Preparation of transparent and conductive Al-doped ZnO thin films by ECR plasma enhanced CVD

The objective of this work is to optimise the deposition conditions of aluminium-doped ZnO by ECR plasma enhanced CVD to produce transparent and conductive thin films. Films were deposited by the reaction of Zn(C2H5)2 and Al(CH3)3 with pure oxygen plasma or mixtures of oxygen and hydrogen plasmas, obtained by an ECR downstream plasma source operated at low pressure (0.1–1 Pa). Control of the resistivity and UV-Vis transparency of the films was achieved by changing the aluminium dose in the film, the preparation temperature and the composition of the plasma (O2:H2 ratio). Optical constants were determined by transmittance data in the UV-Vis region, all samples presenting very good optical characteristics (96–92% transmittance in visible range). On the other hand, resistivities, as obtained at room temperature by a four-point probe, ranged from >10+7 to 6×10−3 Ω-cm, depending on the preparation conditions. Thus, the lowest resistivities were obtained for samples prepared with a plasma of H2+O2 (2.0:1.5). Composition, microstructure, cristallinity and thickness of the films were characterised by XRF, XPS, RBS and XRD.