Properties of ZnO/ZnMgO nanostructures grown on r-plane Al₂O₃ substrates by molecular beam epitaxy

Growths of ZnMgO/ZnO/ZnMgO multiple quantum well (MQW) structures were performed on semi-polar r-plane sapphire substrates by molecular beam epitaxy. It has been shown that it is possible to grow self-organized ZnMgO nanocolumns with MQW structures at a temperature of 550 °C without employing a catalyst. The nanocolumns are symmetrically tilted at an angle of 62° to the substrate surface. Deposition of a low-temperature (450 °C) ZnO buffer layer prior to the growth of ZnO/ZnMgO MQWs results in good quality planar structures. The crystalline quality of the nanostructures was characterized by X-ray diffraction and scanning electron microscopy. Luminescence properties of ZnO/ZnMgO heterostructures and MQWs were studied. The luminescence was dominated by localized exciton emissions below 100 K, while free exciton recombination was the most intense emission at temperatures above 100 K. - Highlights: • First observation of self-organized growth of ZnMgO nanocolumns on r-plane Al₂O₃ without any catalyst is demonstrated. • Nanocolumns exhibit high crystallographic quality and they are tilted 62° to the substrate. • Deposition of a low temperature ZnO buffer layer results in planar growth of the structures. • The MQWs reveal excitonic near-band edge emission at low and room temperatures.