Impact of Cd-addition upon optical properties and dispersion parameters of thermally evaporated CdxZn1-xSe films: Discussions on bandgap engineering, conduction and valence band positions

Abstract

This research was devoted to study the impact of replacing Cd on the account of Zn of ternary chalcogenide CdxZe1-xSe (0 ≤ × ≤ 1.0) films. In addition, to study the optical characteristics of these films. Physical vapor deposition technique under vacuum about 10-5 pa has been used to prepare the film samples. Film thicknesses and the deposition rate were fixed at about 750 nm and 10 nm/S, respectively. The deposited films have been annealed in vacuum at 500 ℃ for 2 hours. X-ray diffraction technique showed that annealing film samples have a polycrystalline nature of face centered cubic structure. The average crystallite size, D of annealed CdxZn1-xSe films proves that these films possess the nanocrystalline structure, where their D-values increase from 26.38 nm to 39.24 nm. Energy dispersion of X-ray spectroscopy technique was used to analyze the elemental composition of films. Optical properties and parameters were deduced from the transmittance and reflectance spectra using spectrophotometric measurements in the range 300 nm - 2500 nm. The single oscillator model of Wemple DiDomenico was utilized also to discuss the dispersion energies of Cd-Zn-Se films. Optical constants (n and k) and the absorption coefficient have been extensively studied. Optical bandgap and band-tail energies, as well as some nonlinear optical parameters were discussed. The chemical bond approach model was used to study the cohesive energy and average coordination number of the films. The position of the valence and conduction bands as well as the CB- and VB- potential values have been studied and discussed.