US 12,084,790 B2
Low etch pit density 6 inch semi-insulating gallium arsenide wafers
Rajaram Shetty, Niskayuna, NY (US); Weiguo Liu, San Leandro, CA (US); and Morris Young, Fremont, CA (US)
Assigned to AXT, Inc., Fremont, CA (US)
Filed by AXT, Inc., Fremont, CA (US)
Filed on Jun. 20, 2023, as Appl. No. 18/337,493.
Application 18/337,493 is a continuation of application No. 16/711,019, filed on Dec. 11, 2019, granted, now 11,680,340.
Claims priority of provisional application 62/779,039, filed on Dec. 13, 2018.
Prior Publication US 2023/0407522 A1, Dec. 21, 2023
Int. Cl. C30B 29/42 (2006.01); C30B 11/00 (2006.01); H01L 29/20 (2006.01); H01L 29/32 (2006.01); H01L 29/36 (2006.01); H01L 29/30 (2006.01); H01S 5/30 (2006.01)
CPC C30B 29/42 (2013.01) [C30B 11/002 (2013.01); C30B 11/006 (2013.01); H01L 29/20 (2013.01); H01L 29/32 (2013.01); H01L 29/36 (2013.01); H01L 29/30 (2013.01); H01S 5/3013 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A method for forming single crystal gallium arsenide substrates, the method comprising:
sealing charge material comprising polycrystalline gallium arsenide, a gallium arsenide seed crystal, B2O3 encapsulant, and carbon in a crucible;
sealing the crucible in a quartz ampoule;
performing a vertical gradient freeze crystal growth process by heating the ampoule using a multi-zone heating system to progressively melt the charge material until a portion of the seed crystal is melted;
starting growth from the partially melted seed by implementing a controlled cooling of the multi-zone heating system at a rate of 0.1 to 2 degree C./hour;
applying a temperature gradient of between 0.2 to 5 C/cm at a melt-crystal interface; and
maintaining a ratio of 1.0 to 4 between a temperature gradient above the melt-crystal interface to a temperature gradient below the melt-crystal interface in the multi-zone heating system to form a solidified gallium arsenide crystal.