Gallium oxide crystal twin growth inhibition method based on thermal field gradient induction

Abstract

The present application relates to the technical field of wide band gap semiconductor material preparation, and particularly relates to a gallium oxide crystal twin crystal growth inhibition method based on thermal field gradient induction, which comprises the following steps: a gallium oxide crystal is prepared by using a guided mode method growth equipment; after the crystal enters a shoulder separation stage, a horizontal direction temperature gradient field is established in an upper region of a mold by regulating a partition power of a heater or starting a local cooling device; according to a position and an extension direction of a twin crystal in a seed crystal, a low-temperature side of the horizontal direction temperature gradient field is arranged in a reverse direction of the extension direction of the twin crystal; the horizontal direction temperature gradient field is maintained for a period of time until it is observed that a growth direction of the twin crystal is deflected to a low-temperature side edge region of the crystal; after the twin crystal is induced to an edge of the crystal or eliminated, the horizontal direction temperature gradient field is gradually reduced, and normal isochiral growth conditions are restored, so that the twin crystal in the existing seed crystal can be directly inhibited without replacing the seed crystal, and production cost and time are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wide bandgap semiconductor material preparation, in particular to a twin crystal growth inhibition method based on thermal field gradient induced gallium oxide crystal, which is particularly suitable for controlling and inhibiting twin crystal defects in the process of growing gallium oxide single crystal by edge-defined film-fed growth (EFG). BACKGROUND

[0002] As a new generation of ultra-wide bandgap semiconductor material, β-Ga2O3 has excellent characteristics such as wide bandgap (about 4.8-4.9 eV), high breakdown electric field (about 8 MV / cm) and good chemical stability, and shows broad application prospects in ultra-high voltage power devices, deep ultraviolet optoelectronic devices, high-brightness LEDs and high-temperature high-frequency electronic devices. With the continuous deepening of these applications, the demand for high-quality, large-size β-Ga2O3 single crystal materials is increasingly urgent.

[0003] At present, the main methods for preparing β-Ga2O3 single crystal include Czochralski method, edge-defined film-fed growth (EFG), vertical Bridgman method and floating zone method. Among them, the edge-defined film-fed growth method has become one of the main methods for producing large-size β-Ga2O3 single crystal because it can control the shape and size of the crystal and has a relatively high growth rate.

[0004] However, during the growth of β-Ga2O3 crystal by edge-defined film-fed growth method, the twin crystal defects existing in the seed crystal often extend and expand in the subsequent growth process, and even penetrate through the entire crystal, which seriously affects the quality and performance of the final crystal. In 2022, Professor Tao Xiutang's team at Shandong University reported the growth research work of 4-inch β-Ga2O3 single crystal, and mentioned that twin crystal defects are still one of the main factors limiting the application of large-size β-Ga2O3 crystal. In addition, studies have shown that twin crystals in β-Ga2O3 crystal can significantly reduce the breakdown voltage and carrier mobility of the device, thereby limiting its application in high-power electronic devices.

[0005] Current methods for inhibiting twin crystal defects in β-Ga2O3 crystal mainly include:

[0006] 1. Optimizing seed crystal selection: by strictly screening seed crystals with no twin crystal or very low twin crystal content, but this method is high in cost and low in efficiency, and cannot fundamentally solve the problem;

[0007] 2. Controlling growth rate: by reducing the growth rate to reduce twin crystal formation and expansion, but it will significantly reduce production efficiency;

[0008] 3. Adjusting the thermal field structure: reducing thermal stress by optimizing the thermal field design, but the effect is limited and not targeted at existing twin crystals.

[0009] Some scholars have mentioned that adjusting the thermal field structure can improve the crystal quality to some extent, but have not proposed a systematic solution for effectively inhibiting twins. Although the formation probability of twins can be reduced by optimizing the growth parameters, there is still a lack of effective means to inhibit existing twins.

[0010] Therefore, it is urgent to develop a new method that can effectively inhibit the extension of twin defects without replacing the seed crystal, in order to improve the quality and production efficiency of β-Ga2O3 single crystals. SUMMARY

[0011] In view of the problems in the prior art, the purpose of the present application is to provide a gallium oxide crystal twin growth inhibition method based on thermal field gradient induction, which changes the melt supersaturation distribution and thermal stress state by introducing a specific horizontal temperature gradient field during the crystal shoulder stage, effectively controls the growth direction of twins, deflects the twins to the edge of the crystal, and ultimately inhibits the extension of twin defects in the main crystal.

[0012] To achieve the above purpose, the present application provides a gallium oxide crystal twin growth inhibition method based on thermal field gradient induction, comprising the following steps:

[0013] Gallium oxide crystals are prepared using a guide mode method growth device. After the crystal enters the shoulder stage, a horizontal temperature gradient field is established in the upper region of the mold by adjusting the power of the heater partition or starting a local cooling device.

[0014] According to the position and extension direction of the twin in the seed crystal, the low-temperature side of the horizontal temperature gradient field is set in the opposite direction of the twin extension direction.

[0015] The horizontal temperature gradient field is maintained for a period of time until the growth direction of the twin is deflected to the low-temperature side edge region of the crystal.

[0016] When the twin is induced to the edge of the crystal or eliminated, the horizontal temperature gradient field is gradually reduced to restore the normal isodiametric growth conditions.

[0017] In a preferred embodiment of the present application, the guided mode growth apparatus comprises: a multi-zone independently controlled heating system, wherein an independently controlled auxiliary heater is installed on both sides of the region above the mold, the auxiliary heater has a power range of 0-2000W and a temperature control accuracy of ±1℃; an adjustable cooling device is installed on one side of the region above the mold, the cooling device adopts water cooling or air cooling, the water cooling system has a flow control range of 0.5-5 liters per minute, and the air cooling system has a flow control range of 1-10 liters per minute; and a temperature monitoring system comprising a plurality of thermocouples and infrared thermometers uniformly distributed in the horizontal direction, which monitors the temperature distribution near the growth interface in real time.

[0018] Further, the size of the horizontal temperature gradient field is 5-20℃ per centimeter, and the specific gradient value is selected according to the twin type and severity: for a slight twin with an area ratio of less than 5%, the horizontal temperature gradient is 5-8℃ per centimeter; for a moderate twin with an area ratio of 5-15%, the horizontal temperature gradient is 8-15℃ per centimeter; and for a severe twin with an area ratio of more than 15%, the horizontal temperature gradient is 15-20℃ per centimeter.

[0019] Preferably, the time for maintaining the horizontal temperature gradient field is determined according to the severity of the twin: for a slight twin with an area ratio of less than 5%, the maintenance time is 20-40 minutes; for a moderate twin with an area ratio of 5-15%, the maintenance time is 40-80 minutes; and for a severe twin with an area ratio of more than 15%, the maintenance time is 80-120 minutes.

[0020] The present application also provides a specific method for establishing a horizontal temperature gradient field, which is achieved by any of the following ways: increasing the power of the high-temperature side auxiliary heater by 10-30% while reducing the power of the low-temperature side auxiliary heater by 5-15%; or keeping the power of the high-temperature side auxiliary heater unchanged and starting the cooling device on the low-temperature side, with the cooling intensity starting from the minimum value and gradually increasing to the set value.

