Semiconductor laser element, method for manufacturing same, and light-emitting device

Abstract

A semiconductor laser element 100 comprises a laminated structure 102 including a GaN substrate 110, an n-type semiconductor layer 120, an active layer 130, and a p-type semiconductor layer 140. The laminated structure 102 is provided with a current constriction structure 141 extending in a first direction orthogonal to the lamination direction, and a diffraction grating 150 adjacent to the current constriction structure 141 in a second direction perpendicular to the first direction. The diffraction grating 150 includes a plurality of grooves 152 each extending in the second direction. The depths of the plurality of grooves 152 are substantially constant in an outer region B relatively far from the current constriction structure 141 in the second direction, and are shallower in an inner region A than in the outer region B, the inner region A being relatively close to the current constriction structure 141 in the second direction.

Description

Semiconductor laser element, manufacturing method thereof, and light-emitting device

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

[0002] Until now, 254 nm UV germicidal lamps have been widely used for sterilization purposes. However, irradiating humans with this light poses the risk of developing skin cancer and keratitis. In contrast, in recent years, many medical institutions and universities both in Japan and overseas have reported that 222 nm UV light emitted by KrCl excimer lamps is far safer. Furthermore, its effectiveness against the novel coronavirus is also being verified. This virus inactivation system using KrCl excimer lamps is attracting attention as it can inactivate viruses without restricting human activity in medical institutions, schools, public and commercial facilities, restaurants, and other facilities, contributing to both pandemic containment and social activity.

[0003] To further improve the quietness and miniaturization of this virus inactivation system, one possible approach would be to replace the KrCl excimer lamp with a semiconductor light-emitting device incorporating a semiconductor light-emitting element. However, there are currently no semiconductor light-emitting elements that emit high-power light around 222 nm. Therefore, one possible approach is to use harmonic generation by a wavelength conversion element to convert 444 nm light into a second harmonic of 222 nm.

[0004] To increase the conversion efficiency of the second harmonic, a single-longitudinal mode, high-power semiconductor laser is required as the 444 nm light source. Generally, a distributed feedback laser (DFB-LD) is used as a single-longitudinal mode laser (Patent Documents 1 and 2).

[0005] JP 2023-039519 A JP 2018-037495 A

[0006] Various configurations have been proposed for DFB-LDs, including the laterally coupled DFB-LD. One type of laterally coupled DFB-LD has a laminated structure of an N-type cladding layer, an active layer, and a P-type cladding layer, and a ridge section (mesa structure) is formed in the P-type cladding layer as a current confinement structure. A diffraction grating is then formed adjacent to the ridge section in the P-type cladding layer. Furthermore, for the purpose of suppressing leakage current, SiO ２ An insulating layer made of the above is formed.

[0007] The inventors have studied the laterally coupled DFB-LD having the above structure and have come to recognize the following problem. In the laterally coupled DFB-LD having the above structure, an insulating layer is formed so as to fill the grooves of the diffraction grating. When the insulating material is filled into the grooves of the diffraction grating, the insulating material does not easily penetrate near the mesa portion, and voids are likely to occur. The voids in the grooves of the diffraction grating reduce the reproducibility of the refractive index distribution and cause variations in characteristics between elements.

[0008] The present disclosure has been made in light of the above-mentioned circumstances, and an exemplary purpose of an embodiment thereof is to provide a semiconductor laser device with reduced variations in characteristics from device to device.

[0009] One aspect of the present disclosure relates to a distributed feedback semiconductor laser device. The semiconductor laser device has a layered structure including a substrate, a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. The layered structure is provided with a current confinement structure extending in a first direction perpendicular to the layering direction, and a diffraction grating adjacent to the current confinement structure in a second direction perpendicular to the first direction. The diffraction grating includes a plurality of grooves each extending in the second direction. The depth of the plurality of grooves is substantially constant in an outer region that is relatively far from the current confinement structure in the second direction, and is shallower in an inner region that is relatively close to the current confinement structure in the second direction than in the outer region.

[0010] Any combination of the above elements, or mutual substitution of elements or expressions between methods, devices, systems, etc., are also valid aspects of the present invention or the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not explain all essential features of the present invention, and therefore, subcombinations of the described features may also constitute the present invention.

