Preparation method of nitride semiconductor laser

Abstract

The invention discloses a preparation method of a nitride semiconductor laser. The method comprises the following steps: providing a gallium nitride substrate; sequentially growing a P-type waveguide layer, a quantum well layer and an N-type waveguide layer on the gallium surface of the gallium nitride substrate; wherein the doping concentration of the P-type waveguide layer is gradually changed along the growth direction; firstly removing the gallium nitride substrate, and then bonding a heat dissipation heat sink on one side, far away from the quantum well layer, of the P-type waveguide layer; or, a heat dissipation heat sink is bonded on the side, away from the quantum well layer, of the N-type waveguide layer, and then the gallium nitride substrate is removed. The gallium surface serves as a growth surface, heat scattering is facilitated, the high-power output performance is improved, the P-type waveguide layer is formed firstly, the crystal quality and the doping effect of the P-type waveguide layer can be improved, the hole transmission path is shortened, the non-radiative recombination loss is reduced, meanwhile, the doping concentration of the P-type waveguide layer is gradually changed, and the efficiency is improved. Lattice mismatch of the substrate and the epitaxial layer can be absorbed step by step through staged lattice matching, and penetration dislocation is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, and in particular to a method for preparing a nitride semiconductor laser. Background Art

[0002] Gallium nitride-based lasers have broad application prospects in optical communications, solid-state lighting, laser displays, and other fields due to their advantages such as wide emission wavelength range, high efficiency, and long life. However, the preparation of gallium nitride-based lasers in existing technologies usually 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 disadvantages:

[0003] 1. Since the P-type region layer is located at the top and the N-type region layer is located at the bottom, and the hole mobility is lower than the electron mobility (the hole mobility is only about 1 / 10 of the electron mobility), the hole transmission path from the electrode to the light-emitting quantum well layer is long, resulting in large non-radiative recombination losses.

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

[0005] 3. The poor quality of the P-type region layer affects the performance of the laser, which is mainly reflected in the following aspects: (a) Decreased carrier injection efficiency: The P-type region layer has a low hole concentration and poor mobility, resulting in asymmetric carrier injection with the N-type region layer, reducing the electron-hole recombination efficiency of the quantum well layer; (b) Increased series resistance: The poor conductivity of the P-type region layer will increase the series resistance of the device, resulting in an increase in the operating voltage (requiring a higher drive current) and exacerbating the thermal effect; (c) Increased optical loss: Defects in the P-type region layer (such as dislocations) will become light scattering centers, increase internal absorption losses, and reduce the slope efficiency of the laser. Defects may also cause non-radiative recombination (such as Auger recombination), reducing the internal quantum efficiency; (d) Reliability issues: High defect density may accelerate device degradation and shorten the laser life. Summary of the Invention

[0006] To address the above-mentioned technical problems, the present invention aims to provide a method for fabricating a nitride semiconductor laser. This method utilizes a gallium surface as a growth surface during the fabrication process, which facilitates heat scattering and improves the high-power output performance of the device. Furthermore, a P-type waveguide layer is formed first during fabrication, which improves the crystal quality and doping effect of the P-type waveguide layer, shortens the hole transport path, and reduces non-radiative recombination losses. Furthermore, gradient doping of the P-type waveguide layer (i.e., the doping concentration of the P-type waveguide layer gradually changes along the device growth direction) can be combined with staged lattice matching to gradually absorb the lattice mismatch between the substrate and the epitaxial layer, thereby reducing threading dislocations.

[0007] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0008] A method for preparing a nitride semiconductor laser comprises the following steps:

[0009] Providing gallium nitride substrates;

[0010] A P-type waveguide layer, a quantum well layer, and an N-type waveguide layer are sequentially grown on the gallium surface of the gallium nitride substrate; wherein the doping concentration of the P-type waveguide layer gradually changes along the growth direction;

[0011] First, the gallium nitride substrate is removed, and then a heat sink is bonded to the side of the P-type waveguide layer away from the quantum well layer; alternatively, a heat sink is bonded to the side of the N-type waveguide layer away from the quantum well layer, and then the gallium nitride substrate is removed.

[0012] The P-type waveguide layer formed by the present invention features a gradient doping, with the doping concentration varying from high to low along the growth direction. This creates a built-in electric field, accelerating hole injection and carrier migration into the quantum well layer, reducing Auger recombination and improving optical confinement. Furthermore, the P-type waveguide layer with a gradient doping concentration modifies the material's refractive index profile, forming a specific refractive index gradient, thereby providing enhanced confinement for the optical field and enabling more efficient light propagation within the quantum well layer and waveguide layer (including the P-type waveguide layer and the N-type waveguide layer), reducing light scattering and loss. Furthermore, the gradient refractive index distribution of the P-type waveguide layer, combined with the uniform refractive index of the N-type waveguide layer, enables the construction of an asymmetric optical waveguide.

[0013] The growth of the P-type waveguide layer preferably adopts two technical solutions:

[0014] The temperature of the reaction chamber is gradually increased from a first preset temperature to a second preset temperature, and a doping source is introduced into the reaction chamber to grow a doping concentration of 1×10 19 cm -3 Gradient to 5×10 17 cm -3 wherein the first preset temperature and the second preset temperature are 1000-1100°C, and the ratio of the absolute value of the difference between the first preset temperature and the second preset temperature to the growth time of the P-type waveguide layer is 0.5°C.

[0015] Alternatively, under the condition of a temperature of 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, so as to grow a doping concentration from 1×10 19 cm -3 Gradient to 5×10 17 cm-3 P-type waveguide layer.

[0016] Compared with the preparation process in which the P-type waveguide layer is formed later, the quantum well layer is not formed when the P-type waveguide layer is formed in the present invention. The formation temperature of the P-type waveguide layer in the present invention can be controlled between 1000-1100°C. The high temperature can further improve the growth quality of the P-type waveguide layer and avoid the precipitation of In from the quantum well layer during high-temperature growth, which affects the growth.

[0017] Furthermore, before growing the P-type waveguide layer, the preparation method further includes:

[0018] forming a buffer layer and a P-type light confinement layer in sequence on the gallium surface of the gallium nitride substrate;

[0019] The buffer layer is removed together with the gallium nitride substrate; the thickness of the buffer layer is 20-80 nm, and the P-type light confinement layer includes 50-400 first superlattice structures stacked in sequence along the gallium surface.

