Nitride semiconductor laser

Abstract

The utility model discloses a nitride semiconductor laser, which comprises a heat dissipation heat sink and a laser structure, and is characterized in that the laser structure comprises a first type waveguide layer, a quantum well layer and a second type waveguide layer which are stacked in sequence; wherein the first type is a P type, and the second type is an N type; or, the first type is an N type, and the second type is a P type; the doping concentration of the P-type waveguide layer is gradually changed along the growth direction of the device; the nitride semiconductor laser is obtained by growing and stripping on the gallium surface of the gallium nitride substrate. The gallium-based solar cell is obtained by growing and stripping on a gallium surface, thereby being beneficial to heat scattering and improving the high-power output performance of the device; and meanwhile, in cooperation with gradient doping of the P-type waveguide layer, penetration dislocation can be reduced through staged lattice matching.

Description

A nitride semiconductor laser Technical Field

[0001] This utility model relates to the field of semiconductor laser technology, and in particular to a nitride semiconductor laser. Background Technology

[0002] Gallium nitride (GaN)-based lasers have broad application prospects in optical communication, solid-state lighting, and laser displays due to their advantages such as a wide emission wavelength range, high efficiency, and long lifetime. However, the fabrication of existing GaN-based lasers typically involves first growing an N-type region layer on a substrate, then growing a light-emitting quantum well layer, and finally growing a P-type region layer. This structure has the following drawbacks:

[0003] 1. Since the P-type region layer is located on top and the N-type region layer is located below, and the hole mobility is lower than the electron mobility (the hole mobility is only about 1 / 10 of the electron mobility), the hole transport path from the electrode to the light-emitting quantum well layer is longer, resulting in greater non-radiative recombination loss.

[0004] 2. The thicker N-type region at the bottom layer is prone to higher stress, which increases dislocation density and affects device performance.

[0005] 3. Poor quality of the P-type region layer affects laser performance, mainly in the following aspects: (a) Decreased carrier injection efficiency: The low hole concentration and poor mobility of the P-type region layer lead to asymmetry in carrier injection with the N-type region layer, reducing the electron-hole recombination efficiency of the quantum well layer; (b) Increased series resistance: Poor conductivity of the P-type region layer increases the series resistance of the device, resulting in higher operating voltage (requiring higher drive current) and exacerbating thermal effects; (c) Increased optical loss: Defects (such as dislocations) in the P-type region layer become light scattering centers, increasing internal absorption loss and reducing laser slope efficiency. Defects may also cause nonradiative recombination (such as Auger recombination), reducing internal quantum efficiency; (d) Reliability issues: High defect density may accelerate device degradation and shorten laser lifetime. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a nitride semiconductor laser. This nitride semiconductor laser is obtained by growing and peeling off gallium surfaces on a gallium nitride substrate, which facilitates heat scattering and improves the high-power output performance of the device. Furthermore, the gradient doping of the P-type waveguide layer (i.e., the doping concentration of the P-type waveguide layer gradually changes along the growth direction of the device) can gradually absorb the lattice mismatch between the substrate and the epitaxial layer during fabrication through staged lattice matching, thereby reducing through-dislocations.

[0007] To achieve the above-mentioned technical objectives and effects, this utility model is implemented through the following technical solution:

[0008] A nitride semiconductor laser includes: a heat sink and a laser structure stacked sequentially, wherein the laser structure includes a first type waveguide layer, a quantum well layer and a second type waveguide layer stacked sequentially, and the first type waveguide layer is disposed between the heat sink and the quantum well layer.

[0009] Among them, the first type is P-type (i.e., the first type waveguide layer is a P-type waveguide layer), and the second type is N-type (i.e., the second type waveguide layer is an N-type waveguide layer); or, the first type is N-type (i.e., the first type waveguide layer is an N-type waveguide layer), and the second type is P-type (i.e., the second type waveguide layer is a P-type waveguide layer);

[0010] The doping concentration of the P-type waveguide layer gradually changes along the device growth direction, which is from the P-type waveguide layer to the N-type waveguide layer; the nitride semiconductor laser is obtained by growing and peeling off the gallium surface of a gallium nitride substrate.

[0011] Furthermore, the formation time of the P-type waveguide layer is earlier than the formation time of the N-type waveguide layer.

[0012] In this invention, the P-type waveguide layer is formed earlier than the N-type waveguide layer, improving the crystal quality and doping effect of the P-type waveguide layer. Simultaneously, the P-type waveguide layer, located at the bottom of the nitride semiconductor laser, shortens the hole propagation path from the P-type electrode structure to the quantum well layer, reducing non-radiative recombination loss. Furthermore, the use of a gradient-doped P-type waveguide layer, combined with the technique of forming the P-type waveguide layer before the N-type waveguide layer, allows the P-type waveguide layer to serve as the substrate for the growth of the N-type waveguide layer. Through staged lattice matching, the lattice mismatch between the substrate and the epitaxial layer during fabrication can be gradually absorbed, reducing through-dislocations.

[0013] Furthermore, the doping concentration of the P-type waveguide layer gradually decreases from high to low along the growth direction of the device.

[0014] The P-type waveguide layer in this invention is a graded-doped P-type waveguide layer with the doping concentration decreasing from high to low along the growth direction. This creates a built-in electric field, accelerating hole injection into the quantum well layer, accelerating carrier migration into the quantum well layer, reducing Auger recombination, and improving optical confinement. Furthermore, the graded-doping P-type waveguide layer alters the refractive index distribution of the material, creating a refractive index gradient, which better confines the light field, allowing light to propagate more effectively in the quantum well layer and waveguide layer (including the P-type and N-type waveguide layers), reducing light scattering and loss. The graded refractive index distribution of the P-type waveguide layer, combined with the uniform refractive index of the N-type waveguide layer, can construct an asymmetric optical waveguide.

[0015] The formation time of the P-type waveguide layer is earlier than that of the N-type waveguide layer. Since the quantum well layer has not yet been formed when the P-type waveguide layer is formed, the formation temperature of the P-type waveguide layer can be controlled between 1000-1100℃. High temperature can improve the growth quality of the P-type waveguide layer and avoid the easy precipitation of In in the quantum well layer during high temperature growth, which affects the growth.

[0016] Furthermore, the thickness of the P-type waveguide layer is less than the thickness of the N-type waveguide layer.

[0017] Furthermore, the laser structure also includes a first type of electrode structure, which is disposed on the side of the first type of waveguide layer near the heat sink.

[0018] Furthermore, a first type of optical confinement layer is provided between the first type of electrode structure and the first type of waveguide layer; wherein, the first type of optical confinement layer includes a plurality of first superlattice structures stacked sequentially along the gallium surface.

[0019] Furthermore, the laser structure also includes a second type of electrode structure, which is disposed on the side of the second type waveguide layer away from the quantum well layer.

[0020] Furthermore, a second type of optical confinement layer and a second type of electrode contact layer are provided between the second type of waveguide layer and the second type of electrode structure; the second type of electrode contact layer is disposed between the second type of electrode structure and the second type of optical confinement layer; wherein, the second type of optical confinement layer includes a plurality of second superlattice structures stacked sequentially along the gallium surface, the thickness of the second type of optical confinement layer is 100-200nm, and the thickness of the second type of electrode contact layer is 100-200nm.

