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

Abstract

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 100K, while free exciton recombination was the most intense emission at temperatures above 100 K.