[0021] In addition, the rate of gradually reducing the horizontal temperature gradient field is 1-5℃ per centimeter per hour, and is selected according to the twin deflection effect: for a case where the deflection effect is obvious, a faster rate of 3-5℃ per centimeter per hour is used; for a case where the deflection effect is general, a medium rate of 2-3℃ per centimeter per hour is used; and for a case where the deflection effect is weak, a slower rate of 1-2℃ per centimeter per hour is used.

[0022] The present application is particularly suitable for suppressing twin defects of different crystal orientations of β-Ga2O3: for suppressing 〈010〉-oriented twins, the horizontal temperature gradient is 10-15℃ per centimeter, the gradient direction is perpendicular to the direction of 〈010〉, and the gradient maintaining time is 40-60 minutes; for suppressing 〈100〉-oriented twins, the horizontal temperature gradient is 8-12℃ per centimeter, the gradient direction is perpendicular to the direction of 〈100〉, and the gradient maintaining time is 50-70 minutes; for suppressing 〈-201〉-oriented twins, the horizontal temperature gradient is 12-18℃ per centimeter, the gradient direction is perpendicular to the direction of 〈-201〉, and the gradient maintaining time is 30-50 minutes.

[0023] In the horizontal temperature gradient induction stage, in order to further improve the twin suppression effect, the crystal growth rate is reduced to 65-85% of the original growth rate, and the crystal rotation speed is reduced to 4-9 revolutions per minute to reduce the influence of centrifugal force on the flow of the melt; after the horizontal temperature gradient field is eliminated, the crystal growth rate is restored to 2-4 millimeters per hour, and the crystal rotation speed is restored to 10-20 revolutions per minute, and the isometric growth is continued to the predetermined length.

[0024] The beneficial effects of the present application include:

[0025] 1. By introducing a horizontal temperature gradient field, the growth direction of the twin is effectively controlled and deflected to the edge of the crystal, thereby suppressing the extension of the twin in the main crystal, and significantly improving the crystal quality;

[0026] 2. The method does not need to replace the seed crystal, and can directly suppress the twin in the existing seed crystal, reducing the production cost and time;

[0027] 3. The horizontal temperature gradient parameters can be flexibly adjusted according to the specific type and position of the twin, and have strong applicability;

[0028] 4. The method is simple in process and easy to realize on the existing template method growth equipment, and has strong operability;

[0029] 5. By reasonably controlling the thermal field gradient, not only the twin can be suppressed, but also the density of other defects can be reduced, and the overall crystal quality can be improved. DETAILED DESCRIPTION

[0030] The present application will be further described in detail below in conjunction with specific embodiments, but the embodiments of the present application are not limited thereto.

[0031] In the implementation process of the present application, first, the conventional template method crystal growth equipment needs to be specially modified and configured to realize accurate control of the horizontal temperature gradient.

[0032] Generally speaking, the guide mode method growth equipment mainly includes growth cavity, vacuum system, gas system, heating system, crystal pulling system and observation system and other components. The key of the present application lies in the special design of the heating system and the control method of the horizontal temperature gradient. The main equipment components are described in detail below.

[0033] The heating system of the conventional guide mode method growth equipment usually adopts axisymmetric structure to maintain uniform temperature field. In the present application, in order to realize the accurate control of the horizontal temperature gradient, we specially design the heating system. Specifically, auxiliary heaters independently controlled are installed on both sides of the upper region of the mold, and the power of these heaters can be adjusted individually, thereby forming a controllable temperature gradient in the horizontal direction.

[0034] The auxiliary heater is made of tungsten wire (W, purity ≥ 99.95%), and the wire diameter is selected between 0.5-0.8 mm. In terms of coil design, the inner diameter is controlled between 40-60 mm, the outer diameter is 50-70 mm, the height is between 20-40 mm, the number of turns is 15-25 turns, and the turn spacing is kept between 1.5-2.5 mm. This design enables the auxiliary heater to provide a power density of 30-50 watts per square centimeter, with a maximum working temperature of up to 2200°C, which is sufficient to meet the temperature requirements of β-Ga2O3 crystal growth.

[0035] The power supply control of the auxiliary heater adopts a DC stabilized power supply with a voltage range of 0-60 volts and a current range of 0-100 amperes, and the power control accuracy reaches ±0.5%, the response time is not more than 100 milliseconds, and the PID control mode with adjustable parameters is adopted to ensure the accuracy and stability of temperature regulation.

[0036] In order to realize more flexible control of the horizontal temperature gradient, the present application also installs adjustable cooling devices on one side of the upper region of the mold, which can be used in cooperation with the auxiliary heater or used alone to establish a horizontal temperature gradient.

[0037] The cooling system has two options: water cooling system and air cooling system. The water cooling system uses stainless steel (316L grade) or copper (purity ≥ 99.9%) made cooling pipe, with an outer diameter of 6-10 mm and an inner diameter of 4-8 mm, and the cooling medium is deionized water with a resistivity greater than 10 mega ohm centimeter. The system is equipped with a constant temperature water circulation device, with a temperature control range of 15-40°C and an accuracy of ±0.5°C. The flow is controlled by an electromagnetic flowmeter, with a range of 0.5-5 liters per minute and an accuracy of ±2%. The pressure is controlled at 0.2-0.5 mega pascal, and is equipped with a pressure sensor and a safety relief valve.

[0038] The gas cooling system uses high-purity argon (purity ≥ 99.999%) as the cooling medium, which is transported through stainless steel or copper pipes with an outer diameter of 8-12 mm and an inner diameter of 6-10 mm. The flow rate is precisely adjusted by a mass flow controller, with a range of 1-10 liters per minute and an accuracy of ±1%. To improve cooling efficiency, the system can be equipped with a gas cooling device, with a temperature control range of 10-30°C.

[0039] Both cooling systems are equipped with a three-axis fine adjustment mechanism with an adjustment accuracy of ±0.5 mm and an adjustment range of ±15 mm for the X and Y axes and ±30 mm for the Z axis, to accurately control the cooling position.

[0040] Accurate temperature monitoring is crucial for precise control of the horizontal temperature gradient. The invention uses a multi-point temperature monitoring system, including a thermocouple array and an infrared temperature measurement system.

[0041] Five W-5%Re / W-26%Re thermocouples are evenly arranged in the horizontal direction above the mold, with a diameter of 0.3-0.5 mm, a temperature measurement range of 0-2300°C, an accuracy of ±2°C or 0.5% of the reading (whichever is greater), and a response time of not more than 1 second. The thermocouples are spaced 10-15 mm apart and 10-30 mm away from the growth interface to monitor the horizontal temperature distribution comprehensively.

[0042] At the same time, the system is also equipped with a dual-color infrared temperature measurement instrument with a wavelength range of 0.7-1.1 microns, a temperature measurement range of 600-2000°C, an accuracy of ±3°C or 0.3% of the reading (whichever is greater), a field of view angle of 1-3°, and a response time of not more than 10 milliseconds. The infrared temperature measurement instrument is aligned with the growth interface through the observation window to achieve non-contact temperature monitoring.

