METHOD FOR PRODUCING BETA-GA2O3/BETA-GA2O3 MULTILAYER BODY

Abstract

A method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body, wherein a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body is obtained by mixing and melting Ga.sub.2O.sub.3, which serves as a solute, and PbO and Bi.sub.2O.sub.3, which serve as solvents, and subsequently bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the thus-obtained melt, thereby growing a -Ga.sub.2O.sub.3 single crystal on the -Ga.sub.2O.sub.3 substrate by liquid-phase epitaxial growth.

Claims

1. A method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body, the method comprising mixing and melting Ga.sub.2O.sub.3 as a solute and PbO and Bi.sub.2O.sub.3 as solvents, then bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the resulting melt, and allowing a -Ga.sub.2O.sub.3 single crystal to grow on the -Ga.sub.2O.sub.3 substrate by a liquid-phase epitaxial growth method, thereby obtaining the -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body.

2. The method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to claim 1, wherein a mixing ratio of Ga.sub.2O.sub.3 as the solute and PbO and Bi.sub.2O.sub.3 as the solvents is solute: solvents=5-30 mol %: 95-70 mol %, and a mixing ratio of the solvents, PbO and Bi.sub.2O.sub.3, is PbO: Bi.sub.2O.sub.3=0.1-95 mol %: 99.9-5 mol %.

3. A method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body, the method comprising mixing and melting Ga.sub.2O.sub.3 as a solute and PbO and PbF.sub.2 as solvents, then bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the resulting melt, and allowing a -Ga.sub.2O.sub.3 single crystal to grow on the -Ga.sub.2O.sub.3 substrate by a liquid-phase epitaxial growth method, thereby obtaining the -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body.

4. The method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to claim 3, wherein a mixing ratio of Ga.sub.2O.sub.3 as the solute and PbO and PbF.sub.2 as the solvents is solute: solvents=2-20 mol %: 98-80 mol %, and a mixing ratio of the solvents, PbO and PbF.sub.2, is PbO:PbF.sub.2=2-80 mol %: 98-20 mol %.

5. The method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to claim 1, wherein the layer containing the -Ga.sub.2O.sub.3 single crystal formed by the liquid-phase epitaxial growth method comprises foreign elements in an amount of 0.01 mol % or more but 20 mol % or less.

6. The method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to claim 5, wherein the foreign 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.

7. A -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body comprising a layer containing a -Ga.sub.2O.sub.3 single crystal on a -Ga.sub.2O.sub.3 substrate, wherein a full width at half maximum of a rocking curve of the layer containing the -Ga.sub.2O.sub.3 single crystal is 5-100 arcsec.

8. The method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to claim 3, wherein the layer containing the -Ga.sub.2O.sub.3 single crystal formed by the liquid-phase epitaxial growth method comprises foreign elements in an amount of 0.01 mol % or more but 20 mol % or less.

9. The method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to claim 8, wherein the foreign 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.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 shows a phase diagram of PbOBi.sub.2O.sub.3.

[0018] FIG. 2 shows a phase diagram of PbOPbF.sub.2.

[0019] FIG. 3 shows a schematic diagram of one typical LPE growing furnace.

[0020] FIG. 4 shows a X-ray rocking curve of the (002) plane of the epitaxial layer of the multilayer body obtained in Example 1.

DESCRIPTION OF EMBODIMENTS

[0021] A first embodiment of the present invention is a method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body, the method comprising mixing and melting Ga.sub.2O.sub.3 as a solute and PbO and Bi.sub.2O.sub.3 as solvents, then bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the resulting melt, and allowing a -Ga.sub.2O.sub.3 single crystal to grow on the -Ga.sub.2O.sub.3 substrate by a liquid-phase epitaxial growth method, thereby obtaining the -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body.

[0022] Hereinafter, the principle of the first embodiment of the present invention will be described.

