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Strain distributions and their influence on electronic structures of WSe2–MoS2 laterally strained heterojunctions

Abstract

Monolayer transition metal dichalcogenide heterojunctions, including vertical and lateral p–n junctions, have attracted considerable attention due to their potential applications in electronics and optoelectronics. Lattice-misfit strain in atomically abrupt lateral heterojunctions, such as WSe2–MoS2, offers a new band-engineering strategy for tailoring their electronic properties. However, this approach requires an understanding of the strain distribution and its effect on band alignment. Here, we study a WSe2–MoS2 lateral heterojunction using scanning tunnelling microscopy and image its moiré pattern to map the full two-dimensional strain tensor with high spatial resolution. Using scanning tunnelling spectroscopy, we measure both the strain and the band alignment of the WSe2–MoS2 lateral heterojunction. We find that the misfit strain induces type II to type I band alignment transformation. Scanning transmission electron microscopy reveals the dislocations at the interface that partially relieve the strain. Finally, we observe a distinctive electronic structure at the interface due to hetero-bonding.

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Fig. 1: STM images of the WSe2–MoS2 lateral heterojunction.
Fig. 2: Imaging the anisotropic strain in the WSe2–MoS2 lateral heterojunction.
Fig. 3: The electronic structure and its dependence on the strain distribution.
Fig. 4: Determinations of band edges, interface states and band alignment by constant I spectroscopy.

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Acknowledgements

This research was supported with grants from the Welch Foundation (F-1672), the US National Science Foundation (NSF) (DMR-1306878, EFMA-1542747) and the Materials Research Science and Engineering Center (DMR-1720595). L.J.L. acknowledges support from KAUST (Saudi Arabia), MOST and TCECM, Academia Sinica (Taiwan) and AOARD FA23861510001 (USA). C.Z acknowledges support from the National Natural Science Foundation of China (Grant No. 11774268). Y.S.S acknowledges support from the Yan Jici Talent Students Program. This work made use of the electron microscopy facility of the Cornell Center for Materials Research with support from the NSF (DMR-1719875 and DMR-1429155).

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Contributions

C.Z. carried out the STM/S measurements. M.-Y.L. and L.-J.L. performed the chemical vapour deposition growth of WSe2–MoS2 heterojunctions. Y.S. helped determine strain tensors from distorted moiré patterns. Y.H. and D.A.M. performed the scanning transmission electron microscopy investigations. J.T. identified the mechanisms of strain relaxation and explained the strain distribution. C.-K.S. advised on the experiments and provided input on the data analysis. C.-K.S. and C.Z. wrote the paper with input from the co-authors.

Corresponding authors

Correspondence to Chendong Zhang or Chih-Kang Shih.

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Supplementary Figures 1–12, Supplementary references

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Zhang, C., Li, MY., Tersoff, J. et al. Strain distributions and their influence on electronic structures of WSe2–MoS2 laterally strained heterojunctions. Nature Nanotech 13, 152–158 (2018). https://doi.org/10.1038/s41565-017-0022-x

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