Method and apparatus for producing conductive bulk β-GA2O3 single crystals, and conductive bulk β-GA2O3 single crystals

Abstract

Conductive bulk β-Ga grown from the melt, especially by the Czochralski method 2 O 3 Method and apparatus for producing single crystals of β-Ga with high electrical conductivity and large diameters greater than 1 inch combined with lengths greater than 25 mm. 2 O 3 To grow the single crystal (7), the growth furnace is provided with an internal insulation (8) with low radiation reflectance (R) in the near infrared spectral range of 1-3 μm that reduces the reflection of heat back to the growing single crystal (7) and thus increases the heat dissipation from the growing single crystal (7). Low reflectance can be achieved either by high emissivity or high transmittance. Furthermore, β-Ga 2 O 3 The single crystal (7) grows at a rate that dynamically decreases as the growth proceeds, dynamically decreasing the latent heat of crystallization and the amount of heat dissipated from the growing single crystal (7).

Description

[Technical Field]

[0001] Technical field The present invention relates to a method and apparatus for growing bulk β-Ga2O3 single crystals by the Czochralski method in general, and more specifically, to a method and apparatus for large-diameter conductive crystals. The present invention also relates to large-diameter conductive bulk β-Ga2O3 single crystals grown by the Czochralski method. [Background technology]

[0002] Background of the Invention The beta phase of Ga2O3 (β-Ga2O3) is an emerging ultrawide bandgap n-type oxide semiconductor with high potential for UV photoelectronic and high-power electronic applications. This is a result of its wide bandgap of 4.85 eV and high theoretical breakdown field of 8 MV / cm, which makes the compound transparent down to the UV spectral region.

[0003] The device requires a bulk single crystal, which serves as a substrate for the epitaxial layer, on which the device structure is then fabricated. While foreign substrates can be used for this purpose, they typically degrade the layer quality and, consequently, the device performance due to lattice mismatch between the substrate and the layer. Therefore, natural substrates are preferred.

[0004] β-Ga2O3-based power devices, such as Schottky diodes and field-effect transistors (FETs), can be economically efficient in terms of energy saving and energy management. They can find applications in several industrial sectors, including mobile transport, including electric vehicles, aircraft, and ships, as well as railways and power grids. Generally, power switching devices can be designed in two configurations: horizontal (planar) and vertical. In a horizontal configuration, the substrate is electrically insulating and acts as a support for the layers on which all the contacts, such as the source, drain, and gate contacts within the FET device. In a vertical configuration, the substrate is highly conductive and acts as an electrical contact in addition to supporting the epitaxial layer. Devices in a vertical configuration can switch higher voltages compared to those in a horizontal configuration.

[0005] Bulk β-Ga2O3 single crystals are well known in the art and can be grown from molten material using various techniques: Optical Floating Zone (OFZ), Edge-Defined Film-Fed Growth (EFG), Bridgman or Vertical Gradient Freeze (VGF), and Czochralski method.

[0006] The OFZ method is a crucible-less method and can only produce crystals with a diameter of no more than 1 inch. Examples of this method used to grow bulk β-Ga2O3 single crystals can be found in the paper by EG Villora et al. entitled "Large-size β-Ga2O3 single crystals and wafers," J.Cryst.Growth 270(2004)420-426, and in U.S. Patent No. 8,747,553. Because the OFZ method allows growth to proceed on top of the seed crystal, it is possible to grow both electrically insulating and conductive bulk β-Ga2O3 single crystals along different crystallographic directions.

[0007] The EFG method for growing bulk β-Ga2O3 single crystals uses an Ir crucible and an Ir die (shaper) located on top of the crucible. Typically, the crystal has a (-201) or (001) principal plane (i.e., the larger plane of the slab) that can reach a size of 4 or 6 inches. <010> It grows in slab form along the crystallographic direction. However, the (010) oriented substrate is 10 × 15 mm 2 It can be fabricated solely from the cross-section of the crystal slab. An example of this method related to bulk β-Ga2O3 single crystals is "High-quality β-Ga2O3 single crystals grown by edge-defined film-fed This is disclosed in the paper by A. Kuramata et al. titled "growth," Jpn.J.Appl.Phys.55(2016)1202A2, and in the patent / patent application documents: International Publication No. 2013172227 (corresponding to Japanese Patent Publication No. 6,421,357, European Patent No. 2851458, and U.S. Patent Application Publication No. 2015125699), International Publication No. 2013073497 (Japanese Patent Publication No. 5,491,483, European Patent No. 2,801,645, and U.S. Patent Application Publication No. 2014352604), and International Publication No. 2014073314 (Japanese Patent Publication No. 5,756,075, European Patent No. 2,933,359, and U.S. Patent No. 9,926,646). Cylindrical β-Ga2O3 crystals grown by the EFG method are disclosed, for example, in Chinese Patent Application No. 112210823.

