METHOD AND APPARATUS FOR PRODUCING ELECTRICALLY CONDUCTING BULK ß-GA2O3 SINGLE CRYSTALS AND ELECTRICALLY CONDUCTING BULK ß-GA2O3 SINGLE CRYSTAL

Abstract

Electrically conducting bulk -Ga.sub.2O.sub.3 single crystals can be produced by the Czochralski (CZ) method to have a pre-defined cylindrical diameter and a pre-defined cylindrical length. The method uses a growth furnace having a noble metal crucible with a Ga.sub.2O.sub.3 starting material. An inner thermal insulation is provided in the growth furnace with a radiative reflectivity lower than 0.4 in a near infrared spectral region of 1-3 m to decrease reflections of heat back to the growing single crystal, and thus, to increase the heat dissipation from the growing single crystal. Also, in the CZ method, when puling a single crystal from seeding to separation, a dynamic decrease of the growth rate is achieved from the initial growth rate of 1-10 mm/h, to a final growth rate of 0.2-1 mm/h, to dynamically decrease the latent heat of crystallization as the growth proceeds.

Claims

1. A method for producing electrically conducting bulk -Ga.sub.2O.sub.3 single crystals by the Czochralski method having a pre-defined cylindrical diameter and a pre-defined cylindrical length, the method comprising: (i) providing, to a growth chamber, a growth furnace comprising a noble metal crucible with a Ga.sub.2O.sub.3 starting material therein, a thermal insulation surrounding the crucible from all sides with a free space to accommodate a growing bulk -Ga.sub.2O.sub.3 single crystal, and an inductive radio frequency (RF) coil for heating up the crucible and control a melt temperature during crystal growth, wherein the RF coil is powered by an RF generator, while a growing crystal is fixed through a crystal seed, a seed holder, and a pulling rod to a translation and rotating mechanisms; (ii) providing, to the Ga.sub.2O.sub.3 starting material, a dopant forming a shallow donor in the Ga.sub.2O.sub.3 single crystal; (iii) providing, to the growth chamber and thus to the growth furnace, a growth atmosphere containing oxygen mixed with at least one non-reducing gas; (iv) heating up the crucible with the Ga.sub.2O.sub.3 starting material by the RF coil and subsequently melting the Ga.sub.2O.sub.3 starting material; (v) dipping the oriented crystal seed into the molten starting material; (vi) pulling the crystal seed up with the translation rate to achieve a predefined growth rate while rotating at a rotation rate; (vii) while pulling, expanding the seed diameter to a final cylindrical diameter of the single crystal; (viii) pulling the single crystal with the cylindrical diameter to the predefined cylindrical length; (ix) separating the single crystal from the melt, and (x) cooling the growth furnace with the grown single crystal down to room temperature, wherein: the step (i) additionally comprises providing, to the growth furnace, an inner thermal insulation of a radiative reflectivity lower than 0.4 in a near infrared spectral region of 1-3 m to decrease reflections of heat back to the growing single crystal, and thus, to increase the heat dissipation from the growing single crystal; and the steps (vi), (vii), and (viii) of puling the single crystal from seeding to separation further comprise a dynamic decrease of the growth rate from the initial growth rate of 1-10 mm/h at the beginning of the growth to a final growth rate of 0.2-1 mm/h at the end of the growth when the single crystal had achieved the predefined cylindrical length, to dynamically decrease the latent heat of crystallization as the growth proceeds and the amount of the heat to be dissipated from the growing single crystal.

2. The method according to claim 1, wherein the inner thermal insulation with the radiative reflectivity lower than 0.4 has a emissivity in the near infrared spectral region of above 0.3 at room temperature.

3. The method according to claim 1, wherein the inner thermal insulation with the radiative reflectivity lower than 0.4 has a transmissivity in the near infrared spectral region of above 0.3 at room temperature.

4. The method according to claim 1, wherein the growth rate decreases from the initial growth rate to the final growth rate linearly.

