  Cost-effective mid-wave infrared (MWIR) optoelectronic devices are of utmost
importance to a plethora of applications such as night vision, thermal sensing,
autonomous vehicles, free-space communication, and spectroscopy. To this end,
leveraging the ubiquitous silicon-based processing has emerged as a powerful
strategy that can be accomplished through the use of group IV germanium-tin
(GeSn) alloys. Indeed, due to their compatibility with silicon and their
tunable bandgap energy covering the entire MWIR range, GeSn semiconductors are
frontrunner platforms for compact and scalable MWIR technologies. However, the
GeSn large lattice parameter has been a major hurdle limiting the quality of
GeSn epitaxy on silicon wafers. Herein, it is shown that sub-20 nm Ge nanowires
(NWs) provide effective compliant substrates to grow Ge$_{1-x}$Sn$_{x}$ alloys
with a composition uniformity over several micrometers with a very limited
build-up of the compressive strain. Ge/Ge$_{1-x}$Sn$_{x}$ core/shell NWs with
Sn content spanning the 6 to 18 at.$\%$ range are demonstrated and integrated
in photoconductive devices exhibiting a high signal-to-noise ratio at room
temperature and a tunable cutoff wavelength covering the 2.0 $\mu$m to 3.9
$\mu$m range. Additionally, the processed NW-based detectors were used in
uncooled imagers enabling the acquisition of high-quality images under both
broadband and laser illuminations without a lock-in technique.
