A method for preparing alpha-phase gallium oxide crystals

Abstract

The present invention provides a method for preparing α-phase gallium oxide crystals. By designing a cavity structure, selecting a crucible and a molten salt material, α-phase gallium oxide crystals are successfully grown in a high-temperature, high-pressure six-sided top press. The above method includes the following steps: taking 5N gallium oxide powder (β phase) of a certain particle size and a molten salt material, mixing them in a certain proportion, and then statically pressing them into shape; placing a gallium oxide seed crystal (α phase) at the bottom of a crucible in a glove box and pressing the formed raw material into the crucible; sealing the crucible using a conventional sealing method and placing it in a six-sided top press; after increasing the pressure and temperature, growing for a certain period of time using conventional methods including slow cooling method, temperature gradient method, and cooling and pressure reduction method to obtain millimeter-scale α-phase gallium oxide crystals.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials, and in particular to a method for preparing a gallium oxide single crystal, and in particular to a method for preparing an α-phase gallium oxide single crystal. Background Art

[0002] Gallium oxide is an ultra-wide bandgap semiconductor, with bandgap energies ranging from 4.5 to 5.3 eV across its various crystal structures. This is significantly higher than conventional wide-bandgap semiconductors such as SiC and GaN (3.3 eV and 3.4 eV, respectively). Therefore, gallium oxide holds great promise for future power device applications, and its performance is expected to be significantly improved compared to SiC or GaN power devices currently in commercial development. Gallium oxide has five isomers: α, β, γ, ε, and δ. The α phase has the widest bandgap, approximately 5.3 eV. The α-phase gallium oxide has a corundum-type crystal structure, allowing various oxides to form pn junctions with it through heteroepitaxial growth, enabling device integration and application. Furthermore, α-phase gallium oxide has similar crystal structures to α-phase indium oxide and sapphire. Therefore, the α-(In, Ga, Al)2O3 ratio can be manipulated to achieve epitaxial growth of 3.8 to 8.8 eV epitaxial layers on α-phase gallium oxide. Therefore, α-(Ga,Al)2O3 heterojunction has great application prospects in high-power and radio frequency devices.

[0003] Because α-phase gallium oxide is a metastable phase at normal pressure and cannot be grown by melt method, α-phase gallium oxide crystals are currently mainly grown by heteroepitaxial growth on sapphire substrates. However, due to the lattice mismatch between sapphire and α-phase gallium oxide, the dislocation density after heteroepitaxial growth is as high as 10 10 cm -2 However, device development has placed higher demands on dislocation density. The present invention uses conventional α-phase gallium oxide seed crystals as initial seed crystals, and through multiple rounds of iteration, achieves larger, higher-quality α-phase gallium oxide crystals. This provides high-quality seed crystals for subsequent growth of α-phase gallium oxide crystals. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a method for growing α-phase gallium oxide crystals.

[0005] The present invention provides a method for growing an α-phase gallium oxide crystal, comprising the following steps:

[0006] 1. Thoroughly mix β-phase gallium oxide powder (4-20 g / cm²) and caustic soda in water. Pour the mixed solution into a crucible and place it in a conventional heating furnace. Evacuate the furnace and introduce a flowing inert gas atmosphere. Heat the crucible to 200-300°C for 0.5-3 hours to remove moisture. Static press the resulting powder into a compact and place it in a drying oven for later use.

[0007] 2. Place the raw materials, α-phase gallium oxide seed crystals, and crucible into a glove box filled with inert gas. Place the seed crystals at the bottom of the crucible, press the formed raw materials into the crucible, and weld the crucible to seal.

[0008] 3. Press the crucible and assembly block Figure 1 The shown assembly is then placed in a six-sided top press.

[0009] 4. Raise the system temperature to 900-1100° C. at a rate of 100-200° C. per hour while raising the system pressure to 3-5 GPa; and perform growth for 0.5-100 hours using conventional methods.

