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

Abstract GaN single crystals were synthesized at 750–775°C and 5 MPa 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.

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