Impact of the annealing atmosphere in the electrical and optical properties of ZnO thin films

ZnO thin films were obtained using sol–gel method at room temperature; these films were deposited over glass substrates using dip-coating technique. ZnO thin films were subjected to post-deposition annealing in different atmospheres (air, nitrogen and forming gas), to study the changes in optical, morphological and electrical properties. ZnO thin films were highly transparent (above 80 %) and have an optical band gap of 3.2 eV. The deposition of contacts (100 nm of Al) over the thin film surface was defined by photolithography process. According to the results, electrical resistivity of ZnO thin films was calculated at 2.85 × 10², 3.51 × 10⁴ and 1.83 × 10⁴ Ω-cm for thin films annealed in nitrogen, air and forming gas atmosphere, respectively. The current–voltage (I–V) characteristics were measured for each film in dark current illuminating with a blue laser (405 nm). The current measured in dark was 10⁻⁶ A, and the current measured with the blue laser was 10⁻⁵ A independent of annealed atmosphere.