Effect of post-annealing on the properties of copper oxide thin films obtained from the oxidation of evaporated metallic copper
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Thin films of copper oxide were obtained through thermal oxidation (100-450 degrees C) of evaporated metallic copper (Cu) films on glass substrates. The X-ray diffraction (XRD) studies confirmed the cubic Cu phase of the as-deposited films. The films annealed at 100 degrees C showed mixed Cu-Cu(2)O phase, whereas those annealed between 200 and 300 degrees C showed a single cubic Cu(2)O phase. A single monoclinic CuO phase was obtained from the films annealed between 350 and 450 degrees C. The positive sign of the Hall coefficient confirmed the p-type conductivity in the films with Cu(2)O phase. However, a relatively poor crystallinity of these films limited the p-type characteristics. The films with Cu and CuO phases show n-type conductivity. The surface of the as-deposited is smooth (RMS roughness of 1.47 nm) and comprised of uniformly distributed grains (AFM and SEM analysis). The post-annealing is found to be effective on the distribution of grains and their sizes. The poor transmittance of the as-deposited films (<1%) is increased to a maximum of similar to 80% (800 nm) on annealing at 200 degrees C. The direct allowed band gap is varied between 2.03 and 3.02 eV.