[0008] The Bridgman and VGF methods used to grow bulk β-Ga2O3 single crystals utilize noble metal crucibles, such as Pt-Rh alloy (Bridgman) or Ir (VGF), where the molten material solidifies into a single crystal on top of a seed crystal, which may have different crystallographic orientations. This method allows for the growth of both electrically insulating and conductive β-Ga2O3 single crystals. The VGF method, described in the paper "Scaling-Up of Bulkβ-Ga2O3Single Crystals by the Czochralski Method" by Galazka et al., ECS J.Solid State Sci.Technol.6(2017)Q3007~Q3011, allows for the growth of highly conductive β-Ga2O3 single crystals with a diameter of approximately 2 inches, although they are short, not exceeding 20 mm. The growth of bulk β-Ga2O3 single crystals by the Bridgman method is disclosed in U.S. Patent No. 10,570,528 by K. Hoshikawa et al. The Bridgman technique reported by K. Hoshikawa et al. in the paper entitled "2-inch diameter (100)β-Ga2O3 crystal growth by the vertical Bridgman technique in a resistance heating furnace in ambient air," J.Cryst.Growth, 545(2020)125724, enables the growth of electrically insulating crystals perpendicular to the (100) plane with a diameter of 2 inches, but their cylindrical length does not exceed approximately 25 mm. The same crystal dimensions relate to conductive crystals grown by the Bridgman technique perpendicular to the (001) plane, as described in the paper by Hoshikawa et al. entitled "50 mm diameter Sn-doped (001)β-Ga2O3 crystal growth using the vertical Bridgeman technique in ambient air," J.Cryst.Growth, 546(2020)125778.

[0009] The Czochralski method, combined with its high structural quality, offers the potential to grow the largest bulk β-Ga2O3 single crystals in terms of volume. Electrically insulating crystals with a diameter of 2 inches can have lengths of 60–100 mm, as reported by Galazka et al. in the papers "Scaling-Up of Bulk β-Ga2O3 Single Crystals by the Czochralski Method," ECS J.Solid State Sci.Technol.6(2017)Q3007~Q3011, "β-Ga2O3 for wide-bandGap electronics and optoelectronics," Semicond.Sci.Technol.33(2018)113001, and "Bulk single crystals of β-Ga2O3 and Ga-based spinels as ultra-wide bandGap transparent semiconducting oxides," Prog.Cryst.Growth Charact.Mater.67(2021)100511. To grow such large crystals, a high oxygen partial pressure in the growth atmosphere is necessary to minimize the formation of elemental Ga in the Ga2O3 molten material, which, if achieved, has a significant adverse effect on the growth process, crucible lifetime, and crystal quality. This requirement is necessary for all melt growth methods used for β-Ga2O3 single crystals, including noble metal crucibles, as taught by Galazka et al. in European Patent Specification No. 3,242,965 (corresponding U.S. Patent No. 11,028,501).

