A method for removing gas bubbles from a gallium oxide melt

Abstract

This invention relates to the field of semiconductor material preparation technology, specifically a method for removing bubbles from gallium oxide melt. The method includes the regulation of process steps such as raw material pretreatment, segmented sintering, and dynamic crucible rotation control. By precisely controlling key parameters such as forming pressure, sintering conditions and temperature, dynamic stirring of the melt, and holding time, the bubble removal rate within the gallium oxide melt and crystal can be increased to over 92%, and the dislocation density can be controlled at 2.5 × 10⁻⁶. 3 cm ‑2 The resistivity radial deviation is ≤3%. The process method of this invention is efficient and economical, reducing process steps and potential sources of contamination, ensuring product purity and reliability, and also reducing operational difficulty and time costs. The technical solution of this invention directly solves the technical problem of increased crystal defects and performance degradation caused by bubbles, improving the overall quality of the crystal. The obtained gallium oxide crystal better meets the high material standards required for high-performance electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material preparation technology, specifically relating to a technology for removing bubbles in the melt during gallium oxide single crystal growth, thereby improving the quality and purity of crystal products. Background Technology

[0002] Gallium oxide (GaO), a fourth-generation semiconductor, is an important ultra-wide bandgap semiconductor material with a bandgap of 4.9 eV. The theoretical breakdown field strength of β-Ga2O3 single crystal material can reach 8 MV / cm, far exceeding the limits of materials such as GaN and SiC. Furthermore, under the same voltage withstand conditions, GaO-based power devices have lower on-resistance, resulting in higher power conversion efficiency and lower conduction loss. It has broad application prospects in electronic power systems in fields such as new energy vehicles and rail transportation.

[0003] During gallium oxide single crystal growth, the presence of bubbles in the melt affects crystal quality, leading to increased defects and decreased performance. These bubbles, besides being caused by factors such as temperature fluctuations or pressure changes during growth, are mainly caused by impurities and residual gases in the powder raw materials. Although the industry has taken a series of measures to reduce bubble formation, such as optimizing raw material purity and precisely controlling growth conditions, existing technologies still struggle to completely eliminate these bubbles. Therefore, effectively removing bubbles from the gallium oxide melt and improving crystal quality has become a pressing technical challenge.

[0004] In a high-temperature furnace at 1800℃ (the melting point of gallium oxide), conventional methods such as physical stirring and ultrasonic treatment are ineffective. Although increasing the temperature can reduce the viscosity of the melt and improve its fluidity, the higher the temperature, the more significant the volatilization and decomposition of gallium oxide becomes, and the more it accelerates the corrosion process of the crucible. Sometimes, the number of bubbles at the bottom of the crucible will increase, leading to instability at the crystal growth interface.

[0005] Chinese patent CN202210482935.2 (Invention title: A method for doping raw materials to change the fluidity of gallium oxide melt) discloses a method in which elemental Ga is reacted with hydrochloric acid to form a solution, followed by doping, drying, and oxidation. Alkali metals such as Li, Na, and K are used to improve the fluidity of the gallium oxide melt, thereby expelling gases from the raw materials and eliminating pores in the crystal. However, this method is complex and involves numerous steps. Although alkali metals have low segregation coefficients in gallium oxide melt, trace amounts of alkali metals still remain, and they can easily cause gallium oxide contamination during oxidation and crushing. Furthermore, the introduction of alkali metals may alter the chemical equilibrium of the melt, affecting the intrinsic defect concentration of the crystal and thus degrading device performance.

[0006] Therefore, there is an urgent need for a more efficient, economical method to remove bubbles from high-temperature gallium oxide melts that does not cause raw material contamination during the preparation process. Summary of the Invention

[0007] To address at least one of the aforementioned technical problems, this invention provides an efficient, economical method for removing bubbles from high-temperature gallium oxide melt without contaminating the gallium oxide raw material. On one hand, the method minimizes residual gas in the raw material through a sintering process following pressing and forming; on the other hand, it eliminates bubbles through process control during melt holding, such as acceleration, deceleration, and reverse rotation. This method is expected to significantly reduce the number of bubbles in gallium oxide crystals, improve the overall quality of the crystals, and thus meet the high requirements of high-performance electronic devices for gallium oxide materials.

[0008] According to one aspect of the present invention, a method for removing bubbles from a gallium oxide melt is provided, the method comprising the following steps: Step (1): Raw material pretreatment. Select β-gallium oxide powder with a purity ≥99.999%, place it in a mold, and apply pressure at a uniform speed. Control the pressing pressure to be 100-300 MPa and the holding time to be more than 2 minutes to press the gallium oxide powder into shape. Precisely control the pressing pressure and holding time to ensure that the powder particles are tightly combined to form a compact and uniform blank.

[0009] Step (2) Segmented sintering treatment: The pressed gallium oxide blank is placed in a sintering furnace and first subjected to low-temperature initial sintering at a temperature not exceeding 1000℃, and then the temperature is raised to a temperature range of 1500-1700℃ for high-temperature sintering to obtain a dense gallium oxide sintered body.

[0010] Step (3) Melt stirring control: The gallium oxide sintered body is placed in a crucible for melting and crystal growth. During the melt holding stage, the crucible rotation is controlled according to a pre-set dynamic rotation mechanism. The dynamic rotation includes alternating clockwise acceleration and counterclockwise deceleration cycles, with a speed range of 5-30 rpm and at least two cycles. By precisely controlling the crucible rotation parameters, a uniform temperature field and flow field are formed inside the melt, promoting the aggregation and floating of bubbles.

[0011] In one embodiment of the present invention, in step (1), the average particle size D of the β-gallium oxide is less than 4.5 μm or less than 4 μm.

[0012] In another embodiment of the present invention, in step (1), gallium oxide powder is pressed into shape using a hot isostatic pressing process.

[0013] In one embodiment of the present invention, in step (2), the low-temperature initial firing is carried out in an air environment with a heating rate of 5-10℃ / min and a holding time of 2-10 h; the high-temperature sintering is carried out in an air environment with a heating rate of 1-5℃ / min and a holding time of 2-10 h.

[0014] In another embodiment of the present invention, in step (2), the gallium oxide blank is sintered using a microwave sintering method.

[0015] In one embodiment of the present invention, in step (3), in a single cycle mechanism, the rotation is first clockwise at a predetermined acceleration to 10-30 r / min, maintained for a first rotation time, and then switched to counterclockwise rotation at a predetermined deceleration to 5-15 r / min, maintained for a second rotation time, wherein the sum of the first rotation time and the second rotation time is not less than 30 minutes.

[0016] In another embodiment of the present invention, in step (3), the dynamic rotation further includes accelerating clockwise, stopping, and then decelerating counterclockwise, with a single cycle period of 30-90 minutes.

[0017] In another embodiment of the invention, step (3) may further include introducing an external physical field, such as a magnetic field or an electric field, to assist in the removal of bubbles. These external physical fields can affect the fluidity of the melt and the trajectory of the bubbles, promoting the aggregation and floating of bubbles, thereby improving the bubble removal efficiency.

[0018] In another embodiment of the present invention, step (4) is also included. In the crystal growth process of step (4), the crystal rotation speed is V1, the crystal growth rate is V2, the axial temperature gradient of the melt is G, and the product of the rotation speed V1 and the axial temperature gradient of the melt, V1×G, is controlled to be no greater than 350. The surface of the melt is basically horizontal or concave towards the center of the melt. The product of the crystal growth rate V2 and the axial temperature gradient of the melt, V2×G, is controlled to be no greater than 35. The value range of V1 is 1-15 rpm, the value range of V2 is 0.5-5 mm / h, and the value range of G is 5-70℃ / cm.

