Melt descending type single crystal growth equipment and method for preparing gallium oxide single crystal by using cold crucible

Abstract

The invention provides melt descending type single crystal growth equipment for preparing gallium oxide single crystals by using a cold crucible. The melt descending type single crystal growth equipment comprises a crucible body, a crucible bottom, a crystallizer, a cooler, a power supply heating system, a driving device and an ignition device, the crucible bottom runs through the crucible body, the crystallizer and the cooler to guide crystal growth; a seed crystal pit for mounting seed crystals is formed in the center of the crucible bottom; the power supply heating system comprises a high-frequency power supply, a cable or a copper bar and an induction coil, the cable or the copper bar is used for conveying high-frequency current to the induction coil from the high-frequency power supply, and the induction coil is a solenoid surrounding the crucible body; when the crucible bottom is pulled down, pulling the gallium oxide melt into the crystallizer, and cooling, solidifying and growing crystals in the crystallizer; the cooler is arranged below the crystallizer; the driving device comprises a pull rod, a linear driver and a rotary driver, the pull rod is mounted on the bottom surface of the crucible bottom, and the linear driver and the rotary driver are both combined with the pull rod; the ignition device is used for preheating the gallium oxide to a temperature higher than the conduction temperature of the gallium oxide.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor material preparation, and in particular relates to a melt-descent type single crystal growth device and method for preparing gallium oxide single crystals using a cold crucible. Background Art

[0002] Gallium oxide single crystal is a newly developed fourth-generation semiconductor material. It has the advantages of large bandgap, high breakdown voltage and high temperature resistance. It is an ideal material for high-power and high-voltage semiconductor power devices. my country and other technologically advanced countries are working hard to develop this material, with the goal of improving quality and performance and reducing preparation costs.

[0003] The methods currently published for developing and growing gallium oxide single crystals include melt pulling method, guided mold method, crucible descent method and floating zone method. The most commonly used crucible is the metal iridium crucible. The technology of using iridium crucible is relatively simple, but iridium crucible is very expensive and the cost of preparing single crystals is very high. Moreover, metal iridium will pollute the gallium oxide melt. Water-cooled copper crucibles can be reused many times to reduce the preparation cost, and this crucible almost does not pollute the gallium oxide melt. However, the cold crucible technology also has some difficulties in growing single crystals. First, the electromagnetic field directly acts on the material, causing the melt to stir, which has a destructive effect on crystal growth. This difficulty is particularly prominent when using the pulling method; second, the crucible body produces a radial temperature gradient on the melt, which has a destructive effect on the axial growth of the crystal. In the crucible descent method, this effect is particularly obvious.

[0004] This patent uses cold crucible technology as the basic method for growing gallium oxide single crystals, with the purpose of reducing preparation costs and eliminating crucible contamination. This patent slightly eliminates the interference of electromagnetic stirring and radial temperature gradient on crystal growth, and develops a new technology for growing crystals - melt descent method. Summary of the invention

[0005] In order to solve the above problems, the present invention designs a cold crucible device for growing gallium oxide single crystals. The main structure of the device is composed of a water-cooled crucible body, a water-cooled crucible bottom that can be separated from the crucible body, a crystallizer and a cooler arranged from top to bottom, which constitute the melting zone, crystallization zone and cooling zone for growing single crystals. A gallium oxide seed crystal is placed in the center of the crucible bottom, and a gallium oxide raw material is placed in the crucible. A high-frequency power supply is started to heat the ignition material, so that the gallium oxide is heated to a temperature higher than the conductive temperature. Under the action of the electromagnetic field, the high-temperature gallium oxide continues to heat and melt. In the process of slowly lowering the crucible bottom, the gallium oxide melt drops, cools, solidifies and grows upward from the seed crystal into a single crystal. Adjusting the temperature of the crystallizer can eliminate the radial temperature gradient during the solidification process of the melt, and the cooler provides an auxiliary axial temperature gradient to the solidification process of the melt. A water-cooled crucible cover is installed at the upper opening of the crucible body, which has the function of condensing and falling the volatilized gallium oxide back into the crucible body, and provides a sealed condition for transporting oxygen into the crucible.

[0006] The present invention provides a melt-descent single crystal growth device for producing gallium oxide single crystal using a cold crucible, comprising a crucible, a crystallizer, a cooler, a power heating system, a driving device and an ignition device, wherein the crucible comprises a crucible body and a crucible bottom;

[0007] Among them, the crucible body, crucible bottom, crystallizer and cooler arranged from top to bottom constitute the melting zone, crystallization zone and cooling zone for growing single crystals; the crucible bottom runs through the crucible body, crystallizer and cooler to guide the crystal growth;

[0008] The crucible body is configured as a cylindrical structure for accommodating gallium oxide materials and melts, and the crucible bottom is configured as a structure that can be separated from the crucible body and seals the lower opening of the crucible body, and its outer shape matches the inner shape of the lower opening of the crucible body;

[0009] A seed crystal pit for installing a seed crystal is provided at the center of the bottom of the crucible, and the lower end of the β-Ga2O3 seed crystal is installed in the seed crystal pit;

[0010] The power heating system includes a high-frequency power supply, a cable or a copper bar, and an induction coil, wherein the cable or the copper bar is used to transmit a high-frequency current from the high-frequency power supply to the induction coil, and the induction coil is configured as a solenoid surrounding the crucible body;

[0011] When the bottom of the crucible is pulled down, the gallium oxide melt is pulled into the crystallizer, where it cools, solidifies, and grows crystals;

[0012] The cooler is arranged below the crystallizer to provide an auxiliary axial temperature gradient to the melt solidifying in the crystallizer;

[0013] The driving device comprises a pull rod, a linear drive and a rotary drive, the pull rod is mounted on the bottom surface of the bottom of the crucible, and the linear drive and the rotary drive are both combined with the pull rod;

[0014] The ignition device is used to preheat the gallium oxide to a temperature higher than the conductive temperature of the gallium oxide.

[0015] Further, it is characterized in that the crucible also includes a water jacket;

[0016] The crucible body is made of copper and is divided into petals along the height direction. The cross-section shape and size of each petal are the same. A pipeline serving as a cooling water channel is arranged in each petal.

[0017] An oxide coating layer is made on the outside of the crucible body, and the cooling water pipelines of each petal are centrally connected to the water jacket, which is connected to the water supply system of the equipment through the water main pipe of the water jacket.

[0018] Furthermore, the gap width between the petals of the crucible body is selected within the range of 0.1 to 10 mm, and the optimal width range is 0.3 to 5 mm.

