Optical properties of nanocrystalline CdTe thin films

CdTe thin films were prepared by vacuum evaporation on glass substrates. The XRD diffractogram revealed a zinc blend structure with a strong reflection from the (1 1 1) plane. The diameter of the nanocrystallites was estimated by using the XRD pattern and the Scherrer formula and found to be 23 nm. The transmittance and absorbance measurements were recorded in the wavelength range 600–1100 nm. The first derivative of the absorbance was used to estimate the effective bandgap energies of the nanocrystallites and the hyperbolic band model was used to estimate their radii. The photoluminescence (PL) signal was weak but contains a set of strong sharp lines. These sharp lines are interpreted in terms of the discrete transitions between the valence and conduction bands of the quantum dots. Also the hyperbolic band model was used to estimate the radii of the nanocrystallites depending on the PL spectra.