A method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal

Abstract

The present invention belongs to the technical field of group III oxide thin films and device manufacturing, and relates to a method for preparing a gallium oxide epitaxial layer by using a liquid gallium-based metal. The preparation is carried out by using an ECR-PEMOCVD device. First, a gallium oxynitride buffer layer is prepared on the upper surface of a substrate after hydrogen-nitrogen plasma cleaning. Then, a liquid gallium-based metal lattice is prepared on the upper surface of the gallium oxynitride buffer layer. Next, the upper surface of the gallium oxynitride buffer layer is treated with hydrogen plasma to generate a gallium-rich layer. Furthermore, by utilizing the good wettability between the liquid gallium-based metal and the gallium-rich layer, a continuous and uniformly distributed liquid gallium-based metal layer is formed by self-propagation on the upper surface of the gallium-rich layer. Finally, the upper surface of the liquid gallium-based metal layer is oxidized by oxygen plasma to prepare a gallium oxide epitaxial layer. This method has a low preparation temperature, high crystal quality, can precisely control the thickness of the gallium oxide epitaxial layer and the p-type or n-type doping concentration, and can reduce carbon pollution and improve the carrier mobility.

Description

Technical Field

[0001] The present invention belongs to the technical field of group III oxide thin films and device manufacturing, and relates to a method for preparing a gallium oxide epitaxial layer, specifically a method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal. Background Art

[0002] The fourth-generation semiconductor gallium oxide (Ga2O3) is an extremely important wide-bandgap semiconductor material, which has broad application prospects in the fields of optoelectronic devices and optoelectronic integrated circuits, including photovoltaic cells, optical sensors, gas sensors, liquid crystal displays, optoelectronic integrated circuits, solar panels, optical communication, etc.; however, traditional methods for preparing gallium oxide thin films often face a series of challenges. Currently, researchers mostly use the metalorganic chemical vapor deposition (MOCVD) method, using trimethylgallium TMGa or triethylgallium TEGa as the gallium source and oxygen as the oxygen source to prepare gallium oxide thin films at a temperature of 550 - 850 °C. Its disadvantages are that the preparation temperature is relatively high, substrates that are not heat-resistant cannot be used, and the carbon impurity content in the prepared gallium oxide thin film is high, resulting in a low mobility of the gallium oxide thin film and affecting the use of the device; although some researchers have also used the method of first coating a liquid gallium metal film on the substrate and then high-temperature oxidation to prepare gallium oxide thin films, it is difficult to precisely control the thickness of the gallium oxide thin film, and it is relatively difficult to prepare a stable p-type gallium oxide thin film by the above methods. These problems restrict the crystal quality of the gallium oxide thin film and the performance of the device. Summary of the Invention

[0003] The present invention aims to provide an innovative method for preparing a gallium oxide epitaxial layer at low temperature on different types of substrates (such as sapphire, silicon carbide, metal, glass, conductive glass, etc.) to solve the deficiencies of the prior art.

[0004] The technical solution for the present invention to achieve its purpose is as follows:

[0005] A method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal, which is prepared using the ECR-PEMOCVD equipment in the invention patent 201210247144.8, and includes the following steps:

[0006] Step 1: Chemically clean and dry-pretreat the surface of the substrate;

[0007] Step 2: Clean the upper surface of the substrate with a hydrogen-nitrogen mixed plasma: On the ECR-PEMOCVD equipment, transfer the substrate to the material platform in the vacuum reaction chamber. When the background pressure of the vacuum reaction chamber is pumped to 1×10 -5 ~5×10 -4After reaching Pa, heat the susceptor temperature to room temperature to 550 °C; after the susceptor temperature stabilizes, introduce a mixed gas of nitrogen and hydrogen into the quartz cup discharge chamber above the vacuum reaction chamber, where the flow rate of nitrogen is 40 to 200 sccm and the flow rate of hydrogen is 40 to 200 sccm, and control the pressure in the vacuum reaction chamber to 0.1 to 5 Pa; after the pressure in the vacuum reaction chamber stabilizes, set the microwave power supply power to 300 to 1000 W, turn on the microwave power supply for discharge, and start using the hydrogen-nitrogen mixed plasma to clean the upper surface of the substrate. The cleaning time is 2 to 10 min. After the upper surface of the substrate is cleaned, turn off the microwave power supply and turn off the mixed gas of nitrogen and hydrogen;

