CN115312584A - Gallium nitride epitaxial wafer and preparation method thereof - Google Patents

Abstract

The present application belongs to the technical field of semiconductors, and discloses a gallium nitride epitaxial wafer and a preparation method in order to solve the problem of warpage of the existing epitaxial wafers easily caused by lattice mismatch or stress. The gallium nitride epitaxial wafer includes: a substrate, and a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum graded layer, a gallium nitride transition layer and a gallium nitride epitaxial layer that are sequentially arranged on the substrate. The low temperature AlN buffer layer and the high temperature AlN buffer layer can buffer the lattice mismatch between the substrate and the gallium nitride transition layer, the loose AlGaN layer can play a role in stress relief, and the aluminum graded layer can improve the stability of the gallium nitride layer above. Lattice matching, and gallium nitride epitaxy can further reduce the stress caused by lattice mismatch between the substrate and the epitaxial layer through the gallium nitride transition layer, and can prevent large-scale epitaxial wafers from being caused by lattice mismatch or stress. warping. The gallium nitride epitaxial layer can be prepared by CVD equipment.

Description

A gallium nitride epitaxial wafer and its preparation method

technical field

The application belongs to the technical field of semiconductors, and in particular relates to a gallium nitride epitaxial wafer and a preparation method thereof.

Background technique

Gallium Nitride (GaN), as the third-generation wide-bandgap semiconductor material, has high application value in the field of microwave devices due to its good physical properties and stability, and is more expected to be used in aviation, high-temperature radiation, radar, communication , automotive electronics and other aspects play an important role. GaN single crystal substrates are difficult to prepare, and are usually formed by heteroepitaxy. In this method, the epitaxial wafers are prone to warping due to lattice mismatch or stress when the size is large. Increase, the warping problem will be more prominent. Therefore, it is urgent to solve the problems of stress and warpage caused by lattice mismatch in the prior art.

Contents of the invention

In order to solve the warping problem of existing epitaxial wafers easily caused by lattice mismatch or stress, a gallium nitride epitaxial wafer and its preparation method are proposed.

In order to achieve the above object, the application adopts the following technical solutions:

A gallium nitride epitaxial wafer comprises a substrate on which a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum graded layer, a gallium nitride transition layer and a gallium nitride epitaxial layer are sequentially arranged.

Preferably, the loose AlGaN layer is formed by depositing an AlInGaN layer on the high-temperature AlN buffer layer and then depositing all indium.

Preferably, after forming the loose AlGaN layer, nitrogen gas is used to purge the loose AlGaN layer to remove all indium precipitated from the AlInGaN layer.

Preferably, the substrate includes a sapphire substrate; the thickness of the low-temperature AlN buffer layer is 10-15 nm, and the formation temperature is 500-650 degrees Celsius; the thickness of the high-temperature AlN buffer layer is 40-55 nm, and the formation temperature is 800 -1100 degrees Celsius; the thickness of the AlInGaN layer is 100-300nm; the thickness of the aluminum gradient layer is 80-150nm; the thickness of the gallium nitride transition layer is 50-100nm.

Preferably, the gallium epitaxial layer is composed of a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer, the total thickness of the gallium epitaxial layer is 1.5-2 microns, wherein the thickness of the first gallium nitride epitaxial layer is 100- 180nm.

Based on the above-mentioned preparation method of a gallium nitride epitaxial wafer, it includes the following steps: setting a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, and an AlInGaN layer on the substrate in sequence, and depositing all the indium in the AlInGaN layer to form a loose AlGaN layer , on the loose AlGaN layer, sequentially deposit an aluminum graded layer, a gallium nitride transition layer and a gallium nitride epitaxial layer.

Concrete described preparation method comprises the following steps:

Step S1: putting the substrate into the reaction chamber;

Step S2: introducing an aluminum source and a nitrogen source into the reaction chamber, and controlling the temperature in the reaction chamber to a first temperature, and forming a low-temperature AlN buffer layer on the substrate;

Step S3: increasing the temperature in the reaction chamber to a second temperature, and continuing to feed aluminum and nitrogen sources to form a high-temperature AlN buffer layer on the low-temperature AlN buffer layer; the second temperature is greater than the first temperature;

Step S4: keep the aluminum source and the nitrogen source connected, and feed the indium source and the gallium source into the reaction chamber to form an AlInGaN layer on the high-temperature AlN buffer layer; then stop the aluminum source, nitrogen source, indium source and gallium at the same time The source is introduced, and the loose AlGaN layer is formed after all the indium in the AlInGaN layer is precipitated, and the surface of the loose AlGaN layer is purged with nitrogen gas to remove all the indium precipitated from the AlInGaN layer;

Step S5: controlling the pressure and temperature in the reaction chamber to remain constant, reducing the introduction of aluminum sources, and forming an aluminum gradient layer on the surface of the loose AlGaN layer;

Step S6: stop feeding the aluminum source, and form a gallium nitride transition layer on the surface of the aluminum gradient layer;

Step S7: forming a GaN epitaxial layer on the GaN transition layer.