[0019] Furthermore, the bottom of the crucible is divided into petals along its radial direction, and the number of petals is equal to or less than the number of petals of the crucible body, and a water channel for cooling water is also arranged in each petal, and water is supplied by the water channel in the pull rod installed at the bottom of the crucible;

[0020] The bottom of the crucible is also provided with a locking mechanism for combining the gallium oxide material.

[0021] Furthermore, the crucible also includes a crucible cover to close the upper opening of the crucible;

[0022] The crucible cover is made of a water-cooled double-layer copper plate, with a cooling water channel between the two layers;

[0023] The crucible cover is provided with two pipe interfaces, which are respectively used for the gas supply port and the gas exhaust port. A connecting structure which can be combined with each other is provided between the crucible cover and the upper opening of the crucible body.

[0024] Furthermore, the crystallizer includes a crystallization tube, a heating tube and a power supply; wherein the crystallization tube is configured as a tubular structure coaxial with the crucible body and is tightly installed under the crucible body, and when the bottom of the crucible is pulled down, the gallium oxide melt is pulled into the crystallization tube, and is cooled, solidified, and crystals are grown in the crystallization tube;

[0025] The heating tube is a heating element that surrounds the crystallization tube and provides the crystallization temperature to the crystallization tube;

[0026] Alternatively, the lower section of the crucible body is used as a crystallizer, and the induction coil is configured to cover only the middle and upper sections of the crucible body, and the initial position of the crucible bottom is located in the middle section of the crucible body.

[0027] Furthermore, the crystal tube is made of high temperature resistant ceramic material or metal, preferably, made of zirconium oxide ceramic, yttria stabilized zirconium oxide ceramic, magnesium oxide ceramic or metal iridium, and can also be made of gallium oxide ceramic;

[0028] And / or, the heating tube material is graphite, or a high temperature resistant metal material, such as molybdenum, tungsten, iridium metal or alloy;

[0029] And / or, the power source for heating the heating tube is a medium frequency power source, and the heating tube obtains high temperature through induction heating; or, the power source for heating the heating tube adopts low-voltage and high-current alternating current, and the heating tube is made into a resistance heater.

[0030] Furthermore, the cooler includes a metal cylinder, and the metal cylinder is coaxial with the crucible body, and has upper and lower openings for the crucible bottom to pass through; two gas delivery pipes are arranged on the side of the metal cylinder, which are a gas supply pipe and an exhaust pipe respectively.

[0031] Furthermore, the cooling direction of the cooler with respect to the center of the crystallizer is configured with an inclination angle α relative to the axis, and the distance between the cooler and the crystallizer is controlled such that the angle α is ≤15°, and ≤5° is optimal.

[0032] Furthermore, the ignition device includes an ignition material and a lifting frame. Before the high-frequency power source is started, the ignition material is buried in the gallium oxide material. After the high-frequency power source is started, the ignition material heats the gallium oxide until it begins to melt, and then the ignition material is immediately pulled above the crucible body by the lifting frame.

[0033] Alternatively, the ignition device includes a non-transferred arc type plasma torch and a plasma power supply.

[0034] Furthermore, the ignition material may be selected from rod-shaped graphite or high temperature resistant metal, and iridium metal is the preferred material among the metals.

[0035] Furthermore, a feeder is arranged above the crucible body for adding gallium oxide material into the crucible body.

[0036] The present invention also proposes a melt-descent single crystal growth method for producing gallium oxide single crystals using a cold crucible, using the above-mentioned equipment, comprising the following steps:

[0037] S1. Before the equipment is put into operation, the bottom of the crucible with β-Ga2O3 seed crystal installed is installed into the lower opening of the crucible body, high-purity gallium oxide raw material is loaded into the crucible body, and the lower end of the ignition material is inserted into the gallium oxide;

[0038] S2, start the high-frequency power supply and heat the ignition material; when the gallium oxide around the ignition material heats up, conducts electricity and melts, the ignition material is taken out of the crucible, the crucible cover is closed, and oxygen is filled into the crucible; under this condition, the partially melted gallium oxide heats the surrounding gallium oxide to exceed the conduction temperature, and continues to heat up and melt under the action of the electromagnetic field until all the gallium oxide in the crucible is melted; during this period, the melt at the center of the crucible bottom fuses with the upper end of the seed crystal;

[0039] S3, starting the driving device to move the bottom of the crucible downward and rotate. In the initial stage of the bottom of the crucible descending into the crystallizer, the melt begins to solidify and crystallize at the position where the seed crystal and the gallium oxide melt are fused. Under the control of the axial temperature gradient provided by the bottom of the crucible, the crystal grows upward along the axial direction. In the process of the bottom of the crucible continuing to descend in the crystallizer, a plurality of crystals growing upward are formed from the surface of the bottom of the crucible. The crystals grow laterally while growing upward, and gradually block the crystals growing from other parts of the bottom of the crucible, so that the melt develops into a single crystal during the solidification process. In this process, the gallium oxide solidified in the locking mechanism of the bottom of the crucible is combined with the crystal solidified on it.

[0040] S4. After the bottom of the crucible with the solidified gallium oxide rod is pulled out of the crystallizer, the melt in the crucible body continues to fall into the crystallizer. During the solidification process, they grow upward along the surface of the gallium oxide single crystal rod, so that the length of the single crystal rod gradually increases; when the bottom of the crucible and the single crystal rod are pulled into the cooler, the gap between the single crystal rod and the upper opening of the cooler is filled with sealing material, and liquid gas is introduced into the cooler to provide an auxiliary axial temperature gradient to the single crystal rod; when the melt in the crucible body is completely pulled out of the crucible body, the crystal pulling process is terminated, and the single crystal rod is removed from the bottom surface of the crucible.

[0041] Furthermore, during the melting and crystal growth process, the temperature of the gallium oxide melt in the crucible should be controlled within the range of 1750-1850°C, with 1760-1780°C being the best.

[0042] And / or, the temperature in the crystallizer is controlled within the temperature range of 1680-1730°C, with 1710-1720°C being optimal.

[0043] Furthermore, during the process of the bottom of the crucible descending, the descending speed of the pull rod controlled by the linear drive can be adjusted within the range of 1 to 200 mm / h, and the best descending speed is selected within the range of 2 to 20 mm / h;

[0044] And / or, the rotation speed of the rotary drive can be adjusted within the range of 1 to 120 rph.