[0010] 5. After the furnace drops to room temperature and pressure, take out the crucible and cut it, then take out the finished product and wash it with pure water to obtain a transparent α-phase gallium oxide single crystal.

[0011] Preferably, the molar ratio of the β-phase gallium oxide powder to the caustic soda is 5:1 to 5:3.

[0012] Preferably, the furnace body is a muffle furnace and a conventional heating furnace body.

[0013] Preferably, the raw material crucible is any one of zirconium oxide, boron nitride and magnesium oxide.

[0014] Preferably, the crucible is one or a combination of a tantalum crucible, a nickel crucible, and a platinum-rhodium crucible, and has a diameter of 3 to 45 mm and a height of 6 to 45 mm.

[0015] Preferably, the assembly block is composed of an outer graphite bushing and an inner insulation layer. The outer side of the graphite bushing is composed of conventional materials such as NaCl, dolomite, pyrophyllite, etc.

[0016] Preferably, the temperature gradient in the vertical direction of the system is 10-50° C. under the action of the graphite heating system and the thermal insulation material.

[0017] Based on the above scheme, it can be seen that the method of the present invention has the following beneficial effects compared with the prior art:

[0018] The process method provided by the present invention optimizes the temperature gradient of the system under high temperature and high pressure, provides a stable growth environment for the growth of α-phase gallium oxide single crystals, improves the size and crystal quality of α-phase gallium oxide single crystals, reduces production costs, and has a certain promoting effect on the development of the α-phase gallium oxide single crystal substrate industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is a structural schematic diagram of a crucible and assembly block for growing α-phase gallium oxide single crystals according to the present invention, wherein: 1. graphite sheet; 2. insulation layer; 3. outer crucible; 4. graphite outer lining; 5. raw material; 6. α-phase gallium oxide seed crystal; 7. inner crucible. DETAILED DESCRIPTION

[0020] The present application will be further explained below with reference to the embodiments:

[0021] Example 1

[0022] Take 125 mg of β-phase gallium oxide powder with a particle size of 3-5 and 45 mg of caustic soda and mix them thoroughly in 50 mL of water. Add the mixed solution to a zirconia crucible and place it in a muffle furnace. Evacuate the furnace body and pass it through with flowing Ar gas. Heat the raw material crucible to 200°C and keep it for 0.5 hours to fully remove moisture. The obtained powder is statically pressed into shape (3 mm in diameter and 6 mm in height) and placed in a drying oven for standby use. The obtained raw materials, α-phase gallium oxide seed crystals (1 mm in diameter and 0.5 mm in height), and tantalum crucibles (3 mm in inner diameter and 6 mm in height) are placed in a glove box filled with Ar gas. After placing the seed crystals at the bottom of the crucible in the glove box, press the formed raw materials into the crucible and seal the crucible. Press the crucible and assembly block into place. Figure 1 The assembly is then placed in a six-sided press. The system temperature is raised to 1000°C at a rate of 200°C / hour, while the system pressure is simultaneously raised to 3.9-4.1 GPa. This temperature and pressure are maintained for one hour. The temperature is then lowered to room temperature at a rate of 1000°C / hour. After the pressure in the furnace is reduced to atmospheric pressure, the crucible is removed. The crucible is then cut and the finished product is removed. After rinsing with pure water, a transparent α-phase gallium oxide single crystal is obtained.