Preferably, the gallium nitride epitaxial layer includes: a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer; the temperature and pressure in the reaction chamber during the growth stage of the first gallium nitride epitaxial layer are both higher than that of the first gallium nitride epitaxial layer The temperature and pressure in the reaction chamber during the growth stage of the GaN epitaxial layer, but the growth rate of GaN in the growth stage of the first GaN epitaxial layer is less than that in the growth stage of the second GaN epitaxial layer Nitride Gallium growth rate.

Specifically, the step S2: the nitrogen source is ammonia gas, the aluminum source is trimethylaluminum, the first temperature is 500-650 degrees Celsius, and the thickness of the low-temperature AlN buffer layer is 10-15 nm;

Step S3: the first temperature is 800-1100 degrees Celsius, and the thickness of the high-temperature AlN buffer layer is 40-55nm; Step S4: the gallium source is trimethylgallium, the indium source is trimethylindium, and the pressure in the reaction chamber is 150 -200mbar, the temperature is 1050-1100 degrees Celsius, while suspending the introduction of aluminum source, nitrogen source, indium source and gallium source for 30-60S; control the introduction of nitrogen gas and the direction of nitrogen blowing, and droplet indium from the surface of the AlInGaN layer Blow away, and collect the droplet indium blown away in the recovery device.

A low-temperature AlN buffer layer is formed next to the substrate. When the fine and dense grain-shaped aluminum nitride forms a low-temperature AlN buffer layer, there will be a certain gap between the island-shaped grains; in order to reduce the surface energy, the grains will deformation, the gap is closed, and a high-temperature AlN buffer layer is set on the low-temperature AlN buffer layer. The ability to form a dense high-temperature AlN buffer layer at a high temperature can improve the formation quality of the epitaxial wafer.

The microstructure of the formed loose AlGaN layer presents an irregular porous structure, which can play a role in stress relief, and the aluminum graded layer can improve the lattice matching of the upper gallium nitride layer. Depositing a GaN transition layer between the Al gradient layer and the GaN epitaxial layer can further reduce the stress caused by the lattice mismatch between the substrate and the epitaxial layer, and prevent large-scale epitaxial wafers from Warpage due to lattice mismatch or stress.

It is worth noting that the "low temperature" and "high temperature" in the "low temperature AlN buffer layer" and "high temperature AlN buffer layer" described in this application are adopted for the convenience of distinguishing the AlN buffer layers formed at two different temperatures. The name of the high temperature and low temperature here does not refer to the temperature range. The "low-temperature AlN buffer layer" and "high-temperature AlN buffer layer" can also be replaced by "the first AlN buffer layer" and "the second AlN buffer layer", and the formation temperature of the first AlN buffer layer is lower than that of the second AlN buffer layer. formation temperature.

Description of drawings

FIG. 1 is a schematic cross-sectional structure diagram of a gallium nitride epitaxial wafer structure according to an embodiment of the present application.

FIG. 2 is a schematic diagram of a growth process for preparing a gallium nitride epitaxial layer according to an embodiment of the present application.

Illustration: 1-substrate, 2-low temperature AlN buffer layer, 3-high temperature AlN buffer layer, 4-loose AlGaN layer, 5-aluminum gradient layer, 6-gallium nitride transition layer, 7-gallium nitride epitaxial layer .

Detailed ways

The above solution will be further described below in conjunction with specific embodiments. It should be understood that these examples are used to illustrate the present application and not limit the scope of the present application. The implementation conditions adopted in the examples can be further adjusted as the conditions of specific manufacturers, and the implementation conditions not indicated are usually the conditions in routine experiments.

Embodiment 1. A gallium nitride epitaxial wafer as shown in FIG. 1 , including a substrate 1, on which a low-temperature AlN buffer layer 2, a high-temperature AlN buffer layer 3, a loose AlGaN layer 4, and an aluminum gradient layer are sequentially arranged. Layer 5, GaN transition layer 6 and GaN epitaxial layer 7.

