High temperature 'variable range hopping' conductivity in silicon inversion layers

The conductivity of n channel MOSFET devices has been measured in the temperature range 4.2K<or=T<or=77K in samples with varying densities of interface charge. Contrary to previous results in this temperature range, the conductivity obeys the law lg sigma varies as T-1/3 indicative of a variable range hopping mechanism. The minimum metallic conductivity is found to vary linearly with the average separation of the oxide charge, contrary to prediction.