[0020] Regarding the technical solution: first, the gallium nitride substrate is removed, and then a heat sink is bonded to the side of the P-type waveguide layer away from the quantum well layer. The preparation method further includes:

[0021] After forming the N-type waveguide layer, etching the N-type waveguide layer to form a ridge waveguide structure with a height of 2-3 μm; the ridge waveguide structure includes a first N-type sub-waveguide structure and a second N-type sub-waveguide structure stacked along the gallium surface, wherein a projection of the first N-type sub-waveguide structure on the gallium nitride substrate covers a projection of the second N-type sub-waveguide structure on the gallium nitride substrate;

[0022] An N-type light confinement layer and an N-type electrode contact layer are sequentially formed on the second N-type sub-waveguide structure; wherein the N-type light confinement layer includes 50-200 second superlattice structures sequentially stacked along the gallium surface, and the electron concentration of the N-type light confinement layer is 10 17 -10 19 cm -3 ;

[0023] forming an insulating layer with a thickness of 20-50 nm on the second N-type sub-waveguide structure and the N-type electrode contact layer;

[0024] Etching the insulating layer to form an opening exposing the N-type electrode contact layer;

[0025] An N-type electrode structure is formed in the opening and on the insulating layer.

[0026] Furthermore, before removing the gallium nitride substrate, the preparation method further includes:

[0027] Disposing a supporting substrate on a side of the N-type electrode structure away from the gallium nitride substrate;

[0028] Alternatively, forming a protective layer on a side of the N-type electrode structure away from the gallium nitride substrate, and bonding the protective layer to a support substrate;

[0029] After bonding the heat sink, the method further includes: removing the support substrate.

[0030] Furthermore, a heat sink is bonded to a side of the P-type waveguide layer away from the quantum well layer, comprising:

[0031] forming a P-type electrode structure on a side of the P-type light confinement layer away from the P-type waveguide layer;

[0032] A heat sink is bonded to a side of the P-type electrode structure away from the P-type waveguide layer.

[0033] Regarding the technical solution: first bonding a heat sink to a side of the N-type waveguide layer away from the quantum well layer, and then removing the gallium nitride substrate, the preparation method further includes:

[0034] forming an N-type light confinement layer on a side of the N-type waveguide layer away from the quantum well layer;

[0035] An N-type electrode structure is formed on a side of the N-type light confinement layer away from the N-type waveguide layer;

[0036] A heat sink is bonded to a side of the N-type electrode structure away from the N-type light confinement layer.

[0037] Furthermore, the preparation method further comprises:

[0038] After removing the gallium nitride substrate and the buffer layer, the P-type waveguide layer and the P-type light confinement layer are etched to form a ridge waveguide structure and a P-type light confinement structure with a height of 2-3 μm; wherein the ridge waveguide structure includes a first P-type sub-waveguide structure and a second P-type sub-waveguide structure arranged in a stacked manner, and the projection of the first P-type sub-waveguide structure on the N-type electrode structure covers the projection of the second P-type sub-waveguide structure on the N-type electrode structure;

[0039] forming a P-type electrode contact layer on the P-type light confinement structure;

[0040] forming an insulating layer with a thickness of 20-50 nm on the P-type electrode contact layer;

[0041] Etching the insulating layer to form an opening exposing the P-type electrode contact layer;

[0042] A P-type electrode structure is formed in the opening and on the insulating layer.

[0043] In the preparation method of the present invention, before bonding the heat sink, the preparation method further comprises:

[0044] A Bragg reflection layer is formed on a side of the P-type waveguide layer away from the quantum well layer; or a Bragg reflection layer is formed on a side of the N-type waveguide layer away from the quantum well layer; wherein the Bragg reflection layer is a non-conductive layer structure.

[0045] The beneficial effects of the present invention are:

[0046] 1. In the preparation process, the present invention uses the gallium surface as the growth surface, and the subsequent structure is grown on the gallium surface. The high thermal conductivity of the gallium surface is utilized to facilitate heat scattering and improve the high power output performance of the device.

[0047] 2. The present invention first forms a P-type waveguide layer, which improves the crystal quality and doping effect of the P-type waveguide layer; at the same time, the P-type waveguide layer in the lower part of the nitride semiconductor laser can shorten the transmission path of holes from the P-type electrode structure to the quantum well layer, reducing non-radiative recombination losses. In addition, the present invention forms a high-quality gradient-doped P-type waveguide layer, which effectively solves the laser performance problems caused by the poor quality of the P-type regional layer in the prior art. Specifically, it improves the carrier injection efficiency. The built-in electric field formed by the gradient doping accelerates the injection of holes into the quantum well layer, improves the symmetry of carrier injection, 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 regional layer in the prior art; secondly, it reduces the series resistance. The high-quality P-type waveguide layer improves the conductivity of the P-type region, reduces the series resistance of the device, and reduces It reduces the operating voltage and driving current requirements, and alleviates the problem of aggravated thermal effects caused by poor conductivity of the P-type region layer; thirdly, it reduces optical losses, and gradient doping optimizes the refractive index distribution to form an asymmetric optical waveguide structure, enhances light 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 non-radiative recombination, and significantly improves internal quantum efficiency; fourthly, it improves reliability. By reducing defect density, it delays the degradation process of the device, extends the service life of the nitride semiconductor laser, and solves the device reliability problem caused by high defect density.

[0048] 3. A gradient-doped P-type waveguide layer is used, and the P-type waveguide layer is formed before the N-type waveguide layer. This allows the P-type waveguide layer to serve as the substrate for the growth of the buffer layer and the N-type waveguide layer. Through staged lattice matching, the lattice mismatch between the substrate and the epitaxial layer can be gradually absorbed, reducing threading dislocations. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic flow chart of the method for preparing a nitride semiconductor laser according to solution 1 of the present invention.

[0050] Figure 2 This is a schematic diagram of the structure formed by steps S1 to S4 of the method for preparing a nitride semiconductor laser according to solution 1 of the present invention.

[0051] Figure 3 This is a schematic diagram of the structure formed by steps S5 to S6 of the method for preparing a nitride semiconductor laser according to solution 1 of the present invention.

