Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Ultra-thin InxGa1-xN/GaN quantum wells (QWs) embedded in short period superlattices (SPSs) are promising for bandgap engineering and for exploring topological insulator behavior. In order to achieve such feats, it is required to reach high In contents at thicknesses of few atomic monolayers, while avoiding plastic relaxation despite the large misfit. Previous theoretical and experimental works supported the existence of a compositional limit around 33% In in such QWs. In this work, an alternative growth model is proposed, overcoming this limit. Multi-QW (MQW) heterostructures were grown by plasma-assisted molecular beam epitaxy (PAMBE) under metal-rich conditions varying the growth temperatures of the QWs and GaN spacers. The structural quality, strain state, and composition of the QWs were investigated using aberration-corrected scanning transmission electron microscopy (HRSTEM) [1]. Experimental observations were combined with atomistic calculations across the whole compositional range, using an empirical interatomic potential as well as density functional theory. Multislice image simulations of the atomistic supercells were compared quantitatively to the HRSTEM observations using peak finding, thus resulting in the QW composition and strain with monolayer spatial resolution. The growth of monolayer-thick QWs with In-content near 50% was demonstrated and confirmed by photoluminescence measurements. The observed dependence of the QW composition on the growth temperature, and the self-limited QW thickness under metal-rich growth conditions, suggest the existence of a substitutional synthesis mechanism, comprising the surface exchange between In and Ga atoms. The proposed mechanism is promising for further increasing the composition towards binary InN/GaN QWs.

[1] I. G. Vasileiadis, L. Lymperakis, A. Adikimenakis, A. Gkotinakos, V. Devulapalli, C. H. Liebscher, M. Androulidaki, R. Hübner, Th. Karakostas, A. Georgakilas, Ph. Komninou, E. Dimakis and G. P. Dimitrakopulos, Sci. Rep., 11, 20606 (2021)