2, Argonne National Laboratory, Argonne, Illinois, United States
3, Aix-Marseille University, Marseille, , France
4, Argonne National Laboratory, Argonne, Illinois, United States
5, Technische Universiteit Munchen, Garching, , Germany
6, Brookhaven National Laboratory, Upton, New York, United States
7, Paul-Drude-Institut für Festkörperelektronik (PDI), Berlin, , Germany
8, University of Siegen, Siegen, , Germany
Ternary (In,Al,Ga)-As (III-As) nanowire (NW) heterostructures are promising near-infrared emitter/detectors for applications including on-chip photonic information transfer. However, they commonly exhibit nanoscale structural inhomogeneities such as nanofaceting, stacking faults, and polytype insertions, which cause modulations of the bandgap. Composition fluctuations and the resulting lattice strain can also modify the bandgap. Correlated measurements of strain, structure, and composition in three dimensions (3D) are necessary to understand nanowire electronic structure and how growth conditions influence the evolution of non-planar heterostructures. Towards this end, we will describe the application of coherent nano-focused x-rays for the non-destructive imaging of strain and local structural features in III-As nanowire heterostructures over a large field of view. We have developed a new approach to 3D coherent diffraction imaging, multi-angle Bragg projection ptychography (maBPP), that can probe strain and structural defects in 3D while utilizing fewer angles and coarser position alignment than traditional 3D Bragg ptychography. Utilizing maBPP implemented at the Hard X-ray Nanoprobe at NSLS-II, we reconstruct a 3D image of strain in a single InGaAs nanowire. Additionally, by accessing a second Bragg reflection sensitive to variations in the wurtzite stacking order, we image stacking defects with better than 3 nm resolution. Nanoscale 3D measurements are combined with coarse scanning nano-diffraction measurements to investigate single nanowires over multiple microns. Analysis of InGaAs quantum wells grown on GaAs nanowires using direct space nanoscale imaging with scanning diffraction x-ray microscopy at the Hard X-ray Nanoprobe at the Advanced Photon Source will also be discussed. Multiple strain components, as well as structural variations in individual nanowires, are correlated with spatially-resolved cathodoluminescence and 3D composition mapping using atom probe tomography to unravel the origins of their unusual emission characteristics.