Method for fabricating gallium nitride-based laser

Abstract

The application provides a preparation method of a gallium nitride-based laser, which can be applied to the technical field of gallium nitride semiconductor lasers. The method comprises the following steps: providing a gallium nitride substrate; sequentially growing a gallium nitride buffer layer, a lower confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, an electron blocking layer, a novel upper confinement layer, a novel p-type gallium nitride layer, an ohmic contact layer on the gallium nitride substrate to obtain an epitaxial structure; and preparing an electrode, wherein the growth method of the novel upper confinement layer and the novel p-type gallium nitride layer is a step-by-step doping method; and the structure of the novel upper confinement layer and the novel p-type gallium nitride layer is a superlattice structure. The step-by-step doping method and the superlattice polarization-induced doping method improve the doping efficiency and ionization efficiency of Mg impurities at a low growth temperature, a large Mg doping concentration and a high hole concentration can be realized at a low growth temperature, the preparation of a low-temperature p-type AlGaN and GaN layer is realized, and the photoelectric performance of a gallium nitride-based blue-green laser is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of gallium nitride semiconductor lasers, in particular to a preparation method of a gallium nitride-based laser. BACKGROUND

[0002] As a leading semiconductor optoelectronic device, the gallium nitride-based laser is widely used in many frontier fields such as laser display, laser communication and laser surgery. In particular, laser display technology is praised as the pinnacle of display technology, and in this field, the chip-level semiconductor red-green-blue three-primary-color laser plays an important role. At present, the development of red and blue semiconductor lasers has been relatively mature, while the green semiconductor laser is still in the initial exploration stage. The gallium nitride-based blue-green semiconductor laser is considered as a promising solution in the blue-green laser field due to its excellent performance. It not only can realize continuous wavelength tuning, but also can realize monolithic integration of three-primary-color lasers to meet diversified needs.

[0003] In the development process of green laser, the p-type preparation technology is a basic and thorny problem. Due to the high requirement of blue-green quantum well on thermal stability, the p-type aluminum gallium nitride (AlGaN) and gallium nitride (GaN) layer grown at high temperature often causes damage to the quantum well, thereby affecting the overall performance of the device. Therefore, the growth conditions of p-type AlGaN and GaN layer for blue-green laser are strictly required: low-temperature growth, high-doping efficiency and high-activation efficiency.

[0004] In the preparation of p-type AlGaN and GaN, magnesium (Mg) is often used as a p-type dopant. However, Mg is easy to form Mg-H complex in GaN, which needs very high ionization energy to activate the acceptor impurity. This leads to the use of higher growth temperature when growing p-type AlGaN and GaN by metal-organic chemical vapor deposition (MOCVD), and high-temperature annealing treatment after epitaxial growth to activate the acceptor impurity. This process is in sharp contrast to the low-temperature growth requirement of blue-green laser. In addition, Mg atoms also have memory effect, floating effect and self-compensation effect during the doping process, which further increases the difficulty of realizing high-efficiency doping of p-type AlGaN and GaN layer at lower growth temperature. SUMMARY

[0005] (I) Technical problems to be solved

[0006] To solve at least one of the above problems in the prior art, embodiments of the present application provide a preparation method of a gallium nitride-based laser, which improves the doping efficiency and ionization efficiency of Mg impurities at a low growth temperature by using a stepwise doping method and a superlattice polarization-induced doping method, and can realize a large Mg doping concentration and a high hole concentration at a low growth temperature of 800-950 DEG C, thereby realizing the preparation of a low-temperature p-type AlGaN and GaN layer.

[0007] The technical scheme

[0008] In view of the above problems, embodiments of the present application provide a preparation method of a gallium nitride-based laser.

[0009] According to a first aspect of the present application, a preparation method of a gallium nitride-based laser is provided, which comprises: providing a gallium nitride substrate; sequentially growing a gallium nitride buffer layer, a lower confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, an electron blocking layer, a new upper confinement layer, a new p-type gallium nitride layer, and an ohmic contact layer on the gallium nitride substrate to obtain an epitaxial structure; and preparing an electrode, wherein the growth method of the new upper confinement layer is a stepwise doping method; the growth method of the new p-type gallium nitride layer is a stepwise doping method; the structure of the new upper confinement layer is a superlattice structure; and the structure of the new p-type gallium nitride layer is a superlattice structure.

