WO2019146321A1 - Semiconductor laser element - Google Patents

Abstract

This semiconductor laser element (1) is provided with: a first conductivity-type first semiconductor layer (20); an active layer (32) disposed over the first semiconductor layer (20); and a second conductivity-type second semiconductor layer (40) disposed over the active layer (32). A stacked structure (90), which includes the first semiconductor layer (20), the active layer (32), and the second semiconductor layer (40), includes a pair of opposing resonator end surfaces (95f and 95r) and a waveguide (90a) which is disposed between the pair of resonator end surfaces (95f and 95r) and formed with a diffraction grating (70). If a direction orthogonal to the pair of resonator end surfaces (95f and 95r) is a waveguide direction, the filling factor of the diffraction grating (70) in the waveguide direction is varied depending on the position in a direction orthogonal to the direction in which the waveguide direction and the stacked structure (90) are stacked.

Description

Semiconductor laser device

The present disclosure relates to a semiconductor laser device having a diffraction grating.

In addition, this application applies to the National Research and Development Corporation New Energy and Industrial Technology Development Organization "High brightness and high efficiency next-generation laser technology development / new light source / element technology development for next-generation processing / high efficiency processing" in fiscal 2016 Development of GaN-based high-power, high-beam quality semiconductor lasers "is a patent application subject to the application of Article 19 of the Industrial Technology Strengthening Act.

In recent years, semiconductor laser devices are used as light sources for image display devices such as displays and projectors, light sources for vehicle headlamps, light sources for industrial lighting and consumer lighting, or industries such as laser welding devices, thin film annealing devices, and laser processing devices. It attracts attention as a light source of various uses, such as a light source of equipment. In addition, for the semiconductor laser device used as a light source for the above-mentioned application, it is desired to achieve high output and high beam quality in which the light output largely exceeds 1 watt.

As a method of increasing the output of a semiconductor laser device, a method of forming an array by arranging a plurality of wide waveguides in parallel is widely used. In the array type semiconductor laser device, since a plurality of light emitting portions are formed, the light is collected at one place using an optical system. In particular, in order to combine a plurality of laser beams of different emission wavelengths on a predetermined optical axis with high accuracy, it is important to control the oscillation wavelength of each laser beam. As a structure capable of precisely controlling the oscillation wavelength, a DFB (Distributed Feedback) laser device, a DBR (Distributed Bragg Reflector) laser device or the like is used.

In order to achieve high beam quality, it is desirable to oscillate in the fundamental transverse mode in the semiconductor laser device. However, for higher power output, it is advantageous for the waveguide width to be wider, so that the transverse mode of high power laser light whose light output exceeds 1 watt is a multimode including higher order modes. There are many. As a method for solving such a trade-off between beam quality and output, a method is proposed in which a fundamental transverse mode is selectively oscillated by providing a gain difference in the transverse mode (Patent Document 1).

Patent Document 1 discloses a conventional DFB laser device. FIG. 22 is a perspective view showing the configuration of the conventional DFB laser device disclosed in Patent Document 1. As shown in FIG.

The conventional semiconductor laser device shown in FIG. 22 has a multimode waveguide 931 whose refractive index is changed in the lateral direction, and a DFB type that utilizes optical feedback by a diffraction grating 932 formed in a guide layer 913. It is a semiconductor laser device. In the semiconductor laser device shown in FIG. 22, by providing the diffraction grating only in the portion where the light intensity of the selected transverse mode is maximum, the amount of optical feedback of the selected transverse mode is made larger than that of the other modes. I'm trying to oscillate only the mode.

Japanese Patent Application Laid-Open No. 6-310801

However, if the diffraction grating is arranged only at the portion where the light intensity is maximum, the light intensity at the lateral end of the diffraction grating is large, so the power light conversion efficiency of the semiconductor laser device is reduced due to light scattering at the end. Becomes noticeable.

An object of the present disclosure is to provide a DFB type semiconductor laser device which has a good beam quality and can suppress a decrease in power-to-light conversion efficiency.

In order to achieve the above object, one aspect of a semiconductor laser device according to the present disclosure includes a first semiconductor layer of a first conductivity type, an active layer disposed above the first semiconductor layer, and the active layer A stacked structure including a second semiconductor layer of a second conductivity type disposed on the upper side, the stacked structure including the first semiconductor layer, the active layer, and the second semiconductor layer, and a pair of opposing resonator end faces; And a waveguide disposed between the pair of resonator end faces and having a diffraction grating formed thereon, and the direction orthogonal to the pair of resonator end faces is a waveguide direction, the diffraction in the waveguide direction The filling factor of the grating varies depending on the waveguide direction and the position in the direction orthogonal to the stacking direction of the stacked structure.

As described above, the desired light feedback amount distribution can be obtained by changing the filling factor of the diffraction grating depending on the waveguide direction and the position in the direction orthogonal to the stacking direction. Therefore, by appropriately adjusting the filling factor of the diffraction grating, it is possible to suppress light scattering due to the diffraction grating and to selectively oscillate a desired transverse mode corresponding to the light feedback amount distribution. Therefore, it is possible to realize a DFB type semiconductor laser device which is excellent in beam quality and can suppress a decrease in power-light conversion efficiency.

Further, in one aspect of the semiconductor laser device according to the present disclosure, the diffraction grating has a structure which is intermittently interrupted in the waveguide direction, and a length in which the diffraction grating is continuous in the waveguide direction is It may be changed depending on the waveguide direction and the position in the direction orthogonal to the stacking direction.

As described above, when the diffraction grating has a structure that is periodically interrupted in the waveguide direction, the filling factor of the diffraction grating is defined using the period of the diffraction grating and the continuous length of the diffraction grating. Therefore, for example, when making the period of the diffraction grating constant, the waveguide direction and the waveguide direction and the position in the direction orthogonal to the stacking direction are changed by changing the length in which the diffraction grating continues in the waveguide direction. It is possible to realize a semiconductor laser device having a diffraction grating whose filling factor changes with the position in the direction orthogonal to the stacking direction.

In one aspect of the semiconductor laser device according to the present disclosure, the period of the diffraction grating may be changed depending on the position in the direction perpendicular to the waveguide direction and the stacking direction.

With such a configuration, for example, a semiconductor laser having a diffraction grating whose filling factor changes depending on the position in the direction orthogonal to the waveguide direction and the stacking direction by making the length in which the diffraction grating continues in the waveguide direction constant. A device can be realized.

In one aspect of the semiconductor laser device according to the present disclosure, the filling factor may be larger than at least one end at the center of the waveguide in the direction orthogonal to the waveguide direction and the stacking direction.

Thus, for example, when the filling factor of the diffraction grating is set to 0.5 or less, the optical feedback amount at the center of the waveguide direction by the diffraction grating and the direction orthogonal to the stacking direction is the optical feedback at the end in the orthogonal direction It is possible to make it larger than the amount. Therefore, the amount of optical feedback of the fundamental transverse mode whose electric field strength is larger than that of the end can be selectively increased at the center of the orthogonal direction, so that oscillation of the fundamental transverse mode can be promoted.

In one aspect of the semiconductor laser device according to the present disclosure, the filling factor may be smaller than at least one end at the center of the waveguide in the direction orthogonal to the waveguide direction and the stacking direction.

Thus, for example, when the filling factor of the diffraction grating is set to 0.5 or more, the optical feedback amount at the center of the waveguide direction by the diffraction grating and the direction orthogonal to the stacking direction is the optical feedback at the end in the orthogonal direction It is possible to make it larger than the amount. Therefore, the amount of optical feedback of the fundamental transverse mode whose electric field strength is larger than that of the end can be selectively increased at the center of the orthogonal direction, so that oscillation of the fundamental transverse mode can be promoted.

In one aspect of the semiconductor laser device according to the present disclosure, the second semiconductor layer includes a ridge portion having a longitudinal direction in the waveguide direction, and the filling factor is orthogonal to the waveguide direction and the stacking direction. In the lower region of the ridge, and may change exponentially outside the lower region of the ridge.

As a result, the electric field strength distribution of the fundamental transverse mode and the amount of optical feedback can be made to coincide with each other inside and outside the waveguide, so that the selectivity of the fundamental transverse mode by the diffraction grating can be further improved.

In one aspect of the semiconductor laser device according to the present disclosure, the first semiconductor layer may be a cladding layer, and the diffraction grating may be disposed in the first semiconductor layer.

