Electrical functional properties of surface superstructures on semiconductors

We have found that the electrical conductivity parallel to the surface of a bulk silicon crystal is crucially influenced by the surface superstructures formed only on the topmost atomic layers of the surface. We have demonstrated this influence by depositing metal (Au, Ag, Cu, Pb, or In) on Si(111) surfaces that had a variety of surface superstructures such as Si(111)-7 × 7 clean, √3 × √3, 5 × 2, and so on. The increase in surface electrical conductance compared with the clean Si(111) surface were due either to conduction through the surface space-charge layer, to the two-dimensional surface-state bands, or to the conductive metal layers grown on the surface, depending on the combination of the deposit and the substrate-surface structure. This is the first investigation directly correlating the electrical conductivity to the surface structures. This result may lead to nanometer-scale electronic devices that use the electrical conduction restricted within a few atomic layers on the surface with controlled domains of surface superstructures.