5. The method according to claim 1, wherein the growth rate decreases from the initial growth rate to the final growth rate non-linearly.

6. The method according to claim 1, wherein the growth rate decreases from the initial growth rate to the final growth rate at different rates.

7. The method according to claim 1, wherein the growth rate decreases from the initial growth rate to the final growth rate continuously.

8. The method according to claim 1, wherein the growth rate decreases from the initial growth rate to the final growth rate in blocks combining constant and decreasing growth rates.

9. The method according to claim 1, wherein the step of providing the growth atmosphere comprises providing, in addition to oxygen, He in a concentration of 10-95 vol. %.

10. An electrically conducting bulk -Ga.sub.2O.sub.3 single crystal comprising: a cylindrical diameter larger than one inch, a cylindrical length larger than 25 mm, a free electron concentration of 1-1010.sup.18 cm.sup.3, measured by Hall effect, an electron mobility of more than 50 and less than 120 cm.sup.2V.sup.1s.sup.1, measured by Hall effect, and a resistivity of more than 0.01 and less than 0.04 cm.

11. The bulk -Ga.sub.2O.sub.3 single crystal according to claim 10, wherein its cylindrical diameter is two inches or larger.

12. The bulk -Ga.sub.2O.sub.3 single crystal according to claim 10, wherein the dopants forming shallow donors are Si and/or Sn.

13. An apparatus for producing electrically conducting bulk -Ga.sub.2O.sub.3 single crystals by the Czochralski method having a pre-defined cylindrical diameter and a pre-defined cylindrical length, the apparatus comprising: (i) a growth chamber, (ii) a growth furnace comprising a noble metal crucible with a Ga.sub.2O.sub.3 starting material therein, a thermal insulation surrounding the crucible from all sides with a free space to accommodate a growing bulk -Ga.sub.2O.sub.3 single crystal, and an inductive radio frequency (RF) coil configured to heat up the crucible and to control a melt temperature during crystal growth: (iii) an RF generator configured to power the RF coil; (iv) translation and rotation mechanisms coupled with a crystal seed through a seed holder, and a pulling rod; and (v) a scale connected with the pulling rod or the growth furnace for monitoring growth rate of the bulk -Ga.sub.2O.sub.3 single crystal, wherein: the growth furnace further comprises an inner thermal insulation of low radiative reflectivity in the near infrared spectral region of 1-3 m that decreases reflections of heat back to the growing single crystal and thus increases the heat dissipation from the growing single crystal.

14. The apparatus according to claim 13, wherein the inner thermal insulation with low radiative reflectivity has high emissivity in the near infrared spectral region, above 0.3 at room temperature.

15. The apparatus according to claim 13, wherein the inner thermal insulation with low radiative reflectivity is selected from the group consisting of opaque alumina, zirconia, magnesia, and yttria.

16. The apparatus according to claim 13, wherein the inner thermal insulation with low radiative reflectivity has high transmissivity in the near infrared spectral region, above 0.3 at room temperature.

17. The apparatus according to claim 13, wherein the inner thermal insulation with low radiative reflectivity is transparent ceramic selected from the group consisting of alumina, yttria, and yttrium aluminum garnet.

18. The apparatus according to claim 13, wherein the inner thermal insulation with low radiative reflectivity is a crystalline sapphire.

19. The apparatus according to claim 13, wherein the growth atmosphere contains, in addition to oxygen, a non-reducing gas of high thermal conductivity, preferably He in a concentration of 5-95 vol. %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:

[0015] FIG. 1 is a schematic growth furnace for oxide single crystals grown by the Czochralski method in a cross-sectional view;

[0016] FIG. 2 shows different profiles of growth rates of bulk -Ga.sub.2O.sub.3 single crystals grown by the Czochralski method; and

[0017] FIG. 3 shows a real growth rate profile outputted from a growth run of bulk -Ga.sub.2O.sub.3 single crystal grown by the Czochralski method.

