A method for producing an oxide single crystal thick film

Abstract

The application provides a preparation method of an oxide single crystal thick film, which comprises the following steps: transferring a metal source precursor into a crucible in a metal source area of a vacuum growth device, and placing a substrate on a substrate support in a growth area of the vacuum growth device; performing vacuumizing treatment on the vacuum growth device, and heating the metal source area and the growth area from room temperature; filling inert gas into the vacuum growth device, and continuously heating the growth area to 900-1400 DEG C, and continuously heating the metal source area to 1100-1500 DEG C; keeping the temperature of the metal source area and the growth area unchanged, and introducing carrier gas and reaction gas into the vacuum growth device, the carrier gas directionally transports the metal sub-oxide formed by the reaction of the metal source precursor after being heated to the surface of the substrate, and the reaction gas and the metal sub-oxide are fully mixed and reacted on the surface of the substrate to grow the oxide single crystal thick film. The preparation method is simple and inexpensive, and is suitable for large-scale batch production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor materials, in particular to a preparation method of oxide single crystal thick film. BACKGROUND

[0002] With the rapid development of new energy, rail transit and smart grid fields, people's demand for semiconductor power devices working at high voltage and high power is increasingly urgent. As a new type of ultra-wide bandgap semiconductor material, semiconductor oxide single crystal material is very suitable for solar blind ultraviolet detection, high-power electronic equipment and other fields due to its large bandgap (3.6 eV~4.9 eV), high breakdown field strength and good thermal stability, and has become the focus of researchers' attention.

[0003] Large-size wafer growth of oxide single crystal material is the basis for the development of semiconductor power devices and integrated circuits. Due to the high melting point of gallium oxide (1740℃), and due to the particularity of oxide single crystal material itself, it is easy to decompose to generate oxygen and sub-oxide or even metal elements under high-temperature oxygen-deficient conditions. The growth of oxide single crystal material with stable crystal phase by using the melting method (CZ- Czochralski method, EFG- edge defined film growth method, VB- vertical Bridgman method) needs to be carried out in a high-temperature oxygen-rich environment, and the selection of the crucible is narrow, only noble metals such as iridium and platinum-rhodium alloy can resist corrosion in such a high-temperature oxygen-rich environment, which greatly increases the preparation cost of semiconductor power devices.

[0004] In the method of using gas phase epitaxy, the price of the equipment required by the molecular beam epitaxy (MBE) and the metal organic chemical vapor deposition (MOCVD) process is as high as tens of millions of yuan, and the working conditions are harsh, requiring complex equipment structure and gas circuit. In addition, the pulse laser deposition (PLD), low pressure chemical vapor deposition (LPCVD) and ultrasonic atomization chemical vapor deposition (Mist-CVD) processes have low growth rate of oxide single crystal material due to the limitation of their working conditions, which is not proportional to energy consumption, and are not suitable for large-scale industrial production. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of oxide single crystal thick film, which can improve the technical problems of the prior art that the preparation method of oxide single crystal thick film is difficult to adapt to industrial production due to high production cost and low thick film growth rate.

[0006] To solve the above technical problems, the present application provides a preparation method of oxide single crystal thick film, which comprises:

[0007] S10, transferring the metal source precursor into the crucible in the metal source area of the vacuum growth equipment, and placing the substrate on the substrate support in the growth area of the vacuum growth equipment;

[0008] S20, vacuumizing the vacuum growth device, and heating the metal source region and the growth region from room temperature;

[0009] S30, filling the vacuum growth device with inert gas, and continuing to heat the growth region to 900-1400℃ and the metal source region to 1100-1500℃;

[0010] S40, keeping the temperature of the metal source region and the growth region unchanged, and introducing carrier gas and reaction gas into the vacuum growth device, the carrier gas carrying the metal sub-oxide formed by the reaction of the metal source precursor after being heated to the substrate surface, mixing with the reaction gas, and reacting on the substrate surface to grow the oxide single crystal thick film.

[0011] Preferably, the metal source precursor is a uniform mixture of metal oxide powder and corresponding metal element particles.

[0012] Preferably, the metal element particles are made of any one of Ga, Sn or In, and the metal oxide powder is made of any one of Ga2O3, SnO2 or In2O3.

[0013] Preferably, the molar ratio of the metal oxide powder to the metal element particles in the metal source precursor is 1: (1-6).

[0014] Preferably, in the step S10, the vacuum growth device comprises an outer tube for constructing a chamber required for crystal growth and an inner tube for protecting the metal source precursor from oxidation, the outer wall of the inner tube and the inner wall of the outer tube forming a sandwich.

[0015] Preferably, the inner tube comprises a crucible for carrying the metal source precursor and a flow guide pipe connected to the crucible, the flow guide pipe being provided with an output port on the side close to the substrate holder, the output port being located in the growth region and coaxial with the substrate holder.

[0016] Preferably, in the step S10, the substrate comprises any one of a single crystal substrate with any crystal plane orientation and the same material as the oxide single crystal thick film to be grown, a hetero-substrate, and a hetero-substrate with a buffer layer material of the same material as the oxide single crystal thick film to be grown.

[0017] Preferably, the hetero-substrate is any one of a c-plane sapphire single crystal substrate with a 0-6° offcut along the a-axis, a (100) plane MgO single crystal substrate, a r-plane sapphire single crystal substrate, a m-plane sapphire single crystal substrate, and a (001) plane yttrium stabilized zirconia single crystal substrate.

[0018] Preferably, in the steps S30 and S40, the carrier gas and the inert gas are at least one of Ar and N2, and the reaction gas is at least one of CO2 and O2.

[0019] Preferably, in the step S40, the flow ratio of the carrier gas to the reaction gas introduced into the vacuum growth device is 4: (1-5).

[0020] Preferably, in the step S40, the carrier gas is used to direct the metal suboxide to the substrate in the growth zone through the inner tube, and the reaction gas or the mixed gas is used to transport to the substrate in the growth zone through the interlayer; the mixed gas comprises the reaction gas and the inert gas.

[0021] Preferably, in the step S20, the vacuum growth device is subjected to vacuumizing treatment, so that the air pressure in the vacuum growth device reaches the limit pressure of the vacuumizing device, and the metal source zone and the growth zone are both heated from room temperature to a temperature not higher than the reaction temperature of the metal source precursor; in the step S30, the air pressure in the vacuum growth device after the inert gas is filled is close to normal pressure; in the step S40, the air pressure in the vacuum growth device is (0.8-1.2) x 10 5 Pa; the oxide single crystal thick film is a stable phase oxide formed by complete oxidation of the metal suboxide.

