GEOMETRIC AND ELECTRONIC-STRUCTURE OF A MAGNESIUM OVERLAYER ON THE GAAS(110) SURFACE

The electronic structure of a magnesium overlayer on the GaAs(110) sur face is calculated in the self-consistent tight-binding approximation. ft is found that the surface relaxation structure is important for lo w-coverage adsorption, and for determining the bonding energy state in particular. The Fermi level is pinned close to the top of the valence band by the covalent hybridization of the highly localized adatom Mg s orbitals and the surface Ga sp3 dangling bonds. Our results show a h igher density of unoccupied states than occupied states on Mg atoms, w hich is in good agreement with scanning tunnelling microscopy (STM) im ages. A comparison is made with theoretical and experimental results o f free and other adsorbate GaAs(110) surfaces.