[0023] FIG. 1 shows a phase diagram of PbOBi.sub.2O.sub.3(Source: Temperature/combination phase diagram of the system Bi.sub.2O.sub.3PbO, J. Am. Chem. Soc., 64[3], 182-184, 1981). PbO and Bi.sub.2O.sub.3 form a eutectic system, and they can be mixed to lower the melting point. By mixing PbO and Bi.sub.2O.sub.3 to give the PbO concentration in the range of 0.1-95 mol %, the melting point of the PbO+Bi.sub.2O.sub.3 mixture can be reduced to be lower than or equal to the melting point of PbO alone or Bi.sub.2O.sub.3 alone. This indicates that the amount of vaporization of PbO or Bi.sub.2O.sub.3 in the above PbO concentration range can be suppressed compared to that of PbO or Bi.sub.2O.sub.3 alone.

[0024] The solvent composition is preferably PbO: Bi.sub.2O.sub.3=0.1-95 mol %: 99.9-5 mol %. More preferably, the solvent composition is PbO: Bi.sub.2O.sub.3=20-90 mol %: 80-10 mol %, and particularly preferably PbO: Bi.sub.2O.sub.3=50-80 mol %: 50-20 mol %. Since the LPE growth temperature (temperature at the time of epitaxial growth) is higher when PbO or Bi.sub.2O.sub.3 alone is used as the solvent, a mixed solvent such as the one mentioned above is favorable.

[0025] The mixing ratio of Ga.sub.2O.sub.3 as the solute and PbO and Bi.sub.2O.sub.3 as the solvents is preferably solute: solvents=5-30 mol %: 95-70 mol %. More preferably, the solute concentration is 14 mol % or more but 27 mol % or less. Solute concentrations lower than 5 mol % may result in a slow crystal growth rate while solute concentrations higher than 30 mol % may result in a high LPE growth temperature and increased solvent volatilization. It may also result in a faster crystal growth rate and poor crystal quality.

[0026] In the first embodiment of the present invention, the growth rate of the layer containing a -Ga.sub.2O.sub.3 single crystal (epitaxial layer) formed by the liquid-phase epitaxial growth method is preferably 10-50 m/hr, and more preferably 20-30 m/hr. Growth rates lower than 10 m/hr may result in a slow growth rate and increased cost. In addition, growth rates higher than 50 m may result in poor crystal quality. Here, the growth rate can be obtained from the difference in film thickness before and after LPE growth and the growth time.

[0027] Next, a second embodiment of the present invention is a method for producing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body, the method comprising mixing and melting Ga.sub.2O.sub.3 as a solute and PbO and PbF.sub.2 as solvents, then bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the resulting melt, and allowing a -Ga.sub.2O.sub.3 single crystal to grow on the -Ga.sub.2O.sub.3 substrate by a liquid-phase epitaxial growth method, thereby obtaining the -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body.

[0028] The principle of the second embodiment of the present invention will be described.

[0029] FIG. 2 shows a phase diagram of PbOPbF.sub.2 (Source: C. Sandonnini Atti, Accad. Naz. Licei, C1. Sci. Fis. Mat. Nat., 23[Ser.5, Pt.1], 962-964 (1914)). PbO and PbF.sub.2 form a eutectic system, and they can be mixed to lower the melting point. By mixing PbO with PbF.sub.2 to give the PbF.sub.2 concentration in the range of about 0.01-86 mol %, the melting point of the PbO+PbF.sub.2 mixture can be reduced to be lower than or equal to the melting point of PbO alone or PbF.sub.2 alone. This indicates that the amount of vaporization of PbO or PbF.sub.2 in the above PbO+PbF.sub.2 concentration range can be suppressed compared to that of PbO or PbF.sub.2 alone.

[0030] The solvent composition is preferably PbO:PbF.sub.2=2-80 mol %: 98-20 mol %. More preferably, the solvent composition is PbO:PbF.sub.2=20-80 mol %: 80-20 mol %, and particularly preferably PbO:PbF.sub.2=40-60 mol %: 60-40 mol %. Since the LPE growth temperature is higher when PbO or PbF.sub.2 alone is used as the solvent, a mixed solvent such as the one mentioned above is favorable.

