CN115261973A - A kind of growth method of large size gallium oxide crystal - Google Patents

Abstract

The invention provides a method for growing large-size gallium oxide crystals, in particular to beta-Ga more than 3 inches ₂ O ₃ And (4) growing a single crystal. The method mainly comprises the steps of charging, setting high pressure (0.1)<p<0.7 MPa), pure oxygen atmosphere, melting, growing and cooling, and the method can effectively avoid the problem of raw material decomposition in the gallium oxide growth process.

Description

A kind of growth method of large-size gallium oxide crystal

technical field

The invention belongs to the field of crystal growth, and in particular relates to a gallium oxide crystal growth method, especially for the growth of β-Ga ₂ O ₃ single crystals larger than 3 inches.

Background technique

Gallium oxide (β-Ga ₂ O ₃ ), as an ultra-wide bandgap (E _g = 4.5-4.9V) semiconductor material, has the advantages of high breakdown electric field strength, stable chemical properties, and low cost of large-scale growth. Its Baliga device is excellent The values are 4 times and 10 times that of GaN and SiC, respectively, providing a broader vision for the development of high-voltage and high-power devices in the future.

镓和铱坩埚反应形成共晶金属间GaIr相，损坏坩埚，特别是在较大尺寸的氧化镓晶体生长过程中，Ga单质的含量升高，对铱坩埚损耗严重；同时，熔体中的产生的氧气会产生大量的氧空位，影响氧化镓晶体质量与掺杂，进而严重影响器件性能。虽然光学浮区法不需要使用坩埚，且生长速率较高，生长得到的氧化镓晶体纯度高，但是制备的晶体尺寸较小，远远无法满足大尺寸应用的需求。However, there are huge challenges in the growth of large-sized gallium oxide single crystals. One of the important factors is that gallium oxide itself has a high melting point (about 1790 ° C), and it is very easy to decompose and volatilize at high temperatures, which is especially important for crystal growth equipment. Crucible is extremely demanding. At present, the methods for preparing gallium oxide from the melt mainly include the optical floating zone method, the pulling method, the crucible drop method and the guided mode method. Among them, the pulling method, the crucible falling method and the guided mode method can all realize the preparation of large-sized gallium oxide crystals (≥2 inches), but these methods need to use noble metal iridium crucibles, which are costly; and in high temperature environments, gallium oxide raw materials It is easily decomposed into elemental gallium and oxygen, and the decomposition reaction is as follows:

Gallium and iridium crucibles react to form eutectic intermetallic GaIr phase, which damages the crucible, especially during the growth of large-sized gallium oxide crystals, the content of Ga elemental substance increases, which seriously damages the iridium crucible; at the same time, the melt produced Oxygen will generate a large number of oxygen vacancies, which will affect the quality and doping of gallium oxide crystals, and then seriously affect the device performance. Although the optical floating zone method does not require the use of a crucible, the growth rate is high, and the purity of the gallium oxide crystals obtained by growth is high, but the size of the prepared crystals is small, which is far from meeting the needs of large-scale applications.

In order to suppress the decomposition of gallium oxide during the growth process, in the prior art, an inert gas and a mixed gas are usually selected as a protective atmosphere. For example, in Chinese patents CN 114381800 A and CN 114086249 A, argon, nitrogen, argon/nitrogen/ Oxygen mixed gas or oxygen/carbon dioxide mixed gas to protect the crucible; Chinese patent CN 107177885 B feeds 7 to 12 bar high-purity air to suppress the decomposition of Ga ₂ O ₃ , but these methods have low efficiency, poor effect, and a small range of applications . The Leibniz Institute of Crystal Growth in Germany once proposed that during the growth of gallium oxide, the increase of oxygen partial pressure can significantly improve the quality of crystal growth and inhibit the decomposition reaction, especially when the crystal size reaches 3 inches, at least 100vol.% of Oxygen can effectively inhibit the precipitation of Ga single crystals (Zbigniew Galazka, et. al. Scaling-Up of Bulkβ-Ga2O3Single Crystals by the Czochralski Method, ECS Journal of Solid State Science and Technology, 2017, 6(2)Q3007-Q3011). However, it should be emphasized that the increase of oxygen partial pressure also means that iridium is more likely to react with oxygen, which will also cause damage to the noble metal crucible in the prior art.

Contents of the invention

In view of the above-mentioned problems, especially the high-temperature decomposition of gallium oxide and the dependence of high-cost precious metal crucibles, the present invention proposes a crystal growth method that can effectively inhibit the decomposition of gallium oxide. This method has low cost and wider application range, and can realize Growth of large-sized gallium oxide crystals.

Technical scheme of the present invention is as follows:

A large-size gallium oxide crystal growth method, which is characterized in that a cold crucible or an alloy crucible is used to fill a gallium oxide raw material, and the gallium oxide crystal is grown under a pure oxygen atmosphere with a pressure range of 0.1<p<0.7MPa; the alloy crucible It is an alloy of Pt and any one or more metals of Ir and Rh, wherein the content of Pt is 75% to 90%.

