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ZnO:Al and ZnO with oxygen vacancies (ZnO:OV) films were prepared by co-sputtering Zn and either ZnO:Al (Al2O3 2 wt %) or ZnO. The influence of the additional Zn supply on ZnO:Al film properties was investigated and compared with the data of ZnO:OV films. The additional Zn supply improved the film crystallinity and reduced the film resistivity. This was ascribed to the decrease of defects in ZnO:Al films due to the improvement of crystallinity, because the maximum carrier concentration in a ZnO:OV film was much smaller than that in a ZnO:Al film where the carrier concentration was created by Al donors. ZnO:Al films prepared by co-sputtering of ZnO:Al (2 wt %) and either ZnO:Al (6 wt %) or Al targets were also investigated. The doping of Al donors, in the first case, decreased the carrier mobility and increased the carrier concentration, in the second case, the carrier mobility increased with further doping.
Tominaga et al. (Thu,) studied this question.