[0011] According to a semiconductor laser device according to an aspect of the present disclosure, it is possible to reduce variations in characteristics between devices.

[0012] 13 is a perspective view of a distributed feedback semiconductor laser element according to embodiment 1. FIG. 14 is a cross-sectional view of the semiconductor laser element of FIG. 1 taken along line A-A'. FIG. 15 is a cross-sectional view of the semiconductor laser element of FIG. 1 taken along line B-B'. FIG. 16 is a cross-sectional view of a semiconductor laser element according to a comparative technique. FIG. 17 is a cross-sectional view showing the relationship between the waveguide mode light intensity distribution and region A. FIG. 18 is a cross-sectional view of a semiconductor laser element according to modification 1. FIG. 19 is a cross-sectional view of a semiconductor laser element according to modification 2. FIG. 20 is a cross-sectional view of a semiconductor laser element according to modification 3. FIG. 21 is a diagram illustrating a first manufacturing method of a semiconductor laser element. FIG. 22 is a diagram illustrating an example of step S300. FIG. 23 is a diagram illustrating another example of step S300. FIG. 24 is a diagram illustrating yet another example of step S300. FIG. 25 is a perspective view of a semiconductor laser element according to a modification. FIG. 26 is a cross-sectional view of the semiconductor laser element of FIG. 13 taken along line A-A'. FIG. 27 is a diagram illustrating a light emitting device according to an embodiment.

[0013] (Summary of the Embodiments) A summary of some exemplary embodiments of the present disclosure will be provided. This summary is intended as a prelude to the detailed description that follows, or to provide a basic understanding of the embodiments. The summary is intended to briefly explain some concepts of one or more embodiments and is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not an exhaustive overview of all possible embodiments, nor does it limit essential elements of the embodiments. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0014] (Overview of Embodiments) A distributed feedback semiconductor laser device according to one embodiment includes a layered structure including a substrate made of GaN or the like, a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer. The layered structure includes a current confinement structure extending in a first direction perpendicular to the stacking direction, and a diffraction grating adjacent to the current confinement structure in a second direction perpendicular to the first direction. The diffraction grating includes a plurality of grooves each extending in the second direction. The depth of the plurality of grooves is substantially constant in an outer region that is relatively far from the current confinement structure in the second direction, and is shallower in an inner region that is relatively close to the current confinement structure in the second direction than in the outer region.

[0015] With this configuration, the grooves of the diffraction grating are shallower immediately adjacent to the current confinement structure, allowing the insulating material to easily penetrate and preventing voids from forming. This makes it possible to suppress variations in the refractive index distribution caused by voids and reduce variations in the characteristics of the semiconductor laser. A substantially constant depth means, for example, that the error or tolerance is within ±10% of the average depth.

[0016] In one embodiment, the grooves of the diffraction grating may become progressively deeper in the inner region as they move away from the current confinement structure.

[0017] In one embodiment, the grooves of the diffraction grating may deepen at a constant gradient in the inner region, i.e., the bottom surface of the grooves of the diffraction grating may be flat.

[0018] In one embodiment, the grooves of the diffraction grating may deepen non-linearly, in other words, curvedly, in the inner region, i.e., the bottom surface of the grooves of the diffraction grating may be curved.

[0019] In one embodiment, the grooves of the diffraction grating may be discontinuously deeper in the inner region as they move away from the current confinement structure, or may be stepped in depth in the inner region as they move away from the current confinement structure.

[0020] In one embodiment, the active layer comprises In ｘ Al ｙ Ga １－ｘ－ｙN (0≦x≦1, 0≦y≦1, 0≦x+y≦1).

[0021] In one embodiment, the grating may have phase-shifting regions in a first direction.

[0022] In one embodiment, the beam intensity at the output end face is adjusted at a position x １ When normalized as 1, the boundary x between the inner and outer regions ２ is the beam intensity 1 / e ２ Position x where ３ This can prevent a decrease in the coupling efficiency of the diffraction grating.

[0023] In one embodiment, the length of the inner region in the second direction may be 90 to 220 nm, which can further suppress the occurrence of voids.

[0024] A light emitting device according to one embodiment includes any one of the distributed feedback semiconductor laser elements described above, a nonlinear optical element that generates a second harmonic of light emitted from the distributed feedback semiconductor laser element, and a filter that transmits the second harmonic and removes the light emitted from the semiconductor laser element.