[0023] Example 2

[0024] Take 120 mg of β-phase gallium oxide powder with a particle size of 5 to 8 and 50 mg of caustic soda and mix them thoroughly in 50 mL of water. Add the mixed solution to a zirconia crucible and place it in a muffle furnace. Evacuate the furnace body and pass it with flowing Ar gas. Heat the raw material crucible to 250°C and keep it for 1 hour to fully remove moisture. The obtained powder is statically pressed (3 mm in diameter and 6 mm in height) and placed in a drying oven for use. The obtained raw materials, α-phase gallium oxide seed crystals (1 mm in diameter and 0.5 mm in height), and nickel crucibles (3 mm in inner diameter and 6 mm in height) are placed in a glove box filled with Ar gas. After placing the seed crystals at the bottom of the crucible in the glove box, press the formed raw materials into the crucible and seal the crucible. Press the crucible and assembly block into place. Figure 1The assembly is then placed in a six-sided press. The system temperature is raised to 1000°C at a rate of 500°C / hour, while the system pressure is simultaneously raised to 4.4-4.6 GPa. This temperature and pressure are maintained for 1.5 hours. The temperature is then lowered to room temperature at a rate of 2000°C / hour. After the pressure in the furnace is reduced to atmospheric pressure, the crucible is removed. The crucible is then cut and the finished product is removed. After rinsing with pure water, a transparent α-phase gallium oxide single crystal is obtained.

[0025] Example 3

[0026] Take 580 mg of β-phase gallium oxide powder with a particle size of 5 to 8 and 200 mg of caustic soda and mix them thoroughly in 80 mL of water. Add the mixed solution to a zirconia crucible and place it in a muffle furnace. Evacuate the furnace body and pass flowing N2 gas. Heat the raw material crucible to 230°C and keep it for 1 hour to fully remove moisture. The obtained powder is statically pressed (5 mm in diameter and 10 mm in height) and placed in a drying oven for use. The obtained raw materials, α-phase gallium oxide seed crystals (1 mm in diameter and 0.5 mm in height), and platinum-rhodium crucibles (5 mm in inner diameter and 10 mm in height) are placed in a glove box filled with N2 gas. After placing the seed crystals at the bottom of the crucible in the glove box, press the formed raw materials into the crucible and seal the crucible. Press the crucible and assembly block into place. Figure 1 The assembly is then placed in a six-sided press. The system temperature is raised to 1050°C at a rate of 500°C / hour, while the system pressure is simultaneously raised to 4.6-4.8 GPa. This temperature and pressure are maintained for one hour. The temperature is then lowered to room temperature at a rate of 2000°C / hour. After the pressure in the furnace is reduced to atmospheric pressure, the crucible is removed. The crucible is then cut and the finished product is removed. After rinsing with pure water, a transparent α-phase gallium oxide single crystal is obtained.

[0027] Example 4

[0028] Take 37g of β-phase gallium oxide powder with a particle size of 3-5 and 13g of caustic soda and mix them thoroughly in 200mL of water. Add the mixed solution to a magnesium oxide crucible and place it in a muffle furnace. Evacuate the furnace body and pass it with flowing N2 gas. Heat the raw material crucible to 230℃ and keep it for 3 hours to fully remove moisture. The obtained powder is statically pressed (10mm in diameter and 20mm in height) and placed in a drying oven for standby use. The obtained raw materials, α-phase gallium oxide seed crystals (4mm in diameter and 0.5mm in height), inner platinum-rhodium crucible (inner diameter 10mm and 20mm in height) and outer tantalum crucible are placed in a glove box filled with N2 gas. After placing the seed crystal at the bottom of the crucible in the glove box, press the formed raw material into the crucible, and weld the crucible to seal it. Press the crucible and assembly block into place. Figure 1The assembly is then placed in a six-sided press. The system temperature is raised to 950°C at a rate of 400°C / hour, while the system pressure is simultaneously raised to 3.9-4.1 GPa. This temperature and pressure are maintained for three hours. The temperature is then lowered to room temperature at a rate of 800°C / hour, and the pressure in the furnace is reduced to atmospheric pressure before the crucible is removed. The crucible is then cut and the finished product is removed. After rinsing with pure water, a transparent α-phase gallium oxide single crystal is obtained.

