CN110444640A - A kind of multi-wavelength GaN base core-shell nanometer rod LED device structure and preparation method thereof - Google Patents

Abstract

The invention discloses a multi-wavelength GaN-based core-shell nanorod LED device structure and a preparation method thereof. Using the self-organized Ni nano-islands formed by high-temperature ammonia annealing as a template to prepare highly consistent GaN nanorods, and then using wet etching technology to repair the dry etching damage on the surface of the nanorods, on the resulting GaN nanorod arrays Perform n-type GaN regrowth to form hexahedral columns with top cones, and then sequentially stack multiple quantum well layers and p-type GaN layers clad on each surface of the GaN nanorod array to obtain multi-wavelength GaN-based core-shell nanorods LED device structure. The GaN nanorod array and the multi-quantum well layer covering each surface and the P-type GaN layer form a three-dimensional core-shell structure, which can generate more photons at the same current density and improve the internal quantum efficiency of the LED epitaxial structure . The method of the invention does not need a patterned substrate, has low process cost, is simple and easy to implement, and is suitable for large-scale production. The obtained core-shell nanorod array can be widely used in optoelectronic devices and microelectronic devices.

Description

A multi-wavelength GaN-based core-shell nanorod LED device structure and its preparation method

technical field

The invention relates to the field of semiconductor light-emitting devices, in particular to a multi-wavelength GaN-based core-shell nanorod LED device structure and a preparation method thereof.

Background technique

Among wide-bandgap semiconductors with direct bandgap, GaN-based semiconductors have the most development potential and development prospects. With their wide bandgap [0.64 eV (InN), 3.4eV (GaN), 6.2eV, (AlN)] and superior The performance (thermal stability, chemical stability and high thermal conductivity, etc.) has become a hot spot and focus in the research of optoelectronic materials and devices in recent years. GaN-based white light LEDs have the advantages of long service life, small size, high photoelectric conversion efficiency and low heat generation, and have been widely used in instrument and equipment lighting, aircraft lighting, automotive lighting, mobile phones, and decorative lighting.

Traditional white LEDs mainly use ultraviolet/violet/blue LEDs to excite yellow or multi-color phosphors to obtain mixed white light; some studies also use multi-color LEDs to achieve mixed white light. However, the light emission research of single-chip white non-phosphor powder is mainly realized by blue and green InGaN/GaN multiple quantum wells distributed laterally or by cascaded InGaN and AlGaInP multiple quantum wells, which is relatively difficult. Moreover, it is difficult to match the luminous efficiency of each color, which has become a major problem in the research of single-chip white light. For general lighting applications, the two most important factors affecting the luminous efficiency are the strong polarization field and the poor crystal quality of high indium In _x Ga _1-x N, which is the main reason why it is difficult to improve the internal quantum efficiency of green polar LEDs. . Because the polarization field is mainly generated and exists in the polar growth direction [(0002) c-axis direction], in order to overcome the influence of the polarization field, the epitaxial InGaN active layer on the semi-polar/non-polar surface can reduce/eliminate the polarization field Negative effect on glow. GaN nanorods with nonpolar and semipolar surfaces have become a research hotspot.

Since the development of GaN nanostructures, many domestic and foreign scientists have synthesized them through different methods. For example, Kim et al. used metal organic hydride vapor phase epitaxy (MOHVPE) to prepare GaN double quantum well nanorod arrays and high-brightness LED devices in 2004 and 2005 respectively; in 2006, groups such as J. Goldberger and T. kuykendall both Single-crystal one-dimensional GaN nanotubes and nanocolumn arrays were synthesized by metal-organic vapor phase epitaxy (MOCVD); R. Calarco and LWTu et al. successively synthesized GaN nanowires by molecular beam epitaxy (MBE); Deb et al. used silicon dioxide As a template, vertically aligned GaN nanorods were prepared by MOVPE. The methods mentioned above are the so-called "bottom-up" methods, which require growth from the atomic or molecular level, then to molecular clusters, and then to nanostructures. Although many people have researched and achieved certain results, these methods are difficult to control the size, length and crystal orientation of GaN nanocolumns and are difficult to succeed. The "bottom-up" method has encountered challenges in the large-scale preparation of GaN nanocolumns. . Different from the above-mentioned growth methods, another "top-down" method to obtain GaN nanostructures is another option, and this invention only introduces one of them, using the inductively coupled plasma etching (ICP) method to prepare GaN nanopillars. There have been many reports on the specific method of inductively coupled plasma etching (ICP) GaN. For example, Shul et al. used Cl ₂ /H ₂ /Ar mixed gas to etch GaN film to obtain an etching rate of about 0.5 μm/min; Smith et al. found that the highest rate of using Cl ₂ /Ar as the etching gas was 980nm/min; Shul's group also found that in the mixed gas of Cl ₂ /N ₂ /Ar, the etching rate decreased with the increase of the partial pressure of N ₂ ; Kim et al. also studied the related issues of etching GaN in Cl ₂ /BCl ₃ plasma. Before ICP, it is necessary to obtain nanoparticles with uniform size and shape distribution as a mask. Although techniques such as electron beam lithography and photolithography can be used to prepare nano-templates, the high cost also prevents them from being used in large-scale preparations. application.

