Effect of heat treatment on the structural and optical characteristics of polycrystalline ZnTe thin films

Zinc telluride (ZnTe) thin films (d = 0.12 - 1.92 mu m) were prepared by vacuum evaporation (quasi-closed volume technique) onto glass substrates. The structural analysis of the films was performed by X-ray diffraction (XRD) technique and atomic force microscopy (AFM). It was found that the films were polycrystalline and have a zinc blende (cubic) structure. AFM images showed that the films have a grain like surface morphology. The values of the absorption coefficient were determined from transmission and reflection spectra. After different heat treatments transmission coefficient strongly decreases. We consider that this effect is due to tellurium excess atoms which diffuse at crystallite boundaries and form microcristallites. Optical energy gap, calculated from the absorption spectra (for allowed band-to-band transitions) was in the range 2.0 eV - 2.2 eV.