Method for growing β phase of gallium oxide ([β]-Ga2O3) single crystals from the melt contained within a metal crucible
A method for growing beta phase of gallium oxide (β-Ga 2 O 3 ) single crystals from the melt contained within a metal crucible surrounded by a thermal insulation and heated by a heater. A growth atmosphere provided into a growth furnace has a variable oxygen concentration or partial pressure in such a way that the oxygen concentration reaches a growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) in the concentration range (SC) of 5-100 vol. % below the melting temperature (MT) of Ga 2 O 3 or at the melting temperature (MT) or after complete melting of the Ga 2 O 3 starting material adapted to minimize creation of metallic gallium amount and thus eutectic formation with the metal crucible. During the crystal growth step of the β-Ga 2 O 3 single crystal from the melt at the growth temperature (GT) the growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) is maintained within the oxygen concentration range (SC).
1. A method for growing beta phase of gallium oxide (β-Ga 2 O 3 ) single crystals from a melt contained within a metal crucible, comprising the steps of:
providing into a growth chamber a thermal system or growth furnace ( 100 , 200 , 300 , 400 , 500 , 600 ) comprising the metal crucible ( 101 , 201 , 301 , 401 , 501 , 601 ) containing the Ga 2 O 3 starting material ( 102 , 202 , 302 , 402 , 502 , 602 ), a thermal insulation ( 103 , 203 , 303 , 403 , 503 , 603 ) surrounding the metal crucible ( 101 , 201 , 301 , 401 , 501 , 601 ) and a heater ( 104 , 204 , 304 , 404 , 504 , 604 ) disposed around the metal crucible ( 101 , 201 , 301 , 401 , 501 , 601 );
providing or creating a crystal seed ( 105 , 205 , 305 , 405 , 505 , 605 ) within the growth furnace ( 100 , 200 , 300 , 400 , 500 , 600 );
introducing at least into the growth furnace ( 100 , 200 , 300 , 400 , 500 , 600 ) a growth atmosphere ( 120 , 220 , 320 , 420 , 520 , 620 ) containing oxygen;
heating up the metal crucible ( 101 , 201 , 301 , 401 , 501 , 601 ) by the heater ( 104 , 204 , 304 , 404 , 504 , 604 ), which in turns heats up the Ga 2 O 3 starting material ( 102 , 202 , 302 , 402 , 502 , 602 ) until melting;
contacting the crystal seed ( 105 , 205 , 305 , 405 , 505 , 605 ) with the molten Ga 2 O 3 starting material ( 102 , 202 , 302 , 402 , 502 , 602 ) contained within the metal crucible ( 101 , 201 , 301 , 401 , 501 , 601 );
growing a β-Ga 2 O 3 single crystal ( 110 , 210 , 310 , 410 , 510 , 610 ) on the crystal seed ( 105 , 205 , 305 , 405 , 505 , 605 ) by temperature gradients between the crystal seed and the melt;
cooling down the grown β-Ga 2 O 3 single crystal ( 110 , 210 , 310 , 410 , 510 , 610 ) to room temperature (RT) once the crystal growth step has been completed;
characterized in that it further comprises the steps of:
i) providing into the growth furnace ( 100 , 200 , 300 , 400 , 500 , 600 ) the growth atmosphere ( 120 , 220 , 320 , 420 , 520 , 620 ) consisting of a mixture of pure oxygen and at least one non-reducing gas selected from the group consisting of Ar, N 2 , He Xe, Ne, and CO 2 , with a variable oxygen concentration (OC) or partial pressure at substantially atmospheric pressure in such a way that the oxygen concentration (OC) reaches a growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) in the concentration range (SC) of 5-100 vol. % below ( 8 , 9 ) the melting temperature (MT) of Ga 2 O 3 or at ( 6 , 7 ) the melting temperature (MP) or after ( 5 ) complete melting of the Ga 2 O 3 starting material ( 102 , 202 , 302 , 402 , 502 , 602 ) adapted to minimize creation of metallic gallium amount (CR 1 , CR 2 , CR 3 ) and thus eutectic formation with the metal crucible ( 101 , 201 , 301 , 401 , 501 , 601 ) and to improve stoichiometry of the Ga 2 O 3 starting material ( 102 , 202 , 302 , 402 , 502 , 602 ) and crystal growth stability; and
ii) maintaining the growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) within the oxygen concentration range (SC) during the crystal growth step of the β-Ga 2 O 3 single crystal ( 110 , 210 , 310 , 410 , 510 , 610 ) from the melt at the growth temperature (GT).