[0031] The mixing ratio of Ga.sub.2O.sub.3 as the solute and PbO and PbF.sub.2 as the solvents is preferably solute: solvents=2-20 mol %: 98-80 mol %. More preferably, the solute concentration is 10 mol % or more but 20 mol % or less. Solute concentrations lower than 2 mol % may result in a slow growth rate while solute concentrations higher than 20 mol % may result in a high LPE growth temperature and increased solvent volatilization. It may also result in a faster crystal growth rate and poor crystal quality.

[0032] In the second embodiment of the present invention, the growth rate of the layer containing a -Ga.sub.2O.sub.3 single crystal (epitaxial layer) formed by the liquid-phase epitaxial growth method is preferably 10-50 m/hr, and more preferably 20-30 m/hr. Growth rates lower than 10 m/hr may result in a slow growth rate and increased cost. In addition, growth rates higher than 50 m may result in poor crystal quality. Here, the growth rate can be obtained from the difference in film thickness before and after LPE growth and the growth time.

[0033] In the first and second embodiments of the present invention, for the purposes of controlling the LPE growth temperature, adjusting the solvent viscosity, and doping foreign elements, one or more third components can be added to the solvent to the extent that the solubility of Ga.sub.2O.sub.3 and the amount of PbO+Bi.sub.2O.sub.3 or PbO+PbF.sub.2 vaporization are not significantly changed. Examples of the third component include B.sub.2O.sub.3, V.sub.2O.sub.5, P.sub.2O.sub.5, MoO.sub.3, and WO.sub.3. Bi.sub.2O.sub.3 may also be added as a third component to the solvent of the second embodiment.

[0034] The most preferred growth method for a -Ga.sub.2O.sub.3 multilayer body according to the present invention is a liquid-phase epitaxial growth method using a -Ga.sub.2O.sub.3 substrate.

[0035] In a -Ga.sub.2O.sub.3 multilayer body useful as a power device, the residual electron density in the epitaxial layer needs to be controlled. Ga in -Ga.sub.2O.sub.3 is a trivalent oxide and generally exhibits n-type conductivity. In the first and second embodiments of the present invention, the residual electron density, band gap, insulating property, etc. can be imparted by doping a foreign element into -Ga.sub.2O.sub.3. For example, doping divalent impurities MgO or ZnO into -Ga.sub.2O.sub.3 can reduce the residual electrons. On the other hand, the residual electron density can be increased by doping tetravalent impurities SiO.sub.2 or SnO.sub.2. In addition, Fe.sub.2O.sub.3 doping can provide an insulating property. Meanwhile, the band gap can be increased by doping MgO or Al.sub.2O.sub.3, which has a wider band gap than -Ga.sub.2O.sub.3, to obtain a mixed crystal. On the other hand, the band gap can be reduced by doping ZnO or CdO to obtain a mixed crystal.

[0036] A layer containing the -Ga.sub.2O.sub.3 single crystal formed by the liquid-phase epitaxial growth method contains, one or more foreign 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, preferably in the range of 0.01-20 mol %, more preferably in the range of 0.1-10 mol %. Doping amounts of foreign elements less than 0.01 mol % may result in poor properties, and doping amounts greater than 20 mol % may cause difficulties in crystal growth.

[0037] FIG. 3 shows a schematic diagram of a typical LPE growing furnace. Inside the LPE growing furnace, a platinum crucible 7, in which raw materials are melted and stored as a melt 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) that heat and melt the raw materials in the platinum crucible 7 are provided outside and to the side of the platinum crucible 7. The heater outputs are independently controlled, and the amount of heat applied to the melt 8 is independently adjusted. A mullite furnace core tube 11 is placed between the heaters and the inner wall of the production furnace, and a mullite furnace lid 12 is placed above the furnace core tube 11. A pull-up mechanism is provided above the platinum crucible 7. An alumina growing shaft 5 is secured to the pull-up mechanism, and a substrate holder 6 and a substrate 4 secured by the holder are provided at one end of the shaft. A mechanism for rotating the shaft is provided at the top of the growing shaft 5. In addition, a thermocouple 10 is provided at the bottom of the crucible.

