Ultralow-noise Terahertz Detection by p–n Junctions in Gapped Bilayer Graphene

Abstract

Graphene shows strong promise for the detection of terahertz (THz) radiation due to its high carrier mobility, compatibility with on-chip waveguides and transistors, and small heat capacitance. At the same time, weak reaction of graphene's physical properties on the detected radiation can be traced down to the absence of a band gap. Here, we study the effect of electrically induced band gap on THz detection in graphene bilayer with split-gate p-n junction. We show that gap induction leads to a simultaneous increase in current and voltage responsivities. At operating temperatures of ∼25 K, the responsivity at a 20 meV band gap is from 3 to 20 times larger than that in the gapless state. The maximum voltage responsivity of our devices at 0.13 THz illumination exceeds 50 kV/W, while the noise equivalent power falls down to 36 fW/Hz 1/2 .

Terahertz Detection by Asymmetric Dual Grating Gate Bilayer Graphene FETs with Integrated Bowtie Antenna

“…The plasmonic drag effect leads to the generation of the photocurrent as observed in our experiments. In a bilayer graphene channel, an opening of the gap could be induced for the same biasing conditions as previously reported [ 48 , 49 , 50 ] that would also lead to a behavior very similar to the one observed in the present study.…”

Terahertz Antenna Impedance Matched to a Graphene Photodetector

“…In BLG, the presence of a bandgap at the charge neutrality point (CNP) of approximately Δ ≈ 250 meV facilitates effective modulation of carrier density, enhancing THz frequency responsivity through differential Seebeck effects across the p–n junction. The maximum Seebeck coefficient difference on both sides of the junction, which scales linearly with the bandgap, arises when the Fermi level crosses the conduction band in the n-region and the valence band in the p-region, boosting the photovoltage responsivity . The presence of a bandgap not only enhances the Seebeck coefficient but also reduces the phonon-aided cooling due to a decreased density of available states for interband electron transitions, which diminishes completely when ℏω ph = Δ.…”

“…The maximum Seebeck coefficient difference on both sides of the junction, which scales linearly with the bandgap, arises when the Fermi level crosses the conduction band in the n-region and the valence band in the p-region, boosting the photovoltage responsivity. 32 The presence of a bandgap not only enhances the Seebeck coefficient but also reduces the phononaided cooling due to a decreased density of available states for interband electron transitions, which diminishes completely when ℏω ph = Δ. This reduction in phonon-aided cooling, coupled with a decrease in electronic heat conductance, leads to stronger localized electron heating (ΔT e ) hence elevating the device's responsivity ( ).…”