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Leonardo Viti, Lili Shi, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Miriam S. Vitiello

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[Quantum Sensitive, Record Dynamic Range Terahertz Tunnel Field-Effect Transistor Detectors Exploiting Multilayer Graphene/hBN/Bilayer Graphene/hBN Heterostructures](https://mdr.nims.go.jp/datasets/9d1f827e-4f87-496d-ad7a-44395d88e460)

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Quantum Sensitive, Record Dynamic Range Terahertz Tunnel Field-Effect Transistor Detectors Exploiting Multilayer Graphene/hBN/Bilayer Graphene/hBN HeterostructuresQuantum Sensitive, Record Dynamic Range Terahertz Tunnel Field-Effect Transistor Detectors Exploiting Multilayer Graphene/hBN/Bilayer Graphene/hBN HeterostructuresLeonardo Viti,* Lili Shi, Kenji Watanabe, Takashi Taniguchi, and Miriam S. Vitiello*Cite This: Nano Lett. 2025, 25, 6005−6012 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: Sensitive photodetectors showing large quantum efficiencies andbroad dynamic ranges are essential components for on-chip integrated photonicquantum platforms and for probing quantum correlations in metrologicalsources. However, at terahertz (THz) frequencies, this is a very challenging taskowing to the lack of high-absorption materials and thermal effects that impacttheir noise figure. Here, we develop antenna-coupled tunnel field-effecttransistors, based on multilayer graphene/hBN/bilayer graphene/hBN thatdetect multiwavelength beams at frequencies ∼3 THz with record performances.We reach noise-equivalent powers of ∼10−12 WHz−1/2, a power dynamic rangeexceeding 5 orders of magnitude, limited by the maximum output power (0.8mW) of the employed source, and a minimum detectable power at the nW-level, in a frequency-scalable device architecture. Ourresults open intriguing perspectives for the statistical analysis of quantum intensity correlations in nonclassical light sources operatingin the underexploited THz frequency gap, between technologically mature domains (microwave, visible, near-infrared) that currentlydominate the field of quantum technologies.KEYWORDS: Quantum detectors, terahertz, graphene, scalable nanodevicesThe quest for far-infrared (FIR) (1−15 THz) photo-detectors providing quantum enhanced sensitivity andhigh saturation intensities (>1 W/cm2) is currently drivingextensive research efforts in astronomy,1 spectroscopy,2 andquantum information.3 Traditional technological platforms,such as cryogenically cooled radiation detectors, have beendominant for decades. These detectors primarily rely onsuperconducting hot electron bolometers (HEBs),4 super-conducting transition-edge sensors (TESs),5 and kineticinductance detectors (KIDs),6−8 operating at sub-Kelvintemperatures. These technologies have evolved over time,achieving the astrophysical photon noise limit, with a noiseequivalent power (NEP, power required to obtain a unitarysignal-to-noise ratio) as low as 10−20 WHz−1/2.9 As a result ofthese advancements, photon counting in the terahertz (THz)frequency range has become possible,10 and the demonstrationof single THz photon detection has been recently reported, ina narrow band, around 1.5 THz, using quantum capacitancedetectors (QCDs).11Alongside these established technologies, new materialplatforms and innovative device concepts have been proposedto address the challenge of sensitive photodetection, mostly athigh (>3 THz) frequencies. For example, two-dimensional(2D) graphene has been recently used to realize a HEB basedon a superconductor−graphene−superconductor (SGS) junc-tion,12 achieving NEP ≈ 3 × 10−20 WHz−1/2. Furthermore,atomically thin layered van der Waals materials offer thepossibility of being assembled with layer-by-layer control,enabling the realization of layered material heterostructures(LMHs) with novel and distinctive functionalities.13 Specifi-cally, controlling the twist angle between consecutive graphenelayers (their relative crystallographic orientations) allows forthe realization of twisted-magic-angle bilayer graphene (BLG),which exhibits superconducting behavior. This property hasbeen leveraged in the development of ultrasensitive THznanocalorimeters.14A challenge in developing FIR photodetectors is