In the present invention, high-temperature ammonia annealing is used to form self-organized Ni nano-islands as a template, high-temperature ammonia annealing can control the size and density of Ni nano-islands, etc., and the size and distribution of Ni islands are related to the high-temperature ammonia annealing time, Temperature is related to original Ni film thickness etc.; this method cost is lower, and it is easier to control the size and length of nanorods, and can be applied to large-scale preparation of nanorods. The present invention uses the Ni nanometer island mask obtained by this method to prepare Highly consistent GaN nanopillars. Due to the stable chemical properties of GaN materials, dry etching is usually used. Compared with wet etching, dry etching has the advantages of good anisotropy and line width control, but due to the high energy of plasma, it will bring great damage to the surface of the etched material, resulting in the degradation of device performance. This has become an urgent problem to be solved in dry etching. The invention is dedicated to preparing GaN nano rods by ICP etching, and establishes a method for repairing the etching damage of the nano rods. Using a combination of dry etching and wet etching to obtain high-quality GaN nanorods as templates, epitaxially grow core-shell InGaN/GaN quantum well LED structures, and form InGaN/GaN quantum wells by epitaxy on GaN nanorods The core-shell structure realizes multi-wavelength light emission. By adjusting the size and height of the nanorods and the In composition, a single-chip white light LED is obtained. This is a possible way to achieve a single-chip white light emission without phosphor powder.

Contents of the invention

The object of the present invention is to provide a multi-wavelength GaN-based core-shell nanorod LED device structure and its preparation method, so as to solve the above technical problems.

To achieve the above object, the present invention adopts the following technical solutions:

A multi-wavelength GaN-based core-shell nanorod LED device structure, including deposition of a Ni layer and high-temperature ammonia annealing to form Ni nano-islands; also includes using a Ni nano-island mask to prepare highly consistent GaN nano-columns, and using wet etching Repair the dry etching damage on the surface of the nanorods, perform n-type GaN regrowth on the resulting GaN nanorod arrays, form hexahedral columns with hexagonal pyramids at the top, and then stack multiple quantum wells covering the GaN nanorod arrays in sequence layer and P-type GaN layer.

As a further solution of the present invention: the thickness of the Ni layer is 15nm-35nm, and the Ni nano-islands are formed by high-temperature ammonia annealing, and the size of the Ni nano-islands is 300nm-500nm.

As a further solution of the present invention: using dry etching to form nanorods with steep sidewalls in the GaN-based structure film, the dry etching is ion beam etching, inductively coupled plasma etching or reactive ion etching.

As a further solution of the present invention: the height of the GaN nanorod array is 4 μm-7 μm, the diameter is 200 nm-350 nm, and the Ni nano-islands at the top of the nano-rods are removed by nitric acid.

As a further solution of the present invention: use KOH solution to repair the dry etching damage on the surface of GaN nanorods. After the KOH solution is repaired, leaving chemical pollution on the surface of GaN nanorods will cause leakage current, and use aqua regia to remove surface chemical pollution. .

As a further solution of the present invention: re-grow n-type GaN on the GaN nanorod array to form (1-100) nonpolar planes and (1-101) semipolar planes with nanometer dimensions.

As a further solution of the present invention: the multi-quantum well layer is an InGaN/GaN multi-quantum well layer, the thickness of the InGaN well layer is 4nm-6nm, the thickness of the GaN barrier layer is 10nm-15nm, and the period is 5-15. The well layer has nanometer-sized (1-100) nonpolar planes and (1-101) semipolar planes.