[0010] Electrically insulating bulk β-Ga2O3 single crystals can be large in size in terms of diameter and cylindrical length, but this is not related to conductive crystals that undergo so-called free carrier absorption. Simply put, the heat generated during the liquid-solid phase transition (latent heat of crystallization) cannot be easily dissipated by the growing crystal because most of the heat is absorbed by free carriers in the growing crystal in the near-infrared spectral region, which are carried through the growing crystal. This causes a temperature rise near the growth interface, resulting in an interface inversion from convex to concave towards the molten material. Such concave-forming long interfaces result in growth instability that changes the growth morphology from cylindrical to corkscrew (helical). The helical shape makes it impossible to manufacture wafers of the required diameter. This phenomenon, associated with bulk β-Ga2O3 single crystals grown by the Czochralski method, is discussed in "On the bulk β-Ga2O3 single crystals grown by the Czochralski method," J.Cryst.Growth 404 (2014) 184-191, "Czochralski-grown bulk β-Ga2O3 single crystals doped with mono-, di-, tri-, and tetravalent ions," J.Cryst.Growth 529 (2020) 125297, "Bulk β-Ga2O3 single crystals doped with Ce, Ce+Si, Ce+Al, and Ce+Al+Si for detection of nuclear radiation," J.Alloy.Compd. 818 (2020) 152842, and "Transparent Semiconducting Oxides-Bulk Crystal Growth and Fundamental Properties," Chapter 4, Jenny Stanford. This is described by Galazka et al. in a paper titled Publishing (2020). As a result, the free electron concentration is 10 18 cm -3Highly conductive crystals exceeding a certain value can be grown by the Czochralski method as short cylinders of approximately 30 mm for crystal diameters of 1 inch or less, and less than 25 mm for two-diameter crystals. For economic reasons, especially when considering the very high cost of crystal growth, the cylindrical portion of the crystal must be as long as possible to produce as many wafers as possible from a single crystal while maintaining the given electrical properties for electronic devices, particularly in vertical configurations. The Czochralski method is, <010> This enables the growth of crystals along the crystallographic direction, and thus allows for (010) oriented wafers to be manufactured from the cross-section of a cylindrical part. For example, <010> Crystals grown along the orientation, with a diameter of 2 inches, enable the production of 2-inch diameter (010) oriented wafers with high electrical conductivity, suitable for vertically configured power devices.

[0011] The conductivity of undoped bulk β-Ga2O3 single crystals, regardless of the growth method, arises from residual impurities, mainly silicon and / or hydrogen, and is due to a free electron concentration of approximately 10⁻¹⁰. 18 cm -3 Conductivity can be induced that is classified as a normal semiconductor, not exceeding a certain value. For higher conductivity, intentional doping is required, which is usually done with silicon (Si) or tin (Sn) doping, as described in the latest techniques mentioned above. Other dopants such as Nb, Hf, or Zr may also be used to induce conductivity in β-Ga2O3. [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] Summary of the Invention The object of the present invention is to provide conditions for producing bulk β-Ga2O3 single crystals from a molten material, particularly by the Czochralski process, thereby enabling the reliable growth of crystals with high conductivity, large size, and high structural quality. [Means for solving the problem]

[0013] Another object of the present invention is to provide bulk β-Ga2O3 single crystals with high conductivity and large size, preferably with a diameter of at least 2 inches and a length exceeding 1 inch.

[0014] A further object of the present invention is to provide an apparatus for producing β-Ga2O3 single crystals from a molten material, particularly by the Czochralski method, thereby enabling the method to be carried out and resulting in the growth of crystals with high conductivity, large size, and high structural quality.

[0015] In a more general embodiment, another object of the present invention is to provide a method and apparatus for producing different oxide compounds by the Czochralski process, which have a high melting point (above 1400°C) and exhibit strong absorption in the near-infrared spectral region.

[0016] According to a first aspect of the present invention, a method for producing a conductive bulk β-Ga2O3 single crystal by the Czochralski method comprises providing a growth chamber with a growth furnace comprising a noble metal crucible having a Ga2O3 starting material therein, an insulating material surrounding the crucible from all sides having free space for accommodating the bulk β-Ga2O3 single crystal under growth, and an induction RF coil for heating the crucible and controlling the melting temperature during crystal growth, the RF coil being powered by an RF power supply, and the crystal under growth being fixed to a translational and rotational mechanism via a seed crystal, a seed crystal holder, and a pull-up rod. The method further comprises providing the Ga2O3 starting material with a dopant to form shallow donors in the Ga2O3 single crystal, and providing the growth chamber, and therefore the growth furnace, with a growth atmosphere containing oxygen mixed with at least one non-reducing gas. The crucible having the Ga2O3 starting material is then heated by the RF coil until the Ga2O3 starting material melts. After melting the Ga2O3 starting material, an oriented seed crystal is immersed in the molten starting material and then pulled up at a moving speed, rotating at a predetermined rotational speed to achieve a predetermined growth rate. During the initial pulling, the diameter of the seed is expanded to the final cylindrical diameter, and it is pulled up to a predetermined cylindrical length. Once the predetermined cylindrical length is achieved, the single crystal is separated from the molten material and cooled to room temperature along with the growth furnace.