[0019] According to another aspect of the present invention, a crystal growth apparatus for removing bubbles in gallium oxide melt is also provided. The crystal growth apparatus is equipped with a crucible speed control rotation system for performing programmable rotation drive on the crucible, which is adapted to a composite rotation mode of clockwise acceleration and counterclockwise deceleration. The temperature measuring device includes an infrared thermometer and / or thermocouple for synchronous monitoring of temperature and interface state; and a temperature measurement-control linkage system that links the temperature measuring device with the heating system and crucible speed control rotation system of the crystal growth equipment. When the temperature measuring device detects an abnormal temperature, the system automatically triggers an adjustment command to adjust the heating power or change the crucible rotation speed.

[0020] In one embodiment of the present invention, the crystal growth apparatus for removing bubbles in gallium oxide melt is further equipped with an annular gradient temperature control hot screen, which surrounds the outside of the crucible to make the axial temperature gradient of the crucible uniform and stable.

[0021] According to another aspect of the present invention, a β-Ga₂O₃ single crystal is provided, which can be prepared according to the method described in any embodiment of the first aspect. The β-gallium oxide single crystal has a bubble removal rate ≥90% and a resistivity radial deviation ≤3%.

[0022] According to another aspect of the present invention, a power device based on β-Ga2O3 single crystal is also provided, including but not limited to field-effect transistors, diodes, or deep ultraviolet photodetectors. According to the present invention, since the power device uses the aforementioned tin-doped Ga2O3 single crystal thin film as the core material, it exhibits excellent electrical performance and reliability, making it suitable for next-generation power electronics and optoelectronic applications.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: According to the method of this invention, by synergistically controlling three process steps—raw material pretreatment, segmented sintering, and melt stirring control—the three main sources of bubbles—volatile impurities / adsorbed gases in the raw materials, thermal decomposition during growth, and gas encapsulation at the solid-liquid interface—can be effectively addressed. This significantly eliminates bubbles within the melt, resulting in a substantial improvement in crystal transparency. The final β-gallium oxide single crystal exhibits a bubble removal rate ≥90% and a resistivity radial deviation ≤3%. By optimizing the pressing process and combining it with gallium oxide purity and particle size control, the voids between gallium oxide raw material powders are effectively reduced, lowering the residual gas content in the pressed blank. This creates favorable conditions for further gas removal during subsequent sintering, thereby ensuring the quality of the final gallium oxide crystal. The segmented sintering method proposed in this invention first performs pre-sintering at a lower temperature, allowing organic matter and moisture in the blank to evaporate and powder particles to initially combine, further eliminating residual gases and reducing defects caused by rapid gas escape during subsequent high-temperature sintering. Subsequently, the temperature is raised to a higher temperature for primary sintering, allowing sufficient diffusion and bonding between powder particles to form a denser structure. This further improves the strength and density of the green body, providing a high-quality green body foundation for subsequent crystal growth processes, thereby ensuring the performance of the final gallium oxide crystal. This application also creatively proposes that a dynamic rotation mechanism for the crucible can effectively reduce bubble generation and quickly remove microbubbles generated in the melt. By first accelerating clockwise rotation and then decelerating counterclockwise, a strong shear flow is generated through directional rotation, disrupting the bubble adhesion interface and promoting the merging and floating of small bubbles. Simultaneously, alternating speed changes can avoid crystal defects caused by melt turbulence. Furthermore, combined with appropriate holding time, sufficient time is ensured for bubbles to escape from the melt, thereby effectively reducing the bubble content in the gallium oxide melt and improving the crystal growth quality and performance stability. The above description is merely an overview of the technical solutions of the embodiments of this application. To better understand the technical means of the embodiments of this application and to implement them according to the description, and to make the above and other objects, features, and advantages of the embodiments of this application more apparent and understandable, specific implementation methods of the embodiments of this application are described below. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are merely some exemplary embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the exemplary embodiments of the present invention and these drawings without any creative effort.

[0025] Figure 1 This is a flowchart illustrating one embodiment of the present invention. Figure 1The process shown includes steps such as raw material pretreatment, segmented sintering, and crucible rotation control.

[0026] Figure 2 This is a flowchart illustrating another embodiment of the present invention. Figure 2 The process shown includes raw material pretreatment, segmented sintering, crucible rotation control, and crystal growth process parameter control.

[0027] Figure 3 This is a single crystal growth apparatus for removing bubbles from gallium oxide melt, as described in this embodiment of the invention. It includes a crystal growth device, a crucible speed control and rotation system, a temperature measuring device, etc. Wherein: 1-Crystal growth equipment, 2-Crucible, 3-Melted material, 4-Crucible base, 5-Equipment base, 6-Temperature measuring device, 7-Metal cover, 8-Furnace lining, 9-Heating system, 10-Annular temperature control heat shield, 11-Crucible speed control rotation system, 12-Heat insulation baffle.

[0028] Figure 4 This diagram illustrates the sampling locations for the radial resistivity deviation of gallium oxide single crystals in this embodiment of the invention. Several test points were selected radially outward from the center of the single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, to perform resistivity radial deviation tests. The test results show that the radial resistivity deviation of the gallium oxide single crystal is less than or equal to 3%. Invention Details The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Those skilled in the art will appreciate that many technical details have been provided in the various embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in this invention can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Unless otherwise stated, the terms “include,” “including,” “have,” “contain,” etc., used in this document are open-ended terms, meaning that they include but are not limited to.

[0032] It should be understood that, for the numerical range in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Detailed Implementation

[0033] See Figure 1 , Figure 1 A detailed flowchart of the method for removing bubbles from Ga2O3 melt according to the present invention is shown. The method includes the following steps: Step (1): Raw material pretreatment. Select β-gallium oxide powder with a purity ≥99.999%, place it in a mold, and apply pressure at a uniform speed. Control the pressing pressure to be 100-300 MPa and the holding time to be more than 2 minutes to press the gallium oxide powder into shape. Precisely control the pressing pressure and holding time to ensure that the powder particles are tightly bonded and form a compact and uniform blank.

[0034] In this invention, ultra-high purity Ga2O3 powder is used as the starting material. Low-purity raw materials contain metallic or non-metallic impurities, such as SiO2 and CuO, which may decompose at high temperatures, releasing gases. These gases are difficult to escape during high-temperature melting and easily form bubbles that are trapped within the crystal. By selecting β-gallium oxide powder with a purity ≥99.999%, the gas source introduced by impurities can be significantly reduced, thereby effectively suppressing bubble formation. Simultaneously, high-purity raw materials help improve the electrical uniformity and structural integrity of the final single crystal, laying the foundation for the subsequent growth of high-quality gallium oxide single crystals. Furthermore, to ensure the consistency of each batch of raw materials, all batches of β-gallium oxide powder must be tested by ICP-MS to confirm that the impurity content meets the standards before use, or trace element analysis of each batch of raw materials must be performed using methods such as GDMS.

[0035] The average particle size D of β-gallium oxide is preferably below 5 μm, or below 4.5 μm, or even below 4 μm. The particle size of the raw material determines the density of the pressed gallium oxide blank. The smaller the particle size, the smaller the gaps between the powders, and the less gas is contained in the blank. Therefore, controlling the particle size of the raw material not only helps to improve the density of the blank, but also effectively reduces the residual gas trapped in the gaps between the particles during the pressing process. During the subsequent heating process, smaller pores are more easily discharged through diffusion mechanisms, reducing the probability of stable bubbles forming in the melt. At the same time, the fine and uniform particle distribution is conducive to the uniform transmission of the heat and stress fields, avoiding bubble formation caused by local overheating or uneven melting. Combining the dual advantages of high purity and ultra-fine particle size, the generation of bubble defects can be significantly suppressed from the source.

