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 method, Na2B4O7-metal fluoride is used as a fluxing agent system for growth of the beta-Ga2O3 crystal, the molar ratio of Na2B4O7 to metal fluoride is (1-0.8): (0.05-0.2), and the crystal growth temperature interval is 680-1150 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, corrosion of the fluxing agent to a crucible is effectively reduced, the saturation point temperature of beta-Ga2O3 crystals can be greatly reduced, the fluxing agent system is low in viscosity and less in volatilization of system components, mass transfer and heat transfer are facilitated, and the fluxing agent system is suitable for industrial production. The growth speed and quality of the crystal are improved, 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. However, there are still problems in crystal growth, such as high-temperature decomposition of β-Ga2O3 crystals, oxidation of iridium crucibles in an oxygen-rich atmosphere, and unstable crystal growth. Compared with the high-temperature melt method, the flux method can greatly reduce the temperature of crystal growth (generally below 1600℃), but the flux method requires toxic and harmful components such as PbO, PbSO4, PbF2, Bi2O3, and V2O5. Lead and bismuth fluxes are highly corrosive to platinum crucibles. In addition, these solvent systems also have problems such as melt volatilization, narrow crystallization range, large saturation point temperature fluctuations, and poor crystal growth stability, which are not conducive to the growth of high-quality β-Ga2O3 crystals.

[0004] Therefore, further improving the flux system is an urgent task 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 for the growth of β-Ga2O3 crystals and a crystal growth method, by exploring a low-temperature, green and environmentally friendly flux system to prepare high-quality β-Ga2O3 crystals.

[0006] The conception process of the present invention is as follows: the present invention adopts a Na2B4O7-metal fluoride 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 in crystal growth; and by introducing metal fluorides, the viscosity of the system can be reduced, which is beneficial to the solute transport during the crystal growth process, and can effectively avoid the generation of inclusions, which 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 of a sodium tetraborate-metal fluoride system, and the molar ratio of sodium tetraborate to metal fluoride in the flux is 1-0.8:0.05-0.2.

[0009] Preferably, the molar ratio of the sodium tetraborate to the metal fluoride is 1:0.05-0.12.

[0010] Furthermore, the preparation method of sodium tetraborate 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 sodium tetraborate. 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 sodium tetraborate 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 β-Ga2O3 crystal growth flux 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 0.5 to 1.3:1.

[0018] Furthermore, in S1, the temperature at which the solvent and the β-Ga2O3 powder are completely melted is 700 to 1180°C.

[0019] Preferably, in S1, the temperature at which the solvent and the β-Ga2O3 powder are completely melted is 760 to 956°C.

[0020] Furthermore, in S1, the constant temperature stirring time is 24 to 36 hours, and the constant temperature stirring rate is 20 to 30 rpm.

[0021] Furthermore, in S2 and S3, the saturation point temperature is 680-1150°C.

[0022] Preferably, in S2 and S3, the saturation point temperature is 726-926°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 15-18 rpm.

[0025] Sodium tetraborate contains two four-coordinated boron atoms (two BO4 tetrahedra) and two three-coordinated boron atoms (two BO3 triangles). The boron content is relatively high, and its high-temperature melt has a large viscosity, which is not conducive to the transport of solutes. By adding an appropriate amount of metal fluoride to the melt, the BO bond chain can be effectively broken, which helps to reduce the melt viscosity and 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 Na2B4O7-metal fluoride 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 and deviation of melt components. In addition, the flux of the present invention does not contain toxic raw materials such as PbO, PbSO4, PbF2, etc., thus avoiding the potential safety hazards of crystal growth.

[0028] (2) The Na2B4O7 in the flux of the present invention can reduce the high melting point of gallium oxide due to its low melting point. The introduction of metal fluoride can further reduce the melting point of gallium oxide and reduce the viscosity of the solution, which is beneficial to solute transport and heat conduction, and can effectively avoid the formation of inclusions, improve the stability of crystal growth, and increase the crystallization temperature range of crystal growth, which is beneficial to the growth of large-sized, high-quality β-Ga2O3 single crystals.