DETAILED DESCRIPTION

[0018] Aspects of the present disclosure provide conditions for producing bulk -Ga.sub.2O.sub.3 single crystals from the melt, especially by the Czochralski method, which will ensure the grow the crystals of high electrical conductivity, large size, and high structural quality.

[0019] Another aspect of the present disclosure provides bulk -Ga.sub.2O.sub.3 single crystals of high electrical conductivity and large size, preferably of at least 2 inch diameter and over one inch long.

[0020] Yet another aspect of the present disclosure provides an apparatus for producing -Ga.sub.2O.sub.3 single crystals from the melt, especially by the Czochralski method, which will enable to carry out the said method and thus to grow the crystals of high electrical conductivity, large size, and high structural quality.

[0021] A further aspect of the present disclosure provides a method and apparatus for producing different oxide compounds by the Czochralski method, which have high melting points (above 1400 C.) and show strong absorption in the near infrared spectral region.

[0022] According to an aspect of the present disclosure, a method for producing electrically conducting bulk -Ga.sub.2O.sub.3 single crystals by the Czochralski method is provided that comprises the step of providing, to a growth chamber, a growth furnace comprising a noble metal crucible with a Ga.sub.2O.sub.3 starting material therein, a thermal insulation surrounding the crucible from all sides with a free space to accommodate a growing bulk -Ga.sub.2O.sub.3 single crystal, and an inductive RF coil for heating up the crucible and control the melt temperature during crystal growth, wherein the RF coil is powered by an RF generator, while the growing crystal is fixed through a crystal seed, seed holder, and a pulling rod to a translation and rotating mechanisms. The method further comprises the step of providing, to the Ga.sub.2O.sub.3 starting material, a dopant forming a shallow donor in the Ga.sub.2O.sub.3 single crystal, as well as the step of providing to the growth chamber and thus to the growth furnace a growth atmosphere containing oxygen mixed with at least one non-reducing gas. Next the crucible with the Ga.sub.2O.sub.3 starting material is heated-up by the RF coil until melting the Ga.sub.2O.sub.3 starting material. After melting the Ga.sub.2O.sub.3 starting material, the oriented crystal seed is dipped into the molten starting material, which is than pulled up with a translation rate to achieve a predefined growth rate while rotating at a predefined rotation rate. During initial puling, the seed diameter is expanded to a final cylindrical diameter, which is pulled to a predefined cylindrical length. Once the predefined cylindrical length is achieved, the single crystal is separated from the melt and cooled down, together with the growth furnace, to room temperature.

[0023] An aspect of the present disclosure provides to the growth furnace an inner thermal insulation of low radiative reflectivity in the near infrared spectral region of 1-3 m to decrease reflections of heat back to the growing single crystal and thus to increase the heat dissipation from the growing single crystal. This is combined with a dynamic decrease of the growth rate from the beginning of pulling up the crystal seed to crystal separation. The growth rate decreases from the initial growth rate of 1-10 mm/h at the beginning of the growth to a final growth rate of 0.2-1 mm/h at the end of the growth when the single crystal had achieved the predefined cylindrical length. This solution dynamically decreases the latent heat of crystallization as the growth proceeds and the amount of the heat to be dissipated from the growing single crystal.

[0024] Preferably, the inner thermal insulation with low radiative reflectivity has high emissivity or high reflectivity in the near infrared spectral region, above 0.3 at room temperature.

[0025] The growth rate may decrease from the initial growth rate to the final growth rate either linearly or non-linearly.

[0026] In a preferred embodiment, the growth rate decreases from the initial growth rate to the final growth rate at different rates.

[0027] In another preferred embodiment, the growth rate may decrease from the initial growth rate to the final growth rate continuously or in blocks combining constant and decreasing growth rates.

[0028] Advantageously, the growth atmosphere comprises, in addition to oxygen, a non-reducing gas of high thermal conductivity, preferably He in a concentration of 10-95 vol. % to further enhance heat dissipation from the growing crystal via gas convection.

