METHOD FOR MANUFACTURING β-Ga2O3 / β-Ga2O3 LAMINATE

Abstract

To provide a method for laminating a β-Ga2O3 single crystal having high crystallinity and a fast growth rate on a β-Ga2O3 substrate by a liquid phase epitaxial growth method to manufacture a β-Ga2O3 / β-Ga2O3 laminate.SOLUTION: A method for manufacturing a β-Ga2O3 / β-Ga2O3 laminate comprises: mixing and melting solute Ga2O3, and PbO and Bi2O3 used as a solvent; directly contacting a β-Ga2O3 substrate to the obtained melt; and growing a β-Ga2O3 single crystal on the β-Ga2O3 substrate by a liquid phase epitaxial growth method to obtain a β-Ga2O3 / β-Ga2O3 laminate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a β-Ga2O3 / β-Ga2O3 laminate and a laminate obtained by the manufacturing method.

Background Art

[0002] Power devices are one of the key devices for improving power utilization efficiency to achieve a low-carbon society, and are mainly used as elements for constructing an inverter that performs DC-AC power conversion and AC voltage / frequency adjustment. In the above conversion, energy loss based on the resistance when current flows through the element and the generation of waste current associated with the recovery process of the charge distribution in the element when the voltage applied to the element is switched cannot be avoided. Although the loss ratios vary depending on the power and frequency, they generally range from a few percent to a dozen or so percent. Although the device structure of conventional Si-based power semiconductors has been improved, Si is approaching its physical property limit, making it difficult to further improve efficiency. Therefore, development of SiC and GaN as power device materials to replace Si has been underway. The bandgap of SiC is 3.3 eV, and the bandgap of GaN is 3.4 eV, which are wide bandgap materials compared to 1.1 eV of Si. The wider the bandgap of the material, the larger the breakdown voltage representing the electric field that prevents charges from gushing out in the semiconductor, and a device structure that can withstand a larger voltage can be adopted.

[0003] β-Ga2O3 is a type of oxide semiconductor that has been used in applications such as transparent conductive substrates for GaN-based LEDs and UV detection elements for solar blinds. In recent years, it has also attracted attention as a power device material, and is expected to enable the realization of high-voltage, high-efficiency power semiconductors that surpass SiC and GaN. This is due to the fact that the band gap of β-Ga2O3 is expected to be 4.5-4.9 eV, which is wider than that of SiC and GaN. Another advantage of β-Ga2O3 compared to SiC and GaN is that it can be grown from a melt. Crystal growth from a melt is difficult for SiC and GaN, and substrate costs are high. On the other hand, β-Ga2O3 has a melting point at atmospheric pressure and can be grown in bulk, and research and development is progressing using the EFG (Edge-Defined Film-fed Growth) method and the vertical Bridgman method. Substrates of 2-4 inches are commercially available for the former growth method, and 4-inch substrates are being developed for the latter growth method.

[0004] To apply β-Ga2O3 to power devices, a β-Ga2O3 (epitaxial layer) / β-Ga2O3 (substrate) laminate is required, consisting of two layers of β-Ga2O3 with different residual electron concentrations. The epitaxial layer needs to be several μm to about 20 μm thick, and conventional vapor phase growth methods such as metal-organic vapor deposition (MOCVD), molecular beam epitaxy (MBE), mist vapor deposition (CVD), and halide vapor deposition (HVPE) have been used. However, vapor phase growth methods are non-thermodynamic growth methods and have the disadvantages of low crystal quality and slow growth rates.

[0005] For example, Non-Patent Document 1 discloses a method for epitaxially growing β-Ga2O3 on a sapphire substrate using the HVPE method. According to this method, because the crystal structures of the sapphire substrate and β-Ga2O3 are different, multiple rotational domains exist, and the epitaxial layer is not a single domain. Strictly speaking, this layer is not a single crystal and cannot be applied to power devices. Furthermore, the X-ray rocking curve full width at half maximum of the epitaxial layer obtained by this method is 0.5 deg (1800 arcsec), indicating low crystallinity. Also, Patent Document 1 discloses a method for obtaining a β-Ga2O3 / β-Ga2O3 laminate (hereinafter sometimes simply referred to as "β-Ga2O3 laminate") by epitaxially growing β-Ga2O3 on a β-Ga2O3 substrate using the HVPE method. According to this method, a β-Ga2O3 / β-Ga2O3 laminate can be obtained, but the growth rate of the epitaxial layer is low, at 2.7 to 6.0 μm / hr.

