CN109023515A - Prepare GaN substrate from separation method - Google Patents

Abstract

The invention discloses it is a kind of prepare gallium nitride substrate from separation method, step include: on a sapphire substrate growth thickness range at 1-5 microns and the gallium oxide film that is evenly distributed；Surface layer part nitridation is carried out to film in ammonia atmosphere, forms gallium nitride/gallium oxide laminated film of porous web trellis structure distribution；The halide gas phase epitaxial growth that gallium nitride thick film is carried out on the laminated film, obtains low stress high-quality gallium nitride thick film；After the completion of extension, it is cooled to room temperature, natural separation between epitaxial nitride gallium thick film and substrate obtains self-support gallium nitride substrate material.

Description

Self-separation method for preparing GaN substrate

technical field

The invention relates to a self-separation method for preparing a GaN substrate, which belongs to the technical field of semiconductor materials.

Background technique

Group III-V nitride materials (also known as GaN-based materials) mainly composed of GaN, InGaN, and AlGaN alloy materials are new semiconductor materials that have attracted much attention in the world in recent years. GaN-based materials are direct bandgap wide bandgap semiconductor materials with continuously variable direct bandgap between 1.9-6.2eV, excellent physical and chemical stability, high saturation electron drift velocity, high breakdown field strength and high thermal conductivity It has important applications in the preparation of short-wavelength semiconductor optoelectronic devices and high-frequency, high-voltage, and high-temperature microelectronic devices. It can be used to manufacture light-emitting devices such as blue, purple, and ultraviolet bands, detectors, high-temperature, high-frequency, High-field high-power devices, field emission devices, radiation-resistant devices, piezoelectric devices, etc.

The melting point of GaN single crystal is as high as 2300°C, and the decomposition point is around 900°C. The growth requires an extreme physical environment, and large-sized GaN single crystal cannot be obtained by traditional crystal growth methods. Therefore, most GaN thin films are epitaxially obtained on heterogeneous substrates. GaN currently used in semiconductor technology is mainly prepared on substrates such as sapphire, SiC or Si by heteroepitaxy. In heteroepitaxy, due to the large lattice mismatch and thermal expansion coefficient mismatch between the GaN material and the heterogeneous substrate, and whether mechanical polishing or laser lift-off is used to remove the heterogeneous substrate, the stress will still exist in the GaN In the material, there will be stress in the obtained GaN epitaxial layer and generate a dislocation density on the order of 10 ⁸ -10 ⁹ /cm ² . These defects reduce the quality of the epitaxial layer and limit the thermal conductivity and electron saturation of the GaN material. Parameters such as speed greatly affect the reliability and yield of the device, and the huge stress will cause GaN thick film and heterogeneous substrate to break into pieces, so it cannot be applied. Therefore, the use of homoepitaxy is beneficial to reduce the stress in the epitaxial film and improve the quality and yield.

GaN substrate growth mainly includes gas phase method and liquid phase method. Liquid-phase methods include high-pressure nitrogen solution method, sodium flux method, and ammonothermal method; gas-phase methods include gas-phase transport method and halide vapor-phase epitaxy method, etc. At present, the main method to obtain high-quality GaN self-supporting substrates and realize mass production is to use methods such as lateral epitaxy and suspension epitaxy, supplemented by halide vapor phase epitaxy and high-rate epitaxy to grow thick films, and finally remove the original substrate, so that A self-supporting GaN substrate material with low dislocation density is obtained. So far, self-supporting GaN substrates obtained by adopting various techniques and supplemented by halide vapor phase epitaxy have a dislocation density of less than 10 ⁶ cm ^-2 and an area of 2 inches. But it is still far from meeting the needs of practical applications.

Gallium oxide (Eg=4.8-4.9eV), as a new type of ultra-wide bandgap semiconductor, has the advantages of high conductivity, high breakdown field strength, etc., and has high transparency in both visible and ultraviolet light regions. The (100) dissociation plane of β-Ga ₂ O ₃ will undergo surface reconstruction under the nitriding action of high-temperature NH ₃ atmosphere, and the surface reconstruction will produce a surface that matches the GaN lattice, which can be used as a buffer layer for subsequent epitaxial growth of GaN thick film. This homogeneous substrate epitaxial growth will significantly reduce the stress and dislocation density in thick films and improve the quality of GaN materials.

Contents of the invention

The object of the present invention is to realize a self-separation method of a self-supporting gallium nitride substrate.

