Effect of Bi additive on structure and optical properties of amorphous BixIn25-xSe75 chalcogenide films

We report the structure and optical properties of thermally evaporated BixIn25-xSe75 (0 <= x <= 7) films by using X-ray diffraction and optical spectroscopic techniques. The as-prepared samples were found to be amorphous by X-ray diffraction while the crystallization of Se, In2Se3 and Bi2Se3 phases has been observed upon annealing the films at 440 K. The enhancement in the main diffraction peak intensity was accepted as the increase in the crystalline character for the devitrified films with Bi content. The addition of 5 at.% of Bi results in the large change in the electrical parameters due to the carrier type reversal in the as-prepared samples. The red shift in the absorption edge along with a decrease in the transmittance has been observed for the as-prepared samples. The inverse relationship between optical gap and the tailing parameter (except x = 1) were observed with the increase in Bi content. The optical gap was found to increase up to x <= 1 and thereafter, resulted in the decrease in it for the thermally annealed samples. These results have been discussed in conjunction with the structural relaxation and impurity mediated heterogeneous crystallization of the film network. (C) 2012 Elsevier B.V. All rights reserved.