Thermally stimulated current studies of sillénite-type oxide crystals: Retrapping kinetics and identity of trapped carriers

Thermally stimulated currents (TSC) of Bi12SiO 20 and Bi12GeO20 crystals were measured after uv excitation at two different temperatures. This double excitation technique was demonstrated to be a simple but effective means of studying the detrapping and retrappping kinetics. In particular, it leads us to suggest that most, if not all, of the trap levels detected by TSC may be hole traps, and calls into question the general belief that these traps are electron traps. In addition, our previous contention regarding the stepwise trapping kinetics among the major traps observed in the TSC spectra was confirmed by this technique. It was found that some of the minor but deeper trap levels at higher temperatures are also related to shallower traps by such stepwise kinetics.