Thus, the diffraction grating can be formed in the laminated structure without separately providing a layer for disposing the diffraction grating.

Further, one aspect of the semiconductor laser device according to the present disclosure includes a guide layer disposed between the first semiconductor layer and the active layer, and the diffraction grating is disposed in the guide layer. It is also good.

Thus, the diffraction grating can be formed in the laminated structure without separately providing a layer for disposing the diffraction grating.

It is possible to provide a DFB type semiconductor laser device which is excellent in beam quality and can suppress a decrease in power-light conversion efficiency.

FIG. 1A is a schematic top view showing the configuration of the semiconductor laser device according to the first embodiment. FIG. 1B is a schematic cross-sectional view showing the configuration of the semiconductor laser device according to the first embodiment. FIG. 2A is a schematic cross-sectional view showing a first step of the method of manufacturing a semiconductor laser device according to the first embodiment. FIG. 2B is a schematic cross-sectional view showing a second step of the method of manufacturing a semiconductor laser device according to the first embodiment. FIG. 2C is a top view showing a second step of the method of manufacturing a semiconductor laser device according to the first embodiment. FIG. 2D is a schematic cross sectional view showing a third step in the method for manufacturing a semiconductor laser device according to the first embodiment. FIG. 2E is a schematic cross sectional view showing a fourth step of the method for manufacturing the semiconductor laser device according to the first embodiment. FIG. 2F is a schematic cross-sectional view showing a fifth step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 2G is a schematic cross sectional view showing a sixth step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 2H is a schematic cross-sectional view showing a seventh step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 2I is a schematic cross sectional view showing an eighth step of the method for manufacturing the semiconductor laser device according to the first embodiment. FIG. 2J is a schematic cross-sectional view showing a ninth step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 2K is a schematic cross-sectional view showing a tenth step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 2L is a schematic cross-sectional view showing an eleventh step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 2M is a schematic cross-sectional view showing a twelfth step of the method for manufacturing the semiconductor laser device in accordance with the first embodiment. FIG. 3 is a diagram for explaining the electric field distribution in the transverse mode of the semiconductor laser device according to the first embodiment. FIG. 4A is a schematic cross-sectional view showing the configuration of the diffraction grating when the filling factor f of the diffraction grating of the semiconductor laser device according to the first embodiment is 0.5. FIG. 4B is a schematic cross-sectional view showing the configuration of the diffraction grating when the filling factor f of the diffraction grating of the semiconductor laser device according to the first embodiment is 0.25. FIG. 4C is a graph showing the relationship between the filling factor f of the diffraction grating according to Embodiment 1 and the amount of optical feedback by the diffraction grating. FIG. 5 is a view showing the relationship between the filling rate of the diffraction grating and the position in the direction orthogonal to the waveguide direction and the stacking direction of the semiconductor laser device according to the first embodiment. FIG. 6 is a graph showing the relationship between the amount of optical feedback and the electric field intensity distribution of laser light according to Embodiment 1, and the positions in the direction of the waveguide and in the direction perpendicular to the stacking direction. FIG. 7 is a top view showing the shape of the diffraction grating according to the first embodiment. FIG. 8 is a top view showing the shape of a diffraction grating according to a modification of the first embodiment. FIG. 9 is a schematic cross-sectional view showing the configuration of the semiconductor laser device according to the second embodiment. FIG. 10A is a schematic cross sectional view showing a first step of a method of manufacturing a semiconductor laser device according to a second embodiment. FIG. 10B is a schematic cross-sectional view showing a second step of the method for manufacturing the semiconductor laser device in accordance with the second embodiment. FIG. 10C is a schematic cross-sectional view showing a third step of the method for manufacturing the semiconductor laser device in accordance with the second embodiment. FIG. 10D is a schematic cross-sectional view showing a fourth step of the method for manufacturing the semiconductor laser device in accordance with the second embodiment. FIG. 11 is a diagram showing the relationship between the position in the direction orthogonal to the waveguide direction and the stacking direction of the semiconductor laser device according to the second embodiment and the filling factor of the diffraction grating. FIG. 12 is a graph showing the electric field intensity distribution of laser light and the optical feedback amount distribution by the diffraction grating in the semiconductor laser device according to the second embodiment. FIG. 13 is a top view showing the shape of the diffraction grating according to the second embodiment. FIG. 14 is a diagram showing the relationship between the position in the direction orthogonal to the waveguide direction and the stacking direction of the semiconductor laser device according to the third embodiment and the filling factor of the diffraction grating. FIG. 15 is a graph showing the electric field intensity distribution of laser light and the optical feedback amount distribution by the diffraction grating in the semiconductor laser device according to the third embodiment. FIG. 16 is a top view showing the shape of the diffraction grating according to the third embodiment. FIG. 17 is a top view showing the shape of a diffraction grating according to a modification of the third embodiment. FIG. 18A is a graph showing the relationship between the filling factor of the diffraction grating and the position in the direction orthogonal to the waveguide direction and the stacking direction of the diffraction grating according to the fourth embodiment. 18B is a top view showing the shape of the diffraction grating according to Embodiment 4. FIG. FIG. 19 is a top view showing the shape of the diffraction grating according to the fifth embodiment. FIG. 20 is a diagram showing the relationship of the amount of optical feedback to the period of the diffraction grating according to the fifth embodiment. FIG. 21 is a diagram showing the calculation result of the relationship between the filling factor and the amount of optical feedback when the fifth order diffraction grating is used. FIG. 22 is a diagram showing the configuration of the conventional semiconductor laser device disclosed in Patent Document 1. As shown in FIG.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The embodiments described below each show a preferable specific example of the present disclosure. Accordingly, the numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps (steps) and order of steps, etc. shown in the following embodiments are merely examples and limit the present disclosure. It is not the main point to do. Therefore, among the components in the following embodiments, components that are not described in the independent claims indicating the highest concept of the present disclosure are described as optional components.

Each figure is a schematic view, and is not necessarily strictly illustrated. Therefore, the scale and the like do not necessarily match in each figure. In the drawings, substantially the same components are denoted by the same reference numerals, and redundant description will be omitted or simplified.

Further, in the present specification and drawings, the X axis, the Y axis, and the Z axis represent three axes of a three-dimensional orthogonal coordinate system. The X axis and the Y axis are axes orthogonal to each other, and both orthogonal to the Z axis.

Moreover, in the present specification, the terms "upper" and "lower" do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute space recognition, but are based on the stacking order in the lamination configuration. It is used as a term defined by the relative positional relationship to Also, the terms "upper" and "lower" are not only used when two components are spaced apart from one another and there is another component between the two components, but two components It applies also when arrange | positioned in the mutually adjacent state.

Embodiment 1
[Configuration of semiconductor laser device]
First, the configuration of the semiconductor laser 1 according to the first embodiment will be described with reference to FIGS. 1A and 1B. 1A and 1B are a schematic top view and a cross-sectional view showing the configuration of a semiconductor laser device 1 according to the present embodiment, respectively. FIG. 1B shows a cross section of the semiconductor laser device 1 taken along line IB-IB in FIG. 1A.

The semiconductor laser device 1 shown in FIGS. 1A and 1B is a DFB laser device in which a diffraction grating 70 is formed. In the present embodiment, the semiconductor laser device 1 is mainly made of a nitride semiconductor. As shown in FIG. 1B, the semiconductor laser device 1 includes a substrate 10, a first semiconductor layer 20, a light emitting layer 30, a second semiconductor layer 40, an electrode member 50, a dielectric layer 60, and a diffraction grating 70. And an n-side electrode 80. The light emitting layer 30 includes an n-side light guide layer 31, an active layer 32 and a p-side light guide layer 33. The second semiconductor layer 40 includes an electron barrier layer 41, a p-side cladding layer 42, and a p-side contact layer 43. As shown in FIG. 1B, the semiconductor laser device 1 includes a laminated structure 90 including a first semiconductor layer 20, an active layer 32, and a second semiconductor layer 40. As shown in FIG. 1A, the laminated structure 90 includes a pair of opposed resonator end faces 95f and 95r, and a waveguide 90a disposed between the pair of resonator end faces 95f and 95r, in which the diffraction grating 70 is formed. And. The pair of resonator end faces 95 f and 95 r are disposed at the end in the direction perpendicular to the stacking direction of the stacked structure 90.

