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Jung Ho Kim, Soumya Sarkar, Yan Wang, [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), Manish Chhowalla

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[Room Temperature Negative Differential Resistance with High Peak Current in MoS<sub>2</sub>/WSe<sub>2</sub> Heterostructures](https://mdr.nims.go.jp/datasets/9be8942a-2ab6-41e3-be1b-5fd816a84cf2)

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Room Temperature Negative Differential Resistance with High Peak Current in MoS2/WSe2 HeterostructuresRoom Temperature Negative Differential Resistance with High PeakCurrent in MoS2/WSe2 HeterostructuresJung Ho Kim, Soumya Sarkar, Yan Wang, Takashi Taniguchi, Kenji Watanabe, and Manish Chhowalla*Cite This: Nano Lett. 2024, 24, 2561−2566 Read OnlineACCESS Metrics & More Article Recommendations *sı Supporting InformationABSTRACT: Two-dimensional transition metal dichalcogenide (2DTMD) semiconductors allow facile integration of p- and n-type materialswithout a lattice mismatch. Here, we demonstrate gate-tunable n- and p-type junctions based on vertical heterostructures of MoS2 and WSe2using van der Waals (vdW) contacts. The p−n junction shows negativedifferential resistance (NDR) due to Fowler−Nordheim (F−N)tunneling through the triangular barrier formed by applying a globalback-gate bias (VGS). We also show that the integration of hexagonalboron nitride (h-BN) as an insulating tunnel barrier between MoS2 andWSe2 leads to the formation of sharp band edges and unintentionalinelastic tunnelling current. The devices based on vdW contacts, globalVGS, and h-BN tunnel barriers exhibit NDR with a peak current (Ipeak) of 315 μA, suggesting that the approach may be useful forapplications.KEYWORDS: 2D materials, negative differential resistance, tunnel transistor, MoS2/WSe2 heterostructure, h-BN tunnel barrierDevices with negative differential resistance (NDR) exhibitmultiple threshold voltages, making them attractive formultivalue logic systems1,2 and radio frequency oscillators.3NDR devices are based on the transition of carrier transportfrom quantum mechanical tunnelling to thermionic emissionby sweeping the applied voltage.4 To use NDR for functionaldevices, the output characteristics of the transistor in the NDRregime should have a high peak current (Ipeak) and a high peak-to-valley current ratio (PVCR). The importance of high Ipeakand high PVCR lies in their role in enabling efficient signalamplification, reliable switching behavior, and optimization ofdevice performance for various high-frequency applications.5,6Two-dimensional transition metal dichalcogenide (2DTMD) semiconductors are ideally suited for realizing NDRbecause they can be easily assembled, and sharp interfaces canbe formed without lattice mismatch.7 A variety of NDR devicesbased on heterostructures of 2D semiconductors have beenreported. In particular, heterostructures using SnSe28−10 orblack phosphorus (BP)11,12 have been studied because bothare highly doped degenerate 2D semiconductors�SnSe2 beingn-type and BP being p-type. Despite the ease of forming typeIII band alignment due to the degeneracy, the low ambientstability and consequential surface oxidation make it difficult toachieve clean interfaces.8 Conversely, widely used 2D TMDssuch as MoS2 and WSe2 can provide improved ambientstability. Thus, several reports have explored tunnel devicesusing MoS2 and WSe2 heterostructures. Roy et al. havereported a dual-gate MoS2/WSe2 heterojunction, which showsNDR behavior at low temperatures.13 Here, the dual-gatestructure plays a key role in electrostatically doping the twomaterials to split the band alignment. Additionally, Nour-bakhsh et al. have shown room-temperature (RT) NDR withMoS2/WSe2 heterostructure with back-gate bias (VGS)modulation.1 Through calculated band diagrams, the authorsdetermined the optimal thicknesses of the two materials thatwould allow tunneling in the transverse direction. However,the low Ipeak of a few hundred pA should be improved forpractical application.In this work, we demonstrate RT gate-tunable MoS2 