Apparatus for manufacturing oxide single crystals, method for manufacturing gallium oxide single crystals using the apparatus, and gallium oxide single crystal manufactured thereby

Abstract

To provide an apparatus for manufacturing oxide single crystals, a method for manufacturing gallium oxide single crystals using the apparatus, and a gallium oxide single crystal manufactured thereby. [Solution] By applying a method that uses the oxide pellet itself, which is to be made into a single crystal, as the crucible without using a separate crucible, the problem of impurities entering due to the crucible is minimized. Furthermore, by applying a method that mixes hydrocarbon fuel gas and oxygen gas and generates heat using a flame, the growth atmosphere for the oxide single crystal can be maintained in a high-oxygen atmosphere, enabling the production of high-quality oxide single crystals with few defects.

Description

Technical Field

[0001] The present invention relates to an apparatus for manufacturing an oxide single crystal, a method for manufacturing a gallium oxide single crystal, and a gallium oxide single crystal.

Background Art

[0002] Since single crystals of gallium oxide (particularly, β-Ga2O3 single crystals; hereinafter described as β-Ga2O3 single crystals) were reported on single crystal growth by the FZ method and the CZ method by Y. Tom et al. in 2000, research and development on crystal growth have been initially carried out for use as a substrate for fabricating GaN thin films for LEDs.

[0003] In recent years, the realization of FETs for power devices using β-Ga2O3 single crystals by M. Higashiwaki et al. has been reported, and strong interest has been shown in the production of high-quality, large-sized, and low-cost β-Ga2O3 single crystals for realizing a wide-bandgap semiconductor substrate for power devices.

[0004] β-Ga2O3 single crystals considering device applications can be grown by methods such as the floating zone (FZ) method, the Czochralski (CZ) method, the edge-defined film-fed growth (EFG) method, the vertical Bridgman (VB) method, and the HB method. Among these crystal growth methods, the FZ method does not require a container for maintaining the raw material melt from the principle of crystal growth, so a means for heating to a high temperature (melting point) for melting the raw material can be relatively easily realized, and many studies have been conducted so far. However, the FZ method has technical limitations in increasing the size of high-quality crystals with suppressed structural defects such as dislocations from the viewpoints of its growth principle and temperature environment. Although many studies have been conducted in the past 10 years, it can be said that the current situation is not sufficient to fully meet device applications.

[0005] On the other hand, the CZ method and EFG method have been widely used for single crystal growth as methods for producing large, high-quality single crystals that can be industrially applied. It can be inferred that research and development of the CZ method and EFG method for β-Ga2O3 single crystal growth has been actively conducted since 2000. However, the provision of high-quality, large, and low-cost β-Ga2O3 single crystals that can meet the needs of future power device applications has not yet been achieved.

[0006] Currently, the VB method has recently attracted attention as a way to solve the aforementioned problems, and methods for producing high-quality, large, and low-cost β-Ga2O3 single crystals using this method are being actively researched.

[0007] When growing crystals using the CZ method and EFG method, a crucible is essential to maintain the molten raw material. Since the melting point of β-Ga2O3 is high at approximately 1800°C, high-melting-point metals such as Ir, Mo, and W are considered suitable crucible materials from the perspective of melting point.

[0008] However, when β-Ga2O3 is melted in a crucible at temperatures exceeding 1800°C, Mo and W, acting as the crucible material, have a strong reducing power. They decompose by removing oxygen from β-Ga2O3 and oxidize themselves, making them completely unsuitable as crucible materials. As a result, it is recognized that Ir is the only high-melting-point metal that can be used for CZ crucibles, EFG crucibles, and die materials.

[0009] However, through various experiments and theoretical considerations, we have come to realize that there are actually significant problems with Ir, which is the crucible material currently used by the CZ method and the crucible material (including die material) used by the EFG method.

[0010] In other words, it was found that under oxygen partial pressures exceeding several percent in blast furnaces exceeding 1800°C, the oxidation reaction of Ir proceeds, making it difficult to use as a stable crucible material. On the other hand, it was also found that at high temperatures exceeding 1800°C, β-Ga2O3 undergoes a decomposition reaction that loses oxygen under oxygen partial pressures of 10% or less, making it difficult to exist as a stable β-Ga2O3 molten material.

[0011] As mentioned above, it is clear that the oxygen partial pressure conditions required for the molten raw material β-Ga2O3 in the blast furnace and the oxygen partial pressure conditions required for the Ir crucible that maintains it are contradictory. In other words, it is recognized that Ir is also not a suitable crucible material for containing the molten β-Ga2O3 raw material.

[0012] Incidentally, while β-Ga2O3 crystal growth using conventional Ir crucibles via the CZ and EFG methods is possible under narrow oxygen partial pressure ranges of a few percent within the furnace, experimental studies have revealed problems such as the generation of high-density oxygen vacancies, which frequently occur in oxide crystals grown under oxygen-deficient conditions, evaporation loss due to Ir oxidation, and degradation in the grown β-Ga2O3 crystals. Furthermore, these oxygen vacancies act like n-type impurities, generating high concentrations of donors, making the realization of p-type β-Ga2O3 extremely difficult, thus posing many challenges to the realization of semiconductor devices.

[0013] To address this, a method was proposed to grow β-Ga2O3 crystals in an atmospheric environment using the VB method with a Pt-Rh alloy crucible. Since the β-Ga2O3 crystals are grown in air, the decomposition of β-Ga2O3 is suppressed, and the problem of the crucible being oxidized at high temperatures using a Pt-Rh crucible is resolved. However, experimental studies have shown that when molten β-Ga2O3 is exposed to high temperatures in a Pt-Rh crucible for extended periods, a large amount of Rh is detected as an impurity in the grown β-Ga2O3 crystals.