[0038] A third embodiment of the present invention is a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body having a layer containing a -Ga.sub.2O.sub.3 single crystal on a -Ga.sub.2O.sub.3 substrate, wherein the full width at half maximum of the rocking curve of the layer containing the -Ga.sub.2O.sub.3 single crystal is 5-100 arcsec.

[0039] The above-described -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body of the present invention can favorably be produced by the first and second embodiments of the present invention described above.

[0040] According to the present invention, the full width at half maximum of the rocking curve of the layer containing the -Ga.sub.2O.sub.3 single crystal is 5-100 arcsec, preferably 5-80 arcsec, and more preferably 5-50 arcsec. The full width at half maximum above 100 arcsec may result in low crystallinity and performance of the power device may be degraded. The -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body of the present invention is characterized by its high crystallinity. In the present invention, the method described in the examples described below can be adopted as the method for measuring a full width at half maximum of a rocking curve.

EXAMPLES

[0041] Hereinafter, a method of depositing a -Ga.sub.2O.sub.3 epitaxial layer on a -Ga.sub.2O.sub.3 substrate will be described as a method for growing a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body according to one embodiment of the present invention. The present invention should not be limited in any way to the following examples.

[0042] Hereinafter, an exemplary production method of the present invention will be described with reference to FIG. 3.

[0043] A platinum crucible 7, in which raw materials are melted and stored as a melt 8, is placed on a crucible stand 9. Three-stage side heaters (upper heater 1, middle heater 2, and lower heater 3) that heat and melt the raw materials in the platinum crucible 7 are provided outside and to the side of the platinum crucible 7. The heater outputs are independently controlled, and the amount of heat applied to the melt 8 is independently adjusted. A furnace core tube 11 is placed between the heaters and the inner wall of the production furnace, and a furnace lid 12 is placed above the furnace core tube 11. A pull-up mechanism is provided above the platinum crucible 7. An alumina growing shaft 5 is secured to the pull-up mechanism, and a substrate holder 6 and a substrate 4 (-Ga.sub.2O.sub.3 substrate) secured by the holder are provided at one end of the shaft. A mechanism for rotating the shaft is provided at the top of the growing shaft 5. In addition, a thermocouple 10 is provided at the bottom of the crucible.

[0044] In order to melt the raw materials in the platinum crucible 7, the production furnace is heated until the raw materials are melted. Preferably, the temperature is raised to 600-1000 C., more preferably to 700-900 C., and the raw material melt is allowed to stand for 2-3 hours to homogenize. Instead of leaving it stationary, a platinum plate attached to one end of the alumina shaft can be immersed in the melt to stir and homogenize the melt by rotating the shaft. It is desirable to allow a -Ga.sub.2O.sub.3 single-crystal layer to grow only directly below the substrate. If the growth of the -Ga.sub.2O.sub.3 single crystal occurs in the melt where it is not directly below the substrate, the grown single crystal will adhere to the substrate by convection currents in the melt, resulting in phases with different growth orientations, which is undesirable. Therefore, a temperature gradient is applied to the three-stage heaters so that the temperature of the crucible bottom is a few degrees higher than that of the melt surface. After the temperature of the melt has stabilized, a seed crystal substrate is brought into contact with the melt surface. After the seed crystal substrate comes into uniform contact with the melt, the temperature is kept constant, or the temperature is lowered at a rate of 0.025-5 C./hr, to allow a -Ga.sub.2O.sub.3 single-crystal layer of interest to grow on the surface of the seed crystal substrate. During the growth, the seed crystal substrate is rotated at 5-300 rpm by the rotation of the growing shaft, and the rotation direction is reversed at regular intervals. After allowing a crystal to grow for about 30 minutes to 24 hours, the growing shaft is lifted to separate the grown crystal from the melt, and the melt attached to the surface of the grown crystal is removed by rotating the growing shaft at 50 to 300 rpm. The temperature is then allowed to cool to room temperature over a period of 1-24 hours to obtain the desired -Ga.sub.2O.sub.3/.sub.2O.sub.3 multilayer body.