[0045] Compared with the prior art, the advantages of the present invention are:

[0046] 1. The cold crucible technology is the technical basis of the present invention. Compared with the expensive iridium crucible which is damaged during use, the water-cooled copper crucible has a lower preparation cost and does not suffer damage or loss during use. The iridium crucible will also cause some pollution to the gallium oxide melt, while the water-cooled copper crucible will not cause any pollution at all;

[0047] 2. In the cold crucible Czochralski method for growing single crystals, the electromagnetic field will stir the melt during the heating process, making the melt surface unstable. In addition, a film of contaminants will form on the melt surface, all of which make it difficult to grow single crystals using the Czochralski method in a cold crucible. In the cold crucible melt descent technology of the present invention, the melt solidifies and crystallizes at the position of the bottom of the crucible away from the electromagnetic field. The melt is less disturbed by the electromagnetic field, and the melt is very pure, which is conducive to the growth of single crystals.

[0048] 3. In the technology of growing single crystals by descending a cold crucible, although the location of melt cooling and solidification is also at the bottom of the crucible, the solidification process is always under the cool radial cooling effect of the water-cooled crucible wall, and the crystal nucleus is formed from the crucible wall. The tendency of radial growth of the crystal is difficult to avoid. Moreover, the height of the crucible body limits the length of the prepared crystal. When the melt descending technology of this patent is adopted, the melt solidifies in the crystallizer heated under the crucible body, eliminating the radial temperature gradient in the crystallization process. Moreover, the melt is pulled out to the bottom of the crucible for solidification, and its length is not limited by the height of the crucible body. With the help of a feeding device to continuously feed into the crucible body, a very long single crystal rod can be obtained;

[0049] 4. In order to realize the growth of single crystals by cold crucible melt descent technology, the present invention designs a water-cooled crucible bottom with a special structure: the crucible bottom is designed with a petal structure, which provides conditions for magnetic lines of force to pass through the crucible bottom, so that the gallium oxide on the surface of the crucible bottom is completely melted and forms close contact with the crucible bottom, and the axial cooling effect of the crucible bottom on the material is efficiently obtained; a locking mechanism is set on the surface of the crucible bottom, which can lock the bottom of the material and pull the crystals and melts on the crucible bottom to descend with the crucible bottom. This locking mechanism also has the advantage of not hindering the separation of finished crystals from the crucible bottom.

[0050] 5. Using a cold crucible to grow oxide single crystals requires additional ignition technology. The present invention proposes a method to reduce and eliminate the pollution caused by the ignition material to the melt. The first method is to immediately remove the ignition material after the ignition material heats and melts the gallium oxide around it, so that the locally melted gallium oxide material heats the surrounding materials; the second method is to continue to heat the melt after the gallium oxide is completely melted in the case of graphite as the ignition material, so that the remaining carbon in the melt is completely burned and escaped; the third method is to use a plasma torch to heat the gallium oxide to form a completely pollution-free ignition effect.

[0051] 6. The crucible cover can reduce the heat loss in the crucible and the leakage of gallium oxide vapor and dust. It can also form a suitable oxygen partial pressure in the crucible to maintain the stability of the Ga2O3 valence. When the crucible cover is made of metal material, a petal structure is set for the crucible cover to provide a channel for the magnetic field lines to enter the crucible. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0053] Figure 1 This is a schematic diagram of the structure of a cold crucible gallium oxide single crystal growth device;

[0054] Figure 2 is a schematic diagram of a cold crucible structure;

[0055] Figure 3 It is a schematic diagram of the crystallizer and cooler structure;

[0056] Figure 4 This is a structural diagram of using the lower section of the crucible body as a crystallizer;

[0057] Figure 5 This is the effect of the position of the cooler on the shape of the isothermal surface in the crystallizer;

[0058] Figure 6 is a schematic diagram of the ignition process;

[0059] Figure 7 This is a diagram of a plasma torch ignition device;

[0060] Figure 8 Figure 2. The melting process of gallium oxide after the ignition material is raised.

[0061] Fig. 9 Schematic diagram of the single crystal growth process.

[0062] In the figure, 01-crucible body, 02-crucible bottom, 03-crystallizer, 04-cooler, 05-power heating system, 06-driving device, 07-ignition device, 08-feeder, 09-water jacket, 10-crucible cover, 11-material, 12-pipeline, 13-coating layer, 14-water main pipe, 15-water channel, 16-pull rod, 17-seed crystal pit, 18-seed crystal, 19-locking mechanism, 20-cooling water channel, 21-pipe interface, 22-connection structure, 23-high frequency power supply, 24-cable or copper busbar, 25-induction coil, 26-crystallization tube, 27-heating tube, 28-power supply, 2 9- gallium oxide melt, 30- crystals grown from the surface of the seed crystal in the crystallizer, 31- other crystals grown in the crystallizer, 32- lower section, 33- metal cylinder, 34- opening, 35- gas delivery pipe, 36- cooling direction, 37- isothermal surface, 38- linear drive, 39- rotary drive, 40- ignition material, 41- lifting frame, 42- plasma torch, 43- plasma power supply, 44- gallium oxide 44 around the ignition material, 45- material that is heated by the initial melt to a temperature higher than the conductive temperature and then melted by the electromagnetic field, 46- single crystal rod, 47- sealing material, 48- added material. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0064] like Figure 1 As shown, this embodiment provides a melt-descent single crystal growth device for producing gallium oxide single crystals using a cold crucible, including a crucible, a crystallizer 03, a cooler 04, a power heating system 05, a driving device 06, an ignition device 07, and a feeder 08, wherein the crucible includes a crucible body 01 and a crucible bottom 02. It should be noted that the main structure of the device is a device composed of a crucible body 01, a crucible bottom 02, a crystallizer 03, and a cooler 04 arranged from top to bottom, which constitute the melting zone, crystallization zone, and cooling zone of the growing single crystal; the crucible bottom 02 runs through the crucible body 01, the crystallizer 03, and the cooler 04, and is the core component for guiding the crystal growth.

[0065] like Figure 2 As shown, the crucible belongs to the structural type of water-cooled copper crucible for induction heating, and specifically, the crucible also includes a water jacket 09 and a crucible cover 10. In other words, the crucible is mainly composed of four parts: a crucible body 01, a water jacket 09, a crucible bottom 02 and a crucible cover 10.

