Phonon-polaritonic long-wavelength infrared photodetectors

Long-wavelength infrared (LWIR) photodetectors are widely used in both military and civilian fields. Compared with traditional LWIR photodetectors, surface plasmon polaritons (SPPs) excited by the coupling of metal microstructures with photons can improve the responsivity and detection dimension of LWIR photodetectors. However, their photodetection performance is limited by two factors: strong absorption competition between metal microstructures and LWIR absorption layers, and weak localization of SPPs to LWIR photons. To overcome these limitations, we propose a paradigm for LWIR photodetection based on surface phonon polaritons (SPhPs). As a proof of the paradigm, we integrate pin-doped HgCdTe with SiC gratings to design an LWIR photodetector with high speed, high response, and multi-dimensional detection. Firstly, SPhPs excited by the coupling of SiC gratings and LWIR photons can enhance the optical absorption of HgCdTe and the generation of photocarriers. Secondly, the pin-doped HgCdTe homojunction with deep sub-wavelength thickness can reduce the transit time of charge carriers and increase the separation speed of photocarriers. Finally, the HgCdTe LWIR photodetector can achieve polarization detection by the polarization-dependent SPhPs excited by SiC gratings. Therefore, we establish a photoelectric joint simulation model based on the finite element method and simulate the photoelectrical characteristics of the proposed HgCdTe LWIR photodetector. Simulation results demonstrate a high absorptivity of 0.7, a large responsivity of 1.95 A/W, and a high detectivity of 2.38 × 10¹⁰cm Hz^1/2 W^-1, a fast response speed of 15.1 ps, a high polarization ratio (PR) of 2.3 × 10³ at 11μm incident light. This work reveals the great potential of SPhP in LWIR photodetection.