[0010] In some exemplary embodiments, the new upper confinement layer is grown by using the stepwise doping method, which comprises: performing nitridation on the epitaxial surface of a first epitaxial structure obtained after the growth of the electron blocking layer by using nitrogen; growing a first pre-set thickness of undoped gallium nitride layer on the electron blocking layer by using trimethyl gallium as a gallium source; stopping the growth of the undoped gallium nitride layer and maintaining the ammonia flow to perform nitridation on the surface of the undoped gallium nitride layer; maintaining the ammonia flow to perform p-type doping on the nitrided undoped gallium nitride layer by using dimethyl magnesium as a magnesium source until a first pre-set doping concentration is reached to obtain a p-type doped gallium nitride layer; and growing an undoped aluminum gallium nitride layer on the p-type doped gallium nitride layer by using trimethyl aluminum as an aluminum source and trimethyl gallium as a gallium source, wherein the growth temperature of the new upper confinement layer grown by using the stepwise doping method is 800-950 DEG C.

[0011] In some exemplary embodiments, the superlattice structure of the new upper confinement layer comprises 60 periods of p-type doped gallium nitride layer and undoped aluminum gallium nitride layer, and growing the new upper confinement layer by using the stepwise doping method comprises repeating the method of claim 2 for 60 times.

[0012] In some example embodiments, the new p-type gallium nitride layer is grown by a step-by-step doping method, including: nitriding an epitaxial surface of a second epitaxial structure obtained after growing the new upper confining layer by nitrogen; growing a second pre-set thickness of undoped gallium nitride layer on the new upper confining layer using trimethylgallium as a gallium source; stopping the growth of the undoped gallium nitride layer and keeping ammonia flowing to nitride the surface of the undoped gallium nitride layer; keeping ammonia flowing to p-type dope the nitrided undoped gallium nitride layer using bis-methyl magnesium as a magnesium source until a second pre-set doping concentration is reached to obtain a p-type doped gallium nitride layer; and growing an undoped gallium nitride layer on the p-type doped gallium layer using trimethylgallium as a gallium source, wherein the growth temperature of the new p-type gallium nitride layer grown by the step-by-step doping method is 800-950°C.

[0013] In some example embodiments, the superlattice structure of the new p-type gallium nitride layer includes 6 periods of p-type doped gallium nitride layer and undoped gallium nitride layer, and growing the new p-type gallium nitride layer by the step-by-step doping method includes repeating the method of claim 4 for 6 times.

[0014] In some example embodiments, the preparing the electrodes includes: forming an n-type electrode on a side of the substrate away from the gallium nitride buffer layer; and forming a p-type electrode on a side of the ohmic contact layer away from the substrate.

[0015] In some example embodiments, at least one of the following features is included: the material of the gallium nitride buffer layer includes gallium nitride; the material of the lower confining layer includes aluminum gallium nitride; the material of the lower waveguide layer includes indium gallium nitride; the material of the upper waveguide layer includes indium gallium nitride; the material of the electron blocking layer includes aluminum gallium nitride; and the material of the ohmic contact layer includes gallium nitride.

[0016] In some example embodiments, at least one of the following features is included: the doping type of the gallium nitride substrate is unintentional doping; the doping type of the gallium nitride buffer layer is n-type doping with a doping concentration of 1x10 18 cm -3 -5x10 18 cm -3 ; the doping type of the lower confining layer is n-type doping with a doping concentration of 1x10 18 cm -3 -5x10 18 cm -3 ; the doping type of the lower waveguide layer is n-type doping with a doping concentration of 8x10 16 cm -3 -2x10 17 cm -3 ; the doping type of the upper waveguide layer is p-type doping with a doping concentration of 3x10 19 cm -3 -7x10 19 cm-3 The doping type of the electron blocking layer is p-type doping, and the doping concentration is 3×10 19 cm -3 -7×10 19 cm -3 The doping type of the ohmic contact layer is p-type doping, and the doping concentration is 8×10 19 cm -3 -2×10 20 cm -3 .