[0014] Although the CZ, EFG, and VB methods are all advantageous for scaling up, large amounts of unintended Si impurities are still detected. It has become clear that when devices are fabricated using β-Ga2O3 crystals containing large amounts of Si impurities, they do not provide sufficient insulation and are unsuitable for use as substrates for device fabrication. Furthermore, it has been revealed that in β-Ga2O3 crystals grown by the CZ and EFG methods, large amounts of Ga impurities generated by the decomposition of β-Ga2O3 under a low-oxygen atmosphere are detected within the grown β-Ga2O3 crystals. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Japanese Patent Application Publication No. 2013-237591 [Non-patent literature]

[0016] [Non-Patent Document 1] N. Ueda, H. Hosono, R. Waseda, H. Kawazoe, Appl. Phys. Lett. 70 (1997) 3561. [Overview of the project] [Problems that the invention aims to solve]

[0017] The present invention was made to solve the aforementioned problems, and the object of the present invention is to provide a single crystal manufacturing apparatus that prevents the inclusion of unintended impurities and produces high-quality oxide crystals of ultra-wide bandgap semiconductor gallium oxide, which is essential for the manufacture of extreme environment materials and devices and power devices, without a crucible to house the molten gallium oxide using the Bernoulli method (flame melting method), and a method for manufacturing gallium oxide single crystals using the same.

[0018] The technical problems that this invention aims to solve are not limited to those mentioned above, and other technical problems not mentioned can be clearly understood by a person with ordinary skill in the art to which this invention belongs from the following. [Means for solving the problem]

[0019] To achieve the above object, the present invention provides an apparatus for manufacturing an oxide single crystal, comprising a heat source unit 100 for melting an oxide pellet, a growth unit 200 made of a refractory material for loading the oxide pellet and serving as a space for growing an oxide single crystal, a driving unit 300 for moving the entire growth unit to grow the oxide single crystal, and a measuring unit 400 for measuring the temperature of the growth unit throughout the oxide single crystal growth process.

[0020] The heat source unit 100 includes a fuel gas supply unit 101 composed of a hydrocarbon, an oxygen gas supply unit 102, a fuel pressure regulator 103 for adjusting the pressure of the fuel injected into the fuel pipe, an oxygen pressure regulator 104 for adjusting the pressure of oxygen, a pre-mixing region unit 107 which is a space where the fuel gas and the oxygen gas are mixed, a fuel pipe 109 through which the fuel gas flows into the pre-mixing region unit 107, an oxygen pipe 110 through which the oxygen gas flows into the pre-mixing region unit 107, a fuel flow regulator 105 for adjusting the amount of the fuel gas flowing into the pre-mixing region unit 107, an oxygen flow regulator 106 for adjusting the amount of the oxygen gas, a nozzle 108 through which the mixed gas of the fuel gas and the oxygen gas mixed in the pre-mixing region unit 107 is discharged to the outside, and a height regulator 111 for adjusting the distance between the growth unit 200 and the nozzle 108.

[0021] The growth unit 200 includes a heat-resistant refractory and heat-insulating material 201 for forming an oxygen atmosphere independent of the heat generated from the heat source unit 100 and the ambient air.

[0022] The driving unit 300 includes a support base 304 for supporting the growth unit 200, a conveyor belt 301 for linearly moving the entire support base 304, a motor 302 for driving the conveyor belt 301, a microcontroller 303 for controlling the driving of the motor 302, and a computer C for controlling the microcontroller 303.

[0023] The measurement unit 400 is characterized by including an infrared camera 401 that measures the temperature of the growth unit 200 and a computer C that receives temperature data measured by the infrared camera.

[0024] The present invention also provides a method for manufacturing a gallium oxide single crystal, characterized by including a sample preparation stage S1 of processing gallium oxide powder to produce gallium oxide pellets, a growth preparation stage S2 of loading the gallium oxide powder pellets into an apparatus for manufacturing an oxide single crystal to form a growth atmosphere and preheating, and a single crystal growth stage S3 of driving a motor to grow a single crystal to produce a gallium oxide single crystal.

[0025] The sample preparation stage S1 is characterized by including a calcination stage S110 of removing organic impurities and moisture from the oxide powder and converting the oxide powder into beta-phase oxide powder, a stage S120 of mixing the calcined oxide powder, a cold pressing stage S130 of making the mixed oxide powder into compressed powder, and a sintering stage S140 of heat-treating the cold-pressed oxide powder to produce pellets.

[0026] The growth preparation stage S2 is characterized by including a stage S210 of loading the oxide pellets produced in the sample preparation stage S1 into an apparatus for manufacturing an oxide single crystal, a stage S220 of adjusting the pressures of fuel gas and oxygen gas for initial flame ignition, a stage S230 of adjusting the flow rates of the fuel gas and oxygen gas, an ignition stage S240 of generating a flame, a stage S250 of preheating the growth unit and the oxide pellets after raising the temperature until just before the melting point of the oxide pellets, a stage S260 of adjusting the ratio of the fuel gas to the oxygen gas so that the melting region of the oxide pellets becomes an oxygen atmosphere, and a melting stage S270 of raising the temperature above the melting point of the oxide pellets to heat the sample.