[0052] Figure 4 This is a schematic diagram of the structure formed in step S7 of the method for preparing a nitride semiconductor laser according to solution 1 of the present invention.

[0053] Figures 5 to 7 This is a schematic diagram of the structure formed in step S8 of the method for preparing a nitride semiconductor laser according to solution 1 of the present invention.

[0054] Figure 8 This is a schematic structural diagram of a nitride semiconductor laser obtained by the preparation method according to Scheme 1 of the present invention.

[0055] Figure 9 This is a schematic flow chart of the method for preparing a nitride semiconductor laser according to solution 2 of the present invention.

[0056] Figure 10 This is a schematic diagram of the structure formed by steps S1′ to S5′ of the method for preparing a nitride semiconductor laser according to solution 2 of the present invention.

[0057] Figure 11 This is a schematic diagram of the structure formed in step S6' of the method for preparing a nitride semiconductor laser according to solution 2 of the present invention.

[0058] Figures 12 to 13 This is a schematic diagram of the structure formed by steps S7′ to S8′ of the method for preparing a nitride semiconductor laser according to solution 2 of the present invention.

[0059] In the figure, 1: heat sink, 2: Bragg reflection layer, 3: P-type electrode structure, 4: P-type light confinement layer, 5: P-type waveguide layer, 51: first P-type sub-waveguide structure, 52: second P-type sub-waveguide structure, 6: quantum well layer, 7: N-type waveguide layer, 71: first N-type sub-waveguide structure, 72: second N-type sub-waveguide structure, 8: N-type light confinement layer, 9: N-type electrode contact layer, 10: insulating layer, 11: N-type electrode structure, 12: gallium nitride substrate, 13: buffer layer, 14: supporting substrate; 15: P-type electrode contact layer. DETAILED DESCRIPTION

[0060] The preferred embodiments of the present invention are described in detail below 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 precise definition of the protection scope of the present invention.

[0061] Please refer to Figures 1 to 8 , Figure 1 This is a flow chart of a method for preparing a nitride semiconductor laser according to Scheme 1, which specifically includes the following steps:

[0062] Step S1: Figure 2 As shown, 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 .

[0063] In the present invention, the gallium surface of the gallium nitride substrate 12 is used as the growth surface for epitaxial growth. Before the growth, the gallium nitride substrate 12 may be subjected to certain treatments, including cleaning, surface polishing, and surface activation.

[0064] Furthermore, the cleaning steps include: 1) organic solvent cleaning: ultrasonically cleaning the GaN substrate using an organic solvent such as acetone or ethanol to remove impurities such as oil and organic residue from the GaN substrate surface; 2) acid cleaning: soaking and cleaning the GaN substrate using an acid such as dilute hydrochloric acid or dilute sulfuric acid to remove metal impurities and oxide layers from the GaN substrate surface; and 3) deionized water cleaning: removing residual acid and other impurities from the cleaning process to ensure that the GaN substrate surface is clean and free of contamination. The surface polishing step includes polishing the GaN surface using mechanical polishing or chemical mechanical polishing to obtain an atomically flat surface. A flat surface facilitates uniform epitaxial layer growth, reduces the impact of surface roughness on the growth process, and improves the interface quality between the epitaxial layer and the substrate. The surface activation step includes: activating the gallium surface using plasma treatment and thermal annealing methods. Plasma treatment can generate some active sites on the surface of the gallium nitride substrate, which is conducive 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 is convenient for migration and arrangement during the growth process, thereby promoting epitaxial growth.

[0065] Using the gallium surface of the GaN substrate as the epitaxial growth surface has the following advantages:

[0066] (1) Good crystal quality: The atomic arrangement of the 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.

[0067] (2) Uniform growth rate: The chemical properties of the gallium surface are relatively stable, and it has good uniformity in the adsorption and deposition of atoms of the epitaxial material during the growth process, which is conducive to achieving uniform epitaxial growth and obtaining an epitaxial layer with uniform thickness and consistent performance.

[0068] (3) The processed gallium surface has excellent properties: A good interface can be formed between the surface-activated gallium surface and the epitaxial layer. After surface activation treatment, stress can be eliminated and surface active sites can be increased, which is beneficial to the transmission of electrons at the interface, facilitates heat conduction, improves thermal conductivity, reduces adverse factors such as interface thermal resistance, and is beneficial to improving the performance of the device.

[0069] In one 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 setting 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.

[0070] 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. 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.

[0071] Step S2: As Figure 2 shown, a P-type waveguide layer 5 with a gradually changing doping concentration is formed on the P-type optical confinement layer 4.

[0072] 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 with a gradually decreasing growth doping concentration can be achieved by increasing the growth temperature to reduce the incorporation amount of the P-type dopant. Specifically, the temperature of the reaction chamber is increased from the first preset temperature gradient to the 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 -3wherein the first preset temperature and the second preset temperature are controlled within a range of 1000-1100° C., and the ratio of the absolute value of the difference between the first preset temperature and the second preset temperature to the growth time of the P-type waveguide layer is 0.5° C. Specifically, the first preset temperature and the second preset temperature may be 1000° C., 1010° C., 1020° C., 1030° C., 1040° C., 1050° C., 1060° C., 1070° C., 1080° C., 1090° C., or 1100° C.

[0073] During the growth process, increasing the temperature increases the diffusion coefficient of the dopant, making the distribution of the dopant more uniform at the growth front and reducing the doping concentration there. As the temperature increases, the diffusion of the dopant is enhanced to a certain extent, forming a gradient doping distribution. In another embodiment, the growth of the P-type waveguide layer 5 can also achieve a gradient of doping concentration by controlling the doping flow rate. Specifically, under the condition of a temperature of 1000-1100°C, the flow rate of the doping source entering the reaction chamber is reduced from a first preset flow rate to a second preset flow rate, so as to grow the doping concentration on the gallium nitride substrate 12 from 1×10 19 cm -3 Gradient to 5×10 17 cm -3 The P-type waveguide layer 5. Reducing the P-type dopant flow rate reduces the amount of dopant entering the growth region per unit time. As the growth proceeds, the concentration of the dopant in the growth direction gradually decreases, forming a distribution from high to low.

