Atomic layer deposited ZnO films implanted with Yb: The influence of Yb location on optical and electrical properties

Epitaxial ZnO films implanted with ytterbium have been studied by combination of channeling Rutherford backscattering spectrometry and Hall measurements. This approach is able to shed more light onto the difficult problem of optical activation of Yb implanted into the ZnO lattice. ZnO films grown by atomic layer deposition on a GaN/Al2O3 substrate were implanted with Yb+ ions to the fluences of 5 × 1014, 1 × 1015 and 5 × 1015 at./cm2. RBS/c spectra show that for as implanted samples the fraction of implanted Yb ions occupying substitutional lattice positions amounts to 72%, 54% and 22%, respectively. Annealing under an ambient atmosphere at 800 °C leads to a partial recovery of the crystal lattice but also substantially reduces substitutional fraction of Yb atoms. Photoluminescence studies on the as-implanted samples revealed a very weak luminescent peak in the near-infrared region, which slightly increases with a fluence. The annealing process leads to optical activation of Yb3 + ions and significantly increases the previously observed the near-infrared inter-ionic emission. The results obtained from Hall measurements indicate that after implantation Yb ions are mainly in the 2 + state and are transformed to the optically active 3 + state as a result of annealing. It suggests that the process of optical activation via annealing is related not only to lattice recovery, but also to Yb diffusion from substitutional to interstitial positions, where Yb ions are in the optically active 3 + state.