[0025] (Embodiments) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are illustrative and do not limit the disclosure or invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure or invention.

[0026] In addition, the dimensions (thickness, length, width, etc.) of each member shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple members do not necessarily represent the relative size of each other, and even if a member A is depicted as being thicker than another member B in the drawings, member A may actually be thinner than member B.

[0027] 1 is a perspective view of a distributed feedback semiconductor laser device 100 according to embodiment 1. The semiconductor laser device 100 includes an n-type GaN substrate 110, an n-type semiconductor layer 120, an active layer 130, a p-type semiconductor layer 140, and an insulating film 160.

[0028] The GaN substrate 110 is a nitride semiconductor. ｘ Al ｙ Ga １－ｘ－ｙ The GaN substrate 110 may have a composition of 0≦x≦1, 0≦y≦1, 0≦x+y≦1. To generate blue laser light at 444 nm, the material of the GaN substrate 110 may be GaN (x=y=0). The GaN substrate 110 is not limited to this, and any substrate that has the same effect may be used; for example, a Si substrate or a sapphire substrate may also be used.

[0029] The n-type semiconductor layer 120 , the active layer 130 , and the p-type semiconductor layer 140 are formed in this order on the n-type GaN substrate 110 by epitaxial growth, forming a stacked structure 102 .

[0030] The n-type semiconductor layer 120 may include an n-type cladding layer and an n-type guide layer. For example, the material of the n-type cladding layer is n-Al. ０．０５ Ga ０．９５ The material of the n-type guide layer is n-GaN.

[0031] 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 set to 444 nm, the material of the quantum well structure includes In as a barrier layer. ０．０１ Ga ０．９９ N as a well layer and In as an ０．１５ Ga ０．８５ You can choose N.

[0032] In order to suppress the diffusion of impurities from the n-type semiconductor layer 120 to the active layer 130, an undoped nitride guide layer (not shown) In is provided between them. ０．０２ Ga ０．９８ N can be inserted.

[0033] The p-type semiconductor layer 140 may include a carrier block (electron block EB) layer, a p-type guide layer, a p-type cladding layer, and a contact layer. For example, the material of the p-type guide layer may be p-In ０．０２ Ga ０．９８ N, and the material of the p-type cladding layer is p-Al ０．０４ Ga ０．９６ The material of the contact layer is p-GaN.

[0034] In order 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.

[0035] A ridge portion (also called a mesa portion) 142 is formed in the p-type semiconductor layer 140 (p-type cladding layer) as a current confinement structure 141. The height of the ridge portion 142 can be several hundred nanometers, and the width of the ridge portion 142 (mesa width) can be several microns. For example, the height may be 500 nm and the width may be 2 μm.

[0036] The coupling coefficient κ, which will be described later, also varies depending on the mesa width; the narrower the mesa width, the larger the coupling coefficient κ. However, when the mesa width is less than 1 μm, the lateral confinement weakens, and the laser characteristics begin to deteriorate. On the other hand, when the mesa width exceeds 3 μm, the transverse single mode changes to transverse multimode. Therefore, in order to obtain a high coupling coefficient κ in the transverse single mode, it is preferable that the mesa width Wm be 1 μm≦Wm≦3 μm.

[0037] The p-type cladding layer 140 having the ridge portion 142, together with the active layer 130 and the n-type cladding layer 120, forms a ridge-type waveguide 144. The ridge-type waveguide 144 extends in a first direction (the z-axis direction in the drawing).

[0038] The n-side electrode 171 is formed on the back surface of the GaN substrate 110 , and the p-side electrode 172 is formed on the top surface of the ridge portion 142 .

[0039] Diffraction gratings 150_1 and 150_2 are formed on both sides of the mesa adjacent to the ridge waveguide 144 in the second direction (x-axis direction). Each of the diffraction gratings 150_1 and 150_2 has a plurality of grooves 152 formed in the p-type semiconductor layer 140 on either side of the mesa. The plurality of grooves 152 are adjacent to each other in the first direction, and each groove extends in the second direction.

[0040] An insulating film 160 is formed on the p-type semiconductor layer 140. The insulating film 160 is formed so as to fill the grooves 152 of the diffraction grating 150.