Gallium nitride epitaxy can play a role in stress relief through the loose AlGaN layer, and the aluminum graded layer can improve the lattice matching of the upper gallium nitride layer, and the gallium nitride transition layer can reduce the lattice between the substrate and the epitaxial layer The stress generated by the mismatch can prevent large-scale epitaxial wafers from warping due to lattice mismatch or stress. The gallium nitride epitaxial layer can be prepared by CVD equipment.

Embodiment 2. A method for preparing a gallium nitride epitaxial wafer, comprising the following steps: setting a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, and an AlInGaN layer on the substrate in sequence, and depositing all the indium in the AlInGaN layer to form a loose substrate. AlGaN layer, and use nitrogen to blow the surface of the loose AlGaN layer, and then sequentially deposit aluminum gradient layer, gallium nitride transition layer and gallium nitride epitaxial layer on the loose AlGaN layer.

A preferred embodiment: the schematic diagram of the growth process for the preparation of gallium nitride epitaxial layer is shown in FIG. 2 .

First, put the substrate into the reaction chamber, where the substrate can be a sapphire substrate. Before the substrate is put into the reaction chamber, a cleaning step is performed first. Cleaning can remove contamination particles and impurities on the surface of the substrate. Cleaning includes wet cleaning and dry cleaning. Wet cleaning is performed first, using deionized water to clean the surface of the substrate, and then dry cleaning, such as nitrogen blowing the surface of the substrate, drying the substrate to reduce moisture The possible impact of the gas;

Secondly, control the temperature in the reaction chamber at 500-650 degrees Celsius, feed aluminum source and nitrogen source to form a low-temperature AlN buffer layer, the thickness of the low-temperature AlN buffer layer is 10-15nm; then increase the temperature in the reaction chamber to 800 Between -1100 degrees Celsius, and continue to feed aluminum source and nitrogen source to form a high-temperature AlN buffer layer, the thickness of the high-temperature AlN buffer layer is 40-55nm, wherein the aluminum source is trimethylaluminum, and the nitrogen source is ammonia gas; In the present invention, a low-temperature AlN buffer layer is first formed on the surface of the substrate. Since the sapphire substrate is made of alumina, it has better lattice matching with AlN, and the stress between AlN and the substrate is smaller, and at a lower temperature The AlN layer formed below, due to the temperature range between 500-650 degrees Celsius, forms a plurality of fine and dense grain-shaped aluminum nitride. When forming the aluminum nitride layer, there will be a certain gap between the island-shaped grains. Gaps, forming a polycrystalline AlN layer. A dense high-temperature aluminum nitride layer can be formed at a high temperature as a single-crystal AlN layer with a dense structure, which can improve the formation quality of epitaxial wafers.

After the high-temperature AlN buffer layer is formed, the aluminum source and the nitrogen source are maintained, and the indium source and the gallium source are introduced into the reaction chamber to form an AlInGaN layer on the high-temperature AlN buffer layer. The gallium source is trimethylgallium, indium The source is trimethyl indium, the pressure in the reaction chamber is 150-200mbar, the temperature is 1050-1100 degrees centigrade, and the thickness of the formed AlInGaN layer is 100-300nm. The AlInGaN layer is formed for the subsequent formation of a loose AlGaN layer. When forming an AlInGaN layer with a certain thickness, when the thickness is greater than 300nm, the indium in the AlInGaN layer is difficult to precipitate at high temperature, and it is easy to form an In-AlGaN alloy. The thickness is less than 100nm After the AlInGaN layer is formed with a loose AlGaN layer, it is difficult to better achieve stress relief through the loose structure. Therefore, when forming the AlInGaN layer in the present invention, the thickness is controlled within the range of 100-300nm, which can facilitate the formation of the loose AlGaN layer and utilize its loose structure to relieve stress.

Then stop the feeding of aluminum source, nitrogen source, indium source and gallium source at the same time, the time of stopping feeding is 30-60S, while stopping feeding reaction source gas, because the temperature in the reaction chamber is higher, at the deposition temperature Nearby (above 1000 degrees Celsius), the In in it is easy to precipitate, and the indium will be precipitated from the AlInGaN during the time when the feed is suspended, and all the indium in the AlInGaN layer can be precipitated during this period of time;

Controlling the pressure and temperature in the reaction chamber to be constant, reducing the introduction of the aluminum source, and forming an aluminum gradient layer;

Stop feeding the aluminum source, and form a gallium nitride transition layer on the surface of the aluminum gradient layer;

Subsequently, a GaN epitaxial layer is formed on the GaN transition layer.