Example 1

[0045] A platinum crucible 7 with inner diameter of 120 mm, height of 150 mm, and thickness of 1 mm was filled with 2661.2 g of PbO (purity: 99.999%), 2777.7 g of Bi.sub.2O.sub.3 (purity: 99.999%), and 561.2 g of Ga.sub.2O.sub.3 (purity: 99.999%) as raw materials. The mixing ratio of Ga.sub.2O.sub.3 as the solute to PbO and Bi.sub.2O.sub.3 as the solvents was solute: solvents=14.3 mol %: 85.7 mol %, and the mixing ratio of the solvents, PbO and Bi.sub.2O.sub.3, was PbO: Bi.sub.2O.sub.3-67 mol %: 33 mol %. The platinum crucible 7 fed with the raw materials was placed in a LPE furnace shown in FIG. 3, and the temperature at the bottom of the crucible was set at about 850 C. to melt the raw materials. After stirring the melt using a platinum plate for 6 hours, the temperature was lowered until the temperature at the bottom of the crucible reached 750 C., and a 11 mm11 mm650 m thick, C-plane oriented -Ga.sub.2O.sub.3 substrate grown by the EFG method was brought into contact with it. Growth was allowed to continue for 3 hours at the same temperature while rotating the growing shaft 5 made of alumina at 60 rpm. The rotation direction was reversed every 5 minutes. Thereafter, the substrate was separated from the melt by pulling up the growing shaft 5 and the melt components were removed by rotating the growing shaft 5 at 200 rpm. The temperature was then allowed to cool to room temperature to obtain a -Ga.sub.2O.sub.3/.sub.2O.sub.3 multilayer body. Melt components that could not be removed completely were removed using hydrochloric acid. The average thickness of the epitaxial layer was about 90 m. The average growth rate was about 30 m/hr.

Comparative Examples 1-2

[0046] Attempts were made to produce -Ga.sub.2O.sub.3/.sub.2O.sub.3 multilayer bodies in the same manner as in Example 1 except that the composition of the feed was changed to give the composition shown in Table 1 below, and the temperature at which the raw materials were melted, and the growth temperature were changed as shown in Table 1.

[0047] Here, the crystallinity of the epitaxial layer of the -Ga.sub.2O.sub.3/.sub.2O.sub.3 multilayer body obtained in Example 1 was evaluated by the full width at half maximum of the rocking curve of the (002) plane. The result is shown in FIG. 4. The full width at half maximum of the rocking curve of the (002) plane was 0.0042 deg (=15 arcsec). The full width at half maximum of the rocking curve was measured using an X-ray diffractometer (X'pert MRD from Spectris plc). Using the same apparatus, 2, , , and were adjusted for axis alignment that allows detection of the peak of the (002) plane of -Ga.sub.2O.sub.3, 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 Ge(220) planes of four crystals. Other measurement conditions were as follows. [0048] Light source; Cu-Ku [0049] Wavelength; 0.15418 nm [0050] Measurement mode; -scan (incident angle scan) [0051] range; Angle at which the -Ga.sub.2O.sub.3 (002) plane appears was set for each sample [0052] range; 0.1 deg [0053] step; 0.0005 deg [0054] 2 position; Angle at which the -Ga.sub.2O.sub.3 (002) plane appears was set for each sample [0055] Collimator diameter; 0.5 mm [0056] Anti-scattering slit; 1.5 mm

Examples 2-8

[0057] -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer bodies were obtained in the same manner as in Example 1 except that the composition of the feed was changed to give the composition shown in Table 1 below, and the temperature at which the raw materials were melted and the growth temperature were changed as shown in Table 1. The epitaxial layer obtained in Example 2 was a mixed layer of -Ga.sub.2O.sub.3 and MgO, and the epitaxial layer obtained in Example 5 was a mixed layer of -Ga.sub.2O.sub.3 and Al.sub.2O.sub.3.

