Pixel-scale broadband absorption enhancement in PbSe thin films via a multimode-coupled metasurface

Infrared detectors are essential for military and civilian applications, yet high-performance mid-infrared (MIR) detection still predominantly relies on cryogenically cooled narrow-bandgap semiconductors, which severely limits portability and scalability, particularly for imaging applications. Although PbSe enables room-temperature operation and is fully compatible with silicon-based processing, the thin-film PbSe active layer suffers from insufficient optical absorption, which fundamentally constrains its achievable performance. Here, we propose and experimentally demonstrate a metasurface-integrated PbSe active layer that overcomes this bottleneck by engineering multi-modal hybridization to realize broadband, high-efficiency light trapping. The metasurface supercell simultaneously excites gap-surface plasmon (GSP), Fabry-Pérot (FP) cavity modes, localized surface plasmon (LSP), magnetic dipole (MD), and guided-mode resonance (GMR), forming a continuous coupled modal landscape that yields a ∼4.5-fold enhancement in PbSe-layer absorption over a bandwidth exceeding 2.5 μm and peak absorption in the PbSe layer approaching 90%. The device further exhibits polarization-insensitive performance (<1% variation from 0-360°) and angular robustness up to 15° incidence. Importantly, strong enhancement persists in compact pixels comprising only a 2×2 metasurface unit-cell footprint (∼9.2 μm), confirming pixel-level scalability compatible with realistic MIR FPAs. These results establish multi-modal metasurface hybridization as a powerful route to overcome fundamental absorption limitations in PbSe films and open a promising pathway toward next-generation high-performance uncooled MIR imaging systems.