Cubic GaN formation under nitrogen-deficient conditions

We have studied crystal structure and associated defects in GaN/alpha-Al2O3 (0001) films grown under nitrogen-deficient conditions by metalorganic che mical vapor deposition and pulsed laser deposition. N-deficient films exhib it polycrystalline structure with a mixture of cubic zinc-blende and wurtzi te hexagonal GaN grains retaining tetragonal bonding across the boundaries and hence the epitaxial orientations and polarity. Renucleation of the wurt zite phase at different {111} planes of cubic GaN results in a rough and fa ceted surface of the film. We elucidate that the cubic phase is more stable under the nitrogen deficiency. (C) 1999 American Institute of Physics. [S0 003-6951(99)00317-4].