[0029] According to an aspect of the present disclosure, an electrically conducting bulk -Ga.sub.2O.sub.3 single crystal grown by the Czochralski method is provided according to the above-described method. The -Ga.sub.2O.sub.3 single crystal has the cylindrical diameter larger than one inch, cylindrical length larger than 25 mm, and the following electrical properties formed by shallow donors according to Hall effect measurements: free electron concentration of 1-1010.sup.18 cm.sup.3, electron mobility of 50-120 cm.sup.2V.sup.1s.sup.1, and the resistivity of 0.01-0.04 cm.

[0030] In a preferred embodiment of the present disclosure, the -Ga.sub.2O.sub.3 single crystal has the cylindrical diameter of two inch or larger.

[0031] Advantageously, the dopants forming shallow donors are Si and/or Sn.

[0032] According to an aspect of the present disclosure, an apparatus is provided for producing electrically conducting bulk -Ga.sub.2O.sub.3 single crystals by the Czochralski method having a pre-defined cylindrical diameter and cylindrical length. The apparatus comprises a growth chamber and a growth furnace comprising a noble metal crucible with a Ga.sub.2O.sub.3 starting material therein, a thermal insulation surrounding the crucible from all sides with a free space to accommodate a growing bulk -Ga.sub.2O.sub.3 single crystal, and an inductive RF coil for heating up the crucible and control the melt temperature during crystal growth. The apparatus further comprises an RF generator powering the RF coil, translation and rotation mechanisms coupled with a crystal seed through a seed holder, and a pulling rod, as well as a scale connected with the pulling rod or the growth furnace for monitoring growth rate of the bulk -Ga.sub.2O.sub.3 single crystal.

[0033] According to the present disclosure, the growth furnace further comprises an inner thermal insulation of low radiative reflectivity in the near infrared spectral region of 1-3 m that decreases reflections of heat back to the growing single crystal and thus increases the heat dissipation from the growing single crystal.

[0034] Advantageously, the inner thermal insulation with low radiative reflectivity has high emissivity in the near infrared spectral region, above 0.3 at room temperature. Here, the inner thermal insulation is preferably selected from the group consisting of opaque alumina, zirconia, magnesia, and yttria.

[0035] In another advantageous solution of the present disclosure, the inner thermal insulation with low radiative reflectivity has high transmissivity in the near infrared spectral region, above 0.3 at room temperature. This is preferably met by transparent ceramic selected from the group consisting of alumina, yttria, and yttrium aluminum garnet, or by a crystalline sapphire.

[0036] In a preferred embodiment of the apparatus, the growth atmosphere contains, in addition to oxygen, a non-reducing gas of high thermal conductivity, most preferably He in a concentration of 5-95 vol. % to further enhance heat dissipation from the growing crystal via gas convection

[0037] More advantages and other features of the inventive method and apparatus for growing bulk -Ga.sub.2O.sub.3 single crystals or other oxide crystals revealing high absorption in the near infrared spectral region will be apparent from the detailed description of the embodiments in reference to the drawings.

DETAILED DESCRIPTION

[0038] The growth furnace 1 shown in FIG. 1 is adapted for growing bulk oxide single crystals by the Czochralski method in general, and in particular for growing bulk -Ga.sub.2O.sub.3 single crystals by the Czochralski method. The growth furnace 1 is accommodated within a water-cooled growth chamber to which a pre-defined growth atmosphere 2 is introduced. The furnace 1 consists of a noble metal crucible 3 containing a Ga.sub.2O.sub.3 starting material 4, preferably with a lid 5 thereon, and a thermal insulation 6 surrounding the crucible from all sides. Above the crucible there is a free space (growth zone) that accommodates a growing bulk -Ga.sub.2O.sub.3 single crystal 7. The growth furnace 1 further includes an inner thermal insulation 8 of defined optical properties, as explained further below. The noble metal crucible 5 is inductively heated by an RF coil 9 situated outside the thermal insulation 6 and powered by a RF generator. The bulk -Ga.sub.2O.sub.3 single crystal 7 is grown on a crystallographically oriented -Ga.sub.2O.sub.3 crystal seed 10 that is fixed to a seed holder 11 connected to a pulling rod 12. The pulling rod 12 is connected to a pulling and rotation mechanisms for translating TR and rotating R the growing -Ga.sub.2O.sub.3 single crystal 7, and to a scale for weighting the growing -Ga.sub.2O.sub.3 single crystal 7. Alternatively, the scale is coupled with the growth furnace 1. In each case, the scale indicates the growth rate of the growing single crystal 7 by weighting directly the crystal mass or a mass difference between the furnace and the growing crystal 7. A signal from the scale is coupled with a controller that controls the generator power, and thus the melt temperature.

