Polarization-sensitive GeSn mid-infrared membrane photodetectors with integrated plasmonic metasurface

Germanium–tin (GeSn) semiconductors are promising for mid-infrared photodetectors owing to their silicon compatibility, tunable bandgap, and potential for room-temperature operation. Released GeSn membranes provide an additional degree of freedom to extend the operation wavelength through epitaxial strain relaxation, while their transferability expands design flexibility. Meanwhile, metasurfaces have become an effective strategy for engineering light–matter interactions, and their integration with photodetectors can enhance performance and introduce new functionalities. Here, we demonstrate a mid-infrared photodetector consisting of a transfer-printed Ge0.89Sn0.11 membrane integrated with a Au plasmonic metasurface. The photodetector exhibits a wavelength cutoff exceeding 3.0 μm and a nearly fourfold increase in responsivity at 2.5 μm compared to unreleased films, attributed to Fabry–Pérot resonance. Furthermore, by introducing an anisotropic metasurface, the obtained detectors display a strong polarization sensitivity, achieving a measured contrast ratio of ∼4:1 between orthogonal polarizations. Moreover, the operation wavelength of the photodetector can be selectively tuned by varying the geometric scale of the metasurface. The experimental results show excellent agreement with simulations, confirming the effectiveness and versatility of this integrated metasurface-membrane design.