Deposition of ZnTe thin films by Close Spaced Sublimation: Structural and electrical studies

Zinc telluride has the potential of being a low-cost, environmentally stable, low-resistance and easily manufacturable back contact for CdS/CdTe solar cells. Close Spaced Sublimation (CSS) technique is used to deposit thin films of ZnTe. The results are reported in this study. The effects of substrate temperature and film thickness on the structural properties of the deposited thin films are studied. X-ray diffractograms show that all the films prominently exhibit presence of (111) and (200) orientations. However, the degree of the preferred orientation changes as a function of the film thickness. increase in film thickness reduces the preferential orientation. The as deposited ZnTe thin films, being that of p-type semiconductor, are highly resistive. In order to effectively use these as contact to CdS/CdTe solar cells, they are made more conductive by doping copper. The doping is effected by dipping the films in alcoholic solution of copper chloride, followed by air annealing at 200 degrees C. The resistivity of all the doped films drops drastically in the initial 10 minutes of annealing. The extent of doping is controlled by varying the dipping time. The effects of substrate temperature, film thickness and doping, on the stoichiometry of the films, are studied using Atomic Absorption Spectroscopy (AAS).