[0006] On the other hand, liquid phase growth has the advantage of being able to produce higher quality crystals than vapor phase growth because, in principle, crystal growth proceeds in thermal equilibrium. β-Ga2O3 has a high melting point of around 1970°C, and it is difficult to maintain a stable melt surface near the melting point, making growth difficult using the Czochralski method, which is used for silicon single crystals. Therefore, single crystal growth is performed using the EFG method and the vertical Bridgman method as described above. However, β-Ga2O3 laminates cannot be obtained using the EFG method or the vertical Bridgman method. Methods for growing the target material from a melt include the static slow cooling method, the flux method, the floating zone method, the TSSG method (Top Seeded Solution Growth), the solution pulling method, and the liquid phase epitaxy (LPE).

[0007] Patent Document 2 discloses a method for obtaining a β-Ga2O3 epitaxial layer by the LPE method. According to this method, a β-Ga2O3 single crystal layer is stacked on a sapphire substrate using the LPE method. However, because the substrate is sapphire, a β-Ga2O3 laminate cannot be obtained. Furthermore, the sapphire substrate has a corundum crystal structure, while β-Ga2O3 has a monoclinic crystal structure, so the crystal structures are different. In addition, there was a problem of low crystal quality due to the mismatch of lattice constants.

[0008] When growing a β-Ga2O3 single crystal layer using liquid phase growth methods such as LPE, a solvent capable of dissolving β-Ga2O3 is required. Patent Document 2 exemplifies PbO or PbF2 as solvents, and one of them is used. In order to establish a stable and reproducible single crystal growth method, it is common practice to maintain the melt at a temperature about 100 to 200°C above its melting point so that the solvent and solute are uniformly mixed. In Patent Document 2, the melt is maintained at 1100°C. The melting point of PbO is approximately 886°C, and the melting point of PbF2 is approximately 824°C. Generally, if the melt temperature containing either PbO or PbF2 exceeds 1000°C, some of the PbO or PbF2 will volatilize, changing the melt composition, which is undesirable for stably and reproducibly growing β-Ga2O3 single crystals. Furthermore, the evaporated PbO or PbF2 reacts with the furnace materials that make up the growth furnace, reducing the number of times the materials can be used and causing harmful Pb to volatilize, which necessitates a sealed structure for the growth furnace and thus increases costs.

[0009] As mentioned above, the method of vapor-phase growth of β-Ga2O3 on a β-Ga2O3 substrate to obtain β-Ga2O3 laminates useful as power devices has the drawbacks of low crystal quality and slow growth rate. On the other hand, when using liquid-phase growth, which is in principle close to thermal equilibrium growth and can be expected to have high crystallinity and growth rate, conventional methods have the problem that β-Ga2O3 laminates cannot be obtained. Furthermore, conventional liquid-phase growth methods use either PbO or PbF2 as a solvent, and have the problem that the vapor pressure is high, making it difficult to grow β-Ga2O3 single crystals stably and at low cost. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 6744523 [Patent Document 2] Patent No. 5794955

[0011] [Non-Patent Document 1] Journal of the Japanese Society for Crystal Growth Vol.42, No.2, (2015) P.141~147 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention aims to solve at least one of the above-mentioned conventional problems. Furthermore, the present invention aims to provide a method for producing a β-Ga2O3 / β-Ga2O3 laminate by stacking β-Ga2O3 single crystals having high crystallinity and a fast growth rate on a β-Ga2O3 substrate using a liquid-phase epitaxial growth method. In this specification, a β-Ga2O3 / β-Ga2O3 laminate refers to a laminate in which an epitaxial layer containing β-Ga2O3 is stacked on a substrate containing β-Ga2O3. [Means for solving the problem]