andWSe2 heterostructures. We use In/Au van der Waals (vdW)contacts for n-type transport in MoS214 and Pt vdW contactsfor p-type transport in WSe2,15 which help in boosting electronand hole injection, respectively. We compare the performanceof the MoS2/WSe2 junctions when they are directly in contactwith each other and when a thin hexagonal boron nitride (h-BN) tunnel barrier is inserted between them. We observe thatthe devices with a h-BN tunnel barrier and vdW contactsexhibit an Ipeak of 315 μA, which is among the highest valuesreported at RT.For the NDR, forming an effective p−n junction isnecessary. We applied three strategies to form an effectivep−n junction. First, for all devices, we have used WSe2Received: November 27, 2023Revised: February 5, 2024Accepted: February 6, 2024Published: February 16, 2024Letterpubs.acs.org/NanoLett© 2024 The Authors. Published byAmerican Chemical Society2561https://doi.org/10.1021/acs.nanolett.3c04607Nano Lett. 2024, 24, 2561−2566This article is licensed under CC-BY 4.0Downloaded via 202.208.135.133 on March 2, 2024 at 03:21:58 (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="Jung+Ho+Kim"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Soumya+Sarkar"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yan+Wang"&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="Kenji+Watanabe"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/doSearch?field1=Contrib&text1="Manish+Chhowalla"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://pubs.acs.org/action/showCitFormats?doi=10.1021/acs.nanolett.3c04607&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?goto=articleMetrics&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?goto=recommendations&?ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?goto=supporting-info&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=tgr1&ref=pdfhttps://pubs.acs.org/toc/nalefd/24/8?ref=pdfhttps://pubs.acs.org/toc/nalefd/24/8?ref=pdfhttps://pubs.acs.org/toc/nalefd/24/8?ref=pdfhttps://pubs.acs.org/toc/nalefd/24/8?ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://pubs.acs.org?ref=pdfhttps://doi.org/10.1021/acs.nanolett.3c04607?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/4.0/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/consisting of two or three layers and MoS2 of >10 layers,fabricated on h-BN on SiO2 (90 nm)/Si substrates (devicefabrication is described in detail in the Supporting Information,Experimental Methods). We selected the layer thicknessesbased on an earlier study, which calculated the optimalthicknesses for NDR.1 The use of h-BN as a substrate helpsreduce hysteresis due to substrate traps,16 interface phononscattering,17 and most importantly electron doping fromSiO2,15 essential for achieving p-type (WSe2) and improvingdevice performance (Figure S1). Finally, we used In (8 nm)/Au (80 nm) and Pt (20 nm capped with 60 nm of Au) vdWcontacts for the MoS2 and WSe2 FETs, respectively. Theoptical microscope (OM) image of MoS2 and WSe2 FETs withvdW contacts is shown in Figure 1a. Our prior investigationrevealed that vdW contacts, specifically In/Au on MoS2 and Pton WSe2, exhibit distinct n- and p-type transport behavior,originating from clean metal/semiconductor interfaces thatprevent Fermi-level pinning (FLP).14,15We compared the characteristics of FETs with vdW contactswith non-vdW contacts based on Cr (5 nm)/Au (80 nm),commonly used for 2D TMD FETs (Figure 1b and c). BothIn/Au and Cr/Au contacts show n-type behavior,18 while In/Au contacts show an improved on/off ratio. In contrast, Cr/Aucontacts on few-layer WSe2 exhibit n-type transport while thevdW Pt contacts show p-type-dominant behavior.19 This resultis consistent with previous studies showing that vdW contactsare effective in achieving p-type transport in WSe2.15,20 Inaddition, temperature-dependent transport measurementsshowing stable transport behavior over a large temperaturerange are shown in Figure S2.The p-type behavior with Pt vdW contacts can beunderstood by using the energy band diagram in Figure 1d.According to the band alignment, Cr/Au contact is expected toshow