Graphene-based photodetectors have attracted much attention due to their unique properties, such as high-speed and wide-band detection capability. However, they suffer from very low external quantum efficiency in the infrared (IR) region and lack spectral selectivity. Here, we construct a plasmon-enhanced macro-assembled graphene nanofilm (nMAG) based dual-band infrared silicon photodetector. The Au plasmonic nanostructures improve the absorption of long-wavelength photons with energy levels below the Schottky barrier (between metal and Si) and enhance the interface transport of electrons. Combined with the strong photo-thermionic emission (PTI) effect of nMAG, the nMAG-Au-Si heterojunctions show a strong dual-band detection capability with responsivities of 52.9 mA/W@1342 nm and 10.72 mA/W@1850 nm, outperforming the IR detectors without plasmonic nanostructure by 58-4562 times. The synergy between plasmon-exciton resonance enhancement and the PTI effect opens a new avenue for invisible light detection.

Localized surface plasmon resonance (LSPR) occurs when the incident light frequency matches the free electrons' oscillation frequency in a designed metallic nanostructure. This phenomenon results in the generation of surface plasmons at the metallic-dielectric interface and generates an intense and highly localized electromagnetic field . This property has been widely exploited to enhance the QE . In the infrared range, metallic nanostructures are also integrated with semiconductor detectors to enhance photon absorption and improve carrier transport efficiency. Moreover, surface plasmon polaritons coupled to the graphene surface demonstrate unique features such as high modal indices, relatively low loss, and flexible tunability through electric and magnetic fields.

To surmount the limitations posed by the monolayer graphene absorption and attain the practical benefits of graphene-based photodetectors, a new approach is presented in this study for constructing highly sensitive dual-band photodetectors. This approach integrates the localized electric field generated from metallic plasmonic nanostructure with the unique absorption characteristic and strong PTI effect of nMAG. Plasmonic nanostructures composed of metal on the top and bottom surfaces of silicon cylinders can enhance optical detection and photoresponse at specific plasmon resonance frequencies, thereby enabling sensitive responses from a dual-band of 1342 nm and 1850 nm in nMAG-Au-Si photodetectors. Photoresponse studies show that integrating the plasmonic nanostructure can significantly improve photocurrent up to 5800%, achieving a responsivity of 52.9 mA/W and a detectivity of 4.77 × 10¹⁰ Jones. Implementing this dual-band detector provides a new approach to surpass the performance limitations of traditional silicon-based infrared photodetectors.