Preparation and characterization of CdO thin films obtained by thermal oxidation of evaporated Cd thin films

Abstract CdO thin films ( d  = 300–400 nm) were prepared by thermal oxidation of metallic Cd thin films, vacuum evaporated onto unheated glass substrates. The as-deposited Cd films were subsequently heat treated in open atmosphere in two manners: by slowly heating, with rate of 5 K/min up to the temperature of 650 K and maintained at this temperature for 5 min, and by flash heating for 5 min at the same temperature of 650 K. The effect of oxidation procedure on the crystalline structure and electrical (temperature dependence of electrical conductivity) and optical (transmission and reflection spectra) properties of as obtained CdO films was investigated. All obtained CdO films are polycrystalline with strong preferential orientation with (1 1 1) plane parallel to the substrate. Depending on the oxidation conditions, the electrical conductivity at room temperature varied in the range 5 × 10 to 5 × 10 4  Ω −1  m −1 . Also, the optical band gap was found to be of 2.20–2.22 eV for direct transitions and of 1.83–1.92 eV for the indirect ones. In this paper, the obtained results are correlated with the oxidation process that takes place during film annealing.