Growth of high-quality ZnMgO epilayers and ZnO∕ZnMgO quantum well structures by radical-source molecular-beam epitaxy on sapphire

We report on a specific growth procedure combining low-temperature growth of ZnMgO and postgrowth annealing at intermediate temperatures. Despite the large lattice misfit induced by the sapphire substrate, layer-by-layer growth is accomplished up to the phase-separation limit found at a c-lattice constant of 0.5136nm and Mg mole fraction of 0.40. The procedure allows us to grow quantum wells with atomically smooth interfaces in a wide range of structural designs exhibiting prominent emission features up to room temperature.