In a preferred embodiment, after all the indium in the AlInGaN layer is precipitated, the AlInGaN layer is purged with nitrogen gas, and the introduction of nitrogen gas and the direction of blowing nitrogen gas are controlled, so that the precipitated indium in the form of droplets is removed from the surface of the AlInGaN layer. Blow away, and collect the droplet indium blown away in the recovery device to prevent contamination of other layer structures. Due to the precipitation of indium, it will adhere to the surface of the loose AlGaN layer to form droplet-shaped indium, which is easy to form an alloy layer with the subsequently formed indium structure during subsequent deposition. The GaN layer forms an In-GaN alloy. After the alloy layer is formed, on the one hand, it is difficult to separate the epitaxial wafer from the substrate. On the other hand, the presence of indium will change the conductivity of the GaN layer, whether it is used as an LED material or a laser substrate. Materials will affect the luminous performance.

The AlInGaN layer is formed on the high-temperature AlN layer. When forming AlN, the aluminum source and the nitrogen source are passed in. After forming a high-temperature AlN layer with a predetermined thickness, the aluminum source and the nitrogen source are kept flowing in and fed to the reaction. Indium source and gallium source are passed into the chamber, wherein the aluminum source is trimethylaluminum, the gallium source is trimethylgallium, the indium source is trimethylindium, the nitrogen source is NH ₃ , and the pressure in the reaction chamber is 150- 200mbar, the temperature is 1050-1100 degrees Celsius, form the AlInGaN layer, and then stop the feed of the aluminum source, nitrogen source, indium source and gallium source at the same time, and the pause time is 30-60S.

Among them, after the AlInGaN layer is deposited, the growth is suspended, and the suspension growth time is 30-60S. Because at high temperature (the temperature for forming the AlInGaN layer is 1050-1100 degrees Celsius, the temperature will be maintained near the growth temperature during the suspension of growth) Indium is easy to precipitate , the precipitated indium will adhere to the surface of the AlInGaN layer. After the indium in AlInGaN is precipitated, the AlInGaN layer will form a loose AlGaN layer structure. By controlling the growth pause time, all the indium in the AlInGaN layer will be precipitated, so that a loose AlGaN layer can be formed. layer, because of its loose structure, the loose AlGaN layer can be used as a stress buffer layer to achieve stress buffering.

After suspending the feed of the reaction source for a preset time, control the temperature in the reaction chamber to be 1150-1200°C (the formation temperature is higher than the temperature when forming the AlInGaN layer), and feed the aluminum source, gallium source and nitrogen source into the reaction chamber, Control the input of aluminum source, gallium source and nitrogen source to form an Al _x Ga _1-x N aluminum graded layer, where x is the content of Al, 0≤x<1, and continuously reduce the Al source during the input process The input amount until the aluminum source is completely stopped, and the GaN layer is formed when the aluminum source is completely stopped. Methylaluminum, wherein the flow rate of trimethylaluminum is 150-200sccm, the nitrogen source is ammonia gas, the time from reducing the introduction of aluminum source to no introduction of aluminum source is 10-25min, and the thickness of the formed AlxGa1-xN layer is 80- 150nm. After the formation of the loose AlGaN layer, although the stress can be relieved, due to the loose gaps inside the AlGaN layer, when the gallium nitride layer is epitaxially formed above it, the crystal quality of the epitaxial layer will be affected due to the poor crystal quality of the loose structure below. , will have a great impact on the quality of the epitaxial wafer. Increasing the formation temperature of the Al _x Ga _1-x N aluminum graded layer can improve the crystallization quality of the aluminum graded layer, and reduce the aluminum content. The formed aluminum graded layer is the same as the above The gallium nitride epitaxial layer to be formed has good lattice matching, preventing stress caused by lattice mismatch.

After gradually reducing the amount of aluminum source introduced until no aluminum source is introduced at all, when the aluminum source is not introduced, the temperature and pressure in the reaction chamber are continuously maintained, and the nitrogen source and gallium source are continuously introduced to form a transition layer of gallium nitride. There is no need to change the reaction conditions, just continue to maintain the reaction conditions and continue to feed the reaction source. After stopping the feed of the aluminum source, keep the time at 2-10min to form a 50-100nm thick gallium nitride transition layer. This part The gallium nitride transition layer is mainly to improve the crystallization quality of the subsequent gallium nitride epitaxial wafer. Since it is formed under high temperature and high pressure, and the epitaxial speed is slow, a certain thickness of the gallium nitride transition layer can improve the crystallization of the upper epitaxial wafer. The quality is enough, and there is no need to form a thicker thickness, which can improve the effect of production.

