Structure and electrical properties of gold-germanium interfaces

The structure and electrical properties of ultrathin (a few angstroms) gold films on amorphous germanium, as well as between Ge layers, are investigated. These films were fabricated by simple vacuum evaporation, without the need for UHV or epitaxy techniques, due to the discovery of room-temperature layered growth by electron-beam evaporation on amorphous Ge. These layers become electrically continuous at a very low average thickness (1.5), due to good wetting and the possible formation of a surface Au-Ge alloy. The growth occurs at room temperature, without the morphology of the bulk amorphous Ge underlayer changing significantly. On the first (few) monolayers, Au growth continues by the formation of small grains. In Ge/Au/Ge sandwiches, superconductivity can be observed over a limited range of Au thicknesses, with maximum critical temperature Tc1 K and critical current Jc(0)105 A/cm2 at d11, as well as an anisotropic critical magnetic field. The samples also show an anomalous Hall effect, having a very low Hall voltage for low thicknesses.