Nitride semiconductor laser element, method for manufacturing same, and light-emitting device
By forming a ridge waveguide and a control diffraction grating structure in a GaN-based semiconductor laser element, the problem of a small optical coupling coefficient κ is solved and a high-output longitudinal single-mode semiconductor laser is realized.
Patent Information
- Application Number
- CN202410973040.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-07-21
- Filing Date
- 2024-07-19
- Publication Date
- 2025-01-21
AI Technical Summary
In GaN-type materials, it is difficult to obtain sufficient refractive index difference, resulting in a small optical coupling coefficient of the diffraction grating, and it is difficult to realize a high-output longitudinal single-mode semiconductor laser.
By forming a ridge waveguide in a stacked structure of semiconductor laser elements and forming first and second diffraction gratings thereon, the groove depth and duty cycle of the diffraction gratings are controlled to increase the optical coupling coefficient κ.
A semiconductor laser element with high output in longitudinal single mode is realized, the optical coupling coefficient κ is improved, and the performance of the laser is enhanced.
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Figure CN119340783A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a nitride semiconductor laser device. Background Art
[0002] So far, 254nm ultraviolet sterilization lamps have been widely used for sterilization purposes. However, if irradiated to humans, there is a risk of skin cancer and keratitis. In contrast, in recent years, many medical institutions and universities at home and abroad have reported that the 222nm ultraviolet rays using KrCl excimer lamps are much safer. In addition, it has also been proven to be effective against the new coronavirus. The virus inactivation system using this KrCl excimer lamp can inactivate viruses without restricting human activities in medical institutions, schools, public and commercial facilities, and catering facilities, and has attracted attention as a system that can contribute to both epidemic suppression and social activities.
[0003] In order to further improve the quietness of the virus inactivation system or to make it smaller, a method of replacing the KrCl excimer lamp with a semiconductor light-emitting device equipped with a semiconductor light-emitting element is considered. However, there is no semiconductor light-emitting element that emits light near 222nm. Therefore, a method of converting 444nm light into a second harmonic (SHG: Second harmonic Generation wave) of 222nm using high-order harmonic generation based on a wavelength conversion element is considered.
[0004] In order to improve the conversion efficiency of SHG waves, a longitudinal single-mode and high-output semiconductor laser is required as a 444nm light source. Generally, a distributed feedback semiconductor laser (DFB-LD: Distributed FeedBack Laser Diode) is used as a longitudinal single-mode laser.
[0005] Prior art literature
[0006] Non-patent literature
[0007] Non-patent document 1: "InGaAs / AlGaAs Quantum Well Laterally-Coupled DistributedFeedback Laser", Japanese Journal of Applied Physics, volume 43, Number 5R, pp.25-49 (2004)
[0008] Non-patent document 2: "Continuous-wave operation of a semipolar InGaN distributed-feedback blue laser diode with a first-order indium tin oxidesurface grating", Optics Letters vol.44pp.3106-3109(2019) Summary of the invention
[0009] Problems that the invention will solve
[0010] GaN-based materials are widely used as semiconductor light emitting elements that emit light in the ultraviolet and visible wavelength bands. However, it is difficult to obtain a sufficient refractive index difference in GaN-based materials, and it is difficult to increase the optical coupling coefficient κ of the diffraction grating.
[0011] The present disclosure has been made under such circumstances, and one of the exemplary objects of one embodiment thereof is to provide a semiconductor laser element that obtains high output in a longitudinal single mode.
[0012] Means for solving problems
[0013] A certain embodiment of the present disclosure relates to a distributed feedback semiconductor laser element. The semiconductor laser element has: a stacked structure including a GaN substrate, a first conductive semiconductor layer, a light emitting layer, and a second conductive semiconductor layer, forming a ridge waveguide; and a first diffraction grating formed on both sides adjacent to the ridge waveguide. The depth d of the groove of the first diffraction grating is included in the range of 50nm≤d≤200nm, and the duty ratio duty is included in the range of inequality (1) using constants a, b, c, and n that define the order of diffracted light.