[0066] Continue reading Figure 2 The crucible body 01 is a cylindrical structure that accommodates gallium oxide material 11 and melt. Specifically, the crucible body 01 is made of copper and is divided into petals along the height direction. The cross-sectional shape and size of each petal are the same. The number of petals increases with the size of the crucible and is selected in the range of 8 to 80 petals. A pipeline 12 serving as a cooling water channel is provided in each petal. The petaled crucible body can be made by cutting and slitting a whole copper tube, or it can be assembled from a group of copper tubes. The gap width between the petals of the crucible body can be selected in the range of 0.1 to 10 mm, and the optimal width range is 0.3 to 5 mm. The principle for determining the gap width is that the larger the cross-sectional size of the crucible, the wider the gap. For the crucible body 01 used for gallium oxide, the gap of the petals of the crucible body can be selected with a larger width within the above range to improve the penetration efficiency of the electromagnetic field. In order to prevent the melt from leaking from the gaps between the crucible petals, an oxide coating layer 13, such as a coating layer of aluminum oxide, zirconium oxide, or magnesium oxide, can be made on the outside of the crucible body 01. The cooling water pipelines 12 of each petal are centrally connected to the water jacket 09, and the water main pipe 14 of the water jacket 09 is connected to the water supply system of the equipment.

[0067] The crucible bottom 02 is a copper component that can be separated from the crucible body 01. It is a structure that closes the lower opening of the crucible body 01, and its outer shape matches the inner shape of the lower opening of the crucible body 01. The crucible bottom 02 is divided into petals along its own radial direction, and the number of petals is equal to or less than the number of petals of the crucible body 01. A water channel 15 for cooling water is also provided in each of its petals, and water is supplied by the water channel in the pull rod 16 installed in the crucible bottom 02. A seed crystal pit 17 for installing seed crystals is provided in the center of the crucible bottom 02, and the lower end of the β-Ga2O3 seed crystal 18 is installed in the seed crystal pit 17. A locking mechanism 19 for combining gallium oxide material is also provided in the crucible bottom 02. When the melt solidifies in the locking mechanism 19, it can be locked in it. It combines the solidified gallium oxide and the melt above it to move downward with the crucible bottom 02. The locking mechanism 19 can have a variety of structures, such as an annular groove engraved with threads, or dovetail grooves arranged in parallel. When the crucible bottom 02 descends and draws the gallium oxide melt to the bottom of the crucible body 01, its cooled surface provides an axial temperature gradient to the melt, which is the basic guarantee for the axial growth of the crystal.

[0068] The crucible cover 10 is a cover plate that closes the upper opening of the crucible. Specifically, the crucible cover 10 is made of a water-cooled double-layer copper plate, and there is a cooling water path 20 between the two layers. The crucible cover 10 has the function of shielding the gallium oxide vapor from leaking out, and can make the gallium oxide vapor condense and return to the crucible. The crucible cover 10 is provided with two pipe interfaces 21, which are used for the gas supply port and the exhaust port respectively. Gas can be transported into the crucible through the gas supply port and the exhaust port to maintain the oxygen partial pressure in the crucible and ensure the stability of the Ga2O3 valence. A connecting structure 22 that can be combined with each other is provided between the crucible cover 10 and the upper opening of the crucible body 01, such as a threaded structure or a bayonet structure. With this structure, the crucible cover 10 can be easily combined with the upper opening of the crucible body 01.

[0069] The crucible cover can be made of a high temperature resistant metal material, such as tungsten, molybdenum, tantalum, niobium and other metals. The crucible cover can also be made of a water-cooled double-layer copper plate, with a cooling water channel 20 provided between the two layers. The crucible cover can also be made of a high temperature resistant ceramic material, such as magnesium oxide, aluminum oxide, zirconium oxide and other materials. In order not to block the passage of magnetic lines of force entering the crucible, the crucible cover made of metal material is preferably set to a petal combination structure.

[0070] Combination Figure 1 The power heating system 05 includes a high-frequency power supply 23, a cable or copper busbar 24 and an induction coil 25. The frequency of the high-frequency power supply 23 is selected in the range of 100kHz to 10MHz. The smaller the size of the crucible, the higher the selected frequency. The cable or copper busbar 24 is a component that transmits high-frequency current from the power supply to the induction coil 25. The induction coil 25 is a solenoid surrounding the crucible. The high-frequency current forms an electromagnetic field in the induction coil 25 to heat the material in the crucible.

[0071] like Figure 3As shown, the crystallizer 03 includes a crystallization tube 26, a heating tube 27 and a power supply 28. The crystallization tube 26 is a tubular structure coaxial with the crucible body 01 and is tightly installed below the crucible body 01. When the crucible bottom 02 is pulled down, the gallium oxide melt 29 is pulled into the crystallization tube 26, and is cooled, solidified, and crystals 30 and 31 are grown in the crystallization tube 26. The crystallization tube 26 is made of high-temperature resistant ceramic materials or metals, such as zirconium oxide ceramics, yttria-stabilized zirconium oxide ceramics, magnesium oxide ceramics or metal iridium, and can also be made of gallium oxide ceramics. The heating tube 27 is a heating element that surrounds the crystallization tube 26 and provides the crystallization temperature to the crystallization tube 26. In order to avoid radial temperature gradients during the crystallization process (in this embodiment, the direction perpendicular to the height direction of the crucible body 01 is referred to as "radial"), the temperature of the heating tube 27 should be constantly maintained in a very narrow temperature range slightly lower than the solidification temperature. The material of the heating tube 27 can be graphite, or a high temperature resistant metal material, such as molybdenum, tungsten, iridium or other metals or alloys. The power supply 28 for heating the heating tube 27 can be a medium frequency power supply. In this case, the heating tube 27 obtains a high temperature through induction heating; the power supply 28 for heating the heating tube 27 can also use low voltage and high current alternating current. In this case, the heating tube 27 should be made into a resistance heater.

[0072] like Figure 4 As shown, this embodiment has a special design for the crystallizer 03, using the lower section 32 of the crucible body 01 itself as the crystallizer 03. Specifically, the induction coil 25 is configured to cover only the middle and upper sections of the crucible body 01, and the initial position of the crucible bottom 02 is located in the middle section of the crucible body 01. Start the high-frequency power supply 23, when the gallium oxide melts, the crucible bottom 02 drops to the lower section of the crucible body 01, and the melt 29 on the crucible bottom 02 begins to cool down and solidify. In order to make the temperature of the melt in the lower section 32 of the crucible body obtain a preset solidification temperature, the position of the induction coil 25 can be adjusted so that the induction coil 25 can retain a certain electromagnetic field strength in this area.

