Localized Field Enhancement via S-Shaped Grating for High Absorption Narrowband Dual-Color QWIP

This paper presents a dual-band quantum well infrared photodetector (QWIP) based on a vertically stacked quantum well (QW) structure, integrated with a plasmonic microcavity design. The device employs a top S-shaped grating, a quantum well section, and a bottom metal layer to form a metal-dielectric-metal (MDM) microcavity. Leveraging the unique S-shaped grating structure, it achieves surface plasmon resonance at different positions for different response wavelengths, exciting plasmonic modes to enhance the electric field. The device demonstrates ultra-high absorption at wavelengths of 5.7 µm and 6.7 µm. Our study indicates that this grating structure enables a synergistic effect through the dual-resonance mechanism of surface plasmon polariton (SPP) and localized surface plasmon (LSP) modes. Under the influence of SPP, LSP further enhances the electric field, achieving high absorption in both bands. This structure enables dual-band detection with a high absorption efficiency of 99%, combining the advantages of narrow-band operation and 67% high intersubband absorption, along with ultra-narrow bandwidths of 0.14 µm and 0.11 µm at the two response wavelengths.