Existence of localized interface states in metal/GaAs(100) junctions: Au versus Al contacts

Using an nb initio pseudopotential approach, we have investigated the existence of localized interface states in epitaxial Al/caAs and Au/GaAs(100) junctions. In spite of the fact that the Al/GaAs and Au/GaAs(100) contacts possess relatively similar Schottky barrier heights, their interface-band structures differ significantly in the region of the GaAs fundamental band gap. Our results indicate that truly localized interface states can exist near the Fermi energy in Au/GaAs(100) junctions, even at defect-free interfaces, whereas no such states are allowed in Al/GaAs(100) junctions. For the abrupt As-terminated Au/GaAs(100) junctions, in particular, we find As-bridge-bond interface states located near the Fermi energy, which derive from frustrated covalent bonds at the interface. The presence of such states could explain the recent observation, by nonlinear spectroscopy, of a sharp midgap interface-state peak in As-rich Au/GaAs(100) junctions.