[0017] The essence of this invention is to further provide the growth furnace with an internal insulator with low radiative reflectance in the 1-3 μm near-infrared spectral region to reduce the reflection of heat back to the growing single crystal and thus increase heat dissipation from the growing single crystal. This is combined with a dynamic decrease in the growth rate from the start of pulling the seed crystal to crystal separation. The growth rate decreases from an initial growth rate of 1-10 mm / h at the start of growth to a final growth rate of 0.2-1 mm / h at the end of growth when the single crystal achieves a predetermined cylindrical length. This solution dynamically reduces the latent heat of crystallization as growth progresses and dynamically reduces the amount of heat dissipated from the growing single crystal.

[0018] Preferably, the internal heat insulating material having a low radiation reflectivity has a high emissivity or a high reflectivity in the near infrared spectral region exceeding 0.3 at room temperature.

[0019] The growth rate may decrease linearly or non-linearly from the initial growth rate to the final growth rate.

[0020] In a preferred embodiment, the growth rate decreases from the initial growth rate to the final growth rate at different ratios.

[0021] In another preferred embodiment, the growth rate may decrease continuously from the initial growth rate to the final growth rate, or in blocks combining a constant growth rate and a decreasing growth rate.

[0022] Advantageously, the growth atmosphere contains, in addition to oxygen, a non-reducing gas with high thermal conductivity, preferably He at a concentration of 10 to 95 vol%, in order to further enhance the heat dissipation from the growing crystal through gas convection.

[0023] According to a second aspect of the present invention, a conductive bulk β-Ga2O3 single crystal grown by the Chochralski method is provided according to the method described above. The β-Ga2O3 single crystal has a cylindrical diameter greater than 1 inch, a cylindrical length greater than 25 mm, and the following electrical properties formed by shallow donors by Hall effect measurement: 1 to 10×10 18 cm -3 free electron concentration of, 50 to 120 cm 2 V -1 s -1 electron mobility of, and a resistivity of 0.01 to 0.04 Ωcm.

[0024] In a preferred form of the present invention, the β-Ga2O3 single crystal has a cylindrical diameter of 2 inches or more. Advantageously, the dopant forming the shallow donor is Si and / or Sn.

[0025] According to a third aspect of the present invention, an apparatus is provided for producing a conductive bulk β-Ga2O3 single crystal by the Czochralski method having a predetermined cylindrical diameter and cylindrical length. The apparatus comprises a growth chamber and a noble metal crucible having a Ga2O3 starting material therein, an insulating material surrounding the crucible from all sides having free space for accommodating the bulk β-Ga2O3 single crystal under growth, and a growth furnace comprising an induction RF coil for heating the crucible and controlling the melting temperature during crystal growth. The apparatus further comprises an RF power supply for powering the RF coil, a translation and rotation mechanism coupled to a seed crystal via a seed crystal holder, and a pull-up rod, as well as a scale connected to the pull-up rod or the growth furnace for monitoring the growth rate of the bulk β-Ga2O3 single crystal.

[0026] According to the present invention, the growth furnace further comprises an internal thermal insulator with low radiant reflectance in the 1-3 μm near-infrared spectral region, which reduces the reflection of heat returning to the single crystal during growth and thus increases heat dissipation from the single crystal during growth.

[0027] Advantageously, internal insulation materials with low radiative reflectance have high emissivity in the near-infrared spectral region above 0.3 at room temperature. Here, the internal insulation material is preferably selected from the group consisting of opaque alumina, zirconia, magnesia, and yttria.

[0028] In another advantageous solution of the present invention, an internal insulating material having low radiative reflectance has high transmittance in the near-infrared spectral region above 0.3 at room temperature. This is preferably filled with a transparent ceramic or crystalline sapphire selected from the group consisting of alumina, yttria, and yttrium aluminum garnet.

