Structural and optical studies of ZnO thin films deposited by r.f. magnetron sputtering: influence of annealing

Zinc oxide thin films were deposited on various substrates by sputtering from a ZnO target. The sputtering gas was obtained from an argon–oxygen mixture (95–5%), at 1 Pa pressure and using a r.f. power density of 0.89 W cm−2. The structural and optical properties of ZnO deposits, submitted to an annealing treatment in the 373–673 K ranges are studied by X-ray diffraction (XRD) and UV-visible spectrometry. XRD measurements show that all the films are crystallised in the würtzite phase and present a preferential orientation along the c-axis. Only one peak, corresponding to the (002) phase (2θ≈34.4°), appears on the diffractograms. The crystallite size, the density and the O/Zn atomic ratio increases with the treatment temperature. These modifications influence the optical properties. The refractive index n, the absorption coefficient α and the optical gap Eg, increase with the treatment temperature, and are sensitive to the oxygen incorporation.