[0008] Step 3: Prepare gallium oxynitride GaO x N y Buffer layer: When the background pressure in the vacuum reaction chamber is pumped down to 1×10 -5 to 5×10 -4 Pa, heat the susceptor to room temperature to 550 °C. After the temperature stabilizes, introduce the required oxygen and nitrogen into the quartz cup discharge chamber above the vacuum reaction chamber, where the flow rate of oxygen is 0 to 200 sccm and the flow rate of nitrogen is 0 to 200 sccm, and the flow rates of oxygen and nitrogen cannot be zero at the same time. Adjust the pressure in the vacuum reaction chamber to 0.1 to 5 Pa; after the pressure in the vacuum reaction chamber stabilizes, adjust the microwave source power to 300 to 1500 W, start the microwave source, and when the microwave discharge is stable, introduce trimethylgallium TMGa into the vacuum reaction chamber through the gas-phase metal organic gas supply pipeline, where the molar flow rate of trimethylgallium TMGa is 1×10 -6 to 1×10 -5 mol / min, and prepare a gallium oxynitride GaO x N y buffer layer on the upper surface of the substrate, and control the thickness of the gallium oxynitride GaO x N y buffer layer to 20 to 300 nm. After the preparation time ends, set the heating temperature of the susceptor to room temperature. After the susceptor temperature drops to 100 °C, turn off the microwave source and turn off all gas lines;

[0009] Step 4: Prepare a liquid gallium-based metal lattice: Transfer the substrate from the susceptor in the vacuum reaction chamber to the loading chamber, and then transfer it from the loading chamber to a glove box filled with high-purity nitrogen (where the nitrogen purity is above 99.9%), and then use a fine needle (the needle tip diameter is 120 to 175 microns) on the gallium oxynitride GaO x N yThe upper surface of the buffer layer is micro-droplet infused with liquid gallium-based metal droplets, and the liquid gallium-based metal droplets are arranged periodically to prepare a liquid gallium-based metal lattice; the volume of each gallium-based metal droplet in the liquid gallium-based metal lattice is 20 - 40 nL, and the center distance between the two nearest gallium-based metal droplets is 0.32 - 1.6 cm; among them, when preparing an undoped gallium oxide epitaxial layer or a nitrogen-doped p-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is liquid pure gallium metal; when preparing a zinc-doped p-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a zinc-doped liquid gallium-based metal, and the molar ratio of zinc to gallium is 1:100000 - 1:100; when preparing a magnesium-doped p-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a magnesium-doped liquid gallium metal, and the molar ratio of magnesium to gallium is 1:100000 - 1:100; when preparing a silicon-doped n-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a silicon-doped liquid gallium-based metal, and the molar ratio of silicon to gallium is 1:100000 - 1:10;

[0010] Step 5. Preparation of a gallium-rich layer by hydrogen plasma treatment: The substrate with the liquid gallium-based metal lattice is transferred from the glove box (where the nitrogen purity is above 99.9%) of the ECR-PEMOCVD equipment to the loading chamber, and then from the loading chamber to the stage in the vacuum reaction chamber. When the background pressure of the vacuum reaction chamber is pumped to 1×10 -5 ~5×10 -4 Pa, the temperature of the stage is heated to room temperature - 500°C; after the temperature of the stage is stable, hydrogen is introduced into the quartz cup discharge chamber above the vacuum reaction chamber, and the flow rate of hydrogen is 50 - 200 sccm, so that the pressure of the vacuum reaction chamber is controlled at 0.1 - 5 Pa; after the pressure of the vacuum reaction chamber is stable, the microwave power supply power is set to 300 - 1000 W, the microwave power supply is turned on for discharge, and each gallium-based metal droplet in the liquid gallium-based metal lattice and the gallium oxynitride GaO x N y on the upper surface of the buffer layer are treated with hydrogen plasma; after the preparation of the gallium-rich layer by hydrogen plasma treatment is completed, the microwave power supply is turned off, and the hydrogen is turned off; the hydrogen plasma treatment can remove the natural oxide layer on the surface of each gallium-based metal droplet, and a gallium-rich layer is formed on the upper surface of the gallium oxynitride GaO x N y on the upper surface of the buffer layer through the reduction effect of the hydrogen plasma;

[0011] Step 6. Preparation of a liquid gallium-based metal layer by self-propagating liquid gallium-based metal lattice: The substrate with the liquid gallium-based metal lattice and the gallium-rich layer is heated to 100 - 500°C and kept at a constant temperature. Utilizing the good wettability between the liquid gallium-based metal and the gallium-rich layer, the liquid gallium-based metal self-propagates along the upper surface of the gallium-rich layer and forms a continuous and uniformly distributed liquid gallium-based metal layer, and the thickness of the liquid gallium-based metal layer is controlled at 0.074 - 3.7 μm;

