Oxygen flux influence on the morphological, structural and optical properties of Zn1−xMgxO thin films grown by plasma-assisted molecular beam epitaxy

The Zn1−xMgxO thin films were grown on Al2O3 substrate with various O2 flow rates by plasma-assisted molecular beam epitaxy (P-MBE). The growth conditions were optimized by the characterizations of morphology, structural and optical properties. The Mg content of the Zn1−xMgxO thin film increases monotonously with decreasing the oxygen flux. X-ray diffractometer (XRD) measurements show that all the thin films are preferred (0 0 2) orientated. By transmittance and absorption measurements, it was found that the band gap of the film decreases gradually with increasing oxygen flow rate. The surface morphology dependent on the oxygen flow rate was also studied by field emission scanning electron microscopy (FE-SEM). The surface roughness became significant with increasing oxygen flow rate, and the nanostructures were formed at the larger flow rate. The relationship between the morphology and the oxygen flow rate of Zn1−xMgxO films was discussed.