A flux for β-Ga2O3 crystal growth and a crystal growth method

Abstract

This invention relates to a flux and a method for growing β-Ga₂O₃ crystals. The invention uses LiBO₂-metal fluoride as a composite flux system for β-Ga₂O₃ crystal growth, with a molar ratio of LiBO₂ to metal fluoride of 1–0.8:0.04–0.2, and a crystal growth temperature range of 700–1000℃. Compared with existing technologies, the flux system proposed in this invention does not contain toxic or harmful components such as PbO and PbSO₄ commonly used in high-temperature fluxes. It can significantly reduce the saturation temperature of β-Ga₂O₃ crystals, improve the stability of the growth system, and the metal fluoride can effectively break the B-O bond chain. The solvent viscosity is low, avoiding the formation of inclusions and facilitating the acquisition of high-quality β-Ga₂O₃ crystals.

Description

Technical Field

[0001] This invention relates to a flux system for single crystal growth and a crystal growth method thereof, and more particularly to a flux and a crystal growth method for β-Ga2O3 crystal growth. Background Technology

[0002] β-Ga2O3 has an ultra-wide bandgap of 4.9 eV, belonging to the fourth generation of wide bandgap semiconductor materials. Compared with third-generation semiconductor materials such as silicon carbide and gallium nitride, it has a wider bandgap. It has strong absorption of ultraviolet light with wavelengths around 253 nm and high transmittance of visible light (350-800 nm). Furthermore, β-Ga₂O₃ boasts a breakdown field strength of up to 8 MV / cm, nearly 27 times that of single-crystal silicon and more than twice that of silicon carbide and gallium nitride. Its Baliga figure of merit (FOM) is 3440, more than 10 times that of silicon carbide and more than 4 times that of gallium nitride. From the perspective of power semiconductor characteristics, the loss of gallium oxide is theoretically 1 / 3000 that of silicon, 1 / 6 that of silicon carbide, and 1 / 3 that of gallium nitride. β-Ga₂O₃ possesses excellent physical properties and chemical stability, making it suitable for extreme environmental applications, such as ultra-high and low temperatures, strong radiation, and corrosive environments. It can be used to fabricate solar-blind ultraviolet detectors, high-power devices, high-frequency devices, and radiation-resistant devices. Therefore, ultra-wide bandgap β-Ga₂O₃ semiconductor crystal material is one of the most popular semiconductor materials today and has attracted widespread attention.

[0003] β-Ga₂O₃ crystals have a melting point of 1793℃ and are homogeneous melting compounds, typically prepared using high-temperature melt methods such as the Czochralski method and the mold-guided method. Under high-temperature, oxygen-deficient conditions, β-Ga₂O₃ readily decomposes to form low-valence gallium oxides and elemental gallium. Some of these decomposition products alloy with elemental iridium, corroding the iridium crucible, while others enter the high-temperature melt during crystal growth, leading to defects such as dislocations, twins, and inclusions in the grown gallium oxide crystal, severely impacting crystal quality. To suppress the high-temperature decomposition of β-Ga₂O₃, crystal growth is usually performed in an oxygen-rich atmosphere. However, this approach introduces the problems of high-temperature oxidation of iridium, the generation of waste gas, and oxygen dissolving in the melt, severely jeopardizing the optical quality of the grown crystal. Furthermore, the extremely high growth temperature presents the challenge of high-temperature decomposition of β-Ga₂O₃ crystals and the oxidation of iridium caused by crystal growth in an oxygen-rich atmosphere. Compared to the high-temperature melt method, the flux method can significantly reduce the crystal growth temperature, effectively solving the problems of high-temperature decomposition of β-Ga2O3 crystals and oxidation of iridium crucibles in oxygen-rich atmospheres. Furthermore, the flux method allows for easier adjustment of the interfacial energy between the crystal and the melt, ensuring a stable and smooth solid-liquid interface, and also helps suppress dislocation generation during crystal growth, thus improving crystal quality. However, the flux method requires the use of toxic and harmful components such as PbO, PbSO4, PbF2, Bi2O3, and V2O5. Lead and bismuth-based fluxes are highly corrosive to platinum crucibles. These flux systems also suffer from drawbacks such as high viscosity, the tendency for inclusions to form within the grown crystal, narrow crystallization regions, limited mass transfer, and low crystal growth rates, making it difficult to obtain high-quality β-Ga2O3 crystals.

