Abstract
Zinc oxide (ZnO) thin films prepared on sapphire substrates by employing a pulsed laser deposition (PLD) have been annealed in vacuum, N 2, and O 2 ambient at annealing temperature 600 °C. X-ray diffraction (XRD) and atomic force microscopy (AFM) observation show that the annealed thin films possess (0 0 0 2) textured feature and form better crystal grains with a large size. X-ray photoelectron spectroscopy (XPS) and Raman analysis show the defects of ZnO thin films annealed in different ambient is distinctly different. The film annealed in vacuum possesses large oxygen vacancies (V o) and Zn interstitials (Zn i); while large surface defects exist in film annealed in N 2 ambient. The concentrations of the intrinsic and extrinsic defects are the lowest in ZnO thin film annealed in oxygen gas. Photoluminescence (PL) spectra also reveal that the ultraviolet (UV) emission is the best for thin film annealed in O 2. The blue emission (2.66 eV) is ascribed to the electronic transition from the donor energy level of Zn interstitials to acceptor energy level of Zn vacancies rather than the O vacancy.
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