[0012] Step 7: Preparation of gallium oxide epitaxial layer by oxygen plasma treatment: After the preparation of the liquid gallium-based metal layer from the self-propagating liquid gallium-based metal lattice is completed, the background pressure of the ECR-PEMOCVD vacuum reaction chamber is pumped down to 1×10 -5 ~5×10 -4 Pa. Then, the temperature of the susceptor is raised to 100 - 550 °C. After the temperature stabilizes, the required gases are introduced and the flow rates of various gases in the gas phase are adjusted. Among them, when preparing an undoped gallium oxide epitaxial layer, an n-type gallium oxide epitaxial layer with silicon doping, a p-type gallium oxide epitaxial layer with zinc doping, or a p-type gallium oxide epitaxial layer with magnesium doping, oxygen with a flow rate of 50 - 200 sccm is introduced into the quartz cup discharge chamber above the vacuum reaction chamber. When preparing a nitrogen-doped p-type gallium oxide epitaxial layer, a mixed gas of oxygen and nitrogen is introduced into the quartz cup discharge chamber above the vacuum reaction chamber, and the molar ratio of nitrogen to oxygen is 1:100000 - 1:100, and the total flow rate of the mixed gas is 50 - 200 sccm. Then, the pressure of the vacuum reaction chamber is adjusted to 0.1 - 5 Pa. After the pressure stabilizes, the microwave source power is adjusted to 300 - 1500 W, the microwave source is started, and microwave ECR discharge is used to perform oxygen plasma oxidation treatment on the upper surface of the liquid gallium-based metal layer to prepare the gallium oxide epitaxial layer, and the thickness of the gallium oxide epitaxial layer is controlled to be 0.1 - 5 μm. After the preparation of the gallium oxide epitaxial layer is completed, the heating temperature of the susceptor is set to room temperature, and other preparation processes are maintained unchanged during the cooling process. After the susceptor temperature drops to 100 °C, the microwave source is turned off, all gas lines are closed, and the equipment is shut down in an orderly manner.

[0013] Advantages of the present invention:

[0014] The present invention utilizes the good wettability between the liquid gallium-based metal droplets and the gallium-rich layer, enabling the liquid gallium-based metal droplets on the upper surface of the gallium-rich layer to self-propagate laterally along the gallium-rich layer at a certain temperature, forming a continuous and uniformly distributed liquid gallium-based metal layer on the upper surface of the gallium-rich layer. Further, by controlling the volume of the liquid gallium-based metal droplets and the periodic arrangement spacing of the droplet lattice, the thickness of the liquid gallium-based metal layer can be precisely controlled, thereby precisely controlling the thickness of the subsequent oxidized gallium oxide epitaxial layer. This method uses liquid gallium-based metal as the gallium source and oxygen as the oxygen source, which can effectively avoid the incorporation of carbon impurities during the formation of the gallium oxide epitaxial layer, thereby improving the mobility of the gallium oxide thin film. When an appropriate amount of zinc or magnesium impurities are pre-doped in the liquid gallium-based metal, it can be used to prepare p-type gallium oxide thin films. When an appropriate amount of silicon impurities are pre-doped in the liquid gallium-based metal, it can be used to prepare n-type gallium oxide thin films.

[0015] Since the electron cyclotron resonance - plasma enhanced metalorganic chemical vapor deposition (ECR-PEMOCVD) equipment can provide a high degree of ionization (≥10%) and high density (1010 ~10 12 cm -3 )'s non-equilibrium oxygen plasma source (high electron temperature and low ion temperature), which is suitable for the preparation of gallium oxide thin films with low ion damage; since the ECR oxygen plasma source can provide the reaction particle migration energy on the gallium oxide growth surface without relying on the substrate temperature, high-crystallinity gallium oxide thin films can be prepared even at low temperatures. When using an oxygen plasma source during oxidation, the preparation temperature of the gallium oxide thin film can be greatly reduced, making it possible to use inexpensive conductive substrates that are not heat-resistant. Moreover, during the low-temperature preparation process of the gallium oxide thin film, defects caused by the volatilization of oxygen and gallium can be suppressed, and the crystallinity of the gallium oxide thin film can be improved. When an appropriate amount of nitrogen is doped into the oxygen plasma, it can also be used to prepare nitrogen-doped p-type gallium oxide thin films.

[0016] The preparation method of the present invention has a low preparation temperature, high crystal quality, can precisely control the thickness of the gallium oxide epitaxial layer and the p-type or n-type doping concentration, and can reduce carbon pollution to improve the carrier mobility. Brief Description of the Drawings

[0017] Figure 1 is a top view of the structure of the liquid gallium-based metal lattice described in the present invention. In the figure, 2 is gallium oxynitride GaO x N y buffer layer, 6 is the liquid gallium-based metal lattice, and 7 is the orientation edge of the substrate.

[0018] Figure 2 is a side view of the structure of the liquid gallium-based metal layer on a substrate (such as sapphire, silicon carbide, metal, glass, conductive glass, etc.) after the preparation of the self-propagating liquid gallium-based metal lattice described in the present invention. In the figure, 1 is the substrate (such as sapphire, silicon carbide, metal, glass, conductive glass, etc.), 2 is gallium oxynitride GaO x N y buffer layer, 3 is the gallium-rich layer, and 4 is the liquid gallium-based metal layer.

[0019] Figure 3 is a side view of the structure of the gallium oxide epitaxial layer on a substrate (such as sapphire, silicon carbide, metal, glass, conductive glass, etc.) after the preparation of the gallium oxide epitaxial layer by the oxygen plasma treatment described in the present invention. In the figure, 1 is the substrate (such as sapphire, silicon carbide, metal, glass, conductive glass, etc.), 2 is gallium oxynitride GaO x N y buffer layer, 3 is the gallium-rich layer, and 5 is the gallium oxide epitaxial layer.