[0029] Example 5

[0030] Take 210g of β-phase gallium oxide powder with a particle size of 5-8 and 76g of caustic soda and mix them thoroughly in 700mL of water. Add the mixed solution to a boron nitride crucible and place it in a muffle furnace. Evacuate the furnace body and pass flowing N2 gas. Heat the raw material crucible to 250℃ and keep it for 6 hours to fully remove moisture. The obtained powder is statically pressed (diameter 45mm height 45mm) and placed in a drying oven for standby use. The obtained raw materials, α-phase gallium oxide seed crystals (diameter 10mm height 0.5mm), inner platinum-rhodium crucible (inner diameter 45mm height 45mm) and outer tantalum crucible are placed in a glove box filled with N2 gas. After placing the seed crystal at the bottom of the crucible in the glove box, press the formed raw material into the crucible, and weld the crucible to seal. Press the crucible and assembly block into place. Figure 1 The assembly is then placed in a six-sided press. The system temperature is raised to 1020°C at a rate of 300°C / hour, while the system pressure is simultaneously raised to 4.5-4.8 GPa. This temperature and pressure are maintained for 80 hours. The temperature is then lowered to room temperature at a rate of 100°C / hour, and the pressure in the furnace is reduced to atmospheric pressure before the crucible is removed. The crucible is then cut and the finished product is removed. After rinsing with pure water, a transparent α-phase gallium oxide single crystal is obtained.

[0031] In summary, the process method of the present invention optimizes the temperature gradient of the system under high temperature and high pressure to provide a stable growth environment for the growth of α-phase gallium oxide single crystals, improves the crystal quality of large-size α-phase gallium oxide single crystals, reduces production costs, and has a certain promoting effect on the development of the α-phase gallium oxide single crystal substrate industry.

[0032] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an α-phase gallium oxide single crystal, characterized in that: The invention comprises the following steps: taking β-phase gallium oxide powder with a particle size of 4 to 20 and caustic soda and thoroughly mixing them in water; adding the mixed solution into a raw material crucible and placing the crucible in a conventional heating furnace; evacuating the furnace body and then passing flowing inert gas; heating the raw material crucible to 200 to 300°C and maintaining it for 0.5 to 3 hours to fully remove moisture; statically pressing the obtained powder and placing it in a drying oven for standby use; placing the obtained raw material, α-phase gallium oxide seed crystal, and crucible in a glove box filled with inert gas; placing the seed crystal at the bottom of the crucible in the glove box, pressing the formed raw material into the crucible, and welding the crucible to seal it; assembling the crucible and an assembly block, wherein the crucible is composed of insulation material and graphite discs in the vertical direction and is wrapped with graphite bushings in the radial direction; after the assembly is completed, placing the crucible in a six-sided top press; raising the system temperature to 900 to 1100°C at a rate of 100 to 500°C / hour, and simultaneously raising the system pressure to 3 to 5 GPa, and maintaining the temperature and pressure for 0.5 to 100 hours; after the furnace drops to room temperature and pressure, take out the crucible and cut it, then take out the finished product and wash it with pure water to obtain a transparent α-phase gallium oxide single crystal.

2. The method according to claim 1, characterized in that The molar ratio of the β-phase gallium oxide powder to caustic soda is 5:1 to 5:

3.

3. The method according to claim 1, characterized in that The furnace body is a muffle furnace.

4. The method according to claim 1, wherein The raw material crucible is one or a combination of a zirconia crucible, a boron nitride crucible, and a magnesium oxide crucible.

5. The method according to claim 1, wherein The crucible is one or a combination of a tantalum crucible, a nickel crucible, and a platinum-rhodium crucible.

6. The method according to claim 5, characterized in that The crucible has a diameter of 3 to 45 mm and a height of 6 to 45 mm.

7. The method according to claim 1, characterized in that The assembly block consists of an outer graphite bushing and an inner thermal insulation layer; the outer side of the graphite bushing is made of NaCl, dolomite and pyrophyllite materials.

8. The method according to claim 1, characterized in that Under the action of the graphite heating system and the thermal insulation material, the temperature gradient in the vertical direction of the system is between 10 and 50°C.

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