[0021] Furthermore, the laser structure also includes an insulating layer that covers the second type waveguide layer and the second type electrode contact layer, and the insulating layer has an opening that exposes a portion of the second type electrode contact layer, on the surface of the exposed second type electrode contact layer, where a second type contact electrode is formed.

[0022] Furthermore, the second type waveguide layer includes a second type sub-waveguide structure one and a second type sub-waveguide structure two stacked together. The projection of the second type sub-waveguide structure one onto the first type electrode structure covers the projection of the second type sub-waveguide structure two onto the first type electrode structure. The second type sub-waveguide structure two is disposed on the side of the second type sub-waveguide structure one away from the quantum well layer.

[0023] Furthermore, the nitride semiconductor laser also includes a Bragg reflector layer disposed between the heat sink and the first type of electrode structure.

[0024] The beneficial effects of this utility model are:

[0025] 1. The nitride semiconductor laser of this invention is prepared by epitaxial growth and lift-off on the Ga surface of a GaN substrate. The high thermal conductivity of the Ga surface is used to enhance heat conduction, thereby improving the high power output performance of the device.

[0026] 2. The P-type waveguide layer is a high-quality, gradient-doped waveguide layer, effectively solving the laser performance problems caused by the poor quality of the P-type region layer in existing technologies. Specifically, it improves carrier injection efficiency. The built-in electric field formed by gradient doping accelerates hole injection into the quantum well layer, improves carrier injection symmetry, and solves the problem of low electron-hole recombination efficiency in the quantum well layer caused by the low hole concentration and poor mobility of the P-type region layer in existing technologies. Secondly, it reduces series resistance. The high-quality P-type waveguide layer improves the conductivity of the P-type region, reduces the device series resistance, and lowers the series resistance. The operating voltage and driving current requirements alleviate the problem of increased thermal effects caused by poor conductivity of the P-type region layer; thirdly, optical losses are reduced. Gradient doping optimizes the refractive index distribution, forms an asymmetric optical waveguide structure, enhances optical field confinement, reduces light scattering and absorption losses, improves slope efficiency, and at the same time reduces defects such as dislocations, reduces the occurrence of nonradiative recombination, and significantly improves internal quantum efficiency; fourthly, reliability is improved. By reducing defect density, the degradation process of the device is slowed down, the lifespan of the nitride semiconductor laser is extended, and the device reliability problem caused by high defect density is solved. Attached Figure Description

[0027] Figure 1 is a schematic flowchart of the fabrication method of the nitride semiconductor laser according to Scheme 1.

[0028] Figure 2 is a schematic diagram of the structure formed by steps S1 to S4 of the fabrication method of the nitride semiconductor laser in Scheme 1.

[0029] Figure 3 is a schematic diagram of the structure formed by steps S5 to S6 of the fabrication method of the nitride semiconductor laser in Scheme 1.

[0030] Figure 4 is a schematic diagram of the structure formed by step S7 of the fabrication method of the nitride semiconductor laser in Scheme 1.

[0031] Figures 5 to 7 are schematic diagrams of the structure formed by step S8 of the fabrication method of the nitride semiconductor laser in Scheme 1.

[0032] Figure 8 is a schematic diagram of the structure of a nitride semiconductor laser.

[0033] Figure 9 is a schematic flowchart of the fabrication method of the nitride semiconductor laser according to Scheme 2.

[0034] Figure 10 is a schematic diagram of the structure formed by steps S1′ to S5′ in the fabrication method of the nitride semiconductor laser of Scheme 2.

[0035] Figure 11 is a schematic diagram of the structure formed by step S6′ in the fabrication method of the nitride semiconductor laser of Scheme 2.

[0036] Figures 12 and 13 are schematic diagrams of the structure formed by steps S7′ to S8′ in the fabrication method of the nitride semiconductor laser of Scheme 2; wherein, Figure 13 is another schematic diagram of the structure of the nitride semiconductor laser.

[0037] In the figure, 1: heat sink, 2: Bragg reflector layer, 3: P-type electrode structure, 4: P-type optical confinement layer, 5: P-type waveguide layer, 51: P-type sub-waveguide structure one, 52: P-type sub-waveguide structure two, 6: quantum well layer, 7: N-type waveguide layer, 71: N-type sub-waveguide structure one, 72: N-type sub-waveguide structure two, 8: N-type optical confinement layer, 9: N-type electrode contact layer, 10: insulating layer, 11: N-type electrode structure, 12: gallium nitride substrate, 13: buffer layer, 14: support substrate; 15: P-type electrode contact layer. Detailed Implementation

[0038] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the scope of protection of the present invention.

[0039] The nitride semiconductor laser of this invention is prepared by two different methods.

[0040] Option 1 (hereinafter, P-type refers to type 1, and N-type to type 2):

[0041] Please refer to Figures 1 to 8. Figure 1 is a schematic flowchart of the fabrication method of the nitride semiconductor laser according to Scheme 1, which specifically includes the following steps:

[0042] Step S1: As shown in Figure 2, a gallium nitride substrate 12 is provided, and a buffer layer 13 and a P-type light confinement layer 4 are grown on the gallium nitride substrate 12.

[0043] In this invention, the gallium surface of the gallium nitride substrate 12 is used as the growth surface for epitaxial growth. Before growth, the gallium nitride substrate 12 can be subjected to certain treatments, including cleaning, surface polishing and surface activation.

[0044] Further, the cleaning steps include: 1) Organic solvent cleaning: Ultrasonic cleaning of the gallium nitride substrate using organic solvents such as acetone or ethanol to remove oil stains, organic residues, and other impurities from the surface of the gallium nitride substrate; 2) Acid cleaning: Immersion cleaning of the gallium nitride substrate using acid solutions such as dilute hydrochloric acid or dilute sulfuric acid to remove metallic impurities and oxide layers from the surface of the gallium nitride substrate; 3) Deionized water cleaning: Removal of residual acid and other impurities from the cleaning process to ensure that the surface of the gallium nitride substrate is clean and free of contamination. The surface polishing step includes: Polishing the gallium surface using mechanical polishing or chemical mechanical polishing methods to obtain an atomically flat surface. A flat surface is beneficial for the uniform growth of the epitaxial layer, reduces the influence of surface roughness on the growth process, and improves the interface quality between the epitaxial layer and the substrate. The surface activation steps include: activating the gallium surface using plasma treatment and thermal annealing. Plasma treatment can generate some active sites on the surface of the gallium nitride substrate, which is beneficial to the adsorption and growth of epitaxial material atoms. Thermal annealing can eliminate some surface stress and enable surface atoms to obtain higher energy, which facilitates migration and alignment during the growth process, thereby promoting epitaxial growth.

[0045] Using the gallium surface of a gallium nitride substrate as the epitaxial growth surface has the following advantages:

[0046] (1) Good crystal quality: The atomic arrangement of gallium surface is relatively regular. Epitaxial growth on this surface can make the lattice matching between the epitaxial layer and the gallium nitride substrate better, which helps to grow a high-quality crystal structure, reduce defects and dislocations, and thus improve the quality of the upper epitaxial layer structure.

[0047] (2) Uniform growth rate: The chemical properties of gallium surface are relatively stable, and the atomic adsorption and deposition of epitaxial material during the growth process have good uniformity, which is conducive to achieving uniform epitaxial growth and obtaining epitaxial layers with uniform thickness and consistent performance.

