STRUCTURE OF THE NONPOLAR (10(1)OVER-BAR0) SURFACES OF ALN AND ALPHA-SIC, A PERIODIC HARTREE-FOCK STUDY

The surface relaxation process of the non-polar (<10(1)over bar 0>) su rfaces of AlN and alpha-SiC has been studied by means of periodic Hart ree-Fock total energy calculations on two-dimensional slabs. A relaxat ion 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 determinin g the extent of relaxation: the more covalent the solid is, the larger are the effects of relaxation on its surface structure.