[0043] The temperature data acquisition system has a sampling frequency of 1-10 Hz (adjustable), with not less than 16 channels, a resolution of not less than 16 bits, support for RS-485, USB, and Ethernet interfaces, a data storage capacity of not less than 1 TB, and support for remote data transmission. The system software has real-time display, historical curve query, alarm setting, and data export functions, providing reliable protection for the precise control of the horizontal temperature gradient.

[0044] Before explaining the core technology of the invention - the hot field gradient-induced twin crystal suppression method, first briefly introduce the basic process of β-Ga2O3 crystal growth, including raw material preparation, seed crystal treatment, crystal growth and post-processing.

[0045] 1. Raw material preparation: The main raw material used in the present application is high purity β-Ga203 powder (trigallium dioxide), with a purity of no less than 99.999% (5N) and an average particle size controlled between 1-5 microns, which can be purchased from Sigma-Aldrich Company or Alfa Aesar Company. The main impurity content requirements in the raw material are: Si less than 2 ppm, Al less than 1 ppm, Fe less than 1 ppm, Ca less than 1 ppm, and the total amount of other metal impurities less than 5 ppm.

[0046] In order to further improve the purity of the raw material, the commercial raw material needs to be pretreated. Specifically, the β-Ga203 powder is calcined at 800±20°C for 4-6 hours to remove the surface adsorbed moisture and organic matter; then it is cooled to room temperature under high-purity argon gas (purity ≥ 99.999%) atmosphere and stored in a dry box with a relative humidity of less than 10%. The treated raw material needs to be detected for metal impurity content using inductively coupled plasma mass spectrometry (ICP-MS) to ensure that the above requirements are met.

[0047] 2. Seed crystal preparation: Seed crystal selection is an important factor affecting the final crystal quality. The present application selects a β-Ga203 single crystal with a <010> or <100> orientation as the seed crystal, with a size of (5±0.5) mm x (5±0.5) mm x (20±2) mm.

[0048] The seed crystal treatment process includes cutting, polishing and surface cleaning. First, a diamond wire cutting machine is used to cut the crystal to the required size, with a cutting speed controlled at 0.5-1 mm per minute, and deionized water with a resistivity of more than 18.2 megaohm-cm is used as the cutting liquid. Then, diamond polishing paste with particle sizes of 9 microns, 6 microns, 3 microns and 1 micron is used to mechanically polish the seed crystal, with polishing times of 20 minutes, 15 minutes, 10 minutes and 5 minutes, respectively. The polished seed crystal is ultrasonically cleaned with absolute ethanol (purity ≥ 99.5%) for 15 minutes, then with deionized water for 10 minutes, and finally dried at 100°C for 2 hours.

[0049] The seed crystal quality detection uses an X-ray diffractometer (XRD) to detect the crystal orientation, with a deviation of less than 2°; a polarizing microscope is used to detect the twin crystal distribution and mark the twin crystal position and extension direction; an X-ray rocking curve (XRC) is used to measure the seed crystal quality, with a (400) face full width at half maximum (FWHM) of less than 100 arc seconds. These detection results will provide important basis for the subsequent horizontal temperature gradient design.

[0050] 3. Pre-growth preparation of the crystal: Before crystal growth, the growth system needs to be pretreated. First, the growth cavity is evacuated to 1 x 10 -4After the pressure is reduced to 200 kPa, high-purity argon is filled into the system to 101.3 kPa for 3 times to complete the gas replacement. During the system purification stage, a mixture of oxygen (purity ≥ 99.995%) and argon (oxygen volume fraction of 10-20%) is introduced at a flow rate of 50-100 standard cubic centimeters per minute (sccm) for 8-12 hours.

[0051] During the raw material melting stage, 200-300 grams of β-Ga2O3 powder is loaded into the crucible according to the crucible capacity. The temperature rising program is as follows: from room temperature to 1500°C at a rate of 3-5°C per minute, and maintained for 1 hour; then increased to 1820±10°C at a rate of 2-3°C per minute (the melting point of β-Ga2O3 is about 1820°C), and maintained for 2-4 hours to ensure complete melting. In order to make the melt composition uniform, the rotation speed of the crucible is set to 10-15 revolutions per minute in the molten state for 4-6 hours.

[0052] During the seed preheating and contacting melt stage, the seed is first slowly lowered to about 10 mm from the surface of the melt and maintained for 30-60 minutes to preheat the seed to 1500-1600°C. Then the seed is lowered to contact the melt surface at a rate of 0.5-1 mm per minute, and the observation of the melt wetting the bottom of the seed. The depth of the seed immersed in the melt is controlled to be 1-2 mm, and the system is kept in thermal equilibrium for 10-15 minutes.

[0053] 4. Neck growth and equal diameter growth: Neck growth is a key step in crystal growth. The initial pulling speed is set to 0.5-1 mm per minute, and when the liquid surface is observed to separate from the seed and form a liquid neck, the pulling speed is reduced to 0.3-0.5 mm per hour. The neck diameter is controlled to be 3-5 mm, and the length is 10-15 mm. The rotation speed of the seed is maintained at 5-10 revolutions per minute during this stage, and the rotation direction is clockwise, while the oxygen partial pressure is maintained at 0.1-0.2 atm (10-20 kPa).

[0054] After the neck growth is completed, the equal diameter growth stage is entered. The growth rate during this stage is maintained at 1-3 mm per hour, the rotation speed is 10-15 revolutions per minute, and the melt temperature is maintained at 1825-1835°C by adjusting the power of the main heater. The crystal diameter is observed in real time using a CCD camera, and the diameter is maintained at 15±1 mm by adjusting the pulling speed and temperature. After the equal diameter stage is grown to a length of 30-50 mm, the shoulder stage is prepared.

[0055] The core innovation of the present application is to introduce a horizontal temperature gradient during the crystal shoulder stage, which deflects the twin crystal growth environment to the edge of the crystal, thereby effectively suppressing the twin crystal defects. The process is described in detail below.

[0056] 1. Parameter setting for shoulder stage: When the length of the isometrically grown crystal reaches 30-50 mm, the shoulder stage begins. The purpose of this stage is to gradually expand the crystal diameter from 15 mm to 25-30 mm, with the expansion rate controlled at 0.3-0.5 mm per hour. To ensure the stability of the shoulder process, the pulling rate is reduced to 0.8-1.2 mm per hour, and the rotation speed is reduced to 5-8 revolutions per minute to reduce the influence of centrifugal force on the melt flow.

[0057] 2. Establishment of horizontal temperature gradient: When the crystal diameter expands to 18-20 mm, the horizontal temperature gradient control system is activated based on the observation of the twin crystal position and extension direction in the seed crystal in the early stage. The determination of the gradient direction is crucial, and the low-temperature side should be set in the opposite direction of the twin crystal extension direction to promote the deflection of the twin crystal to the low-temperature side.

[0058] There are mainly two methods to establish the horizontal temperature gradient:

[0059] The first method is to adjust the power of the auxiliary heater. Specifically, increase the power of the high-temperature side auxiliary heater by 10-30%, with a power increase rate of 3-5% per minute; at the same time, reduce the power of the low-temperature side auxiliary heater by 5-15%, with a power decrease rate of 2-3% per minute. In this way, the required horizontal temperature gradient can be established within 15-30 minutes.

