An investigation was made of hetero-epitaxial GaN films on Al2O3 (00•1) by using low-energy electron diffraction, X-ray photo-electron spectroscopy and high-resolution electron energy-loss spectroscopy. Depending upon the preparation conditions, 2 faceted surfaces with differing morphologies, and a flat (3 x 3) reconstructed surface were obtained. A (10•¯2) orientation of the facet planes was determined for one of the faceted surfaces. In the case of samples which were grown by metal-organic chemical vapour deposition, N-termination and (00•¯1) polarity was established by using a combination of high-resolution electron energy-loss spectroscopy and angle-resolved X-ray photo-electron spectroscopy. In the case of samples which were grown by means of molecular beam epitaxy, the same (00•¯1) polarity was identified by observing the (3 x 3) reconstruction using low-energy electron diffraction. It was also shown to be Ga-rich by X-ray photo-electron spectroscopic data. Exposure to atomic H led to the detection of N-H and Ga-H stretching vibrations at 0.403eV and 0.227 to 0.247eV, respectively; as expected for a faceted surface.

Reactivity and Morphology of (10¯1¯2)-Faceted and (3 x 3)-Reconstructed GaN(000¯1) Epilayers Grown on Sapphire (0001). F.S.Tautz, S.Sloboshanin, U.Starke, J.A.Schaefer: Journal of Physics - Condensed Matter, 1999, 11[41], 8035-48