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A room-temperature gate-tunable bipolar valley Hall effect in molybdenum disulfide/tungsten diselenide heterostructures

Nature Electronics volume 5, pages 23–27 (2022)Cite this article

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Abstract

Two-dimensional semiconductors have a valley degree of freedom that could be used as a platform for future optoelectronic devices. The valley Hall effect, caused by electrons in different valleys having opposite Berry curvatures, is important for making such devices, but has only been reported with plasmonic structures or at cryogenic temperatures, limiting practical application. Here we report the observation of the valley Hall effect at room temperature in a molybdenum disulfide/tungsten diselenide van der Waals heterostructure. We show that the magnitude and polarity of the valley Hall effect in the heterostructure are gate tunable, which can be attributed to the contribution of the opposite valley Hall effect from electrons and holes in different layers. We use this gate tunability to create a bipolar valleytronic transistor.

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Fig. 1: VHE at room temperature.
Fig. 2: Gate-dependence measurement of VHE and longitudinal conductivity at 240 K.
Fig. 3: Gate dependence of PC at 240 K.
Fig. 4: Gate-dependence mechanism of VHE and PC.

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Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

We acknowledge the discussion with F. Wang and W. Yao. W.-b.G acknowledges financial support from the Singapore National Research Foundation through its Competitive Research Program (CRP award Nos. NRF-CRP21-2018-0007 and NRF-CRP22-2019-0004), QEP programme and Singapore Ministry of Education (MOE2016-T3-1-006 (S)). Q.X. gratefully acknowledges National Natural Science Foundation of China (no. 12020101003), support from the State Key Laboratory of Low-Dimensional Quantum Physics and Start-up Grant from Tsinghua University. C.J. acknowledges the National Natural Science Foundation of China (no. 61974075); the Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin; and the Engineering Research Center of Thin Film Optoelectronics Technology, Ministry of Education of China. H.M. gratefully acknowledges the National Natural Science Foundation of China (no. 61704121), China Scholarship Council (no. 201709345003) and the Tianjin Natural Science Foundation (no. 19JCQNJC00700).

Author information

Author notes

  1. These authors contributed equally: Chongyun Jiang, Abdullah Rasmita, Hui Ma.

Authors and Affiliations

  1. Division of Physics and Applied Physics, Nanyang Technological University, Singapore, Singapore

    Chongyun Jiang, Abdullah Rasmita, Qinghai Tan, Zhaowei Zhang, Zumeng Huang, Shen Lai, Naizhou Wang, Sheng Liu, Xue Liu, Ting Yu & Wei-bo Gao

  2. School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore

    Chongyun Jiang, Abdullah Rasmita, Qinghai Tan, Zhaowei Zhang, Zumeng Huang, Shen Lai, Naizhou Wang, Sheng Liu, Xue Liu, Ting Yu & Wei-bo Gao

  3. College of Electronic Information and Optical Engineering, Nankai University, Tianjin, People’s Republic of China

    Chongyun Jiang

  4. School of Physical Science and Technology, Tiangong University, Tianjin, People’s Republic of China

    Hui Ma

  5. School of Physics and Technology, Wuhan Univeristy, Wuhan, People’s Republic of China

    Ting Yu

  6. State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing, People’s Republic of China

    Qihua Xiong

  7. Department of Physics, Tsinghua University, Beijing, People’s Republic of China

    Qihua Xiong

  8. Beijing Academy of Quantum Information Sciences, Beijing, People’s Republic of China

    Qihua Xiong

  9. Beijing Innovation Center for Future Chips, Tsinghua University, Beijing, People’s Republic of China

    Qihua Xiong

  10. Frontier Science Center for Quantum Information, Beijing, People’s Republic of China

    Qihua Xiong

  11. The Photonics Institute, Nanyang Technological University, Singapore, Singapore

    Wei-bo Gao

  12. Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore, Singapore

    Wei-bo Gao

Authors
  1. Chongyun Jiang
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Contributions

C.J. and W.-b.G. conceived the project. C.J., Z.Z. and Z.H. performed the measurements. H.M., Q.T., S. Lai, N.W., S. Liu and X.L. fabricated the devices. C.J., Z.Z. and A.R. analysed the data. A.R. performed the theoretical analysis. C.J., H.M., A.R. and W.-b.G. wrote the manuscript. T.Y., Q.X. and W-b.G. supervised the project. All the authors contributed to the discussion of the results.

Corresponding authors

Correspondence to Qihua Xiong or Wei-bo Gao.

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The authors declare no competing interests.

Additional information

Peer review information Nature Electronics thanks Yanping Liu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Gate dependence measurement of VHE and longitudinal conductivity at 240 K in MoS2/WSe2 with 60° twist angle (AB-stacked).