[0074] The first preset flow rate can be 40-80sccm, for example, 40sccm, 45sccm, 50sccm, 55sccm, 60sccm, 65sccm, 70sccm, 75sccm or 80sccm; the second preset flow rate can be 10-30sccm, for example: 10sccm, 12sccm, 14sccm, 16sccm, 18sccm, 20sccm, 22sccm, 24sccm, 26sccm, 28sccm or 30sccm.

[0075] P-type dopants are usually organic compounds containing magnesium, such as biscyclopentadienyl magnesium (Cp2Mg). During the growth process, the flow rate of Cp2Mg is gradually reduced to gradually reduce the concentration of the dopant in the gas phase, thereby achieving a gradual 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 50sccm. As the growth time goes by, the flow rate is reduced linearly or nonlinearly at a certain rate until it reaches about 10sccm at the end of the growth, controlling the Mg doping concentration of the P-type waveguide layer 5 from 1×10 19 cm -3 Gradient to 5×10 17 cm -3。

[0076] As the doping concentration gradually decreases, the over-accumulation of carriers in the high-doping concentration region is avoided, enabling the injected carriers to be more evenly distributed near the quantum well layer, thereby improving the carrier injection efficiency and increasing the recombination efficiency of the quantum well layer; a high doping concentration will lead to an increase in the Auger recombination probability, while the gradual decrease in the doping concentration can effectively reduce this non-radiative recombination process, improve the internal quantum efficiency of the device, and reduce energy loss; the gradually changing doping concentration can change the refractive index distribution of the material, forming a certain refractive index gradient, thereby better restricting the optical field and enabling light to propagate more effectively in the quantum well layer and the waveguide layer, reducing light scattering and loss.

[0077] When forming the P-type waveguide layer 5, the forming temperature can be controlled between 1000 - 1100 °C; in the prior art where the P-type waveguide layer is formed above, the growth temperature of the P-type waveguide layer can only be controlled at about 950 °C. This is because in the prior art, the P-type waveguide layer is formed after the quantum well layer. Since the forming material of the quantum well layer is usually InGaN / AlGaN, which contains In, during high-temperature growth, In will precipitate. Therefore, the forming temperature of the P-type waveguide layer is restricted to be controlled at about 950 °C. In the present invention, the quantum well layer has not been formed when forming the P-type waveguide layer 5. Thus, the forming temperature of the P-type waveguide layer 5 of the present invention can be controlled at a higher temperature. Higher temperature can better improve the growth quality of the layer structure, and there is no need to worry about the problem that In is likely to precipitate in the quantum well layer during high-temperature growth, which affects the growth.

[0078] Moreover, the technical solution of using a P-type waveguide layer 5 with gradient doping 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.

[0079] Step S3: As Figure 2 shown, form a quantum well layer 6 on the P-type waveguide layer 5.

[0080] The quantum well layer 6 is a 1 - 10 period In y Ga 1-y N / GaN quantum well structure, 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, In y Ga 1-yThe thickness of the 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.

[0081] Step S4: Figure 2 As shown, an N-type waveguide layer 7 is formed on the quantum well layer 6 .

[0082] After the quantum well layer 6 is formed, 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, SiH4 is used as the N-type doping source, and the doping concentration of Si is in the range of 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 , 8×10 18 cm -3 , 9×10 18 cm -3 or 10 19 cm -3 .

[0083] Step S5: Figure 3 As shown, the N-type waveguide layer 7 is etched to form a ridge waveguide structure.

[0084] 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 uses a photolithography and etching process, that is, a photoresist layer is formed on the formed N-type waveguide layer 7. After exposure and development, etching is performed to form a ridge waveguide structure with a protrusion. 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.

[0085] Furthermore, the ridge waveguide structure is an N-type ridge waveguide structure, which includes a first N-type sub-waveguide structure 71 and a second N-type sub-waveguide structure 72 stacked along the gallium surface of the gallium nitride substrate, and the projection of the first N-type sub-waveguide structure 71 on the gallium nitride substrate 12 covers the projection of the second N-type sub-waveguide structure 72 on the gallium nitride substrate 12.

[0086] Step S6: Figure 3 As shown, an N-type light confinement layer 8 and an N-type electrode contact layer 9 are formed on the ridge waveguide structure.

[0087] After the ridge waveguide structure is formed, an N-type light confinement layer 8 and an N-type electrode contact layer 9 are formed on the surface of the ridge waveguide structure by deposition.

[0088] Furthermore, the N-type light confinement layer 8 adopts a second superlattice structure with multiple periods (eg, 50-200 periods), and the second superlattice structure is an n-type GaN / AlGaN superlattice structure, and its electron concentration is 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 100-200 nm, for example: 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.

[0089] The N-type electrode contact layer 9 is n-type gallium nitride, specifically, SiH4 is used as an n-type doping source to grow an n-type GaN layer as the N-type electrode contact layer 9, and the thickness of the N-type electrode contact layer 9 is 100-200nm (for example: 100nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm), and the Si doping concentration is 10 19 cm -3 .

[0090] Step S7: Figure 4 As shown, 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 .

[0091] 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 insulating layer 10 is made of silicon oxide or silicon nitride and is deposited by CVD or PVD. After the insulating layer 10 is deposited, the insulating layer 10 is etched using a mask or a patterned photoresist layer formed by a photolithography process as a mask. After etching, a patterned insulating layer 10 is formed, exposing a portion of the N-type electrode contact layer 9 and retaining the insulating layer 10 on the N-type waveguide layer 7.

[0092] 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.

[0093] Step S8: Figures 5 to 7 As shown, the gallium nitride substrate 12 and the buffer layer 13 are removed, and then a P-type electrode structure 3 and a Bragg reflection layer 2 are formed on the P-type light confinement layer 4, and a heat sink 1 is bonded thereto.

[0094] like Figure 5 As shown, before the GaN substrate 12 and the buffer layer 13 are peeled off, the outer side opposite to the GaN 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 GaN 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 GaN substrate 12 and the buffer layer 13 are peeled off and removed.

[0095] like Figure 6As shown, 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 50-100nm, for example: 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm; the material of the P-type electrode structure 3 can be Ti, Au, Ag or their alloys, or transparent metal oxide ITO, etc.

