Modification of ZnO thin films by Ni, Cu, and Cd doping

With the propose of investigating the effect of transition elements in ZnO thin films prepared by the Successive Ion Layer Adsorption and Reaction (SILAR) technique, the deposition solutions were chemically impurified with Ni, Cu, and Cd, as elements of the Ib, IIb, and VIIIa groups, X-ray fluorescence (XRF) analyses confirm that the impurification with Ni and Cu in fact took place but the impurification with Cd did not, while the XRD analyses show that for as prepared and Ni-impurified annealed films, the crystallites are almost oriented along the c axis. The electrical propel ties of the ZnO films were also modified with the impurification, After annealing in air (450 degrees C) the dark conductivity of the films was increased in the case of Ni and Cd impurification up to 1.80x10(-3) and 1.86x10(-2) [Omega cm](-1), respectively, but it decreased drastically in the case of Cu to 5.51 x 10(-7) [Omega cm](-1), as referred to the dark conductivity (1.86 x 10(-4) [Omega cm](-1)) of the pure ZnO sample. The measured activation energy for the electrical conductivity of the modified ZnO thin films is 55 meV for the Ni modification, indicating the existence of donor levels. On the Other hand, the Cu modification increases the activation energy up to 132 meV, which is higher than the activation energy for pure ZnO thin films (98 meV). (C) 1997 Academic Press.