[0060] The second method is to start the cooling device. In this way, the power of the high-temperature side auxiliary heater is kept unchanged, and the cooling device on the low-temperature side is started, with the cooling intensity starting from the minimum value and increasing to the set value at a rate of 5-10% per minute. This method usually takes 20-35 minutes to establish the required temperature gradient.

[0061] During the entire process, the temperature distribution in the area above the mold is monitored in real time by the thermocouple array and the infrared temperature measurement system to ensure that the horizontal temperature gradient is stable within the set range.

[0062] 3. Parameter optimization of horizontal temperature gradient: The size of the horizontal temperature gradient needs to be optimized according to the type and severity of the twin crystal. For slight twin crystals with an area ratio of less than 5%, a horizontal temperature gradient of 5-8°C per centimeter is recommended; for moderate twin crystals with an area ratio of 5-15%, a horizontal temperature gradient of 8-15°C per centimeter is recommended; for severe twin crystals with an area ratio of more than 15%, a horizontal temperature gradient of 15-20°C per centimeter is recommended.

[0063] The gradient maintenance time also needs to be determined according to the severity of the twin crystal: for slight twin crystals, the maintenance time is 20-40 minutes; for moderate twin crystals, the maintenance time is 40-80 minutes; for severe twin crystals, the maintenance time is 80-120 minutes.

[0064] It should be noted that the horizontal temperature gradient should not be too large, the maximum should not exceed 25 °C per centimeter, otherwise new defects may be introduced; at the same time, the gradient should not be too small, the minimum should not be less than 5 °C per centimeter, otherwise the twin deflection effect is not obvious. The longest gradient maintenance time should not exceed 120 minutes, and too long time may lead to the overall quality of the crystal.

[0065] 4. Twin deflection process monitoring: under the action of horizontal temperature gradient, the twin deflection situation needs to be observed in real time through CCD camera combined with polarized light system. When the observation shows that the twin growth direction deviates from the main crystal growth axis by more than 30° and moves to the low temperature side edge, it means that the deflection effect is significant. At this time, the twin position and deflection angle can be recorded every 10 minutes, and the deflection curve is drawn to control the gradient maintenance time more accurately.

[0066] 5. Restore normal growth conditions: when the twin is successfully induced to the edge of the crystal or completely eliminated, the horizontal temperature gradient needs to be gradually reduced to restore the normal growth conditions. The selection of the reduction rate depends on the twin deflection effect: for the case of obvious deflection effect, a faster rate of 3-5 °C per centimeter per hour can be used; for the case of general deflection effect, a medium rate of 2-3 °C per centimeter per hour can be used; for the case of weak deflection effect, a slower rate of 1-2 °C per centimeter per hour can be used.

[0067] If the horizontal temperature gradient is established by the heater power regulation method, then gradually restore the power of the high temperature side and low temperature side heater to the balanced state; if the cooling device regulation method is used, then gradually reduce the cooling intensity of the cooling device to zero.

[0068] When restoring the normal axial temperature distribution, the axial temperature gradient is adjusted to 30-50 °C per centimeter (near the solid-liquid interface), and the adjustment time is 30-60 minutes to ensure the stability of the temperature field. The axial temperature distribution is monitored by the vertical thermocouple array to ensure the restoration to normal.

[0069] When restoring the normal isometric growth parameters, the growth rate is restored to 2-4 mm / h, the rotation speed is restored to 10-20 rpm, the oxygen partial pressure is maintained at 0.1-0.2 atm (10-20 kPa), and the melt temperature is controlled at 1825-1835 °C. During this stage, close attention should be paid to the diameter fluctuation control (≤±0.5 mm), surface quality and interface shape to ensure the stability of the crystal quality.

[0070] After the crystal growth is completed, reasonable cooling and post-processing are needed to eliminate the thermal stress generated during the growth process and further improve the crystal quality.

[0071] 1. Crystal separation: When the crystal grows to a predetermined length (usually 80-120 mm), the separation process is started. First, the pulling rate is increased to 5-8 mm per hour, while the melt temperature is decreased by 2-5 °C. When a thin neck between the bottom of the crystal and the melt is observed, the pulling rate is further increased to 10-15 mm per hour to achieve a fast separation. After the separation is completed, the crystal is immediately lifted to the upper region of the hot zone (temperature about 1200-1400 °C) in preparation for the cooling process.

[0072] 2. Cooling procedure: The crystal cooling is divided into two stages: the first stage (1800-800 °C) is cooled at a rate of 2-5 °C per minute for about 4-8 hours; the second stage (800 °C to room temperature) is cooled at a rate of 1-2 °C per minute for about 10-14 hours. Specifically, in the range of 1800-1500 °C, the cooling rate is 2-3 °C per minute; in the range of 1500-1200 °C, the cooling rate is 3-4 °C per minute; in the range of 1200-800 °C, the cooling rate is 4-5 °C per minute; in the range of 800-500 °C, the cooling rate is 1.5-2 °C per minute; in the range of 500-300 °C, the cooling rate is 1-1.5 °C per minute; in the range of 300 °C to room temperature, the cooling rate is 0.5-1 °C per minute. During the cooling process, the oxygen partial pressure is maintained at 0.1-0.2 atm (10-20 kPa) throughout the process.

[0073] 3. Annealing treatment: In order to eliminate the thermal stress generated during growth, the crystal needs to be annealed. The annealing temperature is selected in the range of 950-1100 °C, preferably 1000-1050 °C; the annealing time is 6-24 hours, preferably 10-16 hours; the annealing atmosphere is air or a mixture containing 20-30% oxygen, with a pressure of 101.3±5 kPa. The heating rate is controlled at 1-3 °C per minute, and the cooling rate is 0.5-2 °C per minute. The annealing device uses a box-type electric furnace with MoSi2 or SiC heating elements, with a temperature uniformity of not more than ±5 °C.

[0074] 4. Surface treatment: The crystal surface treatment includes three steps of mechanical grinding, mechanical polishing and chemical mechanical polishing (CMP). In the mechanical grinding stage, the silicon carbide (SiC) sandpaper with the particle size of 60 mesh, 120 mesh, 240 mesh, 400 mesh, 600 mesh and 1000 mesh is used in sequence for grinding, and the grinding time of each particle size is 10-20 minutes. In the mechanical polishing stage, the diamond polishing paste with the particle size of 9 microns, 6 microns, 3 microns, 1 micron and 0.5 micron is used in sequence for polishing, and the polishing time of each particle size is 15-30 minutes. In the chemical mechanical polishing stage, the alkaline polishing solution (main component is colloidal silicon dioxide, concentration is 5-10 weight percent) with the pH value of 10-12 is used for polishing, the polishing time is 30-60 minutes, the polishing pressure is 20-40 kilopascals, and the rotation speed is 40-60 revolutions per minute. In the last surface cleaning step, the deionized water, acetone (purity ≥ 99.5%) and isopropyl alcohol (purity ≥ 99.5%) are used in sequence for ultrasonic cleaning, and each solvent is cleaned for 10-15 minutes.