[0022] The present application has the following beneficial effects: Different from the prior art, the present application adopts a suboxide chemical vapor transport (SOCVT) method, utilizes the characteristics that the metal suboxide has a gaseous state or a higher saturated vapor pressure than the complete oxide or the metal element, and reduces the growth temperature of the metal oxide single crystal by using a vapor phase epitaxy growth method, so that the high-valence stable phase metal oxide single crystal can be efficiently grown without reaching the melting point, and the raw material only needs to be carried by a common corundum crucible, thereby greatly reducing the growth cost of the metal oxide single crystal. In addition, the present application uses an inner and outer double tube to protect the metal source precursor from being oxidized while ensuring that the reaction gas and the metal source are uniformly mixed only on the substrate surface, and grows the high-valence stable phase metal oxide single crystal thick film, thereby improving the evaporation efficiency and utilization rate of the raw material. The above preparation method has simple and inexpensive devices, can be built by simple modification on the basis of a common growth furnace, all gas paths can be formed by simple processing of common corundum standard parts, the operation steps are simple, and no complex operation process is involved. Moreover, the crystalline quality of the oxide single crystal thick film prepared by the present application is good, the growth rate of the single crystal thick film is high, and the present application can adapt to large-scale batch production, thereby reducing the production cost of the oxide single crystal thick film, and further promoting the application of the oxide single crystal thick film in the field of wide-bandgap semiconductor materials. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a preparation method flow chart of the oxide single crystal thick film provided by the embodiment of the present application;

[0024] Fig. 2is a structural diagram of a vacuum growth device in a preparation method of an oxide single crystal thick film provided by an embodiment of the present application;

[0025] Fig. 3 is a process principle diagram of a preparation method of an oxide single crystal thick film provided by embodiment 1 of the present application;

[0026] Figs. 4a-4e is an XRD spectrum of a Ga2O3 single crystal thick film obtained by a preparation method of an oxide single crystal thick film provided by embodiments 1-5 of the present application; β

[0027] Figs. 5a-5e is a surface SEM image of an oxide single crystal thick film obtained by a preparation method of an oxide single crystal thick film provided by embodiments 1-7 of the present application. β

[0028] Figs. 6a-6g is a cross-sectional SEM image of an oxide single crystal thick film obtained by a preparation method of an oxide single crystal thick film provided by embodiments 1-7 of the present application.

[0029] Figs. 7a-7g is a surface SEM image of an oxide single crystal thick film obtained by a preparation method of an oxide single crystal thick film provided by embodiments 1-7 of the present application.

[0030] Legend of reference signs:

[0031] 101-metal source precursor 102-substrate 200-vacuum growth device

[0032] 201-crucible 202-inner tube 203-substrate holder

[0033] 204-interlayer 205-outer tube 210-metal source area

[0034] 211-first gas inlet 212-second gas inlet 220-growth area DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not 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 scope of protection of the present application.

[0036] ​​The oxide single crystal preparation method of the prior art is difficult to adapt to the technical problem of industrial production due to high production cost and low growth rate, the oxide single crystal thick film is grown by adopting the SOCVT method, the crystallization quality is good, the single crystal thick film growth rate is high, the highest growth rate can reach 251.4 μm / h, large-scale batch production can be adapted, thereby the production cost of the oxide single crystal thick film is reduced, and the application of the oxide single crystal thick film in the wide band gap semiconductor material field is promoted.

[0037] Please refer to Figs. 1-2 , Fig. 1 is a preparation method flow chart of the oxide single crystal thick film provided by the embodiment of the present application; Fig. 2 is a structural diagram of a vacuum growth device 200 in the preparation method of the oxide single crystal thick film provided by the embodiment of the present application; wherein the preparation method comprises:

[0038] S10, the metal source precursor 101 is transferred into the crucible 201 in the metal source area 210 of the vacuum growth device 200, and the substrate 102 is placed on the substrate holder 203 in the growth area 220 of the vacuum growth device 200.

[0039] Specifically, the S10 step further comprises: first, providing a metal source precursor 101, which can be only a metal, but this will cause the oxide film growth rate to be low. For example, when the metal source precursor 101 is Ga, Ga is in a liquid state at 1100℃-1500℃, and the saturation vapor pressure is low at this temperature, so it is difficult to be transported from the crucible 201 in the metal source area 210 to the surface of the substrate 102 by the carrier gas, resulting in β -Ga2O3 film growth rate is low.

[0040] Preferably, the metal source precursor 101 is a uniform mixture of high-purity metal oxide powder and corresponding high-purity metal small particles of the same type as the oxide single crystal thick film to be grown; the high-purity metal small particles and the high-purity metal oxide powder are purchased from the market or prepared by simple processing, and the price is much lower than that of high-priced stable phase oxide single crystal thick film. Since the high-purity metal oxide powder purchased from the market does not have the characteristics of single crystal thick film, it cannot be directly used as a large-size wide band gap semiconductor material single crystal thick film.

[0041] Specifically, when the high-purity metal small particles are Ga, the corresponding high-purity metal oxide powder is Ga2O3 powder; when the high-purity metal small particles are Sn, the corresponding high-purity metal oxide powder is SnO2 powder; when the high-purity metal small particles are In, the corresponding high-purity metal oxide powder is In2O3 powder.

[0042] Preferably, the molar ratio of the metal oxide powder in the metal source precursor 101 to the corresponding metal element particles is 1: (1-6); at this time, the appropriate amount of metal oxide powder can react with the metal element particles at high temperature to generate gaseous metal sub-oxides or vapors of solid or liquid metal sub-oxides with high saturated vapor pressure, so as to be transported by the carrier gas to the surface of the substrate 102.

[0043] Then, a substrate 102 is provided, which is any one of a single crystal substrate of any crystal orientation and of the same type as the oxide single crystal thick film to be grown, a hetero-substrate on which a buffer layer material of the same type as the oxide single crystal thick film to be grown is grown, or a hetero-substrate. The hetero-substrate is any one of a c-plane sapphire single crystal substrate cut 0-6° along the a-axis, a (100) plane MgO single crystal substrate, an r-plane sapphire single crystal substrate, an m-plane sapphire single crystal substrate, and a (001) plane yttrium stabilized zirconia single crystal substrate.

