Elemental Distribution and Structural Characterization of GaN/InGaN Core-Shell Single Nanowires by Hard X-ray Synchrotron Nanoprobes

Abstract

Improvements in the spatial resolution of synchrotron-based X-ray probes have reached the nano-scale and they, nowadays, constitute a powerful platform for the study of semiconductor nanostructures and nanodevices that provides high sensitivity without destroying the material. Three complementary hard X-ray synchrotron techniques at the nanoscale have been applied to the study of individual nanowires (NWs) containing non-polar GaN/InGaN multi-quantum-wells. The trace elemental sensitivity of X-ray fluorescence allows one to determine the In concentration of the quantum wells and their inhomogeneities along the NW. It is also possible to rule out any contamination from the gold nanoparticle catalyst employed during the NW growth. X-ray diffraction and X-ray absorption near edge-structure probe long- and short-range order, respectively, and lead us to the conclusion that while the GaN core and barriers are fully relaxed, there is an induced strain in InGaN layers corresponding to a perfect lattice matching with the GaN core. The photoluminescence spectrum of non-polar InGaN quntum wells is affected by strain and the inhomogeneous alloy distribution but still exhibits a reasonable 20% relative internal quantum efficiency.

Emerging Experimental Strategies for Studies on Inhomogeneous Nanomaterials. Exploring Electronics, Atomic Structure and Properties by Synchrotron X-Ray-Based Techniques

“…Recently, Secco et al (2019) performed a detailed study of GaN/InGaN nanowire (NW) heterostructures. Individual NWs were dispersed on 200 nm-thick SiN windows for measurement at the nanoimaging station ID16B of the European Synchrotron Radiation Facility (ESRF, Grenoble, France).…”

Spatially and Time-Resolved Carrier Dynamics in Core–Shell InGaN/GaN Multiple-Quantum Wells on GaN Wire

“…Although most optoelectronic applications benefit from ensembles of wires, their inherent optical properties are critically determined by local structural fluctuations present in individual wires. , Core–shell InGaN/GaN MQWs wires often suffer from heterogeneities, , including indium fluctuations, formation of dot-like In-rich clusters, mixed polarity domains, voids, and well width deviations along the wire. − Therefore, understanding how these defects affect carrier capture, relaxation, transport, and recombination pathways at high spatial resolution remains quite challenging.…”

Advanced Synchrotron Radiation Techniques for Nanostructured Materials

“…It is composed by eight research articles, that together provide not only an interesting and multi-disciplinary overview on the chemico-physical investigation of nanostructured materials carried out by state-of-the-art synchrotron radiation induced techniques, but also an exciting glance on the future perspectives of nanomaterials characterization methods. The published papers focus on the chemical, structural, and morphological characterization of nanostructured materials of different nature carried out by a wide selection of SR-induced techniques such as the X-ray photoelectron spectroscopy (XPS) [1,2] and near edge X-ray absorption fine structure (NEXAFS) [1], in situ XPS and electrochemistry [3], time-resolved X-ray scattering [4], nuclear forward scattering (NFS) of synchrotron radiation [5], soft X-ray absorption spectroscopy (sXAS) [6], X-ray fluorescence [7], X-ray diffraction [7], X-ray absorption [7] and time-resolved X-ray transmission microscopy [8].…”

“…The findings reported in this publication highlight the importance of electronic structure in controlling the oxide catalytic activity. The X-ray absorption apectroscopy is also used by E. Secco et al [7] to study individual nanowires (NWs) containing non-polar GaN/InGaN multi-quantum-wells, in a multi-technique investigation carried out by hard X-ray spectroscopies: X-ray fluorescence, X-ray diffraction, and X-ray absorption. Thanks to the improvements in the spatial resolution of synchrotron-based X-ray probes, that have now reached the nano-scale, the authors were able to probe the chemical composition of the nanowires as well as to describe the nanomaterial structure observing that while the GaN core and barriers appear fully relaxed, there is an induced strain in InGaN layers corresponding to a perfect lattice matching with the GaN core.…”