[0048] (3) The treated gallium surface has excellent characteristics: After surface activation treatment, a good interface can be formed between the gallium surface and the epitaxial layer. After surface activation treatment, stress can be eliminated and surface active sites can be increased, which is conducive to the transmission of electrons at the interface, facilitates heat conduction, improves thermal conductivity, reduces interface thermal resistance and other adverse factors, which is beneficial to the performance improvement of the device.

[0049] In one embodiment, a buffer layer 13 is first formed on the gallium surface of the gallium nitride substrate 12. The buffer layer 13 is an undoped gallium nitride layer with a thickness of 20-80 nm. By setting the buffer layer 13, the properties of the surface of the gallium nitride substrate 12 can be further improved, such as adjusting the lattice constant of the surface and reducing the surface stress, thus providing a better foundation for subsequent high-quality epitaxial growth.

[0050] Then, a P-type optical confinement layer 4 is formed on the buffer layer 13. The P-type optical confinement layer 4 includes multiple periods of a first superlattice structure, and the first superlattice structure is a GaN / Al , 17 , 19 , -3 , 17 , -3 , -3 , ,

[0053] ,

[0054] Ga 1-x N superlattice structure (0 < x < 1), and the number of periods is 50 - 400, for example: 50, 100, 150, 200, 250, 300, 350 or 400.

[0051] Step S2: As shown in Figure 2, a P-type waveguide layer 5 with a gradually changing doping concentration is formed on the P-type optical confinement layer 4.

[0052] The doping concentration of the P-type waveguide layer 5 gradually changes from high to low along the epitaxial growth direction. In one embodiment, the doping concentration of the P-type waveguide layer can be gradually reduced by increasing the growth temperature, thereby achieving the growth of a P-type waveguide layer with a doping concentration gradually decreasing from high to low. Specifically, the temperature of the reaction chamber is increased from a first preset temperature gradient to a second preset temperature, and a doping source is introduced into the reaction chamber to grow a P-type waveguide layer on the gallium nitride substrate with a doping concentration gradually changing from 1×10 19 cm -3 to 5×10 17 cm -3 ; wherein, the first preset temperature and the second preset temperature are controlled at 1000 - 1100°C, and the absolute value of the difference between the first preset temperature and the second preset temperature and the growth time of the P-type waveguide layer is 0.5°C. Specifically, the first preset temperature and the second preset temperature can be 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C.

[0053] During the growth process, increasing the temperature will increase the diffusion coefficient of the dopant, making the distribution of the dopant at the growth front more uniform and reducing the doping concentration at that place. As the temperature increases, the diffusion of the dopant is enhanced to a certain extent, forming a gradually changing doping distribution. In another embodiment, the growth of the P-type waveguide layer 5 can also achieve a gradual change in doping concentration by controlling the doping flow rate. Specifically, under the condition that the temperature is 1000 - 1100°C, the flow rate of the doping source introduced into the reaction chamber is reduced from a first preset flow rate to a second preset flow rate to grow a P-type waveguide layer 5 with a doping concentration gradually changing from 1×10 19 cm -3 to 5×10 17 cm -3 on the gallium nitride substrate 12. Reducing the flow rate of the P-type dopant reduces the number of dopants entering the growth region per unit time. As the growth progresses, the concentration of the dopant in the growth direction can be gradually reduced, forming a distribution from high to low.

[0054] The first preset flow rate can be 40-80 sccm, for example, 40 sccm, 45 sccm, 50 sccm, 55 sccm, 60 sccm, 65 sccm, 70 sccm, 75 sccm or 80 sccm; the second preset flow rate can be 10-30 sccm, for example: 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm, 20 sccm, 22 sccm, 24 sccm, 26 sccm, 28 sccm or 30 sccm.

[0055] P-type dopants are typically magnesium-containing organic compounds, such as dicyclopentadienylmagnesium (Cp₂Mg). During growth, the flow rate of Cp₂Mg is gradually reduced, causing a gradual decrease in the dopant concentration in the gas phase, thus achieving a gradual change in dopant concentration along the growth direction. For example, at the beginning of growth, the flow rate of Cp₂Mg is set to 50 sccm. As the growth time progresses, the flow rate is reduced linearly or non-linearly at a certain rate, reaching approximately 10 sccm at the end of growth, controlling the Mg doping concentration of the P-type waveguide layer 5 from 1 × 10⁻⁶ Mg⁺. 19 cm -3 Gradient to 5×10 17 cm -3 .

[0056] As the doping concentration gradually decreases, excessive carrier aggregation in high-doped regions is avoided, allowing injected carriers to be distributed more uniformly near the quantum well layer. This improves carrier injection efficiency and increases the recombination efficiency of the quantum well layer. High doping concentration leads to an increased Auger recombination probability, while gradually decreasing the doping concentration effectively reduces this non-radiative recombination process, improving the internal quantum efficiency of the device and reducing energy loss. Gradual doping concentration can change the refractive index distribution of the material, forming a certain refractive index gradient, which better confines the optical field, allowing light to propagate more effectively in the quantum well layer and waveguide layer, reducing light scattering and loss.

[0057] When forming the P-type waveguide layer 5, the formation temperature can be controlled between 1000-1100℃. However, in existing technologies where the P-type waveguide layer is formed above, the growth temperature can only be controlled at around 950℃. This is because in existing technologies, the P-type waveguide layer is formed after the quantum well layer. Since the quantum well layer is typically formed using InGaN / AlGaN, which contains In, In precipitation occurs during high-temperature growth. Therefore, the formation temperature of the P-type waveguide layer is limited to around 950℃. In this invention, the quantum well layer is not formed before the P-type waveguide layer 5 is formed. Therefore, the formation temperature of the P-type waveguide layer 5 can be controlled at a higher temperature. Higher temperatures improve the growth quality of the layer structure, and there is no need to worry about In precipitation from the quantum well layer affecting the growth during high-temperature growth.

[0058] Moreover, the technical solution of adopting the gradient-doped P-type waveguide layer 5 and forming the P-type waveguide layer 5 prior to the N-type waveguide layer 7 has a synergistic effect, enabling the P-type waveguide layer 5 to serve as the substrate for the growth of the buffer layer 13 and the subsequent N-type waveguide layer 7. Through staged lattice matching, the lattice mismatch between the gallium nitride substrate and the epitaxial layer can be gradually absorbed, reducing threading dislocations.

[0059] Step S3: As shown in Figure 2, a quantum well layer 6 is formed on the P-type waveguide layer 5.

[0060] The quantum well layer 6 is a 1-10 period In y Ga 1-y N / GaN quantum well structure, where 0 < y < 1. Among them, the thickness of the In y Ga 1-y N layer is between 1-5 nm, and the thickness of the GaN layer is between 3-20 nm. For example, the thickness of the In y Ga 1-y N layer is 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm or 5 nm, and the thickness of the GaN layer is 3 nm, 5 nm, 7 nm, 9 nm, 11 nm, 13 nm, 15 nm, 17 nm, 18 nm, 19 nm or 20 nm.

[0061] Step S4: As shown in Figure 2, an N-type waveguide layer 7 is formed on the quantum well layer 6.

