Flux for beta-Ga2O3 crystal growth and crystal growth method

Abstract

The invention relates to a fluxing agent for beta-Ga2O3 crystal growth and a crystal growth method. According to the invention, LiBO2-metal fluoride is used as a composite fluxing agent system for growth of beta-Ga2O3 crystals, the molar ratio of LiBO2 to metal fluoride is (1-0.8): (0.04-0.2), and the growth temperature interval of the crystals is 700-1000 DEG C. Compared with the prior art, the fluxing agent system provided by the invention does not contain toxic and harmful components such as PbO, PbSO4 and the like which are commonly used in a high-temperature fluxing agent, the saturation point temperature of the beta-Ga2O3 crystal can be greatly reduced, the stability of a growth system is improved, the B-O bond chain can be effectively broken by the metal fluoride, the solvent viscosity is small, the inclusion is prevented from being generated, and the service life of the fluxing agent system is prolonged. And the high-quality beta-Ga2O3 crystal is easy to obtain.

Description

Technical Field

[0001] The invention relates to a flux system for single crystal growth and a crystal growth method thereof, in particular to a flux system for beta-Ga2O3 crystal growth and a crystal growth method thereof. Background Art

[0002] β-Ga2O3 has an ultra-wide bandgap with a width of 4.9eV. It belongs 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 a wavelength near 253nm and has a high transmittance for visible light (350-800nm). In addition, the breakdown field strength of β-Ga2O3 is as high as 8MV / cm, which is nearly 27 times that of single crystal silicon, more than twice that of silicon carbide and gallium nitride; Baliga's figure of merit (FOM) is 3440, which is 10 times and more than 4 times that of silicon carbide and gallium nitride respectively; from the perspective of power semiconductor characteristics, the loss of gallium oxide is theoretically 1 / 3000 of silicon, 1 / 6 of silicon carbide, and 1 / 3 of gallium nitride; β-Ga2O3 has good physical properties and chemical stability, and is suitable for extreme environmental applications, such as ultra-high and low temperatures, strong radiation and corrosive environments, and can be used to prepare 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 hottest semiconductor materials today and has received widespread attention.

[0003] The melting point of β-Ga2O3 crystal is 1793℃, which is a uniformly molten compound. Crystals are usually prepared by high-temperature melt methods such as the Czochralski method and the guided mold method. β-Ga2O3 material is very easy to decompose into low-valent gallium oxides, elemental gallium, etc. under high-temperature oxygen-deficient conditions. Part of the decomposition products form alloys with iridium to corrode the iridium crucible, and the other part of the decomposition products enter the high-temperature melt of the growing crystal, causing the growing gallium oxide crystals to have defects such as dislocations, twins, and encapsulation, which seriously affect the quality of the crystal. In order to inhibit the high-temperature decomposition of β-Ga2O3 materials, crystal growth usually needs to be carried out in an oxygen-rich atmosphere. However, this solution brings about the high-temperature oxidation of iridium and the generation of waste gas, as well as the problem of oxygen dissolving in the melt, which seriously endangers the optical quality of the grown crystal. At the same time, the problem brought about by the ultra-high growth temperature is the high-temperature decomposition of β-Ga2O3 crystals and the oxidation of iridium caused by growing crystals in an oxygen-rich atmosphere. Compared with the high-temperature melt method, the flux method can significantly reduce the temperature of crystal growth, effectively solving the problems of high-temperature decomposition of β-Ga2O3 crystals and oxidation of iridium crucibles in an oxygen-rich atmosphere. Moreover, the flux method can more easily adjust the interfacial energy between the crystal and the melt, ensure the stability and smoothness of the solid-liquid interface, and help inhibit the generation of dislocations during crystal growth and improve 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 fluxes are highly corrosive to platinum crucibles. These flux systems have defects such as high viscosity, inclusions and inclusions in the growing crystals, narrow crystallization areas, limited mass transfer, and low crystal growth rates, making it difficult to obtain high-quality β-Ga2O3 crystals.

[0004] Therefore, further exploring suitable flux systems is imperative for growing high-quality β-Ga2O3 crystals. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a flux and a 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 conceived process of the present invention is as follows: the present invention adopts a LiBO2-metal fluoride composite flux system, so that the method of the present invention can grow β-Ga2O3 crystals in a low-temperature environment, effectively solving the problem of volatilization and decomposition of gallium oxide 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 the solute transport during the crystal growth process, can effectively avoid the generation of inclusions, and is beneficial to the growth of high-quality β-Ga2O3 crystals.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] On the one hand, the present invention provides a flux for the growth of β-Ga2O3 crystals, wherein the flux is a solvent for 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 the lithium metaborate to the metal fluoride is 1:0.04-0.12.

