Black Phosphorus (BP), a van der Waals (vdW) semiconducting material, is studied intensively due to its unique structural and anisotropic optical properties. BP exhibits optical anisotropy with thickness tunable direct bandgap from 0.3–2.0 eV. Many BP‐based photodetectors operating in the mid‐infrared (MIR) band are proposed, but their performance is still limited due to the small optical absorption cross section at room temperature. In this work, a plasmonic metasurface that has localized surface plasmon resonance (LSPR) at 3.7 µm is designed, matching well with the band edge of a BP flake and field confinement around the edge of Au‐disk as confirmed by finite difference time domain simulation and Fourier‐transform infrared spectroscopy measurement results. In addition, a BP flake is integrated on the plasmonic metasurface and a significant quenching (twelve‐fold) is observed in the photoluminescence owing to the Förster resonance energy transfer effect induced by dipole–dipole coupling. Following that, a BP‐based MIR photodetector is fabricated on the plasmonic metasurface. Here, the demonstrated BP/plasmonic metasurface‐based photodetector achieves the peak responsivity of 495.85 mAW−1 and ultrahigh operation speed (>10 MHz) at the power of 8.55 µW under 3.7 µm incident wavelength. This demonstrated photodetector opens a new opportunity for optoelectronic applications in the MIR region.

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Owing to their excellent carrier mobility, high absorption coefficient, exceptional quantum efficiency, and low‐cost solution processability, perovskite quantum dots (PQDs) are a promising candidate for photodetection. However, PQDs‐based photodetectors typically show poor optoelectronic performances, mainly limited by their weak light–matter interaction. In this work, MAPbBr3 PQDs are hybridized with graphene (Gr) and morphologically controlled plasmonic gold nanocrystals (AuNCs) to demonstrate a superior photodetector at 432 nm through a synergetic effect. The experimental results indicate that three shaped AuNCs (i.e., sphere, the octahedron (OD), and rhombic dodecahedron (RD)) all contribute to better photodetection behaviors due to surface trap state passivation and enhanced charge carrier densities with longer lifetime compared to that of pristine PQDs. In particular, the PQDs/RD‐AuNCs/Gr system demonstrates a record‐high responsivity of 2.7 × 105 A W−1, a detectivity of 4.9 × 1013 Jones, and external quantum efficiency (EQE) of 7.9 × 107% at 1.6 µW cm−2 illumination power density of 432 nm wavelength with a lowest applied voltage of 1.0 V for a gate‐free PQDs/AuNCs/Gr‐based photodetector. Furthermore, to the authors’ knowledge, this device shows the highest responsivity among the PQDs/AuNCs/Gr‐based electrostatic gate‐free lateral configuration photodetectors.

Plasmonics has been demonstrated to improve the performance of various optoelectronic devices operating in the infrared to visible wavelength regime. However, limited by optical properties of suitable plasmonic materials in ultraviolet (UV) regimes, rare works have been devoted to UV applications with plasmonic structures. This work deliberately fabricates a heterogeneous array of Al nanocaps (Al‐NC) on a wide‐bandgap semiconductor of GaN truncated nanocones (GaN‐TNC) and then presents a multifunctional plasmonic sensor for excellent UV photodetection and air‐quality‐index (AQI) gas sensing. As a UV photodetector, this work shows maximum responsivity (1.8 × 108 AW−1) and detectivity (1.2 × 1018 Jones) at the resonance wavelength of 355 nm, which based on the current knowledge, is the highest detectivity among GaN‐based UV photodetectors. Such a UV photodetector also introduces a decent response of rise time (78.3 ms) and fall time (303.5 ms), respectively. As a gas sensor, this work detects a key AQI gas of NO2 and provides a superior response of 28% and a detection limit of 500 ppb, respectively.