Abstract
The spatial distribution of Al in magnetron sputtered ZnO:Al films has been investigated in depth. Two different kinds of inhomogeneities were observed: an enrichment in the bulk of the film and an enrichment at the interface to the substrate. This has been correlated to the electrical properties of the films: the former inhomogeneities can lead to trap states at the grain boundaries limiting the free carrier mobility. The latter can promote the formation of secondary phases, which leads to an electrical inactivation of the dopant. Furthermore, this effect can contribute to the thickness dependence of the electrical properties of ZnO:Al films.
Highlights
Research Update: Inhomogeneous aluminium dopant distribution in magnetron sputtered zinc oxide (ZnO):Al thin films and its influence on their electrical properties
The enrichment of the Al at the interface to the substrate becomes obvious from the results of the Rutherford backscattering experiments for ZnO:Al films deposited at different temperatures
The observation of the fine crystallites and the increased defect density suggests a possible correlation between this defect rich interface region and the enhanced Al concentration. This is not surprising, because the concentration of Al can exceed the solubility limit in the interface layer of the magnetron sputtered ZnO:Al films leading to the precipitation of secondary phases and a degradation of the crystalline quality
Summary
Research Update: Inhomogeneous aluminium dopant distribution in magnetron sputtered ZnO:Al thin films and its influence on their electrical properties. Sieber et al.[7] performed a study of the microstructural properties of Al-doped ZnO and showed that the Al is present in the form of Zn-Al-O phases at the grain boundaries and in a 10–20 nm thick region at the interface to the Si substrate.
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