Patent ID: 7566641

Claim:
A method for manufacture a gallium based material with a low etch pit density (EPD), the method comprising: performing vertical gradient freeze crystal growth using the polycrystalline gallium based compounds, including: providing a crucible containing a seed crystal, GaAs raw material, and B 2 O 3 material, in an ampoule; providing a solid carbon substance in a lower region of the ampoule outside the crucible; sealing under vacuum the ampoule containing the solid carbon substance and the crucible; heating the sealed ampoule in a controlled manner causing the GaAs raw material to melt, the heat interacting with the solid carbon substance to produce a carbon gas which interacts with the GaAs melt through the B 2 O 3 material; and controlling a temperature gradient at a melt/crystal interface during the vertical gradient freeze crystal growth wherein the temperature gradient at the melt/crystal interface is between 0.1 to 2 degrees Celsius; controlling a crystallization velocity during the vertical gradient freeze crystal growth wherein the crystallization velocity is between 2 and 16 mm/hour; annealing the gallium arsenide based substrate using a single step annealing, wherein annealing the gallium arsenide based substrate further comprises controlling a heating rate during the annealing wherein the heating rate is 900 to 1050 degrees Celsius over 10 to 48 hours, as well as controlling a cooling rate during the annealing wherein the cooling rate is to room temperature in 6 to 24 hours; wherein, as a result of a combination of the vertical gradient steps, the crystallization control steps and the annealing steps, gallium based crystals are reproducibly provided having an etch pit density that is achieved without use of contact or external gas source supplied doping techniques and is less than 600 per square centimeter.