Trapped Charges on Dielectrics

Abstract

IT has been proposed¹ that the charge produced on a dielectric surface by electrical discharges is the result of trapping of electrons at impurity or defect sites in the material. Although numerous experiments on surface charges have been reported^2,3 no direct evidence for a trapping process has been obtained. Assuming that the electrons are held in traps of thermal energy W eV, the probability of escape per second may be expressed as: where A is a constant, k is Boltzmann's constant and T is the absolute temperature. The charge density decay rate is then given by: In order to determine whether the behaviour of a surface charge is consistent with a trapping process, the decay rate at different temperatures has been measured for several dielectric materials using an electrometer technique.