Effects of annealing atmosphere on the structural and optical properties of ZnMgO thin films grown by RF magnetron sputtering

ZnMgO thin films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering. For comparison, two series of identical films were then annealed in air and vacuum atmosphere at temperature in a range of 340-500 °C, respectively. The structural and optical properties of the ZnMgO films were systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), spectrophotometer and photoluminescence (PL) spectra. Experimental results indicate that compared with vacuum annealing, air annealing can promote the formation of ZnMgO nanocrystals. At the same annealing temperature, the samples annealed in air have a more nanocrystalline number, larger size, better uniformity and higher PL peak intensity than the vacuum annealed samples. However, the optical band gap of the film annealed in air is narrower than that of the sample annealed in vacuum. Furthermore, the samples annealed in air atmosphere at 420 °C have the largest number of nanocrystals and the largest size (19.14 nm). These results demonstrate that high quality ZnMgO nanocrystals can be precipitated by air annealing.