Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platform

Journal name:
Nature Nanotechnology
Volume:
10,
Pages:
534–540
Year published:
DOI:
doi:10.1038/nnano.2015.70
Received
Accepted
Published online

Abstract

Atomically thin two-dimensional semiconductors such as MoS2 hold great promise for electrical, optical and mechanical devices and display novel physical phenomena. However, the electron mobility of mono- and few-layer MoS2 has so far been substantially below theoretically predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviours. Potential sources of disorder and scattering include defects such as sulphur vacancies in the MoS2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielectrics. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements in performance, including a record-high Hall mobility reaching 34,000 cm2 V–1 s–1 for six-layer MoS2 at low temperature, confirming that low-temperature performance in previous studies was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also observed Shubnikov–de Haas oscillations in high-mobility monolayer and few-layer MoS2. Modelling of potential scattering sources and quantum lifetime analysis indicate that a combination of short-range and long-range interfacial scattering limits the low-temperature mobility of MoS2.

At a glance

Figures

  1. vdW device structure and interface characterization.
    Figure 1: vdW device structure and interface characterization.

    a, Schematic of the hBN-encapsulated MoS2 multi-terminal device. The exploded view shows the individual components that constitute the heterostructure stack. Bottom: Zoom-in cross-sectional schematic of the metal–graphene–MoS2 contact region. b, Optical microscope image of a fabricated device. Graphene contact regions are outlined by dashed lines. c, Cross-sectional STEM image of the fabricated device. The zoom-in false-colour image clearly shows the ultra-sharp interfaces between different layers (graphene, 5L; MoS2, 3L; top hBN, 8 nm; bottom hBN, 19 nm).

  2. Gate-tunable and temperature-dependent graphene–MoS2 contacts.
    Figure 2: Gate-tunable and temperature-dependent graphene–MoS2 contacts.

    a, Output curves (IdsVds) of the hBN-encapsulated 4L MoS2 device with graphene electrodes at different temperatures. Backgate voltage Vbg was maintained at 80 V with a carrier density of 6.85 × 1012 cm−2 in MoS2. The linearity of the output curves confirms that the graphene–MoS2 contact is ohmic at all temperatures. b, Resistivity ρ of 4L MoS2 (log scale) as a function of Vbg at different temperatures. The resistivity decreases on cooling, showing metallic behaviour, reaching ∼130 Ω at 12 K. The colour legend is the same as in a (from 300 K to 12 K). c, Contact resistance RC of the same device (log scale) as a function of Vbg at different temperatures. The colour legend is the same as in a (but from 250 K to 12 K). Inset: RC as a function of temperature at different Vbg. At high Vbg the contact resistance decreases when decreasing the temperature.

  3. Temperature, carrier density dependence of Hall mobility and scattering mechanism.
    Figure 3: Temperature, carrier density dependence of Hall mobility and scattering mechanism.

    a, Hall mobility of hBN-encapsulated MoS2 devices (with different numbers of layers of MoS2) as a function of temperature. To maintain ohmic contact, a finite Vbg was applied. The measured carrier densities obtained from Hall measurements for each device are listed in Supplementary Table 1. The solid fitting lines are drawn by the model described in the main text. All fitting parameters are listed in Supplementary Table 1. As a visual guide, the dashed line shows the power law μph ∼ Tγ, and fitted values of γ for each device are listed in the inset table. b, Impurity-limited mobility (μimp) as a function of the MoS2 carrier density. For comparison, previously reported values from MoS2 on SiO2 substrates (refs 8,46) are plotted. ce, The solid lines show the theoretically calculated long-range (LR) impurity-limited mobility (c), short-range (SR) impurity-limited mobility (d) and mobility including both LR and SR based on Matthiessen's rule, 1/μ = 1/μLR + 1/μSR, as a function of carrier density for 1L to 6L MoS2 (e). Experimental data from 1L and 6L MoS2 are shown as circles (ce).

  4. Observation of Shubnikov–de Haas oscillations in an hBN-encapsulated MoS2 device.
    Figure 4: Observation of Shubnikov–de Haas oscillations in an hBN-encapsulated MoS2 device.

    a, Longitudinal resistance Rxx (red curve) and Hall resistance Rxy (blue curve) of an hBN-encapsulated CVD 1L MoS2 device as a function of magnetic field B measured at 0.3 K and with a carrier density of 9.7 × 1012 cm−2. Inset: Oscillation amplitude (black curve) as a function of 1/B after subtraction of the magnetoresistance background. The quantum scattering time extracted from the fitted Dingle plot (red dashed line) is 176 fs. b, Rxx (red curve) and Rxy (blue curve) of the hBN-encapsulated 4L MoS2 device as a function of B. Hall measurements were conducted at 0.3 K and at a carrier density of 4.9 × 1012 cm−2. c, Rxx (red curve) and Rxy (blue curve) of an hBN-encapsulated 6L MoS2 device as a function of B. Hall measurements were conducted at 3 K and with a carrier density of 5.3 × 1012 cm−2.

