The Structural and Optical Properties of Zinc Telluride Thin Films by Vacuum Thermal Evaporation Technique

Abstract

Different thicknesseses of polycrystalline ZnTe films have been deposited on to glasssubstrates by vacuum evaporation technique under vacuum 2.1x10-5 mbar. The structuralcharacteristics studied by X-ray diffraction (XRD) showed that the films are polycrystallineand have a cubic (zinc blende ) structure. The calculated microstructure parameters revealedthat the crystallite size increases with increasing film thicknesses. The optical measurementson the deposited films were performed in different thicknesseses [ 400 , 450 and 500]nm, todetermine the transmission spectrum and the absorption spectra as a function of incidentwavelength. The optical absorption coefficient (α) of the films was determined fromtransmittance spectra in the range of wavelength (400-1100) nm. The dependence ofabsorption coefficient, on the photon energy showed the occurrence of a direct transition withband gap energy from 2.24eV to 1.92eV (for ZnTe films of different thicknesseses), wherewith high film thicknesses there are several energy levels resulting in several overlappingenergy bands in the band gap of these films. The overlapping energy bands therefore tend toreduce the energy band gap, resulting in lower band gaps for thicker films.