[0004] Therefore, further exploration of suitable flux systems is an urgent task for the growth of high-quality β-Ga2O3 crystals. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a flux and crystal growth method for β-Ga2O3 crystal growth, by exploring a low-viscosity, low-temperature flux system to prepare high-quality β-Ga2O3 crystals.

[0006] The conceptual process of this invention is as follows: This invention employs a LiBO2-metal fluoride composite flux system, enabling the method of this invention to grow β-Ga2O3 crystals at low temperatures, effectively solving the problem of gallium oxide volatilization and decomposition at high temperatures during crystal growth; and by introducing a low-boron flux, the metal fluoride can effectively break the BO bond chain, further reducing the viscosity of the system, which is beneficial to solute transport during crystal growth, effectively avoiding the formation of inclusions, and facilitating the growth of high-quality β-Ga2O3 crystals.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] On one hand, the present invention provides a flux for the growth of β-Ga2O3 crystals, wherein the flux is a fluxing agent of a lithium metaborate-metal fluoride system, and the molar ratio of lithium metaborate to metal fluoride in the flux is 1-0.8:0.04-0.2.

[0009] Preferably, the molar ratio of lithium metaborate to metal fluoride is 1:0.04 to 0.12.

[0010] Furthermore, the lithium metaborate is prepared by a solid-state method or a synthesis method during crystal growth. The solid-state method involves reacting a boron-containing compound with a sodium-containing compound to prepare lithium metaborate. The synthesis method during crystal growth involves mixing a boron-containing compound, a sodium-containing compound, a metal fluoride, and β-Ga2O3 powder, and reacting them during crystal growth to prepare lithium metaborate.

[0011] Furthermore, the metal fluoride is lithium fluoride, sodium fluoride, or potassium fluoride.

[0012] On the other hand, the present invention also provides a method for growing β-Ga2O3 crystals, which uses the above-mentioned flux for growing β-Ga2O3 crystals and includes the following steps:

[0013] S1. Mix the fluxing agent and β-Ga2O3 powder evenly, transfer the mixture into a single crystal growth furnace, heat the mixture to completely melt the fluxing agent and β-Ga2O3 powder, stir at a constant temperature to obtain a uniform high-temperature solution.

[0014] S2. The high-temperature solution obtained in S1 is kept at a temperature 0.5 to 5°C above the saturation temperature. The seed crystal rod is rotated while the seed crystal is lowered. The seed crystal is lowered to a position 1 to 3 mm below the surface of the high-temperature solution. After holding the temperature for 30 to 90 minutes, the temperature is lowered to the saturation point temperature.

[0015] S3. Starting with the saturation point temperature as the initial temperature, crystal growth begins. The temperature is reduced at a rate of 0.05–0.3 °C / day while the crystal is rotated. Once the crystal has grown to the required size, it is removed from the liquid surface and cooled to room temperature at a rate of 5–50 °C / h to obtain β-Ga2O3 crystals.

[0016] Furthermore, in S1, the molar ratio of the co-solvent to the β-Ga2O3 powder is 0.1 to 2:1.

[0017] Preferably, in S1, the molar ratio of the co-solvent to the β-Ga2O3 powder is 0.9 to 1.5:1.

[0018] Furthermore, in S1, the temperature at which the co-solvent and β-Ga2O3 powder are completely melted is 730–1030 °C.

[0019] Preferably, in S1, the temperature at which the co-solvent and β-Ga2O3 powder are completely melted is 730–914°C.

[0020] Furthermore, in S1, the constant temperature stirring time is 12 to 36 hours, and the constant temperature stirring rate is 10 to 20 rpm.

[0021] Furthermore, in S2 and S3, the saturation point temperature is 700–1000°C.

[0022] Preferably, in S2 and S3, the saturation point temperature is 700–894°C.