[0027] The oxide single crystal growth step S3 is characterized by including: a step S310 in which a linear motor is driven to start the growth of an oxide single crystal when an oxide melt S203 is generated at or above the melting point of the growth preparation step S2; a temperature maintenance step S320 in which the flow rate and pressure of the fuel gas and oxygen gas are adjusted to maintain the temperature of the growth section; an oxygen atmosphere maintenance step S330 in which the flow rate and pressure are adjusted to maintain the oxygen atmosphere of the growth section; a growth step S340 in which the oxide single crystal is grown; a cooling step S350 in which the grown oxide single crystal is cooled; and a single crystal extraction step 360 in which the grown oxide single crystal is extracted from the top of the oxide pellet.

[0028] Furthermore, the present invention provides a gallium oxide single crystal characterized by being manufactured by the above-described manufacturing method. [Effects of the Invention]

[0029] According to the present invention, by applying a method that uses the oxide pellet itself, which is to be made into a single crystal, as the crucible without using a separate crucible, the problem of impurities entering through the crucible can be minimized.

[0030] Furthermore, by applying a method that involves mixing hydrocarbon fuel gas and oxygen gas and generating heat using a flame, it becomes possible to maintain a high-oxygen atmosphere for the growth of oxide single crystals by adjusting the partial pressure of oxygen gas, thereby enabling the production of high-quality oxide single crystals with few defects.

[0031] Furthermore, the single crystals produced by the manufacturing apparatus of the present invention are expected to be of high quality by preventing the inclusion of unintended impurities during growth, and can therefore be used as ultra-wide bandgap semiconductor materials essential for extreme environment materials and devices, as well as for the manufacture of power devices.

[0032] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the claims. [Brief explanation of the drawing]

[0033] [Figure 1] This figure shows an apparatus for manufacturing oxide single crystals according to one embodiment of the present invention. [Figure 2] This figure shows the heat source section 100 of an oxide single crystal manufacturing apparatus according to one embodiment of the present invention. [Figure 3] This figure shows the growth section 200 of an oxide single crystal manufacturing apparatus according to one embodiment of the present invention. [Figure 4] This figure shows the drive unit 300 of an oxide single crystal manufacturing apparatus according to one embodiment of the present invention. [Figure 5] This figure shows the measurement section 400 of an oxide single crystal manufacturing apparatus according to one embodiment of the present invention. [Figure 6] This is a process block diagram illustrating a method for manufacturing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 7] This is a step block diagram illustrating steps S1 to S3 of a method for producing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 8] This figure shows the details of step S1 of the method for producing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 9] This figure shows a temperature graph of the electric furnace during the calcination step S110 of a method for producing gallium oxide single crystals according to one embodiment of the present invention. [Figure 10] This figure shows a photograph of an oxide pellet produced by the cold pressing step S130 of the method for producing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 11] This figure shows a temperature graph of the electric furnace during the sintering step S140 of a method for producing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 12] This figure shows the algorithm for growing a single crystal in the oxide single crystal growth stage S3 of the method for manufacturing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 13] This figure shows a temperature graph at the oxide single crystal growth stage S3 of a method for producing a gallium oxide single crystal according to one embodiment of the present invention. [Figure 14] This figure shows a micrograph of a gallium oxide single crystal sample grown once using a method for producing gallium oxide single crystals according to one embodiment of the present invention. [Figure 15] This figure shows the results of X-ray and neutron diffraction analysis of a gallium oxide single crystal produced by one embodiment of the present invention. (a) shows the X-ray Laue pattern of the (0K0) plane. (b) includes the measurement results of the rocking curve, where the left curve in the region shows the X-ray diffraction data, and the center and right curves show the neutron diffraction data. (c) shows the X-ray 2θ / θ scan data along the (H00) direction. [Figure 16] This figure shows TEM and AFM microscope images of a gallium oxide single crystal produced by one embodiment of the present invention. (a) shows a transmission electron microscope (TEM) image of the (0b0) plane of the gallium oxide single crystal and the electron diffraction pattern along the (0K0) plane. (b) is a magnified TEM image (left) of the region shown in (a), where the unit cell of the gallium oxide single crystal is displayed. A schematic diagram (right) of the unit cell is also shown. (c) shows an atomic force microscope (AFM) image of the grown, undoped gallium oxide single crystal. [Figure 17] This figure shows the measurement results of a gallium oxide single crystal produced by one embodiment of the present invention using ultraviolet-visible-near-infrared spectroscopy. [Figure 18] This figure shows the measurement results obtained by secondary ion mass spectrometry of a gallium oxide single crystal manufactured according to one embodiment of the present invention. [Figure 19] This is a conceptual diagram of a gallium oxide crystal manufacturing system and apparatus and a method for manufacturing gallium oxide crystals according to one embodiment of the present invention. [Modes for carrying out the invention]

[0034] The terminology used in this invention has been selected as widely used and general terms as possible, taking into consideration the function of the invention. However, this may change depending on the intentions of those skilled in the art, precedents, the emergence of new technologies, etc. In certain cases, the applicant may have arbitrarily selected terms, in which case their meaning will be described in detail in the description of the invention. Therefore, the terminology used in this invention is not merely a set of names, but is defined based on the meaning of the term and the overall content of the invention.

[0035] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries shall be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and not as ideal or overly formal unless explicitly defined herein.

[0036] Throughout the specification, if a part is described as "including" a certain component, this does not exclude other components, unless otherwise stated, and means that other components may be included.

[0037] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings, so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be embodied in various different forms and is not limited to the embodiments described herein.