[0044] In the present embodiment, the c-plane sapphire single crystal substrate cut 6° along the a-axis can grow a better quality oxide single crystal thick film than the ordinary c-plane sapphire single crystal substrate, which can greatly improve the orientation and crystallinity of the oxide single crystal thick film. This is mainly due to the following reasons: first, the cut changes the atomic arrangement and step structure of the surface of the substrate 102. This change provides more favorable nucleation sites and growth patterns for the initial growth of the thick film, allowing the thick film to grow more uniformly and orderly, reducing the formation of defects. Second, the cut can change the stress distribution on the surface, which helps to relieve the stress generated during the growth of the thick film due to lattice mismatch, etc., thereby reducing the dislocation density in the thick film and improving the crystalline quality of the thick film. Third, the special cut angle can affect the diffusion and adsorption process of the deposited atoms, making the atoms in the thick film more easily find suitable positions for arrangement, thereby forming a more complete and high-quality crystal structure.

[0045] Finally, a vacuum growth apparatus 200 is provided, and the metal source precursor 101 is transferred into the crucible 201 in the metal source zone 210 of the vacuum growth apparatus 200, and the substrate 102 is placed on the substrate holder 203 in the growth zone 220 of the vacuum growth apparatus 200. Specifically, before placing the substrate 102 on the substrate holder 203 in the growth zone 220 of the vacuum growth apparatus 200, the substrate 102 is sequentially cleaned with acetone, anhydrous ethanol, and deionized water, and dried with high-purity N2 gas to ensure the cleanliness of the substrate 102.

[0046] In the present embodiment, the vacuum growth apparatus 200 includes a metal source zone 210 and a growth zone 220. A central tube 202 is provided in the metal source zone 210, one end of the central tube 202 is in communication with a first gas inlet 211, and the other end of the central tube 202 has an outlet, which is located in the growth zone 220.

[0047] Specifically, the vacuum growth device 200 further comprises a substrate holder 203 for placing the substrate 102, an outer tube 205 for building a chamber required for crystal growth, and a sandwich 204 formed by the inner wall of the outer tube 205 and the outer wall of the inner tube 202 in the vacuum growth device 200, one end of the sandwich 204 being in communication with the second gas inlet 212.

[0048] Specifically, the inner tube 202 contains the above-mentioned crucible 201, the crucible 201 being fixedly connected with the flow guide pipe, the inner tube 202 being coaxial with the substrate holder 203, and the output port of the inner tube 202 being located at a distance of 5-7 cm from the substrate holder 203 in the growth zone 220.

[0049] In the embodiment of the present application, the vacuum growth device 200 is preferably a vertical growth furnace.

[0050] S20, the vacuum growth device 200 is subjected to vacuumizing treatment, and the metal source zone 210 and the growth zone 220 are both heated from room temperature.

[0051] Specifically, the step S20 further comprises:

[0052] Firstly, the vacuum growth device 200 is subjected to vacuumizing treatment, so that the air pressure in the vacuum growth device 200 reaches the limit pressure (0.01-5 Pa) of the vacuumizing device; then, the temperature of the vacuum growth device 200 is heated from room temperature to a first preset temperature at a heating rate of 2-5 ℃ / min through a temperature rising program of the vacuum growth device 200, the first preset temperature being not higher than the temperature at which the metal source precursor reacts. Preferably, the first preset temperature is 150-200 ℃. During the above-mentioned heating process, the air and other impurity gases in the vacuum growth device 200 are continuously exhausted to maintain the air pressure in the vacuum growth device 200 at 0.01-5 Pa, which helps to create a clean environment.

[0053] S30, inert gas is filled into the vacuum growth device 200, and the growth zone 220 is continuously heated to 900-1400 ℃, while the metal source zone 210 is continuously heated to 1100-1500 ℃.

[0054] Specifically, when the temperature of the vacuum growth device 200 reaches the first preset temperature, 1 atm of inert gas is filled into the vacuum growth device 200 through the first gas inlet 211 and all the gas valves are closed to make the air pressure in the vacuum growth device 200 close to normal pressure, at which time the inert gas can play a role in protecting and stabilizing the reaction environment, avoiding the metal source precursor 101 from evaporating in large quantities in advance during the heating process and causing waste of raw materials, so as to ensure the utilization rate of raw materials for subsequent single crystal growth and reduce production cost.

[0055] Then, the temperature of the metal source region 210 is heated from the first preset temperature to 1100-1500°C at a heating rate of 5-10°C / min by the heating program of the vacuum growth apparatus 200, and the temperature of the growth region 220 is heated from the first preset temperature to 900-1400°C at a heating rate of 5-10°C / min by the heating program of the vacuum growth apparatus 200, so that the temperature of the metal source region 210 is higher than the temperature of the growth region 220.

[0056] In this step, the temperature of the metal source region 210 is set to be higher than the temperature of the growth region 220 to provide the temperature distribution required in step S30. On the one hand, a higher temperature can accelerate the evaporation rate of the metal suboxide, so that the metal suboxide can be transported to the surface of the substrate 102 more quickly. On the other hand, when the reaction gas is CO2, the CO2 exhibits reducing property in the metal source region 210 and exhibits oxidizing property in the growth region 220, so that the metal suboxide hardly reacts with CO2 in the metal source region 210, but reacts with CO2 on the surface of the substrate 102.

[0057] In step S40, the temperatures of the metal source region 210 and the growth region 220 are kept unchanged, and a carrier gas and a reaction gas are introduced into the vacuum growth apparatus 200. The carrier gas can transport the metal suboxide formed by the reaction of the heated metal source precursor 101 to the surface of the substrate 102, mix with the reaction gas, and react with the reaction gas to grow an oxide single crystal thick film on the surface of the substrate 102.

[0058] Specifically, step S40 further includes the following steps. First, the temperatures of the temperature zones of the vacuum growth apparatus 200 are kept unchanged, the carrier gas is continuously introduced into the growth apparatus through the first gas inlet 211, and the reaction gas or the gas mixed with the inert gas in any proportion is continuously introduced into the growth apparatus through the gas valve of the second gas inlet 212, and the reacted gas is continuously discharged through the exhaust port below the growth region 220. The carrier gas and the inert gas are at least one of Ar and N2, and the reaction gas is at least one of CO2 and O2.