TABLE-US-00001 TABLE 1 Temperature Full width Amount of at which at half Amount of Amount of foreign Amount raw LPE maximum Components in solvent solute foreign element of materials growth Growth of rocking PbO Bi.sub.2O.sub.3 Ga.sub.2O.sub.3 element MgO Al.sub.2O.sub.3 solvent were melted temperature rate curve (mol %) (mol %) (mol %) (mol %) (mol %) (mol %) ( C.) ( C.) (m/hr) (arcsec) Example 1 67 33 14.3 0 0 85.7 850 750 30 15 Example 2 67 33 11.4 2.9 0 85.7 840 740 25 23 Example 3 67 33 19.8 0 0 80.2 980 818 13 15 Example 4 67 33 21 0 0 79 980 850 13 16 Example 5 67 33 14.3 0 2.9 82.8 980 760 25 28 Example 6 80 20 19.8 0 0 80.2 980 780 15 Example 7 80 20 25 0 0 75 980 910 15 25 Example 8 33 67 19.8 0 0 80.2 980 850 15 Comparative example 1 100 0 14.3 0 0 85.7 1,090 990 Comparative example 2 0 100 14.3 0 0 85.7 1,030 930

[0058] As described above, a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body can be produced by mixing and melting Ga.sub.2O.sub.3 as a solute and PbO and Bi.sub.2O.sub.3 as solvents, then bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the resulting melt. As can be appreciated by comparing Examples 1-8 with Comparative examples 1-2, the melting point of the solvent can be lowered by mixing PbO and Bi.sub.2O.sub.3 compared to PbO or Bi.sub.2O.sub.3 alone. Therefore, both the temperature at which the raw materials were melted and the growth temperature of -Ga.sub.2O.sub.3 were lower than those in the case of using a single solvent. This means that the amount of vaporization of the solvent components can be reduced. According to this method, since evaporation of the solvent is suppressed, stable crystal growth with minimal composition fluctuation can be achieved. Moreover, the consumption of furnace materials is reduced, and it is not necessary for the growth furnace to be a closed system, thereby enabling manufacturing at a lower cost. In addition, as mentioned above, the present invention is a liquid-phase growth method that is close to thermal equilibrium growth. Therefore, as shown in Table 1 above, the growth rate was as fast as 13-30 m/hr, and the full width at half maximum of the rocking curve was as narrow as 15-28 arcsec, showing high crystallinity. On the other hand, in Comparative examples 1-2, multilayer bodies were not produced because the raw materials did not melt unless the heat applied was higher than 1000 C. and the solvent volatilized at a temperature higher than 1000 C.

Example 9

[0059] A platinum crucible 7 with an inner diameter of 120 mm, a height of 150 mm, and a thickness of 1 mm was filled with 1022.3 g of PbO (purity: 99.999%), 4503.7 g of PbF.sub.2 (99%), and 476.2 g of -Ga.sub.2O.sub.3 as raw materials. The mixing ratio of Ga.sub.2O.sub.3 as the solute to PbO and PbF.sub.2 as the solvents was solute: solvents=10.0 mol %: 90 mol %, and the mixing ratio of the solvents, PbO and PbF.sub.2, was PbO:PbF.sub.2=20 mol %: 80 mol %. The platinum crucible 7 fed with the raw materials was placed in a LPE furnace shown in FIG. 3, and the temperature at the bottom of the crucible was set at about 940 C. to melt the raw materials. After stirring the melt using a platinum plate for 6 hours, the temperature was lowered until the temperature at the bottom of the crucible reached 840 C., and a 11 mm11 mm650 m thick, C-plane oriented -Ga.sub.2O.sub.3 substrate grown by the EFG method was brought into contact with it. Growth was allowed to continue for 3 hours at the same temperature while rotating a growing shaft 5 made of alumina at 60 rpm. The shaft rotation was reversed every 5 minutes. Thereafter, the substrate was separated from the melt by pulling up the growing shaft 5 and the melt components were removed by rotating the growing shaft 5 at 200 rpm. The temperature was then allowed to cool to room temperature to obtain a -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer body. Melt components that could not be removed completely were removed using nitric acid. The average thickness of the epitaxial layer was about 69 m. The average growth rate was about 23 m/hr.

Examples 10-11, Comparative Example 3

[0060] -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer bodies were obtained in the same manner as in Example 9 except that the composition of the feed was changed to give the composition shown in Table 2 below, and the temperature at which the raw materials were melted and the growth temperature were changed as shown in Table 2.