[0038] The present invention will be described in detail below with reference to the accompanying drawings.

[0039] The present invention provides an oxide single crystal manufacturing apparatus T, characterized by comprising: a heat source unit 100 for melting oxide pellets; a growth unit 200 made of refractory material which is a space for stacking the oxide pellets and growing oxide single crystals; a drive unit 300 for moving the entire growth unit in order to grow the oxide single crystals; and a measuring unit 400 for measuring the temperature of the growth unit throughout the entire growth process.

[0040] As shown in Figure 2, the heat source unit 100 is characterized by including a fuel gas supply unit 101, an oxygen gas supply unit 102, a pressure regulator 103 for adjusting the pressure of the fuel injected into the fuel pipe, a pressure regulator 104 for adjusting the pressure of oxygen, a pre-mixing region 107 which is a space in which the fuel gas and oxygen gas are mixed, a fuel pipe 109 into which the fuel gas flows into the pre-mixing region 107, an oxygen pipe 110 into which the oxygen gas flows, a fuel flow rate regulator 105 for adjusting the amount of fuel gas flowing into the pre-mixing region 107, an oxygen flow rate regulator 106 for adjusting the amount of oxygen gas, a nozzle 108 into which the mixed fuel gas and oxygen gas mixture in the pre-mixing region 107 is discharged to the outside, and a height regulator 111 for adjusting the distance between the growth unit 200 and the nozzle 108.

[0041] The fuel gas may consist mainly of hydrocarbons and may include gases such as hydrogen, propane, butane, and acetylene.

[0042] The fuel pressure regulator 103, oxygen pressure regulator 104, fuel flow regulator 105, and oxygen flow regulator 106 may be analog or digital devices, and more preferably digital devices with communication capabilities, but are not limited thereto.

[0043] The growth section 200, as shown in Figure 3, is characterized by comprising: a heat-resistant fireproof and heat-insulating material 201 for forming an oxygen atmosphere independent of the surrounding air and the heat generated from the heat source section 100; oxide pellets 202; a flame 204 for forming an oxygen atmosphere and the heat generated from the heat source section 100; an oxide melt 203 formed by the melting of the oxide pellets 202 heated by the flame; and an oxide single crystal 205 formed by the slow cooling and crystallization of the oxide melt 203.

[0044] According to one embodiment of the present invention, the oxide sample is not prepared in powder form because it is subjected to strong gas pressure by the flame, but is prepared in pellet form by cold pressing and sintering processes to prevent loss of raw materials, and the molten material can be stored without a crucible.

[0045] The aforementioned fire-resistant and heat-insulating material 201 can be selected from a suitable material depending on the melting point of the oxide to be melted, and may preferably be made of zirconia, but is not limited thereto.

[0046] As shown in Figure 4, the drive unit 300 is characterized by including a support base 304 that supports the growth unit 200, a conveyor belt 301 that moves the entire support base 304 linearly, a motor 302 for driving the conveyor belt 301, a microcontroller 303 for controlling the driving of the motor 302, and a computer C for controlling the microcontroller.

[0047] Both the fire-resistant and heat-insulating material 201 and the oxide pellets are placed on a conveyor belt, and the material is configured such that when the oxide pellets are heated by a flame and the internal temperature of the fire-resistant and heat-insulating material 201 reaches equilibrium, and melting occurs in the oxide pellets, the entire fire-resistant and heat-insulating material 201 is moved horizontally by the conveyor belt.

[0048] The support base 304 is a part that is exposed to high temperatures during the oxide single crystal growth process, and a suitable metallic material with a sufficiently high melting point can be selected so as not to damage the support base 304. Preferably, it may be one or more selected from the group consisting of aluminum and stainless steel, but is not limited thereto.

[0049] The conveyor belt 301 is connected to a motor 302, the motor 302 is connected to a microcontroller 303, and the movement of the conveyor belt 301 is controlled by the microcontroller 303 and driven by the motor 302.

[0050] The microcontroller 303 is connected to the computer C, and command signals are transmitted by a program installed on the computer C.

[0051] The measurement unit 400 is characterized by including an infrared camera 401 for measuring the temperature of the growth unit 200, as shown in Figure 5, and a computer C for receiving temperature data measured from the infrared camera.

[0052] The infrared camera 401 measures the temperature of the growth section 200 and transmits the temperature data of the growth section 200 to a computer in real time, which is then output as video by a program that allows viewing of the data in real time.

[0053] Furthermore, the system is controlled through an algorithm that measures the temperature of the infrared camera 401 and, when it falls below a temperature set in the program, adjusts the fuel flow regulator 105 to raise the temperature, and when the temperature rises above a temperature set in the program, adjusts the fuel flow regulator 105 to lower the temperature, thereby maintaining the set temperature.

[0054] Furthermore, the present invention provides a method for producing a gallium oxide single crystal, characterized by comprising: a sample preparation step S1 for processing gallium oxide powder to produce gallium oxide pellets; a growth preparation step S2 for loading the gallium oxide powder pellets into an oxide single crystal manufacturing apparatus to form a growth atmosphere and preheat it; and a single crystal growth step S3 for driving a motor to grow a single crystal and produce a gallium oxide single crystal.

[0055] As shown in Figures 7(a) and 8, the sample preparation step S1 is characterized by including a calcination step S110 to remove organic impurities and moisture from the gallium oxide powder and convert the gallium oxide powder into beta-phase gallium oxide powder, a step S120 to mix the calcined powder, a cold pressing step S130 to compress the mixed powder into a compressed powder, and a sintering step S140 to heat-treat the cold-pressed gallium oxide powder to produce pellets.