2. The method according to claim 1 , wherein the oxygen concentration (OC):
iii) does not exceed an intermediate oxygen concentration value (C 1 ) in the range of 0-5 vol. % during the heating up step from room temperature (RT) to an intermediate temperature value (T 1 ), intermediate temperature value (T 1 ) being located within the temperature range (ST) between 1000° C. and the melting temperature (MT) of Ga 2 O 3 ;
iv) increases from the intermediate oxygen concentration value (C 1 ) to the growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) in the oxygen concentration range (SC) of 5-100 vol. % during the heating up step from the intermediate temperature value (T 1 ) to the melting temperature (MT) of Ga 2 O 3 or at the melting temperature (MT) or after complete melting of the Ga 2 O 3 starting material ( 102 , 202 , 302 , 402 , 502 , 602 ) if the intermediate temperature value (T 1 ) substantially equals to the melting temperature (MT).
3. The method according to claim 1 , wherein the oxygen concentration (OC):
v) decreases from the growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) to a final oxygen concentration value (C 3 ) being lower than the growth oxygen concentration value (C 2 , C 2 ′, C 2 ″) during the cooling down step from the growth temperature (GT) to room temperature (RT).
4. The method according to claim 1 , wherein the growth oxygen concentration value (C 2 ) is substantially constant ( 10 ) within the oxygen concentration range (SC) at the growth temperature (GT) during the entire crystal growth step.
5. The method according to claim 1 , wherein the growth oxygen concentration value (C 2 ) decreases ( 10 ′) to a second growth oxygen concentration value (C 2 ′) within the oxygen concentration range (SC) at the growth temperature (GT) after an early stage of the crystal growth step.
6. The method according to claim 1 , wherein the growth oxygen concentration value (C 2 ) increases ( 10 ″) to a third growth oxygen concentration value (C 2 ″) within the oxygen concentration range (SC) at the growth temperature (GT) at the later stage of the crystal growth step.
7. The method according to claim 1 , wherein the growth oxygen concentration value (C 2 ) first decreases ( 10 ′) to a second growth oxygen concentration value (C 2 ′) within the oxygen concentration range (SC) at the growth temperature (GT) after an early stage of the crystal growth step, and increases ( 10 ″) to a third growth oxygen concentration value (C 2 ″) within the oxygen concentration range (SC) at the growth temperature (GT) at the later stage of the crystal growth step.
8. The method according to claim 1 , wherein the growth atmosphere ( 120 , 220 , 320 , 420 , 520 , 620 ) contains in addition to oxygen traces of H 2 and/or H 2 O to modify electrical properties of the β-Ga 2 O 3 single crystals.
9. The method according to claim 1 , wherein the growth atmosphere ( 120 ) is applied to the Czochralski method ( 100 ).
10. The method according claim 1 , wherein the growth atmosphere ( 220 ) is applied to the Kyropolous method ( 200 ).
11. The method according to claim 1 , wherein the growth atmosphere ( 320 ) is applied to the vertical Bridgman or Vertical Gradient Freeze method ( 300 ).
12. The method according to claim 1 , wherein the growth atmosphere ( 420 ) is applied to the horizontal Bridgman method ( 400 ).
13. The method according to claim 1 , wherein the growth atmosphere ( 520 ) is applied to shaped crystal growth techniques selected from the group consisting of the Stepanov, Noncapillary Shaping and Edge-Defined Film-Fed Growth methods ( 500 ).
14. The method according to claim 1 , wherein the growth atmosphere ( 620 ) is applied to the Levitation Assisted Self-Seeding Crystal Growth method ( 600 ).
15. The method according to claim 1 , wherein the growth atmosphere is applied to the Micro-Pulling Down method.