TABLE-US-00002 TABLE 2 Temperature Full width at which at half Amount of Amount raw LPE maximum Components in solvent solute of materials growth Growth of rocking PbO PbF.sub.2 Ga.sub.2O.sub.3 solvent were melted temperature rate curve (mol %) (mol %) (mol %) (mol %) ( C.) ( C.) (m/hr) (arcsec) Example 9 20 80 10 90 940 840 23 39 Example 10 54 46 10 90 700 600 25 35 Example 11 80 20 10 90 950 850 18 43 Comparative 0 100 10 90 1,030 930 example 3

Examples 12-13

[0061] -Ga.sub.2O.sub.3/-Ga.sub.2O.sub.3 multilayer bodies were obtained in the same manner as in Example 9 except that the composition of the feed was changed to give the composition shown in Table 3 below, and the temperature at which the raw materials were melted and the growth temperature were changed as shown in Table 3. If the concentration of Ga.sub.2O.sub.3 as the solute is lower than 2 mol %, the melting point becomes closer to the melting point of the solvent, and stable crystal growth may be difficult due to the viscosity of the solvent. Moreover, a solute concentration higher than 20 mol % may result in a high growth temperature. Therefore, the concentration of Ga.sub.2O.sub.3 as the solute is preferably 2-20 mol %.

TABLE-US-00003 TABLE 3 Temperature Full width at which at half Amount of Amount raw LPE maximum Components in solvent solute of materials growth Growth of rocking PbO PbF.sub.2 Ga.sub.2O.sub.3 solvent were melted temperature rate curve (mol %) (mol %) (mol %) (mol %) ( C.) ( C.) (m/hr) (arcsec) Example 12 54 46 2 98 680 580 20 77 Example 13 54 46 20 80 930 830 29 76

[0062] As described above, a -Ga.sub.2O.sub.3/.sub.2O.sub.3 multilayer body can be produced by mixing and melting Ga.sub.2O.sub.3 as a solute and PbO and PbF.sub.2 as solvents, then bringing a -Ga.sub.2O.sub.3 substrate into direct contact with the resulting melt. As can be appreciated by comparing Examples 9-13 with Comparative examples 1 and 3, the melting point of the solvent can be lowered by mixing PbO and PbF.sub.2 compared to PbO or PbF.sub.2 alone. Therefore, both the temperature at which the raw materials were melted and the growth temperature of -Ga.sub.2O.sub.3 were lower than those in the case of using a single solvent. This means that the amount of vaporization of the solvent components can be reduced. According to this method, since the amount of evaporation of the solvent is suppressed, stable crystal growth with minimal composition fluctuation can be achieved. Moreover, the consumption of furnace materials is reduced, and it is not necessary for the growth furnace to be a closed system, thereby enabling manufacturing at a lower cost. In addition, as mentioned above, the present invention is a liquid-phase growth method that is close to thermal equilibrium growth. Therefore, as shown in Tables 2 and 3 above, the growth rate was as fast as 18-29 m/hr, and the full width at half maximum of the rocking curve was as narrow as 35-77 arcsec, showing high crystallinity. On the other hand, in Comparative example 3, a multilayer body was not produced because the raw materials did not melt unless the heat applied was higher than 1000 C. and the solvent volatilized at a temperature higher than 1000 C.

[0063] As described above, in each of Examples 1-13, the full width at half maximum of the rocking curve of the (002) plane of the -Ga.sub.2O.sub.3 epitaxial layer obtained by the LPE method was 15-77 arcsec, showing extremely high crystalline.

REFERENCE SIGNS LIST

[0064] 1 Upper heater [0065] 2 Middle heater [0066] 3 Lower heater [0067] 4 Substrate [0068] 5 Growing shaft (made of alumina) [0069] 6 Substrate holder [0070] 7 Platinum crucible [0071] 8 Melt in crucible [0072] 9 Crucible stand (made of mullite) [0073] 10 Thermocouple at the bottom of crucible [0074] 11 Furnace core tube (made of mullite) [0075] 12 Furnace lid (made of mullite)