A method for preparing gallium oxide single crystals using a zirconia crucible

Abstract

This invention discloses a method for preparing gallium oxide single crystals. Its key feature is the use of zirconium oxide as the crucible container. The gallium oxide raw material is melted through the combined action of a first heating element (gallium metal) and a second heating element (gallium oxide zirconium crucible), thereby achieving iridium-free growth of gallium oxide single crystals. This invention is simple and effective, avoids the use of the precious metal iridium, and significantly reduces the preparation cost of gallium oxide single crystals, thus facilitating the industrial production and scientific research of gallium oxide single crystals.

Description

Technical Field

[0001] This invention relates to a process method for reducing preparation costs and optimizing crystal quality, and particularly to a solution to the problems of high iridium cost, raw material volatilization, and iridium crucible oxidation in the preparation of gallium oxide single crystals, belonging to the field of semiconductor materials. Background Technology

[0002] Gallium oxide is an ultrawide bandgap semiconductor material with a bandgap of approximately 4.9 eV. It has many advantages, such as a large bandgap, fast saturated electron drift velocity, high breakdown field strength, and stable chemical properties.

[0003] Gallium oxide (GaO) materials have various isomers, but only the β phase exhibits high-temperature stability. Therefore, GaO single-crystal substrates prepared using the melt method are all β-type monoclinic structures. Currently, GaO shows great promise in power electronic devices, solar-blind ultraviolet detectors, and other fields. GaO single-crystal substrates have also attracted significant attention from numerous research institutions and semiconductor companies. Therefore, developing GaO single-crystal substrate preparation technology is of great importance.

[0004] Currently, common methods for preparing gallium oxide single crystals both domestically and internationally include the mode-guided method, the Czochralski method, the crucible lowering method, and the optical floating zone method. Among these, only the optical floating zone method does not require a crucible; it relies on a high-power light source and optical focusing system to heat the raw material and prepare the crystal. However, this method produces crystals with relatively small sizes, which cannot meet market demands for substrates. The mode-guided method and the Czochralski method can both prepare gallium oxide single crystals of 2 inches and above, but currently, iridium crucibles are used as the heating element and container. Strict control of the oxygen partial pressure is required to suppress gallium oxide volatilization and decomposition while preventing crucible oxidation. In particular, the volatilization and decomposition of gallium oxide raw materials under high temperature and low oxygen partial pressure conditions is a significant problem. The volatilized raw materials condense on the surface of the thermal field and crystal, affecting the growth process. The decomposition generates gallium suboxide and gallium metal, resulting in a large number of oxygen vacancies in the crystal, severely affecting crystal quality. Furthermore, gallium metal forms alloys with the iridium crucible and mold, damaging the crucible and drastically increasing costs. Therefore, reducing or avoiding the use of iridium and increasing the oxygen partial pressure during growth are crucial for reducing costs and improving crystal quality during the preparation of gallium oxide single crystals. These are also key points and challenges in the preparation of gallium oxide single crystals. Summary of the Invention

[0005] In view of the impact of raw material volatilization and decomposition and crucible oxidation on crystal quality and preparation cost in the current gallium oxide single crystal preparation process, this invention aims to provide a new process method. By using a zirconium oxide crucible instead of an iridium crucible, the atmospheric conditions during the growth process are changed to save costs and investment, improve crystal quality, and thus better realize the industrial production of gallium oxide.

[0006] The specific principles of this invention are as follows:

[0007] Zirconia, as an inorganic non-metallic material, has a negative temperature coefficient of resistance and good insulation properties at room temperature, with a resistivity greater than 1000 Ω·cm. However, as the temperature increases, its resistance begins to decrease, and it gradually becomes a conductive material. Zirconia begins to conduct electricity at 600℃, and becomes a good conductor at 1000℃. It can be used as a heating element for induction heating. Therefore, if you want to use zirconia as a heating material, you must raise its temperature.