As a further solution of the present invention: the P-type GaN layer is a Mg-doped GaN layer with a thickness of 50 nm˜100 nm.

A method for preparing a multi-wavelength GaN-based core-shell nanorod LED device structure, comprising the steps of:

S1, depositing a Ni layer on the substrate;

S2, high-temperature ammonia annealing to form Ni nano-islands;

S3, using dry etching to form a GaN nanorod array in the GaN-based structure film;

S4, heating with nitric acid to remove the Ni nano-islands at the top of the GaN nanorods;

S5, using KOH solution to repair the dry etching damage on the surface of GaN nanorods;

S6, adopt aqua regia to remove the chemical pollution on the surface;

S7. Perform Si-doped GaN regrowth on the GaN nanorod array to form (1-100) non-polar planes and (1-101) semi-polar planes with nanometer dimensions;

S8. In the step S7, GaN nanorods are clad with InGaN/GaN multiple quantum wells

S9, forming a P-type GaN layer on the multi-quantum well layer in the step S8.

As a further solution of the present invention: in the step S1, the sample is ultrasonically cleaned and dried in acetone, alcohol, and deionized water, and then coated with a layer of 15nm to 35nm thick Ni on its surface by physical vapor deposition (PVD). metal film;

In the step S2, the Ni nano-island formation method is as follows: the Ni/GaN/sapphire sample is placed in a high-temperature furnace at 800° C. to 900° C., and the ammonia gas is passed through for annealing for 10 minutes to 12 minutes. The flow rate of the ammonia gas is 700 to 900 ml. /min, to form a Ni nano-island structure used as a template. After annealing for a certain period of time, nitrogen gas is quickly introduced to remove the ammonia in the furnace and act as a protective gas. Finally, the sample is taken out after the sample is cooled;

In the step S3, the method for forming the GaN nanorod array by dry etching is as follows: using chlorine gas and boron trichloride as etching gases, the flow rates are kept at 40-50 sccm and 5-8 sccm respectively, and the pressure in the cavity, The ICP power and RF power are set to 7.50×10 ^-9 Pa, 300W and 100W respectively;

In the step S4, the method of heating the nitric acid to remove the Ni nano-islands on the top of the GaN nanorods is as follows: temperature: 80-100° C.; time: 5-10 min;

In the step S5, the method for repairing the GaN nanorods with the KOH solution is: corrosion repair in a KOH solution with a concentration of 1-1.5M, the temperature is 80-10°C, and the time is 10-30 minutes;

In the step S6, the method for removing chemical contamination on the surface with aqua regia is: put in aqua regia for 10-20 min, then ultrasonically clean and dry in deionized water;

In the step S7, the n-type GaN nanorod re-growth method is as follows: TMGa is used as gallium source, _SiH4 is used as silicon source, _NH3 is used as nitrogen source, _H2 is used as carrier gas, and the growth temperature is 850°C-1000°C, The pressure is 400mbar, the V/III ratio is 800-1000, and the growth is 10-20min; the Si doping concentration is about 4-6×10 ¹⁸ cm ^-3 ;

In the step S8, the growth method of the multi-quantum well layer is as follows: the growth temperature of the GaN barrier layer is 860°C, the growth temperature of the InGaN well layer is 750-800°C, the pressure of the reaction chamber is controlled at 400mbar, and the growth time of the barrier layer is 350°C. ~400s, TEGa flow rate is 280 SCCM, well layer growth time is 100~120s, TMIn flow rate is set to 1000 SCCM, TEGa flow rate is 280 SCCM, NH ₃ is always kept at 17 slm;

In the step S9, the growth method of the P-type GaN layer is as follows: the thickness is 50nm-100nm, and the Mg doping concentration is about 1-2×10 ²⁰ cm ^-3 .

Compared with the prior art, the present invention has the following advantages:

The invention uses high-temperature ammonia annealing to form Ni nano-islands, uses an etching method to prepare highly consistent GaN nano-pillars, then uses wet etching to repair the dry etching damage on the surface of the nano-rods, and finally undergoes secondary growth to obtain side walls Smooth core-shell nanorod arrays. This preparation method can control the size and density of Ni nano-islands by high-temperature ammonia annealing, and the size and distribution of Ni islands are related to the time, temperature and original Ni film thickness of high-temperature ammonia annealing; this method has low cost, It is also easier to control the size and length of nanopillars, which can be applied to large-scale preparation of nanopillars.

