Photoinjection into SiO2: Electron Scattering in the Image Force Potential Well

Abstract

The voltage dependence of photoinjected currents in SiO₂ films for electric fields less than about 10⁶ V/cm exhibits anomalous behavior. It is shown that the physical mechanism responsible for this behavior is the scattering of photoinjected electrons in the SiO₂ image force potential well between the emitter and the potential maximum. A previously published model attributing the effect to electron trapping in SiO₂ is shown to be inconsistent with the experimental results. A theoretical model is presented and the voltage dependence of photocurrents is derived including the effects of scattering and barrier lowering. Experimental results from MIS structures using thermally grown SiO₂ are found to be in excellent agreement with theoretical predictions when a 34 Å mean free path for scattering in SiO₂ is used in the model.