Thermally stimulated currents in CdTe polycrystalline films

Investigations of trapping centers have been carried out in CdTe polycrystalline films by using the thermally stimulated conductivity (TSC) technique. The measurements were performed in the temperature range from 80 to 300 K. The TSC spectra showed three peaks related to three trapping levels with energy activations of 0.18, 0.29, and 0.32 eV, respectively. The two first trapping levels correspond to known acceptor centers in bulk CdTe previously reported. It is suggested that the level at 0.32 eV is due to grain boundary defects characteristic of the polycrystalline films. The main parameters of these trapping centers have been determined by using known theoretical relations. The temperature dependence of the dark resistivity indicates that the impurity conduction does not make an important contribution to the TSC spectra of the films. From these measurements an activation energy of 0.49 eV for the conductivity of the films was found.