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^-5 A/V and (5±{}1)×{}10^-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.