[0041] Fig. 2 is a cross-sectional view taken along line AA' of semiconductor laser device 100 in Fig. 1. Line AA' is defined so as to pass through grooves 152 of diffraction grating 150, and therefore Fig. 2 shows a cross section of grooves 152. Grooves 152 of diffraction grating 150 are filled with a material that forms insulating film 160.

[0042] In this embodiment, the grooves 152 of the diffraction grating 150 have a substantially constant depth d Ｂ The groove 152 is shallower in the inner region A closer to the ridge waveguide 144 in the second direction (x-axis direction) than in the outer region B. For example, in the outer region B, Ｂ = 150 to 200 nm, and in the inner region A, the depth d Ａ is inclined toward the bottom of the side surface of the ridge portion 142. The height of the ridge portion 142 is about 500 nm.

[0043] Depth d of the groove 152 in the inner region A Ａ depends on the distance x from the mesa portion of the ridge portion 142, and d Ａ (x), and the following relationship holds: d Ａ (x) < d Ｂ

[0044] The position of the mesa side (the side where the mesa rises in Figure 2) is x １ , the position of the boundary between areas A and B is x ２ When the average groove depth of region A is d Ａ＿ＡＶＥ is defined by the following formula: Ａ＿ＡＶＥ =∫Ｘ１～Ｘ２ d Ａ (x) dx / (x ２ -x １ ) Average groove depth d of region A Ａ＿ＡＶＥ and the depth d of region B Ｂ Between Ａ＿ＡＶＥ <d Ｂ The following relationship holds.

[0045] In the example of FIG. Ａ (x １ ) = 0, d Ａ (x ２ ) = d Ｂ The depth d of the groove 152 is Ａ varies linearly with position x.

[0046] Fig. 3 is a cross-sectional view of the semiconductor laser device 100 taken along line BB' in Fig. 1. As shown in the upper part of Fig. 3, the diffraction grating 150 may be a phase-shift diffraction grating 150A having a phase-shift region 151. For comparison, the lower part of Fig. 3 shows a uniform diffraction grating 150B having no phase-shift region 151.

[0047] The phase shift region 151 is provided at the peaks of the diffraction grating 150A. The length of the phase shift region 151 is given by λ / 4n ０ｒ ×(2m+1), where λ is the oscillation wavelength, m is 0 or any positive integer, and n ０ｒ is the effective refractive index experienced by light. ０ｒ is a value that depends on the structure and material of the semiconductor laser element, and can take a value in the range of 1 < n0r < 3. By providing the phase shift region 151, the side mode suppression ratio (SMSR) of the single longitudinal mode can be improved.

[0048] When the output end face is coated with a low-reflection film (e.g., reflectivity less than 2%) and the other end face is coated with a high-reflection film (e.g., reflectivity of 90% or more), the phase shift region 151 is preferably formed closer to the high-reflection end face than the center of the resonator. For example, the phase shift region 151 may be provided at a position that divides the gap between the low-reflection end face (output end face) and the high-reflection end face of the semiconductor laser element in a ratio of 6:4 to 8:2.

[0049] The diffraction grating 150 may be a uniform diffraction grating 150B that does not include a phase shift region.

[0050] The above is the configuration of the semiconductor laser device 100. The advantages of the semiconductor laser device 100 become clear when compared with a comparative technology. Therefore, the comparative technology will be described.

[0051] The perspective view of the semiconductor laser device 100R according to the comparative technique is similar to that of FIG. 1, but the grooves 152 of the diffraction grating 150 are different from those of the embodiment.

[0052] 4 is a cross-sectional view of a semiconductor laser device 100R according to the comparative technique. In the comparative technique, the depth of the grooves 152 of the diffraction grating 150 on the sides of the mesa is constant, which is different from the first embodiment.

[0053] Next, a problem that occurs in the comparative technology will be explained. The insulating film 160 is formed so as to cover the p-type semiconductor layer 140 in which the grooves 152 are formed. In the process of forming the insulating film 160, the insulating material has difficulty penetrating into the region of the grooves 152 that is close to the side surfaces of the ridge portion 142, so voids 190 are likely to occur. The voids 190 in the diffraction grating grooves 152 reduce the reproducibility of the refractive index distribution, causing variations in characteristics between elements.