[0073] Combination Figure 3 and Figure 5Although the water-cooled crucible bottom 02 provides an initial axial temperature gradient for the growth of the crystal (in this embodiment, the height direction of the crucible body is referred to as "axial"), as the crucible bottom 02 moves downward, the distance between the crucible bottom 02 and the solid and liquid cross-sections in the crystallizer 03 gradually increases, and the temperature gradient provided by the crucible bottom 02 becomes smaller and smaller. Therefore, a cooler 04 is provided at a certain distance below the crystallizer 03, and the cooler 04 is used to provide an auxiliary axial temperature gradient for the melt solidifying in the crystallizer 03. The cooler 04 includes a metal cylinder 33, and the metal cylinder 33 is coaxial with the crucible body 01, and the upper and lower openings 34 are provided for the crucible bottom 02 to pass through; two gas delivery pipes are provided on the side of the metal cylinder 33, which are respectively a gas supply pipe and an exhaust pipe, for delivering low-temperature liquid gas into the metal cylinder 33; a variety of liquid gases can be used, and the cost of using liquid oxygen and liquid nitrogen is relatively low. Since the position directly cooled by the cooler 04 is the surface of the solid gallium oxide rod, the cooling direction 36 of the center of the crystallizer 03 is configured with an inclination angle α relative to the axis. The smaller the distance between the cooler 04 and the crystallizer 03, the larger the α angle. In the crystallizer 03, the isothermal surface 37 is perpendicular to the cooling direction, so when the α angle is large, the isothermal surface 37 becomes an upwardly concave curved surface 37, which will destroy the stability of the axial growth of the crystal. To avoid this situation, the cooler 04 should be at a greater distance from the crystallizer 03, and the α angle should be controlled to be ≤15°, and ≤5° is the best.

[0074] Continue reading Figure 1 The driving device 06 includes a pull rod 16, a linear drive 38 and a rotary drive 39. The pull rod 16 is installed on the bottom surface of the crucible bottom 02, and is used to drive the crucible bottom 02 to rise and fall and rotate, and also plays the role of supplying cooling water to the crucible bottom 02. The function of the crucible bottom 02 to descend is to pull the melt out of the crucible body 01 for cooling and solidification; the purpose of the crucible bottom 02 to rotate is to ensure that the peripheral temperature of the material above the crucible bottom 02 is balanced. The linear drive 38 and the rotary drive 39 are both combined with the pull rod, and respectively play the role of driving the pull rod to rise and fall and rotate.

[0075] Combination Figure 1 and Figure 6The ignition device 07 is a device specially set up for growing oxide single crystals with a cold crucible. Gallium oxide is not conductive at room temperature. Gallium oxide must be preheated to a temperature higher than its conductive temperature before it can be heated by the electromagnetic field. When an iridium crucible is used to grow a single crystal, the electromagnetic field heats the crucible to heat the gallium oxide. In this embodiment, the ignition device 07 includes an ignition material 40 and a lifting frame 41. The ignition material 40 can be selected from rod-shaped graphite or high-temperature resistant metal. Among the metals, metallic iridium is the preferred material. The melting point of metallic gallium is too low to be used as an ignition material. If gallium is used as an ignition material, it will melt and sink to the bottom of the crucible at the beginning of the process, and the gallium oxide in the crucible body 01 cannot be heated. Before the high-frequency power supply 23 is started, the ignition material 40 is buried to a certain depth of the gallium oxide material 11. After the high-frequency power supply 23 is started, the ignition material 40 heats the gallium oxide until it begins to melt, and then the ignition material 40 is immediately pulled above the crucible body 01 to reduce the contamination of the ignition material 40 to the gallium oxide. When graphite is used as the ignition material 40, after the ignition process is completed and the gallium oxide is completely melted, heating should be continued for a period of time to allow all the carbon remaining in the gallium oxide to burn and dissipate, thereby minimizing the contamination of the gallium oxide by the graphite.

[0076] like Figure 7 As shown, another structure of the ignition device 07 is to use a plasma torch for ignition. The advantage of this ignition method is that it will not cause pollution to gallium oxide. Specifically, the ignition device 07 includes a non-transferred arc plasma torch 42 and a plasma power supply 43. This plasma torch 42 is suitable for igniting non-conductive oxides. When using the plasma torch 42 for ignition, the gallium oxide raw material needs to be pressed into a block in advance, so as to reduce the scattering of powder during the ignition process.

[0077] Continue reading Figure 1 A feeder 08 may be provided above the crucible body 01 to add gallium oxide material to the crucible body 01. When a longer gallium oxide single crystal is to be prepared, the material in the crucible body 01 generally cannot meet the demand. In this case, when the height of the melt in the crucible body 01 decreases, the feeder 08 needs to be added to the crucible body 01 to maintain the height of the liquid level. The feeding method may be manual or mechanical automatic feeding.

[0078] In this embodiment, some other devices are also provided, such as temperature sensors for measuring the temperature inside the crucible body 01, the crystallizer 03, and the cooler 04, controllers for controlling the temperature at each position and controlling the movement and rotation of the pull rod 16, and a cooling device for providing cooling water to the crucible body 01 and the crucible bottom 02.

[0079] like Figure 1-9 As shown, this embodiment also provides a melt-descent single crystal growth method for producing gallium oxide single crystal using a cold crucible, comprising the following steps:

[0080] Before the equipment is put into operation, the crucible bottom 02 with the β-Ga2O3 seed crystal 18 is installed into the lower opening of the crucible body 01, and the high-purity gallium oxide raw material 11 is loaded into the crucible body 01, and the lower end of the ignition material 40 is inserted into the gallium oxide. The β-Ga2O3 seed crystal is selected to have the best crystal growth direction in the axial direction.

[0081] Then, the high-frequency power supply 23 is started and the ignition material 40 is heated. When the gallium oxide 44 around the ignition material heats up, conducts electricity and melts, the ignition material 40 is taken out of the crucible body 01, the crucible cover 10 is covered, and oxygen is filled into the crucible body 01. The pressure of the oxygen can be selected in the range of 0.1 to 10 MPa. In an oxygen-deficient high-temperature environment, gallium oxide will decompose into low-valent oxides or metallic gallium. The delivery of oxygen into the crucible body 01 can prevent the decomposition of gallium oxide. Under this condition, the locally melted gallium oxide heats the surrounding gallium oxide 45 to exceed the conductive temperature, and continues to heat up and melt under the action of the electromagnetic field until all the gallium oxide in the crucible body 01 is melted. During this period, the melt in the center of the crucible bottom 02 fuses with the upper end of the seed crystal 18. The power of the power supply is controlled during the melting process to keep the temperature of the melt within a limited range.

