Polarity dependence of hexagonal GaN films on two opposite c faces of Al2O3 substrate

GaN films were grown in pairs on two opposite c faces of Al2O3 substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning el ectron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al2O3 whose c face is forward to its crystal seed has [0 001] polarity, and the other film on the C-Al2O3 whose c face is backward t o its crystal seed has [000 (1) over bar] polarity. (C) 2001 American Insti tute of Physics.