Extended Short-Wave Infrared Absorption in Group IV Nanowire Arrays

TL;DR

This paper demonstrates tunable, enhanced short-wave infrared absorption in GeSn nanowire arrays, enabling improved photonic devices through detailed simulations and experimental validation of mode resonances and geometrical effects.

Contribution

It introduces a scalable silicon-integrated platform with GeSn nanowires for tunable e-SWIR absorption, combining simulations and experiments to optimize nanowire geometry and optical response.

Findings

Achieved three-fold absorption enhancement at 2.1 μm with 325 nm diameter nanowires.

Confirmed diameter-dependent leaky mode resonance peaks from 1.5 to 2.2 μm.

Unveiled coupling mechanisms of resonant modes and effects of tapering on absorption.

Abstract

Engineering light absorption in the extended short-wave infrared (e-SWIR) 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 e-SWIR absorption using silicon-integrated platforms consisting of ordered arrays of metastable GeSn nanowires with Sn content reaching 9 at.% and variable diameters. Detailed simulations were combined with experimental analyses to systematically investigate light-GeSn 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 {\mu}m. A three-fold enhancement in the absorption with respect to GeSn layers at 2.1 {\mu}m was achieved using nanowires with a diameter of 325 nm. Finite difference time domain simulations unraveled the underlying mechanisms of the e-SWIR enhanced absorption. Coupling of the HE11 and HE12 resonant modes to nanowires is observed at diameters above 325 nm, while at smaller diameters and longer wavelengths the HE11 mode is guided into the underlying Ge layer. The presence of tapering in NWs further extends the absorption range while minimizing reflection. This ability to engineer and enhance e-SWIR absorption lays the groundwork to implement novel photonic devices exploiting all-group IV platforms.