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Photo-Induced Doping to Enable Tunable and HighPerformance Anti-Ambipolar MoTe2/MoS2 Heterotransistors Enxiu Wu, Yuan Xie, Qingzhou Liu, Xiaodong Hu, Jing Liu, Daihua Zhang, and Chongwu Zhou ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.9b00201 • Publication Date (Web): 11 Apr 2019 Downloaded from http://pubs.acs.org on April 12, 2019

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Photo-Induced Doping to Enable Tunable and High-Performance AntiAmbipolar MoTe2/MoS2 Heterotransistors

Enxiu 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 and Opto-electronics Engineering, Tianjin University, No. 92 Weijin Road, Tianjin, 300072, China §Department of Electrical Engineering, University of Southern California, Los Angeles,

California 90089, United States *Corresponding author: [email protected]; [email protected]; [email protected]

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ABSTRACT: Van der Waals (vdW) p-n heterojunctions formed by two dimensional nanomaterials exhibit many physical properties and deliver functionalities to enable future electronic and optoelectronic devices. In this report, we demonstrate a tunable and high-performance anti-ambipolar transistor based on MoTe2/MoS2 heterojunction through in situ photo-induced doping. The device demonstrates high on/off ratio of 105 with large on-state current of several micro-Amps. Peak position of the drain-source current in the transfer curve can be adjusted through doping level across a large dynamic range. In addition, we have fabricated a tunable multi-value inverter based on the heterojunction that demonstrates precise control over its output logic states and window of mid-logic through source-drain bias adjustment. The heterojunction also exhibits excellent photo detection and photovoltaic performances. Dynamic and precise 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


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The growing inventory of layered two-dimensional (2D) semiconductors with diverse electronic characteristics has allowed atomically thin and dimensionally abrupt heterostructures to be realized.1–3 2D van der Waals heterostructures have enabled a variety of device types including tunneling field-effect transistors (TFETs),4–6 Schottky junctions,7 photovoltaic devices,8–11 light-emitting devices,12–14 inverters,15– 17

nonvolatile memory cells18,19 and multifunctional electronic devices.20–22 Some 2D

heterojunctions exhibit different transfer characteristics when their band alignments are properly configured. The channel conductance reaches its local maximum at a specific gate bias, as opposed to typical V-shape transfer curves of regular ambipolar devices. This behavior is therefore called anti-ambipolarity, which was first observed in gate-tunable carbon nanotube 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 circuits and optoelectronics. For example, it enables both positive and negative transconductance in a single device and a sharp transition between the two states. The flipping of transconductance has been exploited to implement a number of analog 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 least 7 FETs to construct a Gilbert cell, 33 the anti-ambipolar device takes only one p-n junction and a serial resistor to achieve the BPSK or BPSK function, which significantly simplifies the circuit design and implementation. In addition, anti-ambipolar devices can also be used to build ternary logic inverters.20,25 Compared to conventional binary inverters, ternary inverters provide multivalued digital signals and are promising architectures to break fundamental bit limit and enable higher data storage density and more intricate logic devices. Another important feature is its gate-tunable rectification characteristics, which has been widely used to develop gate-tunable rectifier circuits and photodetectors.23,24,27,29,31,34

Despite their potential in a wide range of applications, fabrication of anti-ambipolar


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heterojunctions with reliable and consistent performances remains a challenging task. It requires highly precise control of the turn-on voltages (Von) and carrier densities of both the n-type and p-type transistors in the junction. Concretely, the p- and ntransistors need to have a large positive and large negative turn-on voltages respectively so that both devices can stay on within a wide gate bias window. Meanwhile, the intrinsic carrier densities of both transistors should be at similar levels, as imbalance between the two types of charge carriers can easily lead to domination of unipolar transport. Even though previous demonstrations have achieved basic functionalities, they normally suffer small on-state current and low on/off ratio due to narrow on-state window. In addition, their transport characteristics such as the position of the conductance peak and overall shape of the transfer curve cannot be dynamically adjusted, which largely limits the flexibility and adaptability in many applications.

