Low‐Dimensional Plasmonic Photodetectors: Recent Progress and Future Opportunities

Abstract

to these characteristics, LD photodetectors based on atomically thin 2D materials (e.g., graphene, MoS 2 , WS 2 , etc.), [3][4][5][6][7] 1D semiconductor nanowires (e.g., ZnO, Si, GaN, SnO 2 , etc.), [8] and 0D QDs (such as the PbS QD layer, the HgTe QD layer, and the InAs QDs in quantum wells) [9][10][11][12] are at the forefront of photodetector research for their competitive device performance in terms of higher responsivity, high photoconductive gain, and fast response speed. While the downscaling of devices hastens the electrical signal due to the short length of the electron transport, the small volume of the LD photodetectors also suffers from low absorption of light, e.g., 2.3% for single-layer graphene. [13] Surface plasmon polariton (SPP) is light-excited collective oscillation of free electrons on an interface between a metal layer and a dielectric medium such as air. [14] Under the SPP mode, the electromagnetic energy of light excitation is converted to the energy of an electromagnetic wave on the interface that exhibits characteristics of both the photons and the electrons. Therefore, the SPP mode can confine incident light on the surface of the metal layer below the diffraction limit, and propagate along the surface. Owing to the confinement, the SPP electromagnetic field could be enhanced by up to 10 5 . [15] This provides a promising solution to the dilemma of LD photodetectors and therefore are widely used in thin-film plasmonic optoelectronic devices. [16] However, excitation of SPPs on the metal layers is conditional and normally entails a special excitation setup, such as gold film-coated prism, to meet momentum conservation requirements, and therefore its use in LD photodetectors is limited. In contrast, localized surface plasmons (LSPs) can be excited by direct illumination on metal nanostructures, such as metal nanoparticles (NPs). Compared to SPP, LSP is confined on the NP surface without propagation, and its enhancement depends on NP size and geometry. [17] Thus, well-developed fabrication methods of metal nanostructures have rendered LSPs a dominant technology for boosting the device performance of LD photodetectors in recent years. [18] As the photodetector materials change from bulk or thin film to the LD ones, plasmonic materials also evolve for optimized enhancement depending on the dimensions of the photo detectors of interests. Silver nanowires are deposited on a 2D MoS 2 as an SPP photodetector. [2] Gold NPs are deposited on 1D nanowire as an LSP-enhanced photodetector. [19] Perforated nanohole arrays are made on a gold film to directly excite Plasmonic nanostructures can achieve subdiffraction-limit light confinement with enhanced electric fields. By taking advantage of the light-confinement effect, various plasmonic photodetectors that combine low-dimensional (LD) semiconductor structures and plasmonic materials have recently demonstrated excellent plasmon-enhanced device performance and attracted significant research interest. In this review, the state-of-the-art progress in...

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