[0014] [Formula 1]
[0015]
[0016] Another embodiment of the present disclosure relates to a method for manufacturing a distributed feedback semiconductor laser element. The manufacturing method comprises the following steps: forming a stacked structure, the stacked structure including a GaN substrate, a first conductive semiconductor layer, a light emitting layer, and a second conductive semiconductor layer; forming a ridge stripe structure on the stacked structure; forming a first diffraction grating adjacent to the ridge stripe structure and forming an insulating film inside the grooves of the first diffraction grating. The depth d of the grooves of the first diffraction grating is included in the range of 54.9nm≤d≤200nm, and the duty ratio duty is included in the range of inequality (1) using constants a, b, c, n that define the order of diffracted light.
[0017] In addition, even if the above components are arbitrarily combined, or components, methods, devices, systems, etc. are mutually replaced, they are also effective as the present invention or the mode of the present disclosure. Moreover, the record of this item (means for solving the problem) does not describe all the indispensable features of the present invention, and therefore, a sub-combination of these features can also constitute the present invention.
[0018] Effects of the Invention
[0019] According to the semiconductor laser element of one aspect of the present disclosure, high output can be obtained in a longitudinal single mode. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 This is a perspective view of a distributed feedback semiconductor laser element according to the first embodiment.
[0021] Figure 2 is a diagram illustrating the interaction between light and a diffraction grating.
[0022] Figure 3 : is a graph showing the relationship between the duty ratio of the diffraction grating and the optical coupling coefficient κ.
[0023] Figure 4 It means that the optical coupling coefficient κ is 10cm －1 Graph showing the relationship between the groove depth d and the duty cycle duty.
[0024] Figure 5 This is a perspective view of a semiconductor laser element according to the second embodiment.
[0025] Figure 6 It is a diagram for explaining the interaction between light and the first diffraction grating and the second diffraction grating.
[0026] Figure 7 This is a diagram showing the optical coupling coefficient κ of the first embodiment and the second embodiment.
[0027] Figure 8 It is a diagram for explaining a method for manufacturing a semiconductor laser element.
[0028] Fig. 9 This is a perspective view of a semiconductor laser element according to a third embodiment.
[0029] Fig.10 is a cross-sectional view showing a diffraction grating having a phase shift region.
[0030] Fig.11 It is a diagram showing a light emitting device according to an embodiment. DETAILED DESCRIPTION
[0031] (Overview of Embodiments)
[0032] An overview of several exemplary embodiments of the present disclosure is described. This overview serves as a preface to the detailed description to be described later or is intended to provide a basic understanding of the embodiments. This overview simplifies some concepts of one or more embodiments for illustration and does not limit the breadth of the invention or the disclosure. In addition, this overview is not a comprehensive overview of all conceivable embodiments and does not limit the indispensable constituent elements of the embodiments. For convenience, "one embodiment" is sometimes used to refer to one embodiment (embodiment, variation) or multiple embodiments (embodiment, variation) disclosed in this specification.
[0033] (Overview of Embodiments)
[0034] A distributed feedback semiconductor laser device according to an embodiment includes: a stacked structure including a GaN substrate, a first conductive semiconductor layer, a light emitting layer, and a second conductive semiconductor layer, a ridge waveguide being formed; and a first diffraction grating formed adjacent to the ridge waveguide on both sides. The depth d of the grooves of the first diffraction grating is within the range of 50nm≤d≤200nm, and the duty ratio duty is within the range of inequality (1) using constants a, b, c, and n defining the order of diffracted light.
[0035] [Formula 2]
[0036]
[0037] By controlling the duty ratio within the range defined by equation (1) using the depth of the grooves of the diffraction grating as a parameter, a large optical coupling coefficient κ can be obtained, and the output of the semiconductor laser element can be increased.
[0038] In one embodiment, the order may be 3, a=1000000, b=0.889, c=75.3, n=4, and 75.3 nm≤d≤200 nm.
