A 300nm thin film of ZnO was deposited by magnetron sputtering on hydrothermally grown ZnO and heat treated at temperatures ranging from 500 to 1200C. Secondary ion mass spectrometry was carried out to obtain impurity versus depth profiles around the homojunction. Migration of Al and Mg was observed above 1000C, while lighter elements such as H and Li diffused at lower temperatures. The results showed that several typical impurities were mobile in ZnO during thermal treatments, although the diffusivity for most impurities was too low for an effective out-diffusion in bulk ZnO. The depth distributions of Li clearly demonstrated that Li was mobile below 600C, in contrast to the observation of an overall reduction in Li above 1000C in hydrothermally grown ZnO.

Impurity Migration in Bulk and Thin-Film ZnO. L.Vines, R.Schifano, M.Schofield, B.G.Svensson: Physica Scripta, 2012, T148, 014005