Abstract
In this study, we used helium gas for the rst time for annealing undoped ZnO lms at di erent temperatures in the range of 500 800 C and we report their structural, optical and electrical properties. All measurements were carried out at room temperature. The undoped ZnO samples exhibited a (002) preferential orientation with the c-axis perpendicular to the substrate, suggesting that samples of high quality were prepared. The PL spectra of the ZnO samples revealed a strong near-band-edge ultraviolet (UV) emission peak at 3.26 eV, a strong red emission peak at 1.91 eV and a weak green emission peak at 2.36 eV, which were attributed to a free electron-acceptor transition, a zinc interstitial and a single ionized oxygen vacancy, respectively. All peak strengths in the PL spectra increased with increasing post-annealing temperature. We also con rmed from PL and Hall measurements that all samples revealed n-type conductivity. With increasing post-annealing temperature, the electron carrier concentration and the strength of UV emission peak increased, suggesting that they are related to each other.
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