ambipolar transport closer to p-type.21,22 However, fornon-vdW contacts, defects are formed at the metal/semi-conductor interface leading to FLP close to the conductionband (CB) of WSe2,23 which leads to n-type behavior of Cr/Figure 1. FET comparison of vdW and Cr/Au contacts. (a) OM image of MoS2 and WSe2 FETs. The scale bar is 10 μm. (b,c) VGS-dependenttransfer curves of (b) multilayer MoS2 and (c) few-layer WSe2. Gray-colored curves represent gate-leakage current (IGS). (d) Energy bandalignment of WSe2 and the metal contacts. FLP of Cr contacts induce n-type transport of WSe2.Figure 2. A comparison of NDR from FETs with vdW and Cr/Au contacts. (a, top) OM image of MoS2/WSe2 heterostructure devices. In/Au andPt electrodes were used as electrical contacts on MoS2 and WSe2, respectively. The scale bar is 10 μm. (bottom) A device schematic drawing of thedevice. (b) I−V curves of the vdW (green) and Cr/Au contacts (black). (c) Energy band diagram of the MoS2/WSe2 heterojunction with a vdWgap and F−N tunnelling. The drawing is based on VGS > 0, 0 < VDS < Vpeak conditions. (d) ln(IDS/VDS2) versus 1/VDS plot. Linear region (blackdotted line) refers to the F−N tunnelling.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.3c04607Nano Lett. 2024, 24, 2561−25662562https://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig1&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig2&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig2&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.3c04607?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asAu-WSe2 FETs.24 In contrast, Pt deposition forms a vdW gapbetween the metal and WSe2, which follows the Pt workfunction. This leads to an effective hole injection for p-typeWSe2.Figure 2 describes the role of vdW contacts in hetero-structure performance. We prepared two different sets ofdevices with identical configurations: a stack of multilayerMoS2 flakes on top of few-layer WSe2 on the h-BN bottomlayer. In the first set of devices, we deposited In and Au onMoS2 and Pt on WSe2. Figure 2a displays an OM image of adevice along with a device schematic at the bottom. Forcomparison, we fabricated another set of devices with Cr/Aucontacts (see Figure S3 for an OM image of such a device). Weapplied voltage (drain-source voltage, VDS) to WSe2 (drain)while MoS2 (source) was grounded. The current−voltage (I−V) curves of these two types of devices, measured at RT, areplotted in Figure 2b (the VGS-dependent I−V curves arepresented in Figure S4). The devices with vdW contactsexhibit a clear NDR, whereas it is absent in devices with Cr/Aucontacts. The observation of NDR in the devices with vdWcontacts is evidence of tunneling (the IDS−VGS curve isdepicted in Figure S5).To observe NDR in the forward bias region (VDS > 0) of ap−n junction, a type III junction, with a broken bandalignment at VDS = 0 V is needed. Type III junctions can formwhen both p- and n-type semiconductors are highly doped andare in a degenerate state. However, the materials that we used(MoS2 and WSe2) are not in a degenerate state. Moreover,unlike a dual gate structure,13 global VGS makes it difficult tocontrol the carrier density of each material separately. Notably,in our heterostructures, NDR shows a more distinct trend atVGS > 0, which is also observed in previous works.12,25 Weattribute this to steep band bending of a few layers of WSe2with better VGS coupling due to its proximity to the gate andslight bending of multilayer MoS2 due to screening from WSe2(Figure 2c). At 0 < VDS < 2.35 V (peak voltage, Vpeak), theelectrons from the MoS2 tunnel through the thin triangularbarrier and reach WSe2. With increasing forward bias, theoverlap between the MoS2 CB and the WSe2 VB closes thethin triangular tunnel path, and therefore the tunneling currentbegins to decrease, thereby showing NDR. Conversely, thecase differs when Cr/Au contacts are employed. Because theFermi-level is pinned, WSe2 band bending cannot occureffectively under VGS variation. Hence, the MoS2 electrons willface the midband gap state of WSe2 due to the forming of asmall triangular