Break-down of corner states and carrier localization by monolayer fluctuations in radial nanowire quantum wells

M. M. Sonner, A. Sitek, L. Janker, D. Rudolph, D. Ruhstorfer, M. Döblinger, A Manolescu, J. J. Finley, A. Wixforth, G. Koblmüller, H. J. Krenner

Nano Letters 19, 3336-3343 (2019) DOI: 10.1021/acs.nanolett.9b01028

We report a comprehensive study on the impact of the structural properties of radial GaAs-Al0.3Ga0.7As nanowire-quantum well heterostructure on the optical recombination dynamics and electrical transport properties and we emphasize particularly the role of the commonly observed variations of the quantum well thickness of different facets. Typical thickness fluctuations observed by transmission electron microscopy of the radial quantum well lead to pronounced localization. Our optical data exhibit clear spectral shifts and multi-peak structure of the emission for such asymmetric ring structures resulting from spatially separated, yet interconnected quantum well systems. Charge carrier dynamics induced by a surface acoustic wave are resolved and prove efficient carrier exchange on native, sub-nanosecond timescales within the heterostructure. Experimental findings are corroborated by theoretical modelling, which unambiguously show that electrons and holes localize on facets where the quantum well is the thickest and that even minute deviations of the perfect hexagonal shape strongly perturb the commonly assumed six-fold symmetric ground state.