Nonmetallic transport property of the Si(111)7x7 surface

The electrical surface transport property of the Si(111)7x7 reconstruction associated with the space-charge region and with the surface-state band was studied as a function of temperature (80-400 K) with the micro-four-point probes in ultrahigh vacuum. Electrical conductance near the surface increases with increasing temperature, which is opposite to that of the bulk Si crystal in the temperature range investigated. This can be explained by the hopping conduction of mobile carriers jumping between empty sites of donor-impurities underneath the Si(111)7x7 surface with a small surface-state contribution. The thermally activated hopping conduction through the surface-states is also proposed in terms of localized nature of the adatom dangling bonds.