[0062] After forming the quantum well layer 6, an N-type waveguide layer 7 is deposited on the surface of the quantum well layer 6. The thickness of the N-type waveguide layer 7 is 2-5 μm, for example: 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm. Specifically, an N-type gallium nitride layer is used as the material of the N-type waveguide layer 7, and SiH4 is used as the N-type doping source. The doping concentration range of Si is 10 18 cm -3 -10 19 cm -3 , for example: 10 18 cm -3 、2×10 18 cm -3 、3×10 18 cm -3 、4×10 18 cm -3 、5×10 18 cm -3 、6×10 18 cm -3 、7×10 18 cm -3 、8×1018 cm -3 9×10 18 cm -3 Or 10 19 cm -3 .

[0063] Step S5: As shown in Figure 3, the N-type waveguide layer 7 is etched to form a ridge waveguide structure.

[0064] After forming the N-type waveguide layer 7, the N-type waveguide layer 7 is etched to form a ridge waveguide structure. The etching method employs photolithography and etching processes; that is, a photoresist layer is formed on the formed N-type waveguide layer 7, followed by exposure and development, and then etching to form a ridge waveguide structure with protrusions. Specifically, the height of the ridge waveguide structure is 2-3 μm, for example: 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, or 3 μm.

[0065] Furthermore, the ridge waveguide structure is an N-type ridge waveguide structure, which includes an N-type sub-waveguide structure 71 and an N-type sub-waveguide structure 72 stacked along the gallium surface of the gallium nitride substrate. The projection of the N-type sub-waveguide structure 71 on the gallium nitride substrate 12 covers the projection of the N-type sub-waveguide structure 72 on the gallium nitride substrate 12.

[0066] Step S6: As shown in Figure 3, an N-type optical confinement layer 8 and an N-type electrode contact layer 9 are formed on the ridge waveguide structure.

[0067] After the ridge waveguide structure is formed, an N-type optical confinement layer 8 and an N-type electrode contact layer 9 are deposited on the surface of the ridge waveguide structure.

[0068] Furthermore, the N-type optical confinement layer 8 employs a second superlattice structure with multiple periods (e.g., 50-200 periods). The second superlattice structure is an n-type GaN / AlGaN superlattice structure with an electron concentration of 10. 17 -10 19 cm -3 Between, for example: 10 17 cm -3 2×10 17 cm -3 4×10 17 cm -3 6×10 17 cm -3 8×10 17 cm -3 10 18 cm -3 2×10 18 cm -34×10 18 cm -3 6×10 18 cm -3 8×10 18 cm -3 Or 10 19 cm -3 The thickness of the N-type light confinement layer 8 is 100-200nm, for example: 100nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm.

[0069] The N-type electrode contact layer 9 is n-type gallium nitride, specifically an n-type GaN layer grown using SiH4 as the n-type dopant source. The thickness of the N-type electrode contact layer 9 is 100-200 nm (e.g., 100 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm), and the Si doping concentration is 10. 19 cm -3 .

[0070] Step S7: As shown in Figure 4, an insulating layer 10 is formed on the N-type electrode contact layer 9 and the N-type waveguide layer 7, and a portion of the N-type electrode contact layer 9 is exposed by etching, and an N-type electrode structure 11 is formed on the exposed N-type electrode contact layer 9.

[0071] An insulating layer 10 is formed on the N-type electrode contact layer 9 and the N-type waveguide layer 7. The thickness of the insulating layer 10 is 20-50 nm. The material of the insulating layer 10 is silicon oxide or silicon nitride, and it is deposited by CVD or PVD. After the insulating layer 10 is deposited, a patterned photoresist layer formed by a mask or photolithography process is used as a mask to etch the insulating layer 10. After etching, a patterned insulating layer 10 is formed, exposing part of the N-type electrode contact layer 9, while retaining the insulating layer 10 on the N-type waveguide layer 7.

[0072] An N-type electrode structure 11 is formed on the exposed N-type electrode contact layer 9. The material of the N-type electrode structure 11 is preferably Ti, Au, Ag, or an alloy thereof.

[0073] Step S8: As shown in Figures 5 to 7, remove the gallium nitride substrate 12 and buffer layer 13, then form a P-type electrode structure 3 and a Bragg reflector layer 2 on the P-type light confinement layer 4, and bond a heat sink 1.

[0074] As shown in Figure 5, before peeling the gallium nitride substrate 12 and the buffer layer 13, the outer side opposite to the gallium nitride substrate 12 is adhered to the support substrate 14. That is, the support substrate 14 can be directly adhered or bonded to the side of the N-type electrode structure 11 away from the gallium nitride substrate 12; or, in order to protect the N-type electrode structure 11, a protective layer is first formed, and the protective layer is bonded to the support substrate 14. After bonding, the gallium nitride substrate 12 and the buffer layer 13 are peeled off.

[0075] As shown in Figure 6, after removing the buffer layer 13, a P-type electrode structure 3 is formed on the surface of the P-type light confinement layer 4. The thickness of the P-type electrode structure 3 is between 50-100 nm, for example: 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm or 100 nm. The material of the P-type electrode structure 3 can be Ti, Au, Ag or their alloys, or transparent metal oxide ITO, etc.

[0076] Then, as shown in Figure 6, a Bragg reflector layer 2 is formed on the P-type electrode structure 3. The Bragg reflector layer 2 is made of alternating SiO2 and TiO2 materials. SiO2 has a low refractive index, approximately 1.4-1.5 in the visible and near-infrared bands; TiO2 has a high refractive index, typically around 2.2-2.5. By alternately depositing SiO2 and TiO2 films of different thicknesses, a high-reflectivity Bragg reflector layer 2 can be formed. The thickness of both SiO2 and TiO2 is one-quarter of the wavelength.

[0077] The Bragg reflector layer 2 is a non-conductive layer structure that can provide insulation protection for the P-type electrode structure 3.

[0078] Understandably, Bragg reflector layer 2 is not a necessary setting and can be selectively set according to specific application requirements.

[0079] Then, as shown in Figure 7, the heat sink 1 is bonded to the Bragg reflector layer 2 to facilitate heat conduction of the laser.

[0080] Finally, as shown in Figure 8, after forming the heat sink 1, the support substrate 14 is removed to form a gallium nitride semiconductor laser with gallium surface growth having the heat sink 1.

[0081] The gallium nitride substrate 12 and the buffer layer 13 can be removed by laser lift-off or wet lift-off. Lifting the gallium nitride substrate can reduce the thickness of the device and make the gallium nitride substrate usable. On the other hand, it can bond the heat sink and facilitate the heat transfer of the laser.

[0082] Please refer to Figure 8, which shows a schematic diagram of the structure of a nitride semiconductor laser. The nitride semiconductor laser is obtained by growing and peeling off the gallium surface of a gallium nitride substrate. The nitride semiconductor laser includes: a heat sink 1, a Bragg reflector layer 2 and a laser structure stacked in sequence.

[0083] The Bragg reflector layer 2 comprises multiple reflective structures stacked on the heat sink 1. Each reflective structure includes a first reflective layer and a second reflective layer. The first reflective layer is made of SiO2, and the second reflective layer is made of TiO2. By placing the Bragg reflector layer 2 between the heat sink 1 and the laser structure, the light reflectivity can be improved.

[0084] The laser structure includes, in sequence, a P-type electrode structure 3, a P-type light confinement layer 4, a P-type waveguide layer 5, a quantum well layer 6, an N-type waveguide layer 7, an N-type light confinement layer 8, an N-type electrode contact layer 9, an insulating layer 10, and an N-type electrode structure 11.

