Patent ID: 7767022

Claim:
A method of preparing a stress reduced sublimation grown crystal comprising: (a) providing a growth chamber having therein a graphite crucible including a sublimation source and a seed crystal in spaced relation and an induction coil disposed around the growth chamber and operative in response to electrical power being applied thereto to inductively heat the graphite crucible in the presence of no more than 200 Torr of inert gas in the growth chamber, whereupon a temperature gradient forms in the graphite crucible with the sublimation source at a first, sublimation temperature and the seed crystal at a second, lower temperature, and vapor from the sublimation source condenses on the seed crystal to form a grown crystal; (b) following the growth of the crystal in step (a), increasing the pressure of inert gas in the growth chamber to between 300 and 600 Torr and, simultaneously, controlling the power applied to the induction coil, whereupon the temperature of the graphite crucible remains substantially constant; (c) following step (b), moving the induction coil relative to the graphite crucible, or vice versa, whereupon the temperature gradient in the graphite crucible is reduced; (d) following step (c), controlling the electrical power applied to the induction coil whereupon the temperature in the graphite crucible increases to a temperature sufficient to anneal the grown crystal; and (e) after an annealing period of time has elapsed during which the interior of the graphite crucible is at the temperature sufficient to anneal the grown crystal, controlling the electrical power applied to the induction coil, whereupon the temperature of the interior of the graphite crucible decreases to room temperature over a cooling period of time, wherein steps (a)-(e) are performed without removing the grown crystal from the growth chamber.