Thermally activated conductance of a silicon inversion layer by electrons excited above the mobility edge

Abstract

The thermally activated conductivity sigma of an n-type inversion layer on a (100) oriented silicon surface and its derivative d sigma /dT were measured in the temperature range 1.4K-4.2K. Above T approximately=2.5K both the temperature dependence of (T/ sigma ) (d sigma /dT) and the relation between this quantity and sigma cannot be reconciled with a universal pre-exponential factor, i.e. the minimum metallic conductivity, but are shown to be satisfactorily described by a prefactor which is proportional to the temperature. The experimental results presented are consistent with activation of the number of mobile electrons above a mobility edge in the lowest sub-band, and indicate a mobility which is independent of both temperature and electron density.