US 12,302,542 B2
Method of producing large EMI shielded GaAs infrared windows
Peter G. Schunemann, Hollis, NH (US); and Kevin T. Zawilski, Arlington, MA (US)
Assigned to BAE Systems Information and Electronic Systems Integration Inc., Nashua, NH (US)
Filed by BAE SYSTEMS Information and Electronic Systems Integration Inc., Nashua, NH (US)
Filed on Dec. 1, 2022, as Appl. No. 18/073,179.
Prior Publication US 2024/0188261 A1, Jun. 6, 2024
Int. Cl. C30B 17/00 (2006.01); C09D 5/00 (2006.01); C23C 16/30 (2006.01); C23C 16/52 (2006.01); C30B 29/42 (2006.01); C30B 29/60 (2006.01); C30B 35/00 (2006.01); H05K 9/00 (2006.01)
CPC H05K 9/0005 (2013.01) [C09D 5/006 (2013.01); C23C 16/306 (2013.01); C23C 16/52 (2013.01); C30B 17/00 (2013.01); C30B 29/42 (2013.01); C30B 29/602 (2013.01); C30B 35/002 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A method of producing a GaAs slab having a largest dimension that is greater than eight inches, the slab being suitable for forming an infrared (IR) transparent window having a largest dimension that is greater than eight inches, the method comprising:
providing a boat having a seed crystal region in contact with a crystal growing region, the crystal growing region having a largest dimension that is greater than eight inches;
placing a single crystal of GaAs as a seed crystal in the seed crystal region of the boat;
placing a polycrystalline charge of GaAs in the crystal growing region;
placing the boat within an interior of a horizontal furnace, at least two heating elements of the horizontal furnace being configured to separately control temperatures of the seed crystal region and the crystal growing region;
causing the heating elements to establish and maintain a horizontal temperature gradient across the interior of the furnace, said temperature gradient causing the seed crystal to be lower in temperature than the polycrystalline charge;
heating the interior of the furnace while maintaining said temperature gradient until the polycrystalline charge and a first portion of the seed crystal in contact with the polycrystalline charge are melted, a second portion of the seed crystal remaining solid, a solid/liquid interface being formed between the first and second portions of the seed crystal;
gradually cooling the interior of the furnace while maintaining the horizontal temperature gradient within the interior, so that the solid/liquid interface moves continuously across the crystal growing region, thereby causing directional solidification of the GaAs whereby the solidifying GaAs at the solid/liquid interface attaches to and extends the seed crystal;
removing the boat from the furnace;
removing the grown crystal from the crystal growing region of the boat; and
forming the GaAs IR window slab from the grown crystal.