and impurity contamination compared to conventional methods, namely those that form a rough structure by dry etching and grow crystals in the recesses. As a result, a high-performance, highly reliable embedded nitride semiconductor DFB-LD can be obtained.

[0042] Next, we will explain the manufacturing method of the semiconductor laser 100.

[0043] Figure 2 is a diagram illustrating the manufacturing method of the semiconductor laser 100 shown in Figure 1.

[0044] In this manufacturing method, a porous region is formed in a high-concentration n-type AlGaN layer formed inside the wafer, separated from the outermost surface, by photoelectrochemical etching, thereby creating a diffraction grating structure in which the refractive index changes periodically in the in-plane direction of the wafer.

[0045] Specifically, an AlGaN multilayer structure 210 is formed on a GaN substrate 200 by a MOCVD method or the like (S100). The AlGaN multilayer structure 210 corresponds to an n-type cladding layer 122, and has a Si concentration of 3 × 10⁻⁶. 18 cm -3 A lower concentration n-type AlGaN layer 212 and a Si concentration of 1 × 10 19 cm -3 A higher concentration n-type AlGaN layer 214 and a Si concentration of 3 × 10 18 cm -3 It includes a lower concentration n-type AlGaN layer 216.

[0046] Next, a wafer having a GaN substrate 200 and an AlGaN multilayer structure 210 is immersed in an electrolyte 220 consisting of KOH, NaOH, oxalic acid, etc., and a beam 230 is irradiated by a two-beam interference exposure method or the like to form an optical interference pattern 232 for diffraction grating formation on the wafer (S102).

[0047] As a result, in areas of high illuminance in the optical interference pattern 232 of the high-concentration n-type AlGaN layer 214, a porous structure is formed by photoelectrochemical etching, and porous portions 162 are formed at predetermined intervals. In areas of low illuminance in the optical interference pattern 232 of the high-concentration n-type AlGaN layer 214, the photoelectrochemical etching does not occur, and thus non-porous portions 164 are formed. Thus, a diffraction grating layer 160 is formed on the high-concentration n-type AlGaN layer 214 (S104).

[0048] The impurity concentration in the diffraction grating layer 160 is higher than the impurity concentration in the low-concentration n-type AlGaN layer 216 adjacent to the diffraction grating layer 160. Furthermore, the impurity concentration in the diffraction grating layer 160 is higher than the impurity concentration in the low-concentration n-type AlGaN layer 212 adjacent to the diffraction grating layer 160.

[0049] The bandgap energy of the diffraction grating layer 160 is smaller than the bandgap energy of the low-concentration n-type AlGaN layer 216 formed in contact with the diffraction grating layer 160. Furthermore, the bandgap energy of the diffraction grating layer 160 is smaller than the bandgap energy of the low-concentration n-type AlGaN layer 212 formed in contact with the diffraction grating layer 160.

[0050] Furthermore, an n-type guide layer 124 and a multi-quantum well (MQW) active layer 130 are formed on the wafer again by MOCVD or the like. In addition, a p-type semiconductor layer 140 is formed including an electron barrier layer (EBL), a p-type guide layer, a p-type cladding layer, a p-type contact layer, etc. (S106).

[0051] Next, a striped mask 240 made of SiO2 or the like is formed on the wafer (S108). Then, by dry etching or the like, the parts not covered by the striped mask 240 are removed to form ridge portions 150 (S110). After that, through a normal electrode formation process (not shown), an embedded nitride semiconductor DFB-LD structure having a diffraction grating made of a porous structure is completed.

[0052] According to this manufacturing method, the surface of the low-concentration n-type AlGaN layer 216, which is regrowthed by MOCVD or the like, remains flat and clean even after photoelectrochemical etching, with minimal processing damage and impurity contamination due to etching. Therefore, when an LD structure including an n-type guide layer 124 and an active layer 130 is formed by regrowth, the crystal quality of the LD structure including the active layer 130 can be maintained at a high level, making it possible to provide a high-performance and highly reliable nitride semiconductor DFB-LD.