achievingboth high sensitivity (low NEP) and a large dynamic range.The operation of superconductor-based devices is typicallylimited to optical powers of ∼100 pW due to radiation-inducedsaturation.15 This limitation can hinder their use inapplications where photon statistics are measured, for instance,in the evaluation of quantum intensity correlations betweenoptical modes,16 or in the detection of squeezed states oflight.17Received: October 7, 2024Revised: November 13, 2024Accepted: November 14, 2024Published: April 4, 2025Letterpubs.acs.org/NanoLett© 2025 The Authors. Published byAmerican Chemical Society6005https://doi.org/10.1021/acs.nanolett.4c04934Nano Lett. 2025, 25, 6005−6012This article is licensed under CC-BY-NC-ND 4.0Downloaded via NATL INST FOR MATLS SCIENCE (NIMS) on April 30, 2025 at 09:54:50 (UTC).See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Leonardo+Viti"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Lili+Shi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Kenji+Watanabe"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Takashi+Taniguchi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Miriam+S.+Vitiello"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acs.nanolett.4c04934&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=tgr1&ref=pdfhttps://pubs.acs.org/toc/nalefd/25/15?ref=pdfhttps://pubs.acs.org/toc/nalefd/25/15?ref=pdfhttps://pubs.acs.org/toc/nalefd/25/15?ref=pdfhttps://pubs.acs.org/toc/nalefd/25/15?ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acs.nanolett.4c04934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ashttps://pubs.acs.org/NanoLett?ref=pdfhttps://pubs.acs.org/NanoLett?ref=pdfhttps://acsopenscience.org/researchers/open-access/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/https://creativecommons.org/licenses/by-nc-nd/4.0/Interestingly, 2D materials may provide a valuable solutionin this respect. In particular, photodetectors based on single-layer graphene (SLG) and bilayer graphene (BLG) haveshown large dynamic ranges (up to 4 orders of magni-tude)18−20 due to their high saturation currents and efficientelectron cooling dynamics (electron-optical phonon scatteringtime of ∼1 ps21,22).Additionally, BLG, which is a gapless semiconductor in itspristine form, allows for the induction and tuning of an energygap (Eg) in its band structure through interaction with asubstrate23 or by applying an external out-of-plane electricfield.24 This field can be generated, for example, by breakingthe out-of-plane inversion symmetry with a neighboringcrystal, inducing a finite Eg by proximity. This crystal fieldhas been used to activate a THz gap (Eg = 10 meV25) in large-twist-angle double BLG heterostructures, leading to thedevelopment of ultrabroadband photovoltaic detectors with afrequency coverage spanning from the THz to the near-infrared range.26Importantly, the bandgap of BLG can also be adjusted by anout-of-plane electric field, controlled by external dual-gateelectrodes.27,28 This configuration has been used to realizetunnel field-effect transistors (TFETs) based on BLG, whichoperate as sensitive photodetectors (NEP ≈ 30−300 × 10−15WHz−1/2) at frequencies around 100 GHz in single-top-gated29or top p−n junction30,31 configurations.Here, we propose to employ TFETs as a technologicalapproach for quantum-sensitive THz receivers targetingfrequencies (3 THz) higher than those reported in previousworks,29−31 where a sensitivity drop typically occurs. Byselecting BLG as the core active material, we demonstrate thepowerful and broadband capability of the TFET deviceconcept, in a spectral range never addressed so far, and withstate of the art performances.The proposed photodetector comprises a multilayergraphene (MLG)/hexagonal boron nitride (hBN)/BLG/hBNheterostructure and exploits the tunability of the energy gap ofBLG to create a lateral tunnel junction between the gated andungated portions of the BLG−FET channel. By exploiting thejunction nonlinearity, it rectifies the incoming THz radiation.The subwavelength TFET channel is coupled to the impingingradiation via a planar bow-tie antenna, specifically designed tobe resonant at 3 THz. Remarkably, the proposed concept isfrequency scalable, from 0.1 to 10 THz, across the entire sub-THz and FIR ranges. Importantly, in