Patent ID: 8361225

Claim:
A method of manufacturing a 6 inch diameter gallium arsenide wafer with a low etch pit density (EPD), the method comprising: performing a vertical gradient freeze (VGF) crystal growth process to grow a GaAs ingot, 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; 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 about 0.1 to about 2 degrees Celsius; controlling a shape of the melt/crystal interface during the vertical gradient freeze crystal growth wherein the shape is concave or convex to a melt front at no more than about ±2 mm; controlling a crystallization velocity during the vertical gradient freeze crystal growth wherein the crystallization velocity is between about 2 and about 16 mm/hour; obtaining a gallium arsenide 6 inch diameter wafer from the GaAs ingot; performing an annealing process on the gallium arsenide wafer using a single step anneal, wherein the annealing process comprises controlling a heating rate during the annealing between 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, and removing a portion of the surface of the gallium arsenide wafer, such that the annealing and the surface removal steps provide gallium arsenide crystals having less than a total of 50 light point defects, and a light point defect density of less than about 1 per square centimeter per wafer, with a particle size of equal to or greater than about 0.3 micrometers; wherein, as a result of a combination of the vertical gradient steps, the crystallization control steps and the annealing process, gallium arsenide 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.