Decay of surface charge in the presence of a time-dependent bulk conductivity

Abstract

A theory is developed for the decay of surface charge due to a time-dependent bulk conduction process. Assuming that the time dependence of the conductivity of the insulator is proportional to f(t), specific cases of f(t), e.g., t-0.5 are solved analytically while the more general t-n dependence is solved numerically. The charge decay plots produced show the rapid initial decay followed by a quasi steady level observed by several experimenters. It is suggested that a combination of voltage step-response and charge-decay measurements is necessary to confirm whether the charge-decay process involves injection of the surface charge into the bulk of the insulator.