Temperature dependent metallic conductance above the mobility edge of a silicon inversion layer

The temperature dependence of the conductance of an n-type inversion layer on a (100) silicon surface has been examined between 1.4 K and 4.2K at electron densities at which the Fermi level is close above the mobility edge of the lowest sub-band. It can be explained by assuming a separate band of localised bound states from which electrons are thermally excited into the extended states of the sub-band. The absence of any noticeable change in the conductivity mobility demonstrates that the nature of the electron transport is preserved when the conductivity is lowered from 8 x lo-’ mho to 2 x mho.