[0013] The inventors of the present invention have diligently studied and found that the above problems can be solved by the present invention described below. That is, the present invention is as follows. <1> This method for producing a β-Ga2O3 / β-Ga2O3 laminate is characterized by mixing a solute, Ga2O3, with solvents, PbO and Bi2O3, melting the mixture, directly contacting a β-Ga2O3 substrate with the resulting melt, and growing a β-Ga2O3 single crystal on the β-Ga2O3 substrate by liquid-phase epitaxial growth to obtain a β-Ga2O3 / β-Ga2O3 laminate. <2> The mixing ratio of the solute Ga2O3 and the solvents PbO and Bi2O3 is solute:solvent = 5~30 mol%:95~70 mol%, and the mixing ratio of the solvents PbO and Bi2O3 is PbO:Bi2O3 = 0.1~95 mol%:99.9~5 mol%, <1> This is a method for producing the β-Ga2O3 / β-Ga2O3 laminate described above. <3> This method for producing a β-Ga2O3 / β-Ga2O3 laminate is characterized by mixing a solute, Ga2O3, with solvents, PbO and PbF2, melting the mixture, directly contacting a β-Ga2O3 substrate with the resulting melt, and growing a β-Ga2O3 single crystal on the β-Ga2O3 substrate by liquid-phase epitaxial growth to obtain a β-Ga2O3 / β-Ga2O3 laminate. <4> The mixing ratio of the solute Ga2O3 and the solvents PbO and PbF2 is solute:solvent = 2~20 mol%:98~80 mol%, and the mixing ratio of the solvents PbO and PbF2 is PbO:PbF2 = 2~80 mol%:98~20 mol%, <3> This is a method for producing the β-Ga2O3 / β-Ga2O3 laminate described above. <5> The layer containing the β-Ga2O3 single crystal formed by liquid-phase epitaxial growth contains 0.01 mol% to 20 mol% of heterogeneous elements, <1> from <4> This is a method for producing a β-Ga2O3 / β-Ga2O3 laminate as described in any of the above. <6> The aforementioned heterogeneous element is one or more selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, Fe, Co, Ni, Cu, Zn, Cd, Al, In, Si, Ge, Sn, and Pb. <5> This is a method for producing the β-Ga2O3 / β-Ga2O3 laminate described above. <7> A β-Ga2O3 / β-Ga2O3 laminate having a layer containing a β-Ga2O3 single crystal on a β-Ga2O3 substrate, wherein the rocking curve full width at half maximum in the layer containing the β-Ga2O3 single crystal is 5 to 100 arcsec. [Effects of the Invention]

[0014] According to a preferred embodiment of the present invention, solvent evaporation is suppressed, stable crystal growth with minimal compositional variation is possible, and furnace material consumption is reduced, eliminating the need for a closed-system growth furnace, thus enabling low-cost manufacturing. Furthermore, because the crystal growth method is liquid-phase growth, β-Ga2O3 single crystal layers can be grown with high crystallinity and a high growth rate. The β-Ga2O3 laminate produced in this embodiment can be used in power devices using β-Ga2O3 laminates, which are expected to see further development in the future. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is the phase diagram of PbO-Bi2O3. [Figure 2] Figure 2 is a phase diagram of PbO-PbF2. [Figure 3] Figure 3 is a schematic diagram showing an example of a typical LPE growth furnace. [Figure 4] Figure 4 shows the X-ray rocking curve of the (002) plane of the epitaxial layer of the laminate obtained in Example 1. [Modes for carrying out the invention]

[0016] In the first embodiment of the present invention, after mixing and melting solute Ga2O3, solvent PbO and Bi2O3, a β-Ga2O3 substrate is brought into direct contact with the obtained melt, and a β-Ga2O3 single crystal is grown on the β-Ga2O3 substrate by liquid phase epitaxial growth method to obtain a β-Ga2O3 / β-Ga2O3 laminate. This is a method for manufacturing a β-Ga2O3 / β-Ga2O3 laminate characterized by the above. Hereinafter, the principle of the first embodiment of the present invention will be described. Fig. 1 is a phase diagram of PbO-Bi2O3 (Reference: Temperature / combination phase diagram of the system Bi2O3-PbO J. Am. Chem. Soc., 64 [3] 182-184 1981). PbO and Bi2O3 form a eutectic system, and by mixing both, the melting point can be lowered. By mixing PbO and Bi2O3, within the range where the PbO concentration is 0.1 to 95 mol%, the melting point of the PbO+Bi2O3 mixture can be made lower than the melting point of PbO alone or Bi2O3 alone. This indicates that the evaporation amount of PbO or Bi2O3 within the said PbO concentration range can be suppressed as compared with PbO or Bi2O3 alone.

