Copper doping effect on the properties in ZnO films deposited by sol–gel

Abstract

In this work, an aqueous sol–gel route involving zinc acetate dihydrate and cupric chloride as precursors was used to obtain intrinsic and Cu-doped ZnO thin films onto SiO2/n-Si and glass substrates. Various concentrations of Cu ranging from 1 to 5% were used to modify the ZnO crystal structure. The effect of Cu-doping was evaluated by means of various microscopic and spectroscopic techniques. Scanning electron microscopy (SEM) proved increased grain density and evolution of grain shape from circular to hexagonal with Cu incorporation in the ZnO host lattice. Furthermore, atomic force microscopy (AFM) revealed that grain size increases with increasing Cu concentration. Moreover, X-ray diffraction (XRD) investigations reported a small influence of Cu-doping on the lattice constant value. However, Cu-doping level impacts the mean crystallite size, and consequently, the amount of dislocations emerging from the boundaries of the mosaic blocks. Finally, optical measurements proved the decrease of film transparency, as well as bandgap narrowing effect with increasing dopant concentration from 1 to 5%. As a result, copper incorporation into ZnO films using the proposed low-cost sol–gel method has the ability to tune the bandgap of ZnO-based materials and to promote extra charge carrier generation, which is highly beneficial for UV optoelectronic applications.