[0010] Furthermore, the preparation method of the lithium metaborate is a solid phase method or a synthesis method during crystal growth. The solid phase method is to mix a boron-containing compound and a sodium-containing compound and then react to prepare lithium metaborate. The synthesis method during crystal growth is to mix a boron-containing compound, a sodium-containing compound, a metal fluoride and β-Ga2O3 powder and react to prepare lithium metaborate during the crystal growth process.

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

[0012] On the other hand, the present invention also provides a β-Ga2O3 crystal growth method, which uses the above-mentioned flux for β-Ga2O3 crystal growth to grow, comprising the following steps:

[0013] S1, uniformly mix the co-solvent and β-Ga2O3 powder, move into a single crystal growth furnace, increase the temperature to completely melt the co-solvent and β-Ga2O3 powder, and stir at a constant temperature to obtain a uniform high-temperature solution;

[0014] S2, the high temperature solution prepared in S1 is placed at a temperature 0.5-5°C higher than the saturation temperature, the seed crystal rod is rotated while the seed crystal is lowered, the seed crystal is lowered to 1-3 mm below the liquid surface of the high temperature solution, the temperature is kept constant for 30-90 minutes, and then the temperature is lowered to the saturation point temperature;

[0015] S3. Take the saturation point temperature as the starting temperature to start crystal growth, cool down at a rate of 0.05-0.3°C / day, and rotate the crystal at the same time. After the crystal grows to the required size, separate the crystal from the liquid surface and cool to room temperature at a rate of 5-50°C / h to obtain β-Ga2O3 crystal.

[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 solvent and the β-Ga2O3 powder are completely melted is 730 to 1030°C.

[0019] Preferably, in S1, the temperature at which the solvent and the β-Ga2O3 powder are completely melted is 730 to 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 speed of rotating the crystal is 5 to 50 rpm.

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

[0025] β-Ga2O3 has a high solubility in the high-temperature melt of LiBO2, but since the high-temperature melt of metaborate has a large viscosity, it is not conducive to the transport of solutes. 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 relatively low temperature, effectively solving the problems of high-temperature decomposition of β-Ga2O3 crystals, oxidation of iridium crucibles in an oxygen-rich atmosphere, and composition deviation caused by the entry of single iridium or single gallium into the melt. In addition, the flux of the present invention does not contain toxic and 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, which can effectively break the BO bond chain with the assistance of metal fluoride, further reduce the viscosity of the growth system, and solve the problems of too thick boundary layer, poor solute transport, and difficulty in impurity removal caused by high-viscosity melt. It can effectively avoid the formation of inclusions, and the flux is easy to separate from the growing crystal, which is conducive to obtaining high-quality β-Ga2O3 single crystals without defects such as inclusions and scattering particles.

[0029] (3) The flux system of β-Ga2O3 crystal and the growth method thereof of the present invention can significantly reduce the saturation point temperature of β-Ga2O3 crystal and improve the stability of the growth system. Compared with the crystal growth by the flux method reported in the literature, the growth temperature is reduced from 830 to 1350°C reported in the literature to 700 to 1000°C, achieving a reduction of 130 to 650°C. The high-temperature solution is clear and transparent, which is convenient for clear and real-time observation of the crystal growth. At the same time, growing crystals in the composite flux system of the present invention can avoid the loss of iridium, reduce energy consumption, and reduce the cost of crystal growth. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with specific embodiments. Any features such as preparation means, materials, structures or composition ratios not clearly described in this technical solution are regarded as 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 have a purity of 99.9% and were purchased from China Pharmaceutical Group Shanghai Chemical Reagent Company.

[0032] Example 1

[0033] This embodiment uses a LiBO2-LiF flux system to grow β-Ga2O3 crystals.

[0034] Weigh 1 mol B2O3 and 1 mol Li2O, and synthesize LiBO2 using the solid phase method.

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

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

[0037] The saturation point temperature of crystal growth was determined to be 700°C by the trial crystal method, and then the high-temperature solution was heated to 700.5°C (0.5°C above the saturation point temperature). The β-Ga2O3 seed crystal was slowly lowered into the furnace from the small hole on the top until the seed crystal contacted the surface of the solution. The seed crystal was rotated in both directions at a rate of 20 rpm, kept at a constant temperature for 60 minutes, then cooled to 700°C, and then cooled at a rate of 0.5°C / day to allow crystal growth.

[0038] During the growth process, the rotation speed gradually decreases as the crystal grows, and the speed is reduced to 15rpm by adjusting the motor control. After 30 days, the crystal growth ends, the crystal is pulled away from the liquid surface, and cooled to room temperature at a rate of 5°C / h. The obtained β-Ga2O3 crystal has a regular crystal shape without inclusions, which meets the high quality requirements. It can be seen that the metal fluoride in this embodiment effectively interrupts the BO bond chain, further reduces the viscosity of the growth system, and is conducive to obtaining high-quality β-Ga2O3 single crystals.

[0039] Example 2

[0040] This embodiment uses a LiBO2-NaF flux system to grow β-Ga2O3 crystals.

