Growth of cubic GaN crystals from hexagonal GaN feedstock

The ammonothermal transport and spontaneously nucleated recrystallization of cubic GaN using a NH4Cl/LiCl mineralizer system and h-GaN nutrient has been studied. Conditions of temperature, fill and mineralizer concentrations were varied independently to determine their effect on the system. It was found that the rate at which GaN deposits in the cool zone increases with increasing hot-zone temperature and NH3 fill, and that a temperature difference of at least 110 °C between the hot and cool-zones is necessary for transport to occur. Addition of more NH4Cl has little effect on transport rate once a threshold of about 0.015 M is reached. The LiCl co-mineralizer concentration is very significant, and the transport rate is very low when LiCl is absent. There seems to be an effect of scale and run time on the phase purity of the deposit in the cool zone with the fraction of hexagonal phase GaN increasing with both increasing run time and with the amount of mass transported.