Structural, optical and defect state analyses of ZnO nanoparticle films

Synthesis of ZnO nanostructures films by a co-precipitation followed by the deposition processed onto a glass substrate by spin-coating technique was carried out. The effect of annealing temperatures (from 250 to 325 °C for 30 min) on the structural and optical properties of the ZnO films have been investigated. The structural studies reveal that ZnO films are polycrystalline with hexagonal wurtzite structure. The X-ray diffraction (XRD) data show a better crystallinity at (101) crystal plane for the annealed films at 300 °C than the other ZnO films. The average grain size increases (from 31 to 36 nm) with an increase in annealing temperatures. The band gap energy is approximately 3.40 eV for the as-prepared films and varies from 3.25 to 3.18 eV with an increase in annealing temperatures. The photoluminescence (PL) results show a weak ultraviolet and relatively broad visible emissions respect to various defect structures in the ZnO films, in which the interstitial and vacancy oxygen are the main factors influencing the electronic properties in the whole ZnO films.