[0059] Specifically, the carrier gas can transport the gaseous metal suboxide or the vapor of the solid or liquid metal suboxide with high saturated vapor pressure formed by the reaction of the heated metal source precursor 101 to the growth region 220 at the substrate 102, and the reaction gas enters the growth region 220 at the substrate 102 from the interlayer 204, and the two are uniformly mixed. At this time, the gas pressure in the vacuum growth apparatus 200 is normal pressure or near normal pressure, specifically 0.8×10 5 Pa-1.2×10 5 Pa.

[0060] In the first embodiment, the metal source precursor 101 is a mixture of Ga and Ga2O3, the carrier gas is Ar, and the reaction gas is CO2.

[0061] At this time, the main chemical reaction occurring in the metal source region 210 is as follows:

[0062] (1);

[0063] Since the Gibbs free energy of the following reaction (2) increases positively with increasing temperature until it is greater than 0, CO2 hardly oxidizes Ga2O in the metal source region 210. At this time, CO2 exhibits reducing properties, which ensures the gas phase transport of Ga2O.

[0064] When gaseous metal suboxide Ga2O is transported to the surface of substrate 102 in growth region 220 by carrier gas, CO2 exhibits oxidizing properties because the temperature of substrate 102 is lower than that of metal source region 210. CO2 oxidizes Ga2O to Ga2O3 for growth. β The main chemical reactions occurring in the growth region 220 of the Ga2O3 single-crystal thick film are as follows:

[0065] (2).

[0066] In the second embodiment, the metal source precursor 101 is a mixture of Ga and Ga2O3, the carrier gas is Ar, and the reaction gas is O2. Since the vacuum growth equipment 200 is a "dual-pipe design" (including the inner tube 202 channel and the interlayer 204 channel), O2 enters the growth region 220 through the interlayer 204. This design can prevent O2 from oxidizing the metal Ga in the crucible 201 in the metal source region 210 into Ga2O3, which is difficult to evaporate, thus preventing the reaction (1) from proceeding. It can also reduce the risk of Ga2O being oxidized to Ga2O3 during transport and failing to reach the surface of the substrate 102 to grow a Ga2O3 single crystal thick film, thus avoiding waste of metal source material.

[0067] At this time, the main chemical reaction occurring in the metal source region 210 is as follows:

[0068] (1);

[0069] When gaseous metal suboxide Ga2O is transported by Ar to the surface of substrate 102 in growth region 220, O2 can oxidize Ga2O to Ga2O3 for growth. β The main chemical reactions occurring in the growth region 220 of the Ga2O3 single-crystal thick film are as follows:

[0070] (3);

[0071] In a third embodiment, the metal source precursor 101 is a mixture of Sn and SnO2, the carrier gas is Ar, and the reaction gas is CO2. In this case, the main chemical reactions occurring in the vacuum growth apparatus 200 are as follows:

[0072] In the metal source zone 210: (4);

[0073] (5);

[0074] In the growth zone 220: (6);

[0075] In this case, SnO has a high saturated vapor pressure at 1100°C-1500°C, so it is efficiently transported by Ar to the growth zone 220, where it reacts with CO2 to grow a SnO2 single crystal thick film.

[0076] In a fourth embodiment, the metal source precursor 101 is a mixture of In and In2O3, the carrier gas is Ar, and the reaction gas is CO2. In this case, the main chemical reactions occurring in the vacuum growth apparatus 200 are as follows:

[0077] In the metal source zone 210: (7);

[0078] In the growth zone 220: (8);

[0079] In this case, In2O is gaseous, so it is efficiently transported by Ar to the growth zone 220, where it reacts with CO2 to grow an In2O3 single crystal thick film.

[0080] In the above step S40, the flow ratio of the carrier gas to the reaction gas introduced into the growth apparatus is 4: (1-5). If the flow of the reaction gas is too small, it can not provide enough reactants, resulting in incomplete reaction or poor product crystalline quality. If the flow of the reaction gas is too large, it can cause resource waste, reaction out of control, or the production of unnecessary byproducts. Precise control of the flow of different gases in this step can ensure that the oxide single crystal thick film deposited and grown is uniform in thickness, accurate in composition, and good in crystalline quality.

[0081] In one specific embodiment, the flow of the carrier gas introduced into the growth apparatus 200 is 50-300 seem, and the flow of the reaction gas introduced into the growth apparatus 200 is 50-200 seem.

[0082] In this step, the highest growth rate of the oxide single crystal thick film obtained by the present preparation method can reach 251.4 μm / h (relative βThe time of the carrier gas and the reaction gas being introduced is determined according to the thickness requirement of the oxide single crystal thin film, and the thicker the oxide single crystal thin film, the longer the time of the carrier gas and the reaction gas being introduced.

[0083] After the thickness of the oxide single crystal thick film reaches the preset target, the gas valves of the first gas inlet 211 and the second gas inlet 212 and the gas outlet valve are closed simultaneously, and the temperature reduction program is controlled to uniformly reduce the temperature of the vacuum growth device 200 from the second preset temperature to room temperature, so that a high-valence stable phase metal oxide single crystal thick film is finally obtained.

[0084] In the vacuum growth device 200 of the preparation method of the oxide single crystal thick film provided by the embodiment of the present application, the substrate 102 is placed on the substrate holder 203 at the bottom of the vacuum growth device 200, without the need for additional fixing of the substrate 102, and compared with the way of fixing the substrate 102 at the top, the way will not cause the problem of uneven stress on the substrate 102 and the introduction of doped impurities.

[0085] The effects of the foregoing preparation method of the oxide single crystal thick film will be described below through specific examples.