[0020] Figure 4 is a process flow chart of the preparation method described in the present invention.

[0021] Figure 5It is a schematic structural diagram of the ECR-PEMOCVD equipment (invention patent: ZL201210247144.8) used in the present invention. In the figure, 8 is the discharge gas supply pipeline shared by hydrogen, hydrogen sulfide, argon, nitrogen, ammonia and their mixed gases, 9 is the vacuum gauge, 15 is the vacuum reaction chamber, 16 is the microwave coupling antenna with adjustable length, 17 is the cylindrical resonant cavity, 18 is the piston short-circuit breaker in the resonant cavity, 19 is the permanent magnet ring, 20 is the quartz cup, 21 is the gas-phase metal organic compound supply pipeline, 21-1 is the gas-phase metal organic compound supply ring, 22 is the magnetic field coil support cylinder, 23 is the electric heater, 24 is the material stage, 25 is the magnetic / pneumatic feeding device, and 26 is the radio frequency bias power supply. Detailed implementation manners

[0022] The following further illustrates the detailed implementation manners of the present invention in combination with the accompanying drawings and technical solutions.

[0023] Example 1

[0024] The continuous process steps for low-temperature preparation of the undoped β-phase gallium oxide epitaxial layer 5 as shown in Figure 3 on the sapphire substrate are as follows:

[0025] A. Chemically clean and dry-pretreat the surface of the sapphire substrate 1 in a fume hood: First, ultrasonically clean the sapphire substrate 1 successively with acetone, alcohol and deionized water for 5 minutes each time, and then blow it dry with nitrogen;

[0026] B. Clean the upper surface of the substrate 1 with a hydrogen-nitrogen mixed plasma: On the ECR-PEMOCVD equipment, transfer the sapphire substrate 1 to the material stage 24 in the vacuum reaction chamber 15. When the background pressure of the vacuum reaction chamber 15 is pumped to 3×10 -4 Pa, heat the temperature of the material stage 24 to 150°C. After the temperature of the material stage 24 is stable, introduce a mixed gas of nitrogen and hydrogen into the discharge chamber of the quartz cup 20 above the vacuum reaction chamber 15. The flow rate of nitrogen is 40 sccm, and the flow rate of hydrogen is 70 sccm, so that the pressure of the vacuum reaction chamber 15 is controlled at 1.2 Pa. After the pressure of the vacuum reaction chamber 15 is stable, set the microwave power to 600 W, turn on the microwave power for discharge, and start cleaning the upper surface of the sapphire substrate 1 with the hydrogen-nitrogen mixed plasma for 10 minutes. After the upper surface of the sapphire substrate 1 is cleaned, turn off the microwave power and the mixed gas of nitrogen and hydrogen;

[0027] C. Prepare the gallium oxynitride GaO 0.6 N 0.6 buffer layer 2: When the background pressure of the vacuum reaction chamber 15 is pumped to 3×10 -4After reaching -6 Pa, heat the material stage 24 to 300 °C. After the temperature stabilizes, introduce the required oxygen and nitrogen into the quartz cup 20 discharge chamber above the vacuum reaction chamber 15. The flow rate of oxygen is 80 sccm, and the flow rate of nitrogen is 80 sccm. Adjust the pressure of the vacuum reaction chamber 15 to 0.5 Pa. After the pressure of the vacuum reaction chamber 15 stabilizes, adjust the microwave source power to 650 W and start the microwave source. After the microwave discharge stabilizes, introduce trimethylgallium TMGa into the vacuum reaction chamber 15 through the gas-phase metal organic compound supply pipeline 21. The molar flow rate of trimethylgallium TMGa is 6.4×10 0.6 mol / min, and start to prepare the gallium oxynitride GaO 0.6 buffer layer 2 on the upper surface of the sapphire substrate 1 using the ECR-PEMOCVD method, so that the gallium oxynitride GaO 0.6 N 0.6 The thickness of the buffer layer 2 is controlled to be 30 nm. After the preparation time ends, set the heating temperature of the material stage 24 to room temperature. After the temperature of the material stage 24 drops to 100 °C, turn off the microwave source and close all gas lines;

[0028] D. Preparation of the liquid gallium-based metal lattice 6: Transfer the sapphire substrate 1 from the material stage 24 in the vacuum reaction chamber 15 of the ECR-PEMOCVD equipment to the loading chamber, and then transfer it from the loading chamber to the glove box filled with high-purity nitrogen. Then, use a fine needle to micro-drop liquid gallium-based metal droplets on the upper surface of the gallium oxynitride GaO 0.6 N 0.6 buffer layer 2, and arrange the gallium-based metal droplets periodically to prepare the liquid gallium-based metal lattice 6. The liquid gallium-based metal droplets are liquid pure gallium metal. The volume of each gallium-based metal droplet in the liquid gallium-based metal lattice 6 is 20 nL, and the center distance between the two nearest gallium-based metal droplets is 1.6 cm;