[0082] Thereafter, the driving device 06 is started to move the crucible bottom 02 downward and rotate. In the initial stage when the crucible bottom 02 descends into the crystallizer 03, the melt begins to solidify and crystallize at the position where the seed crystal 18 and the gallium oxide melt 29 are fused. Under the control of the axial temperature gradient provided by the crucible bottom 02, the crystal 30 grows axially upward. During the process of the crucible bottom 02 continuing to descend in the crystallizer 03, although a plurality of crystals 31 growing upward are formed from the surface of the crucible bottom 02, since there is no nucleation process when the crystal grows from the surface of the seed crystal, and the seed crystal has the best crystal growth direction, the crystal growth process starting from the seed crystal is the earliest and fastest. This crystal grows horizontally while growing upward, and it gradually blocks the crystals growing from other parts of the crucible bottom 02, so that the melt develops into a single crystal during the solidification process. In this process, the gallium oxide solidified in the locking mechanism 19 of the crucible bottom 02 combines with the crystal solidified on it, and produces a pulling effect on the material on the crucible bottom 02.

[0083] After the crucible bottom 02 is pulled out of the crystallizer 03 with the solidified gallium oxide rod, the melt in the crucible body 01 continues to fall into the crystallizer 03. During the solidification process, they grow upward along the surface of the gallium oxide single crystal rod 46, so that the length of the single crystal rod 46 gradually increases. When the crucible bottom 02 and the single crystal rod 46 are pulled into the cooler 04, the gap between the single crystal rod 46 and the upper opening of the cooler 04 is filled with a sealing material 47, and liquid gas is introduced into the cooler 04 to provide an auxiliary axial temperature gradient to the single crystal rod 46. The sealing material 47 can be made of aluminum silicate felt, aluminum oxide felt, graphite felt and other materials. When the melt in the crucible body 01 is completely pulled out of the crucible body 01, the crystal pulling process is terminated, and the single crystal rod 46 is removed from the surface of the crucible bottom 02.

[0084] During the melting and crystal growth process, the temperature in the crucible body 01 and the crystallizer 03 needs to be strictly controlled and kept constant. In view of the melting point of gallium oxide is 1740°C, in the present invention, the temperature of the gallium oxide melt in the crucible body 01 should be controlled in the range of 1750-1850°C, with 1760-1780°C being the best. Too high a temperature will cause gallium oxide to decompose and volatilize severely. The temperature in the crystallizer 03 must also be strictly controlled and kept constant, and is required to be controlled in the temperature range of 1680-1730°C, with 1710-1720°C being the best. Too low a temperature will produce a radial temperature gradient, which will promote the formation of radial growth of crystal nuclei on the inner wall of the crystallizer 03.

[0085] During the descent of the crucible bottom 02, the linear drive 38 controls the descent speed of the pull rod 16 to be adjusted within the range of 1 to 200 mm / h, and the optimal descent speed is selected within the range of 2 to 20 mm / h. The larger the diameter of the crystal, the lower the selected speed. The rotation speed of the rotary drive 39 can be adjusted within the range of 1 to 120 rph. The principle of determining the descent speed of the pull rod 16 includes two elements: first, the descent speed must be less than the growth speed of the crystal to prevent the formation of new crystal nuclei in the melt where the crystal has not yet grown; second, wait for the temperature conduction to be balanced within the cross section of the crystallizer 03. If the descent speed is too fast, the center temperature will be high and the edge temperature will be low, and the isothermal surface will become a downward concave curved surface, which will destroy the stability of the axial growth of the crystal.

[0086] If a single crystal rod 46 with a large length needs to be prepared, when the liquid level of the melt in the crucible body 01 decreases, gallium oxide material 48 can be added to the crucible body through the feeder 08. In this process, the crystal pulling process is terminated until the pulled single crystal rod 46 reaches the required length.

[0087] In order to better understand the present embodiment, some specific examples are provided here:

[0088] Embodiment 1:

[0089] In this embodiment, the crystal growing equipment is composed of six parts: crucible 01, 02, crystallizer 03, power heating system 05, driving device 06, ignition device 07 and other devices ( Figure 1 ).

[0090] The crucible of the device is composed of a crucible body 01, a water jacket 09, a crucible bottom 02 and a crucible cover 10 ( Figure 2 ). The inner diameter of the crucible body is 80mm and the height is 250mm. It is composed of 18 copper tubes with a diameter of 14mm. Each tube is connected to the water jacket above the crucible body, and the water supply pipe and return pipe of the water jacket are connected to the water supply system of the equipment. The outer diameter of the bottom of the crucible matches the inner diameter of the crucible body. It is divided into 9 petals along the radial direction, and each petal has a cooling water path 15. A seed crystal pit 17 is provided in the center of the bottom of the crucible, and there is an annular locking mechanism around the seed crystal pit, which is a groove 19 engraved with a thread. The crucible cover is made of double-layer copper plates, and there is a water path 20 between the two layers. The crucible cover is provided with an air supply port and an exhaust port 21, and a flange is provided on its edge. A thread 22 is made on the inner edge of the flange, which cooperates with the external thread on the upper mouth of the crucible body.

[0091] The power of the high frequency power supply 23 is 150 kW and the frequency is 300 kHz. The output interface of the power supply is connected to the interface of the induction coil 25 surrounding the crucible body by using a water-cooled copper bar 24 ( Figure 1 ).

[0092] The crystallizer tube 26 made of metal iridium is tightly mounted on the lower edge of the crucible body, with an inner diameter of 80 mm and a height of 60 mm. A tubular graphite heater 27 is mounted around the outside of the crystallizer tube, and a 60V, 1000A power supply 28 is used to supply power to the heater ( Figure 3 ).

[0093] The driving device 06 is composed of three parts: a pull rod 16, a linear drive 36 and a rotary drive 39 ( Figure 1 The pull rod is installed on the bottom surface of the crucible bottom, and the linear drive and the rotary drive are combined with the pull rod, which drives the crucible bottom to produce lifting and rotating motions. The pull rod is provided with cooling water pipelines, which are combined with the water channels in the crucible bottom.

[0094] The device is also equipped with an ignition device 07, which uses a metal iridium tube as an ignition material 40. The diameter of the iridium tube is 40 mm and the length is 120 mm. The iridium rod is suspended by a lifting frame 41. The height of the iridium rod can be raised by rotating the suspension shaft of the lifting frame by hand ( Figure 6 ).