The second semiconductor layer 40 extends in the waveguide direction, assuming that the direction orthogonal to the pair of resonator end faces 95f and 95r is the waveguide direction (that is, the laser resonator direction or the Z-axis direction in FIG. 1B) A ridge portion 40a formed of stripe-shaped (that is, ridge-shaped) convex portions, and a direction perpendicular to the waveguide direction and the lamination direction of the laminated structure 90 (that is, the Y-axis direction) from the root of the ridge portion 40a And the flat part 40b which spreads to.

The width and height of the ridge portion 40a are not particularly limited, but as an example, the width (stripe width) of the ridge portion 40a is 1 μm to 100 μm, and the height of the ridge portion 40a is 100 nm to 1 μm. In order to operate the semiconductor laser device 1 with high light output (for example, watt class), the width of the ridge portion 40a may be 10 μm to 50 μm, and the height of the ridge portion 40a may be 300 nm to 800 nm. In the present embodiment, the width is 10 μm and the height is 500 nm.

The substrate 10 is, for example, a GaN substrate. In the present embodiment, an n-type hexagonal GaN substrate whose main surface is the (0001) plane is used as the substrate 10.

The first semiconductor layer 20 is disposed above the substrate 10 as shown in FIG. 1B. The first semiconductor layer 20 is a semiconductor layer of a first conductivity type, and is, for example, an n-side cladding layer made of n-type AlGaN.

In the present embodiment, the diffraction grating 70 is disposed in the first semiconductor layer 20 which is a cladding layer. The diffraction grating 70 is made of a material having a refractive index different from that of the first semiconductor layer 20. The material forming the diffraction grating 70 is, for example, a dielectric film made of SiO ₂ , SiN, AlN or the like, a semiconductor made of GaN, InGaN or the like, or air. The amount of light feedback by the diffraction grating 70 increases as the difference in refractive index between the first semiconductor layer 20 and the diffraction grating 70 increases. Therefore, in the present embodiment, in order to increase the amount of optical feedback, air having the smallest refractive index is embedded in the first semiconductor layer 20. Although not shown, the diffraction grating 70 may be disposed in the n-side light guide layer 31 (see Embodiment 2 described later), and is formed in the p-side light guide layer 33 or the p-side cladding layer 42. It may be However, as described later, when the diffraction grating 70 is formed by regrowth of a nitride semiconductor, it is known that impurities such as Si and oxygen which work as n-type dopant pile up at the regrowth interface. When the n-type dopant piles up in the p-type semiconductor layer, for example, a voltage increase occurs at the time of laser oscillation of the semiconductor laser device 1, and as a result, the power light conversion efficiency of the semiconductor laser device 1 is reduced. Therefore, when the diffraction grating is formed using regrowth as in the present embodiment, the decrease in the power-to-light conversion efficiency of the semiconductor laser device 1 is suppressed by providing the diffraction grating 70 in the n-type semiconductor layer. it can.

Further, even when the difference in refractive index between the diffraction grating 70 and the first semiconductor layer 20 is small, the light feedback amount of the diffraction grating 70 can be increased by arranging the diffraction grating 70 near the active layer 32. . Specifically, by reducing the thickness of the n-side light guide layer 31, the amount of light feedback of the diffraction grating 70 can be increased. Further, the diffraction grating 70 may be transparent to the oscillation wavelength of the semiconductor laser element 1. Thereby, the light absorption loss by the diffraction grating 70 can be suppressed.

The diffraction grating 70 is formed in the vicinity immediately below the ridge portion 40a, and has a periodic structure in the waveguide direction (Y-axis direction). In the present embodiment, the diffraction grating 70 has a structure that is intermittently interrupted in the waveguide direction. More specifically, as shown in FIG. 1A, in the diffraction grating 70, portions of a specific shape are periodically arranged in the waveguide direction.

The light emitting layer 30 is disposed above the first semiconductor layer 20, as shown in FIG. 1B. In the present embodiment, the light emitting layer 30 is made of a nitride semiconductor. The light emitting layer 30 has, for example, a structure in which an n-side light guide layer 31 made of n-GaN, an active layer 32 made of an InGaN quantum well layer, and a p-side light guide layer 33 made of p-GaN are stacked. Have.

The second semiconductor layer 40 is disposed above the light emitting layer 30, as shown in FIG. 1B. The second semiconductor layer 40 is a semiconductor layer of a second conductivity type different from the first conductivity type, and includes, for example, an electron barrier layer 41 made of AlGaN, a p-side cladding layer 42 made of p-type AlGaN, and p-type GaN. And the p-side contact layer 43 are stacked.

The p-side cladding layer 42 has a convex portion. The p-side contact layer 43 is disposed on the convex portion of the p-side cladding layer 42 as the uppermost layer of the ridge portion 40 a. Thus, the ridge portion 40 a in a stripe shape is configured by the convex portion of the p-side cladding layer 42 and the p-side contact layer 43. In addition, the p-side cladding layer 42 has flat portions forming flat portions 40 b on both sides of the ridge portion 40 a. The uppermost surface of the flat portion 40b is the surface of the p-side cladding layer 42, and the p-side contact layer 43 is not formed on the uppermost surface of the flat portion 40b.

The dielectric layer 60 is an insulating film made of SiO ₂ formed on the side surface of the ridge portion 40 a in order to confine light. Specifically, the dielectric layer 60 is continuously formed from the side surface of the ridge portion 40a to the flat portion 40b. In the present embodiment, the dielectric layer 60 is continuous over the side surface of the p-side contact layer 43, the side surface of the protrusion of the p-side cladding layer 42, and the top surface of the p-side cladding layer 42 around the ridge portion 40a. It is formed.

The shape of the dielectric layer 60 is not particularly limited, but the dielectric layer 60 may be in contact with the side surface of the ridge portion 40 a and the flat portion 40 b. Thus, light emitted immediately below the ridge portion 40a can be stably confined.

The electrode member 50 is disposed above the second semiconductor layer 40. The electrode member 50 is wider than the ridge portion 40a. That is, the width (the width in the X-axis direction) of the electrode member 50 is larger than the width (the width in the X-axis direction) of the ridge portion 40a. The electrode member 50 is in contact with the top surfaces of the dielectric layer 60 and the ridge portion 40a.

In the present embodiment, the electrode member 50 has a p-side electrode 51 for supplying current and a pad electrode 52 disposed above the p-side electrode 51.

The p-side electrode 51 is in contact with the upper surface of the ridge portion 40 a. The p-side electrode 51 is an ohmic electrode in ohmic contact with the p-side contact layer 43 above the ridge portion 40a, and is in contact with the top surface of the p-side contact layer 43 which is the top surface of the ridge portion 40a. The p-side electrode 51 is formed using, for example, a metal material such as Pd, Pt, or Ni. In the present embodiment, the p-side electrode 51 has a two-layer structure of Pd / Pt.

The pad electrode 52 is wider than the ridge portion 40 a and is in contact with the dielectric layer 60. That is, the pad electrode 52 is formed to cover the ridge portion 40 a and the dielectric layer 60. The pad electrode 52 is formed using, for example, a metal material such as Ti, Ni, Pt, Au or the like. In the present embodiment, the pad electrode 52 has a three-layer structure of Ti / Pt / Au.

As shown in FIG. 1A, the pad electrode 52 is formed inside the second semiconductor layer 40 in order to improve the yield when the semiconductor laser element 1 is singulated. That is, when the semiconductor laser 1 is viewed from the top, the pad electrode 52 is not formed at the edge of the end of the semiconductor laser 1. That is, the semiconductor laser device 1 has a non-current injection region in which current is not supplied to the edge of the end. In addition, the cross-sectional shape of the region in which the pad electrode 52 is formed has a structure shown in FIG. 1B in any part.

Further, in the semiconductor laser device 1 intended to operate with high light output (that is, high power operation), an end surface coat film such as a dielectric multilayer film is formed on the resonator end faces 95f and 95r. It is difficult to form this end face coat film only on the end face, and it also wraps around the upper surface of the semiconductor laser device 1. As described above, when the end face coat film is rolled up to the upper surface, the pad electrode 52 is not formed at the end of the semiconductor laser device 1 in the waveguide direction (Z-axis direction). In some cases, the dielectric layer 60 and the end surface coat film come in contact with each other at the end in the waveguide direction. At this time, if the dielectric layer 60 is not formed or the film thickness of the dielectric layer 60 is thin for light confinement, the influence of the end face coating film on the light propagating to the end of the semiconductor laser device 1 in the waveguide direction. Cause loss of light. Therefore, in order to sufficiently confine the light generated in the light emitting layer 30, the film thickness of the dielectric layer 60 may be 100 nm or more. On the other hand, if the film thickness of the dielectric layer 60 is too large, it becomes difficult to form the pad electrode 52. Therefore, the film thickness of the dielectric layer 60 is the height of the ridge portion 40a (that is, the ridge portion 40a is flat portion 40b). It is good to make it below the height which protrudes upwards from.