Further, when a cold crucible is used, metal Ga or graphite flakes are placed in the middle region of the gallium oxide raw material as an igniter.

Further, when an alloy crucible is used, the pressure of the pure oxygen atmosphere is 0.1<p≤0.4MPa.

The diameter-to-depth ratio of the alloy crucible or cold crucible is 1:1-2:1, so that the surface of the melt is fully in contact with oxygen.

A large-size gallium oxide crystal growth method mainly includes the following steps:

①Charging: prepare high-purity gallium oxide raw materials and dry them in a vacuum environment, and put the raw materials into the crucible located in the center of the furnace, and the charging volume is 75% to 90% of the volume of the crucible;

②Vacuumizing: Vacuumize the furnace to below 2×10 ^-3 Pa, and introduce high-purity oxygen atmosphere, the pressure range is: 0.1<p<0.7MPa;

③Heating up: Start the induction heating device to generate high temperature in the crucible and melt the raw material powder, then increase the power supply to gradually expand the melting area, and keep it for 1-3 hours after the temperature reaches 1750-1850 °C;

④Crystal growth: After the raw materials are melted, use crucible lifting method, temperature gradient method, pulling method and other melt methods to grow gallium oxide crystals; after the crystal growth is completed, slowly reduce the power until the crystal cools to room temperature, and the cooling rate is controlled at 5~ 15°C/min;

The used crucible is a cold crucible or an alloy crucible; the alloy crucible is an alloy of any one or more metals of Pt, Ir and Rh, wherein the content of Pt is 70%-90%.

Wherein, the diameter-to-depth ratio of the cold crucible and the alloy crucible is 1:1 to 2:1, so that the surface of the melt is fully in contact with oxygen;

Among them, when using an alloy crucible, the pure oxygen pressure is 0.1<p≤0.4MPa;

The cold crucible is composed of a water-cooled flap and a water-cooled table. During the growth process, the external powder will not be heated and melted due to water cooling, thus forming a layer of unmelted shell, and the melt undergoes crystal growth in the unmelted shell. . When loading the raw material into the cold crucible, evenly put metal Ga or graphite sheet in the middle area of the raw material as the igniter of the raw material;

Preferably, the Ir content in the alloy crucible is 20-25wt%;

Preferably, the Rh content in the alloy crucible is 15-25wt%;

To ensure that the alloy crucible will not melt at around 1900°C.

Technical advantage of the present invention:

(1) The present invention uses a high-pressure pure oxygen atmosphere to suppress the decomposition of gallium oxide during the growth process and improve the quality of crystal growth, especially when growing large-sized gallium oxide crystals larger than 3 inches;

(2) The crucible system of the present invention adopts a cold crucible or an alloy crucible with optimized composition, which can be used under a high-pressure pure oxygen atmosphere to reduce the loss of precious metals and greatly reduce the cost;

(3) The high-pressure pure oxygen atmosphere can effectively inhibit the formation of oxygen vacancies in gallium oxide crystals and improve device performance; in addition, at low oxygen vacancy concentrations, the formation energy of acceptor defects is high, which is conducive to the further development of p-type doped devices.

Description of drawings

Fig. 1 is a flowchart of the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments. The examples here are only used to explain the present invention, not to limit the present invention.

Embodiment one

₃ inch _Ga2O3 crystal growth:

Use gallium oxide powder with a purity of 99.99%, put it into the crucible in the center of the furnace, and the charging volume is 80% of the crucible; the crucible uses a Pt-Rh crucible with a Rh content of 25wt%, the diameter of the crucible is 150mm, and the height is 100mm; turn on the mechanical pump and molecular pump, vacuumize the furnace to 2×10 ^-3 Pa, open the gas valve, fill in 99.99% high-purity oxygen, when the pressure in the furnace reaches 0.2MPa, turn on the power supply, and keep it for 2 hours when the temperature reaches 1800°C to make the raw materials Fully melt; then reduce the heating power and use the pulling method to grow crystals, the pulling speed and rotation speed are 2mm/h and 10rpm respectively, the temperature of the melt gradually drops and crystals grow at the same time; after the growth is completed, reduce the power supply to off, and control the cooling in the furnace The speed is 10°C/min until it cools down to room temperature.

Finally, a crystal blank of φ82mm is obtained, and a 3-inch-level β-Ga ₂ O ₃ single wafer can be obtained after processing; there are no bubbles on the surface of the crystal when observed under a strong light, and no holes when observed under a microscope, FWHM=50arcsec, gallium oxide in the prior art The FWHM of single crystal products is about 100-150arcsec. After this growth, the loss of the alloy crucible is about 0.5g, compared with the loss of about 1.6g in the prior art when the iridium crucible is kept at 1800°C for 1 hour, the loss is reduced by 68%.

