High-quality nonpolar ZnO thin films grown on r-plane sapphire by radio frequency-magnetron sputtering

Nonpolar, a-plane 112¯0 ZnO thin films were epitaxially grown on r-plane 11¯02 sapphire substrate by radio frequency magnetron sputtering. The influence of oxygen partial pressure was studied. With increasing O2 partial pressure of the Ar/O2 sputtering gas, the ridge-like facet structure of the ZnO film altered to a smooth film. Full width half maximum of X-ray rocking curves for the on-axis 112¯0 reflections were 0.45°, 0.36°, 0.09° and 0.25° for samples grown at Ar/O2 ratios of 2/1, 1/1, 1/2 and 1/3, respectively. A smooth surface could be obtained under oxygen rich conditions (Ar/O2 ratio: 1/2), enhancing the lateral growth along the c-axis direction.