Preferential growth of cubic GaN on sapphire (0001) substrates by metal organic molecular beam epitaxy

Preferential growth of high-quality cubic GaN on sapphire (0001) substrates was realized at 800 degrees C under a Ga-rich condition by metal organic molecular beam epitaxy. Hexagonal GaN was grown under a N-rich condition. On the contrary, under the Ga-rich condition, the growing layer changed from a hexagonal phase to a cubic phase as the growth proceeds, which was verified by in situ reflection high-energy electron diffraction. The low-temperature photoluminescence (PL) of this layer was dominated by a sharp and intense excitonic emission of cubic GaN, indicating high crystal quality. The results of PL and x-ray diffraction indicate that the polytype of GaN can be intentionally controlled by changing V/III ratios without serious degradation of crystal quality. In addition, enhancement of cubic phase growth by using a low-temperature grown buffer layer is also discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)02442-5].