Long-Range Surface Plasmon Polaritons for Efficient Optical Coupling in AlGaN/GaN Quantum Well Infrared Photodetector

In this paper, the supermodes, long-range surface plasmon polaritons (LRSPPs), have been theoretically studied to enhance the optical coupling of AlGaN/GaN quantum well infrared photodetector (QWIP) based on gold–Si₃N₄ hybrid architecture. The electromagnetic field, energy flow, and current density are analyzed by finite element method (FEM). In time domain, the electric field component E _z and current density J _z perpendicular to the multi-quantum wells (MQWs) are symmetric and asymmetric distributions over the gold grating, respectively, which precisely prove the existence of LRSPPs. The averaged |E _z |² across the whole quantum well region reaches 1.51?(V/m)² when the electric field intensity (|E ₀|²) of normal incidence is 1?(V/m)² at 4.65 μm. Extraordinarily low loss of the LRSPPs results in a coupling efficiency enhancement ratio of 2.23 in AlGaN/GaN QWIP compared with that obtained via bare gold grating with different polarized sources, exhibiting great potential for application in the focal plane arrays.