barrier. The tunnel transport mechanism isdepicted in Figure 2d to validate the tunnel transportmechanism. The I−V curve in the region of 0 < VDS < Vpeakcan be modeled using the Simmons approximation.26 TheFowler−Nordheim (F−N) tunnelling can be expressed asikjjjjjjjy{zzzzzzzI Vd mheVexp8 23FNT23*Here, d represents the thickness of the tunnel barrier, m*denotes the effective electron mass, φ corresponds to thetunnelling barrier height, and h is the Planck constant. Plottingln(I/V2) versus 1/V should reveal a linear regime with anegative slope (black dotted line) for F−N tunnelling.27,28From the slope of the curve, we can derive the F−N tunnelingbarrier height (φ) of 0.11 eV.We further validate the occurrence of F−N tunneling in ourdevices through temperature-dependent transport measure-ments. In Figure S6, we present the temperature-dependent I−V curves from a device showing NDR with In/Au and Ptcontacts. Here, we can observe that the steep increase oftunnelling current in the reverse bias region (VDS < 0 V) isinsensitive to changes in temperature. Furthermore, the F−Ntunnelling current, which is the increase in current in theforward bias region preceding the NDR effect (0 < VDS <Vpeak), also shows a negligible temperature dependence.However, beyond the NDR effect, the current flow is governedby thermionic emission and is highly sensitive to changes intemperature (Figure S6, inset). The results in Figures 2b,d andS6 suggest that the vdW gap between MoS2/WSe2 alongsidethe contribution of F−N tunneling is critical.Next, we integrated 10 layers (3.4 nm) of h-BN betweenMoS2 and WSe2. The insertion of h-BN as a tunnel barrierserves as an insulating spacer that enables precise bandalignment.17,29,30 The insulating nature of h-BN results inFigure 3. The role of the h-BN tunnel barrier. (a) I−V curves with h-BN tunnel barrier (orange) and without tunnel barrier (green). (b) ln(IDS/VDS2) versus 1/VDS plot depicting DT for the device with an h-BN tunnel barrier. (c) Energy band diagram of MoS2/WSe2 heterojunction with h-BN tunnel barrier. The drawing is based on VGS > 0 and 0 < VDS < Vpeak conditions. (d) NDR behavior of the device with h-BN tunnel barrier at 9K and RT.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.3c04607Nano Lett. 2024, 24, 2561−25662563https://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig3&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig3&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.3c04607?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-assharper band edges for both MoS2 and WSe2. Consequently,the energy levels of the VB and CB experience a sharptransition at the MoS2/h-BN and WSe2/h-BN interfaces,resulting in a well-defined tunnel barrier. However, at the sametime, it requires extra energy for the electrons to tunnelthrough the barrier. Also, due to additional stacking stepsduring fabrication and natural defects in the h-BN crystal,unintentional trap sites may be involved.31 The difference inthe transport behavior between two devices with and withoutthe h-BN tunnel barrier at RT is shown in Figure 3a. Bothdevices show clear NDR behavior. However, the device withthe h-BN tunnel barrier (left y axis, orange) displays asubstantial increase (2 orders of magnitude) in Ipeak comparedto the device without the tunnel barrier (right y axis, green).Additionally, we observe an increase in the VDS, from 2.35 to4.1 V, required to reach the Ipeak. We attribute this to thepresence of an additional tunnel barrier (h-BN), whichnecessitates a higher voltage for carriers to reach the oppositeside (WSe2) of the energy band.To explore the mechanism for higher Ipeak, the I−V curve inthe forward bias region (0 < VDS < Vpeak) is studied. Unlike theF−N tunnelling observed in Figure 2d, Figure 3b follows alogarithmic slope, meaning the device incorporating the h-BNtunnel barrier operates via direct tunnelling (DT).32 The DTcurrent can be expressed asikjjjjjjjy{zzzzzzzI Vd mhexp4 2DT*The possible energy band alignment due to DT transportthrough the h-BN tunnel barrier is shown in Figure 3c.Although precise band alignment