[0017] As the solvent composition, PbO:Bi2O3 = 0.1 to 95 mol%:99.9 to 5 mol% is preferable. More preferably, PbO:Bi2O3 = 20 to 90 mol%:80 to 10 mol%, and particularly preferably, PbO:Bi2O3 = 50 to 80 mol%:50 to 20 mol%. In the case of a single solvent of PbO or Bi2O3, the LPE growth temperature (temperature at the time of epitaxial growth) becomes high, so the above-mentioned mixed solvent is suitable. The mixing ratio of solute Ga2O3, solvent PbO and Bi2O3 is preferably solute:solvent = 5 to 30 mol%;95 to 70 mol%. More preferably, the solute concentration is 14 mol% or more and 27 mol% or less. When the solute concentration is less than 5 mol%, the crystal growth rate is slow, and when it exceeds 30 mol%, the LPE growth temperature becomes high and solvent evaporation may increase. Also, the crystal growth rate may increase and the crystal quality may deteriorate. In the first embodiment of the present invention, the growth rate of a layer (epitaxial layer) containing a β-Ga₂O₃ single crystal formed by liquid-phase epitaxial growth method is preferably 10 to 50 μm / hr, more preferably 20 to 30 μm / hr. If it is less than 10 μm / hr, the growth rate may be slow and the cost may increase. Also, if it exceeds 50 μm / hr, the crystal quality may deteriorate. Here, the growth rate can be determined from the film thickness difference before and after LPE growth and the growth time.

[0018] Next, the second embodiment of the present invention is a method for manufacturing a β-Ga₂O₃ / β-Ga₂O₃ laminate, characterized in that Ga₂O₃ as a solute and PbO and PbF₂ as solvents are mixed and melted, and then a β-Ga₂O₃ substrate is brought into direct contact with the obtained melt, and a β-Ga₂O₃ single crystal is grown on the β-Ga₂O₃ substrate by liquid-phase epitaxial growth method to obtain a β-Ga₂O₃ / β-Ga₂O₃ laminate. The principle of the second embodiment of the present invention will be described. Figure 2 is a phase diagram of PbO-PbF₂ (reference: C. Sandonnini Atti, Accad. Naz. Licei, C1. Sci. Fis. Mat. Nat., 23[Ser.5, Pt.1] 962-964 (1914)). PbO and PbF₂ form a eutectic system, and by mixing them, the melting point can be lowered. By mixing PbO with PbF₂, in the range where the PbF₂ concentration is about 0.01 to about 86 mol%, the melting point of the PbO+PbF₂ mixture can be made lower than the melting point of PbO alone or PbF₂ alone. This indicates that the evaporation amount of PbO or PbF₂ in the concentration range of PbO+PbF₂ can be suppressed as compared with PbO or PbF₂ alone.

[0019] The preferred solvent composition is PbO:PbF2 = 2-80 mol%:98-20 mol%. More preferably, PbO:PbF2 = 20-80 mol%:80-20 mol%, and particularly preferably, PbO:PbF2 = 40-60 mol%:60-40 mol%. Since the LPE growth temperature is high when using PbO or PbF2 as a single solvent, the above-mentioned mixed solvent is preferable. The mixing ratio of the solute Ga2O3 to the solvents PbO and PbF2 is preferably solute:solvent = 2-20 mol%:98-80 mol%. More preferably, the solute concentration is 10 mol% or more and 20 mol% or less. If the solute concentration is less than 2 mol%, the growth rate may be slow, and if it exceeds 20 mol%, the LPE growth temperature may rise and solvent volatilization may increase. In addition, the crystal growth rate may be fast and the crystal quality may be low. In a second embodiment of the present invention, the growth rate of the layer containing the β-Ga2O3 single crystal formed by liquid-phase epitaxial growth (epitaxial layer) is preferably 10 to 50 μm / hr, and more preferably 20 to 30 μm / hr. If the growth rate is less than 10 μm / hr, the growth rate is slow and may increase costs. If the growth rate exceeds 50 μm / hr, the crystal quality may deteriorate. The growth rate can be determined from the difference in film thickness before and after LPE growth and the growth time.