[0053] Next, a modified example of the manufacturing method for the semiconductor laser 100 will be described.

[0054] In the manufacturing method shown in Figure 2, by appropriately selecting the photoelectrochemical etching conditions in step S102, it is possible to form a porous structure only on the high-concentration n-type AlGaN layer 214, with almost no effect on the low-concentration n-type AlGaN layer 216 on the outermost surface.

[0055] However, slight deviations in processing conditions or variations in wafer impurity concentration can leave etching damage or impurity contamination on the surface of the outermost low-concentration n-type AlGaN layer 216, i.e., the regrowth interface.

[0056] To further maintain high crystal quality at the regrowth interface, it is effective to protect the ridge formation region on the surface of the epiwafer (the surface of the low-concentration n-type AlGaN layer 216) where the diffraction grating is to be formed with a dielectric material that is transparent to the beam 230 used for exposure.

[0057] Figure 3 illustrates a manufacturing method according to Modification 1. In this modification, step S101 is inserted between steps S100 and S102 in Figure 2. In step S101, a protective film 250 transparent to the beam 230 is formed on the AlGaN multilayer structure 210 in the area (ridge formation area) 252 where the ridge portion 150 of the LD structure is to be formed. For example, the protective film 250 can be formed of a dielectric, such as SiO2.

[0058] In the subsequent step S102, a periodic porous structure is formed in the high-concentration n-type AlGaN layer 214 by photoelectrochemical etching using a two-beam interference exposure apparatus or the like (S102). At this time, the surface of the low-concentration n-type AlGaN layer 216 covered by the protective film 250 does not come into contact with the electrolyte 220 for photoelectrochemical etching, thus avoiding etching damage and contamination with impurities. Furthermore, since the low-concentration n-type AlGaN layer 216 beneath the protective film 250 is also irradiated with light through the transparent protective film 250, etching proceeds from the side of the protective film 250, allowing for porous formation.

[0059] In step S103, following step S102, the protective film 250 is removed using a buffered hydrofluoric acid solution (BHF) or the like. In the wafer shown in step S104, etching damage and impurity contamination are avoided on the surface of the low-concentration n-type AlGaN layer 216 in the ridge formation area 252. Therefore, when an LD structure including an n-type guide layer 124 and an active layer 130 is formed by regrowth, the crystal quality of the LD structure including the active layer 130 can be maintained at a high level, and a high-performance and highly reliable nitride semiconductor DFB-LD can be provided.

[0060] This modified method allows for even higher crystal quality within the ridge waveguide of the LD structure compared to the manufacturing method shown in Figure 2, thereby providing a higher-performance and higher-quality nitride semiconductor DFB-LD.

[0061] The following describes a method for fabricating nitride semiconductor DFB-LDs that offer even higher performance and greater reliability.

[0062] Figure 4 is a diagram illustrating the manufacturing method related to the modified example 2.

[0063] In this modified example 2, similar to modified example 1, the surface of the ridge formation region 252 of the AlGaN multilayer structure 210 is protected by a protective film 250 such as SiO2 (S101).

[0064] In the modified example 2, a step S120 is added after step S101 to remove the low-concentration n-type AlGaN layer 216 other than the ridge formation region 252 by dry etching or the like.

[0065] Next, in step S102, photoelectrochemical etching is performed using a two-beam interference exposure apparatus or the like. As a result, as shown in step S103, a diffraction grating layer 160 having a periodic porous structure is formed on the high-concentration n-type AlGaN layer 214.

[0066] Then, in step S104, the protective film 250 is removed. The surface of the low-concentration n-type AlGaN layer 216 corresponding to the ridge formation region 252 maintains a flat and clean crystal surface.