[0017] In some exemplary embodiments, at least one of the following features is included: the sum of the thickness of the gallium nitride substrate and the gallium nitride buffer layer is 150 μm ± 10 μm; the thickness of the lower confinement layer is 1 μm ± 0.1 μm; the thickness of the lower waveguide layer is 200 nm ± 20 nm; the thickness of the upper waveguide layer is 100 nm ± 10 nm; the thickness of the electron blocking layer is 20 nm ± 2 nm; and the thickness of the ohmic contact layer is 10 nm ± 1 nm.

[0018] In some exemplary embodiments, the active region includes an indium gallium nitride multi-quantum well layer, wherein the indium gallium nitride multi-quantum well layer includes 3 quantum barriers and 2 quantum wells, wherein the material of the quantum barrier includes indium gallium nitride, the doping type is n-type doping, and the doping concentration is 8×10 16 cm -3 -2×10 17 cm -3 The thickness of the quantum barrier in contact with the lower waveguide layer is 5 nm ± 1 nm, and the thickness of the other two quantum barriers is 10 nm ± 1 nm; the material of the quantum well includes indium gallium nitride, the doping type is n-type doping, and the doping concentration is 3×10 16 cm -3 -7×10 16 cm -3 The thickness of a single quantum well is 2.5 nm ± 0.5 nm; and the content of indium in the quantum well is higher than the content of indium in the quantum barrier.

[0019] (Three) Beneficial Effects

[0020] From the above technical solutions, it can be seen that the embodiments of the present application provide a preparation method of a gallium nitride-based laser at least with the following beneficial effects:

[0021] The step-by-step doping method and the superlattice polarization-induced doping method improve the doping efficiency and ionization efficiency of Mg impurities at low growth temperature, and can realize large Mg doping concentration and high hole concentration at a low growth temperature of 800-950 DEG C, thereby realizing the preparation of low-temperature p-type AlGaN and GaN layers, which can improve the photoelectric performance of gallium nitride-based blue-green laser sensitive to growth temperature, and effectively improve the output characteristics of gallium nitride-based blue-green laser. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above content and other purposes, features and advantages of the present application will be more clearly understood through the following description of the embodiments of the present application with reference to the accompanying drawings, in which:

[0023] Figure 1 The preparation method of a gallium nitride-based laser according to an embodiment of the present application is schematically shown in a flowchart;

[0024] Figure 2 The structure of a gallium nitride-based laser according to an embodiment of the present application is schematically shown in a structural diagram;

[0025] Figure 3 The flowchart of growing a new upper confinement layer by the step-by-step doping method according to an embodiment of the present application is schematically shown in a flowchart;

[0026] Figure 4 The schematic diagram of supplying exogenous substances in the process of growing a new upper confinement layer by the step-by-step doping method according to an embodiment of the present application is schematically shown in a flowchart;

[0027] Figure 5 The flowchart of growing a new p-type gallium nitride layer by the step-by-step doping method according to an embodiment of the present application is schematically shown in a flowchart; and

[0028] Figure 6 The schematic diagram of supplying exogenous substances in the process of growing a new p-type gallium nitride layer by the step-by-step doping method according to an embodiment of the present application is schematically shown in a flowchart.

[0029] 1-n-type electrode; 2-gallium nitride substrate; 3-gallium nitride buffer layer; 4-lower confinement layer; 5-lower waveguide layer; 6-active region; 61-quantum barrier; 62-quantum well; 7-upper waveguide layer; 8-electron blocking layer; 9-new upper confinement layer; 10-new p-type gallium nitride layer; 11-ohmic contact layer; 12-p-type electrode. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0031] Figure 1 A flowchart schematically shows a preparation method of a gallium nitride-based laser according to an embodiment of the present application.

[0032] As shown in Figure 1 , the preparation method of the gallium nitride-based laser according to the embodiment of the present application comprises steps S110-S130.

[0033] In step S110, a gallium nitride substrate 2 is provided.

[0034] In step S120, a gallium nitride buffer layer 3, a lower confinement layer 4, a lower waveguide layer 5, an active region 6, an upper waveguide layer 7, an electron blocking layer 8, a new upper confinement layer 9, a new p-type gallium nitride layer 10 and an ohmic contact layer 11 are sequentially grown on the gallium nitride substrate 2 to obtain an epitaxial structure. The growth method of the new upper confinement layer 9 is a step-doping method; the growth method of the new p-type gallium nitride layer 10 is a step-doping method; the structure of the new upper confinement layer 9 is a superlattice structure; and the structure of the new p-type gallium nitride layer 10 is a superlattice structure.

