Space-Charge Effects in Insulators Resulting from Electron Irradiation

A detailed model of space-charge effects resulting from trapping of thermalized irradiation electrons in insulating materials is presented. Analytical solutions for a particular insulating material (polyethylene terephthalate) have been obtained. When the trapping sites are uniformly distributed in energy below the energy level where charge transport occurs, the rate of charge buildup and release depends primarily on a ratio of the material relaxation time constant ρε to a release rate of electrons from traps. Agreement between theory and experiment is reasonably good in the case of polyethylene terephthalate when this ratio of time constants is approximately unity.