The technical scheme that the present invention takes is:

A self-separation method for preparing a GaN substrate, the steps comprising:

(1) On the sapphire substrate, a Ga ₂ O ₃ thin film with a thickness ranging from 1 to 5 microns and uniform distribution is grown by halide vapor phase epitaxy;

(2) Partially nitriding the Ga ₂ O ₃ film in an ammonia atmosphere, the surface of the Ga ₂ O ₃ film is nitrided to form a GaN single crystal layer with a porous grid structure, and the thickness of the GaN single crystal layer is the original Ga ₂ O ₃ 10%-40% of the film thickness to obtain a GaN/Ga ₂ O ₃ composite film;

(3) Halide vapor phase epitaxial growth of a GaN thick film on a GaN/Ga ₂ O ₃ composite film to obtain a GaN thick film, the thickness of the GaN thick film is greater than 10 microns;

(4) After the epitaxy is completed, the temperature is lowered to room temperature, and the epitaxial GaN thick film is naturally separated from the substrate to obtain a self-supporting GaN thick film.

Preferably, in step (2), the Ga ₂ O ₃ thin film prepared in step (1) is placed in a high-temperature tube furnace, and nitrided for 2-5 hours under an ammonia atmosphere, and the nitriding time is the same as the required nitriding time. The thickness of the layer is related to the thickness of the original gallium oxide, the temperature range is 950-1100°C, and the GaN/Ga ₂ O ₃ composite structure film with porous grid distribution is obtained, and the ammonia gas flow rate is 100-5000 sccm.

Preferably, in step (2), the Ga ₂ O ₃ thin film prepared in step (1) is placed in a high-temperature tube furnace, and nitrided for 2-5 hours in an ammonia-nitrogen mixed gas atmosphere, and the nitriding time and the required The thickness of the nitride layer is related to the thickness of the original gallium oxide. The temperature range is 950-1100°C, and the GaN/Ga ₂ O ₃ composite structure film with porous grid distribution is obtained. 1.

Preferably, in step (1), the substrate is placed in a halide vapor phase epitaxy growth system. In the low temperature region, metal Ga reacts with HCl or Cl to generate _GaCl as a gallium source at a temperature of 800-900° C.; in the high temperature growth region , O ₂ is used as the oxygen source, GaCl and O ₂ are mixed and reacted to obtain a Ga ₂ O ₃ film, the temperature in the high temperature zone is 800-1050 ° C, the pressure is 1 atmosphere, and the O ₂ /Ga input flow ratio is 1.5-15.

Preferably, uniform distribution in step (1) means that the Ga ₂ O ₃ thickness uniformity is above 90%.

Preferably, in step (3), the substrate on which the GaN/Ga ₂ O ₃ composite thin film is grown is placed in a halide vapor phase epitaxy growth system, and in a low temperature region, metal Ga reacts with HCl or Cl ₂ to generate GaCl as a gallium source, The temperature is 800-900°C; in the high-temperature growth zone, ammonia gas is used as a nitrogen source, and GaCl and NH ₃ are mixed and reacted to form a thick GaN film. The temperature in the high-temperature zone is 950-1100°C, the pressure is 1 atmosphere, and the growth time is greater than or equal to 0.5h, the GaN thick film thickness is above 10 microns.

Occasionally, after cooling down to room temperature in step (4), the epitaxial GaN thick film is not completely separated from the substrate. At this time, hydrofluoric acid can be used to etch the GaN/Ga ₂ O ₃ composite film. ₂ O ₃ , to obtain a free-standing GaN thick film.

