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

Abstract

To provide a semiconductor laser element reduced in characteristics variations among elements.SOLUTION: A semiconductor laser element 100 includes 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 a 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, as viewed from the current constriction structure 141, 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, as viewed from the current constriction structure 141.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[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, which utilizes KrCl excimer lamps, can inactivate viruses without restricting human activity in medical institutions, schools, public and commercial facilities, and restaurants, and is attracting attention as a potential contribution to both pandemic containment and social activity.

[0003] To further improve the quietness and miniaturization of this virus inactivation system, it is possible to replace the KrCl excimer lamp with a semiconductor light-emitting device equipped with a semiconductor light-emitting element. However, there are currently no semiconductor light-emitting elements that emit high-power light around 222 nm. Therefore, it is possible 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 a 444 nm light source. Generally, a distributed feedback laser (DFB-LD) is used as a single-longitudinal mode laser (Patent Documents 1 and 2). [Prior art documents] [Non-patent literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-039519 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-037495 Summary of the Invention [Problem to be solved by the invention]

[0006] Various configurations have been proposed for DFB-LDs, including the laterally coupled DFB-LD. One type of laterally coupled DFB-LD has a layered structure of an N-type cladding layer, an active layer, and a P-type cladding layer, with a ridge (mesa structure) formed in the P-type cladding layer as a current confinement structure. A diffraction grating is then formed adjacent to the ridge in the P-type cladding layer. Furthermore, an insulating layer made of SiO2 or the like is formed on the same surface to suppress leakage current, etc.

[0007] The inventors have studied the laterally coupled DFB-LD with the above structure and have come to recognize the following problem. In the laterally coupled DFB-LD with the above structure, an insulating layer is formed so as to fill the grooves of the diffraction grating. When the insulating layer 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 the characteristics of each element.

[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. [Means for solving the problem]

[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. [Effects of the 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. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view of a distributed feedback semiconductor laser device according to a first embodiment. [Figure 2] 2 is a cross-sectional view of the semiconductor laser device of FIG. 1 taken along the line AA'. [Figure 3] 2 is a cross-sectional view of the semiconductor laser device of FIG. 1 taken along the line BB'. [Figure 4] FIG. 10 is a cross-sectional view of a semiconductor laser device according to a comparative technique. [Figure 5] FIG. 10 is a cross-sectional view showing the relationship between the beam radius and the region A. [Figure 6] FIG. 10 is a cross-sectional view of a semiconductor laser device according to a first modification. [Figure 7]FIG. 10 is a cross-sectional view of a semiconductor laser device according to Modification 2. [Figure 8] FIG. 10 is a cross-sectional view of a semiconductor laser device according to Modification 3. [Figure 9] 3A to 3C are diagrams illustrating a first manufacturing method of the semiconductor laser device. [Figure 10] FIG. 10 is a diagram illustrating an example of step S300. [Figure 11A] FIG. 10 is a diagram illustrating another example of step S300. [Figure 11B] FIG. 10 is a diagram illustrating another example of step S300. [Figure 12] FIG. 10 is a diagram illustrating yet another example of step S300. [Figure 13] FIG. 10 is a perspective view of a semiconductor laser device according to a modified example. [Figure 14] 14 is a cross-sectional view of the semiconductor laser device of FIG. 13 taken along the line AA'. [Figure 15] 1A and 1B are diagrams illustrating a light emitting device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Outline of the embodiment) A summary of some exemplary embodiments of the present disclosure is provided below. This summary is intended as a prelude to the more detailed description that follows, or to provide a basic understanding of the embodiments. This 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] (Outline of the embodiment) 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 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.

[0015] With this configuration, the diffraction grating grooves are shallower immediately adjacent to the ridge, allowing the insulating material to easily penetrate and preventing voids from forming. This suppresses variations in the refractive index distribution caused by voids, thereby reducing variations in the semiconductor laser's characteristics. 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 grating may become progressively deeper in the inner region as one moves away from the waveguide.

[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 have a discontinuous depth increasing in the inner region away from the waveguide, or the grooves of the diffraction grating may have a stepped depth increasing in the inner region away from the waveguide.

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

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

[0022] In one embodiment, when the beam intensity at the output end face is normalized to 1 at the position x1 closest to the waveguide in the inner region, the beam intensity at the boundary x2 between the inner region and the outer region is 1 / e 2 This can prevent a decrease in coupling efficiency.

