AB-INITIO STUDY OF ALN AND ALPHA-SIC (11(2)OVER-BAR-0) SURFACE RELAXATION

The surface relaxation process of the nonpolar (11 (2) over bar 0) sur faces of AlN and alpha-SiC has been studied by means of periodic Hartr ee-Fock total-energy calculations on two-dimensional slabs. A relaxati on pattern analogous to those found experimentally for other wurtzite- structure semiconductors is predicted for both AlN and alpha-SiC. Our calculations indicate that ionicity is an important factor determining the extent of relaxation: the more covalent the solid is, the larger are the effects of relaxation on its surface structure.