[0039] In one embodiment, the order may be 1, a=7500000, b=0.738, c=54.9, n=8, and 54.9 nm≤d≤200 nm.
[0040] In one embodiment, the order may be 5, a=7500000, b=0.929, c=88.9, n=4, and 88.9 nm≤d≤200 nm.
[0041] In one embodiment, the order may be 7, a=23000000, b=0.947, c=100.6, n=4, and 100.6 nm≤d≤200 nm.
[0042] In one embodiment, the semiconductor laser element may also include a second diffraction grating formed on the upper surface of the ridge waveguide. The first diffraction grating and the second diffraction grating have the same periodic structure and are continuous when viewed from above. By providing the second diffraction grating, the optical coupling coefficient can be further improved. Moreover, since the first diffraction grating and the second diffraction grating have the same periodic structure, they can be formed simultaneously using the same manufacturing process. As a result, manufacturing becomes easy.
[0043] In one embodiment, the bottom surface of the grooves of the second diffraction grating may be higher than the bottom surface of the grooves of the first diffraction grating.
[0044] In one embodiment, the first diffraction grating may include a phase shift region. In one embodiment, when the oscillation wavelength is λ, m is 0 or an arbitrary positive integer, and n is 0r When the average refractive index of the light is set to λ / 4n, the length of the phase shift region is 0r ×(2m+1).
[0045] In one embodiment, the phase shift region may be provided at a position where the low-reflection end face and the high-reflection end face of the semiconductor laser element are internally divided in a range of 6:4 to 8:2.
[0046] In one embodiment, in the first diffraction grating, at least the groove portion from which light leaks out may be covered with an insulating film, and the insulating film may include at least one element selected from the group consisting of Si, Zr, Al, Ta, Nb, Ti, In, O, and N.
[0047] The light emitting device of one embodiment may also include: a distributed feedback semiconductor laser element as described in any of the above; a nonlinear optical element that generates a second harmonic of the emitted light of the distributed feedback semiconductor laser element; and a filter that transmits the second harmonic. According to this configuration, ultraviolet rays with high safety can be efficiently generated.
[0048] A method for manufacturing a distributed feedback semiconductor laser element according to an embodiment of the present invention comprises the following steps: forming a stacked structure including a GaN substrate, a first conductive semiconductor layer, a light emitting layer, and a second conductive semiconductor layer; forming a ridge stripe structure on the stacked structure; forming a first diffraction grating adjacent to the ridge stripe structure; and forming an insulating film inside the grooves of the first diffraction grating. The depth d of the grooves of the first diffraction grating is within the range of 54.9nm≤d≤200nm, and the duty ratio duty is within the range of inequality (1) using constants a, b, c, and n that define the order of diffracted light.
[0049] The manufacturing method of one embodiment may further include a step of forming a second diffraction grating in a region adjacent to the ridge stripe structure simultaneously with the formation of the first diffraction grating.
[0050] In one embodiment, the insulating film may be formed by an atomic layer deposition (ALD) method.
[0051] (Implementation Method)
[0052] Below, while referring to the attached Figure 1 The preferred embodiments are described. The same or equivalent components, parts, and processes shown in the drawings are marked with the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the embodiments are not limited to the disclosure or invention, but are exemplified, and all the features and their combinations described in the embodiments are not necessarily limited to the essence of the disclosure or invention.
[0053] In addition, the dimensions (thickness, length, width, etc.) of each component recorded in the drawings are sometimes appropriately enlarged or reduced for ease of understanding. Moreover, the dimensions of multiple components do not necessarily represent their size relationship. Even if a certain part A is depicted as thicker than another part B in the drawings, part A may be thinner than part B.
[0054] (Implementation Method 1)
[0055] Figure 1 This 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 112 , an n-type semiconductor layer 120 , an active layer 114 , a p-type semiconductor layer 130 , an n-side electrode 140 , a p-side electrode 142 , and a diffraction grating 150 .