[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.

[0025] (Embodiment) 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 designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. Furthermore, the embodiments are merely examples 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 component shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple components do not necessarily represent their relative sizes, and even if a component A is depicted as being thicker than another component B in the drawings, it is possible that component A is thinner than component B.

[0027] (Embodiment 1) 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 a similar effect may be used; for example, a Si substrate or a sapphire substrate may also be used.

[0029] An n-type semiconductor layer 120, an active layer 130, and a p-type semiconductor layer 140 are formed in this order on an n-type GaN substrate 110 by epitaxial growth, and form 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 N, and 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 the well layer and In as the 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 is 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 nm, 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, 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] An n-side electrode 171 is formed on the back surface of the GaN substrate 110 , and a 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 the sides 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 of the semiconductor laser device 100 of Fig. 1 taken along line A-A'. Line A-A' 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, which is 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, d 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] In addition, when the position of the mesa edge (the side where the mesa rises in Figure 2) is x1 and the position of the boundary between areas A and B is x2, the average groove depth dA_AVE is defined by the following equation. d A_AVE =∫ X1~X2 d A (x)dx / (x2 - x1) The average groove depth d of region A A_AVE and the depth d of region B B satisfy the relation d A_AVE < d B holds.

[0045] In the example of FIG. 2, d A (x1) = 0, d A (x2) = d B and the depth d of the groove 152 A varies linearly with respect to the position x.

[0046] FIG. 3 is a cross-sectional view taken along the line B - B' of the semiconductor laser device 100 of FIG. 1. The diffraction grating 150 may be a phase-shifted diffraction grating 150A having a phase shift region 151 as shown in the upper part of FIG. 3. For comparison, a uniform diffraction grating 150B without a phase shift region 151 is shown in the lower part of FIG. 3.

[0047] The phase shift region 151 is provided in the peak portion of the diffraction grating 150A. The length of the phase shift region 151 can be 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 sensed by light. n 0r is a value depending on the structure and material of the semiconductor laser device and can take values in the range of 1 < n0r < 3. By providing the phase shift region 151, the side mode suppression ratio (SMSR) of the longitudinal single 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 cavity. 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 explained.

[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 of the ridge portion 142, so voids 190 are likely to occur. The voids 190 in the grooves 152 of the diffraction grating 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), and therefore voids 190 are less likely to occur. This improves the reproducibility of the refractive index distribution and reduces the characteristic variations between elements.

[0055] In other words, the width W in the x-axis direction of region A A is determined so that voids 190 do not occur. However, if the width W of region A A is too large, unfavorable effects such as a decrease in the coupling efficiency of the diffraction grating 150 occur. Therefore, the width W A can be determined based on the beam radius and beam profile at the emission end face of the laser.

[0056] FIG. 5 is a cross-sectional view showing the relationship between the beam profile at the emission end face of the laser and region A. At the bottom of FIG. 5, an example of the horizontal light intensity distribution at the emission end face (front end face) is shown.

[0057] The light intensity distribution I(x) at x≧x1 contributes to the coupling coefficient. When the light intensity at x = x1 is set to I(x1)=1, I(x)≒exp(-2·γ·(x - x1)) is represented. Here, γ is the effective refractive index of the waveguide mode as N eff and the average equivalent refractive index in regions A and B (x1≦x≦x3) is N side then, using the wave number k0, γ = k0·√(N eff 2 -N side 2 ), and in the nitride semiconductor light-emitting device, γ / k0≒0.1~0.2.

[0058] If the position where the horizontal (x-direction) light intensity at the emission end face becomes 1 / e 2 is set as x3, most of the beam profile contributing to the coupling coefficient is in a region closer to the mesa side than this. Therefore, in order to suppress a decrease in the coupling efficiency, the boundary x2 between regions A and B needs to be within the range of x1 < x2 < x3. Here, at the oscillation wavelength λ, approximately, x3 - x1≒1 / γ = λ / 2π√(N eff 2 -N side 2 ).

