Broadband absorption enhancement in ultra-thin T2SL-based LWIR detectors with M-type gold nanostructures

This study presents a long-wave infrared (LWIR) detector based on ultrathin Type-II superlattice (T2SL) materials, which is enhanced by an M-type gold nanograting structure utilizing the metal-insulator-metal (MIM) resonant cavity effect to significantly improve light absorption and achieve broadband spectral absorption enhancement. The 14 ML InAs/7 ML GaSb T2SL material was successfully grown using molecular beam epitaxy (MBE), with its excellent crystallinity and surface morphology characterized and verified by X-ray diffraction (XRD) and atomic force microscopy (AFM). The refractive index and absorption coefficient, measured by ellipsometry, provided the required data for the subsequent finite element simulation. The simulation results show that the enhanced LWIR detector achieves peak absorption rates of 99.95% and 99.92% at wavelengths of 9.7 µm and 12.3 µm, respectively, with an average absorption rate of 96.56% across the 9.1-13.3 µm range. This design effectively avoids degradation in electrical performance caused by increased thickness during quantum efficiency (QE) optimization. Furthermore, the detector exhibits no dependence on incident angle, demonstrating significant potential for broad applications in LWIR imaging, sensing, and other advanced infrared technologies.