Strong ultraviolet and green emissions at room temperature from annealed ZnO thin films

Undoped ZnO thin films were grown by rf magnetron sputtering on quartz-glass substrates and thermally annealed under various conditions such as in vacuum, reducing gas (5% H-2 diluted in Ar), oxygen and argon ambient, up to 1100 degreesC. We observed a strong excitonic (UV) emission peak around 3.26 eV, when the films were annealed in the reducing ambient whilst the films annealed in argon and oxygen showed strong deep-level emission peaks. The dependence of the UV and visible emissions on the film crystallinity and annealing is discussed.