Effects of Copper Concentration on Structural and Optical Properties of Copper Doped ZnO Prepared by Sol-Gel Spin Coating Method

Undoped ZnO and copper doped ZnO thin films have been synthesized using sol-gel spin coating method on the n-Si substrate followed by thermal annealing. The effects of copper concentration on the structural, electrical and optical characteristics of ZnO films have been examined. The XRD study reveals that the films possess hexagonal wurtzite structure with c-axis orientation and the grain size decreases with increasing copper concentration. Further, optical band gap and reflectance of Cu-doped ZnO are found to depend on the concentration of copper. The ZnO thin films doped with 5 mol% Cu exhibits the highest reflectance (>85% in the visible region). The electrical conductivity, carrier concentration, mobility and nature of conductivity of the deposited films have been determined by Hall measurement, and hot point probe measurement. The stability of the films have been reviewed as a function of time. Fascinatingly, it has been observed that ZnO thin films continue to retain p-type nature even after eight months when preserved under normal atmospheric conditions.