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JP-7855701-B2 - Method and apparatus for producing conductive bulk β-GA2O3 single crystals, and conductive bulk β-GA2O3 single crystals

JP7855701B2JP 7855701 B2JP7855701 B2JP 7855701B2JP-7855701-B2

Inventors

  • ガラズカ，ズビグニエフ
  • ガンショウ，シュテファン
  • ビッカーマン，マティアス
  • シュレーダー，トーマス
  • ハックル，バルター

Assignees

  • ジルトロニック アクチエンゲゼルシャフト

Dates

Publication Date
20260508
Application Date
20230119
Priority Date
20220131

Claims (9)

  1. A method for producing a conductive bulk β- Ga₂O₃ single crystal having a predetermined cylindrical diameter (D) and cylindrical length (L) by the Czochralski method, (i) To provide a growth furnace (1) in a growth chamber comprising a noble metal crucible (3) containing a Ga₂O₃ starting material ( 4 ), an insulating material ( 6 ) surrounding the crucible (3) from all sides having free space for accommodating a growing bulk β- Ga₂O₃ 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) To provide the Ga2O3 starting material (4) with a dopant that forms a shallow donor within the Ga2O3 single crystal (7), (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) Heating the crucible (3) containing the Ga2O3 starting material (4) with the RF coil (9), and subsequently melting the Ga2O3 starting material (4), (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).
  7. The method according to any one of claims 1 to 3 , characterized in that the growth rate (V) decreases continuously from the initial growth rate (V1) to the final growth rate (V2).
  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. The method according to any one of claims 1 to 3 , characterized in that providing the growth atmosphere (2) (iii) includes providing He in a concentration of 10 to 95 volume percent in addition to oxygen.

Description

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 particularly, 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 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. The device requires a bulk single crystal, which serves as the substrate for the epitaxial layer, upon 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. 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 such as electric vehicles, aircraft, and ships, as well as railways or 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 in the FET device, are located. 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. Bulk β- Ga₂O₃ single crystals are known in the art and can be grown from molten material by various techniques: Optical Floating Zone (OFZ), Edge-Defined Film-Fed Growth (EFG), Bridgman or Vertical Gradient Freeze (VGF), and Czochralski method. The OFZ method is a crucible-free method and can only produce crystals with a diameter of no more than one inch. Examples of this method used to grow bulk β- Ga₂O₃ single crystals can be found in the paper by E. G. 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 bulk β- Ga₂O₃ single crystals that are both electrically insulating and conductive along different crystallographic directions. The EFG method for growing bulk β- Ga₂O₃ single crystals uses an Ir crucible and an Ir die (shaper) located above the crucible. Typically, the crystal grows in slab form along the <010> crystallographic orientation, with a (-201) or (001) main plane (i.e., the larger plane of the slab) that can reach a size of 4 or 6 inches. However, (010) oriented substrates can be fabricated solely from the cross-section of a 10 × 15 mm² crystal slab. An example of this method related to bulk β- Ga₂O₃ single crystals is found in the paper by A. Kuramata et al., entitled "High-quality β- Ga₂O₃ single crystals grown by edge-defined film-fed growth," Jpn. J. Appl. Phys. Disclosed in 55 (2016) 1202A2, and in 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. 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 by Galazka et al. entitled "Scaling-Up of Bulk β- Ga₂O₃ Single Crystals by the Czochralski Method," 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 2