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

Abstract

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(C 2H 5) 2 and Al(CH 3) 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 (O 2:H 2 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 H 2+O 2 (2.0:1.5). Composition, microstructure, cristallinity and thickness of the films were characterised by XRF, XPS, RBS and XRD.