[0029] E. Preparation of the gallium-rich layer by hydrogen plasma treatment: Transfer the sapphire substrate 1 with the liquid gallium-based metal lattice 6 prepared thereon from the glove box of the ECR-PEMOCVD equipment to the loading chamber, and then transfer it from the loading chamber to the material stage 24 in the vacuum reaction chamber 15. When the background pressure of the vacuum reaction chamber 15 is pumped to 3×10 -4 Pa, heat the temperature of the material stage 24 to 250 °C. After the temperature of the material stage 24 stabilizes, introduce hydrogen into the quartz cup 20 discharge chamber above the vacuum reaction chamber 15. The flow rate of hydrogen is 100 sccm. Control the pressure of the vacuum reaction chamber 15 to 0.5 Pa. After the pressure of the vacuum reaction chamber 15 stabilizes, set the microwave power supply power to 650 W and turn on the microwave power supply for discharge. Start to use hydrogen plasma to treat each gallium-based metal droplet in the liquid gallium-based metal lattice 6 and the gallium oxynitride GaO 0.6 N0.6 On the upper surface of the buffer layer 2, after the preparation of the gallium-rich layer 3 by hydrogen plasma treatment is completed, turn off the microwave power supply and the hydrogen gas; the hydrogen plasma treatment removes the natural oxide layer on the surface of each gallium-based metal droplet, and through the reduction effect of the hydrogen plasma, gallium oxynitride GaO that is not covered by the liquid gallium-based metal droplets 0.6 N 0.6 A gallium-rich layer is formed on the upper surface of the buffer layer 2;

[0030] F. Preparation of the liquid gallium-based metal layer 4 by self-propagating liquid gallium-based metal lattice: After the end of step E, heat the sapphire substrate 1 with the liquid gallium-based metal lattice 6 and the gallium-rich layer to 300 °C and keep it at a constant temperature. Utilize the good wettability between the liquid gallium-based metal and the gallium-rich layer 3, so that the liquid gallium-based metal self-propagates along the upper surface of the gallium-rich layer 3 and forms a continuous and evenly distributed liquid gallium-based metal layer 4. The thickness of the liquid gallium-based metal layer 4 is controlled to be 0.074 μm;

[0031] G. Preparation of the β-phase gallium oxide epitaxial layer 5 by oxygen plasma treatment: After the preparation of the liquid gallium-based metal layer 4 by self-propagating liquid gallium-based metal lattice 6 is completed, evacuate the background pressure of the ECR-PEMOCVD vacuum reaction chamber 15 to 3×10 -4 Pa, then raise the temperature of the susceptor 24 to 300 °C. After the temperature stabilizes, introduce oxygen with a flow rate of 100 sccm into the quartz cup 20 discharge chamber above the vacuum reaction chamber 15. Then adjust the pressure of the vacuum reaction chamber 15 to 0.5 Pa. After the pressure stabilizes, adjust the microwave source power to 650 W, start the microwave source, and use microwave ECR discharge to perform oxygen plasma oxidation treatment on the upper surface of the liquid gallium-based metal layer 4 to prepare the β-phase gallium oxide epitaxial layer 5. Control the thickness of the β-phase gallium oxide epitaxial layer 5 to be 0.1 μm. After the preparation of the β-phase gallium oxide epitaxial layer 5 is completed, set the heating temperature of the susceptor 24 to room temperature, and keep other preparation processes unchanged during the cooling process. After the temperature of the susceptor 24 drops to 100 °C, turn off the microwave source, turn off all gas lines, and orderly turn off the experimental equipment.

[0032] Using the above steps, a high-quality β-phase gallium oxide epitaxial layer 5 with a thickness of 0.1 μm was prepared on the sapphire substrate 1; the atomic force microscope AFM test results show that the average grain size of the β-phase gallium oxide epitaxial layer 5 is greater than 108 nm, and the surface roughness is lower than 1.4 nm; the X-ray diffraction test results show that the β-phase gallium oxide epitaxial layer 5 grows in the (-201) orientation, and the full width at half maximum of the rocking curve of the high-resolution X-ray diffraction of the (-201) crystal plane of the β-phase gallium oxide is less than 300 arcseconds. At room temperature, the Hall test shows that the carrier concentration of the undoped β-phase gallium oxide epitaxial layer 5 is 2.5×10 16 cm -3 , and the carrier mobility is 214 cm 2 V -1 s-1 。