[0029] In a preferred embodiment of the apparatus, the growth atmosphere includes, in addition to oxygen, a non-reducing gas with high thermal conductivity, most preferably He, at a concentration of 5-95 volume%, to further enhance heat dissipation from the crystals during growth via gas convection.

[0030] Further advantages and other features of the method and apparatus of the present invention for growing bulk β-Ga2O3 single crystals or other oxide crystals that exhibit high absorption in the near-infrared spectral region will become apparent from the detailed description of the embodiments with reference to the drawings. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic cross-sectional view of a growth furnace for oxide single crystals grown by the Czochralski method. [Figure 2] This figure shows different growth rate profiles for bulk β-Ga2O3 single crystals grown by the Czochralski method. [Figure 3] This figure shows the actual growth rate profile output from a growth run of a bulk β-Ga2O3 single crystal grown by the Czochralski method. [Modes for carrying out the invention]

[0032] Detailed description of the embodiment The growth furnace 1 shown in Figure 1 is generally adapted for growing bulk oxide single crystals by the Czochralski method, and more specifically, for growing bulk β-Ga2O3 single crystals by the Czochralski method. The growth furnace 1 is housed in a water-cooled growth chamber (not shown) into which a predetermined growth atmosphere 2 is introduced. The furnace 1 consists of a noble metal crucible 3 containing a Ga2O3 starting material 4, which preferably has a lid 5 on top, and an insulating material 6 surrounding the crucible on all sides. Above the crucible is a free space (growth zone) for accommodating the bulk β-Ga2O3 single crystal 7 being grown. The growth furnace 1 further includes an internal insulating material 8 with predetermined optical properties, as will be further described below. The noble metal crucible 5 is located outside the insulating material 6 and is inductively heated by an RF coil 9 powered by an RF power supply (not shown). A bulk β-Ga2O3 single crystal 7 is grown on a crystallographically oriented β-Ga2O3 seed crystal 10, which is fixed to a seed crystal holder 11 connected to a pull-up rod 12. The pull-up rod 12 is connected to a pull-up and rotation mechanism (not shown) for translating TR and rotating R the growing β-Ga2O3 single crystal 7, and to a scale (not shown) for weighing the growing β-Ga2O3 single crystal 7. Alternatively, the scale is coupled to a growth furnace 1. In either case, the scale indicates the growth rate of the growing single crystal 7 by directly weighing the crystal mass or the mass difference between the furnace and the growing crystal 7. The signal from the scale is coupled to a controller that controls the generator power and therefore the melting temperature.

[0033] The insulating material 6 is a refractory material that can withstand high temperatures depending on the melting point of the growing oxide crystal. The melting point of Ga2O3 is approximately 1800°C. The insulating material 6 typically includes alumina or zirconia tubes, granules, felt, and quartz tubes in the outer part of the growth furnace 1. The purpose of the insulating material 6 is to reduce heat loss and establish a predetermined temperature gradient within the crucible and growth zone to minimize thermal stress and associated structural and point defects in the growing crystal 7. In detail, a low-temperature gradient is required to grow bulk β-Ga2O3 single crystals, and therefore the best possible insulating properties are necessary. This is a result of the fusion chemistry (decomposition) and monoclinic system of β-Ga2O3, which has anisotropic mechanical, thermal, and optical properties.

[0034] The noble metal crucible 3 for β-Ga2O3 crystals is iridium and its alloys, such as iridium-platinum alloys. Other crucible materials, such as platinum-rhodium alloys, as described by Hoshikawa et al. (mentioned above) for the Bridgman process, can also be considered.

[0035] More specifically, the growth atmosphere 2 for growing large-diameter β-Ga2O3 single crystals 7 greater than 1 inch preferably comprises at least 5 volume% oxygen, as well as at least one other non-reducing gas such as Ar, N2, CO2, He, Xe, and Ne, as described in U.S. Patent No. 11,028,501 by Galazka et al., incorporated herein by reference.

[0036] In the Czochralski method, the β-Ga2O3 seed crystal 10 is crystallographically oriented along the

[0010] direction, which is parallel to both the easy (100) and (001) cleavage planes present in the monoclinic system of β-Ga2O3. Other seed orientations tilted in the

[0010] direction, such as

[0110] , can also be used.