[0020] In the first and second embodiments of the present invention, one or more third components can be added to the solvent for the purpose of controlling the LPE growth temperature, adjusting the solvent viscosity, and doping with different elements, within a range where the solubility of Ga2O3 and the evaporation rate of PbO+Bi2O3 or PbO+PbF2 do not change significantly. Examples include B2O3, V2O5, P2O5, MoO3, and WO3. In addition, Bi2O3 may be added as a third component to the solvent of the second embodiment. In the present invention, the most preferred method for growing the β-Ga2O3 laminate is the liquid-phase epitaxial growth method using a β-Ga2O3 substrate.

[0021] In β-Ga2O3 laminates useful as power devices, it is necessary to control the residual electron concentration of the epitaxial layer. Ga in β-Ga2O3 is a trivalent oxide and generally exhibits n-type conductivity. In the first and second embodiments of the present invention, residual electron concentration, band gap, and insulating properties can be imparted to β-Ga2O3 by doping it with different elements. For example, doping β-Ga2O3 with MgO or ZnO as a divalent impurity can reduce the residual electron concentration. Doping with SiO2 or SnO2 as a tetravalent impurity can increase the residual electron concentration. Doping with Fe2O3 can impart insulating properties. On the other hand, doping with MgO or Al2O3, which have a wider band gap than β-Ga2O3, and then mixing them together can increase the band gap. Doping with ZnO or CdO and then mixing them together can decrease the band gap.

[0022] The layer containing the β-Ga2O3 single crystal formed by liquid-phase epitaxial growth preferably contains one or more heterogeneous elements selected from the group consisting of Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, Fe, Co, Ni, Cu, Zn, Cd, Al, In, Si, Ge, Sn, and Pb in an amount of 0.01 to 20 mol%, and more preferably in an amount of 0.1 to 10 mol%. If the doping amount of heterogeneous elements is less than 0.01 mol%, the properties may not be well exhibited, and if it exceeds 20 mol%, crystal growth may become difficult.

[0023] Figure 3 is a schematic diagram showing an example of a typical LPE growth furnace. Inside the LPE growth furnace, a platinum crucible 7, which melts the raw material and contains it as a molten metal 8, is placed on a crucible stand 9 made of mullite (a compound of aluminum oxide and silicon dioxide). Three-stage side heaters (upper heater 1, middle heater 2, and lower heater 3) are provided on the outside and to the side of the platinum crucible 7 to heat and melt the raw material inside the crucible 7. The output of the heaters is controlled independently, and the amount of heat applied to the molten metal 8 is adjusted independently. A mullite furnace tube 11 is placed between the heaters and the inner wall of the manufacturing furnace, and a mullite furnace lid 12 is placed on top of the furnace tube 11. A lifting mechanism is provided above the platinum crucible 7. An alumina lifting shaft 5 is fixed to the lifting mechanism, and a substrate holder 6 and a substrate 4 fixed by the holder are provided at its tip. A mechanism for rotating the shaft is provided above the lifting shaft 5. In addition, a thermocouple 10 is provided at the bottom of the crucible.

[0024] A third embodiment of the present invention is a β-Ga2O3 / β-Ga2O3 laminate having a layer containing a β-Ga2O3 single crystal on a β-Ga2O3 substrate, wherein the rocking curve full width at half maximum in the layer containing the β-Ga2O3 single crystal is 5 to 100 arcsec. The β-Ga2O3 / β-Ga2O3 laminate of the present invention can preferably be manufactured according to the first and second embodiments of the present invention described above. In the present invention, the full width at half maximum (FWHM) of the rocking curve in the layer containing the β-Ga2O3 single crystal is 5 to 100 arcsec, preferably 5 to 80 arcsec, and more preferably 5 to 50 arcsec. If it exceeds 100 arcsec, the crystallinity is low, and the power device performance may decrease. The β-Ga2O3 / β-Ga2O3 laminate of the present invention is characterized by high crystallinity. In the present invention, the method described in the examples below can be used as the method for measuring the full width at half maximum of the rocking curve. [Examples]

[0025] The following describes a method for growing a β-Ga2O3 / β-Ga2O3 laminate according to one embodiment of the present invention, specifically a method for forming a β-Ga2O3 epitaxial layer on a β-Ga2O3 substrate. The present invention is not limited in any way to the following examples.

