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

Eleonora Secco,Jaime Segura-Ruíz,Alberto García-Cristóbal,Christoph Giesen,Heruy Taddese Mengistu,Andrés Cantarero,Hannes Behmenburg,Michael Heuken,Bartosz Foltynski,Núria Garro,Gema Martínez-Criado

doi:10.3390/nano9050691

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.

Highlights

Nanowire based GaN/InGaN heterostructures, such as quantum wells (QWs), are acknowledged as optimum support for highly efficient optoelectronic devices [1]
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
This is mostly based on two facts: first of all, the wide spectral range potentially covered by InGaN QWs, which suits perfectly the requirements of lighting and photovoltaic solar cells [2] and, on the other hand, the benefits of NW morphology in overcoming the main difficulties affecting planar geometry [3]

Summary

Introduction

Nanowire based GaN/InGaN heterostructures, such as quantum wells (QWs), are acknowledged as optimum support for highly efficient optoelectronic devices [1] This is mostly based on two facts: first of all, the wide spectral range potentially covered by InGaN QWs, which suits perfectly the requirements of lighting and photovoltaic solar cells [2] and, on the other hand, the benefits of NW morphology in overcoming the main difficulties affecting planar geometry [3]. These measurements, tend to be time-costly; difficult; and, most importantly, imply the destruction of a part of the sample

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