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 struc tures formed on a single Si-wafer surface in ultrahigh vacuum. We have found that the surface conductivities for the Si(lll)-root 3 x root 3 -Ag and -5 x 2-Au superstructures are inherently higher than that of t he Si(lll)-7 x 7 clean surface by (11.5 +/- 0.5) x 10(-5) A/V and (5 /- 1) x 10(-5) A/V, respectively. These excess conductivities are esti mated to originate mainly from the surface space-charge layer, althoug h the surface-state-band conduction is considered to partly contribute , especially on the root 3 x root 3-Ag surface.