is difficult to extract andvaries from study to study,1,13,27 we can imagine the presenceof inelastic tunnelling such as phonon-assisted, trap-assisted, orShockley−Read−Hall tunnelling.13,33,34 To obtain more in-sight, we plotted the NDR behavior of the h-BN tunnel barrierdevice at 9 K and RT for comparison (Figure 3d). It shows adistinct increase in the current at RT, and such a temperature-dependent enhancement is absent in devices without an h-BNtunnel barrier (Figure S6). This leads to a higher Ipeak and alarger peak-to-valley current ratio (PVCR) at higher temper-atures due to thermally enhanced inelastic tunnelling. Thus, webelieve that combined effects including the sharp band edges aswell as inelastic tunneling through the h-BN barrier areimportant for the enhanced Ipeak.The properties of devices with the h-BN tunnel barrier werefurther examined by varying VGS. Figure 4a shows an OMimage of a typical device. The three-layer thickness of WSe2enables effective gate tunability of the Fermi level, while theeffect of the VGS on the relatively thick (10 layers) MoS2 issmall. The thicknesses of the layers measured by atomic forcemicroscopy (AFM) topography are presented in Figure S7.Electrical bias was applied to the Pt contact connected toWSe2, while the current was collected from the In/Au contacton MoS2. The gate bias was applied by global VGS (SiO2/Si).The VGS dependence of the NDR at RT is plotted in Figure 4b.With increasing VGS, the NDR becomes more pronounced,resulting in higher current levels.12,25 This behavior can beattributed to the accumulation of electrons in MoS2 as VGS > 0,providing a large number of carriers available for tunnellingwhen a forward bias is applied.The energy band alignment of the WSe2/h-BN/MoS2 deviceunder varying applied VDS is illustrated in Figure S8. Whenreverse bias (VDS < 0) is applied, it allows the tunnelling ofelectrons from filled states in WSe2 through the h-BN barrierto reach the unoccupied states in the MoS2 CB. Thistunnelling phenomenon results in a sharp increase in currentas a larger negative VDS is applied. Conversely, when positivevoltage (VDS > 0) is applied, the direction of carrier injectionreverses. Electrons in the MoS2 CB tunnel through the barrierto reach the WSe2, leading to an inelastic tunnelling current.This current continues to increase until it reaches themaximum value, Ipeak. Beyond Vpeak, electrons from MoS2face the midband gap state of the WSe2, where no density ofstates exists. Thus, the current decreases. Notably, some hotelectrons may still overcome this barrier and contribute to thevalley current (Ivalley). Subsequently, when thermionic emissionprovides sufficient energy for MoS2 electrons to transit to theWSe2 CB, as in a normal diode, the current once again beginsto rise.We extracted the PVCR, which exhibits an increasing trendas VGS increases (Figure 4c). The overall PVCR value is notexceptionally high due to the presence of a substantial Ivalley.This can be attributed to a high probability of inelastictunneling and thermally excited electrons across the tunnelbarrier. Consequently, this results in a relatively small overallPVCR value. Nonetheless, the increase in Ipeak surpasses therise in Ivalley, leading to an elevation in PVCR as VGS increases.To benchmark our results, in Figure 4d we have plotted theJpeak (peak current density, Ipeak/device working area) andPVCR from other devices based on the heterostructure of 2Dsemiconductors.1,2,8−12,25,30,35,36 Among various types ofFigure 4. VGS-dependent NDR with h-BN tunnel barrier. (a) OM image of the heterostructure. The scale bar is 10 μm. (b) VGS-dependent NDR.(c) VGS-dependent PVCR and the (d) benchmark of Jpeak versus PVCR for various reported 2D NDR devices based on tunnelling that operate atRT. The transverse tunnelling transistor31 is not included in this plot due to a different operation mechanism and lack of device size information.Nano Letters pubs.acs.org/NanoLett Letterhttps://doi.org/10.1021/acs.nanolett.3c04607Nano Lett. 2024, 24, 2561−25662564https://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/suppl/10.1021/acs.nanolett.3c04607/suppl_file/nl3c04607_si_001.pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig4&ref=pdfhttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607?fig=fig4&ref=pdfpubs.acs.org/NanoLett?ref=pdfhttps://doi.org/10.1021/acs.nanolett.3c04607?