Influence of d-d transition bands on electrical resistivity in Ni doped polycrystalline ZnO

We report on the transport and optical properties of Ni doped ZnO polycrystalline samples. Ni doping in ZnO could be achieved to a small concentration (2 mol %). Diffuse reflectance spectroscopy of doped ZnO showed the existence of d-d transition bands at 430, 580, and 655 nm which are characteristic of Ni (II) with tetrahedral symmetry. Resistivity was found to be activated. The value of activation energy of undoped ZnO was about 90 meV. It was found to decrease to 60 meV for Zn0.99Ni0.01O and to 10 meV for Zn0.98Ni0.02O. The decrease in resistivity was found to be in accordance with the impurity d-band splitting model. (c) 2006 American Institute of Physics.