An investigation was made of the structural and chemical properties of hetero-epitaxial films of GaN on Al2O3(00•1), using low-energy electron diffraction, X-ray photo-electron spectroscopy and high-resolution electron energy loss spectroscopy. Depending upon the preparation conditions, two faceted surfaces with different morphologies and a flat, (3 x 3)-reconstructed surface were obtained. For one of the faceted surfaces a (10•¯2) orientation of the facet planes could be determined. For a sample grown by metal-organic chemical vapour deposition N-termination and (00•¯1) polarity could be established by a combination of high-resolution electron energy loss spectroscopy and angle-resolved X-ray photo-electron spectroscopy. For a different sample grown by molecular beam epitaxy, the same (00•¯1) polarity could be identified, this time concluded from the observation of the (3 x 3) reconstruction in low-energy electron diffraction, which moreover was shown to be Ga rich by the present X-ray photo-electron spectroscopy measurements. Furthermore, the (00•¯1) surface was found to be highly reactive, causing water from the residual gas to adsorb dissociatively. Finally, exposure to atomic hydrogen led to the observation in high-resolution electron energy loss spectroscopy of N-H and Ga-H stretching vibrations at 403meV and 227 to 247meV, respectively, as expected for a faceted surface. Based upon these observations, a structural model for the facets was proposed.

Reactivity and Morphology of (101¯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