[0059] On the other hand, the closer the boundary x2 between regions A and B is to the mesa (x=x1), the greater the effect on characteristic variations when a void 190 occurs in region B, so the boundary x2 needs to be located away from the mesa. From this perspective, the boundary x2 can be determined so that the integral value of the light intensity in the range x1 to x2 is at least half the integral value of the light intensity in the range x1 to x3. That is, ∫ x1~x2 I(x)dx>1 / 2×∫ x1~x3 I(x)dx The boundary x2 between area A and area B, i.e., the width W of area A, is A It is preferable to define

[0060] From the above, when λ=400 nm, W A = 90 to 180 nm, and x3 - x1 = 300 to 600 nm. Similarly, when λ = 500 nm, W A = 110 to 220 nm, and x3 - x1 = 400 to 800 nm. A =150 nm may also be used.

[0061] In this case, the groove depth in region B does not necessarily have to be substantially constant, and the average groove depth d A_AVE and the average groove depth d in region B B_AVE In between, d 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 essentially 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 Fig. 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 Figure 2, when x = x1, d A (x1)=0, but in Modification 2, d A (x1)>0. In the second modification, the following relational expression holds true: 0 <d A (x1) <d A (x2) <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 method for manufacturing the semiconductor laser device 100 according to the embodiment will be described.

[0067] 9 is a diagram illustrating a first manufacturing method of the semiconductor laser device 100. 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 on a GaN substrate 110 in this order.

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

[0070] In step S300, diffraction grating 150 is formed on both sides of ridge portion 142. Specifically, grooves 152 are formed on both sides of ridge portion 142 as diffraction grating 150 of 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. In FIG. 10, a plan view, a cross section taken along P-P' where the peaks of the diffraction grating 150 are to be formed, and a cross section taken along Q-Q' along the portion where the grooves 152 of the diffraction grating 150 are to be formed are shown.

[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 areas 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 such that 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 number 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 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] In the groove 152 formed by this method, the width in the region A is narrower than the width in the region B.

[0080] Another example of step S300 will be described below. Figures 11A and 11B are views illustrating another example of step S300. In this manufacturing method, etching of the grooves 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 is 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 following step S314, the EB resist 202 is removed, thereby leaving 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 substantially constant from region A to region B.

[0085] In the following 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 grooves 152 of the diffraction grating are to be formed, thereby patterning EB resist 202. After patterning, the portion of EB resist 202 that is within region B of grooves 152 is removed, exposing 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 following step S322, the EB resist 202 is removed, thereby leaving the oxide film 204 with the 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] FIG. 12 is a diagram illustrating yet another example of step S300.

[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.

[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, thereby leaving 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.

[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 height of the upper surface of the waveguide 146 and the upper surface of the diffraction grating 150 are the same.

[0099] Fig. 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 BThe 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 at 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 made of, for example, β-BaB2O4 (BBO) or CsLiB6O 10 (CLBO) or the like is used. By irradiating this wavelength conversion element with a fundamental wave (444 nm) from an appropriate direction, a second harmonic wave (222 nm) can be generated. The filter 220 is a short-pass filter that removes the fundamental wave λ and outputs a second harmonic wave 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. [Explanation of symbols]

[0103] 100 Semiconductor laser element 102 Laminated structure 110 GaN substrate 120 n-type semiconductor layer 130 Active layer 140 p-type semiconductor layer 141 Current confinement structure 142 Ridge 144 Ridge Waveguide 150 Diffraction Grating 152 Groove 160 insulating film 200 Light-emitting device 210 Nonlinear Optical Elements 220 filters

Claims

1. A distributed feedback semiconductor laser element, a laminated structure including a substrate, a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer; The laminated structure includes: a current confinement structure extending in a first direction perpendicular to the stacking direction; a diffraction grating adjacent to the current confinement structure in a second direction perpendicular to the first direction; is provided, the diffraction grating includes a plurality of grooves each extending in the second direction; a semiconductor laser element characterized in that 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. 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 waveguide.

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

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

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

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) is included.

7. 6. The semiconductor laser device according to claim 1, wherein the diffraction grating has a phase shift region in the first direction.

8. The beam intensity at the output end face is calculated by dividing the beam intensity at the position x １ When normalized as 1, the boundary x 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 waveguide than the second electrode.

9. 6. The semiconductor laser device according to claim 1, wherein the length of the inner region in the second direction is 90 to 220 nm.

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

11. 6. A method for manufacturing a semiconductor laser device according to claim 1, comprising the steps of: forming a stacked 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 stacked structure; forming a diffraction grating adjacent to the ridge stripe structure; forming an insulating film inside the grooves of the diffraction grating; A manufacturing method comprising:

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