Frequency Dependence of the ac Resistance of Thin Semiconducting Films

Abstract

The decrease with frequency of the ac "resistance" (reciprocal of the real part of the admittance) of thin semiconducting films is calculated on the assumption that this decrease is due to simple self-capacitance. The basic approach follows an earlier theory of Howe, but the local charge density along the film is determined by an integral transform of the voltage at all points of the film: $q\left(x\right)=\int C(x-x^{\prime })V\left(x^{\prime }\right)d{x}^{\prime }$ rather than by the local voltage $q\left(x\right)=CV\left(x\right)\mathrm{}$, as in the Howe theory. The results agree with the experiments of Broudy and Levinstein. The agreement of the Howe theory with earlier experiments is shown to be partially fortuitous; it was evidently due to the use of physically inhomogeneous films in the earlier experiments.