[0096] Then, if Figure 6 As shown, a Bragg reflector 2 is formed on the P-type electrode structure 3. The materials of Bragg reflector 2 are alternating SiO2 / TiO2. SiO2 has a low refractive index of approximately 1.4-1.5 in the visible and near-infrared bands, while TiO2 has a higher refractive index, typically around 2.2-2.5. By alternating the deposition of SiO2 and TiO2 films of varying thicknesses, a highly reflective Bragg reflector 2 can be formed. The thickness of the SiO2 and TiO2 films is approximately one-quarter of the wavelength.

[0097] The Bragg reflective layer 2 is a non-conductive layer structure, which can provide insulation protection for the P-type electrode structure 3 .

[0098] It is understandable that the Bragg reflective layer 2 is not necessarily provided and can be selectively provided according to specific application requirements.

[0099] Then, if Figure 7 As shown, the heat sink 1 is bonded to the Bragg reflector layer 2 to facilitate heat conduction of the laser.

[0100] Finally, if Figure 8 As shown, after the heat sink 1 is formed, the support substrate 14 is removed, and a gallium nitride semiconductor laser having gallium surface growth on the heat sink 1 is formed.

[0101] The gallium nitride substrate 12 and the buffer layer 13 can be removed by laser stripping or wet stripping. Stripping the gallium nitride substrate can reduce the thickness of the device and allow the gallium nitride substrate to be further used. On the other hand, it can be bonded to a heat sink to facilitate heat transfer of the laser.

[0102] See also Figure 8 , Figure 8 A preferred embodiment of a nitride semiconductor laser obtained by the preparation method of scheme 1 is shown. The nitride semiconductor laser is obtained by growing and peeling off on the gallium surface of a gallium nitride substrate. The nitride semiconductor laser includes: a heat sink 1, a Bragg reflection layer 2 and a laser structure stacked in sequence.

[0103] The Bragg reflector 2 comprises multiple reflective structures stacked on the heat sink 1. Each reflective structure includes a first reflective layer made of SiO2 and a second reflective layer made of TiO2. The placement of the Bragg reflector 2 between the heat sink 1 and the laser structure improves light reflectivity.

[0104] The laser structure includes 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 stacked in sequence.

[0105] The P-type electrode structure 3 is disposed on a 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.

[0106] The P-type light confinement layer 4 includes 80 GaN / Al layers stacked in sequence along the gallium surface. x Ga 1-x N superlattice structure, x=0.5.

[0107] The doping concentration of the P-type waveguide layer 5 gradually changes 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 smaller than that of the N-type waveguide layer 7.

[0108] The quantum well layer 6 is composed of 5 periods of 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 2 nm, and the thickness of the GaN layer is 5 nm.

[0109] The N-type waveguide layer 7 includes a first N-type sub-waveguide structure 71 and a second N-type sub-waveguide structure 72 stacked along the gallium surface of the gallium nitride substrate. The projection of the first N-type sub-waveguide structure 71 on the P-type electrode structure 3 covers the projection of the second N-type sub-waveguide structure 72 on 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 first N-type sub-waveguide structure 71 and the second N-type sub-waveguide structure 72) is 2 μm, and the Si doping concentration of the N-type waveguide layer 7 is 5×10 18 cm -3 .

[0110] The N-type optical confinement layer 8 includes 100 GaN / AlGaN superlattices stacked in sequence along the gallium plane; the thickness of the N-type optical confinement layer 8 is 150 nm.

[0111] The thickness of the N-type electrode contact layer 9 is 150 nm.

[0112] 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 .

[0113] The N-type electrode structure 11 is disposed in the 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 portion of the upper surface covering the N-type electrode contact layer 9). In this embodiment, the thickness of the insulating layer 10 is 25 nm.

[0114] The method for preparing the nitride semiconductor laser of the above structure comprises the following steps:

[0115] Step S1: Figure 2 As shown, 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 .

[0116] 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 50nm. 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 layers stacked in sequence along the gallium surface. x Ga 1-x N superlattice structure, x=0.5.

[0117] Step S2: Figure 2 As shown, a P-type waveguide layer 5 with a gradient doping concentration is formed on the P-type light confinement layer 4 .

[0118] The doping concentration of the P-type waveguide layer 5 gradually changes from high to low along the direction of epitaxial growth. In this embodiment, the growth of the P-type waveguide layer 5 is achieved by controlling the doping flow rate to achieve a gradual change in doping concentration. The dopant is selected as biscyclopentadienyl magnesium. The specific process is: 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 19 cm -3 Gradient to 5×10 17 cm -3 .

[0119] Step S3: Figure 2 As shown, a quantum well layer 6 is formed on the P-type waveguide layer 5 .

[0120] The quantum well layer 6 is composed of 5 periods of In y Ga 1-y N / GaN quantum well structure, y = 0.5; In y Ga 1-yThe thickness of the N layer is 2 nm, and the thickness of the GaN layer is 5 nm.

[0121] Step S4: Figure 2 As shown, an N-type waveguide layer 7 is formed on the quantum well layer 6 .

[0122] After the quantum well layer 6 is formed, 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, SiH4 is used as the N-type doping source, and the doping concentration of Si is 5×10 18 cm -3 .

[0123] Step S5: Figure 3 As shown, the N-type waveguide layer 7 is etched to form a ridge waveguide structure.

[0124] 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 uses a photolithography and etching process. Specifically, a photoresist layer is formed on the formed N-type waveguide layer 7. After exposure and development, etching is performed to form a ridge waveguide structure with a protrusion.

[0125] The ridge waveguide structure includes a first N-type sub-waveguide structure 71 and a second N-type sub-waveguide structure 72 stacked along the gallium surface of the gallium nitride substrate. The projection of the first N-type sub-waveguide structure 71 on the gallium nitride substrate 12 covers the projection of the second N-type sub-waveguide structure 72 on the gallium nitride substrate 12.

[0126] Step S6: Figure 3 As shown, an N-type light confinement layer 8 and an N-type electrode contact layer 9 are formed on the ridge waveguide structure.

[0127] After the ridge waveguide structure is formed, an N-type light confinement layer 8 and an N-type electrode contact layer 9 are formed on the surface of the ridge waveguide structure by deposition.

[0128] The N-type optical confinement layer 8 includes 100 GaN / AlGaN superlattices stacked in sequence along the gallium plane; the thickness of the N-type optical confinement layer 8 is 150 nm.