our geometry, theantenna is asymmetrically coupled to the source (S) and top-gate (TG) electrodes, enabling zero-bias operation of thetunnel-junction rectifier.The demonstrated capability of TFETs to operate asquantum sensitive photodetectors at frequencies of ∼3 THz,combined with the inherent frequency scalability of this deviceconcept, offers concrete perspectives for detecting nonclassicalstates of THz light that could be generated by THz quantumcascade laser (QCL) frequency combs. This opens up excitingopportunities for developing THz quantum platforms based onsolid-state devices. A state-of-the-art combination of perform-ances is demonstrated, achieving a minimum NEP of 10−12WHz−1/2 and a dynamic range exceeding 5 orders ofmagnitude, limited by the maximum output power (0.8 mW)of the employed QCL source.All flakes used for the MLG/hBN/BLG/hBN heterostruc-ture assembly are mechanically exfoliated from bulk crystals(Supporting Information). In order to implement a dual-gatedarchitecture, we positioned BLG, encapsulated in hBN, on athin MLG (8−10 layers) flake, which serves as back-gate (BG)electrode. hBN−BLG−hBN heterostructures are assembledusing a standard dry-transfer technique,32,33 as described in theSupporting Information. An optical image of one of theassembled LMHs, transferred onto a Si/SiO2 substrate, isshown in Figure 1a. After the LMH assembly, the antenna-coupled BLG-FETs are fabricated following the proceduredescribed in the Supporting Information. Figure 1b displays aFigure 1. (a) Optical microscope image of the assembled layered materials heterostructure. The top-hBN flake is 15 nm thick, and the bottom hBNflake is 40 nm thick. (b) False color SEM image of the devised TFET. The bow-tie antenna is connected to the source and top-gate electrodes. (c)Schematic diagram of the BLG−FET active element, indicating the different materials composing the device and the electrical scheme adopted forelectrical and optical characterizations. The gating scheme is indicated on the left-hand side. (d) Schematic longitudinal cross-section of the activeelement, showing five different regions along the BLG channel, which can be described as a series of resistors. The S and D contacts have intrinsiccontact resistance (Rcont). The regions not covered by the top-gate are only influenced by the MLG bottom-gate with resistances RS and RD at thesource and drain sides, respectively. The resistance of the central region (RC) is influenced by the combined action of the two gates.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.4c04934Nano Lett. 2025, 25, 6005−60126006https://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig1&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.4c04934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asfalse-color scanning electron microscope (SEM) picture of oneof the investigated devices. The BLG−FET channel is shapedas a rectangle, with length Lc = 6 μm and width Wc = 3 μm,and is connected to the source (S) and drain (D) electrodes.The top-gate (TG) electrode is electrically isolated from theBLG channel by the top-hBN flake and a 30 nm thick layer ofHfO2 grown by atomic layer deposition (ALD). The THzbow-tie antenna has a radius of 21 μm, set to be resonant with3 THz radiation.34 These dimensions are selected followingthe results of electromagnetic simulations performed with acommercial software (COMSOL Multiphysics35), based on afinite elements method. This system configuration entails arelatively simple device circuitry, as shown schematically inFigure 1c: two hardware switches enable the selection betweenelectrical and optical characterization experiments. We studytwo devices, S#1 and S#2. A description of their geometricalparameters is reported in the Supporting Information.To investigate the performance of the photodetector at lowtemperatures, we mounted the device in a He flow cryostat(Janis Research) with THz optical access and controllableheat-sink temperature (T) between 4.2 and 300 K (roomtemperature, RT). To ensure effective thermal contact betweenthe cryostat’s copper cold unit and the silicon substrate, thesample is soldered onto a copper-carrier using an indium-basedsoldering alloy (Indium Corporation, PTI290/84/F).We examine the impact of vertical