ZnO/ZnMgO heterostructures are promising for applications in ultraviolet light-emitting devices. Recently, we developed a specific procedure for the fabrication of ZnO/ZnMgO single quantum wells with abrupt interfaces and Mg mole fractions as high as x = 0.40 by radical-source MBE. These structures show very narrow luminescence linewidths and distinct excitonic emission up to room temperature (RT). We extended this approach to the growth of ZnO/ZnMgO multiple quantum wells (MQW) on a-plane sapphire and demonstrate RT lasing under optical pumping. To compensate for the lattice mismatch with the substrate, the growth is initiated with a thin ZnMgO nucleation layer followed by a 600 nm thick ZnMgO buffer layer. The five ZnO/ZnMgO MQWs periods are grown combining low-temperature growth of ZnMgO and an annealing step at each interface. TEM data reveal the high quality of the interfaces and uniformity of the layers composing the heterostructure. The thickness of the well layers agrees well with a value calculated from RHEED oscillations ruling out intermixing phenomena. The two ZnMgO buffer layers with significantly different defect densities are clearly distinguished. The substrate/ZnMgO interface region has a much higher dislocation and stacking fault density and dislocation annihilation rate. Above this region, there are threading dislocations with mainly edge character visible. Their density decreases only gradually with layer thickness. Nevertheless, the structures demonstrate strong excitonic emission and lasing under optical pumping with a threshold of 150 kW/cm² at RT. The lasing mechanism differs from the formation of an electron-hole plasma and exciton-exciton scattering, typically observed for ZnO epilayers and ZnO/ZnMgO MQWs. The small energy shift of 64 meV at RT between spontaneous and stimulated emission bands indicates that localized states are responsible for the laser action.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/7941 must be provided.

1. Incoherent and coherent spin manipulation in ferromagnet - dilute magnetic semiconductor hybrids