[0039] The thermal insulation 6 is a refractory material that withstands high temperatures, depending on the melting point of an oxide crystal to be grown. The melting point of Ga.sub.2O.sub.3 is about 1800 C. The thermal insulation 6 typically includes alumina or zirconia tubes, granules, felts, as well as quartz tubes on outer parts of the growth furnace 1. The aim of the thermal insulation 6 is to decrease heat losses and establish pre-defined temperature gradients in the crucible and in the growth zone to minimize thermal stresses and associated structural and point defects in the growing crystal 7. In particular, for growing bulk -Ga.sub.2O.sub.3 single crystals low temperature gradients are required and thus as good thermal insulation as possible. This is the result and melt chemistry (decomposition) and monoclinic system of -Ga.sub.2O.sub.3 having anisotropic mechanical, thermal, and optical properties.

[0040] The noble metal crucible 3 for -Ga.sub.2O.sub.3 crystals is iridium and its alloys, like iridium-platinum alloy. Also, other crucible materials can be considered, like platinum-rhodium alloy, which is described by Hoshikawa et al. (described above) for the Bridgman method.

[0041] The growth atmosphere 2 for growing the -Ga.sub.2O.sub.3 single crystal 7, in particular of large diameter, larger than 1 inch, contains oxygen, preferably at least 5 vol. %, and at least one another non-reducing gas, like Ar, N.sub.2, CO.sub.2, He, Xe, and Ne, as described in the U.S. Pat. No. 11,028,501 B2 to Galazka et al., incorporated here as a reference.

[0042] For the Czochralski method the -Ga.sub.2O.sub.3 crystal seed 10 is crystalographically oriented along the [010] direction, parallel to both easy (100) and (001) cleavage planes that are

[0043] present in the monoclinic system of -Ga.sub.2O.sub.3. Other seed orientations inclined to the [010] direction, e.g. [110], can be used as well.

[0044] A crystal growth process is as follows. After assembling the growth furnace 1, the noble metal crucible 3 with the starting material 4 is heated up by the RF coil 9 until melting the Ga.sub.2O.sub.3 starting material 4. Once the Ga.sub.2O.sub.3 melt is thermally stabilized, the oriented -Ga.sub.2O.sub.3 crystal seed 10 is dipped into the Ga.sub.2O.sub.3 melt while rotating at the rotation rate R. Next the oriented -Ga.sub.2O.sub.3 crystal seed 10 is pulled upwards at the translation rate TR with expanding its diameter to a predefined cylindrical diameter D, by a gradual decrease of the melt temperature via the RF generator. When the crystal achieves a pre-defined cylindrical length L, it is separated from the melt, slowly cooled down to room temperature, and removed from the growth furnace 1.

