GaN single crystal growth using high-purity Na as a flux

GaN single crystals were synthesized at 750-775 °C and 5MPa of N₂ for 200-300 h using Na-Ga melts with the mole fractions of Na/(Ga+Na) of 0.60-0.67 in the starting melt. When 99% pure Na was used, almost all the melt surface was covered with a GaN polycrystalline layer which prevented the single crystal growth. By using 99.95% Na, no polycrystalline layer formed and GaN single crystals of 0.8-1.0 mm grew on the bottom of a sintered BN crucible. A platelet single crystal having a size of 10 mm in the longest direction and 0.1 mm thick was obtained in a pyrolytic BN crucible using Na purified by distillation of the 99.95% Na.