[0056] The GaN substrate 112 is a nitride semiconductor and may have In x Al y Ga 1－x－y The composition of the GaN substrate 112 is N (0≤x≤1, 0≤y≤1, 0≤x+y≤1). In order to generate a 444 nm blue laser, the material of the GaN substrate 112 can be GaN (x=y=0).
[0057] The n-type semiconductor layer 120 , the active layer 114 , and the p-type semiconductor layer 130 are sequentially formed on the n-type GaN substrate 112 by epitaxial growth to form a stacked structure 110 .
[0058] The n-type semiconductor layer 120 may include an n-type cladding layer 122 and an n-type guide layer 124. For example, the material of the n-type cladding layer 122 is n-Al 0.05 Ga 0.95 N, the material of the n-type guide layer 124 is n-GaN.
[0059] An active layer (light emitting layer) 114 having a quantum well structure is formed on the n-type semiconductor layer 120. When the oscillation wavelength is set to 444 nm, In can be selected as the material of the quantum well structure. 0.01 Ga 0.99 N is used as the barrier layer, and In is selected 0.15 Ga 0.85 N serves as a well layer.
[0060] In order to suppress the diffusion of impurities from the n-type semiconductor layer 120 to the active layer 114, a non-doped nitride guide layer (not shown) may be inserted between them. 0.02 Ga 0.98 N.
[0061] The p-type semiconductor layer 130 may include a carrier blocking (electron blocking EB) layer 132, a p-type guide layer 134, a p-type cladding layer 136, and a contact layer 138. For example, the material of the p-type guide layer 134 is p-In 0.02 Ga 0.98 N, the material of the p-type cladding layer 136 is p-Al 0.04 Ga 0.96 N, the material of the contact layer 138 is p-GaN.
[0062] In order to suppress diffusion of impurities from the p-type semiconductor layer 130 to the active layer 114 , a non-doped nitride guide layer (not shown) may be inserted therebetween.
[0063] The n-side electrode 140 is formed on the back surface of the GaN substrate 112 , and the p-side electrode 142 is formed on the upper surface of the contact layer 138 .
[0064] A ridge (mesa) is formed on the p-type cladding layer 136 to form a ridge stripe structure (ridge structure) 160. The ridge height can be several hundred nm, and the ridge width (mesa width) can be several micrometers. For example, the height can be 500 nm and the width can be 2 μm.
[0065] The optical coupling coefficient κ described later varies according to the ridge width. The narrower the table width, the larger the optical coupling coefficient κ. However, starting from the table width less than 1 μm, the lateral restriction becomes weaker and the optical coupling coefficient also begins to decrease. On the other hand, if the table width exceeds 3 μm, the lateral single mode becomes a lateral multimode. Therefore, in order to obtain a higher optical coupling coefficient κ in a lateral single mode, the table width Wm is preferably set to 1 μm ≤ Wm ≤ 3 μm.
[0066] The p-type cladding layer 136 having the ridge stripe structure 160 forms a ridge waveguide together with the active layer 114 and the n-type cladding layer 122 .
[0067] A diffraction grating 150 is formed in a portion of the p-type cladding layer 136 on the side of the mesa adjacent to the ridge stripe structure 160 .
[0068] In addition, an AR (anti-reflection) coating (reflectivity 2% or less) is applied to the emission side (front) end face of the semiconductor laser element 100, and an HR (high reflection) coating (reflectivity 90% or more) is applied to the reflection side (rear) end face. Alternatively, both end faces may be AR coated.
[0069] Figure 2 1 is a diagram illustrating the interaction between light and the diffraction grating 150. Figure 2 1 shows a simplified cross-sectional view of the semiconductor laser element 100. The laser light guided in the ridge waveguide leaks out in the horizontal direction, and the leaked part interacts with the diffraction grating 150 located next to the ridge stripe structure 160. As a result, it works as a distributed feedback laser and can oscillate in a longitudinal single mode.