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-asdevices employing different 2D materials, principles, andenvironments, we have selected devices based on tunnelingthat operate at RT. Our devices exhibit a large Jpeak of 2420 A/cm2. A further increase in PVCR could be accomplished byexploring materials with different band gaps and higher dopinglevels, as well as carefully controlling the inelastic tunneling tominimize the Ivalley. It is noteworthy that the transversetunnelling transistor demonstrated by Xiong et al.31 using blackphosphorus exhibits a large Ipeak and PVCR simultaneously.Employing transverse tunneling may be an alternative route toimprove the PVCR.In summary, our findings demonstrate a high Ipeak NDRdevice by using vdW heterostructures. The utilization of In/Auand Pt vdW contacts facilitates the effective formation of thep−n junction. The devices show NDR, facilitated by F−Ntunneling through a triangular barrier induced by applied VGS.Furthermore, integration of the h-BN tunnel barrier leads toimproved NDR because of sharp band edges as well as inelastictunnelling. This result yields high Ipeak values. These resultspave the way for potential applications in logic devices andoscillators.■ ASSOCIATED CONTENT*sı Supporting InformationThe Supporting Information is available free of charge athttps://pubs.acs.org/doi/10.1021/acs.nanolett.3c04607.Role of h-BN as a substrate, temperature-dependenttransport of MoS2 and WSe2 with vdW contacts, OMimage of the Cr/Au device, VGS-dependent I−V curvesof the MoS2/WSe2 heterostructure with vdW contactsand Cr/Au contacts, VDS-dependent transfer curves ofthe MoS2/WSe2 heterostructure, temperature-depend-ence of the NDR device, thickness of each layer of theheterostructure, energy band diagram of the hetero-junction, OM and I−V characteristics of additional NDRdevices, experimental methods (PDF)■ AUTHOR INFORMATIONCorresponding AuthorManish Chhowalla − Department of Materials Science andMetallurgy, University of Cambridge, Cambridge CB3 0FS,United Kingdom; orcid.org/0000-0002-8183-4044;Email: mc209@cam.ac.ukAuthorsJung Ho Kim − Department of Materials Science andMetallurgy, University of Cambridge, Cambridge CB3 0FS,United Kingdom; orcid.org/0000-0002-7884-2414Soumya Sarkar − Department of Materials Science andMetallurgy, University of Cambridge, Cambridge CB3 0FS,United Kingdom; orcid.org/0000-0002-9715-9004Yan Wang − Department of Materials Science and Metallurgy,University of Cambridge, Cambridge CB3 0FS, UnitedKingdom; orcid.org/0000-0001-9241-3512Takashi Taniguchi − Research Center for MaterialsNanoarchitectonics, National Institute for Materials Science,Tsukuba, Ibaraki 305-0044, Japan; orcid.org/0000-0002-1467-3105Kenji Watanabe − Research Center for Electronic and OpticalMaterials, National Institute for Materials Science, Tsukuba,Ibaraki 305-0044, Japan; orcid.org/0000-0003-3701-8119Complete contact information is available at:https://pubs.acs.org/10.1021/acs.nanolett.3c04607Author ContributionsM.C. designed and supervised the project. J.H.K. fabricatedsamples, performed experiments, and analyzed the data. S.S.and Y.W. supported the data analysis. T.T. and K.W. providedthe bulk h-BN crystals. J.H.K. and M.C. wrote the manuscriptwith support from S.S. and Y.W. All authors discussed theresults and commented on the manuscript.NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSWe acknowledge funding from European Research Council(ERC) Advanced Grant under the European Union’s Horizon2020 Research and Innovation Programme (grant agreementGA 101019828-2D-LOTTO]), EPSRC (EP/T026200/1, EP/T001038/1). Also, K.W. and T.T. acknowledge support fromthe JSPS KAKENHI (grant numbers 21H05233 and23H02052) and World Premier International Research CenterInitiative (WPI), MEXT, Japan. 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