Embodiment two

₄ inch _Ga2O3 crystal growth:

Use gallium oxide powder with a purity of 99.99%, put it into the crucible in the center of the furnace, and the charging volume is 85% of the crucible; use water cooling valves and water cooling tables to form a cold crucible with a diameter of 108 mm and a height of 55 mm. Lay out 100g of graphite flakes as an ignition agent; turn on the mechanical pump and molecular pump, vacuumize the furnace to 2×10 ^-3 Pa, open the gas valve, and fill in 99.99% high-purity oxygen until the pressure in the furnace reaches 0.5MPa , start the power supply, adjust the heating power to produce a small melting zone around the graphite sheet, continue to heat the melt to gradually expand, and form a layer of unmelted shell on the outside due to water cooling. When the temperature reaches 1805 ° C, keep it for 3 hours to make the melt and the outer unmelted shell Reach thermal equilibrium; then slowly lower the cold crucible, so that the lower part of the cold crucible leaves the heating zone, the temperature of the melt decreases and crystallizes. After the growth is over, reduce the power supply to off, control the cooling rate in the furnace to 12°C/min, and take out the crystal block after cooling to room temperature.

Finally, a φ106mm crystal billet is obtained. After processing, a 4-inch β-Ga ₂ O ₃ single wafer can be obtained. There are no bubbles on the surface observed under a strong light, and no holes observed under a microscope. FWHM=58arcsec. This growth uses a cold crucible , no loss of precious metals, the cost is greatly reduced.

Embodiment three

6 inch Ga ₂ O ₃ crystal growth:

Gallium oxide powder with a purity of 99.99% is put into the crucible in the center of the furnace, and the charging volume is 70% of the crucible; a cold crucible with a crucible diameter of 165mm and a height of 85mm is formed by using water-cooling valves and water-cooling tables, and is placed in the middle area of the raw material. Arrange 100g Ga sheets radially as the ignition agent; turn on the mechanical pump and molecular pump, vacuumize the furnace to 2×10 ^-3 Pa, open the gas valve, and fill in 99.99% high-purity oxygen until the pressure in the furnace reaches 0.65MPa At the same time, start the power supply, adjust the heating power to produce a small melting zone around the graphite sheet, continue to heat the melt and gradually expand, and form a layer of unmelted shell on the outside due to water cooling. When the temperature reaches 1805 ° C, keep it for 3 hours to make the melt and the outside unmelted The shell reaches thermal equilibrium; then the heating power is reduced and the crystal is grown by the pulling method, the pulling speed is 1.5mm/h, and the rotation speed is 8rpm. After the growth is over, reduce the power supply to off, and control the cooling rate in the furnace to 12°C/min until it drops to room temperature.

Finally, a φ160mm crystal billet is obtained. After processing, a 6-inch β-Ga ₂ O ₃ single wafer can be obtained. There are no bubbles on the surface observed under a strong light, no holes observed under a microscope, FWHM=65arcsec, and a cold crucible is used for this growth , no loss of precious metals, the cost is greatly reduced.

Claims (8)

1. A method for growing large-scale gallium oxide crystals, characterized in that, a cold crucible or an alloy crucible is used to fill gallium oxide raw materials, and the gallium oxide crystals are grown under a pure oxygen atmosphere with a pressure range of 0.1<p<0.7MPa; The alloy crucible is an alloy of Pt and any one or more metals of Ir and Rh, wherein the content of Pt is 75%-90%. 2. a kind of large-scale gallium oxide crystal growth method as claimed in claim 1 is characterized in that, when adopting cold crucible, put metal Ga or graphite flake as ignition agent in the middle region of gallium oxide raw material. 3. A method for growing large-sized gallium oxide crystals as claimed in claim 1, characterized in that when an alloy crucible is used, the pressure of the pure oxygen atmosphere is 0.1<p≤0.4MPa. 4. A method for growing large-sized gallium oxide crystals according to claim 1, wherein the diameter-to-depth ratio of the alloy crucible or cold crucible is 1:1 to 2:1, so that the surface of the melt is fully in contact with oxygen . 5. A method for growing large-sized gallium oxide crystals as claimed in claim 1, characterized in that in the alloy crucible, the Ir content is 22-28 wt%. 6. A method for growing large-sized gallium oxide crystals as claimed in claim 1, characterized in that the Rh content in the alloy crucible is 15-25 wt%. 7. A method for growing large-sized gallium oxide crystals as claimed in claim 1, wherein the volume of the charge is 75% to 90% of the volume of the crucible. 8. A method for growing a large-scale gallium oxide crystal according to any one of claims 1-7, comprising the following steps: Charging: prepare high-purity gallium oxide raw materials and dry them in a vacuum environment, and put the raw materials into the crucible located in the center of the furnace, and the charging volume is 75% to 90% of the volume of the crucible; Vacuuming: Vacuumize the furnace to below 2×10 ^-3 Pa, introduce high-purity oxygen atmosphere, and the pressure range is: 0.1<p<0.7MPa; Heating: Start the induction heating device to generate high temperature in the crucible and melt the raw material powder, then increase the power supply to gradually expand the melting area, and keep it for 1 to 3 hours after the temperature reaches 1750-1850 °C; Crystal growth: After the raw materials are melted, the gallium oxide crystal is grown by the melt method. After the crystal growth is completed, the power supply is slowly reduced until the crystal cools to room temperature, and the cooling rate is controlled at 5-15°C/min.

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