[0035] Figure 3 A flowchart schematically shows a step-doping method for growing the new upper confinement layer 9 according to an embodiment of the present application; Figure 4 A schematic diagram schematically shows the supply of exogenous substances in the process of growing the new upper confinement layer 9 according to the step-doping method of the embodiment of the present application.

[0036] As shown in Figure 3 and Figure 4 , the step-doping method for growing the new upper confinement layer 9 according to the embodiment of the present application comprises steps S210-S250.

[0037] In step S210, the epitaxial surface of a first epitaxial structure obtained after growing the electron blocking layer 8 is nitrided by nitrogen.

[0038] In step S220, a non-doped gallium nitride layer with a first preset thickness is grown on the electron blocking layer 8 by using trimethylgallium as a gallium source. Preferably, the first preset thickness is 6nm±0.6nm.

[0039] In step S230, the growth of the non-doped gallium nitride layer is stopped, and the ammonia gas is kept flowing to nitride the surface of the non-doped gallium nitride layer.

[0040] In step S240, the ammonia gas is kept flowing to p-type dope the non-doped gallium nitride layer after nitriding by using dimethyl magnesium as the magnesium source until a first preset doping concentration is reached, and a p-type doped gallium nitride layer is obtained. Preferably, the first preset doping concentration is 1×10 19 cm -3 -3×10 19 cm -3 .

[0041] In step S250, a non-doped aluminum gallium nitride layer is grown on the p-type doped nitride layer by using trimethyl aluminum as the aluminum source and trimethyl gallium as the gallium source. Preferably, the thickness of the non-doped aluminum gallium nitride layer is 4 nm.

[0042] The temperature of the above steps S210-S250 is 800-950℃.

[0043] Preferably, the superlattice structure of the new upper confining layer 9 includes 60 periods of the p-type doped gallium nitride layer and the non-doped aluminum gallium nitride layer, and the growth of the new upper confining layer 9 by using the step-by-step doping method includes repeating the method of claim 2 for 60 times.

[0044] Figure 5 A flowchart schematically showing the method of growing the new p-type gallium nitride layer 10 by using the step-by-step doping method according to an embodiment of the present application is shown; Figure 6 A schematic diagram of the supply of the external substances in the process of growing the new p-type gallium nitride layer 10 by using the step-by-step doping method according to an embodiment of the present application is shown.

[0045] As shown in FIG. 3, the method of growing the new p-type gallium nitride layer 10 by using the step-by-step doping method according to an embodiment of the present application includes steps S310-S350. Figure 5 Figure 6 In step S310, the epitaxial surface of the second epitaxial structure obtained after growing the new upper confining layer 9 is nitrided by using nitrogen gas.

[0046] In step S320, a non-doped gallium nitride layer with a second preset thickness is grown on the new upper confining layer 9 by using trimethyl gallium as the gallium source. Preferably, the second preset thickness is 5 nm±1 nm.

[0047] In step S330, the growth of the non-doped gallium nitride layer is stopped, and the ammonia gas is kept flowing to nitride the surface of the non-doped gallium nitride layer.

[0048] In step S330, the growth of the non-doped gallium nitride layer is stopped, and the ammonia gas is kept flowing to nitride the surface of the non-doped gallium nitride layer.

[0049] ​In step S340, ammonia gas is kept flowing, and p-type doping is performed on the non-doped GaN layer after nitrogenization by using dimethyl magnesium as the magnesium source until a second preset doping concentration is reached, thereby obtaining a p-type doped GaN layer. Preferably, the second preset doping concentration is 1x10 19 cm -3 -3x10 19 cm -3 .

[0050] In step S350, a non-doped GaN layer is grown on the p-type doped GaN layer by using trimethyl gallium as the gallium source. Preferably, the thickness of the GaN layer is 5nm±1nm.

[0051] The temperature of steps S310-S350 is 800-950℃.