[0037] The crystal growth process is as follows: After assembling the growth furnace 1, the precious metal crucible 3 containing the starting material 4 is heated by an RF coil 9 until the Ga2O3 starting material 4 is melted. Once the Ga2O3 molten material is thermally stabilized, the oriented β-Ga2O3 seed crystal 10 is immersed in the Ga2O3 molten material while rotating at a rotation speed R. Next, the oriented β-Ga2O3 seed crystal 10 is pulled upward at a moving speed TR, increasing its diameter to a predetermined cylindrical diameter D by gradually decreasing the melting temperature via the RF power supply. When the crystal reaches a predetermined cylindrical length L, the crystal is separated from the molten material, slowly cooled to room temperature, and removed from the growth furnace 1.

[0038] The problem of growing conductive (normal or degraded semiconductor) bulk β-Ga2O3 single crystals as long straight cylinders using the Czochralski method arises from the inherent properties of the compound, namely, the absorption of heat carried through the growing crystal by free carriers. The heat that must be dissipated from the crystal is generated at the growth interface during the liquid-solid phase transition. The interface is convex toward the molten material (i.e., the conical portion of the crystal is immersed in the molten material), ensuring stable growth. The heat absorbed by free carriers raises the temperature of the crystal near the growth interface, and at a certain crystal length, the heat cannot be easily dissipated. When the temperature within the crystal reaches the melting point of Ga2O3, a portion of the crystal immersed in the molten material melts and returns. This phenomenon is called interface inversion. After this interface inversion, the growth becomes unstable, and the growth morphology changes from a straight cylinder to a corkscrew (spiral). Since such a crystal shape does not allow for the production of wafers of the diameter expected from a straight cylinder, only the cylindrical portion of the crystal is usable for wafer production. The cylindrical portion of a highly conductive β-Ga2O3 crystal with a diameter greater than 1 inch has a length of 25 mm or less. The high conductivity of the crystalline β-Ga2O3 crystal is 10 18 cm -3 This is understood as a free electron concentration exceeding a certain value.

[0039] The following technical solutions have been found to be effective in increasing the length of the cylindrical portion of highly conductive β-Ga2O3 crystals with a diameter exceeding 1 inch, grown by the Czochralski method.

[0040] (i) The reduction in the amount of heat reflected from the internal insulating material returning to the growing β-Ga2O3 single crystal, and / or (ii) The dynamic decrease in the latent heat of crystallization as growth progresses.

[0041] As shown in Figure 1, the crystal surface dissipates and exchanges heat with its surroundings in two ways: by gas convection C and radiation RA, the latter being far more effective. In radiation heat exchange, the heat emanating from the crystal surface in all directions interacts with the metal crucible 3 and (if present) its lid 5, as well as the internal insulator 8, where it is partially reflected, partially absorbed, and partially transmitted. This can be described in dimensionless terms as THA = 1 = R + E + T, where THA is the total heat, R is the reflectance, E is the emissivity, and T is the transmittance. Thus, the reflectance can be described as R = 1 - ET. To minimize heat reflection from the internal insulator 8, it should have either a high emissivity E or a high transmittance T. These optical properties R, E, and T relate to the near-infrared (NIR) region, where most of the heat is carried. Considering the melting point of Ga2O3 (1800°C), the blackbody radiation at that temperature, and the lower temperature of the growing crystal (assuming a minimum of 1200°C), the NIR region is between 1 and 3 μm. Therefore, the requirement for the internal insulation material 8 is a low reflectance R in the 1–3 μm spectral region, which can be achieved by a high value of E or T in that spectral region. The optical properties of a material are highly dependent on the spectral region and temperature. For example, emissivity E varies over a wide range within the NIR spectral region even at high temperatures, making it difficult to define an exact value, although a smaller value of E in some subregions of the described NIR region does not significantly affect the overall heat exchange. In any case, the emissivity E, when measured at room temperature, must be greater than 0.3 within the 1–3 μm NIR spectral region. Suitable refractory materials for the internal insulation material 8 are alumina, zirconia, yttria, and magnesia, which preferably have a rough surface to enhance diffuse scattering.