[0036] During pressing, WC cemented carbide molds with a surface roughness of Ra=0.1 μm can be used. This extremely low surface roughness is beneficial for the formation of a dense structure from gallium oxide powder. Alternatively, segmented elastic molds can be used, with independent pressure control for the upper and lower molds. Pressurization can be unidirectional or bidirectional. When using single-stage pressing, the pressing rate is 5-10 MPa / s. After reaching the required pressing pressure, the pressure is held for a predetermined time, such as 4 minutes, 8 minutes, 10 minutes, or 12 minutes, but not less than 2 minutes. When using segmented pressing, the pressing rate remains constant. Pre-pressing can be done at a lower pressure for a certain time, followed by pressing to a higher pressure for holding. The pre-pressing pressure is typically 30%-50% of the final pressure, and the holding time is 30-120 seconds to expel air trapped between powder particles and achieve initial densification. The main pressing stage pressure ranges from 100-300 MPa, with a holding time of at least 4 minutes, ensuring the billet density reaches at least 60% of the theoretical density. The pressure increases by 10% from the center to the edge to reduce cracks and delamination defects caused by stress concentration at the corners. Simultaneously, a stepped depressurization process is employed after the pressure holding period, reducing the pressure by 30-50 MPa at each stage and maintaining it for 30 seconds to prevent cracking of the billet caused by elastic aftereffects. The resulting gallium oxide green billet exhibits high density, low porosity, and good mechanical strength, providing structural support for subsequent cold isostatic pressing or direct hot pressing sintering.

[0037] The entire pressing process can be carried out at room temperature and in air atmosphere, with an ambient humidity of ≤30%. The resulting gallium oxide billet is cylindrical with radial and axial shrinkage rates of less than 1.5%, free from cracks, delamination, or obvious defects. The billet density is controlled to be above 85% of the theoretical density to ensure no residual porosity during subsequent melting.

[0038] In the method of this invention, hot isostatic pressing (HIP) can also be used to pretreat gallium oxide powder. HIP sintering enables the powder material to achieve more thorough densification under the combined action of high temperature and high pressure, effectively eliminating defects such as pores within the material, thereby improving the quality of gallium oxide crystals. For example, in the HIP process, the temperature is typically controlled at 800-1200℃, the pressure at 100-200 MPa, and the holding time is no less than 30 minutes. At high temperatures, the atomic diffusion rate accelerates, and combined with the isotropic high pressure, it can significantly promote grain boundary fusion and pore annihilation. During the cooling stage, programmed temperature control must be used to avoid thermal stress accumulation leading to cracking. By strictly controlling the process parameters, the final density of the blank can approach 98% or more of the theoretical density. HIP sintering equipment is expensive, complex to operate, and has extremely stringent requirements, resulting in high costs and long processing times. Therefore, the HIP process is more suitable for the preparation of high-value-added, high-performance gallium oxide single crystals. To balance cost and performance, a composite process path combining cold isostatic pressing preforming with subsequent vacuum sintering can be adopted to achieve near-densification at a lower cost.

[0039] Step (2) Segmented sintering treatment: The pressed gallium oxide blank is placed in a sintering furnace and first subjected to low-temperature initial sintering at a temperature not exceeding 1000℃, and then the temperature is raised to a temperature range of 1500-1700℃ for high-temperature sintering to obtain a dense gallium oxide sintered body.

[0040] In existing technologies, gallium oxide sintering typically employs a one-step sintering process. To further eliminate volatile impurities and / or adsorbed gases in the gallium oxide powder, a prolonged calcination process is required before placing the gallium oxide blank into the growth furnace. One-step sintering is highly prone to problems such as encapsulation and powder agglomeration. Therefore, this invention proposes a segmented sintering scheme based on the traditional one-step sintering process. Simultaneously, by controlling the heating rate and holding time, the grain boundary structure is further optimized, improving the material's density.

[0041] First, pre-sintering is carried out at a relatively low temperature in an oxygen-containing atmosphere, such as air. The purpose is to volatilize the organic matter and moisture in the green body, rather than densify it. Therefore, the heating rate in the low-temperature initial sintering stage is relatively slow, allowing sufficient time for the gas to slowly diffuse from the interior of the green body to the surface and be carried away by the flowing atmosphere. Generally speaking, the thicker the green body, the longer the path for the gas generated inside to diffuse outward, and the greater the resistance. If the heating rate is too fast, it will lead to internal pressure accumulation, resulting in cracking, blistering, and other phenomena. However, the heating rate in the low-temperature initial sintering stage should not be too slow, otherwise the time cost will be too high. For example, the heating rate in the low-temperature initial sintering stage can be above 5℃ / min, or 5-10℃ / min, or 5-8℃ / min, and the holding time can be 2-10 h, ensuring that the physically adsorbed moisture (H2O) and chemically bonded hydroxyl groups (-OH) in the gallium oxide raw material can be basically removed.

[0042] Subsequently, the temperature is raised to a higher level for primary sintering. A protective atmosphere, such as argon or nitrogen, is preferred for sintering, with a purity ≥99.99%. Simultaneously, to suppress the high-temperature decomposition of gallium oxide, an oxygen atmosphere is sometimes introduced, in which case the oxygen partial pressure can be 10. -2Pa. The heating rate during the high-temperature sintering stage is 1-5℃ / min, or 1-3℃ / min, or 3-5℃ / min, with a holding time controlled between 2-10 h to ensure sufficient grain growth and reduce internal stress. Considering the heating capacity of the sintering furnace itself, the heating rate during the high-temperature sintering stage can be slightly lower than that during the low-temperature initial sintering stage, which is beneficial for suppressing abnormal grain growth and obtaining a microstructure with small grains and high density. However, if the heating is too slow, it will give the grains too much growth time, leading to grain coarsening. Consequently, the coarse grains will encapsulate the pores, making it difficult for them to escape. By segmenting the temperature control, the thermal shock of the billet during the sintering process is effectively mitigated, and the formation of microcracks and pores is suppressed. This further improves the strength and density of the billet, providing a high-quality billet foundation for subsequent crystal growth processes, thereby ensuring the performance of the final gallium oxide crystal.

[0043] In embodiments of the present invention, further heating stages may be included to achieve gradient pre-sintering treatment of the raw materials. Optionally, the first heating stage involves holding the material at room temperature -600°C for 1-2 hours to remove physically adsorbed water and organic matter, preventing the formation of bubbles or cracks during subsequent melting; the second heating stage involves raising the temperature to 600-1100°C and holding it for 2-4 hours to enhance the volatilization of low-boiling-point impurities (such as C and H); the third stage involves raising the furnace temperature to 1200-1400°C and holding it for 2-4 hours after the temperature stabilizes, rapidly passing through the low-temperature zone to suppress Ga2O3 grain coarsening; the fourth stage involves continuing to raise the temperature to 1500-1700°C and holding it for 2-10 hours for high-temperature sintering, promoting sufficient densification between particles and grain growth to form a high-density, low-defect Ga2O3 sintered body. The heating rate at each stage is controlled at 1-15°C / min to avoid powder agglomeration or uneven reaction due to thermal shock. Those skilled in the art can adjust the heating stages according to actual production needs. Multi-stage heating design can effectively improve the density and structural uniformity of the sintered body, significantly reduce the density of grain boundary defects, and achieve a sintered body density of over 95%. This process is particularly suitable for the preparation of large-size, high-quality gallium oxide single crystal growth precursors, providing a reliable blank guarantee for subsequent Czochralski or vertical Bridgman process growth of large-size crystals.

[0044] In the method of this invention, other calcination methods such as microwave sintering can also be used to sinter the gallium oxide blank. Microwave sintering utilizes the direct interaction between microwaves and the gallium oxide blank to heat the entire interior of the sintered body to the sintering temperature, offering advantages such as rapid and uniform heating. This sintering method may reduce thermal stress during the sintering process and avoid defects caused by rapid gas escape due to localized overheating, thereby more effectively reducing the amount of residual gas within the sintered body.