[0023] Furthermore, in S3, the rotation speed of the crystal is 5 to 50 rpm.

[0024] Preferably, in S3, the rotation speed of the crystal is 8 to 15 rpm.

[0025] β-Ga2O3 has high solubility in high-temperature LiBO2 melts. However, the high viscosity of high-temperature metaborate melts is not conducive to solute transport. Adding an appropriate amount of metal fluoride to the melt helps to reduce the melt viscosity, which is beneficial to the nucleation and growth of β-Ga2O3 crystals.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The LiBO2-metal fluoride composite flux of the present invention can grow β-Ga2O3 crystals at a lower temperature, effectively solving the problems of high-temperature decomposition of β-Ga2O3 crystals, oxidation of iridium crucibles under oxygen-rich atmosphere, and compositional deviation caused by the entry of elemental iridium or elemental gallium into the melt. Moreover, the flux of the present invention does not contain toxic or harmful components such as PbO, PbSO4, and PbF2, which is beneficial to human health.

[0028] (2) The composite flux system of the present invention is a low boron flux. With the assistance of metal fluoride, it can effectively break the BO bond chain and further reduce the viscosity of the growth system. It solves the problems of excessively thick boundary layer, poor solute transport and difficulty in removing impurities caused by high viscosity melt. It can effectively avoid the formation of inclusions. Moreover, the flux and the grown crystal are easy to separate, which is conducive to obtaining high-quality β-Ga2O3 single crystals without inclusions, scattering particles and other defects.

[0029] (3) The flux system and growth method for β-Ga2O3 crystals of the present invention can significantly reduce the saturation temperature of β-Ga2O3 crystals and improve the stability of the growth system. Compared with the flux method for crystal growth reported in the literature, the growth temperature is reduced from 830-1350℃ to 700-1000℃, achieving a reduction of 130-650℃. Moreover, the high-temperature solution is clear and transparent, facilitating clear and real-time observation of crystal growth. At the same time, crystal growth in the composite flux system involved in the present invention can avoid iridium loss, reduce energy consumption, and lower crystal growth costs. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments. Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0031] The raw materials Ga2O3, LiF, NaF, KF, Li2O and B2O3 used in the following examples all had a purity of 99.9% and were purchased from China National Pharmaceutical Group Shanghai Chemical Reagent Company.

[0032] Example 1

[0033] In this embodiment, β-Ga2O3 crystals are grown using a LiBO2-LiF flux system.

[0034] Weigh 1 mol of B2O3 and 1 mol of Li2O, and synthesize LiBO2 using a solid-state method.

[0035] Using β-Ga2O3 powder, LiBO2, and LiF as raw materials, and according to the molar ratio of β-Ga2O3:LiBO2:LiF = 0.46:0.51:0.03, 86.22g of β-Ga2O3 powder, 25.37g of LiBO2, and 0.78g of LiF were weighed.

[0036] After grinding and mixing the weighed raw materials evenly, add Φ100×70mm 3 The crucible was placed in a platinum crucible and then placed in a molten salt single crystal growth furnace. The furnace tube of the single crystal growth furnace was a vertical hollow cylindrical tube. The opening at the top of the furnace was sealed with a lid made of insulating material. A small hole was left at the top of the furnace corresponding to the center of the crucible so that the seed crystal rod could enter and exit. The temperature was raised to 730°C to completely melt the above melt and obtain a clear high-temperature solution. A stirrer made of platinum sheet was used to continuously stir the solution at 25 rpm at this temperature for 24 hours. After the high-temperature solution was fully homogenized, the stirrer was lifted.

[0037] The saturation point temperature for crystal growth was determined to be 700℃ using the trial crystal method. Then, the high-temperature solution was heated to 700.5℃ (0.5℃ above the saturation point temperature). The β-Ga2O3 seed crystal was slowly lowered into the furnace through a small hole at the top until it contacted the solution surface. The seed crystal was rotated bidirectionally at a speed of 20 rpm. After being kept at a constant temperature for 60 minutes, the temperature was lowered to 700℃. Then, the temperature was lowered at a rate of 0.5℃ / day to carry out crystal growth.