[0042] Another solution is to increase the transmittance T of the internal insulation material 8. This can be achieved by using an insulation material that is transparent to the NIR spectral region defined above. Since standard refractory materials are basically opaque to NIR, transparent ceramics or crystalline sapphire can be used. Both transparent ceramics, e.g., alumina and yttria, and crystalline sapphire in different shapes (tubes and caps) are available. The same considerations for wavelength and temperature apply to transmittance T as for emissivity E. Also, in this case, transmittance T must be greater than 0.3 in the NIR spectral region of 1-3 μm when measured at room temperature.

[0043] Another solution described above for more effective heat dissipation from the crystal is the dynamic reduction of the amount of heat generated during growth. This is done by dynamically decreasing the growth rate along with the crystal length. Note that the growth rate V is a combination of the crystal migration rate TR and the molten droplets converted into a solid.

[0044] Figure 2 shows the growth rate V profile, which allows for a dynamic reduction of the latent heat of crystallization. Generally, at the start of growth, i.e., during seeding, seed expansion (shoulder), and the beginning of the cylindrical portion, the amount of heat generated is less (seeding, shoulder) or the crystal length is small enough to effectively dissipate the heat (initial cylindrical portion), so the growth rate V1 can be relatively high, between 1 and 10 mm / h. Subsequently, the growth rate decreases to a final value V2 of 0.2 to 1 mm / h, reducing the amount of heat generated. The decrease in growth rate V can be made from the start of growth, especially when the initial growth rate is high, as shown by profiles P1, P2, and P5, or later, as shown by profiles P3 and P4. It can be done linearly or nonlinearly, as a continuous decrease, or in stepwise blocks, as shown by crystal length segments L1, L2, L3, and L4. Figure 3 shows an example of the growth rate from an actual growth experiment. The initial V1 = 1.7 mm / h was constant at the start in the first block 0-L1, then decreased linearly in blocks L1-L3 to a final value V2 = 0.7 mm / h, which remained constant in the final block L3-L4 of the crystal growth.

[0045] An additional tool for thermal control is the use of a non-reducing gas with high thermal conductivity, particularly He, in the growth atmosphere 2. This increases the heat dissipation from the growing crystal 7 due to gas convection C. Preferably, He in the growth atmosphere 2 is used in combination with reducing the amount of reflected heat returning to the crystal and reducing the latent heat of crystallization. The He concentration in the growth atmosphere, in addition to oxygen, is between 10 and 95 volume percent.

[0046] By using the technical solutions described above, it is possible to increase the cylindrical length L of highly conductive bulk β-Ga2O3 single crystals 7 with a diameter greater than 1 inch grown by the Czochralski method. Bulk β-Ga2O3 single crystals with a diameter D = 2 inches could be grown to a cylindrical length L exceeding 25 mm, between 25 and 50 mm. The high conductivity of bulk β-Ga2O3 single crystals can be achieved by intentionally doping the material with elements that form shallow donors. The most effective dopants are Si and Sn, but Nb, Zr, and Hf may also be used. To achieve high conductivity, the Ga2O3 starting material 4 should be doped with 0.05 to 0.3 mol% SiO2, but due to the high partial pressure of Sn-containing species, it should be doped with 0.5 to 4 mol% SnO2. The dopants that form shallow donors can be used individually or in combination. The electrical properties obtained from bulk β-Ga2O3 single crystals doped with Si and / or Sn at the concentrations mentioned above were as follows (from Hall effect measurements): 1~10 × 10 18 cm -3 Free electron concentration and electron mobility = 50-120 cm⁻¹ 2 V -1 s -1 , and resistivity of 0.01-0.04 Ωcm. A 2-inch diameter bulk β-Ga2O3 single crystal 7 having such electrical properties makes it possible to manufacture 2-inch diameter conductive wafers suitable for the fabrication of homoepitaxial and then vertically configured power electronic devices. In detail, such crystals make it possible to produce large wafers with the (010) surface orientation, which exhibits the highest growth rate of homoepitaxial films by molecular beam epitaxy. It is also possible to produce other wafer orientations such as (100) or (001), including a few degrees of break from those orientations. The bulk β-Ga2O3 single crystals obtained by the methods and apparatus described above are crystals of high structural quality, characterized by a narrow rocking curve with a full width at half maximum, usually less than 30 arcseconds, making the manufactured wafers suitable for high-quality homoepitaxial films.