[0075] The mechanism of the heat field gradient induced twinning inhibition method mainly includes the following three aspects:

[0076] 1. Over-saturation distribution regulation mechanism: In the process of growing β-Ga2O3 crystal by the guiding mode method, Ga2O3 molecules in the melt need to go through steps such as diffusion, adhesion and crystal growth. The driving force of this process is the over-saturation of the melt, which is defined as σ = (C-Ceq) / Ceq = (Tm-T) / Tm, wherein C is the actual concentration in the melt, Ceq is the equilibrium concentration, Tm is the equilibrium melting point, and T is the actual temperature.

[0077] When the horizontal temperature gradient is introduced, the over-saturation on the low-temperature side is higher than that on the high-temperature side, resulting in the growth rate V1 = k·σ1 on the low-temperature side being greater than the growth rate V2 = k·σ2 on the high-temperature side. n n Wherein k is the kinetic coefficient (about 0.5-2.0×10 -5 meters / second), and n is the index (about 1.5-2.5).

[0078] When the twinning grows in regions with different growth rates, it will naturally deflect to the region with a higher growth rate. Therefore, the horizontal temperature gradient regulates the local over-saturation distribution, so that the twinning naturally deflects to grow on the low-temperature side.

[0079] Experiments show that when the horizontal temperature gradient is 10℃ per centimeter, a growth rate difference of 15-25% can be caused, which is sufficient to cause the twinning to deflect obviously. The critical deflection angle θc = arcta n[(Vlow-Vhigh) / Vaverage], wherein Vlow is the growth rate on the low-temperature side, Vhigh is the growth rate on the high-temperature side, and Vaverage is the average growth rate.

[0080] ​2. Thermal stress induced mechanism: β-Ga2O3 has obvious anisotropic thermal expansion coefficients: α

[100] = (3.5-4.5) x 10-5 K-1, α

[010] = (2.8-3.8) x 10-5 K-1, α

[001] = (4.2-5.2) x 10-5 K-1. -6 K-1, α

[010] = (2.8-3.8) x 10-5 K-1. -6 K-1, α

[001] = (4.2-5.2) x 10-5 K-1. -6 K-1. When a horizontal temperature gradient is applied, a non-uniform thermal stress field is generated inside the crystal, which interacts with the twin boundary interface, generating a driving force F = σth·b·cosθ, where σth is the thermal stress, b is the Burgers vector, and θ is the angle between the stress direction and the normal of the twin plane.

[0081] The thermal stress can be calculated by the formula σth = E·α·ΔT / (1-ν), where E is the Young's modulus (about 200-250 GPa), α is the thermal expansion coefficient, and ν is the Poisson's ratio (about 0.25-0.30). When the horizontal temperature gradient is 10°C per centimeter, the generated thermal stress is about 2-5 MPa, which has exceeded the critical stress (about 1.5-3.0 MPa) for twin boundary migration, sufficient to drive the twin to move to the low stress area (usually the low temperature side).

[0082] When the thermal stress exceeds the critical value, the twin boundary interface can be promoted to migrate, which provides important theoretical support for the present application.

[0083] 3. Interface morphology regulation mechanism: the horizontal temperature gradient changes the shape of the solid-liquid interface from flat to curved. The relationship between the interface curvature radius R and the temperature gradient G is: R ≈ λ / G, where λ is the thermal conductivity of the solid-liquid interface front (about 10-15 W / m·K).

[0084] When the horizontal temperature gradient is 10°C per centimeter, the interface curvature changes about 2-4 mm. The relationship between the interface inclination angle θ and the horizontal temperature gradient ΔT is: θ ≈ arctan(ΔTh / ΔTv), where ΔTh is the horizontal temperature gradient and ΔTv is the vertical temperature gradient.

[0085] The change of interface morphology has a significant influence on the growth direction of the twin: the curved interface increases the angle between the growth direction of the twin and the main crystal; when the curvature reaches a critical value, the twin will grow along the tangent direction of the interface; eventually leading to the twin gradually deviating from the main crystal, even completely moving out of the effective growth area.

[0086] When the interface curvature radius is less than 10-15 mm, the twin deflection effect is most significant, which is highly consistent with the experimental observation results of the present application.

[0087] The technical solutions and effects of the present application will be described in detail below through specific examples.

[0088] Example 1: Mild horizontal temperature gradient induced <010> twin suppression

[0089] Source material and seed preparation:

[0090] A β-Ga2O3 powder with a purity of 99.999% (Sigma-Aldrich) was used as the source material. After calcination at 800°C for 5 hours, the powder was loaded into a high purity iridium crucible with a loading mass of 250 grams. A <010> oriented β-Ga2O3 single crystal with a size of 5 mm x 5 mm x 20 mm was chosen as the seed crystal. A small amount of twins were observed in the seed crystal by polarized light microscopy, with an area fraction of about 5%.

[0091] Growth process:

[0092] The crucible with the source material was heated to 1825°C to completely melt the Ga2O3, and the melt was kept homogeneous for 4 hours. The seed crystal was preheated to about 1550°C and contacted with the melt with an immersion depth of 1.5 mm, and the system was kept in thermal equilibrium for 15 minutes. The seed crystal was pulled at a rate of 0.8 mm / min to form a neck with a diameter of 4 mm and a length of 12 mm. Subsequently, isothermal growth was performed at a rate of 1.5 mm / hour until the diameter reached 15 mm and the length reached 40 mm.

[0093] Horizontal temperature gradient induction process:

[0094] When the crystal entered the shoulder stage (the diameter expanded from 15 mm to 25 mm), the horizontal temperature gradient control system was activated when the crystal diameter reached 18 mm. According to the position and extension direction of the twins in the seed crystal, the low temperature side was set in the opposite direction of the twin extension direction. By increasing the power of the high temperature side auxiliary heater by 15% and starting the low temperature side cooling device, a horizontal temperature gradient of 6°C / cm was formed in the upper region of the mold. The pulling rate was reduced to 1.2 mm / hour and the rotation speed was reduced to 7 rpm. The horizontal temperature gradient was maintained for 30 minutes, and the twin growth was monitored in real time by polarized light observation system. The twins began to deflect to the low temperature side, and when the deflection angle reached about 25°, the horizontal temperature gradient was gradually reduced at a rate of 4°C / cm per hour, and it took about 1.5 hours to restore the normal temperature distribution. Then the normal isothermal growth conditions were restored, the pulling rate was 3 mm / hour, and the rotation speed was 15 rpm, and the growth continued to a total length of 100 mm.

[0095] Cooling and post-processing:

[0096] After the crystal growth was completed, the temperature was decreased to 800°C at a rate of 3°C per minute, and then cooled to room temperature at a rate of 1.5°C per minute. The crystal was placed in an annealing furnace and annealed at 1000°C for 12 hours to eliminate thermal stress. After conventional surface treatment, the crystal quality was evaluated by methods such as polarized light microscopy, X-ray diffraction, and etch pit method.