[0052] Preferably, the superlattice structure of the new p-type GaN layer 10 includes 6 periods of p-type doped GaN layer and non-doped GaN layer, and the growth of the new p-type GaN layer 10 by using the step-by-step doping method includes repeating the method of claim 4 for 6 times.

[0053] In step S130, an electrode is prepared.

[0054] In some exemplary embodiments, the preparation of the electrode includes: forming an n-type electrode 1 on the side of the substrate away from the GaN buffer layer 3; and forming a p-type electrode 12 on the side of the ohmic contact layer 11 away from the substrate.

[0055] The step-by-step doping method and the superlattice polarization-induced doping method improve the doping efficiency and ionization efficiency of Mg impurities at a low growth temperature, and can achieve a large Mg doping concentration and a high hole concentration at a low growth temperature of 800-950℃, thereby realizing the preparation of a low-temperature p-type AlGaN and GaN layer, which can improve the photoelectric performance of a GaN-based blue-green laser that is sensitive to growth temperature, and effectively improve the output characteristics of the GaN-based blue-green laser. Meanwhile, the new step-by-step multi-segment doping method does not require the introduction of new equipment or additional process methods, does not increase additional manufacturing costs, and is conducive to mass production.

[0056] The structure prepared based on the above method is as shown in Figure 2 , and the materials, thicknesses, and other characteristics of each layer are described in combination with Figure 2 and one embodiment of the present application.

[0057] For example, the n-type electrode 1 is made of a composite structure (Ti / Al / Ti / Au) composed of titanium (Ti), aluminum (Al), titanium, and gold (Au), with thicknesses of 50 nm ± 5 nm, 100 nm ± 10 nm, 50 nm ± 5 nm, and 100 nm ± 10 nm, respectively. The gallium nitride substrate 2 is unintentionally doped. A gallium nitride buffer layer 3 is grown on the substrate using a two-step method. The gallium nitride buffer layer 3 is also n-type doped with a doping concentration of 1 × 10⁻⁶. 18 cm -3 -5×10 18 cm -3 The combined thickness of the gallium nitride substrate 2 and the gallium nitride buffer layer 3 is 150 μm ± 10 μm. A lower confinement layer 4 is grown on the gallium nitride buffer layer 3. The material of the lower confinement layer 4 is aluminum gallium nitride (Al). x Ga 1-x N), where Al component x is 8%, and the lower confinement layer 4 is n-type doped with a doping concentration of 1×10⁻⁶. 18 cm -3 -5×10 18 cm -3 The thickness is 1μm ± 0.1μm. A lower waveguide layer 5 is then grown on the lower confinement layer 4. The material of the lower waveguide layer 5 is indium gallium nitride (In). x Ga 1-x The lower waveguide layer 5 is n-type doped with an In composition of 8% and a thickness of 200 nm ± 20 nm. The doping type of the lower waveguide layer 5 is n-type doped with a doping concentration of 8 × 10⁻⁶. 16 cm -3 -2×10 17 cm -3 Above the lower waveguide layer 5 is the active region 6, which includes an indium gallium nitride (IGaN) multi-quantum well layer 62. This IGaN multi-quantum well layer 62 comprises three quantum barriers 61 and two quantum wells 62. The quantum barriers 61 are made of indium gallium nitride (IGaN). x Ga 1-x N), wherein the In component x is 12%, the doping type is n-type doping, and the doping concentration is 8 × 10⁻⁶. 16 cm -3 -2×10 17 cm -3 The thickness of the quantum barrier 61 in contact with the lower waveguide layer 5 is 5 nm ± 1 nm, and the thickness of the other two quantum barrier layers 61 is 10 nm ± 1 nm; the material of the quantum well 62 includes indium gallium nitride (InGaN). x Ga 1-x N), wherein the In component x is 12%, the doping type is n-type doping, and the doping concentration is 3×10. 16 cm -3 -7×10 16 cm-3 The thickness of the single quantum well 62 is 2.5 nm ± 0.5 nm. Above the active region 6 is an upper waveguide layer 7, which comprises (In x Ga 1-x N) with an In composition x of 4%, a thickness of 100 nm ± 10 nm, an n-type doping, and a doping concentration of 8 x 1018cm 16 -2 x 1019cm -3 -2 x 1019cm 17 -2 x 1019cm -3 Above the upper waveguide layer 7 is an electron blocking layer 8, which comprises aluminum gallium nitride (Al x Ga 1-x N) with an Al composition x of 15%, a thickness of 20 nm ± 2 nm, a p-type doping, and a doping concentration of 3 x 1018cm 19 -7 x 1019cm -3 -7 x 1019cm 19 -7 x 1019cm -3 Above the electron blocking layer 8 is a new upper confinement layer 9, which employs a step-doping method and a superlattice structure. The superlattice structure has 60 periods, each of which comprises a p-type doped gallium nitride (GaN) layer with a thickness of 6 nm ± 0.6 nm and a doping concentration of 1 x 1018cm 19 -3 x 1019cm -3 -3 x 1019cm 19 -3 x 1019cm -3 a non-intentionally doped Al x Ga 1-x N layer with an Al composition x of 8% and a thickness of 4 nm ± 0.4 nm, and a total thickness of the superlattice of 600 nm ± 60 nm. Above the new upper confinement layer 9 is a new p-type gallium nitride layer 10, which employs a step-doping method and a superlattice structure. The superlattice structure has 6 periods, each of which comprises a non-intentionally doped GaN layer with a thickness of 5 nm ± 1 nm, a p-type doped GaN layer with a thickness of 5 nm ± 1 nm and a doping concentration of 1 x 1018cm 19 -3 x 1019cm -3 -3 x 1019cm 19 -3 x 1019cm -3 , and a total thickness of the superlattice of 60 nm ± 6 nm. Above the new p-type gallium nitride layer 10 is an ohmic contact layer 11, which comprises GaN with a thickness of 10 nm ± 1 nm, a p-type doping, and a doping concentration of 8 x 1018cm 19 -2 x 1019cm -3 -2 x 1019cm 20 -2 x 1019cm -3The p-type electrode 12 is formed on the ohmic contact layer 11, and the constituent materials of the p-type electrode 12 are, in order, palladium (Pd), platinum (Pt), and gold (Au) (Pd / Pt / Au), and the thicknesses of the respective layers are, in order, 50 nm ± 5 nm, 50 nm ± 5 nm, and 600 nm ± 60 nm.

