Structural and optical properties of Yb-doped ZnO films deposited by magnetron reactive sputtering for photon conversion

Doping wide band gap semiconductors, such as ZnO, with trivalent rare earth (RE) ions is well known to enhance their optical activity. The present paper shows that high quality ZnO:Yb layers can be obtained by RF magnetron sputtering and that an efficient electronic transfer from ZnO to Yb+3 ions can be achieved. It is also shown that the rare earth is optically active at any deposition temperature and that its contribution to the photoluminescence (PL) is important even at very low concentrations. In particular, for samples deposited at low temperatures, the rare earth strongly enhances the photon conversion, yielding a total PL up to three times more intense. On the other hand, if the layers are exposed to temperatures above 200 °C, either during deposition or upon post-deposition annealing, the presence of Yb quenches the total PL. Thermal annealing of the films at 700 °C under Ar or O2 gas flow highly improves the PL of both ZnO and ZnO:Yb.