[0045] Step (3) Melt stirring control: The gallium oxide sintered body is placed in a crucible for melting and crystal growth. During the melt holding stage, the crucible rotation is controlled according to a pre-set dynamic rotation mechanism. The dynamic rotation includes alternating clockwise acceleration and counterclockwise deceleration cycles, with a speed range of 5-30 rpm and at least two cycles. By precisely controlling the crucible rotation parameters, a uniform temperature field and flow field are formed inside the melt, promoting the aggregation and floating of bubbles.

[0046] The inventors of this application creatively propose that a dynamic rotation mechanism for the crucible can effectively reduce bubble formation and quickly remove microbubbles generated in the melt. By first accelerating clockwise and then decelerating counterclockwise, a strong shear flow is generated through the directional rotation, disrupting the bubble adhesion interface and promoting the merging and floating of small bubbles. Simultaneously, the alternating speed variation avoids crystal defects caused by melt turbulence. Furthermore, combined with an appropriate holding time, for example, a single cycle of no less than 30 minutes, or even no less than 1 hour, ensures that bubbles have sufficient time to escape from the melt, thereby effectively reducing the bubble content in the gallium oxide melt and improving the crystal growth quality and performance stability. After crystal growth is complete, the crystal is cooled to room temperature and removed to obtain a gallium oxide single crystal ingot.

[0047] In an embodiment of the invention, the crystal is first rotated clockwise at a predetermined acceleration to 10-30 r / min, maintained for a first rotation time, and then switched to counterclockwise rotation at a predetermined deceleration to 5-15 r / min, maintained for a second rotation time. The sum of the first and second rotation times is not less than 30 minutes. This dynamic rotation process can be repeated 2-4 times to ensure that bubbles inside the melt are fully expelled. By controlling the acceleration and deceleration within the range of 0.5 rpm / s, drastic disturbances that could cause melt instability are avoided. Simultaneously, matching the timing of the rotation direction switch with the holding phase helps maintain temperature gradient uniformity and reduces disturbances at the crystal growth interface. Experiments show that gallium oxide single crystals using this stirring method have a bubble density that is more than 60% lower than those produced by traditional processes, and significantly improved light transmittance, meeting the requirements of high-end power devices for high-quality substrates.

[0048] According to the preparation process of the present invention, the dynamic rotation further includes clockwise acceleration, a pause for a period of time, and then counterclockwise deceleration, with a single cycle of 30-90 minutes. The pause phase helps eliminate residual shear flow inside the melt, allowing bubbles to further aggregate and grow without external disturbance, thus improving the flotation efficiency. Combined with a complete thermal cycle design, it effectively avoids thermal convection turbulence caused by continuous rotation, ensuring the stability of the crystal growth interface.

[0049] In other embodiments of the present invention, step (3) further includes introducing external physical fields, such as magnetic fields and electric fields, to assist in bubble removal. These external physical fields can affect the fluidity of the melt and the trajectory of the bubbles, promoting bubble aggregation and floating, thereby improving bubble removal efficiency. Specifically, applying an alternating magnetic field can induce Lorentz forces in the melt, driving the directional migration of microbubbles; while the electrostatic field causes the bubbles to move to regions with lower field strength through the dielectrophoresis effect, preventing them from aggregating at the crystal growth interface. The synergistic effect of the external physical field and dynamic rotation further enhances the bubble detachment and transport process, significantly improving removal efficiency.

[0050] In the method for removing bubbles from gallium oxide melt according to the present invention, the cooling process of the sintered body, as the final step in the sintering process, has a significant impact on the sintering effect. If not controlled, it may ultimately lead to cracking, excessive grain growth, and insufficient release of thermal stress, affecting crystal quality. Generally, after high-temperature sintering, the sintered body is slowly cooled to room temperature in the furnace at a cooling rate of 3-10 °C / min. This cooling rate is directly related to factors such as the size and thickness of the billet, and the uniformity of the thermal field within the furnace; for example, the thicker the billet, the slower the cooling rate. In the embodiments of the present invention, a segmented cooling method can be adopted. In the high-temperature zone above 1000 °C, a higher cooling rate of 3-5 °C / min is used for faster cooling to suppress grain growth. Subsequently, in the brittle temperature zone of 600 °C-1000 °C, a very slow cooling rate of 1-2 °C / min or even lower is used to release thermal stress and prevent cracking. In the low-temperature region below 600℃, the risk of thermal stress is reduced, and the cooling rate can be accelerated to improve efficiency, for example, by continuing to cool down to room temperature at a cooling rate of 5-10℃ / min.

[0051] In summary, the method of this invention, through the coordinated control of three process steps—raw material pretreatment, segmented sintering, and melt stirring—solves the three main sources of bubbles: volatile impurities / adsorbed gases in the raw materials, thermal decomposition during growth, and gas encapsulation at the solid-liquid interface. This effectively eliminates bubbles within the melt, significantly improving crystal transparency. The resulting β-gallium oxide single crystal exhibits a bubble removal rate ≥90% and a resistivity radial deviation ≤3%.

[0052] See Figure 2 , Figure 2Specifically shows a flowchart of another method for removing bubbles in a Ga2O3 melt according to the present invention. This method further includes the following steps: Step (4) Crystal growth. During the crystal growth process in step (4), the crystal rotation speed is V1, the crystal growth rate is V2, and the axial temperature gradient of the melt is G. Control the product V1×G of the rotation speed V1 and the axial temperature gradient of the melt to be not greater than 350, the melt surface is basically horizontal or concave towards the center of the melt, and control the product V2×G of the crystal growth rate V2 and the axial temperature gradient G of the melt to be not greater than 35, where the value range of V1 is 1 - 15 rpm, the value range of V2 is 0.5 - 5 mm / h, and the value range of G is 5 - 70 °C / cm.

[0053] Crystal growth process parameters are another key point for reducing or controlling bubble formation. The main process parameters include the crystal rotation speed V1, the crystal growth rate V2, and the axial temperature gradient G of the melt.

[0054] Among them, the crystal rotation speed V1 is a key process parameter that needs attention. Appropriate crystal rotation can stir the melt, make the melt temperature and composition more uniform, and can also change the local flow field at the solid-liquid interface, which helps to "sweep" small bubbles near the interface to the crystal edge and prevent them from being trapped. However, the crystal rotation rate V1 should not be too fast, otherwise it will introduce strong forced melt convection, which may cause temperature fluctuations and even entrain gas.

[0055] Precisely controlling the temperature field and temperature gradient G is an important technical means for removing bubbles in the melt. By designing a reasonable thermal field, it can ensure that the axial temperature gradient G at the solid-liquid interface is moderate, uniform, and stable. An excessive temperature gradient will cause constitutional supercooling, making bubbles or other impurities be quickly trapped in the crystal; a too small temperature gradient may make the interface unstable. In actual production, by optimizing the thermal field, make the solid-liquid interface as flat as possible or slightly concave towards the melt. This is beneficial for bubbles to have enough time and paths to be discharged to the side of the crystal when they form or approach the interface, rather than being wrapped into the crystal interior. An interface concave towards the melt is most likely to trap bubbles.

[0056] The crystal growth rate V2 is another key parameter. Reducing the growth rate is one of the most effective methods for reducing bubble defects. According to the constitutional supercooling theory, the critical growth rate Vc is proportional to the temperature gradient G. When the actual growth rate V2 < Vc, stable planar growth can be maintained to avoid the entrapment of bubbles and impurities. For gallium oxide, relatively slow growth rates are usually adopted, such as 0.5 - 5 mm / h, or 0.8 - 4 mm / h, or even 1 - 3 mm / h, to ensure the stable advancement of the solid-liquid interface and give bubbles enough time to escape.

