Effects of Cooling Process on GaN Crystal Growth by Na Flux Method

The effects of cooling on the yield (percentage of Ga in the original melt that is incorporated into the GaN crystal) and morphology of GaN crystals grown by the Na flux method have been investigated. Yields of pyramidal GaN crystals of up to 94.9% were obtained by spontaneous crystallization using the slow cooling method. A lower cooling rate contributed to higher yield of GaN crystals. Scanning electron microscopy observations indicated that the crystalline perfection increased as the cooling rate was decreased. Instabilities such as macrosteps, cellular structures, and hopper crystals (a form of crystal defined by its "hoppered" shape) were observed after crystal growth at higher cooling rates. These results suggest ways to improve the yield and control the growth of perfect GaN crystals.