[0008] Gallium metal has a melting point of around 30°C and readily oxidizes to form gallium oxide at high temperatures. Given this characteristic, gallium metal can be used as the primary heating element. An electromagnetic induction coil heats the gallium metal, thereby heating the crucible and gallium oxide powder. When the crucible temperature reaches 1000–1400°C, zirconium oxide can then serve as the secondary heating element. Oxygen is then introduced into the furnace to oxidize the gallium metal, forming gallium oxide. Using gallium metal effectively heats the zirconium oxide crucible to the required electrical conductivity temperature while preventing the introduction of impurities.

[0009] The specific method of this invention is as follows:

[0010] Weigh high-quality gallium oxide powder and gallium metal, and place them together in a zirconium oxide crucible. Position the heating element and seed crystal, close the furnace door, evacuate the furnace, and then fill it with a protective gas such as argon. Turn on the induction heating power supply to begin heating, and observe the thermocouple temperature. When the thermocouple temperature reaches 1000℃, gradually introduce oxygen into the furnace to oxidize the gallium metal. When the temperature reaches the melting point of gallium oxide, crystal growth begins. Slowly lower the seed crystal into the crucible and soak it for 30 minutes. Begin crystal pulling at a pulling speed of 1 mm / h and a rotation speed of 5 rpm, following processes such as crystal pulling, necking, shoulder formation, and tailing. Gradually reduce the power supply and cool to room temperature to complete the growth.

[0011] Preferably, when gallium metal is used as the first heating element, it is uniformly mixed with gallium oxide powder raw material in a certain proportion and placed in a gallium oxide zirconium crucible; wherein the mass ratio of gallium metal to gallium oxide powder is in the range of 1:10 to 1:100.

[0012] Preferably, the zirconia crucible is sintered from yttrium-doped zirconia powder, possessing a negative temperature coefficient of resistance, with a resistivity of 1×10⁻⁶ at 700–1000 °C. -3 ~8×10 -3 In the Ω·cm range, at 1500–1800℃, 1×10 -5 ~1×10 -4 The Ω·cm interval.

[0013] Preferably, heating is achieved through induction heating using an electromagnetic coil, with the frequency of the electromagnetic coil in the first heating stage being in the range of 1 to 10 kHz and the frequency in the second heating stage being in the range of 10 to 50 MHz.

[0014] Preferably, the electromagnetic coil first senses the gallium metal as the first heating element to implement the first stage of heating, heating the zirconium oxide crucible to 1000-1400°C; then, the high-temperature zirconium oxide crucible is used as the second heating element to implement the second stage of heating, so that the furnace temperature reaches about 1800°C, and the gallium oxide raw material is completely melted.

[0015] Preferably, in the first heating stage, the furnace is in an oxygen-free environment, and argon or nitrogen is introduced to maintain atmospheric pressure inside the furnace; in the second heating stage, the furnace is in an oxygen-rich environment, and some oxygen is introduced, with an oxygen partial pressure ratio of 10-50%, for gallium metal oxidation.

[0016] Preferably, gallium oxide raw materials are grown from a molten state into single crystals using methods such as the Czochralski method, the mold-guided method, and the crucible lowering method.

[0017] The beneficial effects of this invention are that by changing the material of the crucible and the heating method, the dependence of gallium oxide crystal growth on iridium crucibles is eliminated, the use of precious metals is avoided, and the investment cost is greatly reduced. At the same time, the atmospheric environment during growth is adjusted, which improves the crystal quality and promotes the industrialization of gallium oxide single crystal substrates. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the growth apparatus for growing gallium oxide single crystals according to the present invention. In the figure: 1, induction heating coil; 2, zirconium oxide crucible; 3, insulation material; 4, thermocouple temperature measurement; 5, gallium oxide powder; 6, gallium metal. Specific implementation methods

[0019] Unless otherwise specified, the means involved in the embodiments are all conventional technical means in the art.