[0070] The shape of the grooves of the diffraction grating 150 can generally be considered to be rectangular, but it is not limited to this as long as the same effect can be obtained in practice. For example, the cross-sectional shape of the grooves can also be trapezoidal, wedge-shaped, or other shapes. In the case where the cross-sectional shape of the grooves is non-rectangular, its width can also be defined as the average width.
[0071] Next, the diffraction grating 150 for obtaining high output at 444 nm is described. In a semiconductor laser of a long wavelength (red to infrared region), the optical coupling coefficient κ of the diffraction grating can be easily increased, but in a blue laser, it is difficult to increase the optical coupling coefficient κ, and the structure of the diffraction grating 150 has a great influence on the performance of the semiconductor laser element 100.
[0072] Figure 3 : is a graph showing the relationship between the duty ratio of the diffraction grating and the optical coupling coefficient κ. Figure 3 The optical coupling coefficient κ is calculated for the 1st, 3rd, 5th, and 7th diffracted light. The depth of the groove is set to 50nm, 100nm, 150nm, and 200nm, respectively. The duty cycle of the diffraction grating is represented by the ratio of the width of the groove of the diffraction grating to the period. If the width of the groove is set to w and the period is set to p, then duty = 1-(w / p), which is specified in the range of 0≤duty≤1. The narrower the width w of the groove, the higher the duty cycle.
[0073] One of the important parameters in designing a DFB-LD is the standardized coupling coefficient κL. Here, κ is the optical coupling coefficient, and L is the resonator length. According to experience, this κL is preferably κL ≥ 0.5, and more preferably κL ≥ 1. This is because, in a DFB-LD with a small κL, depending on the driving conditions, the FP (Fabry-Perot) mode and the DFB mode sometimes coexist, and a longitudinal single-mode oscillation with a high SMSR (side mode suppression ratio) cannot be achieved. In addition, in a transverse single-mode nitride semiconductor laser, the ridge width is about 2μm, so in order to obtain an optical output of more than tens of mW, it is empirically expected that the resonator length is set to more than 500μm. This is because, generally speaking, the optical output causes thermal saturation due to the heat generated by power-on, but in the case of a short resonator length, thermal saturation occurs before sufficient optical output is obtained. Therefore, the optical coupling coefficient κ of the DFB-LD is preferably designed to be κ ≥ 10cm －1 .
[0074] Figure 4 It means according to Figure 3 The optical coupling coefficient κ obtained is 10 cm －1 The above diagram shows the range of the groove depth d and the duty ratio duty. Figure 4 Can be
[0075] d = a × (duty - b) n +c…(2)
[0076] This is well represented by equation (2).
[0077] a, b, c, and n are fitting parameters. For a certain depth d, by determining the duty ratio within the range surrounded by equation (2), the optical coupling coefficient κ can be made greater than 10 cm －1 That is, the duty ratio duty may be determined so as to satisfy the following relational expression (1).
[0078] [Formula 3]
[0079]
[0080] Here, the optical coupling coefficient κ depends on the depth d of the groove, and shows a trend that the deeper the groove is, the more monotonically the optical coupling coefficient increases. However, due to limitations of etching technology, the groove cannot be made deeper indefinitely, and the maximum depth is about 200nm. In addition, in the case where the depth of the diffraction grating d is to be deeper than 200nm, in order to ensure sufficient lateral light confinement, it is necessary to increase the height of the ridge stripe structure 160 (the height of the table), but this may lead to an increase in the driving voltage. Considering this limitation, the depth d of the groove is preferably set to a range of 50 to 200nm.
[0081] In one embodiment, the diffraction order can be set to 3. In this case, a=1000000, b=0.889, c=75.3, n=4, and the depth d of the groove that can be obtained is 75.3 nm≤d≤200 nm.
[0082] In one embodiment, the diffraction order can be set to 1. In this case, a=7500000, b=0.738, c=54.9, n=8, and the depth d of the groove that can be obtained is 54.9 nm≤d≤200 nm.