[0056] According to one embodiment of the present invention, the gallium oxide sample is not prepared in powder form because it is subjected to strong gas pressure by the flame, but is prepared in pellet form by cold pressing and sintering processes to prevent loss of raw materials, and the molten material can be stored without a crucible.

[0057] Furthermore, as shown in Figure 7(b), the growth atmosphere formation and preheating step S2 is characterized by including: a step S210 in which the sintered gallium oxide pellets produced in the sample preparation step S1 are loaded into the oxide single crystal production apparatus T; a step S220 in which the pressure of the fuel gas and oxygen gas is adjusted for initial flame ignition; a step S230 in which the flow rate of the fuel gas and oxygen gas is adjusted; an ignition step S240 in which a flame is generated; a step S250 in which the growth section and the gallium oxide pellets are preheated after the temperature has risen to just before the melting point of the gallium oxide pellets; a step S260 in which the ratio of the fuel gas and oxygen gas is adjusted so that the molten region of the gallium oxide pellets becomes an oxygen atmosphere; and a melting step S270 in which the temperature is raised above the melting point of the gallium oxide pellets to heat the sample.

[0058] As shown in Figure 7(c), the single crystal growth step S3 is characterized by including: a step S310 in which a linear motor is driven to start the growth of a gallium oxide single crystal when a gallium oxide melt S203 is generated at or above the melting point of the growth atmosphere formation and preheating step S2; a temperature maintenance step S320 in which the flow rate and pressure of fuel gas and oxygen gas are adjusted to maintain the temperature of the growth section 200; an oxygen atmosphere maintenance step S330 in which the flow rate and pressure are adjusted to maintain the oxygen atmosphere of the growth section 200; a growth step S340 in which a gallium oxide single crystal 205 is grown; a cooling step S350 in which the grown gallium oxide single crystal is cooled; and a single crystal extraction step 360 in which the grown gallium oxide single crystal is extracted from the top of the gallium oxide pellet.

[0059] The method for manufacturing a gallium oxide single crystal according to one embodiment of the present invention will be described in detail for each step below.

[0060] The gallium oxide powder calcination step S110 is characterized by selecting a crucible material that does not react with the gallium oxide powder to form new compounds, loading the gallium oxide powder into the crucible, raising the temperature to an appropriate level in an electric furnace, and maintaining the temperature for an appropriate time to allow it to cool naturally to ambient temperature without a cooling device.

[0061] As the material for the crucible for storing the gallium oxide powder, platinum or a platinum-based alloy that does not chemically react with the gallium oxide powder is most preferable.

[0062] As shown in Figure 9, the gallium oxide powder calcination step S110 is characterized by loading a platinum crucible containing 100g of gallium oxide powder into an electric furnace, raising the temperature to 1,000°C for 6 hours, maintaining the temperature at 1,000°C for 20 hours, and then allowing it to cool naturally to ambient temperature with the power to the electric furnace turned off.

[0063] As shown in Figure 8, the raw material powder mixing step S120 is characterized by performing a milling process to refine the particle size of the gallium oxide powder that has gone through the gallium oxide powder calcination step S110, making the particle size distribution uniform, and ensuring that the gallium oxide powder is well mixed.

[0064] The milling process can be carried out using a mortar and pestle, a ball mill, or a high-energy ball mill apparatus. In this invention, approximately 90-100 g of gallium oxide powder that has undergone the calcination step S110 can be milled using a mortar and pestle for 30 minutes.

[0065] The gallium oxide powder cold pressing step S130 is characterized by placing the powder that has gone through the gallium oxide powder mixing step S120 into an alloy metal die capable of holding it, and pressing it without applying heat to form pellets.

[0066] In the cold pressing step S130 for compressing the mixed powder, 40 g of gallium oxide powder that has gone through the gallium oxide powder mixing step S120 is loaded onto a cylindrical die made of stainless steel with a diameter of 1.5 inches, and after being held at a pressure of 70 MPa for 5 minutes using a hydraulic press, the cold-pressed gallium oxide powder can be separated. The cold pressing step process can be performed similarly twice.

[0067] The sintering step S140 is characterized by loading the pellets produced in the gallium oxide powder cold pressing step S130 into an alumina crucible using a platinum crucible lid, which is not chemically reactive with the pellets, as shown in Figure 10, and then, as shown in Figure 11, raising the temperature to 1,450°C in an electric furnace for 8 hours, maintaining the temperature at 1,450°C for 20 hours, and then allowing it to cool naturally to ambient temperature with the electric furnace power turned off.

[0068] As shown in Figure 3, the gallium oxide pellet loading step S210 is characterized by preparing two gallium oxide pellets 202 produced in the gallium oxide powder sintering step S140 and stacking them on the bottom of the growth section 200 of the single crystal manufacturing apparatus T so that the molten material does not overflow to the bottom of the growth section 200 during the melting process.

[0069] The fuel gas and oxygen gas pressure adjustment step S220 and the fuel gas and oxygen gas flow rate adjustment step S230 are characterized by adjusting to have appropriate pressure and flow rates for igniting the initial flame.

[0070] The flame ignition stage S240 is characterized by applying heat above the ignition point to the tip of the nozzle 108 to generate a flame in the gas coming out of the nozzle 108. The fuel gas used in the flame ignition stage S240 is portable LPG gas, which is a mixture of butane and propane gas in a 9:1 ratio.