[0085] The P-type electrode structure 3 is disposed on the side of the Bragg reflector layer 2 away from the heat sink 1. The thickness of the P-type electrode structure 3 is 75 nm, and the material of the P-type electrode structure 3 is Ag.

[0086] The P-type light confinement layer 4 includes 80 GaN / Al atoms stacked sequentially along the gallium surface. x Ga 1-x N superlattice structure, x = 0.5.

[0087] The doping concentration of the P-type waveguide layer 5 gradually decreases from high to low along the device growth direction, which is from the P-type electrode structure 3 to the N-type electrode structure 11. The thickness of the P-type waveguide layer 5 is less than the thickness of the N-type waveguide layer 7.

[0088] Quantum well layer 6 is a 5-period In y Ga 1-y N / GaN quantum well structure, y = 0.5; In y Ga 1-y The thickness of the N layer is 2nm, and the thickness of the GaN layer is 5nm.

[0089] The N-type waveguide layer 7 includes an N-type sub-waveguide structure 71 and an N-type sub-waveguide structure 72 stacked along the gallium surface of the gallium nitride substrate. The projection of the N-type sub-waveguide structure 71 onto the P-type electrode structure 3 overlaps the projection of the N-type sub-waveguide structure 72 onto the P-type electrode structure 3. In this embodiment, the thickness of the N-type waveguide layer 7 (i.e., the sum of the thicknesses of the N-type sub-waveguide structure 71 and the N-type sub-waveguide structure 72) is 2 μm, and the Si doping concentration of the N-type waveguide layer 7 is 5 × 10⁻⁶. 18 cm -3 .

[0090] The N-type light confinement layer 8 comprises 100 GaN / AlGaN superlattices stacked sequentially along the gallium surface; the thickness of the N-type light confinement layer 8 is 150 nm.

[0091] The thickness of the N-type electrode contact layer 9 is 150 nm.

[0092] The insulating layer 10 covers the surface of the N-type waveguide layer 7 not covered by the N-type light confinement layer 8, the side surface of the N-type electrode contact layer 9, and a portion of the upper surface of the N-type electrode contact layer 9; and the insulating layer 10 has an opening that exposes a portion of the N-type electrode contact layer 9.

[0093] The N-type electrode structure 11 is disposed within an opening exposing the upper surface of the N-type electrode contact layer 9, and covers a portion of the upper surface of the insulating layer 10 (i.e., the upper surface covering a portion of the N-type electrode contact layer 9). In this embodiment, the thickness of the insulating layer 10 is 25 nm.

[0094] The fabrication method of the nitride semiconductor laser in Example 1 specifically includes the following steps:

[0095] Step S1: As shown in Figure 2, a gallium nitride substrate 12 is provided, and a buffer layer 13 and a P-type light confinement layer 4 are grown on the gallium surface of the gallium nitride substrate 12.

[0096] First, a buffer layer 13 is formed on the gallium surface of the gallium nitride substrate 12. The buffer layer 13 is an undoped gallium nitride layer with a thickness of 50 nm. Then, a p-type light confinement layer 4 is formed on the buffer layer 13. The p-type light confinement layer 4 includes 80 GaN / Al atoms sequentially stacked along the gallium surface. x Ga 1-x N superlattice structure, x = 0.5.

[0097] Step S2: As shown in Figure 2, a P-type waveguide layer 5 with gradually varying doping concentration is formed on the P-type optical confinement layer 4.

[0098] The doping concentration of the P-type waveguide layer 5 gradually decreases from high to low along the epitaxial growth direction. In this embodiment, the gradual change in doping concentration is achieved by controlling the doping flow rate. The dopant is dicyclopentadienyl magnesium. Specifically, at a temperature of 1050°C, the flow rate of Cp2Mg is gradually reduced from 50 sccm to 10 sccm to control the Mg doping concentration of the P-type waveguide layer 5 from 1×10⁻⁶ Mg. 19 cm -3 Gradient to 5×10 17 cm -3 .

[0099] Step S3: As shown in Figure 2, a quantum well layer 6 is formed on the P-type waveguide layer 5.

[0100] Quantum well layer 6 is a 5-period In y Ga 1-y N / GaN quantum well structure, y = 0.5; In y Ga 1-y The thickness of the N layer is 2nm, and the thickness of the GaN layer is 5nm.

[0101] Step S4: As shown in Figure 2, an N-type waveguide layer 7 is formed on the quantum well layer 6.

[0102] After forming the quantum well layer 6, an N-type waveguide layer 7 is deposited on the surface of the quantum well layer 6. The thickness of the N-type waveguide layer 7 is 2 μm. Specifically, an N-type gallium nitride layer is used as the material of the N-type waveguide layer 7, and SiH4 is used as the N-type doping source with a Si doping concentration of 5 × 10⁻⁶. 18 cm -3 .

[0103] Step S5: As shown in Figure 3, the N-type waveguide layer 7 is etched to form a ridge waveguide structure.

[0104] After forming the N-type waveguide layer 7, the N-type waveguide layer 7 is etched to form a ridge waveguide structure. The etching method adopts photolithography and etching processes, that is, a photoresist layer is formed on the formed N-type waveguide layer 7, and then after exposure and development, etching is performed to form a ridge waveguide structure with protrusions.

[0105] The ridge waveguide structure includes an N-type sub-waveguide structure 71 and an N-type sub-waveguide structure 72 stacked along the gallium surface of the gallium nitride substrate. The projection of the N-type sub-waveguide structure 71 onto the gallium nitride substrate 12 covers the projection of the N-type sub-waveguide structure 72 onto the gallium nitride substrate 12.

[0106] Step S6: As shown in Figure 3, an N-type optical confinement layer 8 and an N-type electrode contact layer 9 are formed on the ridge waveguide structure.

[0107] After the ridge waveguide structure is formed, an N-type optical confinement layer 8 and an N-type electrode contact layer 9 are deposited on the surface of the ridge waveguide structure.

[0108] The N-type light confinement layer 8 comprises 100 GaN / AlGaN superlattices stacked sequentially along the gallium surface; the thickness of the N-type light confinement layer 8 is 150 nm.

[0109] The N-type electrode contact layer 9 is n-type gallium nitride. An n-type GaN layer is grown using SiH4 as the n-type dopant source. The thickness of the N-type electrode contact layer 9 is 150 nm, and the Si doping concentration is 10⁻⁶. 19 cm -3 .

[0110] Step S7: As shown in Figure 4, an insulating layer 10 is formed on the N-type electrode contact layer 9 and the N-type waveguide layer 7, and a portion of the N-type electrode contact layer 9 is exposed by etching, and an N-type electrode structure 11 is formed on the exposed N-type electrode contact layer 9.

[0111] An insulating layer 10 with a thickness of 25 nm is formed on the N-type electrode contact layer 9 and the N-type waveguide layer 7 using CVD. The insulating layer 10 is made of silicon oxide. After depositing the insulating layer 10, a patterned photoresist layer formed by a mask is used as a mask to etch the insulating layer 10. After etching, a patterned insulating layer 10 is formed, exposing part of the N-type electrode contact layer 9 and retaining the insulating layer 10 on the N-type waveguide layer 7.

[0112] An N-type electrode structure 11 is formed on the exposed N-type electrode contact layer 9. The material of the N-type electrode structure 11 is Ag.