[0058] The above describes embodiments of the present application. However, these embodiments are merely for illustrative purposes, and are not intended to limit the scope of the present application. Although each embodiment is described above separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the present application, and these substitutions and modifications should all fall within the scope of the present application.

Claims

1. A method of fabricating a gallium nitride-based laser, comprising: The method comprises: providing a gallium nitride substrate; sequentially growing a gallium nitride buffer layer, a lower confinement layer, a lower waveguide layer, an active region, an upper waveguide layer, an electron blocking layer, a new upper confinement layer, a new p-type gallium nitride layer, an ohmic contact layer on the gallium nitride substrate to obtain an epitaxial structure; and preparing electrodes, wherein the growth method of the new upper confinement layer is a step-doping method; the growth method of the new p-type gallium nitride layer is a step-doping method; the structure of the new upper confinement layer is a superlattice structure; and the structure of the new p-type gallium nitride layer is a superlattice structure; wherein the superlattice structure of the new upper confinement layer comprises 60 periods of a p-type doped gallium nitride layer and an undoped aluminum gallium nitride layer, and the growth of the new upper confinement layer by the step-doping method comprises repeating the following method 60 times: nitriding the epitaxial surface of a first epitaxial structure obtained after growing the electron blocking layer by nitrogen; growing a first pre-set thickness of an undoped gallium nitride layer on the electron blocking layer by using trimethyl gallium as a gallium source; stopping the growth of the undoped gallium nitride layer, keeping ammonia flowing to nitride the surface of the undoped gallium nitride layer; keeping ammonia flowing to p-type dope the nitrided undoped gallium nitride layer by using dimethyl magnesium as a magnesium source until a first pre-set doping concentration is reached to obtain a p-type doped gallium nitride layer; and growing an undoped aluminum gallium nitride layer on the p-type doped gallium nitride layer by using trimethyl aluminum as an aluminum source and trimethyl gallium as a gallium source, wherein the growth temperature for growing the new upper confinement layer by the step-doping method is 800-950°C.

