High-quality GeSn thin-film resonant cavities for short-wave infrared applications

High-quality infrared (IR) devices made of group IV materials are highly promising to replace traditional III-V semiconductor-based IR optoelectronics due primarily to their compatibility with mature silicon-based technologies and much lower costs. In this regard, germanium tin (GeSn) has emerged as the only direct bandgap material in the group IV family exhibiting superior electrical and optical characteristics. In the past years, GeSn IR optoelectronics including lasers and photodetectors have been realized, although novel device architectures are still needed to enhance their device performance. Here, we experimentally demonstrate high-performance, large-area (mm²) GeSn thin-film resonant cavities (film thickness resonance operating at short-wave IR wavelengths by employing membrane transfer techniques). The fabricated asymmetric air/GeSn/metal structures exhibit high absorptance (>90%) at designed resonance wavelengths, which are easily tuned by tailoring the GeSn layer thickness. The measured resonance absorption reveals excellent agreement with numerical simulations, which further elucidates the mode characteristics of the observed cavity resonances. The demonstrated thin-film device architectures could greatly facilitate the development of novel GeSn photonic devices with tunable wavelengths and enhanced performance enabled by strain engineering, and could allow for the integration of GeSn into many existing group IV-based devices for next-generation IR optoelectronics where high performance, small footprint, and low cost are all required.