Effect of Cu Incorporation on Optoelectronic Properties of e-Beam Evaporated ZnO thin Films by Ellipsometric Investigations

Abstract Electron beam deposition technique has been used to deposit a series of Zn1-xCuxO nanocrystalline thin film on silica substrate with a variety of Cu concentrations. The microstructural, surface morphology and spectroscopic ellipsometry (SE) were used to examine the physical properties of the deposited films. The nanocrystalline nature of the Zn1-xCuxO (0.0≤x≤0.20) thin film has been confirmed by surface morphology studies. The XRD spectrum of the Zn1-xCuxO nanocrystalline film showed a hexagonal wurtzite type structure, and no extra phase was detected. Our results show that as the Cu content increases, the direct optical energy gap Eg decreases without any sign of solubility limit up to x≤0.2. The decrease in Eg can be attributed to the sp-d exchange coupling. In addition, exploring the spectral behavior of the refractive index dispersion from SE of the Cu-doped ZnO shows that as the Cu dopant increments; the refractive index of the deposited film enhances. Further, understand the refractive index dispersion of the deposited film has been performed using a single oscillator model proposed by Wemple-DiDomenico (WDD). Our calculations show that as the Cu concentration increases, the values of oscillator energy Eo decreases however, the dispersion energy Ed increases. As a result, the variation of the optical energy band gap and the tunability of the dispersive oscillator parameters values Eo, Ed, n0, e0, M-1 and M-3 with the increase of the Cu doping level confirm that Cu doped ZnO films are a good candidate for optoelectronic device applications.