Plasmon Excited Ultrahot Carriers and Negative Differential Photoresponse in a Vertical Graphene van der Waals Heterostructure

Abstract

Photogenerated nonequilibrium hot carriers play a key role in graphene's intriguing optoelectronic properties. Compared to conventional photoexcitation, plasmon excitation can be engineered to enhance and control the generation and dynamics of hot carriers. Here, we report an unusual negative differential photoresponse of plasmoninduced "ultrahot" electrons in a graphene−boron nitride− graphene tunneling junction. We demonstrate nanocrescent gold plasmonic nanostructures that substantially enhance the absorption of long-wavelength photons whose energy is greatly below the tunneling barrier and significantly boost the electron thermalization in graphene. We further analyze the generation and transfer of ultrahot electrons under different bias and power conditions. We find that the competition among thermionic emission, the carrier-cooling effect, and the field effect results in a hitherto unusual negative differential photoresponse in the photocurrent−bias plot. Our results not only exemplify a promising platform for detecting low-energy photons, enhancing the photoresponse, and reducing the dark current but also reveal the critically coupled pathways for harvesting ultrahot carriers.

Silicon/2D-material photodetectors: from near-infrared to mid-infrared

“…In contrast, the IPE effect becomes the dominant when light is mainly absorbed by graphene, in which case the hot carriers with sufficient energy are emitted over the G-Si Schottky barrier and then contribute to the photocurrent 98 , 99 . Similar processes also occur in G-TMDC-G 100 and G-hBN-G junctions (hBN is hexagonal boron nitride) 101 . For the G-hBN-G junctions operating with high-bias voltages, the photoresponse may also come from the tunneling effects, namely the DT and F-N tunneling 41 .…”

“…It is possible to achieve high sensitivity due to the dark current suppression. For example, there are several PDs reported with high-specific detectivity of over 10 10 Jones 13 , 86 , 92 , 94 , 101 . However, they mostly have limited bandwidths e.g., less than MHz currently.…”

Infrared Photodetectors Based on 2D Materials and Nanophotonics

“…This can be achieved in two ways: 1) the direct generation of electron-hole pairs in adjacent 2D materials induced by the highly enhanced electromagnetic fields associated with the metal plasmons; 2) the "hot electrons" (highenergy electrons excited through the decay of surface plasmons) can enter the conduction band of 2D materials and thus contribute to the photoresponse. [120][121][122][123]…”

“…[119] The metallic nanostructures not only confined the electromagnetic field at subwavelength scales but also transferred the energy of incident photons to high energy electrons (i.e., hot electrons) through the excitation and decay of surface plasmons. [121,122,[196][197][198] These hot carriers can be transferred to the conduction band of the 2D materials in contact with the metallic nanostructures, which could be leveraged to induce photoresponse in In the columns 3 and 4, the numbers in the brackets indicate the corresponding enhancement value compared with the performance of these photodetectors without using the nanophotonic structures; b) bP: black phosphorus; c) ChG: chalcogenide glass; d) PhC: photonic crystal.…”

“…[ 119 ] The metallic nanostructures not only confined the electromagnetic field at subwavelength scales but also transferred the energy of incident photons to high energy electrons (i.e., hot electrons) through the excitation and decay of surface plasmons. [ 121,122,196–198 ] These hot carriers can be transferred to the conduction band of the 2D materials in contact with the metallic nanostructures, which could be leveraged to induce photoresponse in IR photodetectors combining 2D materials and metallic nanostructures. In addition, since metal electrodes are commonly used in IR photodetectors, they could be conveniently designed into nanoantennas to enhance the light–matter interactions in 2D materials.…”