Effect of annealing temperature on the optical constants of zinc oxide films

In this paper, the effect of annealing temperature on optical constants was studied. The ZnO films were deposited on microscopic glass substrates using the sol–gel method for various annealing temperatures. The deposited zinc oxide (ZnO) films were characterized by an X-ray diffractometer (XRD), a spectrophotometer and scanning electron microscopy (SEM). The transmittance spectra recorded through the spectrophotometer exhibits 90% transmittance. The XRD spectra showed polycrystalline nature of ZnO film. Optical constants were determined through transmittance spectra using an envelope method. It was found that there was a significant effect of annealing temperature on the refractive index and extinction coefficient of deposited ZnO films. In this experiment, the optimum refractive index value of 1.97 was obtained at 350 °C annealing temperature at visible (vis) wavelength. The optical energy gap was found to be of ∼3.2 eV for all the samples. The top view of SEM showed the ZnO grain growth on the glass substrates.