[0083] In one embodiment, the diffraction order can be set to 5. In this case, a=7500000, b=0.929, c=88.9, n=4, and the depth d of the groove that can be obtained is 88.9 nm≤d≤200 nm.
[0084] In one embodiment, the diffraction order can be set to 7. In this case, a=23000000, b=0.947, c=100.6, n=4, and the obtainable groove depth d is 100.6 nm≤d≤200 nm.
[0085] (Implementation Method 2)
[0086] Figure 5 FIG. 1 is a perspective view of a semiconductor laser device 100A according to Embodiment 2. Figure 1 The semiconductor laser element 100 further includes a second diffraction grating 152. In the second embodiment, the diffraction grating 150 adjacent to the ridge stripe structure 160 is referred to as a first diffraction grating 150.
[0087] The second diffraction grating 152 has the same periodic structure as the first diffraction grating 150 , and when the semiconductor laser element 100A is viewed in a plan view, the positions of the corresponding grooves of the first diffraction grating 150 and the second diffraction grating 152 are consistent and continuous.
[0088] Figure 6 1 and 2 are diagrams for explaining the interaction between light and the first diffraction grating 150 and the second diffraction grating 152 . Figure 6 1 shows a simplified cross-sectional view of the semiconductor laser element 100A. The laser light guided in the ridge waveguide leaks out in the horizontal direction, and the leaked part interacts with the first diffraction grating 150 located beside the ridge stripe structure 160. In addition, the laser light also leaks out in the vertical upward direction, and the leaked part interacts with the second diffraction grating 152 located above the ridge stripe structure 160. As a result, the optical coupling coefficient κ can be further improved compared with the first embodiment.
[0089] Figure 7: is a diagram showing the optical coupling coefficient κ of the first embodiment and the second embodiment. The calculation was performed for the third-order diffracted light and the first-order diffracted light. In the third-order diffracted light, the depth of the groove d = 150nm, and the duty cycle is set to 90%. In the first-order diffracted light, the depth of the groove d = 100nm, and the duty cycle is set to 85%. In the second embodiment, the coupling coefficient κ can be increased for either the first-order or third-order diffracted light.
[0090] In addition, the semiconductor laser element 100A of Embodiment 2 can be formed simultaneously by the same manufacturing process because the first diffraction grating and the second diffraction grating have the same periodic structure. In this case, the depths of the grooves of the diffraction gratings 150 and 152 are the same. In other words, the bottom of the groove of the diffraction grating 150 is located at a higher position than the bottom of the groove of the diffraction grating 152.
[0091] When the depth of the diffraction grating d is to be deeper than 200 nm, the height of the ridge stripe structure 160 (the height of the table) needs to be increased to ensure sufficient lateral light confinement, but this may lead to an increase in the driving voltage. In addition, the injected current is also prone to become non-uniform in the resonator direction. In contrast, by limiting the depth d of the groove of the diffraction grating to within the range of 50 to 200 nm, there is no need to increase the height of the table, so there will be no problem of voltage increase and current non-uniformity.
[0092] Figure 8 FIG. 2 is a diagram for explaining a method for manufacturing a semiconductor laser element 100A. In step S1, an insulating film 202 is formed on a stacked structure 201 having a mesa. The stacked structure 201 includes Figure 1 The stacked structure includes a GaN substrate 112, an n-type semiconductor layer 120, an active layer 114, and a p-type semiconductor layer 130. The stacked structure can be manufactured using a known technique.
[0093] In the next step S2 , after a resist 204 is applied on the insulating film 202 , patterns of the diffraction gratings 150 and 152 are formed.
[0094] In the next step S3, the insulating film 202 is etched to remove the resist 204. In the next step S4, the insulating film 202 is removed.