[0086] Example 1:

[0087] Please refer to Fig. 3 , Fig. 3 is the process principle diagram of the preparation method of the oxide single crystal thick film provided by the embodiment 1 of the present application; from Fig. 3 it can be known that the specific preparation process of the preparation method of the oxide single crystal thick film provided by the embodiment 1 of the present application is as follows:

[0088] (1) Provide mixed raw materials of 99.99% purity Ga and 99.99% purity Ga2O3, wherein the raw materials are obtained from the market, and the raw material Ga2O3 is a metal oxide powder of the same type as the oxide single crystal thick film to be grown, and the molar ratio of Ga to Ga2O3 is 4:1 (Ga is 5.98 g, and Ga2O3 is 4.02 g); the mixing method of the mixed raw materials is as follows: a certain amount of Ga2O3 powder is weighed by using a weighing paper and an electronic balance; a reagent bottle containing Ga is slightly heated (the melting point of metallic Ga is 29.76°C), so that the solid Ga is slightly melted, and the liquid Ga is transferred by using a pipette; the mixture of Ga droplets and Ga2O3 powder is stirred by using a ceramic rod until the Ga droplets are dispersed into small droplets coated by Ga2O3 powder, so as to ensure the sufficient contact between Ga and Ga2O3.

[0089] (2) Provide a substrate 102, which is a c-plane sapphire single crystal substrate that is cut along the a-axis at an angle of 6°.

[0090] (3) Put the mixed raw materials of Ga and Ga2O3 into the crucible 201; and put the substrate 102 after being pasted on the substrate holder 203 into the growth zone 220 of the vacuum growth device 200;

[0091] (4) Heat the temperature of the vacuum growth device 200 from room temperature to 150℃ at a heating rate of 5℃ / min; during the above heating process, the mechanical pump is started to continuously pump before 150℃, the gas pressure in the cavity of the vacuum growth device 200 is kept at 5Pa, 1 atm of Ar is filled into the vacuum growth device 200 at 150℃, and all gas valves are closed;

[0092] (5) Heat the temperature of the metal source zone 210 from 150℃ to 1400℃ at a heating rate of 10℃ / min through the temperature rising program of the vacuum growth device 200, and heat the temperature of the growth zone 220 from 150℃ to 1300℃ at a heating rate of 10℃ / min through the temperature rising program of the vacuum growth device 200; then keep the above temperature unchanged, open all gas valves, input Ar gas into the inner tube 202 of the vacuum growth device 200 and keep the flow rate of the Ar gas at 200 sccm, the Ar gas input time is 30 min; at the same time, input the reaction gas CO2 into the interlayer 204 of the vacuum growth device 200 and keep the flow rate of the CO2 at 150 sccm, the CO2 input time is 30 min, the flow rate ratio of Ar:CO2 is kept at 4:3, and the rotation speed of the substrate holder 203 is kept at 10 rpm, and the Ga2O3 single crystal thick film is deposited and grown on the surface of the substrate 102; β -Ga2O3 single crystal thick film; at this time, the gas pressure in the vacuum growth device 200 is 8×10 4 Pa (that is, the mechanical pump of the vacuum growth device 200 is used to pump, and the outlet throttle valve is used to control the gas pressure in the growth device);

[0093] (6) After the growth is completed, all gas valves are closed, and each temperature zone is cooled at a cooling rate of 5℃ / min.

[0094] Embodiment 2:

[0095] The preparation method of the oxide single crystal thick film provided in Embodiment 2 of the present application is basically the same as the preparation method of the oxide single crystal thick film provided in Embodiment 1 of the present application, and the only difference is that the gas pressure in the vacuum growth device 200 is adjusted to 1.0×10 5 Pa in step (5).

[0096] Embodiment 3:

[0097] The preparation method of the oxide single crystal thick film provided in Embodiment 3 of the present application is basically the same as the preparation method of the oxide single crystal thick film provided in Embodiment 1 of the present application, and the only difference is that the gas pressure in the vacuum growth device 200 is adjusted to 1.2×105 Pa (i.e. the throttle valve flow of the gas outlet of the vacuum growth apparatus 200 is reduced so that there is sufficient CO2 to fully react with Ga2O at the substrate 102).

[0098] Example 4:

[0099] The preparation method of the oxide single crystal thick film provided in the embodiment 4 of the present application is substantially the same as the preparation method of the oxide single crystal thick film provided in the embodiment 1 of the present application, and the only difference is that the air pressure in the vacuum growth apparatus 200 is adjusted to 1.0 x 10 5 Pa in step (5); the flow of the reaction gas CO2 introduced into the interlayer 204 of the vacuum growth apparatus 200 in step (5) is 100 sccm, and the introduction time of CO2 is 30 min, ensuring that the Ar:CO2 flow ratio is 2:1.

[0100] Example 5:

[0101] The preparation method of the oxide single crystal thick film provided in the embodiment 5 of the present application is substantially the same as the preparation method of the oxide single crystal thick film provided in the embodiment 1 of the present application, and the only difference is that the air pressure in the vacuum growth apparatus 200 is adjusted to 1.0 x 10 5 Pa in step (5); the flow of the reaction gas CO2 introduced into the interlayer 204 of the vacuum growth apparatus 200 in step (5) is 250 sccm, and the introduction time of CO2 is 30 min, ensuring that the Ar:CO2 flow ratio is 4:5.

[0102] Example 6:

[0103] The preparation method of the oxide single crystal thick film provided in the embodiment 6 of the present application is substantially the same as the preparation method of the oxide single crystal thick film provided in the embodiment 1 of the present application, and the only difference is that:

[0104] In step (1), a mixed raw material of 99.99% purity Sn and 99.99% purity SnO2 is provided, and the molar ratio of Sn to SnO2 is 1:1 (Sn is 4.41 g, and SnO2 is 5.59 g); the blending method of the above mixed raw material is as follows: a certain mass of Sn powder with a particle size of less than 30 μm and SnO2 powder with a particle size of less than 70 nm are weighed by using a weighing paper and an electronic balance; and the Sn powder and the SnO2 powder are ground in a mortar until they are uniformly mixed.

[0105] In step (2), a substrate 102 is provided, which is a c-plane sapphire single crystal substrate along the a-axis inclined by 6°, comprising a SnO2 buffer layer prepared by a magnetron sputtering method.