Although etching damage may remain on the side surfaces of the ridge portion 40a and the flat portion 40b in the etching process for forming the ridge portion 40a and a leak current may be generated, the ridge portion 40a and the flat portion 40b may be dielectric By covering with the body layer 60, the generation of unnecessary leak current can be reduced.

The n-side electrode 80 is disposed on the lower surface of the substrate 10. The n-side electrode 80 is an ohmic electrode in ohmic contact with the substrate 10. The n-side electrode 80 is, for example, a laminated film made of Ti / Pt / Au. The configuration of the n-side electrode 80 is not limited to this. The n-side electrode 80 may be a laminated film in which Ti and Au are laminated.

[Method of manufacturing a semiconductor laser device]
Next, a method of manufacturing the semiconductor laser device 1 according to the present embodiment will be described with reference to FIGS. 2A to 2L. FIG. 2A, FIG. 2B and FIG. 2D to FIG. 2M are schematic cross-sectional views showing each step in the method for manufacturing the semiconductor laser device 1 according to the embodiment. FIG. 2C is a top view showing a second step in the method for manufacturing the semiconductor laser device 1 according to the present embodiment.

First, as shown in FIG. 2A, metalorganic chemical vapor deposition (MOCVD) is used on the substrate 10 which is an n-type hexagonal GaN substrate whose major surface is a (0001) plane. The first semiconductor layer 20 is deposited. Specifically, an n-side cladding layer of n-type AlGaN is grown 3 μm as the first semiconductor layer 20 on the substrate 10.

Next, as shown in FIG. 2B, a first protective film 91 is formed on the first semiconductor layer 20. Specifically, a 300 nm thick silicon oxide film (SiO ₂ ) is formed on the first semiconductor layer 20 as the first protective film 91 by plasma CVD (Chemical Vapor Deposition) method using silane (SiH ₄ ). Do.

In addition, the film-forming method of the 1st protective film 91 is not restricted to plasma CVD method, For example, well-known film-forming methods, such as a thermal CVD method, a sputtering method, a vacuum evaporation method, or a pulse laser film-forming method, are used. It can be used. Further, the film forming material of the first protective film 91 is not limited to the above-described one, and may be, for example, a material having selectivity for etching of the first semiconductor layer 20 described later, such as a dielectric or metal. Just do it. Next, the first protective film 91 is selectively removed using a lithography method and an etching method. As a lithography method, a photolithography method using a short wavelength light source, an electron beam lithography method of direct writing with an electron beam, a nanoimprint method, or the like can be used. As an etching method, for example, dry etching by reactive ion etching (RIE) using a fluorine-based gas such as CF ₄ or wet etching such as hydrofluoric acid (HF) diluted to about 1:10 is used. be able to.

FIG. 2C is a top view of the laminate shown in FIG. 2B. FIG. 2B shows a cross section of the stack taken along line IIB-IIB in FIG. 2C. As shown in FIG. 2C, a plurality of openings 91a having a desired shape are periodically formed in the first protective film 91, and the first semiconductor layer 20 is exposed in the openings 91a. In the present embodiment, the opening 91 a has a diamond shape in a top view of the substrate 10.

Next, as shown in FIG. 2D, the first semiconductor layer 20 is etched using the first protective film 91 formed in a desired shape as a mask to correspond to the plurality of openings 91 a in the first semiconductor layer 20. To form a plurality of recesses 20a. As a method of etching the first semiconductor layer 20, dry etching by RIE using a chlorine-based gas such as Cl ₂ may be used. Although the depth of etching is not particularly limited, in this embodiment, etching is performed to a depth of 200 nm.

Next, as shown in FIG. 2E, the first protective film 91 having a desired shape is removed by wet etching using hydrofluoric acid or the like.

Next, as shown in FIG. 2F, the light emitting layer 30 and the second semiconductor layer 40 are sequentially formed using an organic metal vapor phase growth method.

Specifically, the n-side light guide layer 31 made of n-GaN is grown by 0.2 μm on the first semiconductor layer 20 in which the recess 20 a is formed. At this time, the surface of the n-side light guide layer 31 after the embedding can be made substantially flat by selecting the growth condition in which the lateral growth is dominant so that the air is embedded in the recess 20 a. In order to make the lateral growth of the n-side light guide layer 31 dominant, for example, the growth temperature may be high or the growth pressure may be low. The surface of the n-side light guide layer 31 can be further planarized by forming a thin dielectric layer such as SiO ₂ or AlN on at least one of the side wall and the bottom of the recess 20 a shown in FIG. 2E. Subsequently, an active layer 32 having three cycles of a barrier layer of InGaN and an InGaN quantum well layer is grown. Subsequently, a p-side light guide layer 33 made of p-GaN is grown to a thickness of 0.1 μm. Subsequently, an electron barrier layer 41 made of AlGaN is grown to 10 nm. Subsequently, a p-side cladding layer 42 composed of a 0.48 μm strained superlattice formed by repeating a p-AlGaN layer (1.5 nm) and a GaN layer (1.5 nm) for 160 cycles is grown. Subsequently, a p-side contact layer 43 made of p-GaN is grown by 0.05 μm. Here, in each layer, for example, trimethylgallium (TMG), trimethylammonium (TMA), trimethylindium (TMI) is used as an organometallic raw material containing Ga, Al, and In. In addition, ammonia (NH ₃ ) is used as a nitrogen source.

Next, as shown in FIG. 2G, a second protective film 92 is formed on the second semiconductor layer 40. Specifically, a 300 nm silicon oxide film (SiO ₂ ) is formed as the second protective film 92 on the p-side contact layer 43 by plasma CVD using silane (SiH ₄ ).

Next, as shown in FIG. 2H, the second protective film 92 is selectively removed using a photolithography method and an etching method so that the second protective film 92 remains like a waveguide. As an etching method, for example, dry etching by reactive ion etching (RIE) using a fluorine-based gas such as CF ₄ or wet etching such as hydrofluoric acid (HF) diluted to about 1:10 is used. be able to.

Next, as shown in FIG. 2I, the p-side contact layer 43 and the p-side cladding layer 42 are etched using the second protective film 92 formed in a waveguide shape as a mask to form a ridge on the second semiconductor layer 40. The portion 40a and the flat portion 40b are formed. As etching of the p-side contact layer 43 and the p-side cladding layer 42, it is preferable to use dry etching by RIE using a chlorine-based gas such as Cl ₂ .

Next, as shown in FIG. 2J, after removing the waveguide-like second protective film 92 by wet etching using hydrofluoric acid or the like, the p-side contact layer 43 and the p-side cladding layer 42 are covered. Then, the dielectric layer 60 is formed. That is, the dielectric layer 60 is formed on the ridge portion 40 a and the flat portion 40 b of the second semiconductor layer 40. As the dielectric layer 60, for example, a silicon oxide film (SiO ₂ ) is formed to a thickness of 300 nm by plasma CVD using silane (SiH ₄ ).

Next, as shown in FIG. 2K, only the dielectric layer 60 on the ridge portion 40a is removed by photolithography and wet etching using hydrofluoric acid, and the upper surface of the p-side contact layer 43 is exposed. Let Thereafter, the p-side electrode 51 made of Pd / Pt is formed only on the ridge portion 40a by using a vacuum evaporation method and a lift-off method. Specifically, the p-side electrode 51 is formed on the p-side contact layer 43 exposed from the dielectric layer 60.

In addition, the film-forming method of the p side electrode 51 is not restricted to a vacuum evaporation method, A sputtering method, a pulse laser film-forming method, etc. may be used. Further, the electrode material of the p-side electrode 51 may be any material that is in ohmic contact with the second semiconductor layer 40 (p-side contact layer 43), such as Ni / Au type, Pt type or the like.