[0057] In step (4) of this invention, the crystal growth process can be carried out under a suitable atmosphere. Commonly used growth atmospheres include gases such as air and oxygen, or mixtures of these with inert gases. An oxygen atmosphere helps to suppress the decomposition of Ga2O3 at high temperatures (reaction: Ga2O3(s) → Ga2O(g) + O2(g)). In an environment with a high oxygen partial pressure, the decomposition reaction is suppressed, thereby reducing the generation of bubbles (mainly Ga2O vapor) at the source. Higher pressure can significantly increase the decomposition temperature of Ga2O3, making it essentially non-decomposed below its melting point (~1800°C).

[0058] See Figure 3 , Figure 3 This is a schematic diagram of the crystal growth device used to remove bubbles in gallium oxide melt in an embodiment of the present invention. Figure 3 The crystal growth equipment 1 on display is equipped with a crucible speed control rotation system 11, which is used to perform programmable rotation drive on the crucible 2, and is adapted to a combined rotation mode of clockwise acceleration and counterclockwise deceleration. Temperature measuring device 6, including an infrared thermometer and / or thermocouple, is used to realize synchronous monitoring of temperature and interface state; and observation-control linkage system, which links the observation equipment, the temperature measuring device 6, the heating system 9 and the crucible rotation system 11 of the crystal growth equipment 1. When the observation equipment observes an increase in bubbles, or the temperature measuring device 6 detects an abnormal interface temperature gradient, the system automatically triggers adjustment commands to adjust the heating power and change the crucible rotation speed to suppress bubble generation in a timely manner.

[0059] To obtain β-gallium oxide single crystals with minimal bubble removal, comprehensive control over each process step is crucial, and the choice of crystal growth apparatus is also critical. The melt 3 has the most direct contact with the crucible 2, which is generally selected to have minimal reaction with the Ga2O3 melt and to avoid introducing impurities. It is essential to ensure that the inner wall of crucible 2 is smooth and clean, as any roughness can become a nucleation point for bubbles.

[0060] Uneven heating and crucible wear can lead to gallium oxide decomposition or the generation of impurity gases. Therefore, the heating system needs improvement and the addition of specialized auxiliary equipment to enhance bubble removal. For example, the heating device can be improved by adopting a dual-heating structure: one heating the raw material inside the crucible, and the other regulating the temperature at the bottom of the crucible to prevent localized overheating and excessive gallium oxide decomposition. Simultaneously, a gradient temperature control system can be used to precisely control the heating rate, such as a slow heating at 5°C / min in the low-temperature stage, allowing gases in the raw material to gradually precipitate and reducing sudden bubble formation. In other implementations, crucible isolation and flow guiding devices can be added. A partition wall and sealing screen can be installed inside the crucible to form an independent feeding chamber, equipped with a corresponding automatic feeding device. The raw material is preheated and melted in the feeding chamber before flowing smoothly into the crystallization zone through the flow guiding structure, avoiding direct feeding that could cause melt disturbance and bubble generation. A dedicated oxygen delivery device can also be connected to the feeding chamber to suppress gallium oxide decomposition and gas generation by regulating the oxygen content. A swirling gas-driving device can also be configured to design a driving device that integrates rotation and oscillation for the crucible. Through the meshing transmission of the active bevel gear and the passive bevel gear, the crucible is driven to swirl in three dimensions, and the eddy current effect is used to "squeeze" the bubbles to the surface of the melt. At the same time, a heat insulation layer is added to the device to slow down the cooling rate of the melt and allow sufficient time to expel the bubbles.

[0061] In one embodiment of the present invention, the crystal growth apparatus for removing bubbles from the gallium oxide melt is further equipped with a ring-shaped temperature-controlled heat shield 10. This heat shield surrounds the outside of the crucible, ensuring a uniform and stable axial temperature gradient along the crucible, further reducing thermal disturbance at the crystal growth interface, thereby improving crystal quality and interface stability. By optimizing the heat shield material and cooling rate, system stability and repeatability are further improved, ensuring consistency in the crystal growth process for each batch. For example, high-purity zirconium oxide is selected as the heat shield material, possessing excellent high-temperature resistance and low thermal radiation absorption rate, maintaining stable thermal performance during long-term operation, further ensuring the uniformity and controllability of the crystal growth environment.

[0062] In addition, a tail gas purification and recovery device can be added to the crystal growth equipment of the present invention. A condensation recovery module is set on the tail gas discharge path to recover the gallium vapor in the tail gas and prevent it from flowing back and contaminating the melt to generate bubbles. At the same time, a gas filtration device is provided to prevent impurity particles in the tail gas from entering the growth chamber and reduce polluting gas production.

[0063] Figure 4 This diagram illustrates the sampling locations for the radial resistivity deviation of gallium oxide single crystals in this embodiment of the invention. Several test points were selected radially outward from the center of the single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, to perform resistivity radial deviation tests. The test results show that the radial resistivity deviation of the gallium oxide single crystal is less than or equal to 3%.

[0064] The power devices based on the tin-doped Ga2O3 single crystal according to the present invention include, but are not limited to, field-effect transistors, diodes, or deep ultraviolet photodetectors. According to the present invention, since the power devices use the aforementioned tin-doped Ga2O3 single crystal thin film as the core material, they exhibit excellent electrical performance and reliability, making them suitable for next-generation power electronics and optoelectronic applications.

[0065] Example 1 This embodiment adopts Figure 3 The crystal growth equipment shown provides a method such as Figure 1 The method shown includes the following steps for removing bubbles from gallium oxide melt: (1) Raw material pretreatment steps. β-gallium oxide powder with a purity ≥99.999% was selected, and the average particle size D was 4.5 μm. The gallium oxide powder was placed in a mold and pressed at a uniform speed using a WC hard alloy mold with a surface roughness Ra=0.1μm. The pressing pressure was controlled at 200 MPa, and the holding time was 8 minutes. The gallium oxide powder was pressed into shape at room temperature (25℃). Precise control of the pressing pressure and holding time ensured that the powder particles were tightly bonded, forming a dense and uniform blank. The blank density reached 3.8 g / cm³. 3 The porosity is ≤5%, and the voids between powder particles are uniformly distributed. Measurements using the helium displacement method show that the residual gas content is reduced to 0.3 vol%.

[0066] (2) Segmented sintering step. The pressed gallium oxide blank is placed in a sintering furnace and heated to 900 °C at a heating rate of 5 °C / min under an air atmosphere. It is then held at this temperature for 3 hours for low-temperature initial sintering to remove adsorbed water, crystal water, and trace organic matter from the powder. The atmosphere in the sintering furnace is then changed to a mixed atmosphere of argon and oxygen, with the oxygen partial pressure maintained at 10. -2 Pa was used to suppress the decomposition of gallium oxide. The temperature was increased to 1600℃ at a heating rate of 3℃ / min, and sintered for 5 hours to ensure sufficient grain growth and reduce internal stress. After segmented sintering, the sintered body was cooled to room temperature with the furnace to obtain a dense gallium oxide sintered body with a density of 96%.

[0067] (3) Crucible stirring control steps. 480g of gallium oxide sintered body was placed in a 2-inch alloy crucible with an inner diameter of approximately 55mm for melt crystal growth. First, the temperature was increased to the gallium oxide melting temperature at a heating rate of 3℃ / min and held at 1810℃ for 3 hours. During the melt holding stage, the crucible rotation was controlled according to a pre-set crucible dynamic rotation mechanism. The crucible was first accelerated clockwise at 0.5 rpm / s to 15 rpm and held for 5 minutes; then it was decelerated counterclockwise at 0.3 rpm / s to 10 rpm and held for 30 minutes, and this cycle was repeated 3 times. The strong shear flow generated by the directional rotation disrupted the bubble adhesion interface, promoted the merging and floating of small bubbles, and avoided crystal defects caused by melt turbulence by alternating speed changes. Then, the temperature was lowered to 1805℃ and held for 3 hours for crystal growth.

