Synthesis and characterization of ZnO:Al thin films deposited by RF magnetron sputtering with uniform properties on large scale

The transparent conductive oxide (TCO) films have attracted much attention as transparent conductive materials in recent years due to the great commercial interest in many optoelectronic devices such as flat panel display (FPD) and in progressing solar cells, being necessary as front electrodes for most thin film solar cells. Nowadays indium-tin-oxide (ITO) is the leading material for TCO film applications but its substitution by other TCO films, begins to be necessary since indium resources are supposed to be exhausted in the next few decades [1,2]. Al2O3-doped ZnO thin films (ZnO:Al) are the most interesting emerging alternative candidates, having comparable electrical and optical performances to ITO, low cost and ready availability for large-scale applications [1,2]. Furthermore, some properties particularly attractive for ZnO:Al are the non-toxicity, the high chemical stability in reduction environments, the high mechanical and thermal stability, the good stability in hydrogen plasma and the easy fabrication. Among many deposition techniques used to prepare ZnO:Al films, radiofrequency RF magnetron sputtering is considered to be the most favourable deposition method since it permit to obtain good quality films, avoid the use of toxic gases and is relatively low cost [3]. Nevertheless, the non-uniformity of spatial resistivity distribution on the surface of ZnO:Al thin films remains an unsolved problem. In fact, ZnO:Al films with very low resistivity can be produced but they exhibit the troublesome phenomenon of a spatial distribution of resistivity corresponding to the inhomogeneous erosion pattern of the target [1,4,5]. One of the aim of this work was the preparation of ZnO:Al thin films on large area (50x50 mm) by RF magnetron sputtering with resistivities in the order of 10-4 ?ocm, averaged transmittance above 90%, improved resistance to moisture and oxidizing ambient and with good spatial distribution uniformity for thickness, optical and electrical properties. Moreover, the feasibility of a potential industrial scale-up was demonstrated.