Investigation on the effect of Cu-doping to ZnTe layers by low-cost electrochemical approach

We have reported the electrochemical synthesis zinc telluride (ZnTe) and copper-doped ZnTe (Cu-ZnTe) thin films by electrodeposition technique from non-aqueous electrolyte. Voltammetric investigations under dark and illumination on the deposition were performed to optimize the growth potentials for ZnTe and Cu-ZnTe. The effect of Cu-doping on the structural, morphological, compositional and optical properties has been studied by means of X-ray diffraction, scanning electron microscopy, atomic absorption spectroscopy and UV-Vis spectroscopy. The growth of semiconducting phase was revealed by photovoltammetry. The direction of photocurrent remains unchanged upon the doping of CuCl2 in ZnTe revealed no change in majority charge carriers. The values of the energy band gap of ZnTe and Cu-ZnTe, 10(-4) and 2 x 10(-4) Cu contents were respectively determined as 2.26, 2.23 and 2.21 eV with sharp absorption edge and enhancement in absorption for the sample grown with 1 x 10(-4) M CuCl2. The structure and surface morphology of ZnTe is sensitive to the choice of the deposition potential. The un-doped film deposited at -0.75 and -0.95 V yielded a mixed cubic as well as hexagonal phase of ZnTe along with metallic tellurium. The surface morphology changes from dendritic to globular. Presence of Cu2+ ions in the ZnTe bath not only helped in preventing the formation of tellurium dendrites, it also yielded single hexagonal phase of ZnTe. In case of Cu-doped layer, the surface morphology changes from flake like structure to globular cluster upon changing the growth potential. The un-doped ZnTe samples were Te-rich, whereas Zn/Te ratio for Cu-ZnTe with 10(-4) M CuCl2 was found to be nearly unity. The direction of thermoemf was indicative of a p-type response. The increased electrical conductivity in Cu-ZnTe film is associated to increase in the hole density as Cu plays a role of acceptor in ZnTe.