Effects of substrate position and oxygen gas flow rate on the properties of ZnO: Al films prepared by reactive co-sputtering

Al-doped zinc oxide (ZnO: Al) thin films are deposited at room temperature on rotating glass substrates by direct current co-sputtering of metallic targets under various oxygen partial pressures in the range 0.05-0.067 Pa. The films are polycrystalline with wurtzite structure and show preferential (00 1) orientation when they are transparent. The electrical resistivity is strongly influenced by sample position with the lowest value of 6.6 x 10(-4) Omega cm far from the magnetron axis, where it is directly linked to grain size. As the oxygen gas flow rate is enhanced, the optical transparency rises up and both the electrical conductivity facing the magnetron axis and its lateral homogeneity decrease. A significant reduction in heterogeneity as the draw distance increases suggests an influence of the energy of impinging metal atoms, the instantaneous deposition rate and oxygen reactivity on the electrical behaviour. (C) 2007 Elsevier B.V. All rights reserved.