electrostatic gating on theBLG bandgap by studying electron transport through the BLG-channel at cryogenic temperatures. This electrical character-ization is performed by independently controlling the source−drain bias (VSD), the back-gate voltage (VBG), and the top-gatevoltage (VTG), and measuring the current at the D electrode(ISD) using dc source meters (Keithley, SMU-K2400). Thedependence of the two-terminal channel resistance (R) onVTG, measured at various T values for sample S#2, and atdifferent VBG, is shown in Figure 2a. The transport is stronglyaffected by the out-of-plane displacement field (Df), whichincreases when the top- and back-gates have opposite polarities(see Supporting Information). In particular, for |Df| > 0.3 V/nm, the maximum value of R (Rmax) consistently increases as Tdecreases from 200 to 4.2 K, indicating a gap opening.36 Byanalyzing the temperature dependence of Rmax, it is possible toquantitatively estimate the energy gap of BLG. The Rmax(1/T)trend reveals an activation behavior (Figure 2b,c) that followsan Arrhenius-type dependence: Rmax = R0 + exp(Eg/2kBT),where kB is the Boltzmann constant. By conducting a linear fitto the Arrhenius plots in the temperature range between 40and 200 K, we estimate Eg = 7.2 meV for Df = 0.3 V/nm, Eg =8.5 meV for Df = −0.3 V/nm, Eg = 15.5 meV for Df = 0.47 V/nm, and Eg = 17.4 meV for Df = −0.46 V/nm, confirming thepresence of a gate-tunable bandgap in the BLG channel (datafor |Df| > 0.4 V/nm are shown in the Supporting Information).We note that the estimated Eg values are a factor of ∼2 smallerthan those expected for ultraclean BLG heterostructures atsimilar |Df| values.37,38 The observed discrepancy indicates thepresence of disorder-induced subgap states.38We test the THz photoresponse performance of the TFETusing a focused beam generated by a 3 THz QCL. This allowsus to tune the average optical power (Pt) at the detectorposition up to ∼0.8 mW (see Supporting Information). TheTHz beam, polarized parallel to the TFET antenna axis, isfocused by using two lenses. For optical characterization, theTFET photovoltage (Vphoto, Figure 1c) is measured at the Delectrode using a lock-in amplifier (SR5210) after preampli-fication (dLInstruments, model 1201, gain g = 1000). In orderto reduce the 1/f contribution to the detector’s noise figure,39we electrically modulate the intensity of the QCL with asquare-wave envelope at a frequency of 7.333 kHz.We used BLG-TFET to measure the intensity distribution inthe focal xy plane. Figure 3a shows the intensity profile as amap of Vphoto when Pt = 100 μW. The visible Airy patterndemonstrates the good sensitivity of the photodetector. Wecalculate the beam spot area St as the area of an ellipse withmajor and minor axes given by the half-width at half-maximum(HWHM) of the beam profiles along the x and y directions(dashed lines in Figure 3a).We obtain St = 80 × 10−3 mm2. Since the detector’s activearea is much smaller than St, we estimate the fraction of opticalpower impinging on the TFET as Pa = (Pt*t) × (Sλ/St), whereFigure 2. (a) Isotherm curves showing channel resistance of S#2 as a function of top-gate voltage (VTG), acquired at three different values of VBG:+3 V (red lines), 0 V (blue lines), and −4 V (green lines). The curves for two additional values of VBG (−6 V and +5 V) are reported in theSupporting Information. The temperature is changed from 4 K (darker lines) to 310 K (brighter lines), sweeping through the values (4, 20, 40, 80,120, 160, 200, 240, 280, 294, and 310 K). The vertical dashed lines indicate specific values of the displacement field (D), which is responsible of thebandgap opening in BLG. Since the contact resistance (Rcont) changes as a function of temperature (see Supporting Information), its value has beensubtracted from the data in (a). (b) Scatter plot of the resistance peak as a function of the inverse of the temperature (Arrhenius plot) evaluated atfour different values of the displacement field (Df). (c) Zoom of the graph in (b) in the region of temperatures where the slope of ln(Rmax) vs 1/Tis linear (40 K: 200 K). In this region, we apply a linear fit to ln(Rmax) to evaluate the energy gap.