Annealing Effects of ZnO Thin Films Deposited on Si (100) by Using Pulsed Laser Deposition

ZnO thin films were deposited on Si (100) substrates at different temperatures by using pulsed laser deposition technique. An X-ray diffractometer (XRD), a scanning probe microscope and a spectrometer were used to investigate the structural, morphological and luminescent properties of the thin films. We found that the thin films had a preferred (002) orientation and that the peak intensity of the (002) orientation increased with increasing growth temperature up to 400 degrees C. However, the peak intensity decreased when the growth temperature was over 500 degrees C. The grain size and the roughness of the thin films depended on the growth temperature. The higher the growth temperature, the rougher the surface and the bigger the grain size. The photoluminescence (PL) of the thin films deposited at temperatures lower than 500 degrees C showed near-band-edge (NBE) and deep-level (DL) emissions. The peak intensity of the NBE emission increased with increasing growth temperature. The annealing effects of the thin films grown at room temperature were observed and characterized. We observed that the XRD patterns and the surface morphologies of the as-deposited thin film and the post-annealed films were little different. However, the PL spectra of the thin films annealed at different temperatures were quite different. In order to find the origin of DL emission of the as-deposited thin film, we annealed the thin films in a N-2 ambient. We conclude that the DL emissions of the as-deposited ZnO thin film originated from oxygen vacancies instead of zinc interstitials.