[0054] In contrast, in this embodiment, the depth of the region A of the groove 152 near the side surface of the ridge portion 142 is shallow (see FIG. 2), making it difficult for the void 190 to occur. This improves the reproducibility of the refractive index distribution and reduces the variation in characteristics between elements.

[0055] In other words, the width W of the region A in the x-axis direction Ａ is determined so that no void 190 occurs. Ａ If the width W is too large, undesirable effects occur, such as a decrease in the coupling efficiency of the diffraction grating 150. Ａ can be determined based on the beam radius and beam profile at the output end face of the laser.

[0056] Fig. 5 is a cross-sectional view showing the relationship between the waveguide mode light intensity distribution and region A. The lower part of Fig. 5 shows an example of the light intensity distribution in the horizontal direction at the output end face (front end face).

[0057] The factor that contributes to the coupling coefficient is x ≥ x １ is the light intensity distribution I(x) at x=x １ The light intensity at I(x １ ) = 1, I(x) ≒ exp(-2 γ (x - x １ )) where γ is the effective refractive index of the guided mode, N ｅｆｆ , area A and area B (x １ ≦x≦x ３ ) is the average equivalent refractive index at N ｓｉｄｅ Then, the wave number k ０ Using this, γ = k ０ ・√(N ｅｆｆ ２ -N ｓｉｄｅ ２ ) and in nitride semiconductor light emitting devices, γ / k ０ ≒0.1 to 0.2.

[0058] The light intensity in the horizontal direction (x direction) at the output end surface is 1 / e ２ The position where ３ Then, most of the beam profile that contributes to the coupling coefficient is in the region closer to the mesa side. Therefore, in order to suppress the decrease in coupling efficiency, the boundary x between regions A and B ２ Ha x １ <x ２ <x ３ Here, when the oscillation wavelength is λ, the wavelength is approximately x ３ -x １ ≒1 / γ=λ / 2π√(N ｅｆｆ ２ -N ｓｉｄｅ ２ )

[0059] On the other hand, the boundary x between areas A and B ２ is Mesa (x = x １ ) side, the influence on the characteristic variation when a void 190 occurs in region B becomes larger. ２ must be kept away from the mesa. From this perspective, the range x １~x ２ The integral of the light intensity in the range x １ ~x ３ The boundary x is set to be equal to or greater than half of the integral value of the light intensity at ２ That is, ∫ ｘ１～ｘ２ I(x)dx>1 / 2×∫ ｘ１～ｘ３ I(x)dx is the boundary x between area A and area B. ２ , i.e., the width W of the region A Ａ It is preferable to define

[0060] From the above, when λ=400 nm, W Ａ =90-180nm, x ３ -x １ Similarly, when λ=500 nm, W Ａ =110-220nm, x ３ -x １ In one embodiment, W Ａ = 150 nm.

[0061] In this case, the groove depth in the region B does not necessarily have to be substantially constant, and the average groove depth d Ａ＿ＡＶＥ and the average groove depth d of region B Ｂ＿ＡＶＥ Between Ａ＿ＡＶＥ <d Ｂ＿ＡＶＥ It is sufficient if the following relationship is established.

[0062] Next, a modification of the semiconductor laser device 100 will be described.

[0063] 6 is a cross-sectional view of a semiconductor laser device 100A according to Modification 1. In Modification 1, the depth d Ａ is substantially constant, and d Ａ <d ＢThe relationship between the depth and the beam profile is established. In other words, the bottom surface of the groove 152 changes in a stepwise manner from region A to region B. As a result, even if a void 190 occurs in the boundary between region A and region B in the groove 152 on the region B side, the overlap between the void 190 formed in region B and the beam profile is relatively small, so the effect on the characteristic variations between elements can be reduced compared to the case of Figure 4. Here, the case where the depth changes in two steps has been described, but it may change in three or more steps.

[0064] 7 is a cross-sectional view of a semiconductor laser device 100B according to Modification 2. In Modification 2, the bottom surface of the groove 152 in the region A is inclined at a constant inclination toward the x direction, and has a depth d Ａ (x) varies linearly with the position x. In FIG. 2, x = x １ When , d Ａ (x １ ) = 0, but in Modification 2, d Ａ (x １ )>0. In the second modification, the following relation holds: 0<d Ａ (x １ ) <d Ａ (x ２ ) <d Ｂ

[0065] 8 is a cross-sectional view of a semiconductor laser device 100C according to Modification 3. In the embodiment or Modifications 1 and 2, the bottom surfaces of the grooves 152 in the region A are flat, but in Modification 3, the bottom surfaces of the grooves 152 in the region A are curved.