Then a gallium nitride epitaxial layer is formed on the gallium nitride transition layer, and the subsequent steps of forming the gallium nitride epitaxial layer can refer to the specific steps of the invention.

A GaN epitaxial layer with a total thickness of 1.5-2 microns is formed on the GaN transition layer. This step includes: the formation of the GaN epitaxial layer includes two stages,

The first gallium nitride epitaxial layer and the second gallium nitride epitaxial layer are formed, and the specific formation process is as follows:

The first stage: control the temperature of the reaction chamber, the temperature of the reaction chamber is controlled at 1080-1150 degrees Celsius, the gallium source and the nitrogen source are introduced, the gallium source is trimethylgallium, the flow rate of trimethylgallium is 150-200sccm, and the nitrogen source For NH ₃ , control the flow rate of gallium source and nitrogen source, and control the pressure of the reaction chamber, the pressure is controlled at 300-350mbar, the growth rate of GaN is controlled at 10-15nm/min, and the growth time is controlled. In the first stage of growth The thickness of GaN is 100-180nm. In the first stage, by controlling the reaction chamber to be in a state of high pressure and high temperature for growth, and growing GaN at a slow speed, a dense GaN layer with better lattice constant matching quality can be formed on the transition GaN layer, which can further reduce the above. The stress between the epitaxial layer and the underlying layer structure, and improve the quality of the overall external GaN. However, the growth is slow at this stage, and the growth thickness should not be too thick, which can save the growth time.

In this method, when forming GaN epitaxial wafers, two-stage formation is adopted. In the first stage, the temperature and pressure are relatively high, and the growth rate is relatively slow, so that a high-quality bottom epitaxial wafer can be formed.

The growth speed is controlled in the second stage, thicker epitaxial wafers can be formed quickly, and because the quality of the first layer of epitaxial wafers below is higher, the quality of the upper epitaxial wafers is also high, and the stress is small, preventing warpage , Improve the yield of epitaxial wafer products.

Beneficial effects of the present invention: 1. A low-temperature AlN buffer layer and a high-temperature AlN buffer layer are first formed on the substrate, and the two-layer buffer layer can relieve the stress caused by lattice mismatch between the upper GaN layer and the substrate, and then Forming a loose AlGaN layer on the high-temperature AlN buffer layer can further buffer the stress. The loose AlGaN layer is formed after indium is deposited from the AlInGaN layer. The liquid indium on the surface of the loose AlGaN layer is purged to remove the liquid indium on the surface;

2. Raising the temperature on the loose AlGaN layer to form an aluminum gradient layer can improve the crystallization quality of the upper layer structure and prevent more crystal defects caused by the loose layer;

3. After the aluminum graded layer, keeping the formation conditions unchanged, a gallium nitride transition layer is formed. The gallium nitride transition layer formed under high temperature and high pressure has good crystal quality, which can be improved when forming a gallium nitride epitaxial layer above. The crystalline quality of the epitaxial layer, and due to the stress relief of the two buffer layers and the loose AlGaN layer, can well reduce the stress of the epitaxial wafer and prevent the formation of the epitaxial wafer from warping.

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present application, and the purpose is to enable those familiar with this technology to understand the content of the present application and implement it accordingly, and not to limit the protection scope of the present application. All equivalent changes or modifications made according to the spirit of the present application shall fall within the protection scope of the present application.

Claims (10)

1. A gallium nitride epitaxial wafer comprising a substrate, characterized in that: the substrate is sequentially provided with a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum gradual change layer, a gallium nitride transition layer and a gallium nitride epitaxial layer.

2. A gallium nitride epitaxial wafer according to claim 1, wherein: the loose AlGaN layer is formed by depositing an AlInGaN layer on the high-temperature AlN buffer layer and then precipitating all indium.

3. A gallium nitride epitaxial wafer according to claim 2, wherein: after the loose AlGaN layer is formed, the loose AlGaN layer is purged with nitrogen gas to remove all indium precipitated from the AlInGaN layer.