[0113] Step S8: As shown in Figures 5 to 7, remove the gallium nitride substrate 12 and buffer layer 13, then form a P-type electrode structure 3 and a Bragg reflector layer 2 on the P-type light confinement layer 4, and bond a heat sink 1.

[0114] As shown in Figure 5, the support substrate 14 is directly adhered to the side of the N-type electrode structure 11 away from the gallium nitride substrate 12, and then the gallium nitride substrate 12 and the buffer layer 13 are peeled off by laser lift-off.

[0115] As shown in Figure 6, after removing the buffer layer 13, a P-type electrode structure 3 is formed on the surface of the P-type light confinement layer 4. The thickness of the P-type electrode structure 3 is 75 nm, and the material of the P-type electrode structure 3 is Ag.

[0116] Then, as shown in Figure 6, a Bragg reflector layer 2 is formed on the P-type electrode structure 3. The material of the Bragg reflector layer 2 is SiO2 / TiO2 alternating.

[0117] Then, as shown in Figure 7, the heat sink 1 is bonded to the Bragg reflector layer 2 to facilitate heat conduction of the laser.

[0118] Finally, as shown in Figure 8, after forming the heat sink 1, the support substrate 14 is removed to form a gallium nitride semiconductor laser with gallium surface growth having the heat sink 1.

[0119] Option 2 (hereinafter, N-type refers to type 1, and P-type refers to type 2):

[0120] Please refer to Figures 9 to 13. Figure 9 is a schematic flowchart of the fabrication method of the nitride semiconductor laser according to Scheme 2, which specifically includes the following steps:

[0121] Step S1': As shown in FIG. 10, provide a gallium nitride substrate 12, and grow a buffer layer 13 and a P-type optical confinement layer 4 on the gallium nitride substrate 12.

[0122] In the present utility model, the gallium surface of the gallium nitride substrate 12 is used as the growth surface for epitaxial growth. Before growth, the gallium nitride substrate 12 can be subjected to certain treatments, and the treatment steps include: cleaning, surface polishing, and surface activation. The specific treatment steps are the same as those in Scheme 1 and will not be elaborated here.

[0123] In an embodiment, first, a buffer layer 13 is formed on the gallium surface of the gallium nitride substrate 12. The buffer layer 13 is an undoped gallium nitride layer, and the thickness of the buffer layer 13 is 20 - 80 nm. By providing the buffer layer 13, the properties of the surface of the gallium nitride substrate 12 can be further improved, such as adjusting the surface lattice constant, reducing surface stress, etc., providing a better basis for subsequent high-quality epitaxial growth.

[0124] Then, a P-type optical confinement layer 4 is formed on the buffer layer 13. The P-type optical confinement layer 4 includes multiple periods of a first superlattice structure, and the first superlattice structure is a GaN / Al x Ga 1-x N superlattice structure (0 < x < 1), and the number of periods is 50 - 400, for example: 50, 100, 150, 200, 250, 300, 350, or 400.

[0125] Step S2': As shown in FIG. 10, form a P-type waveguide layer 5 with a gradually changing doping concentration on the P-type optical confinement layer 4.

[0126] The doping concentration of the P-type waveguide layer 5 gradually changes from high to low along the direction of epitaxial growth. In an embodiment, the amount of P-type dopant incorporated can be reduced by increasing the growth temperature, so as to achieve the growth of a P-type waveguide layer 5 with a doping concentration gradually changing from high to low. Specifically, the temperature of the reaction chamber is increased from a first preset temperature gradient to a second preset temperature, and a doping source is introduced into the reaction chamber to grow a P-type waveguide layer 5 with a doping concentration gradually changing from 1×10 19 cm -3 to 5×10 17 cm -3 on the gallium nitride substrate 12; wherein, the first preset temperature and the second preset temperature are controlled at 1000 - 1100 °C, and the absolute value of the difference between the first preset temperature and the second preset temperature and the growth time of the P-type waveguide layer 5 has a ratio of 0.5 °C. Specifically, the first preset temperature and the second preset temperature can be 1000 °C, 1010 °C, 1020 °C, 1030 °C, 1040 °C, 1050 °C, 1060 °C, 1070 °C, 1080 °C, 1090 °C, or 1100 °C.

[0127] During the growth process, increasing the temperature will increase the diffusion coefficient of the dopant, making the distribution of the dopant more uniform at the growth front, reducing the doping concentration there. As the temperature increases, the diffusion of the dopant is enhanced to a certain extent, forming a graded doping distribution. In another embodiment, the growth of the P-type waveguide layer 5 can also achieve a graded doping concentration by controlling the doping flow rate. Specifically: under the condition that the temperature is 1000 - 1100 °C, the flow rate of the doping source introduced into the reaction chamber is reduced from the first preset flow rate to the second preset flow rate, so as to grow a P-type waveguide layer 5 with a doping concentration gradually changing from 1×10 19 cm -3 gradually to 5×10 17 cm -3 . Reducing the P-type dopant flow rate reduces the number of dopants entering the growth region per unit time. As the growth progresses, the concentration of the dopant in the growth direction can be gradually reduced, forming a distribution from high to low.

[0128] The first preset flow rate can be 40 - 80 sccm. For example, 40 sccm, 45 sccm, 50 sccm, 55 sccm, 60 sccm, 65 sccm, 70 sccm, 75 sccm or 80 sccm; the second preset flow rate can be 10 - 30 sccm. For example: 10 sccm, 12 sccm, 14 sccm, 16 sccm, 18 sccm, 20 sccm, 22 sccm, 24 sccm, 26 sccm, 28 sccm or 30 sccm.

[0129] The P-type dopant is usually a magnesium-containing organic compound, such as bis(cyclopentadienyl)magnesium. During the growth process, gradually reducing the flow rate of Cp2Mg makes the concentration of the dopant in the gas phase gradually decrease, thereby achieving a graded change in the doping concentration along the growth direction. For example, at the beginning of the growth, the flow rate of Cp2Mg is set to 50 sccm. As the growth time progresses, the flow rate is linearly or non-linearly reduced at a certain rate and is reduced to about 10 sccm at the end of the growth, controlling the Mg doping concentration of the P-type waveguide layer 5 to gradually change from 1×10 19 cm -3 gradually to 5×10 17 cm -3 .

[0130] Step S3': As shown in FIG. 10, a quantum well layer 6 is formed on the P-type waveguide layer 5.

[0131] The quantum well layer 6 is a 1 - 10 period In y Ga 1-y N / GaN quantum well structure, 0 < y < 1, where In y Ga 1-yThe thickness of the N-layer is between 1-5 nm, and the thickness of the GaN layer is between 3-20 nm. For example, In... y Ga 1-y The thickness of the N layer is 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm or 5nm, and the thickness of the GaN layer is 3nm, 5nm, 7nm, 9nm, 11nm, 13nm, 15nm, 17nm, 18nm, 19nm or 20nm.

[0132] Step S4′: As shown in Figure 10, an N-type waveguide layer 7 is formed on the quantum well layer 6.

[0133] After forming the quantum well layer 6, an N-type waveguide layer 7 is deposited on the surface of the quantum well layer 6. The thickness of the N-type waveguide layer 7 is 2-5 μm, for example: 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. Specifically, an N-type gallium nitride layer is used as the material of the N-type waveguide layer 7, and SiH4 is used as the N-type doping source, with a Si doping concentration ranging from 10⁻⁶. 18 cm -3 -10 19 cm -3 For example: 10 18 cm -3 2×10 18 cm -3 3×10 18 cm -3 4×10 18 cm -3 5×10 18 cm -3 6×10 18 cm -3 7×10 18 cm -3 8×10 18 cm -3 9×10 18 cm -3 Or 10 19 cm -3 .

