Extended Short-Wave Infrared Absorption in Group-IV Nanowire Arrays

Engineering light absorption in the extended short-wave infrared (ESWIR) range using scalable materials is a long-sought-after capability that is crucial to implement cost-effective and high-performance sensing and imaging technologies. Herein, we demonstrate enhanced, tunable ESWIR absorption using silicon-integrated platforms consisting of ordered arrays of metastable ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ nanowires with Sn content reaching 9 at.% and variable diameters. Detailed simulations are combined with experimental analyses to systematically investigate light\ensuremath{-}${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ nanowire interactions to tailor and optimize the nanowire-array geometrical parameters and the corresponding optical response. The diameter-dependent leaky-mode resonance peaks are theoretically predicted and experimentally confirmed with a tunable wavelength from 1.5 to 2.2 \textmu{}m. A threefold enhancement in the absorption with respect to ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ layers at 2.1 \textmu{}m is achieved using nanowires with a diameter of 325 nm. Finite-difference time-domain simulations unravel the underlying mechanisms of the ESWIR-enhanced absorption. The coupling of the ${\mathrm{HE}}_{11}$ and ${\mathrm{HE}}_{12}$ resonant modes to nanowires is observed at diameters above 325 nm, while at smaller diameters and longer wavelengths the ${\mathrm{HE}}_{11}$ mode is guided into the underlying Ge layer. The presence of tapering in nanowires further extends the absorption range while minimizing reflection. This ability to engineer and enhance ESWIR absorption lays the groundwork to implement alternative photonic devices exploiting all-group-IV platforms.