Structural and optical properties of ZnO thin films by rf magnetron sputtering with rapid thermal annealing

Epitaxial ZnO thin films were grown on c-plane sapphire substrates by rf magnetron sputtering at room temperature followed by a rapid thermal annealing process. We found that crystallinity of the films was strongly affected by the partial oxygen pressure during deposition. Both x-ray diffraction and transmission electron microscopy studies revealed that the ZnO films grow epitaxially predominantly with aligned ZnO domains. An unresolved excitonic resonance was observed in the optical absorption spectrum. Nevertheless, refractive index and absorption edge of the ZnO films are similar to that of single crystal ZnO.