Method of seed-pulling beta silicon carbide crystals from a melt containing silver and the product thereof

Claim 1

THE PROCESS OF GROWING A CRYSTAL OF BETA SILICON CARBIDE WHICH COMPRISES FORMING A CHARGE OF SILVER, SILICON AND CARBON OF HIGH PURITY IN A CRUCIBLE HAVING AN INNER SURFACE RESISITANT TO MOLTEN SILICON, THE CHARGE CONTAINING 60% TO 85% SILICON, 15% TO 40% SILVER, AND CARBON IN THE AMOUNT 0.2% TO 1% OF THE SILICON COMBINED AND SILVER, OUTGASSING THE CRUCIBLE AND CHARGE IN A FURNACE UNDER HIGH VACUUM AT A TEMPERATURE OF THE ORDER OF 800* TO 900*C., INTRODUCING AN INERT GAS INTO THE FURANCE TO A PRESSURE OF MORE THAN 1 ATMOSPHERE, MELTING THE CHARE AND ESTABLISHING A TEMPERATURE GRADIENT IN THE MOLTEN BATH IN THE CRUCIBLE, SO THAT THE TOP OF THE MELT IS MORE THAN 50*C. COOLER THAN THE BOTTOM OF THE MELT AND THE TEMPERATURE AT THE TOP OF THE MELT IS BETWEEN 1450*C. AND 1800*C., INTRODUCING A SEED CRYSTAL INTO THE TOP OF THE MELT BY MEANS OF A SEED HOLDER, CAUSING RELATIVE ROTATING MOVEMENT BETWEEN THE HOLDER WITH ITS SEED AND THE CRUCIBLE CONTAINING THE MELT, CAUSING THE SEED TO BE PULLED GRADUALLY UPWARDLY FROM THE MELT, REMOVING THE HEAT OF CRYSTAL FORMATION AS IT IS PRODUCED, CONTINUING THE GROWING PROCESS UNTIL THE SEED HAS ATTAINED A LENGTH OF SEVERAL MILLIMETERS, AND PERMITTING THE CRUCIBLE, MELT AND CRYSTAL TO COOL SLOWLY.