The GaN nanorod array described in the present invention forms a three-dimensional core-shell structure with the multi-quantum well layer and the P-type GaN layer covering each surface, and has a large specific surface area. Compared with thin film materials, it can produce more The number of photons increases the internal quantum efficiency of the LED epitaxial structure. At the same time, this core-shell structure will change the direction of photon propagation and increase the probability of photon emission, so that more photons escape into the air and greatly improve the external quantum efficiency.

The core-shell structure of GaN-based nanorods of the present invention has nanometer-sized (1-101 ) semipolar planes and/(1-100 ) nonpolar planes, which can effectively restrain the Stark effect and reduce the polarization electric field, Improve the probability of electron-hole recombination and improve the internal quantum efficiency of the LED epitaxial structure.

The invention adopts KOH solution to repair the dry etching damage on the surface of the GaN nanorod, effectively improves the quality of the nanorod, thereby reducing the non-radiative recombination center in the active region, and improving the internal quantum efficiency of the LED epitaxial structure.

The InGaN/GaN multi-quantum well layer of the present invention is used as an active region for light emission, (1-101) semipolar plane and (1-100) nonpolar plane, these different planes have different In content and well thickness At the same time, because the diffusion length of In atoms is longer than that of Ga atoms and the nanorods are higher, different In contents and well thicknesses are present at different positions on the sidewalls of the nanorods, which can directly realize multi-wavelength luminescence.

The method of the invention does not need a patterned substrate, is low in cost, simple and easy to implement, and is suitable for large-scale production, and the prepared core-shell nanorod array can be widely used in optoelectronic devices and microelectronic devices.

Description of drawings

Fig. 1 is the preparation flow chart of the present invention.

Figure 2 (a) is a scanning electron microscope photo of Ni nano-islands; (b) is a cross-sectional scanning electron micrograph of GaN-based core-shell nanorod LED device structure; (c) is a single GaN-based core-shell nanorod LED device structure Cross-sectional scanning electron microscope photographs.

Detailed ways

The present invention will be further elaborated below in conjunction with the accompanying drawings and specific embodiments. The fabrication flow chart of the multi-wavelength GaN-based core-shell nanorod LED device structure shown in Figure 1, Figure 2 (a) is the scanning electron microscope photo of Ni nano-islands; (b) is the GaN-based core-shell nanorod LED device structure Cross-sectional scanning electron micrograph; (c) is a cross-sectional scanning electron micrograph of a single GaN-based core-shell nanorod LED device structure. A method for preparing a multi-wavelength GaN-based core-shell nanorod LED device structure of the present invention comprises the following steps:

1) The original sample is a GaN film with a thickness of about 20 μm grown by HVPE on a (0001) sapphire substrate. The sample is ultrasonically cleaned and dried in acetone, alcohol, and deionized water; Its surface is coated with a 25nm thick Ni metal film;

2) Then put the Ni/GaN/sapphire sample into a high-temperature furnace at 850°C and pass through ammonia gas for hot ammonia annealing for 12 minutes. The flow rate of ammonia gas is 800ml/min, and the size of the Ni nano-island is 350nm;

3) Preparation of nanorods by ICP etching process: put them into inductively coupled plasma etching equipment and use Ni islands as templates for etching. During the etching process, chlorine gas and boron trichloride were used as etching gases, and their flow rates were maintained at 48sccm and 6sccm respectively, and the intracavity pressure, ICP power and radio frequency RF power were set to 7.5 × 10 ^-9 Pa, 300W and 100W, respectively;

4) Put the etched sample into nitric acid with a concentration of 100°C for 5 min to remove the Ni nano-islands at the top of the GaN nanorods;

5) Put the etched sample into the KOH solution with a concentration of 1M for corrosion repair, the temperature is 90°C, and the time is 20min;

6) Put the sample in aqua regia for 15 minutes to remove the chemical contamination on the surface, then ultrasonically clean and dry it in deionized water;

7) Re-growth Si-doped GaN nanorods by MOCVD: TMGa as gallium source, SiH ₄ as silicon source, NH ₃ as nitrogen source, H ₂ as carrier gas, growth temperature is 860°C, pressure is 400mbar, Ⅴ The /Ⅲ ratio is 895, grown for 15 minutes; (1-100) nonpolar plane and /(1-101) semipolar plane with nanometer size are formed; Si doping concentration is about 5×10 ¹⁸ cm ^-3 .