[0033] Example 2

[0034] The operation steps in Example 2 are different from those in one of the examples in steps B, C, D, E, F, and G. In step B, the background pressure of the vacuum reaction chamber 15 is pumped to 1×10 -5 Pa, the temperature of the susceptor 24 is heated to 30°C, the flow rate of nitrogen is 100 sccm, the flow rate of hydrogen is 40 sccm, the pressure of the vacuum reaction chamber 15 is controlled to 0.1 Pa, the power of the microwave power supply is set to 300 W, and the cleaning time is 10 min; in step C, the flow rate of oxygen is 45 sccm, the flow rate of nitrogen is 120 sccm, and the molar flow rate of trimethylgallium TMGa is 1×10 -5 mol / min, and a gallium oxynitride GaO 0.3 N 0.8 buffer layer 2 is prepared on the upper surface of the substrate 1, and the thickness of the gallium oxynitride GaO 0.3 N 0.8 buffer layer 2 is controlled to 300 nm; in step D, the volume of each gallium-based metal droplet in the liquid gallium-based metal lattice 6 is 20 nL, and the center distance between the two nearest gallium-based metal droplets is 0.36 cm; in step E, the background pressure of the vacuum reaction chamber 15 is pumped to 1×10 -5 Pa, the temperature of the susceptor is heated to 30°C, the flow rate of hydrogen is 50 sccm, the pressure of the vacuum reaction chamber 15 is controlled to 0.1 Pa, and the power of the microwave power supply is set to 300 W; in step F, the substrate with the liquid gallium-based metal lattice 6 and the gallium-rich layer 3 is heated to 100°C and kept at a constant temperature, and the thickness of the liquid gallium-based metal layer 4 is controlled to 1.54 μm; in step G, after the background pressure of the ECR-PEMOCVD vacuum reaction chamber 15 is pumped to 1×10 -5 Pa, the temperature of the susceptor 24 is raised to 100°C, and a mixed gas of nitrogen and oxygen is introduced into the quartz cup 20 discharge chamber above the vacuum reaction chamber 15. The ratio of nitrogen to oxygen in the mixed gas is 1 / 40000, the total flow rate of the mixed gas is 100 sccm, then the pressure of the vacuum reaction chamber 15 is adjusted to 0.1 Pa, the power of the microwave source is adjusted to 300 W, and the thickness of the gallium oxide epitaxial layer 5 is controlled to 2 μm.

[0035] Using the above steps, a high-quality p-type β-phase gallium oxide epitaxial layer 5 with a thickness of 2 μm and nitrogen doping was prepared on the sapphire substrate 1; the results of atomic force microscope (AFM) testing showed that the average grain size of the p-type β-phase gallium oxide epitaxial layer 5 with nitrogen doping was greater than 59 nm, and the surface roughness was lower than 1.6 nm; the results of X-ray diffraction testing showed that the p-type β-phase gallium oxide epitaxial layer 5 with nitrogen doping grew in the (-201) orientation, and the full width at half maximum of the rocking curve of the high-resolution X-ray diffraction of the (-201) crystal plane of the p-type β-phase gallium oxide was less than 313 arcseconds. At room temperature, the Hall testing showed that the carrier concentration of the p-type β-phase gallium oxide epitaxial layer 5 with nitrogen doping was 8.2×10 17 cm -3 , and the carrier mobility was 37 cm 2 V -1 s -1 .

[0036] Example 3

[0037] The differences between steps B to F in Example 3 and one of the examples lie in steps B, C, D, E, F, and G. In step B, the background pressure of the vacuum reaction chamber 15 was pumped to 5×10 -4 Pa, the temperature of the susceptor was heated to 550 °C, the flow rate of nitrogen was 200 sccm, the flow rate of hydrogen was 200 sccm, the pressure of the vacuum reaction chamber 15 was controlled to 5 Pa, the power of the microwave power supply was set to 1000 W, and the cleaning time was 2 min; in step C, the flow rate of oxygen was 120 sccm, the flow rate of nitrogen was 20 sccm, the molar flow rate of trimethylgallium (TMGa) was 1×10 -6 mol / min, and a gallium oxynitride GaO 1.2 N 0.2 buffer layer 2 was prepared on the upper surface of the substrate 1, and the thickness of the gallium oxynitride GaO 1.2 N 0.2 buffer layer 2 was controlled to 20 nm; in step D, the volume of each gallium-based metal droplet in the liquid gallium-based metal lattice 6 was 40 nL, the center distance between the two nearest gallium-based metal droplets was 0.32 cm, and the liquid gallium-based metal droplet was a gallium-silicon alloy with a silicon-to-gallium ratio of 1 / 100000; in step E, the background pressure of the vacuum reaction chamber 15 was pumped to 5×10 -4 Pa, the temperature of the susceptor 24 was heated to 500 °C, the flow rate of hydrogen was 200 sccm, the pressure of the vacuum reaction chamber 15 was controlled to 5 Pa, and the power of the microwave power supply was set to 1000 W; in step F, the substrate with the liquid gallium-based metal lattice 6 and the gallium-rich layer 3 was heated to 500 °C and kept at a constant temperature, and the thickness of the liquid gallium-based metal layer 4 was controlled to 3.7 μm; in step G, the background pressure of the ECR-PEMOCVD vacuum reaction chamber 15 was pumped to 5×10 -4After reaching 2 Pa, raise the temperature of the material table 24 to 550 °C, introduce oxygen with a flow rate of 200 sccm into the quartz cup 20 discharge chamber above the vacuum reaction chamber 15, then adjust the air pressure of the vacuum reaction chamber 15 to 5 Pa, adjust the microwave source power to 1500 W, and control the thickness of the gallium oxide epitaxial layer 5 to 5 μm.