[0129] The N-type electrode contact layer 9 is n-type gallium nitride, and SiH4 is used as an n-type doping source to grow an n-type GaN layer as the N-type electrode contact layer 9. The thickness of the N-type electrode contact layer 9 is 150nm, and the Si doping concentration of the N-type electrode contact layer 9 is 10 19 cm -3 .

[0130] Step S7: Figure 4As shown, 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 .

[0131] An insulating layer 10 is formed on the N-type electrode contact layer 9 and the N-type waveguide layer 7 by CVD. The thickness of the insulating layer 10 is 25 nm and the material of the insulating layer 10 is silicon oxide. After the insulating layer 10 is deposited, the insulating layer 10 is etched using a patterned photoresist layer formed by a mask as a mask. After etching, a patterned insulating layer 10 is formed, exposing a portion of the N-type electrode contact layer 9 and retaining the insulating layer 10 on the N-type waveguide layer 7.

[0132] 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.

[0133] Step S8: Figures 5 to 7 As shown, the gallium nitride substrate 12 and the buffer layer 13 are removed, and then a P-type electrode structure 3 and a Bragg reflection layer 2 are formed on the P-type light confinement layer 4, and a heat sink 1 is bonded thereto.

[0134] like Figure 5 As shown, a 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 and removed by a laser lift-off method.

[0135] like Figure 6 As shown, 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.

[0136] Then, if Figure 6 As shown, a Bragg reflective layer 2 is formed on the P-type electrode structure 3 , and the material of the Bragg reflective layer 2 is formed by alternating SiO 2 and TiO 2 .

[0137] Then, if Figure 7 As shown, the heat sink 1 is bonded to the Bragg reflector layer 2 to facilitate heat conduction of the laser.

[0138] Finally, if Figure 8 As shown, after the heat sink 1 is formed, the support substrate 14 is removed, and a gallium nitride semiconductor laser having gallium surface growth on the heat sink 1 is formed.

[0139] Please refer to Figures 9 to 13 , Figure 9 The flowchart of the method for preparing a nitride semiconductor laser according to scheme 2 specifically includes the following steps:

[0140] Step S1': As shown in Figure 10 , a gallium nitride substrate 12 is provided, and a buffer layer 13 and a P-type optical confinement layer 4 are grown on the gallium nitride substrate 12.

[0141] In the present invention, the gallium face 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.

[0142] In one embodiment, first, a buffer layer 13 is formed on the gallium face 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 foundation for subsequent high-quality epitaxial growth.

[0143] 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. 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.

[0144] Step S2': As shown in Figure 10 , a P-type waveguide layer 5 with a gradually changing doping concentration is formed on the P-type optical confinement layer 4.

[0145] 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 amount of P-type dopant incorporated can be reduced by increasing the growth temperature, thereby achieving the growth of a P-type waveguide layer 5 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 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.

[0146] 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, reducing the doping concentration at this point. 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 gradual change in the 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 to 5×10 17 cm -3 on the gallium nitride substrate 12. 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.

[0147] 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.

[0148] 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 gradual 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 by 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 to 5×10 17 cm -3 .

[0149] Step S3': As Figure 10 shown, a quantum well layer 6 is formed on the P-type waveguide layer 5.

[0150] 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 Ga1-y The thickness of the N layer is between 1-5nm, and the thickness of the GaN layer is between 3-20nm. y Ga 1-y The thickness of the 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.

[0151] Step S4′: Figure 10 As shown, an N-type waveguide layer 7 is formed on the quantum well layer 6 .

[0152] After the quantum well layer 6 is formed, 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, SiH4 is used as the N-type doping source, and the doping concentration of Si is in the range of 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 , 8×10 18 cm -3 , 9×10 18 cm -3 or 10 19 cm -3 .

[0153] Step S5′: Figure 10 As shown, an N-type light 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 light confinement layer 8 .

[0154] First, an N-type light confinement layer 8 is formed on a 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 a side of the N-type light confinement layer 8 away from the N-type waveguide layer 7 .

[0155] Furthermore, the N-type light confinement layer 8 adopts a second superlattice structure with multiple periods (eg, 50-200 periods), and the second superlattice structure is an n-type GaN / AlGaN superlattice structure, and its electron concentration is 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 100-200 nm, for example: 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.

[0156] Step S6′: Figure 11 As shown, a Bragg reflective layer 2 is formed on the N-type electrode structure 11 , and a heat sink 1 is bonded on the Bragg reflective layer 2 .

[0157] First, a Bragg reflector 2 is formed on the N-type electrode structure 11. The materials of Bragg reflector 2 are alternating SiO2 / TiO2. SiO2 has a low refractive index, approximately 1.4-1.5 in the visible and near-infrared bands; TiO2 has a higher refractive index, typically around 2.2-2.5. By alternating the deposition of SiO2 and TiO2 films of varying thicknesses, a highly reflective Bragg reflector 2 is formed. The thickness of the SiO2 and TiO2 films is one-quarter of the wavelength.

[0158] Furthermore, the Rager reflective layer 2 is a non-conductive layer structure, which can provide insulation protection for the N-type electrode structure 11 .

[0159] It is understandable that the Bragg reflective layer 2 is not necessarily provided and can be selectively provided according to specific application requirements.

[0160] Then, if Figure 11 As shown, the heat sink 1 is bonded to the Bragg reflector layer 2 to facilitate heat conduction of the laser.

[0161] Step S7′: Figure 12 As shown, the gallium nitride substrate 12 and the buffer layer 13 are removed; Figure 13 As shown, the P-type waveguide layer 5 and the P-type light confinement layer 4 are etched to form a ridge waveguide structure and a P-type light confinement structure.

[0162] After removing the gallium nitride substrate 12 and the buffer layer 13, the P-type waveguide layer 5 and the P-type light confinement layer 4 are etched to form a ridge waveguide structure and a P-type light confinement structure with a height of 2-3 μm (i.e., the P-type light confinement layer after etching); wherein, the ridge waveguide structure is a P-type ridge waveguide structure, which includes a first P-type sub-waveguide structure 51 and a second P-type sub-waveguide structure 52 stacked together, and the projection of the first P-type sub-waveguide structure 51 on the N-type electrode structure 11 covers the projection of the second P-type sub-waveguide structure 52 on the N-type electrode structure 11.