References

  1. Radisavljevic, B., Radenovic, A., Brivio, J., Giacometti, V. & Kis, A. Single-layer MoS2 transistors. Nature Nanotech. 6, 147150 (2011).
  2. Lee, G. H. et al. Flexible and transparent MoS2 field-effect transistors on hexagonal boron nitride–graphene heterostructures. ACS Nano 7, 79317936 (2013).
  3. Mak, K., Lee, C., Hone, J., Shan, J. & Heinz, T. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).
  4. Lee, C. H. et al. Atomically thin p–n junctions with van der Waals heterointerfaces. Nature Nanotech. 9, 676681 (2014).
  5. Lee, C. et al. Anomalous lattice vibrations of single- and few-layer MoS2. ACS Nano 4, 26952700 (2010).
  6. Kim, S. et al. High-mobility and low-power thin-film transistors based on multilayer MoS2 crystals. Nature Commun. 3, 1011 (2012).
  7. Das, S., Chen, H-Y., Penumatcha, A. & Appenzeller, J. High performance multilayer MoS2 with scandium contacts. Nano Lett. 13, 100105 (2013).
  8. Baugher, B., Churchill, H., Yang, Y. & Jarillo-Herrero, P. Intrinsic electronic transport properties of high-quality monolayer and bilayer MoS2. Nano Lett. 13, 42124216 (2013).
  9. Radisavljevic, B. & Kis, A. Mobility engineering and a metal–insulator transition in monolayer MoS2. Nature Mater. 12, 815820 (2013).
  10. Xiao, D., Liu, G-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).
  11. Mak, K., McGill, K., Park, J. & McEuen, P. Valleytronics. The valley Hall effect in MoS2 transistors. Science 344, 14891492 (2014).
  12. Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nature Nanotech. 7, 490493 (2012).
  13. Jiang, T. et al. Valley and band structure engineering of folded MoS2 bilayers. Nature Nanotech. 9, 825829 (2014).
  14. Mak, K., He, K., Shan, J. & Heinz, T. Control of valley polarization in monolayer MoS2 by optical helicity. Nature Nanotech. 7, 494498 (2012).
  15. Bao, W., Cai, X., Kim, D., Sridhara, K. & Fuhrer, M. High mobility ambipolar MoS2 field-effect transistors: substrate and dielectric effects. Appl. Phys. Lett. 102, 042104 (2013).
  16. Choi, M., Lee, G. H., Yu, Y., Lee, D. & Lee, S. Controlled charge trapping by molybdenum disulphide and graphene in ultrathin heterostructured memory devices. Nature Commun. 4, 1642 (2013).
  17. Wang, H. et al. Integrated circuits based on bilayer MoS2 transistors. Nano Lett. 12, 46744680 (2012).
  18. Yu, L. et al. Graphene/MoS2 hybrid technology for large-scale two-dimensional electronics. Nano Lett. 14, 30553063 (2014).
  19. Sundaram, R., Engel, M., Lombardo, A. & Krupke, R. Electroluminescence in single layer MoS2. Nano Lett. 13, 14161421 (2013).
  20. Britnell, L. et al. Strong light–matter interactions in heterostructures of atomically thin films. Science 340, 13111314 (2013).
  21. Yoon, J. et al. Highly flexible and transparent multilayer MoS2 transistors with graphene electrodes. Small 9, 32953300 (2013).
  22. Qiu, H. et al. Electrical characterization of back-gated bi-layer MoS2 field-effect transistors and the effect of ambient on their performances. Appl. Phys. Lett. 100, 123104 (2012).
  23. Kaasbjerg, K., Thygesen, K. & Jacobsen, K. Phonon-limited mobility in n-type single-layer MoS2 from first principles. Phys. Rev. B 85, 115317 (2012).
  24. Ma, N. & Jena, D. Charge scattering and mobility in atomically thin semiconductors. Phys. Rev. X 4, 011043 (2014).
  25. Li, X. et al. Intrinsic electrical transport properties of monolayer silicene and MoS2 from first principles. Phys. Rev. B 87, 115418 (2013).
  26. Novoselov, K. et al. Two-dimensional atomic crystals. Proc. Natl Acad. Sci. USA 102, 1045110453 (2005).
  27. Kappera, R., Voiry, D., Yalcin, S. E., Jen, W. & Acerce, M. Metallic 1T phase source/drain electrodes for field effect transistors from chemical vapor deposited MoS2. Appl. Phys. Lett. 2, 092516 (2014).
  28. Guo, Y. et al. Study on the resistance distribution at the contact between molybdenum disulfide and metals. ACS Nano 8, 77717779 (2014).
  29. Kappera, R. et al. Phase-engineered low-resistance contacts for ultrathin MoS2 transistors. Nature Mater. 13, 11281134 (2014).
  30. Schmidt, H. et al. Transport properties of monolayer MoS2 grown by chemical vapor deposition. Nano Lett. 14, 19091913 (2014).
  31. Yu, Z. et al. Towards intrinsic charge transport in monolayer molybdenum disulfide by defect and interface engineering. Nature Commun. 5, 5290 (2014).
  32. Zhu, W. et al. Electronic transport and device prospects of monolayer molybdenum disulphide grown by chemical vapour deposition. Nature Commun. 5, 3078 (2014).
  33. Qiu, H. et al. Hopping transport through defect-induced localized states in molybdenum disulphide. Nature Commun. 4, 2642 (2013).
  34. Wang, L. et al. One-dimensional electrical contact to a two-dimensional material. Science 342, 614617 (2013).
  35. Roy, T. et al. Field-effect transistors built from all two-dimensional material components. ACS Nano 8, 62566264 (2014).
  36. Haigh, S., Gholinia, A., Jalil, R., Romani, S. & Britnell, L. Cross-sectional imaging of individual layers and buried interfaces of graphene-based heterostructures and superlattices. Nature Mater. 11, 764767 (2012).
  37. Van der Zande, A. M. et al. Grains and grain boundaries in highly crystalline monolayer molybdenum disulphide. Nature Mater. 12, 554561 (2013).
  38. Du, Y., Yang, L., Liu, H. & Ye, P. Contact research strategy for emerging molybdenum disulfide and other two-dimensional field-effect transistors. APL Mater. 2, 092510 (2014).
  39. Das, S. & Appenzeller, J. Where does the current flow in two-dimensional layered systems? Nano Lett. 13, 33963402 (2013).
  40. Liu, H., Neal, A. T. & Ye, P. D. Channel length scaling of MoS2 MOSFETs. ACS Nano 6, 85638569 (2012).
  41. Liu, H. et al. Switching mechanism in single-layer molybdenum disulfide transistors: an insight into current flow across Schottky barriers. ACS Nano 8, 10311038 (2013).
  42. Fivaz, R. & Mooser, E. Mobility of charge carriers in semiconducting layer structures. Phys. Rev. 163, 743755 (1967).
  43. Chen, J-H., Jang, C., Xiao, S., Ishigami, M. & Fuhrer, M. S. Intrinsic and extrinsic performance limits of graphene devices on SiO2. Nature Nanotech. 3, 206209 (2008).
  44. Ando, T., Fowler, A. B. & Stern, F. Electronic properties of two-dimensional systems. Rev. Mod. Phys. 54, 437672 (1982).
  45. Sarma, D., Adam, S., Hwang, E. & Rossi, E. Electronic transport in two-dimensional graphene. Rev. Mod. Phys. 83, 407470 (2011).
  46. Neal, A., Liu, H., Gu, J. & Ye, P. Magneto-transport in MoS2: phase coherence, spin–orbit scattering, and the hall factor. ACS Nano 7, 70771082 (2013).
  47. Stern, F. & Howad, W. E. Properties of semiconductor surface inversion layers in the electric quantum limit. Phys. Rev. 163, 816835 (1967).
  48. Novoselov, K. et al. Electric field effect in atomically thin carbon films. Science 306, 666669 (2004).
  49. Kretinin, A. V. et al. Electronic properties of graphene encapsulated with different two-dimensional atomic crystals. Nano Lett. 14, 32703276 (2014).
  50. Liu, G-B., Shan, W-Y., Yao, Y., Yao, W. & Xiao, D. Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides. Phys. Rev. B 88, 085433 (2013).