[0095] It is better to form the insulating film 206 inside the groove. The insulating film 206 is preferably formed at least in the portion where light leaks out, but may completely fill the groove. In step S5, the insulating film 206 is formed by the ADL (atomic layer deposition) method. By using the ADL method, the insulating film 206 can be well formed on the bottom surface of the groove. As the material of the insulating film 206, an oxide containing one or more elements of Si, Zr, Al, Ta, Nb, Ti, In, O, and N, specifically SiN x , SiO2, ZrO2, Al2O3, Ta2O5, Nb2O5, TiO2, AlN, AlON, AlInN, etc.
[0096] In the next step S6, a portion 208 of the upper surface of the mesa in the insulating film 206 is removed. Then, in step S7, the p-side electrode 142 is formed.
[0097] The above is the method for manufacturing the semiconductor laser device 100A. According to the semiconductor laser device 100A, the first diffraction grating 150 and the second diffraction grating 152 can be formed simultaneously in the same process.
[0098] In the semiconductor laser element 100 of the first embodiment, the diffraction grating 150 needs to be formed while avoiding the table, so the manufacturing difficulty is high. That is, if the diffraction grating 150 is to be brought close to the shoulder of the table, the possibility of forming a groove on the side of the table increases. On the contrary, if the groove on the side of the table is to be prevented, the diffraction grating 150 is away from the shoulder of the table, and the optical coupling coefficient κ is reduced. In the second embodiment, since the first diffraction grating 150 and the second diffraction grating 152 are formed simultaneously in the same process, this problem does not occur.
[0099] (Implementation method 3)
[0100] Fig. 9 This is a perspective view of a semiconductor laser device 100B according to Embodiment 3. The second diffraction grating 152 is formed on the upper surface of the mesa, but no groove is formed within a certain width from the side surface of the mesa. This further suppresses the non-uniformity of current injection.
[0101] In Embodiments 1 to 3, the diffraction gratings 150 and 152 may be provided with phase shift regions. Fig.10 1 is a cross-sectional view showing a diffraction grating 150C having a phase shift region 151. Fig.10 For comparison, the diffraction grating 150 without the phase shift region 151 is shown in the lower layer. The phase shift region 151 is provided at the peak portion of the diffraction grating 150C. The length of the phase shift region 151 can be set to
[0102] λ / 4n 0r ×(2m+1).
[0103] λ is the oscillation wavelength, m is 0 or any positive integer, and n 0r is the average refractive index felt by light. n 0r It depends on the structure and material of the semiconductor laser element, and can be 1<n 0r The value in the range of <3. By providing the phase shift region 151, the side mode suppression ratio (SMSR; Side Mode Suppression Ratio) of the longitudinal single mode can be improved.
[0104] The phase shift region 151 is preferably formed closer to the high reflection facet than the center of the cavity. For example, the phase shift region 151 may be provided at a position where the low reflection facet (emitting facet) and the high reflection facet of the semiconductor laser element are internally divided in a range of 6:4 to 8:2.
[0105] Next, the purpose of the semiconductor laser element 100 will be described.
[0106] Fig.11 1 is a diagram showing a light emitting device 200 according to an embodiment. The light emitting device 200 includes the semiconductor laser element 100 ( 100A, 100B) described above, a nonlinear optical element 210 , and a filter 220 .
[0107] The semiconductor laser element 100 oscillates in a longitudinal single mode at λ=444nm. The nonlinear optical element 210 is a wavelength conversion element that generates the second harmonic λ / 2 (wavelength 222nm) of the output light of the semiconductor laser element 100. For example, β-BaB2O4 (BBO), CsLiB6O 10 (CLBO) etc. By allowing the fundamental wave (444 nm) to enter the wavelength conversion element from an appropriate direction, the second harmonic (222 nm) can be generated. The filter 220 is a short-pass filter, which removes the fundamental wave λ and emits the second harmonic λ / 2.
[0108] The embodiments merely illustrate the principles and applications of the present invention, and many modifications and changes in configuration are permitted in the embodiments without departing from the spirit of the present invention defined in the claims.