In this work, we developed a tunable high-performance anti-ambipolar device based on MoTe2/MoS2 heterojunction through photo-induced doping. The approach enables precise tuning of the doping level and effective modulation of the transport behavior in a large dynamic range, allowing the heterostructure to be reversibly switched between anti-ambipolar and unipolar-dominated operational regimes. In addition, the anti-ambipolar device provides large on-state current (~µA) and very high on/off ratio of ~105, roughly 1 to 4 orders of magnitude higher than previous works. We then demonstrated a tunable multivalue inverter by engineering the partition load and matching, and achieved precise control over the output logic state and window of mid-logic through driving bias. Finally, we built a photovoltaic device based on this anti-ambipolar devices and achieved excellent performance with a maximum power conversion efficiency of 0.55% and external quantum efficiency of 56 %. The photo responsivity and response time reached 0.25 A/W and 2ms, respectively.


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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 the control gate, and h-BN and SiO2 are the gate dielectric. (b) False-colored SEM image of the device. Scale bar is 5 um. (c) Raman spectrum of a MoS2/MoTe2/BN triple-layer sample. (d) Transfer characteristics of the MoTe2 FET, MoTe2 FET and MoS2/MoTe2 heterotransistor in both linear (solid line) and semi-log (dashed line) scales. (e) Output characteristics of MoS2/MoTe2 heterotransistor at different gate-source bias Vgs.

RESULTS AND DISCUSSION Figure 1a shows the structural configuration of the MoTe2/MoS2 heterojunction device used in our study. The whole device is back gated through the Si/SiO2


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substrate. We placed a thin layer of h-BN under the heterojunction, which creates two interfaces on the top and bottom surfaces of the BN. As will be discussed in the following sections, the BN-SiO2 interface can effectively trap charges and modulate the transport behaviors of the heterojunction device. Figure 1b presents a falsecolored scanning electron microscopy (SEM) image of the structure. Two pairs of Cr/Au electrodes labeled as 1/2 and 3/4 define two separate transport channels in MoTe2 and MoS2 FET, respectively. The transport channel between electrode 2 and 3 constitutes a MoS2/MoTe2 heterotransistor. Thicknesses of the MoTe2, MoS2 and hBN flakes were measured to be 10, 13 and 20.0 nm using atomic force microscope (AFM), as shown in Figure S1. The Raman spectrum in Figure 1c confirms the lattice structures of all three layers. The three peaks at 169, 232 and 287 cm-1 are characteristic peaks of MoTe2. The two peaks at 382 and 403 cm-1 characterize single crystalline MoS2 and the peak at 1363 cm-1 originates from longitudinal mode phonons in h-BN.

Figure 1d shows the transfer characteristics of the MoTe2 (red), MoS2 (violet) and the heterojunction devices (blue). The gate-source bias (Vgs) was scanned from +60 to 60V while the drain-source bias (Vds) remained at +2 V. Results of the MoS2 and MoTe2 FETs are consistent with most previous studies.35–37 The MoS2 shows n-type transport throughout the entire scan from -60 to +60V, while the transport in MoTe2 is dominated by n- and p-type carriers under positive and negative gate biases respectively, resulting in the ambipolar transfer characteristics (red dashed curve) in Figure 1d. The MoTe2/MoS2 heterojunction exhibits ambipolar transfer characteristic as well (blue dashed curve). However, since the current transport is essentially dominated by electrons, polarity switching occurs at a very negative gate bias around -52V. Unlike the MoTe2/MoS2 devices reported in previous works,38,39 our device did not show anti-ambipolar behavior in these measurements. The result is not surprising since the onset of anti-ambipolar transport requires two conditions. First, doping concentrations on the p- and n- sides of the junction should be in good balance with each other. Second, there exists a gate bias window within which both the p- and n-


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branches can operate in on-state. Our device meets none of these conditions according to the transfer characteristics of individual FETs, primarily because hole doping of the MoTe2 FET is far from its optimal level. Figure 1e shows the output characteristics of the heterojunction under different Vgs. It is worth noting that the curves show no rectification despite that the energy bands are aligned in type-II configuration at the junction. This can be attributed to un-optimized device doping level as well.

Figure 2 Transport characteristics of MoTe2 (a) and MoS2 (b) FETs at Vds = 2V in linear (solid line) and semi-log (dashed line) scales after photo-induced doping. Curves in different colors correspond to different “writing voltages” during the doping process. The curve of “0V” (leftmost one with the charge neutrality point close to Vgs = 0V) is taken with the pristine sample prior to doping treatment. The photo-induced doping is done by exposing the device to UV illumination for 1 second at different writing voltage from 10 V to 80 V with a 10 V step. (c) Threshold turn-on voltages (Vth) of the MoTe2 (blue diamonds) and MoS2 (purple circles) FETs as a function of writing voltage. (d) Transfer characteristics of the MoTe2 and MoTe2 FETs and the MoS2/MoTe2 heterojunction at Vds = 2V in semi-log scale after photoinduced doping under 80 V writing voltage.


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We developed a versatile photo-induced doping approach that enables highly effective and non-volatile band modulation of MoTe2 and MoS2 transistors. The doping is done by applying a large gate bias (referred to as “writing voltage” in the following discussion) and UV illumination on the device at the same time, for typically less than a second. After that we turn off the UV light and writing voltage and record a transfer curve of the doped device to characterize its transport behavior. We note both the writing voltage and UV illumination have to present at the same time to enable this doping process. The device will not make any non-volatile change if either activation is absent. The results with different writing voltages are shown in Figure 2a and 2b, for the MoTe2 and MoS2 FETs, respectively. The solid and dash lines are linear and semi-log plots. The writing voltages are listed in the annotation with font colors matching those of the transfer curves. The curve corresponding to “0V” writing voltage shows no difference from the un-treated device, as UV illumination by itself is a fully recoverable treatment. However, the combination of UV light and large writing voltage can induce permanent changes to the material that last even after both activations are withdrawn. Magnitude of the change is qualitatively proportional to the writing voltage. As shown in Figure 2a, the MoTe2 FET transforms from an electron-dominated ambipolar device (red curve) to a highly-doped unipolar p-type FET (black curve) as the writing voltage increases from 0 to 80 V. The results suggest that the internal E-field induced by the dual activation of UV illumination and electrostatic gating is nonvolatile and able to electrostatically dope the MoTe2 channel to sufficiently deep levels. The doping scheme works very similarly to a multi-level floating gate memory. The UV photons generate a large number of free electrons and holes in the MoTe2 channel. When a positive writing voltage is applied in the vertical direction, it drives electrons to tunnel through the BN layer. At the same time, the UV illumination also excites defect states at the BN/SiO2 interface to trap and anchor these electrons.40 As the result, even after the photo-induced activation is withdrawn, the electrons stay at the interface permanently, creating a negative gate bias to electrostatically dope the MoTe2 channel to p-type.


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In contrast to MoTe2, the MoS2 FET undergone the same treatment showed very little response despite a gradual reduction in on-state current from 65 to 31 µA at Vgs = 60V (Figure 2b). The weak response to the doping treatment results from very strong Fermi-level pinning at the metal-MoS2 interface.41 In Figure 2c we plot the turn-on voltages (Von) of both devices as a function of writing bias. The Von of MoTe2 increases linearly with the writing bias from 1.2 to 62.4 V (blue diamonds), whereas the MoS2 FET kept its Von at around -54 V regardless of the writing voltage (purple circles).

Through the photo-induced doping treatment we were able to configure the MoTe2 and MoS2 FETs to the optimal conditions to form an anti-ambipolar device. They now meet both requirements: comparable doping levels in the p- and n- branches, and substantial overlapping of the two on-states. The measurement 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. The heterojunction shows a clear antiambipolar pattern, with one conductance peak near Vgs = 0 and two minimums around -54 V and +62 V. This is easy to understand as the junction is formed by a p- and an n- FET in series, in which the total current reaches maximum when both transistors are turned on around Vgs = 0V, and drops to minimum when either device is off. Two valleys of the junction’s transfer curve correspond to the depletion of the p- and nFETs respectively. The output characteristics of the doped MoTe2 and MoS2 FETs at different gate biases are plotted in Figure S2, indicating good ohmic contacts at the semiconductor-metal interfaces. This verifies that the anti-ambipolar transport behavior has nothing to do with these interfaces, but rather the heterojunction formed between the two FETs. The anti-ambipolar device can achieve a very high current on/off ratio exceeding 105, making it an ideal component to implement a wide range of advanced logic circuitries.23–32 It is worth noting that the subthreshold regimes of the MoTe2 and MoS2 FETs coincide with the junction’s transfer curve very well. This results from negligible hysteresis in the transfer characteristics of heterojunction


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device owing to the photo-induced doping treatment (Figure S3). Such level of hysteresis minimization has been rarely achieved in previous studies23,24,27 despite its great importance in practical applications. 2.0 1.6 1.2 0.8 0.4

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Figure 3 (a) Transfer characteristic curves of the MoS2/MoTe2 heterojunction at Vds = 2V in both linear (a) and semi-log (b) scales after doping under different writing biases. (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 = 0V after photo-induced doping at different levels. (f) Plot of device rectification ratio at Vgs = 0 V with respect to different writing voltages. The forward (Vds = +2V) and reverse (Vds = -2V) drain-source current after doping under different writing voltages is shown in the inset.


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In Figure 3a and 3b we characterize the transport behavior of the heterojunction after doping under different writing voltages, where we can clearly visualize the gradual transition from ambipolar to anti-ambipolar transfer characteristics. Concretely, both parameters are changing with the increasing writing voltage from 10 to 80 V, which are the height (Figure 3c) and position (Figure 3d) of the Ids peak. Both changes are associated with the increasing doping level of the MoTe2 FET (Figure 2c). The photoinduced hole doping greatly raises the on-state current of the MoTe2 FET, shifts its threshold voltage toward more positive gate bias, and widens the overlap between the on-states of the p- (MoTe2) and n- (MoS2) transistors. Through the photo-induced doping treatment, we can precisely control the transition from the ambipolar to antiambipolar states, and accurately adjust the position of the Ids peak. Position of the peak is critical parameters when these anti-ambipolar transistors are used to build functional blocks such as frequency doubling circuits and more intricate signal conditioning modules. The ability of precise tuning of these parameters would largely improve the flexibility and potential of such devices in a wide range of applications. Throughout the study we have measured multiple devices treated and measured the same way. There are variations in peak position and on-state current in the antiambipolar transfer curves due to differences in material quality, geometry and minute process variations, but all devices behaved qualitatively the same in terms of reversibility between the uni-polar and anti-ambipolar states and tunability of the peak position (Figure S4). We also note that the photo-induced doping is bidirectional and fully reversible. By applying a negative writing bias under UV illumination, we can reduce the hole doping in the MoTe2 FET to a lower doping level, or reset it to its original state if needed (Figure S5). The entire device tuning process is highly flexible, fast, and stable. The output characteristics of the heterojunction is recorded in Figure 3e. In the inset of Figure 3f we plot the forward (blue) and reverse (red) current with respect to the writing voltage, at Vds = +2V and -2V, respectively. As the writing voltage increases, both forward and reverse current drop sharply and reach the minimum around 20 V. As the writing bias further increases, the reverse current rises slightly and the forward current increases linearly. The corresponding rectification ratio, defined as the ratio between the forward and the reverse current, was calculated and plotted in Figure 3f. The result shows a dramatic increase by roughly two orders of magnitude, from 1.5 to 151, which is resulted from the rise of built-in potential of heterojunction with pdoping level of MoTe2. Higher rectification ratio can largely improve the energy conversion efficiency when the anti-ambipolar transistor is configured as a photovoltaic device. More discussions will be followed up in a later section (Figure


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Figure 4 (a) Cross-sectional structure of the heterojunction-based ternary inverter. (b) Transfer characteristics of the heterojunction (solid line) and MoTe2 FET (dashed line) under different source-drain biases (Vds). (c) Inverter formed by a MoTe2 FET and a MoTe2/MoS2 heterojunction showing binary logic under a small driving voltage (Vdd) and ternary logic under a large driving voltage. Vdd varies from 0.1 V to 2 V. (d) Voltage gain of both switching states of the inverter at different Vdd.

Negative transconductance has been demonstrated in various logic circuits23,26,31 as well as optoelectronic devices.24,27,29,30 Among different applications of negative transconductance, multivalued logic (MVL)20,25 has attracted extensive attention. With larger number of logic states, MVL has the potential for higher data storage in less area as compared with binary logic devices. In the experiments in Figure 4, we demonstrate a typical application of the anti-ambipolar transport behavior. It is a ternary inverter formed by a MoTe2/MoS2 heterojunction and a MoTe2 FET connected in series, as shown in the schematic drawing of Figure 4a. The back gate is used to apply the input voltage (Vin), the middle electrode for output voltage (Vout),


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and the side electrodes for the source (GND) and driving voltage (Vdd).

We first characterize the two devices forming the ternary inverter separately. Figure 4b shows the transfer characteristics of the anti-ambipolar junction (solid line) and the p-type MoTe2 FET (dashed line) under different drain-source biases (Vds). It is interesting to find that the current through the heterojunction drops much faster on the right shoulder of the peak (shaded region as highlighted on the figure) under higher Vds, which results in a higher peak-to-valley ratio. For example, the current measured at Vds = 2V (red curve) dropped from 2.1510-6 to 2.0310-7 A by 1 order of magnitude when Vgs scans from 0 to 36 V, whereas the current at Vds = 0.1V dropped by only 2 times within the same Vgs range. We can use the band diagrams in Figure S6a to understand the difference in these transfer curves. Under a forward bias, the energy band of MoTe2 is pulled down, and the barrier height for holes decreases with increasing Vds. When Vds increases further until the valence band of MoTe2 is pulled down below the valence band of MoS2, the barrier for holes vanishes and the MoTe2 channel starts to dominate the current transport. Overall speaking, the larger the drainsource bias, the more effectively the gate bias can modulate the transport channel, and the higher the on-off ratio we can achieve in these devices. On the contrary, when a negative Vds is applied, the drain-source current drops much slower on the right shoulder of 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 multi-value inverter, in which the output logic state and window of mid-logic (logic ½) level can be controlled by source-drain bias. Width of the mid-logic plateau is one of the most important figureof-merits of a ternary invertor that characterizes the tolerance window and stability of this mid-state. As shown in the schematic of Figure 4a, the device is essentially a voltage divider of Vdd. The output voltage depends on the resistance ratio between the two devices in series, the MoTe2 FET and the MoTe2/MoS2 heterojunction. Therefore, keeping the output voltage at a stable level requires the two devices to maintain a


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constant resistance ratio during the scan of Vgs (also Vin). This explains why we observed the biggest logic ½ window at the highest driving voltage of Vdd = 2V (red curve). Higher Vdd leads to higher voltage drop across the heterojunction, and according to Figure 4b, allows sharper “on” to “off” transition of this anti-ambipolar device and makes its negative transconductance better match that of the MoTe2. This enables the conductance of the two devices to drop at a similar rate as Vin increases, therefore maintaining a relatively stable output voltage within this scan range. Concretely, the output logic ½ state under Vdd = 2 V sits at ~ 0.85 V with a window of approximately 20 V (0 V < Vin < 20 V). As Vdd decreases, the mid-state becomes less indistinguishable and completely vanishes when Vdd is less than 0.5 V. Figure 4d plots the corresponding gain of the inverter at different Vdd values. In this plot, we also clearly find the transition of logic state from binary to ternary as Vdd increases. Under a small driving voltage of Vdd = 100 mV, only a single gain from logic 1 to 0 can be detected (green curve). When Vdd reaches 500 mV and above, we start to observe two gains of the ternary inverter. The left three peaks correspond to the voltage gain from logic 1 to ½, and the second three peaks for the voltage gain from logic ½ to 0. In addition, we find that the two gains increase monotonically with Vdd.


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-100 2 ms

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

In addition to applications in logic circuitries such as ternary transistors, the MoTe2/MoS2 heterojunction is also an excellent opto-electronic device with outstanding photovoltaic and photo-switching properties. Figure 5a shows the output characteristics of the heterojunction under light illumination at 600 nm. As the incident power density rises, both the open-circuit voltage (Voc) and short-circuit current (Isc) increase in magnitude, confirming the formation of a photovoltaic junction. Due to the energy gradient of type-II band alignment and 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 photovoltaic device that reaches the highest output power of Pelectrical = 610-3 nW at 150 mV and 40 pA. We


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estimated the incident optical power to be Poptical = 1.1 nW according to the device area and power density of the illumination. The energy conversion efficiency is calculated to be PV = Pelectrical / Poptical ≈ 0.55%. The fill factor (FF), defined as the ratio between the maximum obtainable power and the product of Voc and Isc, is calculated to be 0.35 at 1.1 nW.

Owing to its photovoltaic property, the heterojunction can also work as a selfpowered photo-switch. In Figure 5b, we recorded the photo current at Vds = 0V during five consecutive illumination cycles. Curves in different colors were taken at different laser powers ranging from 0.1 to 1.1 nW. The device exhibits excellent sensitivity, repeatability and stability. The maximum photoresponsivity (R) reached ~ 0.25 A/W as estimated at different incident powers. The external quantum efficiency (EQE) is proportional to R and defined as EQE = hcR/(eλ), with h, c, e and λ being the Planck constant, speed of light, 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 photo diodes based on heterojunction9-12. We also measured photovoltaic responses of MoS2 and MoTe2 transistors at Vds = 0 V and P = 1.1 nW (Figure S7). Neither of them showed detectable signal, which is attributed to quasi-ohmic contact at the TMDmetal interfaces. Figure 5c shows the photosensitivity and photoresponsivity as a function of illumination power. The photosensitivity increases with the incident power while the photoresponsivity drops monotonically. Decreasing photoresponsivity at higher illumination power has also been observed in other photoconductors based on similar materials and structures. 42,43 This is presumably due to reduction of available carriers that can be collected under high photon flux.44 The response time is estimated to be less than 2 ms according to the measurement in Figure 5d, revealing fast and efficient electron–hole separation.

CONCLUSIONS In summary, we developed an effective photo-induced doping approach that enables


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tunable and high-performance anti-ambipolar device based on MoTe2/MoS2 heterojunction. The device shows record-high current on/off ratio greater than 105 with on-state current at uA level and a tunable peak position. Tunable highperformance ternary inverters controlled by drain voltage have been demonstrated by adopting energy band alignment and load matching. Finally, excellent photovoltaic effect and photo detection were demonstrated. The tunable anti-ambipolar transport property may bring broad prospects for next generation optoelectronics and logic electronics.

METHODS Device Fabrication: The heterostructures were produced with a dry transfer technique. First, a h-BN flake was first mechanically exfoliated from bulk h-BN and then transferred onto a 285 nm SiO2/n+ doped Si substrate. Next, a MoTe2 flake was transferred onto h-BN flake. And then, a 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 by Ebeam evaporation after exposure and development, which was followed by a standard liftoff process to complete the fabrication. Characterizations: We used commercial Raman spectrometer (Renishaw, Inc.) to obtain the Raman spectroscopy with a 532 nm laser source. The AFM images were taken with Bruker Dimension Icon. The electrical properties were measured with Agilent B1500A semiconductor parameter analyzer in ambient air. The wavelength and intensity of utilized UV light is 254nm and 2.5mW /cm2, respectively. The photovoltaic properties were performed with a laser 600 nm in wavelength, the power of which can be tuned continually. We used an optical power meter of PM100D to measure the power of the light and calculated the incident light power on the devices according to their area. ASSOCIATED CONTENT


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The authors declare no competing interest.

Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: XXX. AFM images of device (S1); Output characteristic curves of doped MoTe2 and MoS2 transistor (S2); Hysteresis of antiambipolar MoTe2/MoS2 heterotransistor (S3); Transfer characteristics of another two heterojunction samples after different p-doping condition (S4); Transfer characteristic curves of MoTe2 after different photoinduced n-doping level (S5); Energy band diagram and transfer characteristics of antiambipolar MoTe2/MoS2 heterotransistor at different bias conditions (S6); Photo switching behaviors of MoTe2 and MoS2 FETs (S7).

Corresponding Author *E-mails: [email protected]; [email protected]; [email protected]

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally.

ACKNOWLEDGMENT This work is supported by National Science Foundation of China (No. 21405109) and Seed Foundation of State Key Laboratory of Precision Measurement Technology and Instruments, China (No. Pilt1710).


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