[0041] Weigh 1 mol B2O3 and 1 mol Li2O, and synthesize LiBO2 using the solid phase method.

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

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

[0044] The saturation point temperature of crystal growth was determined to be 811°C by the test crystal method, and then the high-temperature solution was heated to 811.5°C (0.5°C above the saturation point temperature). The β-Ga2O3 seed crystal was slowly lowered into the furnace from the small hole on the top until the seed crystal contacted the surface of the solution. The seed crystal was rotated in both directions at a rate of 16 rpm, kept at a constant temperature for 60 minutes, then cooled to 811°C, and then cooled at a rate of 0.15°C / day to allow crystal growth.

[0045] During the growth process, the rotation speed gradually decreases as the crystal grows, and the speed is reduced to 13rpm by adjusting the motor control. After 30 days, the crystal growth ends, the crystal is pulled away from the liquid surface, and cooled to room temperature at a rate of 10℃ / h. The obtained β-Ga2O3 crystal has a regular crystal shape without inclusions, which meets the high quality requirements. It can be seen that the metal fluoride in this embodiment effectively interrupts the BO bond chain, further reduces the viscosity of the growth system, and is conducive to obtaining high-quality β-Ga2O3 single crystals.

[0046] Example 3

[0047] This embodiment uses a LiBO2-KF flux system to grow β-Ga2O3 crystals.

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

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

[0050] The saturation point temperature of crystal growth was determined to be 894°C by the test crystal method, and then the high-temperature solution was heated to 894.5°C (0.5°C above the saturation point temperature), and the β-Ga2O3 seed crystal was slowly lowered into the furnace from the small hole on the top until the seed crystal contacted the surface of the solution. The seed crystal was rotated in both directions at a rate of 10 rpm, kept at a constant temperature for 60 minutes, then cooled to 894°C, and then cooled at a rate of 0.25°C / day for crystal growth.

[0051] During the growth process, the rotation speed gradually decreases as the crystal grows, and the speed is reduced to 8 rpm by adjusting the motor control. After 30 days, the crystal growth ends, the crystal is pulled away from the liquid surface, and cooled to room temperature at a rate of 10 ° C / h. The obtained β-Ga2O3 crystal has a regular crystal shape without inclusions, which meets the high quality requirements. It can be seen that the metal fluoride in this embodiment effectively interrupts the BO bond chain, further reduces the viscosity of the growth system, and is conducive to obtaining high-quality β-Ga2O3 single crystals.

[0052] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the scope of protection of the present invention.

Claims

1. A flux for growing β-Ga2O3 crystals, characterized in that: The flux is a solvent 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.

2. A flux for β-Ga2O3 crystal growth according to claim 1, characterized in that: The preparation method of the lithium metaborate is a solid phase method or a synthesis method during crystal growth; The solid phase method is to prepare lithium metaborate by mixing a boron-containing compound with a lithium-containing compound and reacting them; The synthesis method during the crystal growth process is to mix a boron-containing compound, a lithium-containing compound, a metal fluoride and β-Ga2O3 powder, and react to prepare lithium metaborate during the crystal growth process.

3. A flux for β-Ga2O3 crystal growth according to claim 1, characterized in that: The metal fluoride is lithium fluoride, sodium fluoride, potassium fluoride, etc.

4. A β-Ga2O3 crystal growth method, characterized in that: The growth is carried out using the flux for growing β-Ga2O3 crystals as described in any one of claims 1 to 3.

5. A β-Ga2O3 crystal growth method according to claim 4, characterized in that: The following steps are involved: S1. Evenly mix the co-solvent and β-Ga2O3 powder, raise the temperature to completely melt the co-solvent and β-Ga2O3 powder, and stir at a constant temperature to obtain a uniform high-temperature solution; S2, the high temperature solution prepared in S1 is placed at a temperature 0.5-5°C higher than the saturation temperature, the seed crystal rod is rotated while the seed crystal is lowered, the seed crystal is lowered to 1-3 mm below the liquid surface of the high temperature solution, the temperature is kept constant for 30-90 minutes, and then the temperature is lowered to the saturation point temperature; S3. Take the saturation point temperature as the starting temperature to start crystal growth, cool down at a rate of 0.05-0.3°C / day, and rotate the crystal at the same time. After the crystal grows to the required size, separate the crystal from the liquid surface and cool to room temperature at a rate of 5-50°C / h to obtain β-Ga2O3 crystal.

6. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S1, the molar ratio of the co-solvent to the β-Ga2O3 powder is 0.1 to 2:

1.

7. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S1, the temperature at which the solvent and β-Ga2O3 powder are completely melted is 730 to 1030°C.

8. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S1, the constant temperature stirring time is 12 to 36 hours, and the constant temperature stirring rate is 10 to 20 rpm.

9. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S2 and S3, the saturation point temperature is 700-1000°C.

10. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S3, the speed of rotating the crystal is 5 to 50 rpm.