LOCAL INTERFACE DIPOLES AND THE TUNING OF THE AL GAAS(100) SCHOTTKY-BARRIER HEIGHT WITH ULTRATHIN SI INTERLAYERS/

The modification of the Al/GaAs(100) Schottky barrier produced by ultr athin (1-2 monolayers) Si interlayers is studied with the ab initio ps eudopotential approach. We find large changes in barrier height result ing from the dipole nature of the interlayers which quantitatively exp lain the experimentally observed tuning. We investigate the inhomogene ous screening of the dipole layers near the junction, its correlation with the spatial decay of the metal-induced gap states, and the Si-ind uced changes in the local density of states. Based on this atomic-scal e study, we present a model for screened local dipoles at metal/semico nductor junctions.