Effect of ion beam assistance on Cu- doped ZnO thin films deposited by simultaneous RF and DC magnetron sputtering

Ion-beam-assisted Cu-doped ZnO (CZO) thin films were deposited on unheated glass substrates by simultaneous RF and DC magnetron sputtering of zinc oxide (ZnO) and copper (Cu) respectively. The as-deposited films were subjected to thermal annealing at 200 °C for one hour. The effects of ion-beam-assistance and thermal annealing on the structural, morphological and optical properties of CZO films have been systematically studied. From XRD studies, it was found that the deposited films were polycrystalline in nature with (002) as a predominant characteristic orientation of ZnO crystallized in hexagonal wurtzite structure along the c-axis perpendicular to the substrate surface. Ion-beam-assistance on CZO films significantly influenced the predominant (002) reflection. Additional diffusion energy gained by the adatoms during film growth enhances the Cu concentration in ZnO host lattice, leads to disruption of (002) reflection. In addition, the surface morphology of deposited films displayed the presence of hexagonal granular-shaped grains vertical to the substrate. Furthermore, we observed that optical transmittance of the as-deposited and annealed films decreased with effect of ion-beam-assistance. Consequently, the optical absorption edge gradually shifted towards longer wavelength side, it resulted to decrease of band gap energy.