Strained GaAs/InGaAs Core-Shell Nanowires for Photovoltaic Applications.

We report on the successful growth of strained core-shell GaAs/InGaAs nanowires on Si (111) substrates by molecular beam epitaxy. The as-grown nanowires have a density in the order of 10(8) cm(-2), length between 3 and 3.5 µm, and diameter between 60 and 160 nm, depending on the shell growth duration. By applying a range of characterization techniques, we conclude that the In incorporation in the nanowires is on average significantly smaller than what is nominally expected based on two-dimensional growth calibrations and exhibits a gradient along the nanowire axis. On the other hand, the observation of sharp dot-like emission features in the micro-photoluminescence spectra of single nanowires in the 900-1000-nm spectral range highlights the co-existence of In-rich enclosures with In content locally exceeding 30 %.

Extraction of absorption coefficients from as-grown GaN nanowires on opaque substrates using all-optical method.

We demonstrate a new all-optical method to measure absorption coefficients in any family of as-grown nanowires, provided they are grown on a substrate having considerable difference in permittivity with the nanowire-air matrix. In the case of high crystal quality, strain-free GaN nanowires, grown on Si (111) substrates, the extracted absorption coefficients do not exhibit any enhancement compared to bulk GaN values, unlike relevant claims in the literature. This could be attributed to the relatively small diameters, short heights, and high densities of our nanowire arrays.