In the present invention, the thickness _of the _Ga2O3 film is controlled at 1-5 microns, the surface layer is nitrided, and a gridded GaN/ _Ga2O3 composite film can be formed, and the GaN single crystal will present a grid _- like distribution in the film state, the thickness of the GaN single crystal layer obtained by nitridation is about 10%-30% of the thickness of the original Ga ₂ O ₃ film. Halide vapor phase epitaxial growth of thick-film GaN on the above-mentioned substrate containing GaN single crystal layer can obtain low-stress and high-quality GaN thick-film material. Nitriding the gallium oxide film to form nitride can be used as a homoepitaxial layer of gallium nitride, and it can also prevent the oxygen in the Ga ₂ O ₃ film from diffusing into GaN to reduce the quality of the material during the subsequent halide vapor phase epitaxy. Due to the gallium nitride grid structure formed by gallium oxide nitride, the interface contact with gallium oxide is reduced and the internal stress of the gallium nitride layer is released. After the epitaxy is completed, the GaN thick film and sapphire Self-separation of the substrate to obtain a self-supporting GaN substrate material. If the epitaxial thin film and sapphire are not completely separated, the auxiliary method of hydrofluoric acid etching can be further used to obtain a self-supporting GaN thick film. The HVPE growth and nitriding of the above-mentioned gallium oxide thin film and the HVPE growth of GaN thick film can be completed in situ in the HVPE system; the HVPE growth of gallium oxide can also be carried out first, and after the sample is taken out, it is nitrided in the annealing furnace, and then placed in the annealing furnace. Into the HVPE system for GaN thick film growth, after cooling down to get a self-supporting GaN thick film. The above in-situ epitaxial gallium oxide, nitridation and re-epitaxy processes are simple and complete at one time, and are also conducive to preventing unnecessary impurities from being introduced. The grid-shaped GaN/Ga ₂ O ₃ composite substrate formed in this patent is placed in a halide vapor phase epitaxy reaction chamber to epitaxially GaN thick film, which is similar to lateral epitaxial growth. For specific implementation methods, please refer to the patent: "Lateral Epitaxy Technology Growth High-quality gallium nitride thin film", patent number ZL021113084.1), can obtain high-quality and low dislocation density GaN thick film, and it is easier to achieve self-stripping.

Description of drawings

FIG. 1 is an SEM image of the surface morphology of the gallium oxide thin film in Example 1 of the present invention after partial nitriding.

Fig. 2 is a schematic diagram of an embodiment of the present invention, a cross-sectional SEM image of a GaN thick film grown by halide vapor phase epitaxy on a GaN/Ga ₂ O ₃ composite film substrate. It can be seen from the figure that a clear separation occurs between the epitaxial GaN thick film and the GaN _{/ Ga2O3} composite thin film.

FIG. 3 is an X-ray diffraction analysis diagram of the surface layer of the gallium oxide thin film in Example 1 after partial nitriding, showing that the surface layer is entirely gallium nitride.

Detailed ways

Example 1

The self-separation method for preparing GaN substrates, the steps include:

(1) Clean and treat the substrate sapphire, and use halide vapor phase epitaxy to grow uniformly distributed Ga ₂ O ₃ thin films on the sapphire substrate. The reaction system mainly includes two temperature zones. In the low temperature zone, metal gallium reacts with HCl to form GaCl as Gallium source, the temperature is controlled at 850°C; oxygen is used as the oxygen source, and GaCl and _O2 are mixed and reacted in the high-temperature growth area to obtain a gallium oxide film, and the temperature in the high-temperature area is 1000°C. The pressure is 1 atmosphere, and the O ₂ /Ga input flow ratio is 3. By adjusting the growth time, gallium oxide films with different thicknesses can be obtained. The growth thickness of the Ga ₂ O ₃ film is controlled to be 3 microns, and the thickness uniformity of the Ga ₂ O ₃ is above 90%.

(2) Place the Ga ₂ O ₃ thin film substrate in a high-temperature tubular quartz furnace, pass through ammonia gas, and nitride it at a specific temperature for a certain period of time to obtain a partially nitrided GaN/Ga ₂ O ₃ composite thin film. Ammonia gas flow: 3000 sccm, temperature: 1050°C, nitriding time: 3h. The thickness of the GaN layer formed by nitriding is about 1.2 microns, and the porous grid-like GaN single crystal layer/Ga ₂ O ₃ composite film is formed by nitriding, as shown in Figure 1 and Figure 3, the visible surface is porous grid-like results, X-ray Diffraction analysis shows that the surface layer is entirely GaN.

(3) Halide vapor phase epitaxy growth of GaN thick film on the GaN/Ga ₂ O ₃ composite film to obtain GaN thick film; after nitriding is completed, in the low temperature region of the halide vapor phase epitaxy system, metal Ga reacts with HCl to form GaCl is used as the gallium source, and the temperature is 850°C; in the high-temperature growth area, ammonia gas is used as the nitrogen source, and GaCl and NH ₃ are mixed and reacted to obtain a GaN thick film. The temperature in the high-temperature area is 1050°C; the pressure is 1 atmosphere, and the growth time is controlled. , so that the thickness of the GaN thick film is above 10 microns.