[0026] An example of the manufacturing method of the present invention will be described below using Figure 3. A platinum crucible 7, which melts the raw materials and contains the molten material 8, is placed on a crucible stand 9. Three tiers of side heaters (upper heater 1, middle heater 2, and lower heater 3) are provided on the outside and to the side of the platinum crucible 7 to heat and melt the raw materials inside the crucible 7. The output of the heaters is controlled independently, and the amount of heat applied to the molten material 8 is adjusted independently. A furnace tube 11 is placed between the heaters and the inner wall of the manufacturing furnace, and a furnace lid 12 is provided above the furnace tube 11. A lifting mechanism is provided above the platinum crucible 7. An alumina lifting shaft 5 is fixed to the lifting mechanism, and a substrate holder 6 and a substrate 4 (β-Ga2O3 substrate) fixed by the holder are provided at its tip. A mechanism for rotating the shaft is provided above the lifting shaft 5. In addition, a thermocouple 10 is provided at the bottom of the crucible.

[0027] To melt the raw materials in the platinum crucible 7, the manufacturing furnace is heated until the raw materials have melted. Preferably, the temperature is raised to 600-1000°C, more preferably to 700-900°C, and the mixture is left to stand for 2-3 hours to homogenize the molten raw materials. Alternatively, instead of standing, a platinum plate may be fixed to the tip of an alumina shaft, immersed in the molten material, and the molten material may be homogenized by stirring by rotating the shaft. It is desirable that the growth of the β-Ga2O3 single crystal layer proceeds only directly beneath the substrate. If β-Ga2O3 single crystal growth proceeds in the molten material other than directly beneath the substrate, the grown single crystal will adhere to the substrate due to convection in the molten material, resulting in different phases with different growth orientations, which is undesirable. Therefore, the three-stage heater is offset and adjusted so that the bottom of the crucible is several degrees higher than the surface of the molten material. After the temperature of the molten material has stabilized, the seed crystal substrate is brought into contact with the surface of the molten material. After introducing the seed crystal substrate into the melt, the temperature is kept constant or the temperature is lowered at 0.025~5°C / hr to grow the desired β-Ga2O3 single crystal layer on the surface of the seed crystal substrate. During growth, the seed crystal substrate rotates at 5~300 rpm by the rotation of the growth axis, and is rotated in the reverse direction at regular intervals. After crystal growth for about 30 minutes to 24 hours, the grown crystal is separated from the melt by raising the growth axis, and the molten components adhering to the surface of the grown crystal are separated by rotating the growth axis at 50~300 rpm. After that, it is cooled to room temperature over 1~24 hours to obtain the desired β-Ga2O3 / β-Ga2O3 laminate.

[0028] (Example 1) Platinum crucible 7, with an inner diameter of 120 mm, a height of 150 mm, and a thickness of 1 mm, was loaded with 2661.2 g of PbO (99.999% purity), 2777.7 g of Bi2O3 (99.999% purity), and 561.2 g of Ga2O3 (99.999% purity) as raw materials. The mixing ratio of the solute Ga2O3 to the solvents PbO and Bi2O3 was solute:solvent = 14.3 mol%:85.7 mol%, and the mixing ratio of the solvents PbO and Bi2O3 was PbO:Bi2O3 = 67 mol%:33 mol%. Platinum crucible 7 containing the raw materials was placed in the LPE furnace shown in Figure 3, and the raw materials were melted at a crucible bottom temperature of approximately 850°C. After stirring the molten material with a platinum plate for 6 hours, the crucible bottom temperature was reduced to 750°C, and a β-Ga2O3 substrate with a C-plane orientation, 11 mm × 11 mm × 650 μm thickness, grown by the EFG method, was brought into contact with the molten material. The substrate was grown at the same temperature for 3 hours while rotating an alumina pulling shaft 5 at 60 rpm. During this time, the shaft rotation was reversed every 5 minutes. Subsequently, the pulling shaft 5 was pulled up to separate it from the molten material, and the molten components were separated by rotating the pulling shaft 5 at 200 rpm. After that, the material was cooled to room temperature to obtain a β-Ga2O3 / β-Ga2O3 laminate. Any remaining molten components were removed using hydrochloric acid. The average thickness of the epitaxial layer was approximately 90 μm. The average growth rate was approximately 30 μm / hr.

