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 ultrathin (1-2 monolayers) Si interlayers is studied with the ab initio pseudopotential approach. We find large changes in barrier height resulting from the dipole nature of the interlayers which quantitatively explain the experimentally observed tuning. We investigate the inhomogeneous screening of the dipole layers near the junction, its correlation with the spatial decay of the metal-induced gap states, and the Si-induced changes in the local density of states. Based on this atomic-scale study, we present a model for screened local dipoles at metal/semiconductor junctions.