(4) After the epitaxy is completed, the temperature is lowered to room temperature, and the epitaxial GaN thick film and the substrate can be separated naturally to obtain a self-supporting GaN thick film, as shown in Figure 2.

Example 2

The self-separation method for preparing GaN substrates, the steps include:

(1) Clean and treat the substrate sapphire, and use halide vapor phase epitaxy to grow a uniformly distributed Ga ₂ O ₃ film on the sapphire substrate. The reaction system mainly includes two temperature zones. In the low temperature zone, metal gallium reacts with Cl ₂ to form GaCl As a gallium source, the temperature is 800°C; oxygen is used as an oxygen source, and GaCl and _O2 are mixed and reacted in the high-temperature growth area to obtain a gallium oxide film, and the temperature in the high-temperature area is 800°C. The pressure is 1 atmosphere, and the O ₂ /Ga input flow ratio is 1.5. By adjusting the growth time, gallium oxide films with different thicknesses can be obtained. The growth thickness of the Ga ₂ O ₃ film is controlled to be 1 micron, and the thickness uniformity of the Ga ₂ O ₃ is above 90%.

(2) Place the Ga ₂ O ₃ thin film substrate in a high-temperature tubular quartz furnace, pass through ammonia gas, and nitride it at a specific temperature for a certain period of time to obtain a partially nitrided GaN/Ga ₂ O ₃ composite thin film. Ammonia gas flow: 100 sccm, temperature: 950°C, nitriding time: 5h. The thickness of the GaN layer formed by nitriding is about 0.1 micron, and the porous grid-like GaN single crystal layer/Ga ₂ O ₃ composite thin film is formed by nitriding.

(3) Halide vapor phase epitaxy growth of GaN thick film on GaN/Ga ₂ O ₃ composite film to obtain GaN thick film; after nitriding is completed, metal Ga reacts with Cl ₂ in the low temperature area of the halide vapor phase epitaxy system Generate GaCl as the gallium source at a temperature of 800°C; in the high-temperature growth zone, ammonia gas is used as the nitrogen source, GaCl and NH ₃ are mixed and reacted to obtain a GaN thick film, the temperature in the high-temperature zone is 950°C; the pressure is 1 atmosphere, and the growth is controlled time, the thickness of the GaN thick film is above 10 microns.

(4) After the epitaxy is completed, the temperature is lowered to room temperature, and the epitaxial GaN thick film and the substrate can be separated naturally to obtain a self-supporting GaN thick film.

Example 3

The self-separation method for preparing GaN substrates, the steps include:

(1) Clean and treat the substrate sapphire, and use halide vapor phase epitaxy to grow uniformly distributed Ga ₂ O ₃ thin films on the sapphire substrate. The reaction system mainly includes two temperature zones. In the low temperature zone, metal gallium reacts with HCl to form GaCl as Gallium source, the temperature is 900°C; Oxygen is used as the oxygen source, and GaCl and _O2 are mixed and reacted in the high temperature growth area to obtain a gallium oxide film, and the temperature in the high temperature area is 1050°C. The pressure is 1 atmosphere, and the O ₂ /Ga input flow ratio is 15. By adjusting the growth time, gallium oxide films with different thicknesses can be obtained. The growth thickness of the Ga ₂ O ₃ film is controlled to be 5 microns, and the thickness uniformity of the Ga ₂ O ₃ is above 90%.

(2) Place the Ga ₂ O ₃ thin film substrate in a high-temperature tubular quartz furnace, pass it into a mixed gas of ammonia and nitrogen, and nitride it at a specific temperature for a certain period of time to obtain a partially nitrided GaN/Ga ₂ O ₃ composite film. Total flow: 5000sccm, temperature: 1100°C, nitriding time: 2h. The thickness of the GaN layer formed by nitriding is about 2 microns, the flow ratio of ammonia and nitrogen is 1, and the porous grid-like GaN single crystal layer/Ga ₂ O ₃ composite thin film is formed by nitriding.

(3) Halide vapor phase epitaxy growth of GaN thick film on GaN/Ga ₂ O ₃ composite film to obtain GaN thick film; after nitriding is completed, metal Ga reacts with Cl ₂ in the low temperature area of the halide vapor phase epitaxy system Generate GaCl as the gallium source at a temperature of 900°C; in the high-temperature growth zone, ammonia gas is used as the nitrogen source, GaCl and NH ₃ are mixed and reacted to obtain a GaN thick film, the temperature in the high-temperature zone is 1100°C; the pressure is 1 atmosphere, and the growth is controlled time, the thickness of the GaN thick film is above 10 microns.

