Absorption enhancement in LWIR detector via waveguide and plasmonic modes engineering

A high-temperature long-wavelength infrared (LWIR) photodetector based on a thin InAs/InAsSb type-II superlattice (T2SL) absorber is presented, utilizing enhanced optical absorption. This enhancement arises from the excitation of planar waveguide and surface plasmon polariton (SPP) modes, both strongly confined within the absorber and enabled by an adjacent highly doped semiconductor contact (HDSC) layer. Although SPP modes contribute to absorption near the SPP resonance (10 μm), the dominant mechanism, which exhibits stronger absorption, is due to cavity-like guided modes excited between 7 μm and 9 μm. The absorber-HDSC interface exhibits unique optical properties due to a large and tailorable Fresnel reflection phase, governed by a lossless Drude-like index contrast, even though both materials are dissipative. This configuration offers advantages over conventional dielectric or metallic claddings in terms of mode confinement, phase control, and fabrication feasibility. The results obtained in this study confirm the novel approach to achieve strong absorption in thin photodetector structures and open new avenues for subwavelength photonic device design.