[0066] (Manufacturing Method) Next, a manufacturing method of the semiconductor laser device 100 according to the embodiment will be described.

[0067] 9A and 9B are diagrams illustrating a first manufacturing method of the semiconductor laser element 100. Here, the manufacturing method of the semiconductor laser 100A of Fig. 6 will be described as an example. The manufacturing method includes step S100 of forming a semiconductor laminated structure by epitaxial growth, step S200 of forming a ridge portion 142, step S300 of forming a diffraction grating, and step S400 of forming an insulating film.

[0068] In step S100, an n-type semiconductor layer 120, an active layer 130, and a p-type semiconductor layer 140 are formed in this order on a GaN substrate 110.

[0069] In step S200, the p-type semiconductor layer 140 is etched to form the ridge portion 142.

[0070] In step S300, the diffraction grating 150 is formed on both sides of the ridge portion 142. Specifically, grooves 152 are formed on both sides of the ridge portion 142 as the diffraction grating 150 of the p-type semiconductor layer 140.

[0071] In step S400 , the insulating film 160 is formed on the p-type semiconductor layer 140 .

[0072] In step S300, as described above, the groove 152 is formed so as to have different depths in the region A and the region B. Several specific examples of step S300 will be described.

[0073] 10 is a diagram illustrating an example of step S300. Illustrated in FIG. 10 is a plan view, a cross section taken along line P-P' where the peaks of the diffraction grating 150 are to be formed, and a cross section taken along line Q-Q' along the portion where the grooves 152 of the diffraction grating 150 are to be formed.

[0074] Step S302 is a step of patterning an EB resist. Prior to step S302, an oxide film 204 is formed on the p-type semiconductor layer 140 in which the ridge portion 142 is formed, and an EB (electron beam) resist 202 is formed thereon.

[0075] In step S302, an electron beam EB is irradiated along the locations where the grooves 152 of the diffraction grating 150 are to be formed, thereby patterning the EB resist 202. After patterning, the portions of the EB resist 202 where the grooves 152 of the diffraction grating 150 are to be formed are removed, exposing the oxide film 204. The dose of the electron beam EB has a distribution in which the dose is low in region A and high in region B. In FIG. 10 , the dose of the electron beam EB is schematically indicated by the amount of dots in the arrows. The smaller the dose, the narrower the line width of the drawn pattern. Therefore, the line width of the drawn pattern, i.e., the opening width of the EB resist 202, is narrower in region A and wide in region B.

[0076] In the subsequent step S304, the oxide film 204 is dry-etched. Specifically, the oxide film 204 in the portion not covered with the EB resist 202 is removed.

[0077] In the following step S306, the EB resist 202 is removed, thereby leaving the oxide film 204 with openings in the areas where the grooves 152 of the diffraction grating 150 will be formed. The opening width of the oxide film 204 is narrow in region A and wide in region B.

[0078] In the subsequent step S308, the p-type semiconductor layer 140 is dry-etched. As a result, the portions of the p-type semiconductor layer 140 that are not covered with the oxide film 204 are etched, and the grooves 152 are formed. The depth of the grooves 152 increases as the opening width increases. As a result, it is possible to form grooves 152 that are relatively deep in region B and relatively shallow in region A.

[0079] The groove 152 formed in this manner has a width in region A that is narrower than the width in region B.

[0080] Another example of step S300 will be described. Figures 11A and 11B are views illustrating another example of step S300. In this manufacturing method, etching of the groove 152 is performed in two stages.

[0081] 11A shows steps S310 to S316 for forming the first-stage groove 152. Prior to step S310, an oxide film 204 is formed on the p-type semiconductor layer 140 in which the ridge portion 142 has been formed, and an EB resist 202 is formed thereon.

[0082] In step S310, an electron beam is irradiated along the locations where the grooves 152 of the diffraction grating 150 are to be formed, thereby patterning the EB resist 202. After patterning, the portions of the EB resist 202 where the grooves 152 of the diffraction grating 150 are to be formed are removed, exposing the oxide film 204. The dose of the electron beam EB is uniform, and the line width written is substantially constant across regions A and B.

