Effects of thickness variation on properties of ZnO:Al thin films grown by RF magnetron sputtering deposition

• RF magnetron sputter-growth of ZnO:Al thin films at room temperature.
• The grains exhibit a strong preferential orientation along (0 0 2) axis.
• Strong dependence of resistivity on thickness (very low resistivity 1500 nm-thick film).
• High transmittance (greater than 90% in visible region) for all films.

Polycrystalline transparent conductive aluminum doped zinc oxide (ZnO:Al) films, have been grown successfully on glass and silicon substrates by RF magnetron sputtering technique at room temperature. The thickness effect on the structural, optical and electrical properties of these samples is then studied. The structural characterization was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The dc electrical resistivity measurement is achieved in dark at room temperature using four-point probes technique. UV–visible spectroscopy was carried out for the optical characterization. The results show that all the deposited films present a crystalline wurtzite structure with a strong preferred (0 0 2) orientation. The intrinsic compressive stress was found to decrease with the increase of the film thickness. The electrical resistivity decreases with the increase of the film thickness and the smallest measured value was 8 × 10−4 Ω cm for the 1500 nm thick film. The obtained ZnO:Al films, not only have an average transmittance greater than 90% in the visible region, but also have an optical band gap between 3.32 and 3.49 eV depending on the film thickness.