Influence of post-deposition heat treatment on optical properties derived from UV-vis of cadmium telluride (CdTe) thin films deposited on amorphous substrate

In this work, we report on post-deposition heat treatment (annealing)-induced change in optical properties derived from UV-vis study of CdTe thin films prepared on amorphous glass substrate by electron beam evaporation technique. Annealing effect gives rise to the enhancement in crystalline nature (zinc blende structure) of CdTe films with (1 1 1) preferred orientation. The average transmittance was increased with the annealing temperature and the slight shift in transmission threshold towards higher wavelength region revealed the systematic reduction in optical energy band gap. The existence of shallow level just below the conduction band, within the band gap was identified in the range of 0.23 and 0.14 eV for the films annealed at 200 and 450 degrees C, respectively. The optical quality of deposited films was confirmed by the photoluminescence study. In addition, the scanning electron microscopic measurement supports the result of X-ray diffraction study. The Swanepoel, Herve-Vandamme, and Wemple DiDomenico models have been employed to evaluate the various optical parameters of CdTe films. These results are correlated well with other physical properties and discussed with the possible concepts underlying the phenomena. (C) 2015 Elsevier B.V. All rights reserved.