[0029] (Comparative Examples 1-2) Except for changing the starting composition to match the composition shown in Table 1 below, and changing the raw material dissolution temperature and growth temperature as described in Table 1, we attempted to fabricate a β-Ga2O3 / β-Ga2O3 laminate using the same method as in Example 1. Here, the crystallinity of the epitaxial layer of the β-Ga2O3 / β-Ga2O3 laminate obtained in Example 1 was evaluated by the full width at half maximum (FWHM) of the rocking curve of the (002) plane. The results are shown in Figure 4. The FWHM of the rocking curve of the (002) plane was 0.0042 deg (= 15 arcsec). The FWHM of the rocking curve was measured using an X-ray diffractometer (X'pertMRD, Spectris). Using this diffractometer, 2θ, ω, χ, and φ were adjusted to align the axis so that the peak of the (002) plane of β-Ga2O3 could be detected, and then the measurement was performed with a tube voltage of 45 KV and a tube current of 40 mA. The incident light was monochromatized using four Ge(220) crystals. Other measurement conditions were as follows. Light source;Cu-Kα Wavelength: 0.15418nm Measurement mode: ω scan (incident angle scan) ω range; the angle at which the β-Ga2O3(002) plane appears is set for each sample. ω range; 0.1deg ω step; 0.0005 degrees 2θ position; The angle at which the β-Ga2O3(002) plane appears is set for each sample. Collimator diameter: 0.5 mm Anti-scattering slit; 1.5mm

[0030] (Examples 2-8) A β-Ga2O3 / β-Ga2O3 laminate was obtained in the same manner as in Example 1, except that the starting composition was changed to match the composition shown in Table 1 below, and the raw material dissolution temperature and growth temperature were changed as described in Table 1. The epitaxial layer obtained in Example 2 was a mixed crystal layer of β-Ga2O3 and MgO, and the epitaxial layer obtained in Example 5 was a mixed crystal layer of β-Ga2O3 and Al2O3.

[0031] [Table 1]

[0032] As described above, a β-Ga2O3 / β-Ga2O3 laminate can be manufactured by mixing and dissolving the solute Ga2O3 with the solvents PbO and Bi2O3, and then directly contacting the resulting melt with a β-Ga2O3 substrate. As can be seen by comparing Examples 1-8 with Comparative Examples 1-2, mixing PbO and Bi2O3 can lower the solvent melting point compared to PbO or Bi2O3 alone. Therefore, both the raw material dissolution temperature and the β-Ga2O3 growth temperature are lower than when using a single solvent. This means that the amount of solvent evaporation can be reduced. According to this method, because the amount of solvent evaporation is suppressed, stable crystal growth with less composition variation is possible, and furnace material consumption is suppressed, eliminating the need for a closed-system growth furnace, thus enabling low-cost manufacturing. Furthermore, as mentioned above, the present invention is a liquid-phase growth method close to thermal equilibrium growth. Therefore, as shown in Table 1 above, the growth rate is fast at 13-30 μm / hr, the rocking curve full width at half maximum is narrow at 15-28 arcsecs, and it exhibits high crystallinity. On the other hand, Comparative Examples 1 and 2 did not dissolve unless heated to over 1000°C, and at temperatures above 1000°C the solvent evaporated, making it impossible to manufacture laminates.

