EXPERIMENTAL-EVIDENCE FOR THE EXISTENCE OF A MOBILITY EDGE IN SILICON-CARBIDE INVERSION-LAYERS

The low- and high-field conductivities of SiC metal-oxide-semiconductor field-effect transistors have been studied as a function of temperature. Transport in the inversion layer is found to be thermally activated. The behaviour of the activation energy as a function of gate voltage agrees with the predictions of a simple analytical model, attributing the conduction mechanism to electrons thermally excited above a mobility edge. The existence of localized states is probably due to a large positive oxide charge and the presence of dipoles near the interface. The mobility edge position is of the order of 200 meV, which induces electron localization even at high temperatures. The effect of electron screening on the mobility edge can be experimentally demonstrated, and the potential fluctuations cannot be removed by applying a large longitudinal electric field.