[0067] In step S106, recrystallization growth is performed, and the remaining portion of the n-type cladding layer 122, the n-type guide layer 124, the active layer 130, and the p-type semiconductor layer 140 are stacked in sequence. Then, in the same manner as in steps S108 and S110 in Figure 2, a ridge is formed in the p-type semiconductor layer 140.

[0068] In the modified example 2, in step S102, the high-concentration n-type AlGaN layer 214 other than the ridge formation region 252 comes into direct contact with the electrolyte 220. This improves the controllability and stability of periodic porous structure formation by photoelectrochemical etching.

[0069] On the other hand, the surface of the low-concentration n-type AlGaN layer 216 in the ridge formation region 252 is protected by the protective film 250, so there is no etching damage or impurity contamination. Therefore, a porous diffraction grating with high crystal quality and controllability at the regrowth interface can be stably formed, and a high-quality semiconductor laser 100 can be manufactured with a high yield.

[0070] In the above description, a diffraction grating layer 160 was formed on an n-type semiconductor layer 120, but the present disclosure is not limited thereto, and a diffraction grating layer 160 may also be formed on a p-type semiconductor layer 140.

[0071] Figure 5 is a perspective view of the semiconductor laser 100A according to Modification 3. In Modification 3, a diffraction grating layer 160 is formed on the p-type guide layer 144.

[0072] Figure 6 is a diagram illustrating the manufacturing method of the semiconductor laser 100A shown in Figure 5. In step S200, an n-type semiconductor layer 120, an active layer 130, and a p-type semiconductor layer 300 are formed on the GaN substrate 110 using the MOCVD method or the like. The n-type semiconductor layer 120 includes an n-type cladding layer and an n-type guide layer. The p-type semiconductor layer 300 includes an electron barrier layer (EBL) 302, a high-concentration p-type AlGaN layer 304, and a low-concentration p-type AlGaN layer 306.

[0073] Next, the wafer is immersed in an electrolyte 220 consisting of KOH, NaOH, oxalic acid, etc., and irradiated with a beam 230 of the two-beam interference lithography method to form an optical interference pattern 232 for diffraction grating formation on the p-type semiconductor layer 300 (S202).

[0074] As a result, in areas of high illuminance in the optical interference pattern 232 of the high-concentration p-type AlGaN layer 304, a porous structure is formed by photoelectrochemical etching, and porous portions 162 are formed at predetermined intervals. In areas of low illuminance in the optical interference pattern 232 of the high-concentration p-type AlGaN layer 304, the photoelectrochemical etching does not occur, and thus non-porous portions 164 are formed. Thus, a diffraction grating layer 160 is formed on the high-concentration p-type AlGaN layer 304 (S204).

[0075] In the subsequent step S206, a p-type semiconductor layer 320 is formed again by the MOCVD method or the like. The p-type semiconductor layer 320 includes a p-type cladding layer 322 and a p-type contact layer 324.

[0076] The subsequent steps are the same as steps S108 and S110 in Figure 2.

[0077] This manufacturing method provides a high-performance, high-quality nitride semiconductor DFB-LD with less damage to the active layer and other components compared to conventional methods that form a diffraction grating structure on the p-type semiconductor layer side by dry etching or the like.

[0078] The technology described herein can also be applied to distributed black reflective LDs (DBR-LDs).

[0079] Figure 7 is a perspective view of a semiconductor laser 100B according to Modification 4. This semiconductor laser 100B is a DBR-LD, and a diffraction grating 180 is formed as a mirror on the end face of the resonator. The diffraction grating 180 includes porous portions 182 and non-porous portions 184 that are periodically repeated in the direction of the resonator.

[0080] In this embodiment, the diffraction grating 180 is formed within the n-type semiconductor layer 120, more specifically, within the n-type cladding layer 122.

