Electrical and optical properties of thermally evaporated thin films of (As 2S 3) 1− x(PbS) x

Abstract

An investigation of the electrical and optical properties of amorphous thin films of alloys in the pseudo-binary system (As 2S 3) 1−x(PbS) x ( x = 0, 0.1, 0.4 and 0.5) prepared by flash evaporation has been carried out. The synthesized films were characterized by X-ray diffraction, electron spectroscopy for chemical analysis and scanning electron microscopy techniques. The study shows that the stoichiometric composition ( x = 0.5 ) exhibits electronic properties which are quite different from those of the other compositions. The optical energy gap decreases with the addition of PbS. The electrical transport takes place predominantly in the extended states. The alternating current (a.c.) conductivity results show that, at lower temperatures, conduction occurs via bipolaron hopping, while, at higher temperatures, it predominantly takes place by single polaron hopping. In contrast to the bulk glasses, no broad peak is observed in the temperature dependence of the a.c. conductivity of the thin films. The thin films appear to be homogeneous, while the corresponding bulk compositions show phase separation. The structural and electronic features of these semiconductors arc affected by the increasing Pb coordination number with the increase in the PbS content; the coordination number is 9 in the composition with x = 0.5.