[0095] Before the equipment is put into operation, <100> The oriented β-Ga2O3 seed crystal 18 is placed in the seed crystal pit 17 of the crucible bottom 02, and the lower end of the seed crystal is buried in the seed crystal pit. The crucible bottom is raised to the inside of the crucible body 01, and the lower opening of the crucible body is sealed. 3 kg of gallium oxide powder compact 11 with a purity of 5N is placed in the crucible body, and the lower end of the iridium rod 40 is inserted into the gallium oxide to a depth of 100 mm. Then, the high-frequency power supply 23 is started to heat the iridium rod, so that the gallium oxide around the iridium rod heats up, conducts electricity, and melts 44 ( Figure 6 ). At this time, the iridium rod is taken out of the crucible, the crucible cover 10 is screwed on, and 0.2MPa of oxygen is introduced into the crucible. In the subsequent process, the locally melted gallium oxide heats the surrounding gallium oxide, causing the gallium oxide to continue to heat up and melt under the action of the electromagnetic field. Figure 7 ) until all the gallium oxide in the crucible is melted. During this period, the melt 29 at the center of the crucible bottom fuses with the upper end of the seed crystal 18. During the melting process, the power supply automatically controls the temperature of the melt in the crucible to be kept within the range of 1760℃±5℃.

[0096] After that, the driving device 06 is started to move the crucible bottom 02 downward and rotate, and the descending speed is controlled to 2 mm / h and the rotation speed is controlled to 30 rph. In the initial stage of the bottom of the crucible descending into the crystallization 03, the melt in the area where the seed crystal and the melt are fused begins to solidify and crystallize ( Figure 3 ), under the control of the axial temperature gradient provided by the bottom of the crucible, the crystal grows upward along the axial direction, and as the bottom of the crucible continues to descend, the crystal gradually develops into a single crystal.

[0097] After the crucible bottom with the solidified gallium oxide rod is pulled out of the crystallizer, the melt in the crucible body continues to fall into the crystallizer. During the solidification process, they grow upward along the surface of the gallium oxide single crystal rod, making the length of the single crystal rod gradually increase ( Figure 8 ) until all the melt in the crucible is pulled out of the crucible.

[0098] After the process was completed, a gallium oxide single crystal with a diameter of about 70 mm, a length of about 150 mm, and a weight of 1.9 kg was obtained.

[0099] Embodiment 2:

[0100] The equipment used in this embodiment is basically the same as that in Embodiment 1, except for the following points:

[0101] 1. The crystallizer tube 26 is made of yttria-stabilized zirconia;

[0102] 2. The ignition material 40 is a graphite rod;

[0103] 3. Cooler 04 is set at 200mm below the crystallizer. The cooler is a stainless steel pipe with an inner diameter of 100mm and a height of 100mm. There are covers at the upper and lower ends, and there is an opening with a diameter of 85mm in the cover. An air supply pipe is set on the side of the upper section of the cooler.

[0104] The process of preparing gallium oxide single crystal is also similar to that of Example 1, except that:

[0105] 1. After the ignition process is completed, the graphite rod 40 is pulled out of the crucible 01, and the gallium oxide is completely melted, and then the heating is continued for 20 minutes to oxidize all the remaining carbon in the gallium oxide and escape from the melt;

[0106] 2. During the melting and crystal growth process, the crucible cover 10 is not covered, and the oxygen delivery tube is hung on the crucible body to blow oxygen to the surface of the melt;

[0107] 3. During the crystal pulling process, when the liquid level of the melt in the crucible is found to be significantly lowered, a block of gallium oxide powder is manually fed into the crucible to keep the liquid level constant;

[0108] 4. After the crucible bottom 02 is pulled out of the crystallizer 03, it continues to be pulled downward, and when it enters the cooler 04, liquid oxygen is blown into the cooler;

[0109] 5. After the crucible bottom 02 is pulled out of the cooler 04, stop feeding the gallium oxide compact into the crucible 01, and continue pulling the crucible bottom until all the melt in the crucible is pulled out of the crucible.

[0110] This process produced a gallium oxide single crystal with a diameter of about 70 mm, a length of about 250 mm, and a weight of 3.3 kg.

[0111] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A melt-descent single crystal growth device for producing gallium oxide single crystals using a cold crucible, characterized in that: It includes a crucible, a crystallizer, a cooler, a power heating system, a driving device and an ignition device, and the crucible includes a crucible body and a crucible bottom; Among them, the crucible body, crucible bottom, crystallizer and cooler arranged from top to bottom constitute the melting zone, crystallization zone and cooling zone for growing single crystals; the crucible bottom runs through the crucible body, crystallizer and cooler to guide the crystal growth; The crucible body is configured as a cylindrical structure for accommodating gallium oxide materials and melts, and the crucible bottom is configured as a structure that can be separated from the crucible body and seals the lower opening of the crucible body, and its outer shape matches the inner shape of the lower opening of the crucible body; A seed crystal pit for installing a seed crystal is provided at the center of the bottom of the crucible, and the lower end of the β-Ga2O3 seed crystal is installed in the seed crystal pit; The power heating system includes a high-frequency power supply, a cable or a copper bar, and an induction coil, wherein the cable or the copper bar is used to transmit a high-frequency current from the high-frequency power supply to the induction coil, and the induction coil is configured as a solenoid surrounding the crucible body; When the bottom of the crucible is pulled down, the gallium oxide melt is pulled into the crystallizer, where it cools, solidifies, and grows crystals; The cooler is arranged below the crystallizer to provide an auxiliary axial temperature gradient to the melt solidifying in the crystallizer; The driving device comprises a pull rod, a linear drive and a rotary drive, the pull rod is mounted on the bottom surface of the bottom of the crucible, and the linear drive and the rotary drive are both combined with the pull rod; The ignition device is used to preheat the gallium oxide to a temperature higher than the conductive temperature of the gallium oxide.

2. The device according to claim 1, characterized in that The crucible also includes a water jacket; The crucible body is made of copper and is divided into petals along the height direction. The cross-section shape and size of each petal are the same. A pipeline serving as a cooling water channel is arranged in each petal. An oxide coating layer is made on the outside of the crucible body, and the cooling water pipelines of each petal are centrally connected to the water jacket, which is connected to the water supply system of the equipment through the water main pipe of the water jacket.