[0106] In step (3), the mixed raw materials of Sn and SnO2 are loaded into the crucible 201, and the substrate 102 is attached to the substrate holder 203 and placed in the growth zone 220 of the vacuum growth apparatus 200;

[0107] In step (5), the temperature of the metal source zone 210 is heated from 150°C to 1400°C at a heating rate of 10°C / min by the temperature rising program of the vacuum growth apparatus 200, and the temperature of the growth zone 220 is heated from 150°C to 1200°C at a heating rate of 10°C / min by the temperature rising program of the vacuum growth apparatus 200; then the above temperatures are kept unchanged, all the gas valves are opened, the Ar gas is introduced into the inner tube 202 of the vacuum growth apparatus 200 at a flow rate of 200 sccm, and the Ar gas is introduced for 360 min; at the same time, the reaction gas CO2 is introduced into the interlayer 204 of the vacuum growth apparatus 200 at a flow rate of 200 sccm, and the CO2 is introduced for 360 min, so as to ensure that the flow rate ratio of Ar:CO2 is 1:1, and the rotation speed of the substrate holder 203 is kept at 10 rpm, thereby depositing and growing a SnO2 single crystal thick film on the surface of the substrate 102; at this time, the gas pressure in the vacuum growth apparatus 200 is 1.0×10 5 Pa.

[0108] Embodiment 7

[0109] The preparation method of the oxide single crystal thick film provided in Embodiment 7 of the present application is basically the same as the preparation method of the oxide single crystal thick film provided in Embodiment 6 of the present application, and the only difference is that:

[0110] In step (2), a substrate 102 is provided, which is an r-plane sapphire single crystal substrate comprising a SnO2 buffer layer prepared by a magnetron sputtering method.

[0111] In step (5), the temperature of the metal source zone 210 is heated from 150°C to 1400°C at a heating rate of 10°C / min by the temperature rising program of the vacuum growth apparatus 200, and the temperature of the growth zone 220 is heated from 150°C to 1100°C at a heating rate of 10°C / min by the temperature rising program of the vacuum growth apparatus 200; then the above temperatures are kept unchanged, all the gas valves are opened, the Ar gas is introduced into the inner tube 202 of the vacuum growth apparatus 200 at a flow rate of 200 sccm, and the Ar gas is introduced for 180 min; at the same time, the reaction gas CO2 is introduced into the interlayer 204 of the vacuum growth apparatus 200 at a flow rate of 200 sccm, and the CO2 is introduced for 180 min, so as to ensure that the flow rate ratio of Ar:CO2 is 1:1, and the rotation speed of the substrate holder 203 is kept at 10 rpm, thereby depositing and growing a SnO2 single crystal thick film on the surface of the substrate 102; at this time, the gas pressure in the vacuum growth apparatus 200 is 1.0×10 5 Pa.

[0112] Referring to Figs. 4a-4e , Figs. 4a-4e is an HR-XRD (high resolution X-ray diffraction) pattern of the oxide single crystal thick film prepared by the method for preparing an oxide single crystal thick film according to the embodiments 1-5 of the present application; from Figs. 4a-4e it can be seen that, in the oxide single crystal thick film prepared by the embodiments 1-5 of the present application: the diffraction peak corresponding to the (-310) crystal face of Ga2O3 appears at 37.25°, and the diffraction peak corresponding to the (-620) crystal face of Ga2O3 appears at 79.47°, which proves that the Ga2O3 single crystal thick film grown by the method for preparing an oxide single crystal thick film according to the embodiments 1-5 of the present application is of (-310) orientation. β β β

[0113] Referring to Figs. 5a-5e , Figs. 5a-5e is an XRD rocking curve pattern of the (-310) or (-620) crystal face of the Ga2O3 single crystal thick film prepared by the method for preparing an oxide single crystal thick film according to the embodiments 1-5 of the present application; from β it can be seen that, in the Ga2O3 single crystal thick film prepared by the embodiment 1 of the present application: the Full Width at Half Maximum (FWHM) of the XRD rocking curve corresponding to the (-620) crystal face is 0.177°; in the Ga2O3 single crystal thick film prepared by the embodiment 2 of the present application: the FWHM of the XRD rocking curve corresponding to the (-620) crystal face is 0.116°; in the Ga2O3 single crystal thick film prepared by the embodiment 3 of the present application: the FWHM of the XRD rocking curve corresponding to the (-620) crystal face is 0.170°; in the Ga2O3 single crystal thick film prepared by the embodiment 4 of the present application: the FWHM of the XRD rocking curve corresponding to the (-310) crystal face is 0.182°; in the Ga2O3 single crystal thick film prepared by the embodiment 5 of the present application: the FWHM of the XRD rocking curve corresponding to the (-310) crystal face is 0.245°. Figs. 5a-5e β Specifically, the results of the FWHM of the XRD rocking curve corresponding to the (-310) or (-620) crystal face in the Ga2O3 single crystal thick film prepared by the embodiments 1-5 of the present application show that: the (-310) oriented Ga2O3 single crystal thick film prepared by the embodiments 1-5 of the present application has high crystalline quality and less defects. β

[0114] β β

[0115] Referring to Figs. 6a-6e ,​​​​​​​​Figs. 6a-6e These are cross-sectional SEM (scanning electron microscope) images of oxide single-crystal thick films obtained by the methods for preparing oxide single-crystal thick films provided in Examples 1-5 of this invention; wherein, by Fig. 6a It can be seen that the product prepared in Example 1 of this invention... β The Ga₂O₃ single-crystal thick film is uniform and dense, with a thickness reaching 35.1 μm; Fig. 6b It can be seen that the product prepared in Example 2 of this invention... β The Ga₂O₃ single-crystal thick film is uniform and dense, with a thickness reaching 56.7 μm; Fig. 6c It can be seen that the product prepared in Example 3 of this invention β The Ga₂O₃ single-crystal thick film is uniform and dense, with a thickness reaching 117.4 μm; Fig. 6d It can be seen that the product prepared in Example 4 of this invention... β The Ga₂O₃ single-crystal thick film is uniform and dense, with a thickness reaching 55.4 μm; Fig. 6e It can be seen that the product prepared in Example 5 of this invention... β The Ga2O3 single-crystal thick film is uniform and dense, with a thickness of up to 80.1 μm.

[0116] Specifically, comparing Examples 1 to 3, it can be seen that when the gas pressure inside the vacuum growth equipment 200 in step (5) is 1.2 × 10⁻⁶, the gas pressure is 1.2 × 10⁻⁶. 5 At Pa, the prepared β Ga2O3 single crystal thick films are relatively thick.

[0117] Specifically, comparing Examples 2, 4, and 5, it can be seen that when the flow rate of the reaction gas CO2 introduced into the interlayer 204 of the vacuum growth equipment 200 in step (5) is 250 sccm and the CO2 introduction time is 30 min, that is, the Ar:CO2 flow rate ratio is 4:5, the prepared β Ga2O3 single crystal thick films are relatively thick.

