Electrochemical synthesis of n-type ZnS layers on p-CuO/n-ZnO heterojunctions with different deposition temperatures.

Metal oxide p-n heterojunctions consisting of p-CuO/n-ZnO/n-ZnS nanostructures were deposited on an ITO substrate by three-step electrodeposition. The effect of ZnS layer deposition temperature on the properties of the heterojunction was investigated by different techniques. The Mott-Schottky analysis confirmed the n-type conductivity for ZnO and ZnS and p-type conductivity for the CuO layer, respectively. Also, it showed a decrease of ZnS donor concentration with increasing deposition temperature. The X-ray diffraction (XRD) analysis confirms a pure phase of hexagonal ZnO, cubic ZnS and cubic CuO structures, respectively. The heterojunction with ZnS deposited at 60 °C shows high crystallinity. The morphological measurements by scanning electron microscopy (SEM) indicate that the deposition temperature has a significant influence on the morphology of ZnO and the atomic force microscopy (AFM) images revealed the improvement of CuO morphology by increasing the ZnS deposition temperature. The UV-Vis response shows strong absorption in the visible region and the profile of optical absorption spectra changes with the ZnS deposition temperature. The current-voltage (-) characteristics of the Au/p-CuO/n-ZnO/n-ZnS/ITO heterojunction display well-defined rectifying behavior for the heterojunction with ZnS deposited at 60 °C.