Optical and microstructural characterization of nanocrystalline Cu doped ZnO diluted magnetic semiconductor thin film for optoelectronic applications

A series of Zn1-xCuxO nanocrystalline films were deposited on a silica substrate using e-beam evaporation technology. The physical properties of the deposited film were closely examined using x-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE). The deposited film's structure revealed the formation of a hexagonal wurtzite structure, with no extra phases found. According to AFM analysis, the deposited Zn1-xCuxO (x = 0.0, 0.04, 0.08, 0.12, 0.16, and 0.2) film has nanocrystalline characteristics. The present findings show that increasing Cu content up to x ≤ 0.2 reduces the direct optical energy gap Eg from 3.286 eV (x = 0) to 2.934 eV (x = 0.2), which can be attributed to the sp-d exchange coupling. The refractive index dispersion extracted from SE analysis for Cu-doped ZnO thin films increased as the Cu dopant increased. In addition, the refractive index dispersion of the deposited film was studied using a single oscillator model proposed by Wemple-DiDomenico (WDD). It was found that the oscillator energy Eo decreases as the Cu concentration increases, while the dispersion energy Ed increases. As a result of the improvement in the optical energy band gap and the tunability of the values of the dispersive oscillator parameters Eo, Ed, n0, ε0, M-1, and M-3 with increasing Cu doping levels, Cu doped ZnO films are a good candidate for optoelectronic device applications.