Next, as shown in FIG. 2L, a pad electrode 52 is formed to cover the p-side electrode 51 and the dielectric layer 60. Specifically, a resist is patterned on portions other than portions to be formed by photolithography and the like, and a pad electrode 52 made of Ti / Pt / Au is formed on the entire upper surface of the substrate 10 by a vacuum evaporation method or the like. A pad electrode 52 having a predetermined shape is formed on the p-side electrode 51 and the dielectric layer 60 by removing unnecessary portions of the electrode. Thus, an electrode member 50 composed of the p-side electrode 51 and the pad electrode 52 is formed.

Next, as shown in FIG. 2M, the n-side electrode 80 is formed on the lower surface of the substrate 10. Specifically, an n-side electrode 80 made of Ti / Pt / Au is formed on the back surface of the substrate 10 (that is, the main surface on the back side of the main surface on which the first semiconductor layer 20 etc. are formed) by vacuum evaporation or the like. The n-side electrode 80 having a predetermined shape is formed by patterning using a photolithography method and an etching method. Thereby, the semiconductor laser device 1 according to the present embodiment can be manufactured.

[Operation effect of semiconductor laser device]
Next, the operation and effects of the semiconductor laser device 1 according to the present embodiment will be described with reference to FIGS. 3 to 8.

First, the light distribution of a waveguide type laser device such as the semiconductor laser device 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a diagram for explaining the electric field distribution in the transverse mode of the semiconductor laser device 1 according to the present embodiment. The cross-sectional view (a) of FIG. 3 shows a schematic cross-sectional view of the semiconductor laser device 1, and the graph (b) shows the position of the cross-sectional view (a) in the lateral direction (X-axis direction of FIG. 3) and the laser light The relationship with the electric field strength of the fundamental transverse mode of

As shown in the graph (b) of FIG. 3, the fundamental transverse mode has a distribution in which the electric field strength is maximum at the central portion of the waveguide and the strength decreases as the waveguide end is approached. As a result of calculation using the equivalent refractive index method, the light distribution has a shape that can be expressed by a cosine function inside the waveguide of width W shown in FIG. 3, and outside the waveguide as it goes away from the waveguide 90 a It has an exponentially decreasing shape. Such light distribution is formed in the waveguide type laser because the current is supplied from the ridge portion 40a and light is generated only in the ridge portion 40a, and in the direction orthogonal to the waveguide direction, This is because light is confined by the difference in refractive index between the inside and the outside of the waveguide. Here, assuming that the cosine function is cos (.kappa.X) and the exponential function is exp (-. Gamma.X), in the present embodiment, the refractive index inside the waveguide is 2.5, and the refractive index outside the waveguide is 2.2. By performing calculation with 499 and a waveguide width W of 10 μm, κ = 0.26 and γ = 1.07 can be obtained. Although not shown, the high-order transverse mode has a distribution having a plurality of peaks, and a position where the electric field intensity is maximized exists outside the central portion of the waveguide.

In order to selectively oscillate only the fundamental transverse mode, the same gain distribution as that of the fundamental transverse mode light distribution may be provided. That is, the fundamental transverse mode can be preferentially oscillated by increasing the gain of the fundamental transverse mode and reducing the gain of the high-order transverse mode. The gain in the DFB type laser device in which the diffraction grating 70 is formed can be expressed by the optical feedback amount of the diffraction grating. Here, the relationship between the filling factor f of the diffraction grating and the amount of optical feedback will be described with reference to FIGS. 4A to 4C.

FIGS. 4A and 4B are schematic cross-sectional views showing the configuration of the diffraction grating 70 when the filling factor f of the diffraction grating 70 of the semiconductor laser device 1 according to the present embodiment is 0.5 and 0.25, respectively. It is. 4A corresponds to the cross section of the diffraction grating 70 and the first semiconductor layer 20 at line IVA-IVA in FIG. 1A, and FIG. 4B shows the cross section of the diffraction grating 70 and the first semiconductor layer 20 at line IVB-IVB in FIG. It corresponds to FIG. 4C is a graph showing the relationship between the filling factor f of the diffraction grating 70 according to the present embodiment and the amount of optical feedback by the diffraction grating 70.

As shown in FIGS. 4A and 4B, the filling factor f of the diffraction grating 70 is such that the period of the diffraction grating 70 is a and the diffraction grating 70 is continuous in one period of the diffraction grating 70 (that is, the diffraction grating 70 is continuous) Is represented by f = d / a, where d is a length of The filling factor f of the diffraction grating 70 can be restated as the duty of the diffraction grating 70. Further, assuming that the order of the diffraction grating 70 is m, the oscillation wavelength of the laser light in the semiconductor laser device 1 is λ, and the refractive index is n, a relational expression of a = mλ / 2n holds. For example, in the case of using a nitride semiconductor in the semiconductor laser device 1, when the oscillation wavelength is 400 nm, the refractive index is 2.5, and m = 1, a = 80 nm. Here, in the case of the filling rate f = 0.5, d = 40 nm, and in the case of the filling rate f = 0.25, d = 20 nm.

FIG. 4C is the calculation result of the amount of optical feedback with respect to the filling factor of the diffraction grating in the first-order diffraction grating. In this case, when the filling factor f is 0.5, the amount of optical feedback is the largest, and when the filling factor is 0 or 1, the amount of optical feedback is zero. By changing the filling factor f, the amount of optical feedback can be adjusted to an arbitrary value. The DFB laser device is characterized in that the larger the amount of optical feedback of the diffraction grating 70, the easier it is to oscillate at a specific wavelength. The fundamental transverse mode is adjusted by adjusting the filling factor f according to the position in the direction orthogonal to the waveguide direction and the stacking direction, and matching the amount of optical feedback with the light distribution of the fundamental transverse mode shown in graph (b) of FIG. Selective oscillation is possible.

Such adjustment of the filling factor f will be described with reference to FIG. FIG. 5 is a view showing the relationship between the filling factor of the diffraction grating 70 and the position in the direction orthogonal to the waveguide direction and the stacking direction of the semiconductor laser device 1 according to the present embodiment. The cross-sectional view (a) of FIG. 5 shows a schematic cross-sectional view of the semiconductor laser device 1, and the graph (b) shows the position and diffraction grating in the lateral direction (X-axis direction of FIG. 3) of the cross-sectional view (a). The relationship with the filling rate of 70 is shown.

As shown in FIG. 5, in the semiconductor laser device 1 according to the present embodiment, the filling factor f of the diffraction grating 70 in the waveguide direction changes depending on the position in the direction orthogonal to the waveguide direction and the stacking direction. . In the present embodiment, the filling factor f is set to be 0.5 at the waveguide center (X = 0), and the position 5.9 μm outside the waveguide center (that is, X = 5.9, And, the filling factor is set to be 0 at the position of X = −5.9). The filling factor f linearly decreases from the central portion of the waveguide toward the waveguide end in the direction orthogonal to the waveguide direction and the stacking direction. With such a shape, a gain distribution reflecting the light distribution of the fundamental transverse mode shown in the graph (b) of FIG. 3 can be realized.

Here, the electric field intensity distribution and the light feedback amount distribution of the laser beam of the semiconductor laser device 1 in the case of using the diffraction grating 70 having the filling factor distribution as shown in FIG. 5 will be described with reference to FIG. FIG. 6 is a graph showing the relationship between the amount of optical feedback and the electric field intensity distribution of laser light according to the present embodiment, and the positions in the direction of the waveguide and in the direction perpendicular to the stacking direction. FIG. 6 shows the electric field intensity distribution shown in the graph (b) of FIG. 3 and the calculation results of the amount of optical feedback of the diffraction grating 70 having the filling factor distribution shown in FIG. In FIG. 6, the amount of optical feedback is shown by a broken line and the electric field intensity is shown by a solid line. The vertical axis of the graph shown in FIG. 6 is standardized.

As shown in FIG. 6, the electric field intensity distribution and the light feedback amount distribution match in the waveguide, and by adopting such a light feedback amount distribution in the diffraction grating 70, it is basic in the semiconductor laser device 1 The horizontal mode can be selectively oscillated.

As described above, by changing the filling factor of the diffraction grating 70 depending on the waveguide direction and the position in the direction orthogonal to the stacking direction, a desired light feedback amount distribution can be obtained. Therefore, by appropriately adjusting the filling factor of the diffraction grating 70, it is possible to selectively oscillate the desired transverse mode corresponding to the light feedback amount distribution. Further, light scattering due to the diffraction grating 70 can be suppressed by adjusting the filling factor of the diffraction grating 70 so that the end of the diffraction grating 70 is not arranged in the region where the electric field intensity of the laser light is large. Therefore, according to the semiconductor laser device 1 according to the present embodiment, it is possible to realize a DFB type semiconductor laser device which is excellent in beam quality and can suppress a decrease in power-light conversion efficiency.