[0163] Step S8′: Figure 13 As shown, 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.

[0164] An insulating layer 10 is formed on the uncovered upper surface of the first P-type sub-waveguide structure 51, the upper surface and side surfaces of the P-type electrode contact layer 15, the side surfaces of the second P-type sub-waveguide structure 52, and the side surfaces of the P-type light 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 is deposited by CVD or PVD. After depositing the insulating layer 10, a patterned photoresist layer formed by a mask or a photolithography process is used as a mask to etch the insulating layer 10. After etching, a patterned insulating layer 10 is formed, exposing a portion of the P-type electrode contact layer 15. 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.

[0165] See also Figure 13 , Figure 13 A preferred embodiment of a nitride semiconductor laser obtained by the preparation method of scheme 2 is shown. The nitride semiconductor laser is obtained by growing and peeling off on the gallium surface of a gallium nitride substrate. The nitride semiconductor laser includes: a heat sink 1, a Bragg reflection layer 2 and a laser structure stacked in sequence.

[0166] The Bragg reflector 2 comprises multiple reflective structures stacked on the heat sink 1. Each reflective structure includes a first reflective layer made of SiO2 and a second reflective layer made of TiO2. The placement of the Bragg reflector 2 between the heat sink 1 and the laser structure improves light reflectivity.

[0167] The laser structure includes 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 stacked in sequence.

[0168] The N-type electrode structure 11 is disposed on a side of the Bragg reflector 2 away from the heat sink 1 .

[0169] The N-type optical confinement layer 8 includes 100 GaN / AlGaN superlattices stacked in sequence along the gallium plane; the thickness of the N-type optical confinement layer 8 is 150 nm.

[0170] 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 18 cm -3 .

[0171] The quantum well layer 6 is composed of 5 periods of 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 2 nm, and the thickness of the GaN layer is 5 nm.

[0172] The doping concentration of the P-type waveguide layer 5 gradually changes from high to low along the device growth direction. The thickness of the P-type waveguide layer 5 is less than that of the N-type waveguide layer 7.

[0173] The P-type waveguide layer 5 includes a first P-type sub-waveguide structure 51 and a second P-type sub-waveguide structure 52 stacked along the gallium surface of the gallium nitride substrate. The projection of the first P-type sub-waveguide structure 51 on the N-type electrode structure 11 covers the projection of the second P-type sub-waveguide structure 52 on the N-type electrode structure 11.

[0174] The P-type light confinement layer 4 includes 80 GaN / Al layers stacked in sequence along the gallium surface. x Ga 1-x N superlattice structure, x=0.5.

[0175] Insulating layer 10 covers the surface of P-type waveguide layer 5 not covered by P-type light confinement layer 4, the side surfaces of P-type electrode contact layer 15, and a portion of the upper surface of P-type electrode contact layer 15. Insulating layer 10 also has an opening that exposes a portion of P-type electrode contact layer 15. In this embodiment, insulating layer 10 has a thickness of 25 nm.

[0176] The P-type electrode structure 3 is disposed in the opening exposing the upper surface of the P-type electrode contact layer 15 and covers a portion of the upper surface of the insulating layer 10 (ie, covers a portion of the upper surface of the P-type electrode contact layer 15 ).

[0177] In summary, the solution provided by the present invention has the following advantages:

[0178] 1. The nitride semiconductor laser of the present invention uses the gallium surface as the growth surface during the preparation process, and subsequent structure growth is carried out on the gallium surface. The high thermal conductivity of the gallium surface is utilized to facilitate heat scattering, thereby improving the high-power output performance of the device.

[0179] 2. The present invention first forms a P-type waveguide layer, which improves the crystal quality and doping effect of the P-type waveguide layer; at the same time, the P-type waveguide layer in the lower part of the nitride semiconductor laser can shorten the transmission path of holes from the P-type electrode structure to the quantum well layer, reducing non-radiative recombination losses. In addition, the present invention forms a high-quality gradient-doped P-type waveguide layer, which effectively solves the laser performance problems caused by the poor quality of the P-type regional layer in the prior art. Specifically, it improves the carrier injection efficiency. The built-in electric field formed by the gradient doping accelerates the injection of holes into the quantum well layer, improves the symmetry of carrier injection, 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 regional layer in the prior art; secondly, it reduces the series resistance. The high-quality P-type waveguide layer improves the conductivity of the P-type region, reduces the series resistance of the device, and reduces It reduces the operating voltage and driving current requirements, and alleviates the problem of aggravated thermal effects caused by poor conductivity of the P-type region layer; thirdly, it reduces optical losses, and gradient doping optimizes the refractive index distribution to form an asymmetric optical waveguide structure, enhances light 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 non-radiative recombination, and significantly improves internal quantum efficiency; fourthly, it improves reliability. By reducing defect density, it delays the degradation process of the device, extends the service life of the nitride semiconductor laser, and solves the device reliability problem caused by high defect density.

[0180] 3. A gradient-doped P-type waveguide layer is used, and the P-type waveguide layer is formed before the N-type waveguide layer. This allows the P-type waveguide layer to serve as the substrate for the growth of the buffer layer and the N-type waveguide layer. Through staged lattice matching, the lattice mismatch between the substrate and the epitaxial layer can be gradually absorbed, reducing threading dislocations.

[0181] 4. In terms of heterojunction interface design, the P-type waveguide layer of the present invention achieves stress engineering regulation through thickness control. Its thinness can effectively buffer the difference in thermal expansion coefficient between the epitaxial layer and the substrate in the GaN-based material system, reducing the dislocation proliferation caused by thermal stress at the interface, thereby improving the crystal integrity of the subsequent N-type regional layer.

[0182] 5. The P-type waveguide layer in the present invention is a P-type waveguide layer with gradient doping, 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 to the quantum well layer, reduce Auger recombination and improve optical confinement.

[0183] 6. The present invention uses a gradual change in the P-type doping concentration to change the refractive index distribution of the material, forming a certain refractive index gradient, thereby better limiting the light field, allowing light to propagate more efficiently in the quantum well layer and P-type waveguide layer, reducing light scattering and loss; and the P-type waveguide layer forms a gradual refractive index distribution, which, combined with the uniform refractive index of the N-type layer, can construct an asymmetric optical waveguide.