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.4c04934Nano Lett. 2025, 25, 6005−60126007https://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig2&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.4c04934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-ast = 0.5 represents the transmittance through the high-densitypolyethylene (HDPE) cryostat window, Sλ = λ2/4 representsthe diffraction-limited area40 (see Supporting Information),and the value of the ratio St/Sλ is approximately 50. We thenevaluate the voltage responsivity using the expression:20,41= ×gR2 2 ( /4) VPvphotoa (1)where the factor 2 accounts for the peak-to-peak magnitude,√2 originates from the root means square amplitude of thelock-in amplifier, and π/4 represents the fundamental sinewave Fourier component of the square-wave produced by thesquare-wave envelope used to modulate the QCL.Figure 3b shows the plot of Rv(VBG) acquired at varioustemperatures for sample S#1. The responsivity increases as T islowered, as a result of the sharper nonlinearity in the channelresistance (see Supporting Information).29 It reaches amaximum value of approximately 0.6 kV/W near the CNPfor T = 4.5 K. We note that in this measurement, the top-gatevoltage is not employed, VTG = 0 V; thus, the displacementfield weakly departs from zero, and the photoresponse isdominated by the resistive self-mixing effect, as discussed indetail in the Supporting Information.We then characterize the dynamic range of the detector bysweeping the QCL power from zero to Pt = 800 μW. TheTFET can detect a minimum optical power of ∼5 nW(through the cryostat window) and its response is nearly linearover the entire range of investigated powers, showing a close tounity power-dependence Vphoto ≈ Ptγ, with γ = 0.96 (Figure3c). It is worth noting that the high-power limit of the dynamicrange for the investigated BLG-TFET detector is determinedby the maximum power of the QCL, which represents anintrinsic limitation of our experimental setup.To investigate how the electrical transport and photo-response are influenced by the combined action of the twogates, we map ISD and the responsivity as a function of VTG andVBG. The transport map shown in Figure 4a, relative to sampleS#1, reveals two minima, corresponding to two distinct CNPs:a fixed one (CNP1), described by a vertical line at VBG ≈ −1.5V, and a top-gate-tunable one (CNP2), represented by adiagonal line. We attribute the presence of these two CNPs tothe existence of two distinct regions along the BLG channel.Indeed, in our geometry, the top-gate electrode is narrowerthan the bottom gate, which acts on the BLG regions near theS and D contacts (Figure 1d). These regions are not affectedby VTG, and their transport tunability by VBG is proven byCNP1. Conversely, the diagonal line marks the shift of CNP2under the simultaneous influence of the two gates, in thedouble-gated region of BLG, with a slope determined by theratio of the gate lever arms (see Supporting Information).38Based on this understanding, we can identify four distinctdoping regions in the map of ISD(VBG,VTG): n−p, n−n, p−n,and p−p, with the first letter denoting the dual-gated area.For sample S#1, a strong correspondence is visible betweenthe ISD(VBG,VTG) and Rv(VBG,VTG) maps (Figure 4a,b). Asignificantly larger photovoltage signal is observed when thep−n junction is active, whereas a much smaller signal isdetected in other regions. Importantly, this responsivity patterndiffers from what is typically observed in the photothermo-electric (PTE) effect, which would instead result in a 6-foldpattern.19,31,42 Instead, the retrieved pattern aligns with thosefound in similar single-top-gate TFETs operating at lowerexcitation frequencies.29 We note that for sample S#1, a smallincrease in resistance is visible when moving along the linemarked by CNP2. This is related to the reduced bandgapopening effect under the influence of Df, which we attribute toa inadequately clean LMH: residual impurities and defects canlead to the presence of disorder-induced subgap states.38The situation is different for sample S#2, where R increasesfor larger displacement fields along the diagonal line CNP2(Figure 4c), with ISD changing by 2 orders of magnitudeFigure 3. (a) Lock-in signal (Vphoto) measured by the TFET in thefocal plane, for Pt = 100 μW and T = 4.5 K. The 2 × 2 mm2 map isacquired by translating the optical