The shape of the diffraction grating 70 having the light feedback amount distribution as shown in FIG. 6 will be described with reference to FIGS. 7 and 8. FIG. 7 is a top view showing the shape of the diffraction grating 70 according to the present embodiment. FIG. 8 is a top view showing the shape of a diffraction grating 70a according to a modification.

As shown in FIG. 7, in the present embodiment, the diffraction grating 70 has a diamond shape in top view. Although the period a of the diffraction grating 70 is constant, the length d continuous in the waveguide direction of the diffraction grating 70 changes in the direction orthogonal to the waveguide direction and the stacking direction. For example, if the length at which the diffraction grating 70 in the central portion of the waveguide continues in the waveguide direction is d1 and the length at which the diffraction grating 70 at the waveguide end (ridge end) is continuous in the waveguide direction is d2, There is a relationship of d1> d2. Further, when the respective filling rates are defined as f1 and f2, since the filling rates can be calculated by the formula f1 = d1 / a or f2 = d2 / a, the relation of f1> f2 is established. That is, the filling factor in the waveguide direction changes in the direction orthogonal to the waveguide direction and the stacking direction. The shape of the diffraction grating is not limited to this, and it may be a shape that satisfies the filling factor distribution of the graph (b) of FIG. For example, as in a diffraction grating 70a according to a modification shown in FIG. 8, it may have a triangular shape in top view. Also in this case, if the lengths d1 and d2 continuing in the waveguide direction of the diffraction grating 70a are defined as shown in the figure, the filling factor can be calculated by the equation f1 = d1 / a or f2 = d2 / a. It becomes a relation of> f2.

As described above, in the present embodiment, the diffraction grating 70 has a structure in which it is periodically interrupted in the waveguide direction, and the length in which the diffraction grating 70 is continuous in the waveguide direction is the waveguide direction and the stacking direction It changes with the position of the direction orthogonal to.

Thus, when the period a of the diffraction grating 70 is made constant, the length d where the diffraction grating 70 continues in the waveguide direction is changed by the position in the direction orthogonal to the waveguide direction and the stacking direction. It is possible to realize the semiconductor laser device 1 having the diffraction grating 70 in which the filling factor f changes depending on the direction and the direction orthogonal to the stacking direction.

Further, in the semiconductor laser device 1 according to the present embodiment, the filling factor f is smaller than at least one end at the center in the direction orthogonal to the waveguide direction and the stacking direction of the waveguide 90a.

Thus, when the filling factor of the diffraction grating 70 is set to 0.5 or less, the optical feedback amount at the center of the waveguide direction by the diffraction grating 70 and the direction orthogonal to the stacking direction is the optical feedback at the end in the orthogonal direction. It is possible to make it larger than the amount. Therefore, the amount of optical feedback of the fundamental transverse mode whose electric field strength is larger than that of the end can be selectively increased at the center of the orthogonal direction, so that oscillation of the fundamental transverse mode can be promoted.

Second Embodiment
[Configuration of semiconductor laser device]
In the first embodiment, the structure in which the diffraction grating 70 is formed in the first semiconductor layer 20 has been described. In the second embodiment, a structure in which the diffraction grating 70 is formed in the n-side light guide layer 31 will be described. Further, in the first embodiment, the method of making the electric field distribution in the waveguide and the optical feedback amount of the diffraction grating match is described, but in the present embodiment, the shape of the diffraction grating also takes into consideration the electric field distribution outside the waveguide. explain.

FIG. 9 is a schematic cross-sectional view showing the configuration of the semiconductor laser device 101 according to the present embodiment. As shown in FIG. 9, the semiconductor laser device 101 according to the present embodiment includes the first semiconductor layer 20, the light emitting layer 30 and the second semiconductor layer 40 in the same manner as the semiconductor laser device 1 according to the first embodiment. A laminated structure 190 is provided. In the present embodiment, the laminated structure 190 includes the waveguide 190 a in which the diffraction grating 170 is formed, and the diffraction grating 170 is disposed in the light emitting layer 30. More specifically, the diffraction grating 170 is disposed in the n-side light guide layer 31 of the light emitting layer 30. Further, the diffraction grating 170 according to the present embodiment is different from the diffraction grating 170 according to the first embodiment in the shape in the outside of the waveguide 190a. The shape of the diffraction grating 170 will be described later.

[Method of manufacturing a semiconductor laser device]
Next, a method of manufacturing the semiconductor laser device 101 according to the present embodiment will be described with reference to FIGS. 10A to 10D. 10A to 10D are schematic cross-sectional views showing steps in the method of manufacturing the semiconductor laser device 101 according to the present embodiment. Hereinafter, a method of manufacturing the semiconductor laser device 101 according to the present embodiment will be described focusing on differences from the first embodiment.

First, as shown in FIG. 10A, an n-side cladding layer of n-type AlGaN is grown 3 μm as the first semiconductor layer 20 on the substrate 10.

Next, as shown in FIG. 10B, a silicon oxide film (SiO ₂ ) of 100 nm is formed as the diffraction grating film 93 on the first semiconductor layer 20.

Next, as shown in FIG. 10C, the diffraction grating film 93 is selectively removed using the lithography method and the etching method, and the diffraction grating film 93 remaining after this etching is used as the diffraction grating 170.

Next, as shown in FIG. 10D, the light emitting layer 30 and the second semiconductor layer 40 are sequentially formed using an organic metal vapor phase growth method. As described above, by forming the light emitting layer 30 on the diffraction grating 170, the diffraction grating 170 is disposed in the n-side light guide layer 31 of the light emitting layer 30. Thus, the diffraction grating 170 can be formed in a laminated structure without separately providing a layer for disposing the diffraction grating.

Next, as in the semiconductor laser device 1 according to the first embodiment, by forming the electrode member 50 and the n-side electrode 80, the semiconductor laser device 101 according to the present embodiment as shown in FIG. 9 can be formed. .

[Diffraction grating configuration]
Next, the configuration of the diffraction grating according to the present embodiment will be described with reference to FIG. FIG. 11 is a view showing the relationship between the position in the direction orthogonal to the waveguide direction and the stacking direction of the semiconductor laser device 101 according to the present embodiment and the filling factor of the diffraction grating 170. In FIG. The cross-sectional view (a) of FIG. 11 shows a schematic cross-sectional view of the semiconductor laser device 101, and the graph (b) shows the position and diffraction grating in the lateral direction (X-axis direction of FIG. 11) of the cross-sectional view (a). The relationship with the filling factor f of 170 is shown. As shown in graph (b) of FIG. 11, the filling factor of the diffraction grating 170 according to the present embodiment is different from that of the diffraction grating 70 according to the first embodiment outside the waveguide.

As shown in the graph (b) of FIG. 11, the period of the diffraction grating 170 and the continuous length in the waveguide direction are set so that the filling factor is 0.5 at the waveguide center (X = 0), The filling ratio is changed linearly so as to be 0.08 at X = W / 2 = 5 [μm] or X = -W / 2 = -5 [μm]. Outside the waveguide, the filling factor at X = W / 2 = 5 [μm] or X = -W / 2 = -5 [μm] is set to 0.08, and the exponential function exp ( The fill factor is reduced to 0 in accordance with -γ x). By changing the filling factor in this way, a light feedback amount distribution that reflects the light distribution can be obtained.