[0071] The preheating step S250 is characterized by adjusting the pressure and flow rate of the fuel and oxygen gas to slowly heat the gallium oxide pellets 202 to just before their melting point of approximately 1,850°C, so that the gallium oxide pellets 202 do not crack due to thermal shock, and maintaining this temperature until the temperature of the growth section 200 reaches thermal equilibrium.

[0072] The oxygen atmosphere formation step S260 is characterized by maintaining an appropriate oxygen partial pressure for the gallium oxide pellet 202 to melt, and adjusting the oxygen pressure and flow rate to maintain the temperature in the preheating step S250.

[0073] The melting step S270, in which the sample is heated by raising the temperature above the melting point of the gallium oxide pellets, is characterized by maintaining the oxygen atmosphere formed in the oxygen atmosphere formation step S260 and adjusting the flow rate and pressure of the fuel gas and oxygen gas to heat the sample above its melting point, thereby melting the gallium oxide pellets 202 and producing a gallium oxide melt 203.

[0074] In the melting step S270, the upper part of the gallium oxide pellet 202 must generate a gallium oxide melt capable of producing a sufficient particle size; therefore, the area of ​​the flame 205, which is higher than the melting point, must be sufficiently large.

[0075] Furthermore, if the area of ​​the flame 205, which is higher than the melting point, becomes larger than the diameter of the pellet 202, there is a risk that the gallium oxide molten liquid 203 will overflow to the bottom of the growth section 200. Therefore, the pressure and flow rate of the fuel gas and oxygen gas must be adjusted appropriately to maintain the area of ​​the flame 205.

[0076] The linear motor drive stage S310 and the single crystal growth stage S320 are characterized in that, when the gallium oxide melt 203, which was melted above its melting point in the melting stage S270, reaches a state of thermal equilibrium inside the growth section 200, the linear motor is driven to grow a gallium oxide single crystal, and the pressure and flow rate of the fuel and oxygen gas are continuously adjusted to maintain the temperature and oxygen atmosphere at the time when melting begins.

[0077] The motor's movement speed in the linear motor drive step S310 can be 0.3 to 0.7 mm / min, preferably 0.5 mm / min. The slower the motor's movement speed, the larger the grain size and the better the crystal quality.

[0078] According to one embodiment of the present invention, when the thermal equilibrium state is reached in the linear motor drive stage S310, the temperature is approximately 1,950°C, the fuel gas pressure is approximately 0.05 MPa, and the oxygen gas pressure is approximately 0.02 MPa.

[0079] The single crystal growth stage S320 is characterized in that, as shown in Figure 12, it is controlled by an algorithm to maintain temperature and oxygen atmosphere while the entire growth unit 200 remains mounted on the support base 304 of the drive unit 300 and moves at a constant speed in a straight line.

[0080] Furthermore, the cooling step S330 is characterized in that, once the gallium oxide single crystal growth is complete, the flow rate and pressure of the fuel and oxygen gas are rapidly reduced to lower the temperature of the flame 204, and the upper part of the growth section 200 is covered with fire-resistant and heat-insulating material 201 to slowly cool the temperature of the growth section 200 to ambient temperature.

[0081] Furthermore, the single crystal extraction step S340 is characterized by appropriately processing the gallium oxide single crystal 205 formed on top of the gallium oxide pellet 202, which has been cooled to ambient temperature, to select the single crystals.

[0082] Furthermore, the present invention provides a gallium oxide single crystal characterized by being manufactured by the above-described manufacturing method.

[0083] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples herein are provided to give a more complete explanation of the present invention to a person of average skill in the art. [Examples]

[0084] Fabrication of β-Ga2O3 crystals 1. Production of β-Ga2O3 pellets (a) 100 g of β-Ga2O3 powder was placed in a platinum crucible and positioned in the center of an electric furnace. (b) The sample was heated to 1,000°C in an electric furnace for 6 hours, maintained at 1,000°C for 20 hours, and then allowed to cool naturally to ambient temperature with the electric furnace powered off. The β-Ga2O3 powder that had been calcined in (c)(b) was placed in a mortar and ground for 30 minutes. (d)(c) The β-Ga2O3 powder ground in 40 g was placed in a 1.5-inch diameter circular alloy metal die and maintained at a pressure of 70 MPa for 5 minutes using a hydraulic press. This was repeated twice. (e) The two cold-pressed β-Ga2O3 powder lumps removed from the die were placed on the base of the platinum crucible lid and then placed in an alumina crucible, which was positioned in the center of the electric furnace. (f) The sample was heated to 1,450°C in an electric furnace for 8 hours, maintained at 1,450°C for 20 hours, and then allowed to cool naturally to ambient temperature with the electric furnace power turned off.

[0085] 2. Fabrication of β-Ga2O3 single crystals The β-Ga2O3 pellets sintered in (g)(f) were loaded into the central lower end of the growth section. (h) Using LPG fuel gas, a mixture of propane and butane in a 9:1 ratio, and oxygen gas, the valves of the gas containers were opened to ignite the flame, and the fuel gas pressure regulator and oxygen gas pressure regulator were adjusted appropriately to ignite the flame.

[0086] (i) After the flame was ignited, the fuel gas flow meter and oxygen gas flow meter were slowly opened, and the fuel gas pressure regulator and oxygen gas pressure regulator were adjusted to raise the flame temperature.

[0087] (j) When the flame temperature rose to approximately 1,450°C, the pressure gauge and flow meter were adjusted using the algorithm shown in Figure 12 to create a high-oxygen atmosphere to prevent the β-Ga2O3 pellets from vaporizing and scattering. When the β-Ga2O3 pellets are exposed to a high-oxygen atmosphere, the powder does not vaporize and scatter.

