FORMATION OF A SILVER-RICH SURFACE-LAYER ON ELECTRODEPOSITED CDTE

CdTe thin films were electrodeposited using a nonaqueous solution of propylene carbonate at elevated temperatures (i.e., 95 to 105-degrees-C) and treated with solutions of silver trifluoromethanesulfonate. The silver content of films treated electrochemically with silver salt solution exhibited very little dependence on the applied current density or the silver ion concentration when a constant current was applied for 5 min. Furthermore, if the film was immersed in the silver salt solution for the same length of time with no current applied, the silver content in the film was very nearly the same as that for the electrochemically treated films. These results indicate that the electrochemical treatment has a minimal effect on the incorporation of silver into the film. The silver content in the film reached saturation after a 5 min treatment. The location of the silver in the film as determined by Auger spectroscopy compositional depth profile indicated that the silver was incorporated mainly at the surface of the film in the form of AgxCd(1-x)Te although a small amount of silver penetrated deeply into the film. X-ray photoelectron spectroscopy data supported these conclusions. Hall and resistivity data revealed that the carrier transport properties changed markedly when the silver-rich AgxCd(1-x)Te layer coated the surface. A change in the sign of the Hall coefficient as a function of temperature was observed and was explained in terms of the small bandgap of silver telluride and the different temperature dependence of the electron and hole mobilities.