[0118] Please see Figs. 6f-6g , Figs. 6f-6g These are cross-sectional SEM images of the oxide single-crystal thick film obtained by the method for preparing oxide single-crystal thick films provided in Examples 6-7 of this invention; wherein, by Fig. 6f It can be seen that the SnO2 thick film prepared in Example 6 of the present invention is relatively uniform and dense, with a thickness of up to 18.2 μm; Fig. 6g It can be seen that the SnO2 thick film prepared in Example 7 of the present invention is relatively uniform and dense, and its thickness can reach 25.6 μm.

[0119] Please see Figs. 7a-7e , Figs. 7a-7eis a surface SEM image of the oxide single crystal thick film obtained by the preparation method of the oxide single crystal thick film provided in Embodiments 1-5 of the present application; wherein, the oxide single crystal thick film is grown on a c-plane sapphire single crystal substrate which is cut along the a-axis at an angle of 0-6°, and the surface SEM image is obtained by using a scanning electron microscope (SEM) with an acceleration voltage of 20 kV and a working distance of 8 mm. Fig. 7a As shown in Fig. 7e, the SnO2 thick film prepared in Embodiment 5 of the present application has a relatively smooth surface and less surface defects. β As shown in Fig. 7e, the SnO2 thick film prepared in Embodiment 5 of the present application has a relatively smooth surface and less surface defects.

[0120] As shown in Fig. 7e, the SnO2 thick film prepared in Embodiment 5 of the present application has a relatively smooth surface and less surface defects. Figs. 7f-7g , Figs. 7f-7g is a surface SEM image of the oxide single crystal thick film obtained by the preparation method of the oxide single crystal thick film provided in Embodiments 6-7 of the present application; wherein, the oxide single crystal thick film is grown on a c-plane sapphire single crystal substrate which is cut along the a-axis at an angle of 0-6°, and the surface SEM image is obtained by using a scanning electron microscope (SEM) with an acceleration voltage of 20 kV and a working distance of 8 mm. Fig. 7f As shown in Fig. 7e, the SnO2 thick film prepared in Embodiment 5 of the present application has a relatively smooth surface and less surface defects. Fig. 7g As shown in Fig. 7e, the SnO2 thick film prepared in Embodiment 5 of the present application has a relatively smooth surface and less surface defects.

[0121] Compared with the prior art, the preparation method of the oxide single crystal thick film provided in the present application has the following advantages:

[0122] (1) The preparation method provided in the present application uses metal element particles with a purity of more than 99.99% and metal oxide powders (with the same composition as the oxide single crystal thick film to be grown) with a purity of more than 99.99% to form a uniform mixture, which can fully react at high temperature to generate metal sub-oxides as metal sources to grow the oxide single crystal thick film, thereby effectively improving the raw material utilization rate of the metal source; at the same time, the stable phase metal oxide of the metal sub-oxide relative to the complete oxidation of the metal is gaseous or has a higher saturated vapor pressure, which accelerates the evaporation of the metal source, thereby effectively improving the growth rate of the oxide single crystal thick film;

[0123] (2) The preparation method provided in the present application selects a c-plane sapphire single crystal substrate which is cut along the a-axis at an angle of 0-6° or a c-plane sapphire single crystal substrate which is cut along the a-axis at an angle of 0-6° and has a buffer layer, which can greatly improve the orientation and crystallinity of the oxide single crystal thick film, wherein the material of the buffer layer is the same as that of the oxide single crystal thick film.

[0124] (3) The preparation method provided in the present application mainly selects CO2 as the reaction gas. Compared with O2 which has strong oxidizing property, CO2 can exhibit both oxidizing property and reducing property at different temperature ranges. At a low temperature growth zone 220, CO2 can oxidize the gaseous metal sub-oxide or the vapor of the solid or liquid metal sub-oxide with high saturated vapor pressure into a high-valence stable phase metal oxide, at this time CO2 exhibits oxidizing property; at a high temperature zone, since the Gibbs free energy of the generation of the complete oxide from CO2 and the metal sub-oxide increases positively with temperature until it is greater than 0, CO2 does not tend to oxidize the metal sub-oxide, at this time CO2 exhibits reducing property, thereby ensuring the gas phase transport of the metal sub-oxide.

[0125] (4) The vacuum growth equipment 200 in the preparation method has the following advantages by forming a double-pipe design through setting the inner pipe 202 in the metal source area 210 and the outer pipe 205 of the vacuum growth equipment 200: on the one hand, it avoids the metal or metal suboxide from being oxidized into stable-phase metal oxide by the reaction gas and not being easy to evaporate; on the other hand, it effectively transports the metal suboxide by using the carrier gas to make the metal suboxide meet the oxygen source gas (i.e. the reaction gas) only in the area where the substrate 102 is located (i.e. the growth area 220) to effectively occur the oxidation reaction and grow the high-valence stable-phase metal oxide single crystal thick film;

[0126] (5) The outer pipe 205 of the vacuum growth equipment 200, the crucible 201 for containing the metal source precursor 101 and the inner pipe 202 fixedly connected with the crucible 201 in the preparation method are all ordinary corundum standard parts, which are convenient to process and low in cost; the vacuum growth equipment 200 has multiple temperature intervals which are independently controlled, the metal source area 210 is set to have a temperature of 1100-1500 DEG C, and the growth area 220 is set to have a temperature of 900-1400 DEG C, so that the high-valence stable-phase metal oxide single crystal thick film can be grown in a temperature interval far below the melting point of the oxide;

[0127] (6) The growth gas pressure in the vacuum growth equipment 200 in the preparation method is normal pressure and near normal pressure; the flow ratio of the carrier gas to the reaction gas introduced into the growth equipment is 4: (1-5), which ensures the crystallization quality of the high-valence stable-phase metal oxide single crystal thick film and the thick film growth rate at the same time, and the highest growth rate can reach 251.4 μm / h.