[0068] According to the method of this embodiment, a gallium oxide single crystal with a size of φ55mm×25mm was obtained. Microscopic observation showed no fine bubbles, and spectral analysis showed a bubble removal rate of 92%. Figure 4 The resistivity radial deviation of the gallium oxide single crystal obtained in Example 1 was tested using the following method. Twenty-seven test points (3×9) were selected radially outward from the center of the gallium oxide single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, for resistivity radial deviation testing. The test results are shown in Table 1. The results indicate that the resistivity radial deviation of the gallium oxide single crystal is less than or equal to 3%.

[0069] Table 1

[0070] Example 1 achieves a uniform temperature and flow field inside the melt by precisely controlling the rotation parameters of the crucible, which promotes the aggregation and floating of bubbles. The bubble density inside the gallium oxide single crystal is reduced by more than 60% compared with the traditional process, and the light transmittance is significantly improved, meeting the requirements of high-end power devices for high-quality substrates.

[0071] Example 2 This embodiment adopts Figure 3 The crystal growth equipment shown provides a method such as Figure 2 The method shown includes the following steps for removing bubbles from gallium oxide melt: (1) Raw material pretreatment steps. β-gallium oxide powder with a purity ≥99.999% and an average particle size D of 4.5 μm was selected. A WC cemented carbide mold with a surface roughness Ra=0.1 μm was used. After preheating the mold to 60℃, the gallium oxide powder was placed in the mold and pressed at a uniform speed. The pressing pressure was controlled at 240 MPa, and the holding time was 12 minutes to press the gallium oxide powder into shape. The bulk density reached 4.2 g / cm³. 3The porosity is ≤2%, and the voids between powder particles are uniformly distributed. Measurements using the helium displacement method show that the residual gas content is reduced to 0.1 vol%.

[0072] (2) Segmented sintering step. The pressed gallium oxide blank is placed in a sintering furnace, and then the sintering furnace is evacuated. The vacuum degree can be 10. -2 Pa further removes gas molecules adsorbed on the surface of the gallium oxide sinter and the crucible wall. Then, the temperature is increased to 950 °C at a rate of 5-8 °C / min and held at this temperature for 5 h for low-temperature initial sintering to remove adsorbed water and water of crystallization from the powder and promote the volatilization of low-boiling-point organic impurities. The atmosphere in the sintering furnace is then changed to a mixed atmosphere of argon and oxygen, with the oxygen partial pressure maintained at 10. -2 Pa was used to suppress the decomposition of gallium oxide. The temperature was increased to 1600℃-1700℃ at a heating rate of 3-5℃ / min and held for 5 hours for high-temperature sintering to ensure sufficient grain growth and reduce internal stress. After segmented sintering, the sintered body was cooled to room temperature with the furnace to obtain a dense gallium oxide sintered body with a density increased to 98%.

[0073] (3) Crucible stirring control steps. 550g of gallium oxide sintered body was placed in a 2-inch alloy crucible with an inner diameter of about 55mm for melting and crystal growth. First, the temperature was increased to the gallium oxide melting temperature at a heating rate of 6-8℃ / min and held at 1810℃ for 3 hours. During the melt holding stage, the crucible rotation was controlled according to the pre-set crucible dynamic rotation mechanism. The crucible was first accelerated clockwise at 0.5 rpm / s to 15 rpm and held for 5 minutes; then it was decelerated counterclockwise at 0.3 rpm / s to 10 rpm and held for 30 minutes. This cycle was repeated 3 times. The strong shear flow generated by the directional rotation destroyed the bubble adhesion interface and promoted the merging and floating of small bubbles. At the same time, the alternating speed change avoided crystal defects caused by melt turbulence.

[0074] (4) Crystal growth steps. The temperature in the crystal growth furnace is then lowered to 1805℃ and held at that temperature for 3 hours to allow for crystal growth. The axial temperature gradient and crystal growth rate during the crystal growth stage affect the stability of the solid-liquid interface, preventing impurities or bubbles from being captured in the crystal and causing bubble defects. According to this embodiment, the axial temperature gradient is controlled at 50-60℃ / cm, and the crystal growth rate is controlled within the range of 0.9-1 mm / h. Under these conditions, the solid-liquid interface is relatively stable, and the bubbles generated in the melt have sufficient time to be dispersed to the side of the crystal. At the same time, controlling the crystal rotation speed at 5 rpm also helps to "sweep" small bubbles near the interface to the edge of the crystal, preventing them from being captured by the crystal.

[0075] According to the method of this embodiment, a gallium oxide single crystal with a size of φ55mm×30mm was obtained. Microscopic observation showed no fine bubbles, and spectral analysis showed a bubble removal rate of 97%. Figure 4 The resistivity radial deviation of the gallium oxide single crystal obtained in Example 2 was tested using the same method. Twenty-seven test points (3×9) were selected radially outward from the center of the gallium oxide single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, for resistivity radial deviation testing. The test results showed that the resistivity radial deviation of the gallium oxide single crystal was less than 3%.

[0076] Example 2: By precisely controlling the rotation parameters of the crucible, a uniform temperature field and flow field are formed inside the melt, which promotes the aggregation and floating of bubbles. The bubble density inside the gallium oxide single crystal is greatly reduced and the light transmittance is significantly improved, meeting the requirements of high-end power devices for high-quality substrates.

[0077] Example 3 This embodiment adopts Figure 3 The crystal growth equipment shown provides a method such as Figure 2 The method shown includes the following steps for removing bubbles from gallium oxide melt: (1) Raw material pretreatment steps. β-gallium oxide powder with a purity ≥99.999% was selected, with an average particle size D of 4.5 μm. A segmented elastic mold was used, with independent control of the upper and lower mold pressures. The mold surface roughness Ra=0.1 μm. The gallium oxide powder was placed in the mold and kept in a dry environment at room temperature (humidity ≤30%). It was first pre-pressed at 200 MPa for 2 minutes, then held at 240 MPa for 5-8 minutes, maintaining a pressure gradient of 10% from the center to the edge to press the gallium oxide powder into shape. The bulk density reached 4.0 g / cm³. 3 The porosity is ≤1%, and the voids between powder particles are uniformly distributed with a porosity of 3%. Measurements using the helium displacement method show that the residual gas content is reduced to 0.1 vol.

[0078] (2) Segmented sintering step. The pressed gallium oxide blank is placed in a sintering furnace and heated to 850 ℃ at a heating rate of 5-8 ℃ / min. It is then held at this temperature for 6-8 h for low-temperature initial sintering to remove adsorbed water and crystal water from the powder and promote the volatilization of low-boiling-point organic impurities. Then, the atmosphere in the sintering furnace is changed to a mixed atmosphere of argon and oxygen, with the oxygen partial pressure maintained at 10. -2Pa was used to suppress gallium oxide decomposition. The temperature was increased to 1600℃-1700℃ at a heating rate of 2-4℃ / min and held for 4-6 h for high-temperature sintering to ensure sufficient grain growth and reduce internal stress. After segmented sintering, the sintered body was slowly cooled to room temperature at a cooling rate of 5-8℃ / min to obtain a dense gallium oxide sintered body with a density increased to 97%.