(4) After the epitaxy is completed, the temperature is lowered to room temperature, and the epitaxial GaN thick film and the substrate can be separated naturally to obtain a self-supporting GaN thick film.

Example 4

The self-separation method for preparing GaN substrates, the steps include:

(1) Clean and treat the substrate sapphire, and use halide vapor phase epitaxy to grow uniformly distributed Ga ₂ O ₃ thin films on the sapphire substrate. The reaction system mainly includes two temperature zones. In the low temperature zone, metal gallium reacts with HCl to form GaCl as Gallium source, the temperature is 900°C; Oxygen is used as the oxygen source, and GaCl and _O2 are mixed and reacted in the high temperature growth area to obtain a gallium oxide film, and the temperature in the high temperature area is 1050°C. The pressure is 1 atmosphere, and the O ₂ /Ga input flow ratio is 15. By adjusting the growth time, gallium oxide films with different thicknesses can be obtained. The growth thickness of the Ga ₂ O ₃ film is controlled to be 4 microns, and the thickness uniformity of the Ga ₂ O ₃ is above 90%.

(2) Place the Ga ₂ O ₃ thin film substrate in a high-temperature tubular quartz furnace, pass it into a mixed gas of ammonia and nitrogen, and nitride it at a specific temperature for a certain period of time to obtain a partially nitrided GaN/Ga ₂ O ₃ composite film. Total flow: 2000sccm, temperature: 1100°C, nitriding time: 3h, flow ratio of ammonia to nitrogen is 0.5. The thickness of the GaN layer formed by nitriding is about 1.2 microns, and the porous grid-like GaN single crystal layer/Ga ₂ O ₃ composite thin film is formed by nitriding.

(3) Halide vapor phase epitaxy growth of GaN thick film on GaN/Ga ₂ O ₃ composite film to obtain GaN thick film; after nitriding is completed, metal Ga reacts with Cl ₂ in the low temperature area of the halide vapor phase epitaxy system Generate GaCl as the gallium source at a temperature of 900°C; in the high-temperature growth zone, ammonia gas is used as the nitrogen source, GaCl and NH ₃ are mixed and reacted to obtain a GaN thick film, the temperature in the high-temperature zone is 1100°C; the pressure is 1 atmosphere, and the growth is controlled time, the thickness of the GaN thick film is above 10 microns.

(4) After the epitaxy is completed, the temperature is lowered to room temperature, and the epitaxial GaN thick film and the substrate can be separated naturally to obtain a self-supporting GaN thick film. If the epitaxial GaN thick film is not completely separated from the substrate, place the material in 40% hydrofluoric acid for etching at room temperature to remove Ga ₂ O ₃ in the GaN/Ga ₂ O ₃ composite film. After soaking for 5 hours A self-supporting GaN thick film can be obtained.

Example 5

The self-separation method for preparing GaN substrates, the steps include:

(1) Clean and treat the substrate sapphire, and use halide vapor phase epitaxy to grow uniformly distributed Ga ₂ O ₃ thin films on the sapphire substrate. The reaction system mainly includes two temperature zones. In the low temperature zone, metal gallium reacts with HCl to form GaCl as Gallium source, the temperature is 850°C; oxygen is used as the oxygen source, and GaCl and _O2 are mixed and reacted in the high-temperature growth area to obtain gallium oxide film, and the temperature in the high-temperature area is 900°C. The pressure is 1 atmosphere, and the O ₂ /Ga input flow ratio is 15. By adjusting the growth time, gallium oxide films with different thicknesses can be obtained. The growth thickness of the Ga ₂ O ₃ film is controlled to be 2 microns, and the Ga ₂ O ₃ thickness uniformity is above 90%.

(2) Place the Ga ₂ O ₃ thin film substrate in a high-temperature tubular quartz furnace, pass it into a mixed gas of ammonia and nitrogen, and nitride it at a specific temperature for a certain period of time to obtain a partially nitrided GaN/Ga ₂ O ₃ composite film. Total flow: 1000sccm, temperature: 1000°C, nitriding time: 2.5h, flow ratio of ammonia to nitrogen is 0.1. The thickness of the GaN layer formed by nitriding is about 0.5 micron, and the porous grid-like GaN single crystal layer/Ga ₂ O ₃ composite thin film is formed by nitriding.

