Enhanced Absorption of Extended Short-Wave Infrared in GeSn Nanowire arrays

Engineering light absorption in GeSn structures is crucial to enhance their basic device performance for a variety of applications such as MIR photodetectors. Since Group IV semiconductors typically have large refractive indices compared to air, planar opto-electronic devices are plagued by this refractive index mismatch. A promising method to circumvent this limitation is the use of semiconductor nanowires (NW) arranged in arrays. Top-down etched GeSn NW arrays were microfabricated with varying geometrical configuration. Detailed finite difference time domain (FDTD) simulations were combined with experimental analyses to systematically investigate light-GeSn NW interactions. The diameter-dependent leaky mode resonance peaks are theoretically predicted and experimentally confirmed with a tunable wavelength from 1.5 to 2.2 μm. A three-fold enhancement in the absorption with respect to GeSn thin film at 2.1 µm was achieved using NWs with a diameter of 325 nm. Coupling between the HE₁₁ and HE₁₂ resonant modes manifests at NW diameters above 325 nm and explains the observed absorption enhancement. The ability to manipulate light-matter interactions at the nanometer scale with GeSn is opening up new opportunities for spectral tunability in the extended short-wave infrared range.