[0033] (Example 9) Platinum crucible 7, with an inner diameter of 120 mm, a height of 150 mm, and a thickness of 1 mm, was loaded with 1022.3 g of PbO (99.999%), 4503.7 g of PbF2 (99%), and 476.2 g of β-Ga2O3 as raw materials. The mixing ratio of the solute Ga2O3 to the solvents PbO and PbF2 was solute:solvent = 10.0 mol%:90 mol%, and the mixing ratio of the solvents PbO and PbF2 was PbO:PbF2 = 20 mol%:80 mol%. Platinum crucible 7 containing the raw materials was placed in the LPE furnace shown in Figure 3, and the raw materials were melted at a crucible bottom temperature of approximately 940°C. After stirring the molten material with a platinum plate for 6 hours, the crucible bottom temperature was reduced to 840°C, and a β-Ga2O3 substrate with a C-plane orientation, 11 mm × 11 mm × 650 μm thickness, grown by the EFG method, was brought into contact with the molten material. The substrate was grown at the same temperature for 3 hours while rotating an alumina pulling shaft 5 at 60 rpm. During this time, the shaft rotation was reversed every 5 minutes. Subsequently, the pulling shaft 5 was pulled up to separate it from the molten material, and the molten components were separated by rotating the pulling shaft 5 at 200 rpm. After that, the material was cooled to room temperature to obtain a β-Ga2O3 / β-Ga2O3 laminate. Any remaining molten components were removed using nitric acid. The average thickness of the epitaxial layer was approximately 69 μm. The average growth rate was approximately 23 μm / hr.

[0034] (Examples 10-11, Comparative Example 3) A β-Ga2O3 / β-Ga2O3 laminate was obtained in the same manner as in Example 9, except that the initial composition was changed to match the composition shown in Table 2 below, and the raw material dissolution temperature and growth temperature were changed as described in Table 2.

[0035] [Table 2]

[0036] (Examples 12-13) A β-Ga2O3 / β-Ga2O3 laminate was obtained in the same manner as in Example 9, except that the preparation composition was changed to match the composition shown in Table 3 below, and the raw material dissolution temperature and growth temperature were changed as described in Table 3. If the concentration of the solute Ga2O3 falls below 2 mol%, it approaches the melting point of the solvent, resulting in solvent viscosity and making stable crystal growth difficult. Also, if the solute concentration exceeds 20 mol%, the growth temperature may rise. Therefore, a concentration of Ga2O3 as the solute is preferably between 2 and 20 mol%.

[0037] [Table 3]

[0038] As described above, a β-Ga2O3 / β-Ga2O3 laminate can be manufactured by mixing and dissolving the solute Ga2O3 with the solvents PbO and PbF2, and then directly contacting the resulting melt with a β-Ga2O3 substrate. As can be seen by comparing Examples 9-13 with Comparative Examples 1 and 3, mixing PbO and PbF2 can lower the solvent melting point compared to PbO or PbF2 alone. Therefore, both the raw material dissolution temperature and the β-Ga2O3 growth temperature are lower than when using a single solvent. This means that the amount of solvent evaporation can be reduced. According to this method, because the amount of solvent evaporation is suppressed, stable crystal growth with less composition variation is possible, and furnace material consumption is suppressed, eliminating the need for a closed-system growth furnace, thus enabling low-cost manufacturing. Furthermore, as mentioned above, the present invention is a liquid-phase growth method close to thermal equilibrium growth. Therefore, as shown in Tables 2 and 3 above, the growth rate is fast at 18-29 μm / hr, the rocking curve full width at half maximum is narrow at 35-77 arcsec, and it exhibits high crystallinity. On the other hand, Comparative Example 3 did not dissolve unless heated to over 1000°C, and the solvent evaporated at temperatures above 1000°C, making it impossible to manufacture a laminate.

[0039] As described above, in Examples 1 to 13, the full width at half maximum of the rocking curve of the (002) plane of the β-Ga2O3 epitaxial layer by the LPE method was 15 to 77 arcsecs, indicating extremely high crystallinity. [Explanation of Symbols]

[0040] 1. Top heater 2. Central heater 3. Lower heater 4 circuit boards 5. Lifting shaft (made of alumina) 6. Circuit board holder 7 Platinum Crucible 8. Melt in the crucible 9. Crucible stand (made of mullite) 10. Crucible bottom thermocouple 11. Core tube (made of mullite) 12. Furnace lid (made of mullite)

Claims

[Request 1] β-Ga ２ O ３ β-Ga on the substrate ２ O ３ β-Ga having a layer containing a single crystal ２ O ３ / β-Ga ２ O ３ A laminate, ２ O ３ The β-Ga layer has a rocking curve half width of 15 to 77 arcsec. ２ O ３ / β-Ga ２ O ３ Laminate.

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