[0109] Description of Reference Numerals
[0110] 100 Semiconductor laser element
[0111] 110 stacked structure
[0112] 112 GaN substrate
[0113] 120 n-type semiconductor layer
[0114] 122 n-type cladding
[0115] 124 n-type guide layer
[0116] 114 Active layer
[0117] 130 p-type semiconductor layer
[0118] 132 Carrier blocking layer
[0119] 134 p-type guide layer
[0120] 136 p-type cladding
[0121] 138 contact layer
[0122] 140 n-side electrode
[0123] 142 p-side electrode
[0124] 150 First diffraction grating
[0125] 151 Phase Shift Region
[0126] 152 Second diffraction grating
[0127] 160 Ridge Stripe Structure
[0128] 200 Lighting Device
[0129] 210 Nonlinear Optical Elements
[0130] 220 Filter
Claims
1. A distributed feedback semiconductor laser element, characterized in that: have: A stacked structure comprising a GaN substrate, a first conductive type semiconductor layer, a light emitting layer, and a second conductive type semiconductor layer, forming a ridge waveguide; and A first diffraction grating is formed adjacent to the ridge waveguide on both sides, The depth d of the grooves of the first diffraction grating is within the range of 50 nm ≤ d ≤ 200 nm, and the duty ratio duty is included in the inequality (1) using constants a, b, c, and n that define the order of the diffracted light: within the range.
2. The semiconductor laser element according to claim 1, wherein The order is 3, a=1000000, b=0.889, c=75.3, n=4, and 75.3 nm≤d≤200 nm.
3. The semiconductor laser element according to claim 1, wherein The order is 1, a=7500000, b=0.738, c=54.9, n=8, and 54.9 nm≤d≤200 nm.
4. The semiconductor laser element according to claim 1, wherein The order is 5, a=7500000, b=0.929, c=88.9, n=4, and 88.9 nm≤d≤200 nm.
5. The semiconductor laser element according to claim 1, wherein The order is 7, a=23000000, b=0.947, c=100.6, n=4, and 100.6 nm≤d≤200 nm.
6. The semiconductor laser device according to any one of claims 1 to 5, characterized in that The invention further includes a second diffraction grating formed on an upper surface of the ridge waveguide.
7. The semiconductor laser element according to claim 6, wherein: The bottom surfaces of the grooves of the second diffraction grating are higher than the bottom surfaces of the grooves of the first diffraction grating.
8. The semiconductor laser device according to any one of claims 1 to 5, characterized in that The first diffraction grating has a phase shift region.
9. The semiconductor laser element according to claim 8, wherein: The phase shift region is provided at a position where the low-reflection end face and the high-reflection end face of the semiconductor laser element are internally divided in a range of 6:4 to 8:
2.
10. The semiconductor laser device according to any one of claims 1 to 5, characterized in that In the first diffraction grating, at least the groove portion from which light leaks out is covered with an insulating film, and the insulating film includes at least one element selected from the group consisting of Si, Zr, Al, Ta, Nb, Ti, In, O, and N.
11. A light emitting device, characterized in that: have: The 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 output light of the distributed feedback semiconductor laser element; as well as The filter transmits the second harmonic.
12. A method for manufacturing a distributed feedback semiconductor laser element, characterized in that: The following steps are required: forming a stacked structure, the stacked structure comprising a GaN substrate, a first conductive semiconductor layer, a light emitting layer, and a second conductive semiconductor layer; forming a ridge stripe structure on the stacked structure; forming a first diffraction grating adjacent to the ridge stripe structure; as well as forming an insulating film inside the grooves of the first diffraction grating, The depth d of the grooves of the first diffraction grating is within the range of 54.9 nm ≤ d ≤ 200 nm, and the duty ratio duty is included in the inequality (1) using constants a, b, c, and n that define the order of the diffracted light, that is, within the range.
13. The manufacturing method according to claim 12, characterized in that: The method further includes forming a second diffraction grating in a region adjacent to the ridge stripe structure simultaneously with forming the first diffraction grating.
14. The manufacturing method according to claim 12 or 13, characterized in that: The insulating film is formed by an atomic layer deposition method, namely, an ALD method.