[0079] (3) Crucible stirring control steps. 500g of gallium oxide sintered body was placed in a 2-inch alloy crucible with an inner diameter of about 55mm for melting and crystal growth. First, the temperature was raised to the gallium oxide melting temperature at a heating rate of 6-8℃ / min and held at 1810℃ for 2 hours. During the melt holding stage, the crucible rotation was controlled according to the pre-set crucible dynamic rotation mechanism. The crucible was first accelerated clockwise at 0.5 rpm / s to 12-15 rpm and held for 30 minutes. Then the crucible rotation was stopped and held for 2 minutes to eliminate residual shear flow inside the melt, allowing the bubbles to further aggregate and grow without external disturbance, thus improving the floating efficiency. Then, the crucible was accelerated counterclockwise at 0.3 rpm / s to 8-10 rpm and held for 30 minutes. This cycle was repeated 3 times. The pulsed flow field generated by the variable rotation destroyed the bubble attachment interface, promoted the merging and floating of small bubbles, and avoided crystal defects caused by melt turbulence by alternating speed changes.

[0080] (4) Crystal growth steps. The temperature in the crystal growth furnace is then lowered to 1805℃ and held for 3 hours for crystal growth. The axial temperature gradient and crystal growth rate during the crystal growth stage affect the stability of the solid-liquid interface, preventing impurities or bubbles from being captured in the crystal and causing bubble defects. According to this embodiment, the axial temperature gradient is controlled at 50-60℃ / cm and the crystal growth rate is controlled within the range of 0.9-1 mm / h. Under these conditions, the solid-liquid interface is observed to be relatively stable, and the bubbles generated in the melt have sufficient time to be dispersed to the side of the crystal. At the same time, the crystal rotation speed is controlled at 5 rpm, which also helps to "sweep" small bubbles near the interface to the edge of the crystal and prevent them from being captured by the crystal. After crystal growth, the temperature is held for 2.5 hours for directional annealing to release lattice stress and reduce dislocation density.

[0081] According to the method of this embodiment, a gallium oxide single crystal with a size of φ55mm×28mm was obtained. Microscopic observation showed no fine bubbles, and spectral analysis showed a bubble removal rate of 95%. Figure 4The resistivity radial deviation of the gallium oxide single crystal obtained in Example 3 was tested using the same method. Twenty-seven test points (3×9) were selected radially outward from the center of the gallium oxide single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, for resistivity radial deviation testing. The test results showed that the resistivity radial deviation of the gallium oxide single crystal was less than 3%.

[0082] Example 3: By precisely controlling the rotation parameters of the crucible, a uniform temperature field and flow field are formed inside the melt, which promotes the aggregation and floating of bubbles. The bubble density inside the gallium oxide single crystal is greatly reduced and the light transmittance is significantly improved, meeting the requirements of high-end power devices for high-quality substrates.

[0083] Example 4 Example 4 is similar to Example 1, except that hot isostatic pressing (HIP) is used to press gallium oxide powder into a blank to be sintered. The specific implementation method is as follows: β-gallium oxide powder with a purity ≥99.999% and an average particle size D of 4.5 μm was selected. A flexible isostatic pressing graphite mold with a surface roughness Ra=0.1 μm was used as the pressing mold. The gallium oxide powder was placed in the mold, and the isostatic pressing chamber was kept in an inert atmosphere. The temperature was typically controlled at 800-1200℃, the pressure at 100-200 MPa, and the holding time was 30 minutes to press the gallium oxide powder into shape. In the hot isostatic pressing process, the atomic diffusion rate is accelerated at high temperatures, and combined with the isotropic high pressure, it can significantly promote grain boundary fusion and porosity annihilation. Through strict control of process parameters, the final bulk density obtained is approximately 5.76 g / cm³. 3 It has a density close to 97% of the theoretical density and a porosity of ≤0.3%. Measurements using the helium displacement method show that the residual gas content is reduced to 0.05 vol%.

[0084] According to the method of this embodiment, a gallium oxide single crystal with a size of φ55mm×25mm was obtained. Microscopic observation showed no fine bubbles, and spectral analysis showed a bubble removal rate of over 97%. Figure 4 The resistivity radial deviation of the gallium oxide single crystal obtained in Example 4 was tested using the same method. Twenty-seven test points (3×9) were selected radially outward from the center of the gallium oxide single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, for resistivity radial deviation testing. The test results showed that the resistivity radial deviation of the gallium oxide single crystal was less than 3%.

[0085] Example 4 uses hot isostatic pressing to press gallium oxide blanks, and by precisely controlling the rotation parameters of the crucible, a uniform temperature field and flow field are formed inside the melt, which promotes the aggregation and floating of bubbles. The bubble density inside the gallium oxide single crystal is greatly reduced and the light transmittance is significantly improved, meeting the requirements of high-end power devices for high-quality substrates.

[0086] Example 5 Example 5 is similar to Example 2, except that microwave sintering technology is used during segmented sintering. The specific implementation method is as follows: The pressed gallium oxide blank is placed in a sintering furnace, and then the sintering furnace is evacuated to a vacuum level of 10. -2 Pa further removes gas molecules adsorbed on the surface of the gallium oxide sinter and the crucible wall. Then, the temperature is increased to 950 °C at a rate of 8-10 °C / min and held at this temperature for 2 h for low-temperature initial sintering to remove adsorbed water and water of crystallization from the powder and promote the volatilization of low-boiling-point organic impurities. The atmosphere in the sintering furnace is then changed to a mixed atmosphere of argon and oxygen, with the oxygen partial pressure maintained at 10. -2 Pa was used to suppress the decomposition of gallium oxide. The temperature was increased to 1600℃-1700℃ at a heating rate of 3-5℃ / min and held for 2 hours for high-temperature sintering to ensure sufficient grain growth and reduce internal stress. After segmented sintering, the sintered body was cooled to room temperature with the furnace to obtain a dense gallium oxide sintered body with a density of 98%.

[0087] According to the method of this embodiment, a gallium oxide single crystal with a size of φ55mm×30mm was obtained. Microscopic observation showed no fine bubbles, and spectral analysis showed a bubble removal rate of over 97%. Figure 4 The resistivity radial deviation of the gallium oxide single crystal obtained in Example 5 was tested using the same method. Twenty-seven test points (3×9) were selected radially outward from the center of the gallium oxide single crystal at heights of 0 mm, 10 mm, and 20 mm from the bottom of the crucible, respectively, for resistivity radial deviation testing. The test results showed that the resistivity radial deviation of the gallium oxide single crystal was less than 3%.

[0088] Example 5 employs microwave segmented sintering and precisely controls the crucible rotation parameters to create a uniform temperature and flow field inside the melt, promoting bubble aggregation and floating. This significantly reduces the bubble density inside the gallium oxide single crystal and substantially improves light transmittance, meeting the high-quality substrate requirements of high-end power devices.

[0089] Comparative Example 1 To further verify the effectiveness of this embodiment, the inventors designed Comparative Example 1 for comparative experiments. In Comparative Example 1, the pressing pressure was reduced to 20 MPa, the holding time remained unchanged, and other sintering, melting, and crystal growth processes and procedures were the same as in Example 1. The gallium oxide blank obtained in the raw material pretreatment step of Comparative Example 1 had a density of only 2.9 g / cm³, a porosity as high as 15%, and a residual gas content of 1.2 vol%, which was 4 times that of Example 1. The density of the sintered body was only 82%, the internal residual pore size reached 5-10 μm, and the number of residual pores was ≥20 / mm³. The bubble removal rate of the final gallium oxide crystal was reduced to 58%, and the transmittance of the (001) surface was only 62%, which could not meet the application requirements of high-end power devices.

[0090] Comparative Example 2 In Comparative Example 2, during the segmented sintering step, the main sintering temperature was reduced to 1400℃, while the holding time remained unchanged. Other processes and procedures were the same as in Example 2. After segmented sintering in Comparative Example 2, the sintered body had a density of only 78%, and XRD analysis revealed GaOOH impurities (mainly due to incomplete sintering), with residual pore sizes ≥10μm. During crystal growth, the bubble content in the gallium oxide melt surged, with a bubble removal rate of only 42%. The resulting gallium oxide crystal contained numerous inclusions (bubble diameters of 5-20μm), and its transmittance was only 400-800nm, dropping to 55%, which failed to meet the requirements for device-level applications.