8) The multiple quantum well layer is InGaN/GaN multiple quantum well layer by MOCVD: InGaN well layer growth conditions, temperature is 730°C; pressure is 400 mbar; TEGa flow rate is 280 SCCM; TMI flow rate n is 800 SCCM; NH ₃ flow rate It is 17000SCCM; the time is 110s; grow 10 layers. Barrier layer growth conditions: growth temperature is 820°C; pressure is 400 mbar; TEGa flow rate is 280SCCM; NH ₃ flow rate is 17000 SCCM; time is 390s.

9) A Mg-doped P-type GaN layer was grown by MOCVD with a thickness of 60nm and a Mg doping concentration of 1×10 ²⁰ cm ^-3 .

Traditional white LEDs mainly use ultraviolet/violet/blue LEDs to excite yellow or multi-color phosphors to obtain mixed white light; some studies also use multi-color LEDs to achieve mixed white light. However, the light emission research of single-chip white non-phosphor powder is mainly realized by blue and green InGaN/GaN multiple quantum wells distributed laterally or by cascaded InGaN and AlGaInP multiple quantum wells, which is relatively difficult. Moreover, it is difficult to match the luminous efficiency of each color, which has become a major problem in the research of single-chip white light. The present invention provides a simple and convenient method for obtaining multi-wavelength luminescence, and obtains high-quality GaN nanorods as templates through dry etching and wet repair methods, and epitaxially grows multi-wavelength core-shell InGaN/GaN quantum well LED structures . In addition, the non-polar surface InGaN/GaN quantum well structure eliminates the polarization electric field, reduces the quantum confinement Stokes effect (QCSE), and improves the internal quantum efficiency. At the same time, the core-shell GaN-based nanorod LED structure reduces the probability of total reflection of photons inside, increases the light-emitting area, and ultimately improves the luminous efficiency of the device, and its optical properties are often better than two-dimensional GaN thin films. In addition, during the homoepitaxial growth process, the InGaN/GaN multi-quantum well layer acts as the active region for light emission, and the (1-101) semipolar plane and the (1-100) nonpolar plane have different The In content and the well thickness are high, and the In composition is easier to migrate upward from the bottom of the non-polar surface than Ga, forming a quantum well with a high In composition, thereby realizing multi-wavelength light emission.

The above are preferred embodiments of the present invention. For those of ordinary skill in the art, according to the teachings of the present invention, without departing from the principle and spirit of the present invention, the changes, modifications, Alternatives and modifications still fall within the protection scope of the present invention.

Claims (10)