[0083] In the subsequent step S312, the oxide film 204 is dry-etched. Specifically, the oxide film 204 in the portion not covered with the EB resist 202 is removed.

[0084] In the subsequent step S314, the EB resist 202 is removed, thereby leaving the oxide film 204 with openings in the areas where the grooves 152 of the diffraction grating 150 will be formed. The opening width of the oxide film 204 is substantially constant from region A to region B.

[0085] In the subsequent step S316, the p-type semiconductor layer 140 is dry-etched. As a result, the portions of the p-type semiconductor layer 140 that are not covered with the oxide film 204 are etched, and the grooves 152 are formed. The depth of the grooves 152 is substantially constant.

[0086] FIG. 11B shows steps S318 to S324 for forming the second-stage groove 152.

[0087] An oxide film 204 is again formed on the structure obtained in step S316, and an EB resist 202 is formed thereon.

[0088] In step S318, an electron beam is irradiated onto a portion of region B where the diffraction grating grooves 152 are to be formed, thereby patterning the EB resist 202. After patterning, the portion of the EB resist 202 that is within region B of the grooves 152 is removed, exposing the oxide film 204.

[0089] In the subsequent step S320, the oxide film 204 is dry-etched. Specifically, the oxide film 204 in the portion not covered with the EB resist 202 is removed.

[0090] In the next step S322, the EB resist 202 is removed, thereby leaving the oxide film 204 with openings in the areas included in the regions B within the range where the grooves 152 of the diffraction grating 150 are to be formed.

[0091] In the subsequent step S324, the p-type semiconductor layer 140 is dry-etched, whereby the portions of the p-type semiconductor layer 140 that are not covered with the oxide film 204 are etched, and the depth of the region B of the groove 152 becomes even deeper.

[0092] 12 is a diagram illustrating yet another example of step S300. This example can be applied to the manufacture of the semiconductor laser device 100 of FIG.

[0093] Step S330 is a step of patterning an EB resist. Prior to step S330, an oxide film 204 is formed on the p-type semiconductor layer 140 in which the ridge portion 142 is formed, and an EB (electron beam) resist 202 is formed thereon. The EB resist 202 is formed to have a constant thickness in region B and to become thicker in region A as it approaches the side surface of the ridge portion 142.

[0094] In step S330, an electron beam EB is irradiated along the locations where the grooves 152 of the diffraction grating 150 are to be formed, thereby patterning the EB resist 202. After patterning, the portions of the EB resist 202 where the grooves 152 of the diffraction grating 150 are to be formed are removed, exposing the oxide film 204. The line width of the pattern to be written, i.e., the opening width of the EB resist 202, becomes narrower as the thickness of the EB resist 202 increases and becomes wider as the thickness of the EB resist 202 decreases, so that the line width is narrower in region A and wider in region B. More specifically, the opening width of the EB resist 202 gradually increases with increasing distance from the ridge portion 142.

[0095] In the subsequent step S332, the oxide film 204 is dry-etched. Specifically, the oxide film 204 in the portion not covered with the EB resist 202 is removed.

[0096] In the following step S334, the EB resist 202 is removed. This leaves the oxide film 204 with openings where the grooves 152 of the diffraction grating 150 will be formed. The opening width of the oxide film 204 is narrow in region A and wide in region B. More specifically, the opening width of the oxide film 204 gradually widens with increasing distance from the ridge portion 142.

[0097] In the subsequent step S336, the p-type semiconductor layer 140 is dry-etched. As a result, the portions of the p-type semiconductor layer 140 that are not covered with the oxide film 204 are etched, and the grooves 152 are formed. The depth of the grooves 152 increases as the opening width increases. As a result, it is possible to form grooves 152 that are relatively deep in region B and have inclined bottom surfaces in region A.

[0098] 13 is a perspective view of a semiconductor laser device 100D according to a modified example. In this modified example, a diffraction grating 150 is also formed adjacent to a waveguide 146. This modified example differs from the above-described structure in that the upper surfaces of the waveguide 146 and the diffraction grating 150 are flush with each other.