(a) Optical image of the sample. The red dot is the 220 μW, 726 nm optical excitation location. The electronic configuration is as in Supplementary Fig. 4 in the Supplementary Information (source(drain): electrode 4(2), Hall electrodes: 1 and 3). (b) VH as a function of Vx and Vg. (c) The αH (proportional to VHE) and βH (proportional to CPC) as a function of Vg. The shaded area represents a 95% confidence interval. (d) Gate dependence of the longitudinal conductivity (σxx).

Extended Data Fig. 2 Gate dependence measurement of VHE and longitudinal conductivity at 240 K in MoS2/WSe2 with 20° twist VH angle.

(a) Optical image of the sample. The red dot is the 220 μW, 726 nm optical excitation location. The electronic configuration is as in Supplementary Fig. 4 in the Supplementary Information (source(drain): electrode 4(2), Hall electrodes: 1 and 3). (b) The VH as a function of Vx and Vg. (c) The αH (proportional to VHE) and βH (proportional to CPC) as a function of Vg. The shaded area represents a 95% confidence interval. (d) Gate dependence of the longitudinal conductivity (σxx).

Extended Data Fig. 3 Microscopic processes involved in band shift-induced valley current generation and modulation in MoS2/WSe2 heterostructure.

The yellow (blue) colour represents the MoS2 (WSe2) layer. Filled (empty) circles represent photogenerated electrons (holes). (a) Process 1: optical selection rule and process 2: charge transfer. (1) A circularly polarized light creates photogenerated electrons and holes in WSe2 with wavevector \({\bf{k}}_0\). (2) The electron undergoes charge transfer from WSe2 to MoS2, while the hole stays in WSe2. The optically induced valley current density in MoS2 (\({\bf {J}}_{{{\mathrm{v}}}}^{{{\mathrm{M}}}}\)) and WSe2 (\({\bf{J}}_{{{\mathrm{v}}}}^{{{\mathrm{W}}}}\)) have opposite directions. (b) Charge transfer process in the k space. The yellow (blue) arrows are the MoS2 (WSe2) photogenerated electron wavevectors \({\bf{k}}_i^{{{\mathrm{M}}}}\) (\({{\bf{k}}_i^{{{\mathrm{W}}}}} = {\bf{k}}_0\)), with respect to the MoS2 (WSe2) conduction band minimum (CBM). Due to the twist angle \(\theta\), the wavevector at MoS2 CBM (\({{{\mathrm{K}}}}_{{{\mathrm{M}}}}^{{{\mathrm{C}}}}\)) differs from the wavevector at WSe2 CBM (\({{{\mathrm{K}}}}_{{{\mathrm{W}}}}^{{{\mathrm{C}}}}\)) by \({\mathbf{\Delta}}_i^{{{{\mathrm{rot}}}}}\) (solid black arrows, \({\mathbf{\Delta}}_{3(2)}^{{{{\mathrm{rot}}}}} = R_{ + ( - )2\pi /3}{\mathbf{\Delta}}_1^{{{{\mathrm{rot}}}}}\)). The dashed black arrows (\({\mathbf{\Delta}}_i^{{{{\mathrm{ct}}}}}\)) are the C3 symmetry allowed wavevector change during the charge transfer (that is, \({\mathbf{\Delta}}_{3(2)}^{{{{\mathrm{ct}}}}} = R_{ + ( - )2\pi /3}{\mathbf{\Delta}}_1^{{{{\mathrm{ct}}}}}\)). Inset: addition of wavevectors in MoS2 and WSe2. Regardless of the twist angle, the effective velocity of photogenerated electrons in MoS2 has the same direction as in WSe2. (c) Process 3: current collection. The valley current (\(I_{{{\mathrm{v}}}}\)) is obtained by summing up the valley current from each layer (\(I_{{{\mathrm{v}}}}^{{{\mathrm{M}}}}\)and \(I_{{{\mathrm{v}}}}^{{{\mathrm{W}}}}\)), which depends on the valley current density as well the layer-dependent carrier transport efficiency (\(\eta _{{{{\mathrm{M(W)}}}}}(V_{{{\mathrm{g}}}})\) for MoS2(WSe2)). (d) Illustration of valley current gate dependence. The valley current polarity is gate tunable regardless of the twist angle. Here, \(\gamma _{{{{\mathrm{WM}}}}} = 0.9\) is used. The shaded area, region I, and region II definitions follow the ones in the main text Fig. 4.

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Supplementary Information

Supplementary Figs. 1–23 and Notes 1–6.

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Jiang, C., Rasmita, A., Ma, H. et al. A room-temperature gate-tunable bipolar valley Hall effect in molybdenum disulfide/tungsten diselenide heterostructures. Nat Electron 5, 23–27 (2022). https://doi.org/10.1038/s41928-021-00686-7

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