ENERGETICS OF ALN THIN-FILMS ON THE AL2O3(0001) SURFACE

We present an ab initio study of the energetics and atomic structure o f films consisting of approximately 1 bilayer of AIN on the c-plane sa pphire surface. We show that these films are unstable with respect to three-dimensional islands, and we attribute this instability to both s train and chemical mismatch between the oxide and the nitride. The rel ative stability of the AIN films depends on the chemical potentials of Al and N. Films having (0001) polarity are expected to form under Al- rich conditions. Films with (000 (1) over bar) polarity appear to form only for undersaturation conditions of bulk AIN in the initial stages of growth. (C) 1998 American Institute of Physics.