Theory of Thermally Stimulated Conductivity in a Previously Photoexcited Crystal

Abstract

The theory of thermally stimulated conductivity (TSC) for a single trap depth in the presence of deeper traps, and a single type of recombination center, has been developed in detail without making the customary restrictive approximations and assumptions based on the relative importance of recombination or retrapping, or on the constancy of the lifetime. General conclusions about the shape of the TSC curve are presented, depending on the ratio of recombination to trapping probabilities, and on the ratio of the density of the traps of interest to that of deeper traps. The results of the theory are applied to the particular cases of first-order kinetics, strong retrapping with constant lifetime, and strong retrapping with varying lifetime. A critical discussion is given of the analysis of TSC data according to methods involving the quasi-Fermi-level, the half-widths of the TSC curve, varying heating rates, and the initial activation energy at the beginning of the TSC curve. It is concluded that the method of decayed TSC provides the most reliable determination of trap depth. The results of the theory can be readily adapted for application to systems involving more than one type of recombination center.