4. A gallium nitride epitaxial wafer according to claim 2, wherein: the substrate comprises a sapphire substrate; the thickness of the low-temperature AlN buffer layer is 10-15nm, and the forming temperature is 500-650 ℃; the thickness of the high-temperature AlN buffer layer is 40-55nm, and the forming temperature is 800-1100 ℃; the thickness of the AlInGaN layer is 100-300nm; the thickness of the aluminum gradient layer is 80-150nm; the thickness of the gallium nitride transition layer is 50-100nm.

5. A gallium nitride epitaxial wafer according to any one of claims 1 to 4, wherein: the gallium epitaxial layer consists of a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer, the total thickness of the gallium epitaxial layer is 1.5-2 microns, and the thickness of the first gallium nitride epitaxial layer is 100-180nm.

6. A preparation method of a gallium nitride epitaxial wafer is characterized by comprising the following steps: depositing a low-temperature AlN buffer layer, a high-temperature AlN buffer layer, a loose AlGaN layer, an aluminum gradual change layer, a gallium nitride transition layer and a gallium nitride epitaxial layer on the substrate in sequence.

7. A method for producing a gallium nitride epitaxial wafer according to claim 6, wherein: the preparation method comprises the following steps: the method comprises the steps that a low-temperature AlN buffer layer, a high-temperature AlN buffer layer and an AlInGaN layer are sequentially arranged on a substrate, indium in the AlInGaN layer is completely separated out to form a loose AlGaN layer, and an aluminum gradient layer, a gallium nitride transition layer and a gallium nitride epitaxial layer are sequentially deposited on the loose AlGaN layer.

8. A method for producing a gallium nitride epitaxial wafer according to claim 6, wherein: the preparation method comprises the following steps:

step S1: placing a substrate into a reaction chamber;

step S2: introducing an aluminum source and a nitrogen source into the reaction chamber, controlling the temperature in the reaction chamber to be a first temperature, and forming a low-temperature AlN buffer layer on the substrate;

and step S3: increasing the temperature in the reaction chamber to a second temperature, and continuously introducing an aluminum source and a nitrogen source to form a high-temperature AlN buffer layer on the low-temperature AlN buffer layer; the second temperature is greater than the first temperature;

and step S4: keeping introducing an aluminum source and a nitrogen source, introducing an indium source and a gallium source into the reaction chamber, and forming an AlInGaN layer on the high-temperature AlN buffer layer; then stopping introducing an aluminum source, a nitrogen source, an indium source and a gallium source at the same time, forming a loose AlGaN layer after indium in the AlInGaN layer is completely separated out, and purging the surface of the loose AlGaN layer by using nitrogen to remove the indium completely separated out from the AlInGaN layer;

step S5: controlling the pressure and the temperature in the reaction chamber to be unchanged, reducing the introduction of an aluminum source, and forming an aluminum gradient layer on the surface of the loose AlGaN layer;

step S6: stopping introducing an aluminum source, and forming a gallium nitride transition layer on the surface of the aluminum gradual change layer;

step S7: and forming a gallium nitride epitaxial layer on the gallium nitride transition layer.

9. A method for preparing a gallium nitride epitaxial wafer according to claim 6, wherein: the gallium nitride epitaxial layer includes: a first gallium nitride epitaxial layer and a second gallium nitride epitaxial layer; the temperature and the pressure in the reaction chamber in the growth stage of the first gallium nitride epitaxial layer are both higher than the temperature and the pressure in the reaction chamber in the growth stage of the second gallium nitride epitaxial layer, but the growth speed of gallium nitride in the growth stage of the first gallium nitride epitaxial layer is lower than the growth speed of gallium nitride in the growth stage of the second gallium nitride epitaxial layer.

10. A method for producing a gallium nitride epitaxial wafer according to claim 8, wherein:

step S2: the nitrogen source is ammonia gas, the aluminum source is trimethyl aluminum, the first temperature is 500-650 ℃, and the thickness of the formed low-temperature AlN buffer layer is 10-15nm;

and step S3: the first temperature is 800-1100 ℃, and the thickness of the formed high-temperature AlN buffer layer is 40-55nm;

and step S4: the gallium source is trimethyl gallium, the indium source is trimethyl indium, the pressure in the reaction chamber is 150-200mbar, the temperature is 1050-1100 ℃, and simultaneously 30-60S of introducing the aluminum source, the nitrogen source, the indium source and the gallium source is suspended;

controlling the introduction of nitrogen and the direction of the nitrogen, blowing the droplet indium from the surface of the AlInGaN layer, and collecting the blown droplet indium in a recovery device.

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