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Author information

  1. These authors contributed equally to this work

    • Xu Cui,
    • Gwan-Hyoung Lee &
    • Young Duck Kim

Affiliations

  1. Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA

    • Xu Cui,
    • Young Duck Kim,
    • Ghidewon Arefe,
    • Daniel A. Chenet,
    • Xian Zhang,
    • Lei Wang &
    • James Hone
  2. Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Republic of Korea

    • Gwan-Hyoung Lee
  3. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA

    • Pinshane Y. Huang &
    • David A. Muller
  4. KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701, Republic of Korea

    • Chul-Ho Lee
  5. Department of Material Science and Engineering, Columbia University, New York, New York 10027, USA

    • Fan Ye
  6. Center for Nanostructured Graphene (CNG), DTU Nanotech, Technical University of Denmark, Ørsteds Plads, 345E, Kgs. Lyngby 2800, Denmark

    • Filippo Pizzocchero &
    • Bjarke S. Jessen
  7. National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan

    • Kenji Watanabe &
    • Takashi Taniguchi
  8. Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA

    • David A. Muller
  9. Department of Electrical & Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA

    • Tony Low
  10. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

    • Philip Kim

Contributions

X.C. and G-H.L. designed the research project and supervised the experiment. X.C., G-H.L., Y.D.K., G.A., C-H.L., F.Y., F.P., B.S.J. and L.W. fabricated the devices. X.C., G-H.L. and Y.D.K. performed device measurements with supervision from P.K. and J.H. X.C., G-H.L., G.A. and X.Z. performed optical spectroscopy and data analysis. D.A.C. grew and prepared the CVD MoS2 sample. T.L. performed theoretical calculations. K.W. and T.T. prepared hBN samples. P.Y.H. and D.A.M. performed TEM analyses. X.C., G-H.L., Y.D.K. and J.H. analysed the data and wrote the manuscript.

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The authors declare no competing financial interests.

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