[0045] The problem of growing electrically conducting (normally or degenerately semiconducting) bulk -Ga.sub.2O.sub.3 single crystals by the Czochralski method as long straight cylinders arises from intrinsic properties of that compound, i.e. from the absorption of the heat transported through the growing crystal by free carriers. The heat, that must be dissipated away from the crystal is generated at the growth interface during liquid-solid phase transition. The interface is convex towards the melt (i.e. a conical portion of the crystal is immersed in the melt) and assures a stable growth. The heat absorbed by the free carriers increases temperature of the crystal near the growth interface and at certain crystal length the heat cannot be easily dissipated away. Once the temperature in the crystal reaches the melting point of Ga.sub.2O.sub.3, a portion of the crystal immersed in the melt is melted back. This phenomenon is called an interface inversion. After that interface inversion the growth becomes unstable and the growth morphology changes from a straight cylinder to a corkscrew (spiral). Such crystal shape does not enable to prepare wafers of the diameter as expected from the straight cylinder, so the usable portion of the crystal for wafering is only that cylindrical part. The length of the cylindrical part of highly conducting -Ga.sub.2O.sub.3 crystal with the diameter larger than one inch is not longer than 25 mm. High electrical conductivity of a crystal -Ga.sub.2O.sub.3 crystal is understood as the free electron concentration exceeding a value of 10.sup.18 cm.sup.3.

[0046] To increase the length of the cylindrical part of a highly electrically conducting -Ga.sub.2O.sub.3 crystal of a diameter above 1 inch, grown by the Czochralski method, the following technical solutions were found to be effective: [0047] (i) a decrease of the heat amount reflected form the inner thermal insulation back to the growing -Ga.sub.2O.sub.3 single crystal: and/or [0048] (ii) a dynamic decrease of the latent heat of crystallization as the growth proceeds.

[0049] As shown in FIG. 1, the crystal surface dissipates and exchanges the heat with the surrounding in two ways: by a gas convection C, and by the radiation RA, the latter being much more effective. In the radiative heat exchange, the heat leaving the crystal surface in all directions is interacting with the metal crucible 3 and its lid 5 (if present), and with the inner thermal insulation 8, where it is partly reflected, partly absorbed, and partly transmitted therethrough. This can be described in the dimensionless measure as: THA=1=R+E+T, where THA is the total heat amount, R is the reflectivity, E is the emissivity, and T is the transmissivity. Therefore, the reflectivity can be described as: R=1ET. To minimize heat reflections from the inner thermal insulation 8, it should have either high emissivity E or high transmissivity T. These optical properties R, E, and T relate the near infrared (NIR) region in which the vast majority of heat is transported. Taking into accounts the melting point of Ga.sub.2O.sub.3 (1800 C.), the black body radiation at that temperature, and lower temperature of the growing crystal (assuming 1200 C. as the lowest), the NIR region is between 1-3 m. So, the requirements for the inner thermal insulation 8 is low reflectivity R in the 1-3 m spectral region, which can be achieved by high E or T values in that spectral region. The optical properties of materials strongly depend on the spectral region and temperature. For instance, the emissivity E changes in the NIR spectral region in a wide range, also at high temperatures, therefore, it is difficult to define precise values, however, smaller E values at some subregions of the discussed NIR region will not have a big impact on the overall heat exchange. In any case, the emissivity E should be larger than 0.3 in the NIR spectral region of 1-3 m when measured at room temperature. Suitable refractory materials for the inner thermal insulation 8 are: alumina, zirconia, yttria, and magnesia, preferably with a rough surface to enhance diffuse scattering.

[0050] Another solution is to increase transmissivity T of the inner thermal insulation 8. This can be achieved by thermal insulation transparent to the above-defined NIR spectral region. As the standard refractory materials are basically opaque to NIR, transparent ceramic or crystalline sapphire can be used. Both transparent ceramics, e.g. alumina and yttria, and crystalline sapphire in different shapes (tubes and lids) are available. To the transmissivity T the same considerations apply versus wavelength and temperature as in the case to the emissivity E. Also, in this case the transmissivity T should be larger than 0.3 in the NIR spectral region of 1-3 m when measured at room temperature.

[0051] Another, above-mentioned solution for more effective heat dissipation from the crystal is a dynamic decrease of the amount of heat generated during growth. This is done by a dynamic lowering the growth rate with the crystal length. It should be noted that the growth rate V combines the translation rate TR of the crystal and the melt drop, which is converted to solid.