[0088] (k) When a high-oxygen atmosphere was formed at 1,450°C or higher, the algorithm shown in Figure 12 was applied, similar to (j), to slowly increase the flow rates and pressures of the fuel gas and oxygen gas while melting the β-Ga2O3 pellets to generate a melt and raise the temperature to 1,950°C. The temperature was then maintained for approximately 10 minutes to allow the entire system to reach thermal equilibrium.

[0089] (l) When a β-Ga2O3 melt was formed and reached thermal equilibrium, and the melt area was maintained at a constant level, the motor was driven to start the growth of the single crystal. The motor speed was set so that the entire growth section moved at 0.5 mm / min.

[0090] (m) The algorithm shown in Figure 12 was applied to maintain a stable growth temperature and oxygen atmosphere until single crystal growth was complete.

[0091] (n) Once single crystal growth was complete, the flame temperature was slowly cooled.

[0092] (o) Single crystals were extracted from the top of the cooled β-Ga2O3 pellet. Experimental example

[0093] Evaluation of β-Ga2O3 crystals The β-Ga2O3 single crystal sample shown in Figure 14, which was produced according to one embodiment of the present invention, is a micrograph of a β-Ga2O3 single crystal sample grown once in the process of the above example (production of β-Ga2O3 crystals).

[0094] The structure of a β-Ga2O3 single crystal sample manufactured according to one embodiment of the present invention was measured using single-crystal X-ray diffraction and neutron diffraction analysis shown in Figure 15, as shown in (a), (b), and (c), respectively. (a) is the X-ray Laue pattern along the (0K0) plane, with the (210) plane displayed on the pattern. (b) is the rocking curve data, with X-ray data on the left and neutron data in the center and on the right. The measured planes are (400), (020), and (002), respectively, with full widths at half maximum of 0.12°, 0.14°, and 0.26°. (c) is the X-ray 2θ / θ scan data along the (H00) direction.

[0095] Furthermore, the crystal structure and lattice constants of a β-Ga2O3 single crystal sample produced by one embodiment of the present invention were confirmed by single-crystal X-ray diffraction analysis and are shown in Table 1. Referring to Table 1, the crystal structure is monoclinic, and the lattice constant values ​​are as follows: a = 12.231 Å, b = 3.0329 Å, c = 5.8077 Å, α = 90°, β = 103.784°, γ = 90°, and the unit cell volume is 209.44 Å. 3 We were able to confirm that this was the case.

[0096] [Table 1]

[0097] Furthermore, the atomic arrangement and surface state of a β-Ga2O3 single crystal sample produced by one embodiment of the present invention were confirmed through TEM and AFM microscopy analysis shown in Figure 16, as shown in (a), (b), and (c), respectively. (a) shows an image observed along the (0b0) plane and an electron diffraction pattern along the (0K0) plane, with peaks displayed on the electron diffraction pattern in the directions of the (201) and (400) planes. (b) is a magnified TEM image (left) of the region shown in (a), where the unit cell of the β-Ga2O3 single crystal is displayed, and a schematic diagram of the unit cell is shown on the right. (c) is an atomic force microscope (AFM) image of the grown, undoped β-Ga2O3, where the total horizontal length indicated by the blue arrow is 50 μm, the surface roughness is 0.04 nm, and the step height along the direction indicated by the red arrow corresponds to 0.5a of the β-Ga2O3 unit cell, which is approximately 0.6 nm.

[0098] Furthermore, measurements using ultraviolet-visible-near-infrared spectroscopy of a β-Ga2O3 single crystal sample produced by one embodiment of the present invention confirmed that the direct band gap values ​​were 4.35 to 4.59 eV along the c* and b crystal axes, as shown in Figure 17.

[0099] Furthermore, a β-Ga2O3 single crystal sample produced by one embodiment of the present invention was measured using secondary ion mass spectrometry, and as shown in Figure 18, the Si impurity was 2.28 × 10⁻⁶. 16 Therefore, the Fe impurity is 2.85 × 10⁻⁶ 16 The N impurity is 3.53 × 10⁻⁶. 15 The Sn impurity is 2.38 × 10⁻⁶. 16 It was confirmed that this was the case.

[0100] Specific embodiments of the present invention have been described above. A person with ordinary skill in the art to which the present invention pertains can realize that the present invention can be embodied in modified forms without departing from the spirit of the invention. Accordingly, the embodiments disclosed are considered in an explanatory rather than restrictive view. The scope of the present invention is expressed in the claims rather than in the foregoing description, and all differences within an equivalent scope are included in the present invention. [Explanation of Symbols]

[0101] 100: Heat source part 200: Growth Department 300: Drive unit 400: Measuring part 101: Fuel Gas Supply Department 102: Oxygen gas supply unit 103: Fuel pressure regulator 104: Oxygen pressure regulator 105:Fuel flow regulator 106: Oxygen flow regulator 107: Premix area part 108: Nozzle 109: Fuel pipe 110: Oxygen tube 111: Height adjuster 201: Fireproof and heat insulating materials 202: Raw material powder pellets 203: Molten gallium oxide 204: Flame 205: Gallium oxide single crystal 301: Conveyor belt 302: Motor 303: Microcontroller 304: Support stand 401: Infrared camera C: Computer S1: Sample preparation stage S2: Preparation stage for gallium oxide single crystal growth S3: Single crystal growth stage S110: Gallium oxide powder calcination stage S120: Gallium oxide powder mixing stage S130: Gallium oxide powder cold pressing stage S140: Gallium oxide powder sintering stage S210: Gallium oxide pellet loading stage S220: Fuel gas and oxygen gas pressure adjustment stage S230: Fuel gas and oxygen gas flow rate adjustment stage S240: Flame ignition stage S250: Preheating stage S260: Oxygen atmosphere formation stage S270: Melting stage S310: Motor drive stage S320: Single crystal growth stage S330: Cooling stage S340: Single crystal extraction stage

