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

Abstract

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 °C 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 °C. 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 °C and the decay time, at the same voltage, for film annealed at 450 °C.