Here, the relationship between the electric field intensity distribution of laser light in the semiconductor laser device 101 according to the present embodiment and the amount of optical feedback by the diffraction grating 170 will be described with reference to FIGS. 12 and 13. FIG. FIG. 12 is a graph showing the electric field intensity distribution of laser light in the semiconductor laser device 101 according to the present embodiment and the optical feedback amount distribution by the diffraction grating 170. FIG. 12 shows the electric field intensity distribution shown in the graph (b) of FIG. 3 and the calculation results of the optical feedback distribution of the diffraction grating 170 in the case where the filling factor distribution is shown in the graph (b) of FIG. It is a graph, and a vertical axis is a standardized value. The electric field intensity distribution and the amount of optical feedback coincide with each other inside and outside the waveguide, and this configuration can further improve the selectivity of the fundamental transverse mode. FIG. 13 is a top view showing the shape of the diffraction grating 170 according to the present embodiment. As shown in FIG. 13, the diffraction grating 170 changes its shape exponentially outside the waveguide. Also in the present embodiment, as in the first embodiment, although the period a of the diffraction grating 170 is constant, the length d of the diffraction grating 170 continuing in the waveguide direction is perpendicular to the waveguide direction and the stacking direction. Has changed. For example, when the continuous length of the diffraction grating 170 at the center of the waveguide is defined as d1 and the continuous length of the diffraction grating 170 at the waveguide end (ridge end) is defined as d2, the relationship of d1> d2 is satisfied. Further, when the respective filling rates are defined as f1 and f2, the filling rates can be calculated by the formula f1 = d1 / a or f2 = d2 / a, and the relation of f1> f2 is obtained. Thus, the filling factor f of the diffraction grating 170 changes in the direction orthogonal to the waveguide direction and the stacking direction.

As described above, in the semiconductor laser device 101 according to the present embodiment, the second semiconductor layer 40 includes the ridge portion 40 a having the longitudinal direction in the waveguide direction, and the filling factor f is the waveguide direction and the lamination direction. In the orthogonal direction, it linearly changes in the lower region of the ridge portion 40a, and exponentially changes outside the lower region of the ridge portion 40a.

As a result, the electric field strength distribution of the fundamental transverse mode and the amount of optical feedback can be made to coincide with each other inside and outside the waveguide, so the selectivity of the fundamental transverse mode by the diffraction grating 170 can be further improved.

In the present embodiment, the configuration in which the diffraction grating 170 is formed in the n-side light guide layer 31 and the configuration of the diffraction grating 170 in consideration of the electric field distribution outside the waveguide are adopted. It does not have to be adopted in combination. Only one of these configurations may be employed.

Third Embodiment
The semiconductor laser device according to the third embodiment will be described. The semiconductor laser device according to the present embodiment is different from the first and second embodiments in the filling factor distribution of the diffraction grating. Since the formation position and the manufacturing method of the diffraction grating are the same as in Embodiment 1 or Embodiment 2, the description will be omitted. Hereinafter, the configuration of the diffraction grating according to the present embodiment will be described with reference to FIG.

FIG. 14 is a diagram showing the relationship between the position in the direction orthogonal to the waveguide direction and the stacking direction of the semiconductor laser device 201 according to the present embodiment and the filling factor of the diffraction grating 270. The sectional view (a) of FIG. 14 shows a schematic sectional view of the semiconductor laser device 201, and the graph (b) shows the position of the lateral direction (the X-axis direction of FIG. 14) and the diffraction grating of the sectional view (a). The relationship with the filling factor f of 270 is shown. The filling factor of the diffraction grating 270 according to the present embodiment changes stepwise in the X direction of the diffraction grating 270, as shown in the graph (b) of FIG.

Here, the relationship between the electric field intensity distribution of laser light in the semiconductor laser device 201 according to the present embodiment and the amount of optical feedback by the diffraction grating 270 will be described with reference to FIG. FIG. 15 is a graph showing the electric field intensity distribution of laser light in the semiconductor laser device 201 according to the present embodiment and the optical feedback amount distribution by the diffraction grating 270. FIG. 15 is a graph showing the electric field intensity distribution of laser light in the semiconductor laser device 201 and calculation results of the light feedback amount distribution of the diffraction grating 270 when the filling factor distribution is shown by the graph (b) in FIG. Yes, the vertical axis is a standardized value. As shown in FIG. 15, in the diffraction grating 270 according to the present embodiment, the amount of optical feedback also changes in a stepwise manner, reflecting the filling factor. Even in the case of using such a diffraction grating 270, since the fundamental transverse mode can be selectively oscillated, good beam quality can be obtained. Further, also in the present embodiment, the end portion of the diffraction grating 270 in the lateral direction (X-axis direction) does not exist in the region where the electric field intensity of the laser light is high. It is possible to suppress the decrease in efficiency.

Subsequently, a shape example of the diffraction grating 270 according to the present embodiment will be described with reference to FIG.

FIG. 16 is a top view showing the shape of the diffraction grating 270 according to the present embodiment. The diffraction grating 70 has a shape in which a plurality of rectangles having different lengths in the waveguide direction (Z-axis direction) are combined. Although the period a of the diffraction grating 270 is constant, the length d where the diffraction grating 270 continues in the waveguide direction changes in the direction (X-axis direction) orthogonal to the waveguide direction and the stacking direction. As shown in FIG. 16, when the lengths of the continuous diffraction gratings 270 at respective positions in the X-axis direction of the diffraction grating 270 are defined as d1, d2 and d3, there is a relationship of d1> d2> d3. If the filling factor f at each position is defined as f1, f2 and f3, it can be calculated in the form of f1 = d1 / a, f2 = d2 / a, f3 = d3 / a. Therefore, there is a relationship of f1> f2> f3, and the filling factor changes in the direction orthogonal to the waveguide direction and the stacking direction. The shape of the diffraction grating is not limited to this, and any shape may be used as long as the filling rate shown in the graph (b) of FIG. 14 is satisfied.

Here, the diffraction grating according to the first modification having a shape satisfying the filling factor shown in the graph (b) of FIG. 14 will be described with reference to FIG. FIG. 17 is a top view showing the shape of a diffraction grating 270a according to this modification.

For example, as shown in FIG. 17, rectangular diffraction grating elements 271 to 273 having different widths in the waveguide direction and the direction orthogonal to the stacking direction may be arranged in the waveguide direction. In the diffraction grating 270a having such a shape, the period a is constant. Further, the length d in the waveguide direction of the diffraction grating 270a changes between the portion with the diffraction grating (length d) and the portion without the diffraction grating (length 0). Thereby, the filling factor f = d / a can be changed in the direction orthogonal to the waveguide and the stacking direction.

Embodiment 4
The diffraction grating according to the fourth embodiment will be described. The diffraction grating according to the present embodiment differs from the diffraction grating 170 according to the second embodiment in the filling factor f. Hereinafter, the diffraction grating according to the present embodiment will be described focusing on differences from the diffraction grating 170 according to the second embodiment.

As shown in FIG. 4C, there may be two filling factors f which provide a certain amount of optical feedback. In each of the above-described embodiments, the diffraction grating is shown in which the filling factor f is greater than 0 and not more than 0.5, but the filling factor f of the diffraction grating may be greater than 0.5. Hereinafter, an example of a diffraction grating having a filling factor f larger than 0.5 will be described with reference to FIGS. 18A and 18B. FIG. 18A is a graph showing the relationship between the filling direction f of the diffraction grating 370 and the position in the direction orthogonal to the waveguide direction and the stacking direction of the diffraction grating 370 according to the present embodiment. FIG. 18B is a top view showing the shape of the diffraction grating 370 according to the present embodiment.

As shown in FIGS. 18A and 18B, the same effect as that of the diffraction grating 170 according to the second embodiment can be obtained by using the diffraction grating 370 having a filling factor of 0.5 or more and 1.0 or less. In the present embodiment, as shown in FIGS. 18A and 18B, in the diffraction grating 370 according to the present embodiment, the filling factor at the center of the waveguide is small and the filling factor at both sides of the waveguide is larger than the center. . The diffraction grating 370 is formed in the range of 2 W in width from the center of the waveguide, and the diffraction grating 370 does not exist outside the range of 2 W in width. Also in this embodiment, as in each of the above embodiments, the period a of the diffraction grating 370 is constant, but the length d of the diffraction grating 370 continuing in the waveguide direction is orthogonal to the waveguide direction and the stacking direction Change in the direction of For example, if the length at which the diffraction grating 370 at the center of the waveguide continues in the waveguide direction is d1 and the length at which the diffraction grating 370 at the waveguide end (ridge edge) continues in the waveguide direction is d2, There is a relationship of d1 <d2. Further, when the filling rates are defined as f1 and f2, respectively, the filling rates can be calculated by the equations f1 = d1 / a and f2 = d2 / a, and thus the relationship of f1 <f2 holds. That is, the filling factor in the waveguide direction changes in the direction orthogonal to the waveguide direction and the stacking direction.