[0128] In summary, different from the prior art, the application provides a preparation method of an oxide single crystal thick film, which comprises the following steps: firstly, transferring a metal source precursor 101 into a crucible 201 in a metal source zone 210 of a vacuum growth device 200, and placing a substrate 102 on a substrate holder 203 in a growth zone 220 of the vacuum growth device 200; secondly, performing vacuumizing treatment on the vacuum growth device 200, keeping the air pressure of the vacuum growth device 200 at the limit pressure (0.01-5 Pa) of the vacuumizing device, and heating the temperature of the growth zone 220 and the metal source zone 210 from room temperature to 150-200 DEG C; thirdly, filling inert gas into the growth device 200, keeping the air pressure of the growth device 200 at near normal pressure, heating the temperature of the growth zone 220 to 900-1400 DEG C, and heating the temperature of the metal source zone 210 to 1100-1500 DEG C; and finally, keeping the temperature of the growth zone 220 and the metal source zone 210 unchanged, introducing carrier gas and reaction gas into the vacuum growth device 200, and making the metal suboxide formed by the reaction of the metal source precursor 101 after being heated be directionally transported to the surface of the substrate 102, fully mixed with the reaction gas, and react and grow on the surface of the substrate 102 to form an oxide single crystal thick film. The SOCVT (Suboxide Chemical Vapor Transport) method is adopted in the application, the metal suboxide has the characteristics of being gaseous or having a higher saturated vapor pressure relative to the complete oxide or the metal element of the metal, the growth temperature of the metal oxide single crystal is reduced by the growth method of vapor phase epitaxy, the metal oxide single crystal can be efficiently grown without reaching the melting point, the raw material only needs to be carried by a common corundum crucible, and the growth cost of the metal oxide single crystal is greatly reduced. In addition, the metal source precursor is protected from oxidation by the inner and outer double tubes, the reaction gas and the metal source are uniformly mixed on the surface of the substrate, the high-valence stable phase metal oxide single crystal thick film is reactively grown, the evaporation efficiency of the raw material is improved, and the raw material utilization rate is improved. The preparation method of the oxide single crystal thick film is simple and inexpensive, can be built by simple modification on the basis of a common growth furnace, all gas circuits can be composed of common corundum standard parts by simple processing, the operation steps are simple, and no complex operation process is involved. The crystalline quality of the oxide single crystal thick film prepared by the method is good, the single crystal thick film growth rate is high, and the method can adapt to large-scale batch production, so that the production cost of the oxide single crystal thick film is reduced, and the application of the oxide single crystal thick film in the field of wide-bandgap semiconductor materials is promoted.

[0129] It should be noted that all the above embodiments belong to the same inventive concept, and the description of each embodiment has its own emphasis. If the description is not exhaustive in individual embodiments, the description in other embodiments can be referred to.

[0130] The above embodiments only express the implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application, therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A method for producing an oxide single-crystal thick film, characterized by, The method comprises: S10, transferring a metal source precursor into a crucible in a metal source zone of a vacuum growth device, and placing a substrate on a substrate holder in a growth zone of the vacuum growth device; S20, performing vacuumizing treatment on the vacuum growth device, and heating and raising temperature of the metal source zone and the growth zone from room temperature; S30, filling inert gas into the vacuum growth device, and continuing to heat and raise temperature of the growth zone to 900-1400 ℃, and continuing to heat and raise temperature of the metal source zone to 1100-1500 ℃; S40, keeping the temperature of the metal source zone and the growth zone unchanged, and introducing carrier gas and reaction gas into the vacuum growth device, the carrier gas directionally transports metal sub-oxide formed by reaction of the metal source precursor after being heated to the surface of the substrate, fully mixes with the reaction gas, and reacts to grow an oxide single crystal thick film on the surface of the substrate, the oxide single crystal thick film is a stable phase oxide formed by complete oxidation of the metal sub-oxide; In the step S10, the metal source precursor is a uniform mixture of metal oxide powder and corresponding metal element particles, the metal oxide powder and the metal element particles are of the same type as the oxide single crystal thick film to be grown, the molar ratio of the metal oxide powder to the metal element particles in the metal source precursor is 1:(1-6), the material of the metal element particles is any one of Ga, Sn or In, and the material of the metal oxide powder is any one of Ga2O3, SnO2 or In2O3; In the steps S30 and S40, the carrier gas and the inert gas are at least one of Ar and N2, and the reaction gas is CO2, the flow ratio of the carrier gas to the reaction gas introduced into the vacuum growth device is 4:(1-5); The vacuum growth device comprises an outer tube for constructing a chamber required for crystal growth and an inner tube for protecting the metal source precursor from being oxidized, an outer wall of the inner tube and an inner wall of the outer tube form a sandwich structure; the inner tube comprises a crucible for carrying the metal source precursor and a flow guide pipe connected with the crucible, an output port is arranged on the side of the flow guide pipe close to the substrate holder, and the output port is located in the growth zone and coaxially opposite to the substrate holder.

2. The method of producing an oxide single-crystal thick film according to claim 1, wherein In the step S10, the substrate comprises any one of a single crystal substrate of any crystal face orientation and of the same type as the oxide single crystal thick film to be grown, a hetero-substrate, and the hetero-substrate on which a buffer layer material of the same type as the oxide single crystal thick film to be grown is grown; The hetero-substrate is any one of a c-surface sapphire single crystal substrate obliquely cut along a-axis by 0-6°, a (100) surface MgO single crystal substrate, an r-surface sapphire single crystal substrate, an m-surface sapphire single crystal substrate, and a (001) surface yttrium stabilized zirconia single crystal substrate.

3. The method of producing an oxide single-crystal thick film according to claim 1, wherein In the step S40, the carrier gas carries the metal sub-oxide to the substrate in the growth zone through the inner tube, and the reaction gas or mixed gas is carried to the substrate in the growth zone through the interlayer. The mixed gas includes the reaction gas and inert gas. In the step S40, the carrier gas carries the metal sub-oxide to the substrate in the growth zone through the inner tube, and the reaction gas or mixed gas is carried to the substrate in the growth zone through the interlayer. The mixed gas includes the reaction gas and inert gas.

4. The method of producing an oxide single-crystal thick film according to claim 1, wherein In the step S20, the vacuum growth device is vacuumized to reach the limit pressure of the vacuumization device, and the metal source region and the growth region are heated from room temperature to a temperature not higher than the reaction temperature of the metal source precursor. In the step S30, the pressure of the inert gas filled in the vacuum growth device is close to the normal pressure. In the step S40, the pressure in the vacuum growth device is (0.8-1.2)×10 5 Pa.

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