Theory of radiation-induced and carrier-enhanced conductivity - Space charge and contact effects

The PECK (Parker enhanced carrier kinetics) model is developed for interpreting experimental results on conductivity in dielectrics. In the model, based on steady state solutions of general kinetic equations for electrons and holes, it is assumed that the holes are instantaneously trapped into deep traps, while the electrons hop from shallow trap to shallow trap and are described as quasi-free with a lowered trap-modulated effective mobility. This simplifies the description of the system to the Poisson equation and a single transport equation for the electrons. Raw data on a 6.4-micron biased sample of Kapton, penetrated by a 28-keV incident electron beam, are considered for interpretation. It is shown that current measurements at zero bias can be interpreted in terms of the shape of the excess-charge deposition profile. Measurements at high bias are matched by the model with an appropriate choice for the trap-modulated electron mobility (approximately 7 x 10 to the -15th sq m/V-s), provided injection is assumed to occur at the cathode contact.