Effect of annealing onto physical properties of Co:ZnO thin films prepared by spray pyrolysis technique

In this work, the effect of annealing on the physical properties of Co-doped ZnO thin films has been explored. The Co doping level was fixed at 10 weight (wt) % and deposition has been performed using spray pyrolysis techniques. The deposited film was annealed at temperatures of 400, 450, and 500 ? under an air stream of 5 L min(-1). The effect of annealing on the physical properties of the deposited film was investigated using x-ray diffraction (XRD), scanning electron microscope(SEM), x-ray dispersive spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and optical spectroscopy. XRD results revealed the formation of a single-phase ZnO thin film with no other phases even after annealing. The estimated crystallite size was found to be 34 nm for the un-annealed film which was reduced to 31 nm for film annealed at 400 ?. The SEM images show the formation of large grains which respond differently to the annealing process. Upon annealing the band gap value shows a reduction and the plasma fRequency shows an increase. The performance of all films as UV sensors shows the reduction in the response time for film annealed at 400 ? and the decay time, at the same voltage, for film annealed at 450 ?.