We report on a combined spectroscopic/structural study of MOVPE-grown GaAs-AlGaAs core-multishell nanowires, containing thin GaAs quantum well tubes (QWTs) wrapped around the central GaAs core. Low temperature (7K) cathodoluminescence (CL) spectroscopic imaging combined with Z-contrast scanning transmission electron microscopy (STEM) tomography performed on single core-multishell nanowires allowed robust correlation between QWT emission and the nanowire inner structure down to the nano-scale. Besides the core luminescence and minor defects-related contributions, each nanowire showed one or more QWT peaks in the 1.53-1.65 eV spectral region, which correlated with sections of the nanowire trunk having different diameters. Average values of QWT thickness (in the 3-7 nm range) were thus extracted from measured nanowire diameter through the application of a multishell growth model, the latter validated against experimental data (core/nanowire diameter, shell thicknesses) obtained from 3-dimensional (3D) reconstructed STEM tomograms of single QWT nanowires. Our data evidenced that the QWT emissions appear redshifted (by about 40-120 meV) with respect to values expected for uniform QWTs of the same thickness. CL mapping evidenced nanoscale localization of QWT exciton emissions along the nanowire, demonstrating that their emission is affected by carrier localization at confinement-potential inhomogeneity. The latter have been ascribed to azimuthal asymmetries as well as (azimuthal and axial) random fluctuations of the GaAs QWT thickness within each nanowire, as evidenced by detailed statistical analysis of the 3D tomograms.

Correlating spectroscopic and nanoscale structural properties in quantum well tubes III-V nanowires

Nicola Lovergine
2021

Abstract

We report on a combined spectroscopic/structural study of MOVPE-grown GaAs-AlGaAs core-multishell nanowires, containing thin GaAs quantum well tubes (QWTs) wrapped around the central GaAs core. Low temperature (7K) cathodoluminescence (CL) spectroscopic imaging combined with Z-contrast scanning transmission electron microscopy (STEM) tomography performed on single core-multishell nanowires allowed robust correlation between QWT emission and the nanowire inner structure down to the nano-scale. Besides the core luminescence and minor defects-related contributions, each nanowire showed one or more QWT peaks in the 1.53-1.65 eV spectral region, which correlated with sections of the nanowire trunk having different diameters. Average values of QWT thickness (in the 3-7 nm range) were thus extracted from measured nanowire diameter through the application of a multishell growth model, the latter validated against experimental data (core/nanowire diameter, shell thicknesses) obtained from 3-dimensional (3D) reconstructed STEM tomograms of single QWT nanowires. Our data evidenced that the QWT emissions appear redshifted (by about 40-120 meV) with respect to values expected for uniform QWTs of the same thickness. CL mapping evidenced nanoscale localization of QWT exciton emissions along the nanowire, demonstrating that their emission is affected by carrier localization at confinement-potential inhomogeneity. The latter have been ascribed to azimuthal asymmetries as well as (azimuthal and axial) random fluctuations of the GaAs QWT thickness within each nanowire, as evidenced by detailed statistical analysis of the 3D tomograms.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11587/468365
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