[0038] Using the above steps, a 5-μm-thick high-quality silicon-doped n-type β-phase gallium oxide epitaxial layer 5 was prepared on the sapphire substrate 1; the atomic force microscope AFM test results showed that the average grain size of the silicon-doped n-type β-phase gallium oxide epitaxial layer 5 was greater than 54 nm, and the surface roughness was lower than 1.9 nm; the X-ray diffraction test results showed that the silicon-doped n-type β-phase gallium oxide epitaxial layer 5 grew in the (-201) orientation, and the full width at half maximum of the rocking curve of the high-resolution X-ray diffraction of the gallium oxide (-201) crystal plane was less than 320 arc seconds. At room temperature, the Hall test showed that the carrier concentration of the silicon-doped n-type β-phase gallium oxide epitaxial layer 5 was 4.2×10 17 cm -3 , and the carrier mobility was 121 cm 2 V -1 s -1 .

Claims

1. A method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal, characterized in that, It is prepared by using an ECR-PEMOCVD device, including the following steps: Step 1: Chemically clean and dry-pretreat the surface of the substrate; Step 2: Clean the upper surface of the substrate with a hydrogen-nitrogen mixed plasma; Step 3: Prepare gallium oxynitride GaO x N y Buffer layer; Step 4. Prepare a liquid gallium-based metal lattice: Transfer the substrate from the loading platform in the vacuum reaction chamber to the loading chamber, and then from the loading chamber to the glove box filled with high-purity nitrogen with a nitrogen purity above 99.9%. Then, use a micro-needle with a needle diameter of 120-175 microns to micro-drop liquid gallium-based metal droplets on the upper surface of the gallium nitride GaO x N y buffer layer, and arrange the liquid gallium-based metal droplets periodically to prepare a liquid gallium-based metal lattice; the volume of each gallium-based metal droplet in the liquid gallium-based metal lattice is 20-40 nL, and the center distance between the two nearest gallium-based metal droplets is 0.32-1.6 cm; among them, when preparing an undoped gallium oxide epitaxial layer or a nitrogen-doped p-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a liquid pure gallium metal; when preparing a zinc-doped p-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a zinc-doped liquid gallium-based metal with a molar ratio of zinc to gallium of 1:100,000-1:100; when preparing a magnesium-doped p-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a magnesium-doped liquid gallium metal with a molar ratio of magnesium to gallium of 1:100,000-1:100; when preparing a silicon-doped n-type gallium oxide epitaxial layer, the liquid gallium-based metal droplet is a silicon-doped liquid gallium-based metal with a molar ratio of silicon to gallium of 1:100,000-1:10; Step 5: Treat with a hydrogen plasma to prepare a gallium-rich layer; Step 6: Prepare a liquid gallium-based metal layer by self-propagating liquid gallium-based metal lattices: Heat the substrate with the liquid gallium-based metal lattices and the gallium-rich layer to 100-500 °C and keep it at a constant temperature. Utilize the good wettability between the liquid gallium-based metal and the gallium-rich layer to make the liquid gallium-based metal self-propagate along the upper surface of the gallium-rich layer and form a continuous and uniformly distributed liquid gallium-based metal layer, with the thickness of the liquid gallium-based metal layer controlled to be 0.074-3.7 μm; Step 7: Treat with an oxygen plasma to prepare a gallium oxide epitaxial layer.

2. The method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal according to claim 1, characterized in that, Step 2 is specifically as follows: On the ECR-PEMOCVD device, transfer the substrate to the material stage in the vacuum reaction chamber. When the background pressure of the vacuum reaction chamber is pumped down to 1×10 -5 ~5×10 -4 Pa, heat the temperature of the material stage to room temperature to 550 °C; after the temperature of the material stage is stable, introduce a mixed gas of nitrogen and hydrogen into the quartz cup discharge chamber above the vacuum reaction chamber, where the flow rate of nitrogen is 40 to 200 sccm and the flow rate of hydrogen is 40 to 200 sccm, so that the pressure of the vacuum reaction chamber is controlled to be 0.1 to 5 Pa; after the pressure of the vacuum reaction chamber is stable, set the microwave power supply power to 300 to 1000 W, turn on the microwave power supply for discharge, and start cleaning the upper surface of the substrate with the hydrogen-nitrogen mixed plasma. The cleaning time is 2 to 10 min. After the upper surface of the substrate is cleaned, turn off the microwave power supply and turn off the mixed gas of nitrogen and hydrogen.

