Ellipsometric analysis of Cd1−xZnxSe thin films prepared by a thermal evaporation technique

Cd1−xZnxSe is an important semiconducting alloy because it is possible to tune its physical properties by controlling its composition x. Thin films of Cd1−xZnxSe with different compositions (x=0.2, 0.4, 0.6 and 0.8) were deposited onto a glass substrate by the resistive thermal evaporation technique. Optical properties such as optical constants and band gap energy of these films were examined by using a spectroscopic ellipsometer. It was found that the optical constants (n and k) decrease with the addition of Zn content in the alloy. In comparison, the band gap energy was also determined by using transmission spectra and found to agree with that of the ellipsometric results. These analyses confirm that the band gap energy increases with the increase of Zn content in the alloy. The composition of the films was estimated by energy dispersive analysis of x-ray studies. The structural properties of these films were studied by using an x-ray diffractometer (XRD). The XRD patterns reveal that the two binary compounds have been completely transformed into a ternary compound with hexagonal (wurtzite) structure having preferred orientation along the c-direction with (002) planes.