[0052] FIG. 2 illustrates profiles of the growth rates V that enable to decrease the latent heat of crystallization in a dynamic way. Generally, at the beginning of the growth, i.e. during seeding, seed expansion (shoulder) and the beginning of the cylindrical part, the growth rate V1 can be relatively high, between 1 and 10 mm/h, as the amount of the generated heat is smaller (seeding, shoulder) or the crystal length is small enough to effectively dissipate the heat (early cylindrical part). Later, the growth rate decreases to a final value V2 of 0.2-1 mm/h to decrease the amount of the generated heat. The decrease of the growth rate V can be conducted from the beginning of the growth, as indicated by profiles P1, P2, P5, especially when the initial growth rate is high, or later, as indicated by profiles P3 and P4. It can be done linearly or non-linearly, as a continuous decrease, or in step-wise blocks indicated by crystal length segments L1, L2, L3, and L4. FIG. 3 shows an example of the growth rate from a real growth experiment, where initial V1=1.7 mm/h was constant at the beginning at the first block 0- L1, next decreased in a linear manner in blocks L1-L3 to a final value V2=0.7 mm/h, which was kept constant at the very last block L3-L4 of the crystal growth.

[0053] An additional tool for heat management is the use in the growth atmosphere 2 a non-reducing gas of high thermal conductivity, in particular He. This will enhance heat dissipation form the growing crystal 7 through gas convection C. Preferably, He in the growth atmosphere 2 is used in the combination with the decrease of the amount of the reflected heat back to the crystal, and with the decrease of the amount of the latent heat of crystallization. He concentration in the growth atmosphere, in addition to oxygen, is between 10-95 vol. %.

[0054] By using the above-discussed technical solutions it is possible to increase the cylindrical length L of highly electrically conducting bulk -Ga.sub.2O.sub.3 single crystals 7 grown by the Czochralski method, with the diameter larger than 1 inch. Bulk -Ga.sub.2O.sub.3 single crystals of diameter D=2 inch could be grown with the cylindrical length L exceeding 25 mm, between 25-50 mm. High electrical conductivity of bulk -Ga.sub.2O.sub.3 single crystals can be achieved by intentional doping with elements forming shallow donors in this material. The most effective dopants are Si and Sn, but also could be Nb, Zr, and Hf. To achieve high electrical conductivity, the Ga.sub.2O.sub.3 starting material 4 should be doped with SiO.sub.2 of 0.05-0.3 mol. %, while SnO.sub.2 of 0.5-4 mol. % due to high partial pressure of Sn-containing species. The dopants forming shallow donors can be used separately or in combination. The resulting electrical properties of bulk -Ga.sub.2O.sub.3 single crystals doped with Si and/or Sn at the above-mentioned concentrations, were as follows (from Hall effect measurements): free electron concentration of 1-1010.sup.18 cm.sup.3, the electron mobility=50-120 cm.sup.2V.sup.1s.sup.1, and the resistivity of 0.01-0.04 cm. 2 inch diameter bulk -Ga.sub.2O.sub.3 single crystals 7 with such electrical properties enable to fabricate 2 inch diameter, electrically conducting wafers suitable for homoepitaxy and next for power electronic device fabrication in the vertical configuration. In particular, such crystals enable to prepare large wafers with the (010) surface orientation, which shows the highest growth rate of homoepitaxial films by molecular beam epitaxy. Also, other wafer orientations can be prepared, such as (100) or (001), including offcuts by several degrees from those orientations. The bulk -Ga.sub.2O.sub.3 single crystals obtained by the above-described method and apparatus are of high structural quality, characterized by narrow rocking curves with the full width at half maximum typically below 30 arcsec, making the fabricated wafers suitable for homoepitaxial films of high quality.

[0055] While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.

[0056] The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article a or the in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of or should be interpreted as being inclusive, such that the recitation of A or B is not exclusive of A and B, unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of at least one of A, B and C should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of A, B and/or C or at least one of A, B or C should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.