thickness dependence of structural and optical properties of cdte films

In this work, cadmium telluride (cdte) thin films were deposited on glass substrates at room temperature by vacuum evaporation technique. the deposited cdte thin films were characterized by x-ray diffraction, uv-visible spectroscopy, and field emission scanning electron microscopy (fesem) techniques. structural studies revealed that the cdte films deposited at various thicknesses were crystallized in a cubic structure. the results showed improvement of the film crystallinity upon grain size increment. optical constants such as refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constant, volume energy loss function (velf), and surface energy loss function (self) were calculated using data provided by uv-vis spectra. in addition, band gap and urbach energies were calculated by tauc and asf methods. the band gap energy of the specimens was found to decrease from 1.8 to 1.4ev with increasing the thickness offilms. the absorption coefficient; computed and plotted versus photon energy (liv), and tailing in the optical band gap was observed which was understood based on urbach law. urbach energy variation from 0.125 to 0.620 ev in the samples with higher thicknesses is concluded.