[0097] Result analysis:

[0098] After the thermal field gradient induction process, the deflection angle of the 〈010〉 twin crystal was about 25°, the twin crystal area reduction rate reached about 65%, and the overall quality of the crystal was good without obvious new defects. The dislocation density was 2.3 x 10 4 cm-2, the carrier concentration was 6.5 x 10 16 cm-3, and the Hall mobility was 102 cm2 / V·s (room temperature). The results show that even a slight horizontal temperature gradient can have a significant effect on the growth direction of the twin crystal.

[0099] Example 2: Moderate horizontal temperature gradient induced 〈100〉 twin crystal suppression

[0100] Raw material and seed crystal preparation:

[0101] A β-Ga2O3 powder with a purity of 99.999% (Alfa Aesar Company) was used as the raw material, and the loading amount was 270 grams. A 〈100〉 oriented β-Ga2O3 single crystal with a size of 5.5 mm x 5.5 mm x 22 mm was selected as the seed crystal. Polarized light microscopy observation showed that the seed crystal contained a moderate amount of twin crystals, with an area ratio of about 10%.

[0102] Growth process:

[0103] The raw material melting temperature was controlled at 1830°C for 5 hours to fully homogenize the melt. The seed crystal was preheated to 1580°C and contacted with the melt, with an immersion depth of 1.8 mm. A neck was formed at a rate of 0.7 mm per minute, with a diameter of 3.5 mm and a length of 15 mm. Subsequently, isodiametric growth was performed at a rate of 1.8 mm per hour to a diameter of 15 mm and a length of 45 mm.

[0104] Horizontal temperature gradient induction process:

[0105] When the crystal diameter reached 20 mm, the horizontal temperature gradient control system was activated. The low temperature side was set in the opposite direction of the 〈100〉 twin extension. Using Method 1, the power of the high temperature side auxiliary heater was increased by 22% and the power of the low temperature side auxiliary heater was decreased by 10% to form a horizontal temperature gradient of 10 °C per cm in the area above the mold. The pulling rate was decreased to 1.5 mm per hour and the rotation rate was decreased to 6 rpm. The horizontal temperature gradient was maintained for 60 minutes, and the twins were obviously deflected to the low temperature side with a deflection angle of about 38°. Subsequently, the horizontal temperature gradient was gradually decreased at a rate of 3 °C per cm per hour, and it took about 3.3 hours to restore the normal temperature distribution. The normal isometric growth conditions were restored, the pulling rate was 3.5 mm per hour, the rotation rate was 18 rpm, and the growth continued to a total length of 110 mm.

[0106] Cooling and post-processing:

[0107] A segmented cooling strategy was used: 1800-1500 °C interval at 2.5 °C per minute, 1500-1200 °C interval at 3.5 °C per minute, 1200-800 °C interval at 4.5 °C per minute, 800-500 °C interval at 1.8 °C per minute, 500-300 °C interval at 1.2 °C per minute, and 300 °C to room temperature at 0.8 °C per minute. Annealing was performed at 1050 °C for 14 hours in an atmosphere containing 25% oxygen.

[0108] Result analysis:

[0109] The deflection angle of the 〈100〉 twin reached about 38°, the twin area reduction rate was about 85%, the overall quality of the crystal was good, and only a slight increase in thermal stress was observed in the local area. The dislocation density was 1.8 x 10 4 cm-2, the carrier concentration was 7.2 x 10 16 cm-3, and the Hall mobility was 95 cm2 / V·s (room temperature). The moderate horizontal temperature gradient showed a stronger twin suppression effect and had less impact on the overall quality of the crystal.

[0110] Example 3: 〈-201〉 twin suppression induced by a strong horizontal temperature gradient

[0111] Raw material and seed crystal preparation:

[0112] β-Ga2O3 powder with a purity of 99.999% was used as the raw material, and the loading amount was 300 grams. A 〈-201〉 oriented β-Ga2O3 single crystal with a size of 4.5 mm x 4.5 mm x 18 mm was selected as the seed crystal. Polarization microscope observation showed that there were many twins in the seed crystal, with an area ratio of about 18%.

[0113] Growth process:

[0114] The melt temperature was controlled at 1835 °C for 6 hours. The seed crystal was preheated to 1600 °C and contacted with the melt with a 2 mm immersion depth. The neck was formed at a rate of 0.6 mm / min with a 4 mm diameter and 14 mm length. Subsequently, the isothermal growth was performed at a rate of 2 mm / hour to a diameter of 15 mm and a length of 35 mm.

[0115] Horizontal temperature gradient induction process:

[0116] When the crystal diameter reached 19 mm, the horizontal temperature gradient control system was activated. The low temperature side was set in the opposite direction of the <201> twin extension. Using method two, the low temperature side gas cooling system was activated while keeping the high temperature side auxiliary heater power constant. The cooling gas flow was increased from 2 L / min to 8 L / min, forming a horizontal temperature gradient of 18 °C / cm in the area above the mold. The pulling rate was reduced to 1.3 mm / hour and the rotation rate was reduced to 5 rpm. The horizontal temperature gradient was maintained for 45 minutes, and the twin rapidly deflected to the low temperature side, with a deflection angle of about 45°. Subsequently, the horizontal temperature gradient was gradually reduced at a rate of 2 °C / cm per hour for about 9 hours to restore the normal temperature distribution. The normal isothermal growth conditions were restored, with a pulling rate of 4 mm / hour and a rotation rate of 20 rpm, and the growth continued to a total length of 120 mm.

[0117] Cooling and post-processing:

[0118] A fine segmented cooling strategy was used, with a total cooling time of about 20 hours. Annealing was performed at 1080 °C for 16 hours in an air atmosphere. Surface treatment was performed in three steps: mechanical grinding, mechanical polishing, and chemical mechanical polishing, with a polishing liquid pH of 11.5.

[0119] Result analysis:

[0120] The deflection angle of the <201> twin reached about 45°, and the twin area reduction rate was as high as 95%, with a significant effect. However, a small amount of new dislocations appeared on the high temperature side of the crystal, with a dislocation density of 2.8 x 10 4 cm-2, a carrier concentration of 8.1 x 10 16 cm-3, and a Hall mobility of 88 cm 2 / V·sec (room temperature). This indicates that a strong horizontal temperature gradient, while being the best for twin suppression, may introduce new defects and needs to be used with caution.

[0121] Example 4: Optimization scheme for simultaneous suppression of multiple types of twins

[0122] Raw material and seed crystal preparation:

[0123] The purity of β-Ga2O3 powder used as raw material is 99.999%, and the loading amount is 280 grams. The β-Ga2O3 single crystal containing both 〈010〉 and 〈100〉 twin orientations is selected as the seed crystal, with a size of 5 mm × 5 mm × 20 mm. The total area ratio of the two types of twins is about 12%.

[0124] Growth process:

[0125] The raw material melting, seed preheating, neck growth and initial isodiametric growth are carried out according to the standard procedure.

