  Group IV Ge1-xSnx semiconductors hold the premise of enabling broadband
silicon-integrated infrared optoelectronics due to their tunable bandgap energy
and directness. Herein, we exploit these attributes along with the enhanced
lattice strain relaxation in Ge/Ge0.92Sn0.08 core-shell nanowire
heterostructures to implement highly responsive, room-temperature short-wave
infrared nanoscale photodetectors. Atomic-level studies confirm the uniform
shell composition and its higher crystallinity with respect to thin films
counterparts. The demonstrated Ge/Ge0.92Sn0.08 p-type field-effect nanowire
transistors exhibit superior optoelectronic properties achieving simultaneously
a relatively high mobility, a high ON/OFF ratio, and a high responsivity, in
addition to a broadband absorption in the short-wave infrared range. Indeed,
the reduced bandgap of the Ge0.92Sn0.08 shell yields an extended cutoff
wavelength of 2.1 um, with a room-temperature responsivity reaching 2.7 A/W at
1550 nm. These results highlight the potential of Ge/Ge1-xSnx core/shell
nanowires as silicon-compatible building blocks for nanoscale integrated
infrared photonics.