Claims

1. Conductive bulk β-Ga by the Czochralski method having a predetermined cylindrical diameter (D) and cylindrical length (L) ２ O ３ A method for producing single crystals, (i) Ga ２ O ３ A precious metal crucible (3) containing the starting material (4) and growing bulk β-Ga ２ O ３ The present invention provides a growth furnace (1) in a growth chamber comprising an insulating material (6) surrounding the crucible (3) from all sides having free space for containing a single crystal (7), and an induction RF coil (9) for heating the crucible (3) and controlling the melting temperature during crystal growth, wherein the RF coil (9) is powered by an RF power supply, and the growing crystal (7) is fixed to a translational and rotational mechanism via a seed crystal (10), a seed crystal holder (11), and a pull-up rod (12), (ii) providing a dopant that forms shallow donors in the single crystal (7) of the foregoing Ga ２ O ３ in the starting material (4) of the foregoing Ga ２ O ３ and (iii) Provide the growth chamber and the growth furnace (1) with a growth atmosphere (2) containing oxygen mixed with at least one non-reducing gas, (iv) The RF coil (9) is used to transmit the Ga ２ O ３ The crucible (3) containing the starting material (4) is heated, and then the Ga ２ O ３ The process involves melting the starting material (4) and (v) Immersing the oriented seed crystal (10) in the molten starting material (4), (vi) Pulling up the seed crystal (10) at a moving speed (TR) in order to achieve a predetermined growth rate (V) while rotating at a rotational speed (R), (vii) While pulling up, the diameter of the type is increased to the final cylindrical diameter (D) of the single crystal (7), (viii) Pulling up the single crystal (7) having the cylindrical diameter (D) to a predetermined cylindrical length (L), (ix) Separating the single crystal (7) from the molten starting material, (x) Cooling the growth furnace (1) having the grown single crystal (7) to room temperature, - Step (i) further provides the growth furnace (1) with an internal thermal insulation material (8) located inside the thermal insulation material (6), which has a radiative reflectance (R) of less than 0.4 in the near-infrared spectral region of 1 to 3 μm, in order to increase heat dissipation from the growing single crystal (7) by reducing the reflection of heat returning to the growing single crystal (7), A method characterized in that the steps (vi), (vii), and (viii) of raising the single crystal (7) from seeding to separation include a dynamic decrease in the growth rate (V) from an initial growth rate (V1) of 1 to 10 mm / h at the start of growth when the single crystal (7) reaches the predetermined cylindrical length (L) to a final growth rate (V2) of 0.2 to 1 mm / h at the end of growth, in order to dynamically reduce the latent heat of crystallization and the amount of heat dissipated from the single crystal (7) during growth as the growth progresses.

2. The method according to claim 1, wherein the internal insulating material (8) having a radiative reflectance (R) lower than 0.4 has an emissivity (E) in the near-infrared spectral region greater than 0.3 at room temperature.

3. The method according to claim 1, wherein the internal insulating material (8) having a radiative reflectance (R) lower than 0.4 has a transmittance (T) in the near-infrared spectral region greater than 0.3 at room temperature.

4. The method according to any one of claims 1 to 3, characterized in that the growth rate (V) decreases linearly from the initial growth rate (V1) to the final growth rate (V2).

5. The method according to any one of claims 1 to 3, characterized in that the growth rate (V) decreases non-linearly from the initial growth rate (V1) to the final growth rate (V2).

6. The method according to any one of claims 1 to 3, characterized in that the growth rate (V) decreases at different rates from the initial growth rate (V1) to the final growth rate (V2). Law.

7. The growth rate (V) decreases continuously from the initial growth rate (V1) to the final growth rate (V2), as described in any one of claims 1 to 3. method.

8. The method according to any one of claims 1 to 3, characterized in that the growth rate (V) decreases within a block (L1 to L4) that combines a constant growth rate and a decreasing growth rate from the initial growth rate (V1) to the final growth rate (V2).

9. (iii) Providing the aforementioned growth atmosphere (2) is to provide 10 to 95 volume percent of oxygen in addition to oxygen. The method according to any one of claims 1 to 3, characterized by comprising providing a concentration of He.

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