Claims

1. A heat source unit (100) for melting oxide pellets, A growth section (200) made of refractory material is provided, which is a space for growing oxide single crystals on which the oxide pellets are stacked. A drive unit (300) for moving the entire growth unit in order to grow the oxide single crystal, Includes a measuring unit (400) for measuring the temperature of the growth area throughout the entire growth process of the oxide single crystal. A apparatus for manufacturing oxide single crystals, characterized by the following features.

2. The heat source unit (100) is A fuel gas supply unit (101) consisting of hydrocarbons, Oxygen gas supply unit (102), A fuel pressure regulator (103) for adjusting the pressure of fuel injected into the fuel line, An oxygen pressure regulator (104) for adjusting the oxygen pressure, A pre-mixing region (107) is a space in which the fuel gas and the oxygen gas are mixed, A fuel pipe (109) into which the fuel gas flows into the pre-mixed region (107), The oxygen tube (110) into which the oxygen gas flows, A fuel flow regulator (105) for adjusting the amount of fuel gas flowing into the pre-mixed region (107), An oxygen flow regulator (106) for adjusting the amount of oxygen gas, A nozzle (108) through which the fuel gas and oxygen gas mixture, mixed in the pre-mixing region (107), is discharged to the outside, Includes a height adjuster (111) for adjusting the distance between the growth section (200) and the nozzle (108). The apparatus for producing oxide single crystals according to claim 1.

3. The aforementioned growth portion (200) is The heat source (100) and the heat source (201) are used to create an oxygen atmosphere that is independent of the surrounding air. The apparatus for producing oxide single crystals according to claim 1.

4. The drive unit (300) is A support base (304) that supports the growth portion (200), A conveyor belt (301) moves the entire support base (304) linearly, A motor (302) for driving the conveyor belt (301), A microcontroller (303) for controlling the drive of the motor (302), Includes a computer (C) for controlling the microcontroller (303). The apparatus for producing oxide single crystals according to claim 1.

5. The measuring unit (400) is An infrared camera (401) for measuring the temperature of the growth portion (200), Includes a computer (C) that receives temperature data measured from the infrared camera. The apparatus for producing oxide single crystals according to claim 1.

6. Sample preparation step (S1) involves processing gallium oxide powder to produce gallium oxide pellets, The growth preparation step (S2) involves loading the gallium oxide powder pellets into an oxide single crystal manufacturing apparatus to create a growth atmosphere and preheat it, The process includes a single crystal growth step (S3) in which a motor is driven to grow a single crystal and produce a gallium oxide single crystal. A method for producing gallium oxide single crystals, characterized by the following features.

7. The aforementioned sample preparation step (S1) is, A calcination step (S110) is performed to remove organic impurities and moisture from the gallium oxide powder and convert the gallium oxide powder into beta-phase gallium oxide powder. The step of mixing the calcined gallium oxide powder (S120), A cold pressing step (S130) for compressing the mixed gallium oxide powder into a compressed powder, The process includes a sintering step (S140) in which the cold-pressed gallium oxide powder is heat-treated to produce pellets. The method for producing a gallium oxide single crystal according to claim 6.

8. The aforementioned growth preparation stage (S2) is, The step (S210) involves loading the gallium oxide pellets produced in the sample preparation step (S1) into an oxide single crystal manufacturing apparatus, The step of adjusting the pressure of the fuel gas and oxygen gas for initial flame ignition (S220), The steps include adjusting the flow rates of the fuel gas and oxygen gas (S230), The ignition stage (S240) for generating a flame, After the temperature of the gallium oxide pellet is raised to just before its melting point, the growth section and the gallium oxide pellet are preheated (S250). The step of adjusting the ratio of the fuel gas to the oxygen gas so that the molten region of the gallium oxide pellet is in an oxygen atmosphere (S260), The process includes a melting step (S270) in which the sample is heated by raising the temperature above the melting point of the gallium oxide pellet. The method for producing a gallium oxide single crystal according to claim 6.

9. The aforementioned single crystal growth step (S3) is The process includes: a step (S310) in which a gallium oxide melt is generated at a temperature above the melting point in the growth preparation step (S2), and a step (S310) in which a linear motor is driven to start the growth of a gallium oxide single crystal; A temperature maintenance step (S320) is performed to adjust the flow rate and pressure of the fuel gas and oxygen gas in order to maintain the temperature of the growth portion, The oxygen atmosphere maintenance step (S330) involves adjusting the flow rate and pressure to maintain the oxygen atmosphere in the growth section, The growth step (S340) for growing the gallium oxide single crystal, A cooling step (S350) for cooling the grown gallium oxide single crystal, The step includes a single crystal extraction step (360) for extracting gallium oxide single crystals grown on top of the gallium oxide pellet. The method for producing a gallium oxide single crystal according to claim 6.

10. Manufactured by the manufacturing method described in claim 6 A gallium oxide single crystal characterized by the following features.

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