[0038] During the growth process, the rotation speed gradually decreased as the crystal grew, and was controlled to decrease to 15 rpm by adjusting the motor. After 30 days, the crystal growth was completed, and the crystal was pulled off the liquid surface and cooled to room temperature at a rate of 5℃ / h. The obtained β-Ga2O3 crystals had a regular shape and no inclusions, meeting the high-quality requirements. Therefore, the metal fluoride in this embodiment effectively broke the BO bond chains, further reducing the viscosity of the growth system, which is beneficial for obtaining high-quality β-Ga2O3 single crystals.

[0039] Example 2

[0040] In this embodiment, β-Ga2O3 crystals are grown using a LiBO2-NaF flux system.

[0041] Weigh 1 mol of B2O3 and 1 mol of Li2O, and synthesize LiBO2 using a solid-state method.

[0042] Using β-Ga2O3 powder, LiBO2, and NaF as raw materials, and according to the molar ratio of β-Ga2O3:LiBO2:NaF = 0.5:0.45:0.05, 93.72g of β-Ga2O3 powder, 22.39g of LiBO2, and 2.10g of NaF were weighed.

[0043] After grinding and mixing the weighed raw materials evenly, add Φ100×70mm 3 The crucible was placed in a platinum crucible and then placed in a molten salt single crystal growth furnace. The furnace tube of the single crystal growth furnace was a vertical hollow round tube. The opening at the top of the furnace was sealed with a lid made of insulating material. A small hole was left at the top of the furnace corresponding to the center of the crucible so that the seed crystal rod could enter and exit. The temperature was raised to 841°C to completely melt the above melt and obtain a clear high-temperature solution. A stirrer made of platinum sheet was used to continuously stir the solution at 20 rpm at this temperature for 24 hours. After the high-temperature solution was fully homogenized, the stirrer was lifted.

[0044] The saturation point temperature for crystal growth was determined to be 811℃ using the trial crystal method. Then, the high-temperature solution was heated to 811.5℃ (0.5℃ above the saturation point temperature). The β-Ga2O3 seed crystal was slowly lowered into the furnace through a small hole at the top until it contacted the solution surface. The seed crystal was rotated bidirectionally at a speed of 16 rpm. After being kept at a constant temperature for 60 minutes, the temperature was lowered to 811℃. Then, the temperature was lowered at a rate of 0.15℃ / day to carry out crystal growth.

[0045] During the growth process, the rotation speed gradually decreased as the crystal grew, and was controlled to decrease to 13 rpm by adjusting the motor. After 30 days, the crystal growth was completed, and the crystal was pulled out of the liquid surface and cooled to room temperature at a rate of 10℃ / h. The obtained β-Ga2O3 crystals had a regular shape and no inclusions, meeting the high-quality requirements. Therefore, the metal fluoride in this embodiment effectively broke the BO bond chains, further reducing the viscosity of the growth system, which is beneficial for obtaining high-quality β-Ga2O3 single crystals.

[0046] Example 3

[0047] In this embodiment, β-Ga2O3 crystals are grown using a LiBO2-KF flux system.

[0048] Using β-Ga2O3 powder, B2O3, Li2O, and KF as raw materials, and according to the molar ratio of β-Ga2O3:B2O3:Li2O:KF = 0.54:0.22:0.22:0.05, 101.22g of β-Ga2O3 powder, 15.32g of B2O3, 6.57g of Li2O, and 2.91g of KF were weighed.

[0049] After grinding and mixing the weighed raw materials evenly, add Φ100×70mm 3 The crucible was placed in a platinum crucible and then placed in a molten salt single crystal growth furnace. The furnace tube of the single crystal growth furnace was a vertical hollow round tube. The opening at the top of the furnace was sealed with a lid made of insulating material. A small hole was left at the top of the furnace corresponding to the center of the crucible so that the seed crystal rod could enter and exit. The temperature was raised to 914°C to completely melt the above melt and obtain a clear high-temperature solution. A stirrer made of platinum sheet was used to continuously stir the solution at 12 rpm at this temperature for 24 hours. After the high-temperature solution was fully homogenized, the stirrer was lifted.

