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Author: Trampert, Achim × DDC: 600 × Type: Text × WGL Institute: PDI ×

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    Electron Tomography of Pencil-Shaped GaN/(In,Ga)N Core-Shell Nanowires
    (New York, NY [u.a.] : Springer, 2019) Nicolai, Lars; Gačević, Žarko; Calleja, Enrique; Trampert, Achim
    The three-dimensional structure of GaN/(In,Ga)N core-shell nanowires with multi-faceted pencil-shaped apex is analyzed by electron tomography using high-angle annular dark-field mode in a scanning transmission electron microscope. Selective area growth on GaN-on-sapphire templates using a patterned mask is performed by molecular beam epitaxy to obtain ordered arrays of uniform nanowires. Our results of the tomographic reconstruction allow the detailed determination of the complex morphology of the inner (In,Ga)N multi-faceted shell structure and its deviation from the perfect hexagonal symmetry. The tomogram unambiguously identifies a dot-in-a-wire configuration at the nanowire apex including the exact shape and size, as well as the spatial distribution of its chemical composition. © 2019, The Author(s).
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    Strategies for Analyzing Noncommon-Atom Heterovalent Interfaces: The Case of CdTe-on-InSb
    (Weinheim : Wiley-VCH, 2019) Luna, Esperanza; Trampert, Achim; Lu, Jing; Aoki, Toshihiro; Zhang, Yong-Hang; McCartney, Martha R.; Smith, David J.
    Semiconductor heterostructures are intrinsic to a wide range of modern-day electronic devices, such as computers, light-emitting devices, and photodetectors. Knowledge of chemical interfacial profiles in these structures is critical to the task of optimizing the device performance. This work presents an analysis of the composition profile and strain across the noncommon-atom heterovalent CdTe/InSb interface, carried out using a combination of electron microscopy imaging techniques. Because of the close atomic numbers of the constituent elements, techniques such as high-angle annular-dark-field and large-angle bright-field scanning transmission electron microscopy, as well as electron energy-loss spectroscopy, give results from the interface region that are inherently difficult to interpret. By contrast, use of the 002 dark-field imaging technique emphasizes the interface location by comparing differences in structure factors between the two materials. Comparisons of experimental and simulated CdTe-on-InSb profiles reveal that the interface is structurally abrupt to within about 1.5 nm (10–90% criterion), while geometric phase analysis based on aberration-corrected electron microscopy images reveals a minimal level of interfacial strain. The present investigation opens new routes to the systematic investigation of heterovalent interfaces, formed by the combination of other valence-mismatched material systems. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim