Photoinduced Doping To Enable Tunable andHigh-Performance Anti-Ambipolar MoTe2/MoS2 HeterotransistorsEnxiu Wu,†,§ Yuan Xie,†,§ Qingzhou Liu,‡ Xiaodong Hu,*,† Jing Liu,*,† Daihua Zhang,*,†

and Chongwu Zhou‡

†State Key Laboratory of Precision Measurement Technology and Instruments, School of Precision Instruments andOptoelectronics Engineering, Tianjin University, No. 92 Weijin Road, Tianjin, 300072, China‡Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States

*S Supporting Information

ABSTRACT: van der Waals (vdW) p−n heterojunctions formed by two-dimensional nanomaterials exhibit many physicalproperties and deliver functionalities to enable future electronic and optoelectronic devices. In this report, wedemonstrate a tunable and high-performance anti-ambipolar transistor based on MoTe2/MoS2 heterojunction through insitu photoinduced doping. The device demonstrates a high on/off ratio of 105 with a large on-state current of severalmicro-amps. The peak position of the drain−source current in the transfer curve can be adjusted through the doping levelacross a large dynamic range. In addition, we have fabricated a tunable multivalue inverter based on the heterojunctionthat demonstrates precise control over its output logic states and window of midlogic through source−drain biasadjustment. The heterojunction also exhibits excellent photodetection and photovoltaic performances. Dynamic andprecise modulation of the anti-ambipolar transport properties may inspire functional devices and applications of two-dimensional nanomaterials and their heterostructures of various kinds.KEYWORDS: MoTe2, MoS2, heterojunction, anti-ambipolar, multivalue inverters, photovoltaic

The growing inventory of layered two-dimensional (2D)semiconductors with diverse electronic characteristicshas allowed atomically thin and dimensionally abrupt

heterostructures to be realized.1−3 2D van der Waalsheterostructures have enabled a variety of device typesincluding tunneling field-effect transistors (TFETs),4−6

Schottky junctions,7 photovoltaic devices,8−11 light-emittingdevices,12−14 inverters,15−17 nonvolatile memory cells,18,19 andmultifunctional electronic devices.20−22 Some 2D hetero-junctions exhibit different transfer characteristics when theirband alignments are properly configured. The channelconductance reaches its local maximum at a specific gatebias, as opposed to typical V-shape transfer curves of regularambipolar devices. This behavior is therefore called anti-ambipolarity, which was first observed in gate-tunable carbonnanotube and MoS2 p−n heterojunctions23 and more recently

in 2D p−n heterostructures made of WSe2−MoS2,24−27 BP−

MoS2,20,28 MoTe2−MoS2,

29 WSe2−WS2,30 pentacene−

MoS2,31 and SWCNT−IGZO.32 The anti-ambipolar property

brings important advantages to applications in logic circuitsand optoelectronics. For example, it enables both positive andnegative transconductance in a single device and a sharptransition between the two states. The flipping of trans-conductance has been exploited to implement a number ofanalog devices as frequency doubling, binary phase shift keying(BPSK), and binary frequency shift keying (BPFK) circuits.32

In contrast to conventional integrated circuits that require at

Received: January 9, 2019Accepted: April 11, 2019Published: April 11, 2019

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least seven FETs to construct a Gilbert cell,33 the anti-ambipolar device takes only one p−n junction and a serialresistor to achieve the BPSK or BPSK function, whichsignificantly simplifies the circuit design and implementation.In addition, anti-ambipolar devices can also be used to buildternary logic inverters.20,25 Compared to conventional binaryinverters, ternary inverters provide multivalued digital signalsand are promising architectures to break the fundamental bitlimit and enable higher data storage density and more intricatelogic devices. Another important feature is its gate-tunablerectification characteristics, which have been widely used todevelop gate-tunable rectifier circuits and photodetec-tors.23,24,27,29,31,34

Despite their potential in a wide range of applications,fabrication of anti-ambipolar heterojunctions with reliable andconsistent performances remains a challenging task. It requireshighly precise control of the turn-on voltages (Von) and carrierdensities of both the n-type and p-type transistors in thejunction. Concretely, the p- and n-transistors need to havelarge positive and large negative turn-on voltages, respectively,

so that both devices can stay on within a wide gate biaswindow. Meanwhile, the intrinsic carrier densities of bothtransistors should be at similar levels, as imbalance between thetwo types of charge carriers can easily lead to domination ofunipolar transport. Even though previous demonstrations haveachieved basic functionalities, they normally suffer small on-state current and low on/off ratio due to the narrow on-statewindow. In addition, their transport characteristics such as theposition of the conductance peak and overall shape of thetransfer curve cannot be dynamically adjusted, which largelylimits the flexibility and adaptability in many applications.In this work, we developed a tunable high-performance anti-

ambipolar device based on MoTe2/MoS2 heterojunctionthrough photoinduced doping. The approach enables precisetuning of the doping level and effective modulation of thetransport behavior in a large dynamic range, allowing theheterostructure to be reversibly switched between anti-ambipolar and unipolar-dominated operational regimes. Inaddition, the anti-ambipolar device provides a large on-statecurrent (∼μA) and very high on/off ratio of ∼105, roughly 1−

Figure 1. (a) Schematic of a MoS2/MoTe2/h-BN junction device in which the MoS2/MoTe2 junction serves as the transport channel, Si is thecontrol gate, and h-BN and SiO2 are the gate dielectric. (b) False-colored SEM image of the device. Scale bar is 5 μm. (c) Raman spectrum ofa MoS2/MoTe2/BN triple-layer sample. (d) Transfer characteristics of the MoTe2 FET, MoTe2 FET, and MoS2/MoTe2 heterotransistor inboth linear (solid line) and semilog (dashed line) scales. (e) Output characteristics of MoS2/MoTe2 heterotransistor at different gate-sourcebias Vgs.

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4 orders of magnitude higher than previous works. We thendemonstrated a tunable multivalue inverter by engineering thepartition load and matching and achieved precise control overthe output logic state and window of mid logic through drivingbias. Finally, we built a photovoltaic device based on this anti-ambipolar devices and achieved excellent performance with amaximum power conversion efficiency of 0.55% and externalquantum efficiency of 56%. The photoresponsivity andresponse time reached 0.25 A/W and 2 ms, respectively.

RESULTS AND DISCUSSION

Figure 1a shows the structural configuration of the MoTe2/MoS2 heterojunction device used in our study. The wholedevice is back gated through the Si/SiO2 substrate. We placeda thin layer of h-BN under the heterojunction, which createstwo interfaces on the top and bottom surfaces of the BN. Aswill be discussed in the following sections, the BN/SiO2interface can effectively trap charges and modulate thetransport behaviors of the heterojunction device. Figure 1bpresents a false-colored scanning electron microscopy (SEM)image of the structure. Two pairs of Cr/Au electrodes labeledas 1/2 and 3/4 define two separate transport channels inMoTe2 and MoS2 FET, respectively. The transport channelbetween electrodes 2 and 3 constitutes a MoS2/MoTe2heterotransistor. Thicknesses of the MoTe2, MoS2, and h-BNflakes were measured to be 10, 13, and 20.0 nm using anatomic force microscope (AFM), as shown in Figure S1. TheRaman spectrum in Figure 1c confirms the lattice structures ofall three layers. The three peaks at 169, 232, and 287 cm−1 arecharacteristic peaks of MoTe2. The two peaks at 382 and 403cm−1 characterize single crystalline MoS2, and the peak at 1363cm−1 originates from longitudinal mode phonons in h-BN.

Figure 1d shows the transfer characteristics of the MoTe2(red), MoS2 (violet), and heterojunction devices (blue). Thegate-source bias (Vgs) was scanned from −60 to +60 V, whilethe drain-source bias (Vds) remained at +2 V. The results ofthe MoS2 and MoTe2 FETs are consistent with most previousstudies.35−37 The MoS2 shows n-type transport throughout theentire scan from −60 to +60 V, while the transport in MoTe2 isdominated by n- and p-type carriers under positive andnegative gate biases, respectively, resulting in the ambipolartransfer characteristics (red dashed curve) in Figure 1d. TheMoTe2/MoS2 heterojunction exhibits ambipolar transfercharacteristics as well (blue dashed curve). However, sincethe current transport is essentially dominated by electrons,polarity switching occurs at a very negative gate bias around−52 V. Unlike the MoTe2/MoS2 devices reported in previousworks,38,39 our device did not show anti-ambipolar behavior inthese measurements. The result is not surprising since theonset of anti-ambipolar transport requires two conditions.First, doping concentrations on the p- and n-sides of thejunction should be in good balance with each other. Second,there exists a gate bias window within which both the p- and n-branches can operate in the on-state. Our device meets none ofthese conditions according to the transfer characteristics ofindividual FETs, primarily because hole doping of the MoTe2FET is far from its optimal level. Figure 1e shows the outputcharacteristics of the heterojunction under different Vgs. It isworth noting that the curves show no rectification despite thefact that the energy bands are aligned in a type-II configurationat the junction. This can be attributed to the un-optimizeddevice doping level as well.We developed a versatile photoinduced doping approach

that enables highly effective and nonvolatile band modulation

Figure 2. Transport characteristics of MoTe2 (a) and MoS2 (b) FETs at Vds = 2 V in linear (solid line) and semilog (dashed line) scales afterphotoinduced doping. Curves in different colors correspond to different “writing voltages” during the doping process. The photoinduceddoping is done by exposing the device to UV illumination for 1 s at different writing voltage from 10 to 80 V with a 10 V step. (c) Thresholdturn-on voltages (Vth) of the MoTe2 (blue diamonds) and MoS2 (purple circles) FETs as a function of writing voltage. (d) Transfercharacteristics of the MoTe2 and MoTe2 FETs and the MoS2/MoTe2 heterojunction at Vds = 2 V in semilog scale after photoinduced dopingunder 80 V writing voltage.

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of MoTe2 and MoS2 transistors. The doping is done byapplying a large gate bias (referred to as “writing voltage” inthe following discussion) and UV illumination on the device atthe same time, for typically less than 1 s. After that, we turn offthe UV light and writing voltage and record a transfer curve ofthe doped device to characterize its transport behavior. Wenote both the writing voltage and UV illumination have topresent at the same time to enable this doping process. Thedevice will not make any nonvolatile change if either activationis absent. The results with different writing voltages are shownin Figure 2a,b for the MoTe2 and MoS2 FETs, respectively.The solid and dashed lines are linear and semilog plots. Thewriting voltages are listed in the annotation with font colorsmatching those of the transfer curves. The curve correspondingto “0 V” writing voltage shows no difference from that of theuntreated device, as UV illumination by itself is a fullyrecoverable treatment. However, the combination of UV lightand large writing voltage can induce permanent changes to thematerial that last even after both activations are withdrawn.The magnitude of the change is qualitatively proportional tothe writing voltage. As shown in Figure 2a, the MoTe2 FETtransforms from an electron-dominated ambipolar device (red

curve) to a highly doped unipolar p-type FET (black curve) asthe writing voltage increases from 0 to 80 V. The resultssuggest that the opto-electrical doping effect induced by thedual activation of UV illumination and electrostatic gating isnonvolatile and able to electrostatically dope the MoTe2channel to sufficiently deep levels. The doping scheme worksvery similarly to a multilevel floating gate memory. The UVphotons generate a large number of free electrons and holes inthe MoTe2 channel. When a positive writing voltage is appliedin the vertical direction, it drives electrons to tunnel throughthe BN layer. At the same time, the UV illumination alsoexcites defect states at the BN/SiO2 interface to trap andanchor these electrons.40 As a result, even after thephotoinduced activation is withdrawn, the electrons stay atthe interface permanently, creating a negative gate bias toelectrostatically dope the MoTe2 channel to p-type.In contrast to MoTe2, the MoS2 FET underwent the same

treatment and showed very little response despite a gradualreduction in on-state current from 65 to 31 μA at Vgs = 60 V(Figure 2b). The weak response to the doping treatmentresults from very strong Fermi-level pinning at the metal−MoS2 interface.41 In Figure 2c we plot the turn-on voltages

Figure 3. (a) Transfer characteristic curves of the MoS2/MoTe2 heterojunction at Vds = 2 V in both linear (a) and semilog (b) scales afterdoping under different writing voltages. (c) On-state current as a function of writing voltage. (d) Linear dependence of peak (red) and valley(blue) positions on the writing voltage. (e) Output curves at Vgs = 0 V after photoinduced doping at different levels. (f) Plot of devicerectification ratio at Vgs = 0 V with respect to different writing voltages. The forward (Vds = +2 V) and reverse (Vds = −2 V) drain-sourcecurrent after doping under different writing voltages is shown in the inset.

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(Von) of both devices as a function of writing voltage. The Vonof MoTe2 increases linearly with the writing voltage from 1.2to 62.4 V (blue diamonds), whereas the MoS2 FET kept its Vonat around −54 V regardless of the writing voltage (purplecircles).Through the photoinduced doping treatment, we were able

to configure the MoTe2 and MoS2 FETs to the optimalconditions to form an anti-ambipolar device. They now meetboth requirements: comparable doping levels in the p- and n-branches and substantial overlapping of the two on-states. Themeasurement in Figure 2d verifies the formation of the anti-ambipolar device at the junction of the two FETs. In the figure,we plot the transfer curves of the doped MoTe2 (red), MoS2(violet), and heterojunction (blue) devices together. Theheterojunction shows a clear anti-ambipolar pattern, with oneconductance peak near Vgs = 0 and two minimums around −54and +62 V. This is easy to understand as the junction is formedby a p- and an n-FET in series, in which the total currentreaches maximum when both transistors are turned on aroundVgs = 0 V and drops to a minimum when either device is off.Two valleys of the junction’s transfer curve correspond to thedepletion of the p- and n-FETs, respectively. The outputcharacteristics of the doped MoTe2 and MoS2 FETs atdifferent gate biases are plotted in Figure S2, indicating goodohmic contacts at the semiconductor−metal interfaces. Thisverifies that the anti-ambipolar transport behavior has nothingto do with these interfaces but rather the heterojunctionformed between the two FETs. The anti-ambipolar device canachieve a very high current on/off ratio exceeding 105, makingit an ideal component to implement a wide range of advancedlogic circuitries.23−32 It is worth noting that the subthresholdregimes of the MoTe2 and MoS2 FETs coincide with thejunction’s transfer curve very well. This results from negligiblehysteresis in the transfer characteristics of heterojunction

device owing to the photoinduced doping treatment (FigureS3). Such a level of hysteresis minimization has been rarelyachieved in previous studies23,24,27 despite its great importancein practical applications.In Figure 3a,b we characterize the transport behavior of the

heterojunction after doping under different writing voltages,where we can clearly visualize the gradual transition fromambipolar to anti-ambipolar transfer characteristics. Con-cretely, both parameters are changing with the increasingwriting voltage from 10 to 80 V, which are the height (Figure3c) and position (Figure 3d) of the Ids peak. Both changes areassociated with the increasing doping level of the MoTe2 FET(Figure 2c). The photoinduced hole doping greatly raises theon-state current of the MoTe2 FET, shifts its threshold voltagetoward more positive gate bias, and widens the overlapbetween the on-states of the p- (MoTe2) and n- (MoS2)transistors. Through the photoinduced doping treatment, wecan precisely control the transition from the ambipolar to anti-ambipolar states and accurately adjust the position of the Idspeak. The position of the peak is a critical parameter whenthese anti-ambipolar transistors are used to build functionalblocks such as frequency-doubling circuits and more intricatesignal conditioning modules. The ability of precise tuning ofthese parameters would largely improve the flexibility andpotential of such devices in a wide range of applications.Throughout the study, we have measured multiple devicestreated and measured the same way. There are variations inpeak position and on-state current in the anti-ambipolartransfer curves due to differences in material quality, geometry,and minute process variations, but all devices behavedqualitatively the same in terms of reversibility between theunipolar and anti-ambipolar states and tunability of the peakposition (Figure S4). We also note that the photoinduceddoping is bidirectional and fully reversible. By applying a

Figure 4. (a) Cross-sectional structure of the heterojunction-based ternary inverter. (b) Transfer characteristics of the heterojunction (solidline) and MoTe2 FET (dashed line) under different source-drain biases (Vds). (c) Inverter formed by a MoTe2 FET and a MoTe2/MoS2heterojunction showing binary logic under a small driving voltage (Vdd) and ternary logic under a large driving voltage. Vdd varies from 0.1 to2 V. (d) Voltage gain of both switching states of the inverter at different Vdd.

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negative writing voltage under UV illumination, we can reducethe hole doping in the MoTe2 FET to a lower doping level orreset it to its original state if needed (Figure S5). The entiredevice tuning process is highly flexible, fast, and stable.The output characteristics of the heterojunction are

recorded in Figure 3e. In the inset of Figure 3f we plot theforward (blue) and reverse (red) current with respect to thewriting voltage, at Vds = +2 and −2 V, respectively. As thewriting voltage increases, both forward and reverse currentdrop sharply and reach the minimum around 20 V. As thewriting bias further increases, the reverse current rises slightlyand the forward current increases linearly. The correspondingrectification ratio, defined as the ratio between the forward andthe reverse current, was calculated and is plotted in Figure 3f.The result shows a dramatic increase by roughly 2 orders ofmagnitude, from 1.5 to 151, which results from the rise ofbuilt-in potential of heterojunction with the p-doping level ofMoTe2. A higher rectification ratio can largely improve theenergy conversion efficiency when the anti-ambipolar tran-sistor is configured as a photovoltaic device. More discussionswill be followed up in a later section (Figure 5).Negative transconductance has been demonstrated in

various logic circuits23,26,31 as well as optoelectronicdevices.24,27,29,30 Among different applications of negativetransconductance, multivalued logic (MVL)20,25 has attractedextensive attention. With a larger number of logic states, MVLhas the potential for higher data storage in less area ascompared with binary logic devices. In the experiments inFigure 4, we demonstrate a typical application of the anti-ambipolar transport behavior. It is a ternary inverter formed bya MoTe2/MoS2 heterojunction and a MoTe2 FET connectedin series, as shown in the schematic drawing of Figure 4a. Theback gate is used to apply the input voltage (Vin), the middle

electrode for output voltage (Vout), and the side electrodes forthe source (GND) and driving voltage (Vdd).We first characterize the two devices forming the ternary

inverter separately. Figure 4b shows the transfer characteristicsof the anti-ambipolar junction (solid line) and the p-typeMoTe2 FET (dashed line) under different drain−source biases(Vds). It is interesting to find that the current through theheterojunction drops much faster on the right shoulder of thepeak (shaded region as highlighted in the figure) under higherVds, which results in a higher peak-to-valley ratio. For example,the current measured at Vds = 2 V (red curve) dropped from2.15 × 10−6 to 2.03 × 10−7 A by 1 order of magnitude whenVgs was scanned from 0 to 36 V, whereas the current at Vds =0.1 V dropped by only 2 times within the same Vgs range. Wecan use the band diagrams in Figure S6a to understand thedifference in these transfer curves. Under a forward bias, theenergy band of MoTe2 is pulled down, and the barrier heightfor holes decreases with increasing Vds. When Vds increasesfurther until the valence band of MoTe2 is pulled down belowthe valence band of MoS2, the barrier for holes vanishes andthe MoTe2 channel starts to dominate the current transport.Overall speaking, the larger the drain−source bias, the moreeffectively the gate bias can modulate the transport channel,and the higher the on−off ratio we can achieve in thesedevices. On the contrary, when a negative Vds is applied, thedrain-source current drops much slower on the right shoulderof the peak, resulting in an even lower on−off ratio of ∼1 at Vds= −8 V (Figure S6b).Figure 4c characterizes the performance of the multivalue

inverter, in which the output logic state and window of midlogic (logic 1/2) level can be controlled by source−drain bias.The width of the mid logic plateau is one of the mostimportant figure-of-merits of a ternary invertor that character-

Figure 5. (a) Output characteristic curves of the heterojunction under illumination of 600 nm laser with different light power densities. (b)Photo switching behavior under different illumination power densities at Vds = 0 V and Vgs = 0 V. (c) Photoresponsivity (left axis) andphotosensitivity (right axis) of the heterojunction as a function of incident power. (d) Dynamic photo response of the device at Vds = 0 V andP = 1.1 nW.

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izes the tolerance window and stability of this midstate. Asshown in the schematic of Figure 4a, the device is essentially avoltage divider of Vdd. The output voltage depends on theresistance ratio between the two devices in series, the MoTe2FET and the MoTe2/MoS2 heterojunction. Therefore, keepingthe output voltage at a stable level requires the two devices tomaintain a constant resistance ratio during the scan of Vgs (alsoVin). This explains why we observed the biggest logic 1/2window at the highest driving voltage of Vdd = 2 V (red curve).Higher Vdd leads to higher voltage drop across theheterojunction and, according to Figure 4b, allows sharper“on” to “off” transition of this anti-ambipolar device and makesits negative transconductance better match that of the MoTe2.This enables the conductance of the two devices to drop at asimilar rate as Vin increases, therefore maintaining a relativelystable output voltage within this scan range. Concretely, theoutput logic 1/2 state under Vdd = 2 V sits at ∼0.85 V with awindow of approximately 20 V (0 V < Vin < 20 V). As Vdddecreases, the midstate becomes less indistinguishable andcompletely vanishes when Vdd is less than 0.5 V. Figure 4dplots the corresponding gain of the inverter at different Vddvalues. In this plot, we also clearly find the transition of logicstate from binary to ternary as Vdd increases. Under a smalldriving voltage of Vdd = 100 mV, only a single gain from logic 1to 0 can be detected (green curve). When Vdd reaches 500 mVand above, we start to observe two gains of the ternary inverter.The left three peaks correspond to the voltage gain from logic1 to 1/2, and the second three peaks for the voltage gain fromlogic 1/2 to 0. In addition, we find that the two gains increasemonotonically with Vdd.In addition to applications in logic circuitries such as ternary

transistors, the MoTe2/MoS2 heterojunction is also anexcellent optoelectronic device with outstanding photovoltaicand photoswitching properties. Figure 5a shows the outputcharacteristics of the heterojunction under light illumination at600 nm. As the incident power density rises, both the open-circuit voltage (Voc) and short-circuit current (Isc) increase inmagnitude, confirming the formation of a photovoltaicjunction. Due to the energy gradient of type-II band alignmentand built-in potential between the MoTe2 and MoS2,photoexcited electron−hole pairs can be efficiently separated.When the device is short-circuited, it works as a photovoltaicdevice that reaches the highest output power of Pelectrical = 6 ×10−3 nW at 150 mV and 40 pA. We estimated the incidentoptical power to be Poptical = 1.1 nW according to the devicearea and power density of the illumination. The energyconversion efficiency is calculated to be ηPV = Pelectrical/Poptical ≈0.55%. The fill factor (FF), defined as the ratio between themaximum obtainable power and the product of Voc and Isc, iscalculated to be 0.35 at 1.1 nW.Owing to its photovoltaic property, the heterojunction can

also work as a self-powered photoswitch. In Figure 5b, werecorded the photocurrent at Vds = 0 V during five consecutiveillumination cycles. Curves in different colors were taken atdifferent laser powers ranging from 0.1 to 1.1 nW. The deviceexhibits excellent sensitivity, repeatability, and stability. Themaximum photoresponsivity (R) reached ∼ 0.25 A/W asestimated at different incident powers. The external quantumefficiency (EQE) is proportional to R and defined as EQE =hcR/(eλ), with h, c, e, and λ being the Planck constant, speed oflight, elementary charge, and incident light wavelength,respectively. The EQE is calculated to be 56% in our case.We note that both the photoresponsivity and the EQE are

among the excellent results achieved by photodiodes based onheterojunction.9−12 We also measured photovoltaic responsesof MoS2 and MoTe2 transistors at Vds = 0 V and P = 1.1 nW(Figure S7). Neither of them showed a detectable signal, whichis attributed to quasi-ohmic contact at the TMD−metalinterfaces. Figure 5c shows the photosensitivity and photo-responsivity as a function of illumination power. Thephotosensitivity increases with the incident power, while thephotoresponsivity drops monotonically. Decreasing photo-responsivity at higher illumination power has also beenobserved in other photoconductors based on similar materialsand structures.42,43 This is presumably due to reduction ofavailable carriers that can be collected under high photonflux.44 The response time is estimated to be less than 2 msaccording to the measurement in Figure 5d, revealing fast andefficient electron−hole separation.

CONCLUSIONSIn summary, we developed an effective photoinduced dopingapproach that enables a tunable and high-performance anti-ambipolar device based on MoTe2/MoS2 heterojunction. Thedevice shows a record-high current on/off ratio greater than105 with on-state current at uA level and a tunable peakposition. Tunable high-performance ternary inverters con-trolled by drain voltage have been demonstrated by adoptingenergy band alignment and load matching. Finally, excellentphotovoltaic effect and photo detection were demonstrated.The tunable anti-ambipolar transport property may bringbroad prospects for next-generation optoelectronics and logicelectronics.

METHODSDevice Fabrication. The heterostructures were produced with a

dry transfer technique. First, a h-BN flake was first mechanicallyexfoliated from bulk h-BN and then transferred onto a 285 nm SiO2/n+ doped Si substrate. Next, a MoTe2 flake was transferred onto the h-BN flake, and then an MoS2 flake was stacked onto the MoTe2 flake.Finally, electrodes were patterned by electron beam lithography(EBL) with positive Ebeam resist. 20/30 nm Cr/Au was deposited byEbeam evaporation after exposure and development, which wasfollowed by a standard liftoff process to complete the fabrication.

Characterizations. We used a commercial Raman spectrometer(Renishaw, Inc.) to perform the Raman spectroscopy with a 532 nmlaser source. The AFM images were taken with Bruker DimensionIcon. The electrical properties were measured with an Agilent B1500Asemiconductor parameter analyzer in ambient air. The wavelengthand intensity of the utilized UV light are 254 nm and 2.5 mW/cm2,respectively. The photovoltaic properties were performed with a laser600 nm in wavelength, the power of which can be tuned continually.We used an optical power meter of PM100D to measure the power ofthe light and calculated the incident light power on the devicesaccording to their area.

ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acsnano.9b00201.

AFM images of device (S1); output characteristic curvesof doped MoTe2 and MoS2 transistor (S2); hysteresis ofanti-ambipolar MoTe2/MoS2 heterotransistor (S3);transfer characteristics of another two heterojunctionsamples after different p-doping condition (S4); transfercharacteristic curves of MoTe2 after different photo-induced n-doping level (S5); energy band diagram and

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transfer characteristics of anti-ambipolar MoTe2/MoS2heterotransistor at different bias conditions (S6);photoswitching behaviors of MoTe2 and MoS2 FETs(S7) (PDF)

AUTHOR INFORMATIONCorresponding Authors*E-mail: xdhu@tju.edu.cn.*E-mail: jingliu_1112@tju.edu.cn.*E-mail: zhangdaihua@gmail.com.ORCIDEnxiu Wu: 0000-0001-6060-1180Jing Liu: 0000-0002-8993-4074Chongwu Zhou: 0000-0001-8448-8450Author Contributions§E.W. and Y.X. contributed equally.NotesThe authors declare no competing financial interest.

ACKNOWLEDGMENTSThis work is supported by the National Science Foundation ofChina (No. 21405109) and the Seed Foundation of State KeyLaboratory of Precision Measurement Technology and Instru-ments, China (No. Pilt1710).

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