cryostat using a heavy duty xymechanical stage (Physik Instrumente, LS180). The profiles at thecenter of the beam (dashed lines) give beam waists of 400 and 250μm along the x and y directions, respectively. (b) Responsivity curvesmeasured as a function of VBG, obtained at various operatingtemperatures. (c) Low-temperature Vphoto plotted as a function of Ptin log−log scale, with VBG = −1 V and VTG = 0 V. The dashed linerepresents a linear fit to the data. The shaded area represents theexperimental noise floor (∼20 μV) on the lock-in amplifier. The errorbars indicate the amplitude of the background signal (THz light off)summed to the root-mean-square deviation of the measuredphotovoltage.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.4c04934Nano Lett. 2025, 25, 6005−60126008https://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.4c04934/suppl_file/nl4c04934_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig3&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.4c04934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asbetween different regions of the ISD(VBG,VTG) map. TheRv(VBG,VTG) map shown in Figure 4d presents differentfeatures compared to those of device S#1. First, a 6-foldpattern is visible, indicating a photothermoelectric contributionto the response.31,42 Second, distinctive features appear in themap, represented by faint diagonal lines, almost parallel to themain sign change along CNP2. These features clearly emergein the map of the first derivative of Rv (Figure 4e) and can belinked to the excitation of plasmonic resonances in the gatedBLG channel, in agreement with previous findings in high-quality SLG- and BLG-based THz detectors.43,44 Importantly,Rv increases when gate voltages are swept along the CNP2 line,away from the map center, i.e., for increasing displacementfields (Figure 4f). This can be explained by the onset oftunnelling rectification, which is expected to increase for largeDf.29 Therefore, we conclude that three rectification mecha-nisms contribute to the Rv(VBG,VTG) map of S#2: photo-thermoelectric effect, plasmonic, and tunneling rectifications.We eventually calculated the NEP of the BLG-TFETs. Forthis purpose, we assume that the noise spectral density (NSD),which is the amount of noise power per unit bandwidth, isprimarily due to thermal fluctuations. This assumption is validbecause of the high modulation frequency (7.333 kHz) used inour experiments.36 Using the expression NEP = 1/Rv ×(4kBRT)1/2,39 and the values of R and Rv extracted from themaps in Figure 4a−d, we estimate a minimum NEP of 1.1 ×Figure 4. (a) S#1: electrical transport characterization at 4.5 K: ISD map measured as a function of VBG (span from −9 V to +3 V) and VTG (spanfrom −4.5 V to +4.5 V). Different junction configurations are highlighted (p−p, n−p, etc.). (b) S#1: voltage responsivity map measured as afunction of VBG and VTG. (c) S#2: electrical transport characterization at 4.5 K: ISD map measured as a function of VBG (span from −6 V to +6 V)and VTG (span from −7 V to +7 V). (d) S#2: Rv(VBG,VTG). In this case, a 6-fold pattern appears, indicating a thermoelectric contribution to thephotodetection. Colored boxes indicate regions at high displacement fields near CNP2. (e) Map of the first derivative of Rv(VBG,VTG), with respectto VTG. Oscillations are visible in the background, appearing as diagonal lines, almost parallel to the sign-change line at CNP2. (f) Maximumresponsivity measured in the boxes in (d), plotted as a function of VBG. Rv increases for larger displacement fields.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.4c04934Nano Lett. 2025, 25, 6005−60126009https://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934?fig=fig4&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.4c04934?