[0126] Horizontal temperature gradient induction process:

[0127] For the coexistence of two types of twins, a two-stage gradient induction strategy is adopted. In the first stage, the horizontal temperature gradient direction is set perpendicular to the extension direction of the 〈010〉 twin, with a gradient of 12°C per centimeter, and maintained for 50 minutes to make the 〈010〉 twin begin to deflect; in the second stage, the horizontal temperature gradient direction is adjusted to be perpendicular to the extension direction of the 〈100〉 twin, with a gradient of 10°C per centimeter, and maintained for 55 minutes to make the 〈100〉 twin begin to deflect. The pulling rate is kept at 1.4 mm per hour, and the rotation speed is 6 revolutions per minute. After completing the two-stage treatment, the horizontal temperature gradient is gradually reduced at a rate of 2.5°C per centimeter per hour to restore normal growth conditions.

[0128] Result analysis:

[0129] The two-stage gradient induction strategy has obvious inhibitory effect on both types of twins. The deflection angle of the 〈010〉 twin is about 32°, and the area reduction rate is about 75%; the deflection angle of the 〈100〉 twin is about 35°, and the area reduction rate is about 80%. The overall quality of the crystal is good, with a dislocation density of 2.1 × 10 4 cm-2, a carrier concentration of 7.5 × 10 16 cm-3, and a Hall mobility of 98 cm 2 / V·s (room temperature). This shows that for the coexistence of multiple types of twins, the two-stage gradient induction strategy can achieve good results.

[0130] Example 5: Parameter optimization example - effect of gradient duration

[0131] To study the effect of horizontal temperature gradient duration on twin inhibition, three different gradient durations are set respectively under the condition that other parameters remain unchanged:

[0132] Experimental conditions:

[0133] The raw material and seed crystal preparation are the same as in Example 2, and the horizontal temperature gradient is fixed at 10°C per centimeter, with the gradient direction perpendicular to the extension direction of the 〈100〉 twin.

[0134] Three groups of experiments:

[0135] Group A: Gradient duration of 30 minutes;

[0136] Group B: Gradient duration of 60 minutes;

[0137] Group C: Gradient duration of 90 minutes.

[0138] Result analysis:

[0139] Group A (30 minutes): Twin deflection angle of about 20°, area reduction rate of about 45%;

[0140] Group B (60 minutes): Twin deflection angle of about 38°, area reduction rate of about 85%;

[0141] Group C (90 minutes): Twin deflection angle of about 42°, area reduction rate of about 90%, but slight thermal stress increase was observed in the crystal.

[0142] The results show that the gradient duration has a significant impact on the twin suppression effect, but the suppression effect and potential negative impacts need to be balanced. For 〈100〉 twins, a gradient duration of 60 minutes can achieve good results, further extension of time has diminishing returns, and may introduce new defects.

[0143] To verify the effectiveness and superiority of the present application, the following comparative examples are designed:

[0144] Comparative Example 1: Conventional die method growth without horizontal temperature gradient

[0145] Experimental conditions:

[0146] The raw materials and seed crystal preparation are the same as in Example 2, but no horizontal temperature gradient is introduced during the entire growth process, only a conventional axisymmetric heat field is used.

[0147] Growth process:

[0148] The raw material melting, seed preheating, neck growth, constant diameter growth and shoulder process are carried out according to the standard procedure, the pulling rate is 1.8 mm / h, and the rotation speed is 12 rpm.

[0149] Result analysis:

[0150] Under the condition of no horizontal temperature gradient, 〈100〉 twins extend from the seed to the entire crystal, and no obvious deflection phenomenon is observed. The twin area ratio in the final crystal is about 12%, slightly higher than the initial value in the seed, the dislocation density is 3.2 × 10 4 cm-2, and the carrier concentration is 6.8 × 101 6cm-2, and the Hall mobility is 85 cmV-sec (room temperature). The results show that the conventional edge-die method cannot effectively suppress the twin extension. 2 cm-2, and the Hall mobility is 85 cmV-sec (room temperature). The results show that the conventional edge-die method cannot effectively suppress the twin extension.

[0151] Comparative Example 2: Edge-die method growth with too large horizontal temperature gradient

[0152] Experimental conditions:

[0153] The raw materials and seed crystal were prepared as in Example 3, but the horizontal temperature gradient was set to 25 °C per cm, which is much higher than the recommended value.

[0154] Growth process:

[0155] A strong horizontal temperature gradient of 25 °C per cm was introduced during the shoulder stage, with the gradient direction perpendicular to the 〈-201〉 twin extension direction, and the maintenance time was 40 minutes.

[0156] Result analysis:

[0157] Although the deflection angle of the 〈-201〉 twin reached about 50°, the area reduction rate was as high as 98%, but a large number of new defects appeared in the crystal, especially obvious dislocation networks were observed on the high temperature side, and the dislocation density increased to 5.7 x 10 4 cm-2. In addition, obvious deformation and cracks appeared on the crystal surface, which seriously affected the overall quality of the crystal. The results show that although a too large horizontal temperature gradient can improve the twin suppression effect, it will introduce more defects, which is not worth the cost.

[0158] Comparative Example 3: Edge-die method growth with only reduced growth rate

[0159] Experimental conditions:

[0160] The raw materials and seed crystal were prepared as in Example 1, without introducing a horizontal temperature gradient, but the growth rate was reduced to 0.8 mm per hour during the shoulder stage, which is much lower than the conventional value.

[0161] Growth process:

[0162] The low growth rate of 0.8 mm per hour was maintained during the entire shoulder stage and the subsequent constant diameter growth stage, and the rotation speed was maintained at 15 revolutions per minute.

[0163] Result analysis:

[0164] Under the condition of low growth rate, the extension speed of the 〈010〉 twin was reduced, but no obvious deflection phenomenon was observed. The twin area ratio in the final crystal was about 4.8%, which was slightly lower than the initial value, the dislocation density was 2.5 x 10 4 cm-2, and the carrier concentration was 6.7 x 10 16 cm-3, and the Hall mobility was 95 cmV-sec (room temperature). 2V-sec (room temperature). Although the low growth rate has some effect on inhibiting new twin formation, it has limited effect on existing twins and significantly reduces production efficiency.

[0165] Comparative Example 4: Simple rotation direction change VPD growth

[0166] Experimental conditions:

[0167] The raw materials and seed crystal preparation were the same as in Example 2, but no horizontal temperature gradient was introduced, and the rotation direction was changed from clockwise to counterclockwise during the shoulder stage, while the rotation speed remained unchanged at 12 revolutions per minute.

[0168] Growth process:

[0169] The rotation direction was changed at the beginning of the shoulder stage, and counterclockwise rotation was maintained for 60 minutes, followed by a return to clockwise rotation. The remaining parameters were the same as the standard process.

[0170] Result analysis:

[0171] The change in rotation direction caused the melt flow pattern to change, which had some effect on twin growth, but the effect was limited. The deflection angle of the 〈100〉 twin was only about 10°, and the area reduction rate was about 25%, which was much lower than the effect of the method of the present application. The dislocation density was 2.9 x 10 4 cm-2, the carrier concentration was 7.0 x 10 16 cm-3, and the Hall mobility was 90 cm 2 / V-sec (room temperature). The results show that simply changing the rotation direction is not enough to effectively inhibit twin extension.

[0172] In order to comprehensively evaluate the effectiveness of the method of the present application, a systematic comparative analysis was conducted on the above examples and comparative examples. The main evaluation indicators include: twin deflection angle, twin area reduction rate, dislocation density, carrier concentration, Hall mobility, and production efficiency.

