Surface conductivity for Au or Ag on Si(111)

The surface electrical conductivity was separated from the bulk one by simultaneous conductivity measurements of two different surface structures formed on a single Si-wafer surface in ultrahigh vacuum. We have found that the surface conductivities for the Si(111)-√3×√3-Ag and -5×2-Au superstructures are inherently higher than that of the Si(111)-7×7 clean surface by (11.5±0.5)×${10}^{\mathrm{-}5}$ A/V and (5±1)×${10}^{\mathrm{-}5}$ A/V, respectively. These excess conductivities are estimated to originate mainly from the surface space-charge layer, although the surface-state-band conduction is considered to partly contribute, especially on the √3×√3-Ag surface. © 1996 The American Physical Society.