[0184] 7. Compared to a structure in which the P-type waveguide layer is formed on top, the present invention does not form a quantum well layer when forming the P-type waveguide layer. This pre-processing of the P-type waveguide layer enables the formation temperature of the P-type waveguide layer of the present invention to be controlled between 1000-1100°C. High temperature can further improve the growth quality of the P-type waveguide layer and avoid the problem of In segregation in the quantum well layer under high temperature environment.

[0185] In general, the structure and method of the present invention solve the problems of poor quality of the P-type regional layer, low hole injection efficiency, large difference in thermal expansion coefficient between the epitaxial layer and the substrate, low thermal conductivity, etc., can obtain a high-quality P-type waveguide layer, and can use high-temperature growth to obtain high crystal quality and doping effect, while simplifying the epitaxial layer structure.

[0186] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0187] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a nitride semiconductor laser, characterized in that: The steps include: Providing gallium nitride substrates; A P-type waveguide layer, a quantum well layer, and an N-type waveguide layer are sequentially grown on the gallium surface of the gallium nitride substrate; wherein the doping concentration of the P-type waveguide layer gradually changes along the growth direction; First, the gallium nitride substrate is removed, and then a heat sink is bonded to the side of the P-type waveguide layer away from the quantum well layer; alternatively, a heat sink is bonded to the side of the N-type waveguide layer away from the quantum well layer, and then the gallium nitride substrate is removed.

2. The method for preparing a nitride semiconductor laser according to claim 1, wherein: The growth of the P-type waveguide layer includes: The temperature of the reaction chamber is gradually increased from a first preset temperature to a second preset temperature, and a doping source is introduced into the reaction chamber to grow a doping concentration of 1×10 19 cm -3 Gradient to 5×10 17 cm -3 wherein the first preset temperature and the second preset temperature are 1000-1100°C, and the ratio of the absolute value of the difference between the first preset temperature and the second preset temperature to the growth time of the P-type waveguide layer is 0.5°C.

3. The method for preparing a nitride semiconductor laser according to claim 1, wherein: The growth of the P-type waveguide layer includes: Under the condition of a temperature of 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, so as to grow a doping concentration from 1×10 19 cm -3 Gradient to 5×10 17 cm -3 P-type waveguide layer.

4. The method for preparing a nitride semiconductor laser according to any one of claims 1 to 3, characterized in that: Before growing the P-type waveguide layer, the preparation method further includes: forming a buffer layer and a P-type light confinement layer in sequence on the gallium surface of the gallium nitride substrate; The buffer layer is removed together with the gallium nitride substrate; the thickness of the buffer layer is 20-80 nm, and the P-type light confinement layer includes 50-400 first superlattice structures stacked in sequence along the gallium surface.

5. The method for preparing a nitride semiconductor laser according to claim 4, wherein: The preparation method further comprises: After forming the N-type waveguide layer, etching the N-type waveguide layer to form a ridge waveguide structure with a height of 2-3 μm; the ridge waveguide structure includes a first N-type sub-waveguide structure and a second N-type sub-waveguide structure stacked along the gallium surface, wherein a projection of the first N-type sub-waveguide structure on the gallium nitride substrate covers a projection of the second N-type sub-waveguide structure on the gallium nitride substrate; An N-type light confinement layer and an N-type electrode contact layer are sequentially formed on the second N-type sub-waveguide structure; wherein the N-type light confinement layer includes 50-200 second superlattice structures sequentially stacked along the gallium surface, and the electron concentration of the N-type light confinement layer is 10 17 -10 19 cm -3 ; forming an insulating layer with a thickness of 20-50 nm on the second N-type sub-waveguide structure and the N-type electrode contact layer; Etching the insulating layer to form an opening exposing the N-type electrode contact layer; An N-type electrode structure is formed in the opening and on the insulating layer.

6. The method for preparing a nitride semiconductor laser according to claim 5, wherein: Before removing the gallium nitride substrate, the method further includes: providing a support substrate on a side of the N-type electrode structure away from the gallium nitride substrate; or forming a protective layer on a side of the N-type electrode structure away from the gallium nitride substrate, and bonding the protective layer to the support substrate; After bonding the heat sink, the method further includes: The support substrate is removed.

7. The method for preparing a nitride semiconductor laser according to claim 6, wherein: A heat sink is bonded to a side of the P-type waveguide layer away from the quantum well layer, comprising: forming a P-type electrode structure on a side of the P-type light confinement layer away from the P-type waveguide layer; The heat sink is bonded to a side of the P-type electrode structure away from the P-type waveguide layer.

8. The method for preparing a nitride semiconductor laser according to claim 4, wherein: The preparation method further comprises: forming an N-type light confinement layer on a side of the N-type waveguide layer away from the quantum well layer; forming an N-type electrode structure on a side of the N-type light confinement layer away from the N-type waveguide layer; A heat sink is bonded to a side of the N-type electrode structure away from the N-type light confinement layer.

9. The method for preparing a nitride semiconductor laser according to claim 8, wherein: The preparation method further comprises: After removing the gallium nitride substrate and the buffer layer, the P-type waveguide layer and the P-type light confinement layer are etched to form a ridge waveguide structure and a P-type light confinement structure with a height of 2-3 μm; wherein the ridge waveguide structure includes a first P-type sub-waveguide structure and a second P-type sub-waveguide structure arranged in a stacked manner, and the projection of the first P-type sub-waveguide structure on the N-type electrode structure covers the projection of the second P-type sub-waveguide structure on the N-type electrode structure; forming a P-type electrode contact layer on the P-type light confinement structure; forming an insulating layer with a thickness of 20-50 nm on the P-type electrode contact layer; Etching the insulating layer to form an opening exposing the P-type electrode contact layer; A P-type electrode structure is formed in the opening and on the insulating layer.

10. The method for preparing a nitride semiconductor laser according to claim 1, wherein: Before bonding the heat sink, the preparation method further includes: forming a Bragg reflection layer on a side of the P-type waveguide layer away from the quantum well layer; or forming a Bragg reflection layer on a side of the N-type waveguide layer away from the quantum well layer; Wherein, the Bragg reflection layer is a non-conductive layer structure.

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