[0173] Table 1. Performance comparison of examples and comparative examples

[0174]

[0175] From the data in Table 1, the following conclusions can be drawn:

[0176] 1. The thermal field gradient induction method proposed in the present application has a significant inhibitory effect on all types of twins. The twin deflection angles of Examples 1-4 are 25-45°, and the area reduction rates are 65-95%, which are much higher than those of the comparative examples.

[0177] 2. Twin suppression effect is positively correlated with the size of horizontal temperature gradient, but too large gradient (such as 25℃ / cm in Comparative Example 2) can further improve the suppression effect, but will introduce more defects, and thus reduce the overall quality of the crystal.

[0178] 3. Compared with the method of only reducing the growth rate (Comparative Example 3) or changing the rotation direction (Comparative Example 4), the method of the present application achieves significant twin suppression effect while maintaining high production efficiency (80-90%), and has obvious technical and economic advantages.

[0179] 4. Different types of twins have different responses to horizontal temperature gradient: 〈-201〉 twin is most sensitive to temperature gradient, 〈100〉 twin is less sensitive, and 〈010〉 twin is relatively less sensitive. Therefore, in practical application, the gradient parameter needs to be adjusted according to the type of twin.

[0180] 5. The method of the present application not only effectively suppresses twins, but also reduces dislocation density to a certain extent, improves carrier mobility, and improves the overall quality of the crystal.

[0181] In summary, the method of gallium oxide crystal twin suppression growth based on thermal field gradient induction proposed in the present application realizes effective regulation of the growth direction of twins by introducing a specific horizontal temperature gradient field during the crystal shoulder stage, deflects the growth direction of twins to the edge of the crystal, and thus suppresses the extension of twins in the main crystal. The method has the advantages of simple process, strong applicability, and no influence on production efficiency, and provides a new effective way to improve the quality of β-Ga2O3 crystal, and has important theoretical significance and application value.

Claims

1. A method for suppressing twinning growth of gallium oxide crystals based on thermal field gradient-induced twinning, characterized in that, Includes the following steps: Gallium oxide crystals are prepared using a guided mold growth device. After the crystal enters the shoulder formation stage, a horizontal temperature gradient field is established in the area above the mold by adjusting the power of the heater zones or activating the local cooling device. Based on the position and extension direction of the twin in the seed crystal, the low-temperature side of the horizontal temperature gradient field is set in the opposite direction of the twin extension direction. Maintain the horizontal temperature gradient field for a period of time until the twin growth direction is observed to deflect to the low-temperature edge region of the crystal. Once the twins are induced to the crystal edge or eliminated, the horizontal temperature gradient field is gradually reduced to restore normal constant diameter growth conditions. The magnitude of the horizontal temperature gradient field is 5-20℃ per centimeter, with the specific gradient value selected based on the twin type and severity. For slight twins with an area ratio of less than 5%, the horizontal temperature gradient is 5-8℃ per centimeter; For medium twins with an area ratio of 5-15%, the horizontal temperature gradient is 8-15℃ per centimeter; For severe twins with an area ratio greater than 15%, the horizontal temperature gradient is 15-20℃ per centimeter; The rate at which the horizontal temperature gradient field is gradually decreased is 1-5℃ per centimeter per hour, selected based on the twin deflection effect: For cases where the deflection effect is significant, a faster rate of 3-5°C per centimeter per hour is used. For cases where the deflection effect is mediocre, a moderate rate of 2-3°C per centimeter per hour is adopted; For cases where the deflection effect is weak, a slower rate of 1-2℃ per centimeter per hour is used.

2. The method according to claim 1, characterized in that, The guided mold growth equipment includes: A multi-zone independently controlled heating system, wherein independently controlled auxiliary heaters are installed on both sides of the area above the mold, the auxiliary heaters having a power range of 0-2000W and a temperature control accuracy of ±1℃; An adjustable cooling device is installed on one side of the area above the mold. The cooling device uses either water cooling or air cooling. The flow rate control range for the water cooling system is 0.5-5 liters per minute, and for the air cooling system, it is 1-10 liters per minute. The temperature monitoring system includes multiple thermocouples and infrared thermometers evenly distributed along the horizontal direction to monitor the temperature distribution near the growth interface in real time.

3. The method according to claim 1, characterized in that, The duration for maintaining the horizontal temperature gradient field is determined based on the severity of twinning. For slight twinning with an area ratio of less than 5%, the maintenance time is 20-40 minutes; For medium twins with an area ratio of 5-15%, the maintenance time is 40-80 minutes; For severe twinning with an area ratio greater than 15%, the maintenance time is 80-120 minutes.

4. The method according to claim 1, characterized in that, Establish a horizontal temperature gradient field using any of the following methods: Increase the power of the high-temperature auxiliary heater by 10-30%, while reducing the power of the low-temperature auxiliary heater by 5-15%; or Keep the power of the high-temperature auxiliary heater constant, start the low-temperature cooling device, and gradually increase the cooling intensity from the minimum value to the set value.

5. The method according to claim 1, characterized in that, The gallium oxide crystal uses high-purity β-Ga2O3 powder as raw material. The β-Ga2O3 powder has a purity of not less than 99.999%, an average particle size of 1-5 micrometers, and the main impurity contents are: Si less than 2 ppm, Al less than 1 ppm, Fe less than 1 ppm, Ca less than 1 ppm, and the total amount of other metal impurities less than 5 ppm. The method also includes a raw material pretreatment step: calcining the β-Ga2O3 powder at 800±20℃ for 4-6 hours to remove surface-adsorbed moisture and organic matter.

6. The method according to claim 1, characterized in that, The method also includes crystal cooling and post-processing steps: After crystal growth is complete, the temperature is reduced to 800°C at a rate of 2-5°C per minute; Cooling from 800°C to room temperature at a rate of 1-2°C per minute; The crystal is placed in an annealing furnace and annealed at 950-1100℃ for 6-24 hours to eliminate the thermal stress generated during the growth process.

7. The method according to claim 1, characterized in that: Furthermore, the gradient parameters need to be adjusted according to the twin type: When used to suppress <010> orientation twins, the horizontal temperature gradient is 10-15℃ per centimeter, the gradient direction is perpendicular to the <010> direction, and the gradient maintenance time is 40-60 minutes. When used to suppress <100> orientation twins, the horizontal temperature gradient is 8-12℃ per centimeter, the gradient direction is perpendicular to the <100> direction, and the gradient maintenance time is 50-70 minutes. When used to suppress <-201> orientation twins, the horizontal temperature gradient is 12-18℃ per centimeter, the gradient direction is perpendicular to the <-201> direction, and the gradient maintenance time is 30-50 minutes.

8. The method according to claim 1, characterized in that, During the horizontal temperature gradient induction stage, the crystal growth rate is reduced to 65-85% of the original growth rate, and the crystal rotation speed is reduced to 4-9 revolutions per minute to reduce the influence of centrifugal force on melt flow. After the horizontal temperature gradient field is eliminated, the crystal growth rate is restored to 2-4 mm per hour, and the crystal rotation speed is restored to 10-20 revolutions per minute, and constant diameter growth continues to the predetermined length.

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