As described above, in the diffraction grating 370 according to the present embodiment, the filling factor f is larger than at least one end at the center in the direction orthogonal to the waveguide direction and the stacking direction of the waveguide. Thus, when the filling factor of the diffraction grating 370 is 0.5 or more, the optical feedback amount at the center of the waveguide direction by the diffraction grating 370 and the direction orthogonal to the stacking direction is the optical feedback at the end in the orthogonal direction. It is possible to make it larger than the amount. Therefore, the amount of optical feedback of the fundamental transverse mode whose electric field strength is larger than that of the end can be selectively increased at the center of the orthogonal direction, so that oscillation of the fundamental transverse mode can be promoted.

Fifth Embodiment
The first to fourth embodiments show a method of changing the amount of optical feedback by changing the length d of the diffraction grating continuing in the waveguide direction. In this embodiment, a method of changing the amount of optical feedback by changing the period a of the diffraction grating will be described with reference to FIGS. 19 and 20. FIG. The formation position of the diffraction grating and the manufacturing method are the same as in the first to fourth embodiments, and thus the description thereof is omitted.

FIG. 19 is a top view showing the shape of the diffraction grating 470 according to the present embodiment. As shown in FIG. 19, in the present embodiment, the diffraction grating 470 in which the period in the waveguide direction in the waveguide of width W changes in the direction (X-axis direction) orthogonal to the waveguide direction and the stacking direction It is formed. Specifically, in the diffraction grating 470 according to the present embodiment, the period of the waveguide central portion is a1, and the period of the waveguide end is a2. There is a relationship of a1 <a2 between these periods. Furthermore, as the waveguide approaches from the center to the end in the X-axis direction, the period changes continuously. In the present embodiment, the period is continuously increased as the end portion is approached from the center in the X-axis direction of the waveguide.

FIG. 20 is a diagram showing the relationship of the amount of optical feedback to the period of the diffraction grating 470 according to the present embodiment. FIG. 20 shows the amount of optical feedback when oscillating at a wavelength corresponding to the period a1. As shown in FIG. 20, the amount of optical feedback has a peak at period a1 and decreases with distance from period a1. In the DFB laser device, since the oscillation wavelength is determined according to the period of the diffraction grating 470, the amount of optical feedback can hardly be obtained at periods other than the period corresponding to the oscillation wavelength.

Although the case of a1 <a2 is shown in FIG. 19, the same effect can be obtained even in the case of a1> a2.

Regarding the filling factor, if the filling factor of the part where the period of the diffraction grating 470 is a1 is f1 and the filling factor of the part where the period is a2 is f2, the filling is performed according to the formula f1 = d / a1 and f2 = d / a2. You can calculate the rate. Here, from the magnitude relationship between the cycles a1 and a2, there is a relationship of f1> f2. As shown in FIG. 19, in the present embodiment, the length d of the diffraction grating 470 continuing in the waveguide direction is constant.

As described above, in the diffraction grating 470 according to the present embodiment, the period of the diffraction grating 470 changes depending on the position in the waveguide direction and the direction orthogonal to the stacking direction. With such a configuration, for example, by making the continuous length of the diffraction grating 470 constant in the waveguide direction, it has the diffraction grating in which the filling factor f changes depending on the position in the direction orthogonal to the waveguide direction and the stacking direction. A semiconductor laser device can be realized.

(Modification etc.)
As mentioned above, although the semiconductor light-emitting device concerning this indication was explained based on each embodiment, this indication is not limited to each above-mentioned embodiment.

For example, although the example of the nitride semiconductor laser element was shown as a semiconductor laser element in each said embodiment, the material which forms the semiconductor laser element which concerns on this indication is not limited to a nitride. For example, the semiconductor laser device according to the present disclosure may be formed of a GaAs-based material.

In each embodiment, although the first-order diffraction grating is shown, a high-order diffraction grating can also be used. An example of such a high order diffraction grating will be described with reference to FIG. FIG. 21 is a diagram showing the calculation results of the relationship between the filling factor f and the amount of optical feedback when the fifth order diffraction grating is used. For example, when the fifth order diffraction grating is used under the same conditions as in Embodiment 1, the period a is 400 nm. In this case, there may be ten filling factors f giving a certain amount of optical feedback.

Further, in the present disclosure, a case where oscillation is performed only in the fundamental transverse mode for the purpose of obtaining high beam quality is shown, but it is possible to selectively oscillate only a desired higher order mode by applying the present disclosure. is there. For example, as shown in FIG. 3, the electric field strength of the desired mode is calculated, and using the relationship between the filling factor and the amount of optical feedback shown in FIG. 4C, the filling is performed as shown in graph (b) of FIG. Determine the rate. In this example, the filling factor of the diffraction grating in the part with the highest light intensity is 0.5, and the filling factor in the lowest part is 0. As described above, only the desired high-order mode can be oscillated as long as the filling factor distribution reflects the electric field strength distribution of the desired high-order mode.

In each of the above-described embodiments, the ridge portion 40a is formed in the second semiconductor layer 40 as the waveguide structure. However, in the waveguide structure, light is emitted in the stacking direction and the direction perpendicular to the laser oscillation direction. There is no particular limitation as long as it has a structure for containing For example, a layer having a refractive index lower than that of the second semiconductor layer 40 may be embedded in the second semiconductor layer 40.

In addition, it is realized by arbitrarily combining the components and functions in the above-described embodiments within the scope obtained by applying various modifications that those skilled in the art would think to the above-described embodiments, or within the scope of the present disclosure. The forms to be included are also included in the present disclosure.

The semiconductor laser device according to the present disclosure can be used as a light source of an image display device, illumination, industrial equipment, etc., and is particularly useful as a light source of equipment requiring a relatively high light output.

DESCRIPTION OF SYMBOLS 1, 101, 201 Semiconductor laser element 10 Substrate 20 1st semiconductor layer 20a recessed part 30 light emitting layer 31 n side optical guide layer 32 active layer 33 p side optical guide layer 40 2nd semiconductor layer 40a ridge part 40b flat part 41 electron barrier layer 42 p-side cladding layer 43 p-side contact layer 50 electrode member 51 p-side electrode 52 pad electrode 60 dielectric layer 70, 70a, 170, 270, 270a, 370, 470, 932 diffraction grating 80 n- side electrode 90, 190 laminated structure Body 90a, 190a, 931 Waveguide 91 First protective film 91a Opening 92 Second protective film 93 Diffraction grating film 95f, 95r Resonator end face 271, 272, 273 Diffraction grating element 913 Guide layer

Claims (8)

1. A first semiconductor layer of a first conductivity type,
   An active layer disposed above the first semiconductor layer;
   And a second semiconductor layer of a second conductivity type disposed above the active layer.
   A stacked structure including the first semiconductor layer, the active layer, and the second semiconductor layer is disposed between a pair of opposed resonator end faces and the pair of resonator end faces, and a diffraction grating is formed. And a waveguide,
   Assuming that the direction orthogonal to the pair of resonator end faces is the waveguide direction,
   A filling factor of the diffraction grating in the waveguide direction is changed depending on a position in a direction orthogonal to the waveguide direction and a stacking direction of the multilayer structure.
2. The diffraction grating has a structure periodically interrupted in the waveguide direction,
   The semiconductor laser device according to claim 1, wherein a length in which the diffraction grating is continuous in the waveguide direction varies depending on positions in the waveguide direction and a direction orthogonal to the stacking direction.
3. The semiconductor laser device according to claim 1, wherein a period of the diffraction grating is changed depending on a position in a direction orthogonal to the waveguide direction and the stacking direction.
4. The semiconductor laser device according to any one of claims 1 to 3, wherein the filling factor is larger than at least one end at a center in a direction orthogonal to the waveguide direction and the stacking direction of the waveguide.
5. The semiconductor laser device according to any one of claims 1 to 3, wherein the filling factor is smaller than at least one end at a center in a direction orthogonal to the waveguide direction and the stacking direction of the waveguide.
6. The second semiconductor layer includes a ridge portion having a longitudinal direction in the waveguide direction,
   The filling factor linearly changes in the lower region of the ridge portion and varies exponentially outside the lower region of the ridge portion in the direction orthogonal to the waveguide direction and the stacking direction. The semiconductor laser device according to any one of to 5.
7. The first semiconductor layer is a cladding layer,
   The semiconductor laser device according to any one of claims 1 to 6, wherein the diffraction grating is disposed in the first semiconductor layer.
8. A guide layer disposed between the first semiconductor layer and the active layer;
   The semiconductor laser device according to any one of claims 1 to 6, wherein the diffraction grating is disposed in the guide layer.

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