Determination of electron trapping parameters: A revisit to Urbach's formula

Abstract

Determination of electron trapping parameters in insulating as well as semi-insulating (SI) solids has remained an interesting rewarding field of research in solid state physics. The earliest formula for determination of the trap-depth (E)-the key parameter-was given by Urbach in 1948. Despite being one of the simplest formula that has its own limitations, it is used even today. In this work we revisit the relevance of the formula at a time when whole curve fitting method has been the accepted method not only for evaluation of trap depth (E) but also other trap parameters like the frequency factor (s) and the order of kinetics (b). On the finer aspect of the work we test the historical formula for ZnO based phosphors and provide some insight into thermally stimulated processes (TSPs) as a whole. Finally, we present the philosophical implications of the historical formula by comparing the electron trap parameter (E) obtained by both the methods (Urbach and whole curve fitting).