Electrically active point defects in Co-doped ZnO epilayers grown by molecular beam epitaxy were reported. Using thermally stimulated current and deep-level transient spectroscopy, a deep electron trap having a thermal activation energy of 0.5eV was identified. The density of this centre appeared to decrease upon annealing the samples in ambient air, but it remained unchanged when the annealing was performed in a nitrogen ambient. It also decreases if the samples were illuminated with UV light at a low temperature prior to the deep-level transient spectroscopy measurements, thus showing the metastable nature of the centre. This electron trap was attributed to the isolated oxygen vacancy. A comparison of these findings with those reported in the literature, on the magnetic properties of ZnO:Co, suggested a correlation between the observed ferromagnetism in these materials and the oxygen vacancy.

On Intrinsic Defects in Co-Doped ZnO Thin Films. D.Seghier, H.P.Gislason: Physica Scripta, 2010, T141[1], 014007