[0050] The saturation point temperature for crystal growth was determined to be 894℃ using the trial crystal method. Then, the high-temperature solution was heated to 894.5℃ (0.5℃ above the saturation point temperature). The β-Ga2O3 seed crystal was slowly lowered into the furnace through a small hole at the top until it contacted the solution surface. The seed crystal was rotated bidirectionally at a speed of 10 rpm. After being kept at a constant temperature for 60 minutes, the temperature was lowered to 894℃. Then, the temperature was lowered at a rate of 0.25℃ / day to carry out crystal growth.

[0051] During the growth process, the rotation speed gradually decreased as the crystal grew, and was controlled to a minimum of 8 rpm by adjusting the motor. After 30 days, the crystal growth was completed, and the crystal was pulled out of the liquid surface and cooled to room temperature at a rate of 10℃ / h. The obtained β-Ga2O3 crystals had a regular shape and no inclusions, meeting the high-quality requirements. Therefore, the metal fluoride in this embodiment effectively broke the BO bond chains, further reducing the viscosity of the growth system, which is beneficial for obtaining high-quality β-Ga2O3 single crystals.

[0052] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A flux for β-Ga2O3 crystal growth, characterized by, The fluxing agent is a lithium metaborate-metal fluoride system fluxing agent, and the molar ratio of lithium metaborate to metal fluoride in the fluxing agent is 1-0.8:0.04-0.

2. The metal fluoride is one of lithium fluoride, sodium fluoride and potassium fluoride.

2. The flux for the growth of β-Ga203 crystal according to claim 1, wherein The preparation method of the lithium metaborate is a solid phase method or a synthesis method in a crystal growth process. The solid phase method is to prepare lithium metaborate by mixing and reacting a boron-containing compound and a lithium-containing compound. The synthesis method in the crystal growth process is to mix a boron-containing compound, a lithium-containing compound, a metal fluoride and beta-Ga2O3 powder, and to prepare lithium metaborate by reacting in a crystal growth process.

3. A method for growing a β-Ga2O3 crystal, characterized by, The fluxing agent for beta-Ga2O3 crystal growth according to any one of claims 1-2 is used for growth.

4. The method of growing a β-Ga2O3 crystal according to claim 3, wherein The method comprises the following steps: S1, uniformly mixing the fluxing agent and beta-Ga2O3 powder, heating to completely melt the fluxing agent and beta-Ga2O3 powder, constant temperature stirring to obtain a uniform high-temperature solution; S2, under the condition that the high-temperature solution prepared in S1 is higher than the saturation temperature by 0.5-5 ℃, rotating the seed crystal rod while lowering the seed crystal, lowering the seed crystal to 1-3 mm below the liquid level of the high-temperature solution, and after constant temperature for 30-90 min, lowering the temperature to the saturation point temperature; S3, taking the saturation point temperature as the starting temperature, starting crystal growth, lowering the temperature at a rate of 0.05-0.3 ℃ / day, rotating the crystal at the same time, and after the crystal grows to the required size, making the crystal separate from the liquid level, lowering to room temperature at a rate of 5-50 ℃ / h to obtain beta-Ga2O3 crystal.

5. The method of growing a β-Ga2O3 crystal according to claim 4, wherein In S1, the molar ratio of the fluxing agent to beta-Ga2O3 powder is 0.1-2:

1.

6. The method of growing a β-Ga2O3 crystal according to claim 4, wherein In S1, the temperature for completely melting the fluxing agent and beta-Ga2O3 powder is 730-1030 ℃.

7. The method of claim 4, wherein the β-Ga2O3 crystal is grown by a Bridgman-Stockbarger method. In S1, the constant temperature stirring time is 12-36 h, and the constant temperature stirring rate is 10-20 rpm.

8. The method of growing a β-Ga2O3 crystal according to claim 4, wherein In S2 and S3, the saturation point temperature is 700-1000 ℃.

9. The method of claim 4, wherein the β-Ga2O3 crystal is grown by a Bridgman-Stockbarger method. In S3, the rotating crystal rate is 5-50 rpm.