Structural and optical properties of ZnO and Ni:ZnO thin films: the trace of post-annealing

Nickel-doped zinc oxide thin films (Ni:ZnO) were deposited on quartz substrates by RF magnetron sputtering. The effect of annealing temperatures on the structural, morphological, and optical properties of the Ni:ZnO thin films were investigated. X-ray diffraction analysis revealed that the ZnO and the Ni:ZnO thin films were crystallized in würtzite phase with the crystallites preferentially oriented towards the (002) direction parallel to the c-axis except for Ni:ZnO which annealed at 300 °C. Based on the optical transmittance measurements, the Ni-doped ZnO thin films were found to be almost transparent but darker than the ZnO thin films. The optical band-gap values of the Ni:ZnO thin films decreased from 3.30 to 3.20 eV, by increasing the annealing temperature. In addition, a linear relationship between the band-gap energy and tail width was determined.