3. A method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal according to claim 1, characterized in that, Step 3 is specifically as follows: When the background pressure of the vacuum reaction chamber is pumped down to 1×10 -5 ~5×10 -4 Pa, heat the susceptor to room temperature to 550 °C. After the temperature stabilizes, introduce the required oxygen and nitrogen into the quartz cup discharge chamber above the vacuum reaction chamber. The flow rate of oxygen is 0 to 200 sccm, and the flow rate of nitrogen is 0 to 200 sccm. Moreover, the flow rates of oxygen and nitrogen cannot be zero at the same time. Adjust the pressure of the vacuum reaction chamber to 0.1 to 5 Pa. After the pressure of the vacuum reaction chamber stabilizes, adjust the microwave source power to 300 to 1500 W, start the microwave source. After the microwave discharge stabilizes, introduce trimethylgallium (TMGa) into the vacuum reaction chamber through the gas-phase metal organic compound supply pipeline. The molar flow rate of trimethylgallium (TMGa) is 1×10 -6 ~1×10 - 5 mol / min to prepare a gallium oxynitride GaO x N y buffer layer on the upper surface of the substrate, and control the thickness of the gallium oxynitride GaO x N y buffer layer to 20 to 300 nm. After the preparation time ends, set the heating temperature of the susceptor to room temperature. After the susceptor temperature drops to 100 °C, turn off the microwave source and turn off all gas lines.

4. A method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal according to claim 1, characterized in that, Step 5 is specifically as follows: Transfer the substrate with the prepared liquid gallium-based metal lattice from the glove box of the ECR-PEMOCVD equipment to the loading chamber, and then transfer it from the loading chamber to the material stage in the vacuum reaction chamber. When the background pressure of the vacuum reaction chamber is pumped to 1×10 -5 ~5×10 -4 Pa, heat the temperature of the material stage to room temperature to 500 °C; after the temperature of the material stage is stable, introduce hydrogen into the quartz cup discharge chamber above the vacuum reaction chamber, and the flow rate of hydrogen is 50 to 200 sccm to control the pressure of the vacuum reaction chamber to 0.1 to 5 Pa; after the pressure of the vacuum reaction chamber is stable, set the microwave power supply power to 300 to 1000 W, turn on the microwave power supply for discharge, and start using hydrogen plasma to treat each gallium-based metal droplet in the liquid gallium-based metal lattice and the gallium oxynitride GaO x N y on the upper surface of the buffer layer; after the preparation of the gallium-rich layer by hydrogen plasma treatment is completed, turn off the microwave power supply and turn off the hydrogen; the hydrogen plasma treatment removes the natural oxide layer on the surface of each gallium-based metal droplet, and a gallium-rich layer is formed on the upper surface of the gallium oxynitride GaO x N y buffer layer that is not covered by the liquid gallium-based metal droplet.

5. A method for preparing a gallium oxide epitaxial layer using a liquid gallium-based metal according to claim 1, characterized in that, Step 7 is specifically as follows: After the preparation of the liquid gallium-based metal layer by self-propagating liquid gallium-based metal lattice, the background pressure of the ECR-PEMOCVD vacuum reaction chamber is pumped to 1×10 -5 ~5×10 -4 Pa. Then, the temperature of the material stage is raised to 100 - 550 °C. After the temperature stabilizes, the required gases are introduced and the flow rates of various gases in the gas phase are adjusted. Among them, when preparing an undoped gallium oxide epitaxial layer, a silicon-doped n-type gallium oxide epitaxial layer, a zinc-doped p-type gallium oxide epitaxial layer, or a magnesium-doped p-type gallium oxide epitaxial layer, oxygen with a flow rate of 50 - 200 sccm is introduced into the quartz cup discharge chamber above the vacuum reaction chamber. When preparing a nitrogen-doped p-type gallium oxide epitaxial layer, a mixed gas of oxygen and nitrogen is introduced into the quartz cup discharge chamber above the vacuum reaction chamber, and the molar ratio of nitrogen to oxygen is 1:100000 - 1:100, and the total flow rate of the mixed gas is 50 - 200 sccm. Then, the pressure of the vacuum reaction chamber is adjusted to 0.1 - 5 Pa. After the pressure stabilizes, the microwave source power is adjusted to 300 - 1500 W, the microwave source is started, and microwave ECR discharge is used to perform oxygen plasma oxidation treatment on the upper surface of the liquid gallium-based metal layer to prepare a gallium oxide epitaxial layer, and the thickness of the gallium oxide epitaxial layer is controlled to be 0.1 - 5 μm. After the preparation of the gallium oxide epitaxial layer is completed, the heating temperature of the material stage is set to room temperature, and other preparation processes are maintained unchanged during the cooling process. After the temperature of the material stage drops to 100 °C, the microwave source is turned off, all gas paths are closed, and the equipment is shut down in an orderly manner.

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