[0134] Step S5′: As shown in Figure 10, an N-type optical confinement layer 8 is formed on the N-type waveguide layer 7, and an N-type electrode structure 11 is formed on the N-type optical confinement layer 8.

[0135] First, an N-type optical confinement layer 8 is formed on the side of the N-type waveguide layer 7 away from the quantum well layer 6; then, an N-type electrode structure 11 is formed on the side of the N-type optical confinement layer 8 away from the N-type waveguide layer 7.

[0136] Furthermore, the N-type optical confinement layer 8 employs a second superlattice structure with multiple periods (e.g., 50-200 periods). The second superlattice structure is an n-type GaN / AlGaN superlattice structure with an electron concentration of 10. 17 -10 19 cm -3 Between, for example: 10 17 cm -3 2×10 17 cm -3 4×10 17 cm -3 6×10 17 cm -3 8×10 17 cm -3 10 18 cm -3 2×10 18 cm -3 4×10 18 cm -3 6×10 18 cm -3 8×10 18 cm -3 Or 10 19 cm -3 The thickness of the N-type light confinement layer 8 is 100-200nm, for example: 100nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm.

[0137] Step S6′: As shown in Figure 11, a Bragg reflector layer 2 is formed on the N-type electrode structure 11, and a heat sink 1 is bonded to the Bragg reflector layer 2.

[0138] First, a Bragg reflector layer 2 is formed on the N-type electrode structure 11. The Bragg reflector layer 2 is made of alternating SiO2 and TiO2 materials. SiO2 has a low refractive index, approximately 1.4-1.5 in the visible and near-infrared bands; TiO2 has a high refractive index, typically around 2.2-2.5. By alternately depositing SiO2 and TiO2 thin films of different thicknesses, a high-reflectivity Bragg reflector layer 2 can be formed. The thickness of the SiO2 and TiO2 films is one-quarter of the wavelength.

[0139] Furthermore, the Lagrange reflective layer 2 is a non-conductive layer structure, which can provide insulation protection for the N-type electrode structure 11.

[0140] Understandably, Bragg reflector layer 2 is not a necessary setting and can be selectively set according to specific application requirements.

[0141] Then, as shown in Figure 11, the heat sink 1 is bonded to the Bragg reflector layer 2 to facilitate heat conduction of the laser.

[0142] Step S7′: As shown in Figure 12, remove the gallium nitride substrate 12 and the buffer layer 13; as shown in Figure 13, etch the P-type waveguide layer 5 and the P-type optical confinement layer 4 to form a ridge waveguide structure and a P-type optical confinement structure.

[0143] After removing the gallium nitride substrate 12 and the buffer layer 13, the P-type waveguide layer 5 and the P-type optical confinement layer 4 are etched to form a ridge waveguide structure and a P-type optical confinement structure (i.e., the etched P-type optical confinement layer) with a height of 2-3 μm. The ridge waveguide structure is a P-type ridge waveguide structure, which includes a stacked P-type sub-waveguide structure 51 and a P-type sub-waveguide structure 52. The projection of the P-type sub-waveguide structure 51 on the N-type electrode structure 11 covers the projection of the P-type sub-waveguide structure 52 on the N-type electrode structure 11.

[0144] Step S8′: As shown in Figure 13, a P-type electrode contact layer 15 is formed on the P-type light confinement structure, an insulating layer 10 is formed on the P-type electrode contact layer 15, and a portion of the P-type electrode contact layer 15 is exposed by etching, and a P-type electrode structure 3 is formed on the exposed P-type electrode contact layer 15.

[0145] An insulating layer 10 is first formed on the uncovered upper surface of the P-type sub-waveguide structure 11, the upper surface and side surface of the P-type electrode contact layer 15, the side surface of the P-type sub-waveguide structure 2 52, and the side surface of the P-type optical confinement structure. The thickness of the insulating layer 10 is 20-50 nm. The material of the insulating layer 10 is silicon oxide or silicon nitride, and it is deposited by CVD or PVD.

[0146] Then, a patterned photoresist layer formed by a photomask or photolithography process is used as a mask to etch the insulating layer 10, forming a patterned insulating layer 10 and exposing part of the P-type electrode contact layer 15.

[0147] Finally, a P-type electrode structure 3 is formed on the exposed P-type electrode contact layer 15. The material of the P-type electrode structure 3 is preferably Ti, Au, Ag or an alloy thereof.

[0148] Please refer to Figure 13, which shows another schematic diagram of a nitride semiconductor laser. This nitride semiconductor laser is obtained by growing and peeling off the gallium surface of a gallium nitride substrate. The nitride semiconductor laser includes: a heat sink 1, a Bragg reflector layer 2, and a laser structure stacked in sequence.

[0149] The Bragg reflector layer 2 comprises multiple reflective structures stacked on the heat sink 1. Each reflective structure includes a first reflective layer and a second reflective layer. The first reflective layer is made of SiO2, and the second reflective layer is made of TiO2. By placing the Bragg reflector layer 2 between the heat sink 1 and the laser structure, the light reflectivity can be improved.

[0150] The laser structure includes, in sequence, an N-type electrode structure 11, an N-type light confinement layer 8, an N-type waveguide layer 7, a quantum well layer 6, a P-type waveguide layer 5, a P-type light confinement layer 4, a P-type electrode contact layer 15, an insulating layer 10, and a P-type electrode structure 3.

[0151] The N-type electrode structure 11 is disposed on the side of the Bragg reflector layer 2 away from the heat sink 1.

[0152] The N-type light confinement layer 8 comprises 100 GaN / AlGaN superlattices stacked sequentially along the gallium surface; the thickness of the N-type light confinement layer 8 is 150 nm.

[0153] The thickness of the N-type waveguide layer 7 is 2 μm, and the Si doping concentration of the N-type waveguide layer 7 is 5 × 10⁻⁶. 18 cm -3 .

[0154] Quantum well layer 6 is a 5-period In y Ga 1-y N / GaN quantum well structure, y = 0.5; In y Ga 1-y The thickness of the N layer is 2nm, and the thickness of the GaN layer is 5nm.

[0155] The doping concentration of the P-type waveguide layer 5 gradually decreases from high to low along the device growth direction. The thickness of the P-type waveguide layer 5 is less than the thickness of the N-type waveguide layer 7.

[0156] The P-type waveguide layer 5 includes a P-type sub-waveguide structure 51 and a P-type sub-waveguide structure 52 stacked along the gallium surface of the gallium nitride substrate. The projection of the P-type sub-waveguide structure 51 onto the N-type electrode structure 11 covers the projection of the P-type sub-waveguide structure 52 onto the N-type electrode structure 11.

[0157] The P-type light confinement layer 4 includes 80 GaN / Al atoms stacked sequentially along the gallium surface. x Ga 1-x N superlattice structure, x = 0.5.

[0158] The insulating layer 10 covers the surface of the P-type waveguide layer 5 not covered by the P-type light confinement layer 4, the side surface of the P-type electrode contact layer 15, and a portion of the upper surface of the P-type electrode contact layer 15; and the insulating layer 10 has an opening that exposes a portion of the P-type electrode contact layer 15. In this embodiment, the thickness of the insulating layer 10 is 25 nm.