(3) Halide vapor phase epitaxy growth of GaN thick film on GaN/Ga ₂ O ₃ composite film to obtain GaN thick film; after nitriding is completed, metal Ga reacts with Cl ₂ in the low temperature area of the halide vapor phase epitaxy system Generate GaCl as the gallium source at a temperature of 900°C; in the high-temperature growth zone, ammonia gas is used as the nitrogen source, GaCl and NH ₃ are mixed and reacted to obtain a GaN thick film, the temperature in the high-temperature zone is 1050°C; the pressure is 1 atmosphere, and the growth is controlled time, the thickness of the GaN thick film is above 10 microns.

(4) After the epitaxy is completed, the temperature is lowered to room temperature, and the epitaxial GaN thick film and the substrate can be separated naturally to obtain a self-supporting GaN thick film.

Claims (7)

1. it is a kind of prepare GaN substrate from separation method, step includes:

(1) on a sapphire substrate with halide gas phase epitaxial growth thickness range at 1-5 microns and the Ga that is evenly distributed₂O₃It is thin Film；

(2) to Ga in ammonia atmosphere₂O₃Film carries out partial nitridation, Ga₂O₃Film surface nitrogenizes to form porous web grating texture GaN single crystal layer, GaN single crystal layer is with a thickness of original Ga₂O₃The 10%-40% of film thickness, obtains GaN/Ga₂O₃Laminated film；

(3) in GaN/Ga₂O₃The halide gas phase epitaxial growth that GaN thick film is carried out on laminated film, obtains GaN thick film, and GaN is thick The thickness of film is greater than 10 microns；

(4) after the completion of extension, it is cooled to room temperature, natural separation between extension GaN thick film and substrate obtains Free-standing GaN thick film.

2. preparation GaN substrate according to claim 1 from separation method, it is characterised in that: in step (2), by step (1) Ga made from₂O₃Film is placed in high temperature process furnances, nitrogenizes 2-5h under ammonia atmosphere, and 950-1100 DEG C of temperature range, Obtain porous web trellis distribution GaN/Ga₂O₃Compound structure film, ammonia flow: 100-5000sccm.

3. preparation GaN substrate according to claim 1 from separation method, it is characterised in that: in step (2), by step (1) Ga made from₂O₃Film is placed in high temperature process furnances, in ammonia nitrogen mixed gas nitrogen 2-5h, nitridation time It is related with the nitride thickness of needs and native oxide gallium thickness, 950-1100 DEG C of temperature range, obtain the distribution of porous web trellis GaN/Ga₂O₃Compound structure film, total flow: 100-5000sccm, ammonia nitrogen flow ratio are 0.1-1.

4. preparation GaN substrate according to claim 2 or 3 from separation method, it is characterised in that: in step (1), will serve as a contrast Bottom is placed in halide gas phase epitaxial growth system, in low-temperature space, metal Ga and HCl or Cl₂Reaction generates GaCl as gallium source, temperature Degree is 800-900 DEG C；In high growth temperature area, O₂As oxygen source, GaCl and O₂Mixing reacts, and obtains Ga₂O₃Film, high temperature Area's temperature is 800-1050 DEG C, and pressure is 1 atmospheric pressure, O₂/ Ga input flow rate ratio is 1.5-15.

5. preparation GaN substrate according to claim 4 from separation method, it is characterised in that: step is evenly distributed in (1) Refer to Ga₂O₃The thickness uniformity is 90% or more.

6. preparation GaN substrate according to claim 5 from separation method, it is characterised in that: step has growth in (3) GaN/Ga₂O₃The substrate of laminated film is placed in halide gas phase epitaxial growth system, in low-temperature space, metal Ga and HCl or Cl₂ Reaction generates GaCl as gallium source, and temperature is 800-900 DEG C；In high growth temperature area, ammonia is as nitrogen source, GaCl and NH₃Mixing It reacts, obtains GaN thick film, high-temperature region temperature is 950-1100 DEG C, and pressure is 1 atmospheric pressure.

7. preparation GaN substrate according to claim 2 or 3 from separation method, it is characterised in that: if drop in step (4) It to room temperature, is not properly separated between extension GaN thick film and substrate, erodes GaN/Ga with hydrofluoric acid₂O₃In laminated film Ga₂O₃, obtain Free-standing GaN thick film.