3. The device according to claim 2, characterized in that The gap width between the petals of the crucible body is selected in the range of 0.1 to 10 mm, and the optimal width range is 0.3 to 5 mm.

4. The device according to claim 2, characterized in that The bottom of the crucible is divided into petals along its radial direction, and the number of petals is equal to or less than the number of petals of the crucible body. A water channel for cooling water is also arranged in each petal, and water is supplied by the water channel in the pull rod installed at the bottom of the crucible; The bottom of the crucible is also provided with a locking mechanism for combining the gallium oxide material.

5. The device according to claim 1, characterized in that The crucible also includes a crucible cover to close the upper opening of the crucible; The crucible cover is made of a water-cooled double-layer copper plate, with a cooling water channel between the two layers; The crucible cover is provided with two pipe interfaces, which are respectively used for the gas supply port and the gas exhaust port. A connecting structure which can be combined with each other is provided between the crucible cover and the upper opening of the crucible body.

6. The device according to claim 1, characterized in that The crystallizer includes a crystallization tube, a heating tube and a power supply; wherein the crystallization tube is configured as a tubular structure coaxial with the crucible body and is tightly installed under the crucible body. When the bottom of the crucible is pulled down, the gallium oxide melt is pulled into the crystallization tube, where it is cooled, solidified and crystals are grown; The heating tube is a heating element that surrounds the crystallization tube and provides the crystallization temperature to the crystallization tube; Alternatively, the lower section of the crucible body is used as a crystallizer, and the induction coil is configured to cover only the middle and upper sections of the crucible body, and the initial position of the crucible bottom is located in the middle section of the crucible body.

7. The device according to claim 6, characterized in that The crystal tube is made of high temperature resistant ceramic material or metal, preferably made of zirconia ceramic, yttria stabilized zirconia ceramic, magnesium oxide ceramic or metal iridium, and can also be made of gallium oxide ceramic; And / or, the heating tube material is graphite, or a high temperature resistant metal material, such as molybdenum, tungsten, iridium metal or alloy; And / or, the power source for heating the heating tube is a medium frequency power source, and the heating tube obtains high temperature through induction heating; or, the power source for heating the heating tube adopts low-voltage and high-current alternating current, and the heating tube is made into a resistance heater.

8. The device according to claim 6, characterized in that The cooler comprises a metal cylinder which is coaxial with the crucible body and has upper and lower openings for the crucible bottom to pass through; two gas delivery pipes are arranged on the side of the metal cylinder, which are a gas supply pipe and an exhaust pipe respectively.

9. The device according to claim 8, characterized in that The cooling direction of the cooler to the center of the crystallizer is configured with an inclination angle α relative to the axis. The distance between the cooler and the crystallizer is based on controlling the α angle ≤ 15°, and ≤ 5° is optimal.

10. The device according to claim 1, characterized in that The ignition device includes an ignition material and a lifting frame. Before the high-frequency power source is started, the ignition material is buried in the gallium oxide material. After the high-frequency power source is started, the ignition material heats the gallium oxide until it begins to melt, and then the ignition material is immediately pulled above the crucible body by the lifting frame. Alternatively, the ignition device includes a non-transferred arc type plasma torch and a plasma power supply.

11. The device according to claim 10, characterized in that The ignition material can be selected from rod-shaped graphite or high-temperature resistant metal, and iridium metal is the preferred material among the metals.

12. The device according to any one of claims 1 to 11, characterized in that A feeder is arranged above the crucible body for adding gallium oxide material into the crucible body.

13. A melt-descent single crystal growth method for producing gallium oxide single crystals using a cold crucible, using the apparatus according to any one of claims 1 to 12, characterized in that: The steps include: S1. Before the equipment is put into operation, the bottom of the crucible with β-Ga2O3 seed crystal installed is installed into the lower opening of the crucible body, high-purity gallium oxide raw material is loaded into the crucible body, and the lower end of the ignition material is inserted into the gallium oxide; S2, start the high-frequency power supply and heat the ignition material; when the gallium oxide around the ignition material heats up, conducts electricity and melts, the ignition material is taken out of the crucible, the crucible cover is closed, and oxygen is filled into the crucible; under this condition, the partially melted gallium oxide heats the surrounding gallium oxide to exceed the conduction temperature, and continues to heat up and melt under the action of the electromagnetic field until all the gallium oxide in the crucible is melted; during this period, the melt at the center of the crucible bottom fuses with the upper end of the seed crystal; S3, starting the driving device to move the bottom of the crucible downward and rotate. In the initial stage of the bottom of the crucible descending into the crystallizer, the melt begins to solidify and crystallize at the position where the seed crystal and the gallium oxide melt are fused. Under the control of the axial temperature gradient provided by the bottom of the crucible, the crystal grows upward along the axial direction. In the process of the bottom of the crucible continuing to descend in the crystallizer, a plurality of crystals growing upward are formed from the surface of the bottom of the crucible. The crystals grow laterally while growing upward, and gradually block the crystals growing from other parts of the bottom of the crucible, so that the melt develops into a single crystal during the solidification process. In this process, the gallium oxide solidified in the locking mechanism of the bottom of the crucible is combined with the crystal solidified on it. S4. After the bottom of the crucible with the solidified gallium oxide rod is pulled out of the crystallizer, the melt in the crucible body continues to fall into the crystallizer. During the solidification process, they grow upward along the surface of the gallium oxide single crystal rod, so that the length of the single crystal rod gradually increases; when the bottom of the crucible and the single crystal rod are pulled into the cooler, the gap between the single crystal rod and the upper opening of the cooler is filled with sealing material, and liquid gas is introduced into the cooler to provide an auxiliary axial temperature gradient to the single crystal rod; when the melt in the crucible body is completely pulled out of the crucible body, the crystal pulling process is terminated, and the single crystal rod is removed from the bottom surface of the crucible.

14. The method according to claim 13, characterized in that During the melting and crystal growth process, the temperature of the gallium oxide melt in the crucible should be controlled in the range of 1750-1850°C, with 1760-1780°C being the best. And / or, the temperature in the crystallizer is controlled within the temperature range of 1680-1730°C, with 1710-1720°C being optimal.

15. The method according to claim 13, characterized in that During the process of the crucible bottom descending, the descending speed of the pull rod controlled by the linear drive can be adjusted within the range of 1 to 200 mm / h, and the best descending speed is selected within the range of 2 to 20 mm / h; And / or, the rotation speed of the rotary drive can be adjusted within the range of 1 to 120 rph.

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