[0081] Figure 8 illustrates the manufacturing method of the semiconductor laser 100B shown in Figure 7. The manufacturing method of the semiconductor laser 100B is basically the same as that of Figure 2. The difference is that in step S102, where the diffraction grating 180 is formed, the beam 230 of the two-beam interference exposure is irradiated only to the region where the diffraction grating 180 is to be formed. As a result, as shown in step S104, a DBR mirror is formed on the rear end face side of the semiconductor laser 100B.

[0082] According to this manufacturing method, the surface of the low-concentration n-type AlGaN layer 216, which is regrowthed by MOCVD or the like, remains flat and clean even after photoelectrochemical etching, with minimal processing damage and impurity contamination due to etching. As a result, the crystal quality of the LD structure formed by regrowth can be maintained at a high level, and a high-performance, highly reliable nitride semiconductor DBR-LD can be provided.

[0083] The technology described herein can also be applied to MOPA-LD, which combines a DFB-LD and an optical amplifier.

[0084] Figure 9 is a perspective view of the MOPA-LD100C. This MOPA-LD100C includes a DFB-LD region 400 and an optical amplification region 410. The DFB-LD region 400 has a structure similar to that of the semiconductor laser 100 shown in Figure 1. Specifically, a diffraction grating 190 is formed on the n-type cladding layer 122. This diffraction grating 190 includes porous portions 192 and non-porous portions 194 that are periodically repeated in the direction of the resonator. The diffraction grating 190 can be formed in the same manner as in step S102 of Figure 8.

[0085] This MOPA-LD100C, like the semiconductor laser 100 described above, can maintain high crystal quality in the LD structure formed by regrowth, and therefore possesses high performance and high reliability.

[0086] 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]

[0087] 100 Semiconductor Lasers 110 circuit boards 112 Laminated structure 120 n-type semiconductor layer 122 n-type cladding layer 124 n-type guide layer 160 Diffraction grating layers 162 Porous part 164 Non-porous part 130 Active layer 140 p-type semiconductor layer 142 Electron barrier layer 144 p-type guide layer 146 p-type cladding layer 148 p-type contact layer 150 Ridge section 180 Diffraction Grating 182 Porous part 184 Non-porous part 190 Diffraction Grating 192 Porous part 194 Non-porous part 200 GaN substrate 210 AlGaN multilayer structure 212 Low concentration n-type AlGaN layer 214 High concentration n-type AlGaN layer 216 Low concentration n-type AlGaN layer 250 Protective film 252 Ridge formation planned region 230 beams

Claims

1. Semiconductor substrate and A laminated structure comprising a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, laminated on the aforementioned semiconductor substrate, Equipped with, The aforementioned laminated structure is Resonator and, A diffraction grating layer having a periodic structure including porous and non-porous portions that are periodically repeated in the direction of the resonator, A semiconductor laser characterized by having the following features.

2. The semiconductor laser according to claim 1, characterized in that the impurity concentration of the diffraction grating layer is higher than the impurity concentration of the layer formed in contact with the periodic structure.

3. The semiconductor laser according to claim 2, characterized in that the impurity concentration of the diffraction grating layer is higher than the impurity concentration of the layer formed in contact with the diffraction grating layer.

4. The semiconductor laser according to claim 1 or 2, characterized in that the band gap energy of the diffraction grating layer is smaller than the band gap energy of the layer formed in contact with the diffraction grating layer.

5. The semiconductor laser according to claim 4, characterized in that the band gap energy of the diffraction grating layer is smaller than the band gap energy of the layer formed in contact with the diffraction grating layer.

6. The semiconductor laser according to claim 1, characterized in that the periodic structure has different porous densities directly below the resonator and in other parts.

7. The semiconductor laser according to claim 6, characterized in that the periodic structure has a porous density directly below the resonator that is lower than the porous density of the other parts.

8. The semiconductor laser according to claim 1, characterized in that the resonator is formed in the ridge portion.

9. A method for manufacturing a semiconductor laser according to any one of claims 1 to 3, A method for manufacturing a semiconductor laser, characterized in that a two-beam interference exposure method is used in the step of forming the periodic structure.

Images