Optical absorption in full composition range of ZnCuO thin films synthesized by spray pyrolysis

A systematic investigation of the structural, morphological, and optical properties of Zn 1 − x Cu x O thin films (0 ≤ x ≤ 1) is presented. The films were produced by spray pyrolysis on top of glass substrates employing a clean acetate chemical route. X-ray diffraction patterns show the polycrystalline character of the films without secondary phases in wurtzite (up to x = 0.10) and monoclinic (above x = 0.90) symmetries. The intermediate concentrations present both phases. Electron microscopy images exhibit homogeneous surface with increasing roughness as the amount of copper increases. For intermediate Cu concentrations, the films present phase segregation with constant optical absorption coefficient around 2 × 10 4 cm − 1 in the visible range, while a larger tunable absorbance is available for higher Cu concentrations. The indirect bandgap is reported for Zn 1 − x Cu x O with x > 0.25, whereas the CuO direct bandgap absorption is very sensitive to the introduction of Zn in the lattice.