Room-Temperature Plasmon-Assisted Resonant THz Detection in Single-Layer Graphene Transistors

Abstract

Frequency-selective or even frequency-tunable terahertz (THz) photodevices are critical components for many technological applications that require nanoscale manipulation, control, and confinement of light. Within this context, gate-tunable phototransistors based on plasmonic resonances are often regarded as the most promising devices for the frequency-selective detection of THz radiation. The exploitation of constructive interference of plasma waves in such detectors promises not only frequency selectivity but also a pronounced sensitivity enhancement at target frequencies. However, clear signatures of plasmonassisted resonances in THz detectors have been revealed only at cryogenic temperatures so far and remain unobserved at applicationrelevant room-temperature conditions. In this work, we demonstrate the sought-after room-temperature resonant detection of THz radiation in short-channel gated photodetectors made from high-quality single-layer graphene. The survival of this intriguing resonant regime at room temperature ultimately relies on the weak intrinsic electron−phonon scattering in monolayer graphene, which avoids the damping of the plasma oscillations present in the device channel.

Impact of device resistances in the performance of graphene-based terahertz photodetectors

“…The broadband operation of our photodetector is confirmed by noting that the value of the extracted relaxation time, τ , of our graphene photodetector with an average mobility of 70.000 cm 2 /(V⋅s) at a carrier density of n ≈ 10 15 m −2 is approximately 0.3 ps. At 0.3 THz, this corresponds to a device quality factor below unity, Q = 0.57 ( Q = 2π fτ , with f being the incoming THz frequency), typical of a THz photodetector working in the broadband regime [ 13 , 23 , 37 ], in a clear contrast with photodetectors operating at higher frequencies and exhibiting resonant detection ( Q ≫ 1) at THz fields [ 29 , 32 ].

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“…In practice, such high-quality samples are achieved by encapsulating the monolayer between hexagonal boron nitride (hBN) [ 26 , 27 ]. The device FET architecture is similar to the one used in several studies in literature reporting plasmonic photodetection [ 25 , 28 – 32 ], having a local top-gate (TG) electrode (which does not cover the entire device channel, see experimental details below). Moreover, the presence of a global back-gate (BG) electrode in the system allows us to independently dope channel regions not affected by the top-gate, tune the access resistance of these areas and therefore study their impact on the measured THz photoresponse.…”

Terahertz communication: detection and signal processing

“…Meanwhile, the fabricated FET device could also act as a resonant THz photodetector due the plasmon resonance in the graphene channel, providing a potential plasmonic application in strong magnetic field. In the latest research, Caridad et al [89] have successfully fabricated single-layer graphene FETs and observed the plasmonic resonant THz detection for the first time. The fabricated short-channel FET detectors could achieve larger than 1 quality factor (Q ≫ 1), even under room temperature.…”