Replacement currents in irradiated multilayer structures

An analytical method is described for calculating replacement currents in structures irradiated by x-ray photons, and the method is applied to the case of a structure consisting of plane parallel layers. The analysis consists of a computer-aided computation of photocurrent emission from the material layers; the photocurrents are then used as current generators in an equivalent circuit model, in which transient conductivity in air and dielectric layers is also incorporated. It is shown in particular that the presence of vacuum or air-filled void regions can have a large effect on the magnitude of the replacement currents. Calculated results are compared with experimental measurements for two specific test samples.