[0091] Comparative Example 3 In Comparative Example 3, the dynamic crucible rotation mechanism was omitted during the melting and crystal growth step, eliminating the "crucible acceleration-deceleration-reverse rotation" step. The entire process was static, with other processes and procedures identical to Example 3. In Comparative Example 3, the uniformity of the gallium oxide melt temperature field within the crucible deteriorated, with the axial gradient fluctuation increasing sharply to ±15℃ / cm. Localized eddy dead zones formed within the melt, preventing effective bubble aggregation and floating. Compared to the 95% bubble removal rate in Example 3, the bubble removal rate in the melt of Comparative Example 3 decreased to 38%, with a residual bubble density of 25 bubbles / cm³. The resulting gallium oxide crystal exhibited periodic bubble stratification along the growth direction.

[0092] Comparative Example 4 Comparative Example 4 is similar to Example 2, except that the process parameters in the raw material pretreatment and segmented sintering steps are adjusted. In Comparative Example 4, the pressing pressure in the forming step is set to 30 MPa, and the holding time is 3 minutes. In the segmented sintering step, the initial low-temperature sintering temperature is set to 600°C, the holding time for high-temperature sintering is 1 hour, and the process parameters for the melt crystal growth step are the same as in Example 2.

[0093] The comparative gallium 4 oxide preform had a porosity as high as 20%, but the sintered body density was only 75%, with interconnected pores throughout, the size of which was approximately 10-50 μm. Ultimately, only short ingots with a diameter of φ20 mm × 30 mm were obtained, with surfaces covered in pits left by escaping bubbles, and a dislocation density > 5 × 10⁻⁶. 5 cm -2 It has no practical value.

[0094] Comparative Example 5 Comparative Example 5 is similar to Example 2, except that the process parameters in the melt growth step are adjusted. In Comparative Example 5, the melt holding time in the melt growth step is shortened from 3 hours to 30 minutes, while other parameters remain unchanged. The process parameters for the raw material pretreatment and segmented sintering steps are the same as in Example 2.

[0095] In Comparative Example 5, insufficient bubble escape occurred within the gallium oxide melt, and inadequate holding time resulted in incomplete bubble aggregation and floating, causing the melt bubble removal rate to decrease from 97% to 52%. The final crystal exhibited a large number of microbubbles distributed along the ingot axis, with bubble diameters of 1-3 μm and a density of 80 bubbles / mm³. The resistivity uniformity deviation of the gallium oxide crystal was >15%.

[0096] In summary, the method for removing bubbles from β-gallium oxide melt provided in this application forms a complete and effective technical solution through processes such as raw material pretreatment, segmented sintering, and crucible rotation control. By precisely controlling the conditions and parameters of each process, the bubble removal rate can be increased to over 92%, and the dislocation density can be controlled at 2.5 × 10⁻⁶. 3 cm -2 The resistivity radial deviation is less than 3%, resulting in higher quality gallium oxide single crystal materials, which provides a strong guarantee for the preparation of high-performance power devices.

[0097] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this application may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0098] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the embodiments of this application and form different embodiments. For example, in the following claims, any one of the claimed embodiments can be used in any combination.

Claims

1. A method for removing bubbles from a gallium oxide melt, characterized in that, The method includes the following steps: (1) Raw material pretreatment: Select β-gallium oxide powder with a purity of ≥99.999%, place it in a mold, control the pressing pressure to 100-300 MPa, and hold the pressure for more than 2 minutes to press the gallium oxide powder into shape; (2) Segmented sintering treatment: The pressed gallium oxide blank is placed in a sintering furnace and first subjected to low-temperature initial sintering at a temperature not exceeding 1000°C, and then the temperature is raised to a range of 1500-1700°C for high-temperature sintering to obtain a dense gallium oxide sintered body; wherein the high-temperature sintering is carried out in a mixed atmosphere of protective gas and oxygen, and the oxygen partial pressure is maintained at 10. -2 Pa; (3) Melt stirring control: After the gallium oxide sintered body is placed in the crucible and melted, the crucible is rotated according to the pre-set crucible dynamic rotation mechanism. The dynamic rotation includes alternating clockwise acceleration and counterclockwise deceleration, with a speed range of 5-30 r / min and a cycle number of more than 2 times. In a single cycle mechanism, the crucible is first rotated clockwise at a predetermined acceleration to 10-30 r / min and maintained for the first rotation time. Then, it is switched to counterclockwise rotation at a predetermined deceleration to 5-15 r / min and maintained for the second rotation time. The sum of the first rotation time and the second rotation time is not less than 30 minutes. The clockwise rotation speed is greater than the counterclockwise rotation speed. The final β-gallium oxide single crystal exhibited a bubble removal rate ≥92%, a resistivity radial deviation ≤3%, and a dislocation density ≤2.5×10³cm. - ².

2. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (1), the particle size of the β-gallium oxide is less than 5 μm, and the pressurization method is selected from any of the following: unidirectional pressurization, bidirectional pressurization, cool isostatic pressing, hot isostatic pressing, one-time pressure forming or gradient pressure forming, and the pressurization rate is 5-10 MPa / s.

3. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (2), the low-temperature initial firing is carried out in an air environment with a heating rate of 5-10℃ / min and a holding time of 2-10 h; the high-temperature sintering is carried out in an air environment with a heating rate of 1-5℃ / min and a holding time of 2-10 h.

4. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, In step (3), the dynamic rotation also includes accelerating clockwise, stopping, and then decelerating counterclockwise, with a single cycle of 30-90 minutes.

5. The method for removing bubbles from gallium oxide melt according to claim 1, characterized in that, It also includes step (4), in which the crystal rotation speed is V1, the crystal growth rate is V2, the axial temperature gradient of the melt is G, and the product of the rotation speed V1 and the axial temperature gradient of the melt, V1×G, is controlled to be no greater than 350. The surface of the melt is basically horizontal or concave towards the center of the melt. The product of the crystal growth rate V2 and the axial temperature gradient of the melt, V2×G, is controlled to be no greater than 35. The value range of V1 is 1-15 r / min, the value range of V2 is 0.5-5 mm / h, and the value range of G is 5-70℃ / cm.

6. A crystal growth apparatus for performing the method for removing bubbles from gallium oxide melt according to any one of claims 1 to 5, characterized in that, The crystal growth equipment is equipped with: The crucible speed control rotation system is used to perform programmable rotation drive on the crucible, and is adapted to a combined rotation mode of clockwise acceleration and counterclockwise deceleration. A temperature measuring device, comprising an infrared thermometer and / or a thermocouple, for synchronous temperature monitoring; as well as The control linkage system links the temperature measuring device with the heating system and crucible speed control rotation system of the crystal growth equipment. When the temperature measuring device detects an abnormal temperature gradient, the system automatically triggers an adjustment command to adjust the heating power and / or change the crucible rotation speed.

7. The crystal growth equipment according to claim 6, characterized in that, It is also equipped with an annular gradient temperature control heat shield, which surrounds the outside of the crucible to make the axial temperature gradient of the crucible uniform and stable.

8. The method for removing bubbles from gallium oxide melt according to any one of claims 1 to 5 or the β-gallium oxide single crystal obtained by the crystal growth apparatus according to any one of claims 6 to 7.

9. A power device based on β-gallium oxide single crystal, characterized in that, The power device uses β-gallium oxide single crystal as described in claim 8 as the core material, including field-effect transistors, diodes, or deep ultraviolet light detectors.

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