Dispersive charge transport along the surface of an insulating layer observed by electrostatic force microscopy

Abstract

We report the observation in the direct space of the transport of a few thousand charges submitted to a tunable electric field along the surface of a silicon oxide layer. Charges are both deposited and observed using the same electrostatic force microscope. During the time range accessible to our measurements (i.e., $t=1\ensuremath{-}1000\phantom{\rule{0.3em}{0ex}}\mathrm{s}$), the transport of electrons is mediated by traps in the oxide. We measure the mobility of electrons in the ``surface'' states of the silicon oxide layer and show the dispersive nature of their motion. It is also demonstrated that the saturation of deep oxide traps strongly enhances the transport of electrons in the surface plane, in the direction of the electric field.