Study of ZnO and Ni-doped ZnO synthesized by atom beam sputtering technique

Zinc oxide (ZnO) and Ni-doped zinc oxide (ZnO:Ni) films are prepared by atom beam sputtering with an intent of growing transparent conducting oxide (TCO) material and understanding its physical properties. The crystalline phases of the films are identified by the grazing angle X-ray diffraction (GAXRD) technique. Thicknesses of the films are measured by ellipsometry. Chemical states of the elements present in the films are investigated by X-ray photoelectron spectroscopy (XPS), which indicates the presence of Ni in the ZnO environment in a divalent state. Average transmission across the ZnO:Ni film was determined to be similar to 83% in the visible region, which is less than that (similar to 90%) of undoped ZnO films. The resistivity measured by van der Pauw technique of the ZnO:Ni film (similar to 9x10(-3) Omega cm) is two orders of magnitude smaller as compared to its undoped counterpart (1 Omega cm). For ZnO:Ni film an average carrier concentration of similar to 1.4x10(19) cm(-3) was observed by Hall measurements. Two important mechanisms reported in the literature viz. influence of d-d transition bands and electron scattering from crystallites/grains are discussed as the possible causes for the increase in conductivity on Ni doping in ZnO