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as10−12 WHz−1/2 for S#1 and of 1.3 × 10−12 WHz−1/2 for S#2.These values are not competitive with respect to thesensitivities of more established and technologically maturecommercial devices, such as HEBs,9 QCDs,11 and KIDs,8exhibiting NEPs < 10−21 WHz−1/2. However, the TFET deviceconcept could serve as a complementary technologicalplatform, allowing for less stringent cooling requirements andcovering a range of input powers (above ∼100 fW31) that arenot accessible with superconductor-based devices. Indeed,HEBs show typical saturation powers of ∼10 pW−100 pW(depending on the absorbing element dimensions), QCDsoperate within a power range of 10−22 W to 10−15 W,11 andKIDs exhibit a dynamic range from ∼100 zW to ∼100 fW.8 Inparticular, the large dynamic range (>5 orders of magnitude)demonstrated in this work, combined with an almost lineardependence of the photoresponse on input intensity, makesthe proposed TFETs a suitable direct detector system formeasuring intensity correlations between high-fluence opticalmodes at frequencies of ∼3 THz.We have conceived and devised THz frequency quantumdetectors based on MLG/hBN/BLG/hBN heterostructuresembedded in a TFET architecture, operating as sensitivephotodetectors at ∼3 THz, with a wide and setup-limiteddynamic range exceeding 5 orders of magnitude. The retrievedNEP is ∼10−12 WHz−1/2, with a minimum detectable power atthe nW level. The design is frequency scalable across the entire2−4.5 THz range of available quantum laser sources, e.g.,miniaturized frequency combs, and suitable to be combinedon-chip with coplanar striplines and bandpass filters,potentially pushing their speed limit at the sub-ns level.42We envision several design strategies to further enhance theperformance of this study. For example, using a double-top-gate geometry allows for the creation of an additional p−njunction at the center of the BLG channel, inducing a strongand bandgap-tunable PTE response, which can increase thesensitivity of the detector by approximately five timescompared to the single-top-gate scheme.31 Implementing abetter optical coupling scheme, such as silicon lens coupling,could also improve the responsivity. Additionally, it isnoteworthy that BLG is progressively becoming a maturematerial platform, with the potential of synthesis through lowpressure chemical vapor deposition (LP-CVD)36 and integra-tion into high-quality LMHs.45 This advancement could shiftBLG-TFET technology from laboratory-based fabrications andexperiments to a more technologically mature domain, openingup perspectives for extensive use in the fields of FIR quantumoptics and quantum communications.■ ASSOCIATED CONTENTData Availability StatementThe data that support the plots within this paper and otherfinding of this study are available from the correspondingauthors upon reasonable request.*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acs.nanolett.4c04934.Additional experimental details, materials, and methods,including: experimental details on device fabrication;additional details on the experimental setup for opticalcharacterization; evaluation of the gate lever arms;evaluation of the displacement field; evaluation ofelectrical properties at different temperatures; resistancecurves at higher displacement fields; sample-to-samplevariability; resistive self-mixing photodetection; respon-sivity normalization (PDF)Accession CodesThe codes and simulation files that support the plots and dataanalysis within this paper are available from the correspondingauthor upon reasonable request.■ AUTHOR INFORMATIONCorresponding AuthorsMiriam S. Vitiello − NEST, CNR-NANO and ScuolaNormale Superiore, 56127 Pisa, Italy; orcid.org/0000-0002-4914-0421; Email: miriam.vitiello@sns.itLeonardo Viti − NEST, CNR-NANO and Scuola NormaleSuperiore, 56127 Pisa, Italy; orcid.org/0000-0002-4844-2081; Email: leonardo.viti@nano.cnr.itAuthorsLili Shi − NEST, CNR-NANO and Scuola Normale Superiore,56127 Pisa, ItalyKenji Watanabe − National Institute for Materials Science,Tsukuba 305-0044, Japan; orcid.org/0000-0003-3701-8119Takashi Taniguchi − National Institute for Materials Science,Tsukuba 305-0044, Japan; orcid.org/0000-0002-1467-3105Complete contact information is available at:https://pubs.acs.org/10.1021/acs.nanolett.4c04934NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSThis work was supported by the European Research Councilthrough the ERC project Terascan (101157731), by theEuropean Union under the Italian National Recovery andResilience Plan (NRRP) of Next Generation EU, partnershipon PE0000023-NQSTI), and by the European Union throughthe FET Open project EXTREME IR (944735).■ REFERENCES(1) de Graauw, T.; Helmich, F. 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