1. A multi-wavelength GaN-based core-shell nanorod LED device structure, characterized in that: it includes depositing a Ni layer and high-temperature ammonia annealing to form Ni nano-islands; it also includes using a Ni nano-island mask to prepare highly consistent GaN nano-columns , and use wet etching to repair the dry etching damage on the surface of the nanorods, and perform n-type GaN regrowth on the obtained GaN nanorod arrays to form hexahedral columns with hexagonal pyramids at the top, and then stack and coat GaN nanorods in sequence. The multiple quantum well layer of the rod array and the P-type GaN layer. 2. A multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1, characterized in that: the thickness of the Ni layer is 15nm to 35nm, high-temperature ammonia annealing forms Ni nano-islands, and the Ni The size of the nano-islands is 300nm-500nm. 3. A kind of multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1, characterized in that: dry etching is used to form nanorods with steep side walls in the GaN-based structure film, and the dry method The etching is ion beam etching, inductively coupled plasma etching or reactive ion etching. 4. A multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1, characterized in that: the height of the GaN nanorod array is 4 μm to 7 μm, the diameter is 200 nm to 350 nm, and the top of the nanorod The Ni nano-islands were removed using nitric acid. 5. A multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1, characterized in that: use KOH solution to repair the dry etching damage on the surface of GaN nanorods, after the KOH solution is repaired, the Chemical pollution left on the surface of GaN nanorods will cause leakage current, and aqua regia is used to remove surface chemical pollution. 6. A kind of multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1, characterized in that: n-type GaN re-growth is carried out on the GaN nanorod array to form nanometer-sized (1-100 ) non-polar face and (1-101) semi-polar face. 7. A multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1, characterized in that: the multi-quantum well layer is an InGaN/GaN multi-quantum well layer, and the thickness of the InGaN well layer is 4nm to 6nm , the thickness of the GaN barrier layer is 10nm-15nm, the period is 5-15, and the multi-quantum well layer has nanometer-sized (1-100) nonpolar planes and (1-101) semipolar planes. 8 . The method for preparing a multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 1 , wherein the P-type GaN layer is a Mg-doped GaN layer with a thickness of 50 nm to 100 nm. 9. A method for preparing a multi-wavelength GaN-based core-shell nanorod LED device structure according to any one of claims 1-8, characterized in that: comprising the steps of: S1, depositing a Ni layer on the substrate; S2, high-temperature ammonia annealing to form Ni nano-islands; S3, using dry etching to form a GaN nanorod array in the GaN-based structure film; S4, heating with nitric acid to remove the Ni nano-islands at the top of the GaN nanorods; S5, using KOH solution to repair the dry etching damage on the surface of GaN nanorods; S6, adopt aqua regia to remove the chemical pollution on the surface; S7. Perform Si-doped GaN regrowth on the GaN nanorod array to form (1-100) non-polar planes and (1-101) semi-polar planes with nanometer dimensions; S8. In the step S7, the GaN nanorods are clad with InGaN/GaN multiple quantum wells; S9, forming a P-type GaN layer on the multi-quantum well layer in the step S8. 10. the preparation method of a kind of multi-wavelength GaN-based core-shell nanorod LED device structure according to claim 9, is characterized in that, In the step S1, the sample is ultrasonically cleaned and dried in acetone, alcohol, and deionized water, and then a layer of Ni metal film with a thickness of 15nm to 35nm is coated on the surface by physical vapor deposition (PVD); In the step S2, the Ni nano-island formation method is as follows: the Ni/GaN/sapphire sample is placed in a high-temperature furnace at 800° C. to 900° C., and the ammonia gas is passed through for annealing for 10 minutes to 12 minutes. The flow rate of the ammonia gas is 700 to 900 ml. /min, to form a Ni nano-island structure used as a template. After annealing for a certain period of time, nitrogen gas is quickly introduced to remove the ammonia in the furnace and act as a protective gas. Finally, the sample is taken out after the sample is cooled; In the step S3, the method for forming the GaN nanorod array by dry etching is as follows: using chlorine gas and boron trichloride as etching gases, the flow rates are kept at 40-50 sccm and 5-8 sccm respectively, and the pressure in the cavity, The ICP power and RF power are set to 7.50×10 ^-9 Pa, 300W and 100W respectively; In the step S4, the method of heating the nitric acid to remove the Ni nano-islands on the top of the GaN nanorods is as follows: temperature: 80-100° C.; time: 5-10 min; In the step S5, the method for repairing the GaN nanorods with the KOH solution is: corrosion repair in a KOH solution with a concentration of 1-1.5M, the temperature is 80-10°C, and the time is 10-30 minutes; In the step S6, the method for removing chemical contamination on the surface with aqua regia is: put in aqua regia for 10-20 min, then ultrasonically clean and dry in deionized water; In the step S7, the n-type GaN nanorod re-growth method is as follows: TMGa is used as gallium source, _SiH4 is used as silicon source, _NH3 is used as nitrogen source, _H2 is used as carrier gas, and the growth temperature is 850°C-1000°C, The pressure is 400mbar, the V/III ratio is 800-1000, and the growth is 10-20min; the Si doping concentration is about 4-6×10 ¹⁸ cm ^-3 ; In the step S8, the growth method of the multi-quantum well layer is as follows: the growth temperature of the GaN barrier layer is 860°C, the growth temperature of the InGaN well layer is 750-800°C, the pressure of the reaction chamber is controlled at 400mbar, and the growth time of the barrier layer is 350°C. ~400s, TEGa flow rate is 280 SCCM, well layer growth time is 100~120s, TMIn flow rate is set to 1000 SCCM, TEGa flow rate is 280 SCCM, NH ₃ is always kept at 17 slm; In the step S9, the growth method of the P-type GaN layer is as follows: the thickness is 50nm-100nm, and the Mg doping concentration is about 1-2×10 ²⁰ cm ^-3 .