Radial composition of single InGaN nanowires: a combined study by EDX, Raman spectroscopy, and X-ray diffraction

The radial alloy distribution of In-x Ga1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated by three different techniques with nanometric spatial resolution and capability to study single nanowires. Energy-dispersive X-ray spectroscopy radial line-scans revealed a gradient in the alloy composition of individual nanowires. Resonant Raman scattering and spatially resolved X-ray diffraction showed the existence of three distinctive regions with different alloy composition. The combination of the three techniques provides robust evidence of the spontaneous formation of a core-shell structure with a thin Ga-richer shell wrapping an In-rich core at the bottom part of the nanowires. This composition-modulated nanostructure offers an attractive way to explore new device concepts in fully epitaxial nanowire-based solar cells. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)