[0099] 14 is a cross-sectional view of the semiconductor laser device 100D of FIG. 13 taken along the line AA′. The grooves 152 of the diffraction grating 150 have a substantially constant depth d Ｂ The groove 152 has a depth d that is shallower in the inner region A closer to the waveguide 146 in the second direction (x-axis direction) than in the outer region B. Ａ (x).

[0100] 15 is a diagram showing a light emitting device 200 according to an embodiment. The light emitting device 200 includes the above-described semiconductor laser device 100 (100A, 100B, 100C, 100D), a nonlinear optical element 210, and a filter 220.

[0101] The semiconductor laser element 100 oscillates in a single longitudinal mode with λ=444 nm. The nonlinear optical element 210 is a wavelength conversion element that generates a second harmonic λ / 2 (wavelength 222 nm) of the light emitted from the semiconductor laser element 100. The nonlinear optical element 210 may be, for example, β-BaB ２ O ４ (BBO) and KBe ２ BO ３ F ２ A wavelength conversion element such as a KBBF (Known for Bragg Beam Beam Filter) is used. By irradiating a fundamental wave (444 nm) from an appropriate direction onto this wavelength conversion element, a second harmonic (222 nm) can be generated. The filter 220 is a short-pass filter that removes the fundamental wave λ and transmits the second harmonic λ / 2.

[0102] The embodiments merely illustrate the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments as long as they do not deviate from the spirit of the present invention as defined in the claims.

[0103] The present disclosure relates to a semiconductor laser device.

[0104] REFERENCE SIGNS LIST 100 Semiconductor laser element 102 Layer structure 110 GaN substrate 120 n-type semiconductor layer 130 Active layer 140 p-type semiconductor layer 141 Current confinement structure 142 Ridge portion 144 Ridge-type waveguide 150 Diffraction grating 152 Groove 160 Insulating film 200 Light-emitting device 210 Nonlinear optical element 220 Filter

Claims

1. A distributed feedback semiconductor laser device comprising a layered structure including a substrate, a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, wherein the layered structure is provided with a current confinement structure extending in a first direction perpendicular to the layering direction, and a diffraction grating adjacent to the current confinement structure in a second direction perpendicular to the first direction, wherein the diffraction grating includes a plurality of grooves each extending in the second direction, and the depth of the plurality of grooves is substantially constant in an outer region that is relatively far from the current confinement structure in the second direction, and is shallower in an inner region that is relatively close to the current confinement structure in the second direction than in the outer region.

2. The semiconductor laser device according to claim 1, wherein the grooves of said diffraction grating become continuously deeper in said inner region as they move away from said current confinement structure.

3. The semiconductor laser device according to claim 1, wherein the grooves of said diffraction grating become deeper at a constant gradient in said inner region.

4. The semiconductor laser device according to claim 1, wherein the grooves of said diffraction grating become deeper nonlinearly in said inner region.

5. The semiconductor laser device according to claim 1, wherein the grooves of said diffraction grating become deeper in a stepped manner in said inner region as they move away from said current confinement structure.

6. The active layer is In ｘ Al ｙ Ga １－ｘ－ｙ 6. The semiconductor laser device according to claim 1, wherein N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) is included.

7. A semiconductor laser device according to any one of claims 1 to 5, wherein the diffraction grating has a phase shift region in the first direction.

8. The waveguide mode light intensity distribution at the output end face is measured at the position x closest to the waveguide in the inner region. １ When normalized as 1, the boundary x between the inner and outer regions ２ is the beam intensity 1 / e ２ Position x where ３ 6. The semiconductor laser device according to claim 1, wherein the first electrode is closer to the current confinement structure than the second electrode.

9. A semiconductor laser device according to any one of claims 1 to 5, wherein the length of said inner region in said second direction is 90 to 220 nm.

10. A light emitting device comprising: a distributed feedback semiconductor laser element according to any one of claims 1 to 5; a nonlinear optical element that generates a second harmonic of the light emitted from said distributed feedback semiconductor laser element; and a filter that transmits said second harmonic and removes the light emitted from said semiconductor laser element.

11. A method for manufacturing a semiconductor laser device according to any one of claims 1 to 5, comprising the steps of: forming a layered structure including a GaN substrate, a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer; forming a ridge stripe structure in the layered structure; forming a diffraction grating adjacent to the ridge stripe structure; and forming an insulating film inside the grooves of the diffraction grating.

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