Sub-nanometer mapping of strain-induced band structure variations in planar nanowire core-shell heterostructures
Sara Martí‐Sánchez, Marc Botifoll, Eitan Oksenberg, Christian Koch, Carla Borja, María Chiara Spadaro, Valerio Di Giulio, Quentin M. Ramasse, F. Javier Garcı́a de Abajo, Ernesto Joselevich, Jordi Arbiol
Abstract
Abstract Strain relaxation mechanisms during epitaxial growth of core-shell nanostructures play a key role in determining their morphologies, crystal structure and properties. To unveil those mechanisms, we perform atomic-scale aberration-corrected scanning transmission electron microscopy studies on planar core-shell ZnSe@ZnTe nanowires on α-Al 2 O 3 substrates. The core morphology affects the shell structure involving plane bending and the formation of low-angle polar boundaries. The origin of this phenomenon and its consequences on the electronic band structure are discussed. We further use monochromated valence electron energy-loss spectroscopy to obtain spatially resolved band-gap maps of the heterostructure with sub-nanometer spatial resolution. A decrease in band-gap energy at highly strained core-shell interfacial regions is found, along with a switch from direct to indirect band-gap. These findings represent an advance in the sub-nanometer-scale understanding of the interplay between structure and electronic properties associated with highly mismatched semiconductor heterostructures, especially with those related to the planar growth of heterostructured nanowire networks.