2. The method of claim 1, wherein, The growth of the new p-type gallium nitride layer by the step-doping method comprises: nitriding the epitaxial surface of a second epitaxial structure obtained after growing the new upper confinement layer by nitrogen; growing a second pre-set thickness of an undoped gallium nitride layer on the new upper confinement layer by using trimethyl gallium as a gallium source; stopping the growth of the undoped gallium nitride layer, keeping ammonia flowing to nitride the surface of the undoped gallium nitride layer; keeping ammonia flowing to p-type dope the nitrided undoped gallium nitride layer by using dimethyl magnesium as a magnesium source until a second pre-set doping concentration is reached to obtain a p-type doped gallium nitride layer; and growing an undoped gallium nitride layer on the p-type doped gallium nitride layer by using trimethyl gallium as a gallium source, wherein the growth temperature for growing the new p-type gallium nitride layer by the step-doping method is 800-950°C.

3. The method of claim 2, wherein, The superlattice structure of the new p-type gallium nitride layer comprises 6 periods of a p-type doped gallium nitride layer and an undoped gallium nitride layer, and the growth of the new p-type gallium nitride layer by the step-doping method comprises repeating the method of claim 2 6 times.

4. The method of claim 1, wherein, The preparation of electrodes comprises: forming an n-type electrode on the side of the substrate away from the gallium nitride buffer layer; and forming a p-type electrode on the side of the ohmic contact layer away from the substrate.

5. The method of claim 1, wherein, comprises at least one of the following features: the material of the gallium nitride buffer layer comprises gallium nitride; the material of the lower confinement layer comprises aluminum gallium nitride; the material of the lower waveguide layer comprises indium gallium nitride; the material of the upper waveguide layer comprises indium gallium nitride; the material of the electron blocking layer comprises aluminum gallium nitride; The material of the ohmic contact layer includes gallium nitride.

6. The method of claim 1, wherein, The method includes at least one of the following features: The doping type of the gallium nitride substrate is unintentionally doped; The doping type of the gallium nitride buffer layer is n-type doping, and the doping concentration is 1 x 10 18 cm -3 -5 x 10 18 cm -3 ; The doping type of the lower limiting layer is n-type doping, and the doping concentration is 1 x 10 18 cm -3 -5 x 10 18 cm -3 ; The doping type of the lower waveguide layer is n-type doping, and the doping concentration is 8 x 10 16 cm -3 -2 x 10 17 cm -3 ; The doping type of the upper waveguide layer is p-type doping, and the doping concentration is 3 x 1018cm-3 19 cm -3 -7 x 1018cm-3 19 cm -3 ; The doping type of the electron blocking layer is p-type doping, and the doping concentration is 3 x 10 19 cm -3 -7 x 10 19 cm -3 ; The doping type of the ohmic contact layer is p-type doping, and the doping concentration is 8 x 10 19 cm -3 -2 x 10 20 cm -3 .

7. The method of claim 1, wherein, The method includes at least one of the following features: The sum of the thicknesses of the gallium nitride substrate and the gallium nitride buffer layer is 150 μm ± 10 μm; The thickness of the lower confinement layer is 1 μm ± 0.1 μm; The thickness of the lower waveguide layer is 200 nm ± 20 nm; The thickness of the upper waveguide layer is 100 nm ± 10 nm; The thickness of the electron blocking layer is 20 nm ± 2 nm; The thickness of the ohmic contact layer is 10 nm ± 1 nm.

8. The method of claim 1, wherein, The active region includes an indium gallium nitride multi-quantum well layer, wherein the indium gallium nitride multi-quantum well layer contains 3 quantum barriers and 2 quantum wells, The material of the quantum barrier includes indium gallium nitride, the doping type is n-type doping, and the doping concentration is 8*10 16 cm -3 -2*10 17 cm -3 The thickness of the quantum barrier in contact with the lower waveguide layer is 5nm±1nm, and the thickness of the remaining two quantum barriers is 10nm±1nm. The material of the quantum well comprises indium gallium nitride, the doping type is n-type doping, the doping concentration is 3x10 16 cm -3 -7x10 16 cm -3 -2.5 nm ± 0.5 nm; and The content of indium in the quantum well is higher than the content of indium in the quantum barrier.

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