[0020] This invention employs the Czochralski method to prepare a two-inch gallium oxide single crystal, with the growth direction being the (0 1 0) direction. The specific steps are as follows:

[0021] Step 1: Weigh 500g of high-quality gallium oxide powder and 50g of gallium metal, and place them together in a zirconium oxide crucible.

[0022] Step 2: Place the heating field and seed crystal, close the furnace door, evacuate the furnace, and then fill the furnace with protective gases such as argon.

[0023] Step 3: Turn on the induction heating power supply to start heating up and observe the thermocouple temperature. When the thermocouple temperature reaches 1000℃, gradually introduce oxygen into the furnace to gradually oxidize the gallium metal.

[0024] Step 4: When the temperature reaches the melting point of gallium oxide, crystal growth begins. The seed crystal is slowly lowered into the crucible and soaked for 30 minutes.

[0025] Step 5: Start crystal growth by pulling at a speed of 1 mm / h and rotating at 5 rpm. After crystal growth, the crystal growth process is completed, including crystal pulling, necking, shoulder formation, and tailing.

[0026] Step Six: Gradually reduce the power supply and cool down to room temperature to complete the growth process.

Claims

1. A method for preparing gallium oxide single crystals using a zirconium oxide crucible, characterized in that, Includes the following steps: Weigh out high-quality gallium oxide powder and gallium metal, and place them together into a zirconium oxide crucible; After placing the heating element and seed crystal, close the furnace door, evacuate the furnace, and then fill it with argon protective gas. Turn on the induction heating power supply to start heating and observe the thermocouple temperature. When the thermocouple temperature reaches 1000℃, gradually introduce oxygen into the furnace to oxidize the gallium metal. When the temperature reaches the melting point of gallium oxide, crystal growth begins. Slowly lower the seed crystal into the crucible and soak it for 30 minutes. Begin crystal pulling at a pulling speed of 1mm / h and a rotation speed of 5rpm. The crystal growth process includes crystal pulling, necking, shoulder formation, and tailing. Gradually reduce the power supply and cool the furnace to room temperature. The growth process is now complete. The zirconia crucible is sintered from yttrium-doped zirconia powder and has a negative temperature coefficient of resistance, with a resistivity of 1×10⁻⁶ at 700–1000 °C. -3 ~8×10 -3 In the Ω·cm range, at 1500–1800℃, 1×10 -5 ~1×10 -4 Ω·cm interval; The electromagnetic coil first senses the gallium metal as the first heating element to implement the first stage of heating, heating the zirconium oxide crucible to 1000-1400℃; then the high-temperature zirconium oxide crucible is used as the second heating element to implement the second stage of heating, so that the furnace temperature reaches about 1800℃, and the gallium oxide raw material is completely melted.

2. The method according to claim 1, characterized in that, When gallium metal is used as the first heating element, it is uniformly mixed with gallium oxide powder in a certain proportion and placed in a gallium oxide zirconium crucible; wherein the mass ratio of gallium metal to gallium oxide powder is in the range of 1:10 to 1:

100.

3. The method according to claim 1, characterized in that, Heating is achieved through induction heating using an electromagnetic coil. The frequency of the electromagnetic coil is in the range of 1 to 10 kHz during the first heating stage and in the range of 10 to 50 MHz during the second heating stage.

4. The method according to claim 1, characterized in that, In the first heating stage, the furnace is in an oxygen-free environment, and argon gas is introduced to maintain atmospheric pressure inside the furnace. In the second heating stage, the furnace is in an oxygen-rich environment, and some oxygen is introduced, with an oxygen partial pressure ratio of 10-50%, which is used for gallium metal oxidation.

5. The method according to claim 1, characterized in that, The methods for growing gallium oxide raw materials from a molten state into single crystals are the Czochralski method, the mold-guided method, and the crucible lowering method.

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