[0029] (3) The flux system of the β-Ga2O3 crystal of the present invention and the growth method thereof can significantly reduce the saturation point temperature of the β-Ga2O3 crystal. 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 680 to 1150°C, achieving a reduction of 150 to 670°C. The high-temperature solution is clear and transparent, which facilitates clear and real-time observation of the crystal growth. At the same time, growing crystals in the 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, Na2O, B2O3 and H3BO3 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 Na2B4O7-NaF flux system to grow β-Ga2O3 crystals.

[0034] Weigh 2 mol B2O3 and 1 mol Na2O, and synthesize Na2B4O7 using the solid phase method.

[0035] Use β-Ga2O3 powder, Na2B4O7 and NaF as raw materials, and mix them according to the molar ratio of β-Ga2O3:Na2B4O7:NaF=0.6:0.38:0.02. Weigh 112.46g of β-Ga2O3 powder, 76.46g of Na2B4O7 and 0.84g of NaF.

[0036] After the weighed raw materials are ground and mixed evenly, add Φ100×70mm 3The 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 760°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 30 rpm for 36 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 726°C by the trial crystal method, and then the high-temperature solution was heated to 726.5°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 18 rpm, kept at a constant temperature for 60 minutes, then cooled to 726°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 rotation 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 introduction of metal fluoride in this embodiment effectively interrupts the BO bond chain, further reduces the viscosity of the growth system, and is conducive to the growth of large-sized, high-quality β-Ga2O3 single crystals.

[0039] Example 2

[0040] This embodiment uses a Na2B4O7-LiF flux system to grow β-Ga2O3 crystals.

[0041] Weigh 2 mol B2O3 and 1 mol Na2O, and synthesize Na2B4O7 using the solid phase method.

[0042] Use β-Ga2O3 powder, Na2B4O7 and LiF as raw materials, and mix them according to the molar ratio of β-Ga2O3:Na2B4O7:LiF=0.65:0.315:0.035. Weigh 121.84g β-Ga2O3 powder, 63.38g Na2B4O7 and 0.91g LiF.

[0043] After the weighed raw materials are ground and mixed evenly, add Φ100×70mm 3The 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 position corresponding to the center of the crucible at the top of the furnace. The temperature is raised to 860°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 30 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 830°C by the trial crystal method, and then the high-temperature solution was heated to 830.5°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 830°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 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 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 introduction of metal fluoride in this embodiment effectively interrupts the BO bond chain, further reduces the viscosity of the growth system, and is conducive to the growth of large-sized, high-quality β-Ga2O3 single crystals.

[0046] Example 3

[0047] This embodiment uses a Na2B4O7-KF flux system to grow β-Ga2O3 crystals.

[0048] Use β-Ga2O3 powder, B2O3, Na2O and KF as raw materials, and mix them according to the molar ratio of β-Ga2O3:B2O3:Na2O:KF=0.7:0.54:0.27:0.045. Weigh 131.21g β-Ga2O3 powder, 37.59g B2O3, 16.73g Na2O and 2.61g 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 956°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.

[0050] The saturation point temperature of crystal growth was determined to be 926°C by the test crystal method, and then the high-temperature solution was heated to 926.5°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 25 rpm, kept at a constant temperature for 60 minutes, then cooled to 926°C, and then cooled at a rate of 0.25°C / day to allow crystal growth.

[0051] During the growth process, the rotation speed gradually decreases as the crystal grows, and the rotation speed is reduced to 18rpm 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 introduction of metal fluoride in this embodiment effectively interrupts the BO bond chain, further reduces the viscosity of the growth system, and is conducive to the growth of large-sized, 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 the growth of β-Ga2O3 crystals, characterized in that: The flux is a solubility aid of a sodium tetraborate-metal fluoride system, and the molar ratio of sodium tetraborate to metal fluoride in the flux is 1-0.8:0.05-0.

2.

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

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

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 to 5°C higher than the saturation point, the seed crystal rod is rotated while the seed crystal is lowered, the seed crystal is lowered to 1 to 3 mm below the liquid surface of the high temperature solution, the temperature is kept constant for 30 to 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 700 to 1180°C.

8. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S1, the constant temperature stirring time is 24 to 36 hours, and the constant temperature stirring speed is 20 to 30 rpm.

9. A β-Ga2O3 crystal growth method according to claim 5, characterized in that: In S2 and S3, the saturation point temperature is 680-1150°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.