[0159] The P-type electrode structure 3 is disposed in the opening on the upper surface of the exposed P-type electrode contact layer 15, and covers a portion of the upper surface of the insulating layer 10 (i.e., the upper surface covering a portion of the P-type electrode contact layer 15).

[0160] In summary, the solution provided by this utility model has the following advantages:

[0161] 1. The nitride semiconductor laser of this invention is prepared by epitaxial growth and lift-off on the Ga surface of a GaN substrate. The high thermal conductivity of the Ga surface is used to enhance heat conduction, thereby improving the high power output performance of the device.

[0162] 2. In this invention, the P-type waveguide layer is formed earlier than the N-type waveguide layer, improving the crystal quality and doping effect of the P-type waveguide layer. Simultaneously, the P-type waveguide layer in the lower part of the nitride semiconductor laser shortens the hole propagation path from the P-type electrode structure to the quantum well layer, reducing non-radiative recombination loss. Furthermore, the P-type waveguide layer is a high-quality, gradient-doped waveguide layer, effectively solving the laser performance problems caused by the poor quality of the P-type region layer in existing technologies. Specifically: First, it improves carrier injection efficiency; the built-in electric field formed by gradient doping accelerates hole injection into the quantum well layer, improving the symmetry of carrier injection and solving the problem of low electron-hole recombination efficiency in the quantum well layer due to the low hole concentration and poor mobility of the P-type region layer in existing technologies. Second, it reduces series resistance; the high-quality P-type waveguide layer improves the conductivity of the P-type region, reducing the device's series resistance and lowering the overall resistance. The first benefit is the reduction of operating voltage and driving current requirements, which alleviates the problem of increased thermal effects caused by poor conductivity of the P-type region layer. The second benefit is the reduction of optical losses. Gradient doping optimizes the refractive index distribution, forms an asymmetric optical waveguide structure, enhances optical field confinement, reduces light scattering and absorption losses, and improves slope efficiency. At the same time, it reduces defects such as dislocations, reduces the occurrence of nonradiative recombination, and significantly improves internal quantum efficiency. The third benefit is the improvement of reliability. By reducing defect density, the degradation process of the device is slowed down, the lifespan of the nitride semiconductor laser is extended, and the device reliability problem caused by high defect density is solved.

[0163] 3. The technique of using a gradient-doped P-type waveguide layer and forming the P-type waveguide layer before the N-type waveguide layer allows the P-type waveguide layer to serve as a buffer layer and a substrate for the growth of the N-type waveguide layer. Through staged lattice matching, the lattice mismatch between the substrate and the epitaxial layer can be gradually absorbed, reducing through dislocations.

[0164] 4. In the design of heterojunction interfaces, the P-type waveguide layer of this invention achieves stress engineering control through thickness control. Its thinner characteristics can effectively buffer the difference in thermal expansion coefficients between the epitaxial layer and the substrate in the GaN-based material system during preparation, reduce dislocation multiplication caused by thermal stress at the interface, and thus improve the crystal integrity of the subsequent N-type region layer.

[0165] 5. The P-type waveguide layer in this invention is a graded doped P-type waveguide layer, and the doping concentration changes from high to low along the growth direction, which can form a built-in electric field, accelerate the injection of holes into the quantum well layer, accelerate the migration of carriers into the quantum well layer, reduce Auger recombination, and improve optical confinement.

[0166] 6. This invention employs a gradually varying P-type doping concentration, which can alter the refractive index distribution of the material and create a certain refractive index gradient. This provides better confinement of the optical field, enabling light to propagate more effectively in the quantum well layer and the P-type waveguide layer, reducing light scattering and loss. Furthermore, the gradually varying refractive index distribution of the P-type waveguide layer, combined with the uniform refractive index of the N-type layer, can construct an asymmetric optical waveguide.

[0167] 7. The formation time of the P-type waveguide layer is earlier than that of the N-type waveguide layer. Thus, the quantum well layer has not yet been formed when the P-type waveguide layer is formed. This pre-processing of the P-type waveguide layer allows the formation temperature of the P-type waveguide layer to be controlled between 1000-1100℃. The high temperature can improve the growth quality of the P-type waveguide layer and avoid the In segregation problem of the quantum well layer under high temperature environment.

[0168] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention.

[0169] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A nitride semiconductor laser, characterized in that, include: A heat sink and laser structure are stacked sequentially. The laser structure includes a first type waveguide layer, a quantum well layer, and a second type waveguide layer stacked sequentially, with the first type waveguide layer disposed between the heat sink and the quantum well layer. The first type is P-type, and the second type is N-type; or the first type is N-type, and the second type is P-type. The doping concentration of the P-type waveguide layer gradually changes along the device growth direction, which is from the P-type waveguide layer to the N-type waveguide layer. The nitride semiconductor laser is obtained by growing and peeling off a gallium surface on a gallium nitride substrate.

2. The nitride semiconductor laser according to claim 1, characterized in that, The doping concentration of the P-type waveguide layer gradually decreases from high to low along the growth direction of the device; the formation time of the P-type waveguide layer is earlier than the formation time of the N-type waveguide layer.

3. The nitride semiconductor laser according to claim 1, characterized in that, The thickness of the P-type waveguide layer is less than the thickness of the N-type waveguide layer.

4. The nitride semiconductor laser according to claim 1, characterized in that, The laser structure also includes a first type of electrode structure, which is disposed on the side of the first type of waveguide layer near the heat sink.

5. The nitride semiconductor laser according to claim 4, characterized in that, A first type of optical confinement layer is further provided between the first type of electrode structure and the first type of waveguide layer; wherein, the first type of optical confinement layer includes a plurality of first superlattice structures stacked sequentially along the gallium surface.

6. The nitride semiconductor laser according to claim 1, characterized in that, The laser structure further includes a second type of electrode structure, which is disposed on the side of the second type waveguide layer away from the quantum well layer.

7. The nitride semiconductor laser according to claim 6, characterized in that, A second type of light confinement layer and a second type of electrode contact layer are further provided between the second type of waveguide layer and the second type of electrode structure; the second type of electrode contact layer is disposed between the second type of electrode structure and the second type of light confinement layer; wherein, the second type of light confinement layer includes a plurality of second superlattice structures stacked sequentially along the gallium surface, the thickness of the second type of light confinement layer is 100-200nm, and the thickness of the second type of electrode contact layer is 100-200nm.

8. The nitride semiconductor laser according to claim 7, characterized in that, The laser structure further includes an insulating layer that covers the second type waveguide layer and the second type electrode contact layer, and the insulating layer has an opening that exposes a portion of the second type electrode contact layer, on the surface of the exposed second type electrode contact layer, where a second type contact electrode is formed.

9. The nitride semiconductor laser according to claim 4, characterized in that, The second type waveguide layer includes a second type sub-waveguide structure one and a second type sub-waveguide structure two stacked together. The projection of the second type sub-waveguide structure one onto the first type electrode structure covers the projection of the second type sub-waveguide structure two onto the first type electrode structure. The second type sub-waveguide structure two is disposed on the side of the second type sub-waveguide structure one away from the quantum well layer.

10. The nitride semiconductor laser according to claim 4, characterized in that, The nitride semiconductor laser further includes a Bragg reflector layer disposed between the heat sink and the first type of electrode structure.

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