The effect of La doping concentration on the properties of zinc oxide films prepared by the sol-gel method

Thin films of ZnO with different La doping concentration (0, 1, 3, 5; 10at%) are fabricated by the sol-gel method using the spin-coating technique. The effect of La doping concentration on the properties of ZnO films is investigated. The films are hexagonal wurtzite structures and have highly preferred growth along the c-axis direction. But they show poor crystallization with increasing La concentration and the grain sizes of the films decrease remarkably. The optical transmittance of all films is higher than 85% in the visible region, and doped films become more transparent. The optical energy gap increases from 3.26 to 3.31 eV because some La ions have been incorporated in the ZnO lattice. The surface chemical state of the films is examined by X-ray photoelectron spectroscopy (XPS), and it is shown that the La element exists mainly as La(OH)(3) on the films' surface. Raman scattering spectrum is also employed to analyze the effect of La doping concentration on the films. (C) 2008 Elsevier B.V. All rights reserved.