Chemical structure of microcrystalline CdTe films grown by RF sputtering

Abstract

We have applied X-ray photoemission and Auger spectroscopy techniques to the study of the stoichiometric properties of CdTe thin films grown by RF sputtering. The microcrystalline films were deposited on glass substrates held at temperatures between 50 and 200°C. They contain a mixture of the cubic (zinc-blende) and hexagonal (wurtzite) phases which are nearly stoichiometric. By using bulk and surface sensitive photoemission geometries it is shown that a tellurium oxide overlayer is always formed after exposure to air. A simple calculation shows that this overlayer is at most 10 Å thick. Cadmium seems to be insensitive to the presence of oxygen, as demonstrated by the absence of shifted Cd peaks in the X-ray spectra. It is shown that the low kinetic energy features in the Auger spectra ( <100 eV) are very sensitive to the oxide overlayer and contamination.