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

Using an nb initio pseudopotential approach, we have investigated the exist ence of localized interface states in epitaxial Al/caAs and Au/GaAs(100) ju nctions. In spite of the fact that the Al/GaAs and Au/GaAs(100) contacts po ssess relatively similar Schottky barrier heights, their interface-band str uctures 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 abr upt As-terminated Au/GaAs(100) junctions, in particular, we find As-bridge- bond interface states located near the Fermi energy, which derive from frus trated covalent bonds at the interface. The presence of such states could e xplain the recent observation, by nonlinear spectroscopy, of a sharp midgap interface-state peak in As-rich Au/GaAs(100) junctions.