Optical Properties of Annealed ZnO Thin Films Fabricated by Pulsed Laser Deposition

Abstract

The annealing effects on the structural and optical properties of grown ZnO thin films fabricated by pulsed laser deposition were investigated by using different techniques. The XRD reveals the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The average grain size (D) of annealed ZnO nanocrystalline thin films is found to be in the range 7.77–15.91 nm. SEM of the thin film consisted of many grains distributed uniformly throughout the surface. TEM shows a relatively smooth surface with an average nanocrystalline size of 13 nm in close agreement with the XRD result. The transmittance spectra demonstrate the highly transparent nature of the films in the visible region (>70 %). The calculation of optical band gap energy (Eg) is found to be in the range 2.95-3.23 eV. The PL spectra show that the amorphous film gives a UV emission only and the annealed nanocrystalline films produce UV, violet, blue and green emissions which indicates that the point defects increased as the amorphous film was annealed. It is concluded that the structural, optical and emission properties of ZnO films grown on glass substrates by PLD strongly depend on the annealing times. The results demonstrate that these annealed films are promising materials for optical component applications.