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Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors


As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal–semiconductor interface at the source and drain electrodes increases, dominating the performance of devices1,2,3. Two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS2) have been demonstrated to be excellent semiconductors for ultrathin field-effect transistors4,5. However, unusually high contact resistance has been observed across the interface between the metal and the 2D transition-metal dichalcogenide3,5,6,7,8,9. Recent studies have shown that van der Waals contacts formed by transferred graphene10,11 and metals12 on few-layered transition-metal dichalcogenides produce good contact properties. However, van der Waals contacts between a three-dimensional metal and a monolayer 2D transition-metal dichalcogenide have yet to be demonstrated. Here we report the realization of ultraclean van der Waals contacts between 10-nanometre-thick indium metal capped with 100-nanometre-thick gold electrodes and monolayer MoS2. Using scanning transmission electron microscopy imaging, we show that the indium and gold layers form a solid solution after annealing at 200 degrees Celsius and that the interface between the gold-capped indium and the MoS2 is atomically sharp with no detectable chemical interaction between the metal and the 2D transition-metal dichalcogenide, suggesting van-der-Waals-type bonding between the gold-capped indium and monolayer MoS2. The contact resistance of the indium/gold electrodes is 3,000 ± 300 ohm micrometres for monolayer MoS2 and 800 ± 200 ohm micrometres for few-layered MoS2. These values are among the lowest observed for three-dimensional metal electrodes evaporated onto MoS2, enabling high-performance field-effect transistors with a mobility of 167 ± 20 square centimetres per volt per second. We also demonstrate a low contact resistance of 220 ± 50 ohm micrometres on ultrathin niobium disulfide (NbS2) and near-ideal band offsets, indicative of defect-free interfaces, in tungsten disulfide (WS2) and tungsten diselenide (WSe2) contacted with indium alloy. Our work provides a simple method of making ultraclean van der Waals contacts using standard laboratory technology on monolayer 2D semiconductors.

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Fig. 1: Atomic resolution imaging and chemical analyses of In/Au-MoS2 interface.
Fig. 2: Contact resistance and device properties of In/Au electrodes on monolayer MoS2.
Fig. 3: Contact properties of In/Au electrodes on 2D NbS2 and WS2.
Fig. 4: In alloy contacts on ultrathin WSe2.

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Data availability

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


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M.C., Y.W. and J.Y. acknowledge support from the US National Science Foundation (Civil, Mechanical and Manufacturing Innovation 1727531, Electrical Communications and Cyber Systems 1608389) and Air Force Office of Scientific Research Award FA9550-16-1-0289. M.C. and X.S. acknowledge support from the Shenzhen Peacock Plan (grant number KQTD2016053112042971). J.M. acknowledges support from the Rutgers RiSE summer internship programme. H.Y.J. acknowledges support from the Creative Materials Discovery Program through the National Research Foundation of Korea (NRF-2016M3D1A1900035). R.J.W. and A.M. acknowledge partial support from US NSF MRSEC Award DMR-1420013 for Characterization Facility at the University of Minnesota.

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Authors and Affiliations



M.C. conceived the idea, supervised the project and wrote the paper. Y.W. prepared and measured all devices. J.C.K. and H.Y.J. performed sample fabrication using focused ion beam and STEM on monolayer MoS2, NbS2 and WSe2. R.J.W. and A.M. performed STEM on few-layered MoS2. J.M. assisted in making contacts and measured work functions. X.S. synthesized 2D materials by CVD. J.Y. performed XPS and analysed data. F.Z. assisted in device fabrication and In deposition. All authors read the paper and agreed on its content.

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Correspondence to Manish Chhowalla.

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Extended data figures and tables

Extended Data Figure 1 Atomic resolution imaging and chemical analyses of the In/Au–MoS2 interface.

a, Broader view STEM images of three-dimensional metal on 2D semiconductor. Cross-sectional STEM image of interface between In/Au and monolayer MoS2. Scale bar, 5 nm. b, Cross-sectional STEM image of interface between In/Au and multi-layered MoS2. Scale bar, 2 nm. c, Bright-field STEM of In/Au contact to monolayer MoS2. The intensity profile shows that the distance between the In/Au atoms of the electrode metal to sulfur atoms in the first layer is 2.4 Å. d, ADF-STEM and intensity profile of In/Au contact to multilayer MoS2. The intensity profile shows that the MoS2 interlayer distance is 6.2 Å, which is consistent with the literature34. The distance between the sulfur atoms in adjacent layers is 2.7 Å and the distance between the In/Au atoms and sulfur atoms in the first layer is also 2.7 Å for multi-layered samples, indicating a van der Waals contact at the interface. e, XPS image of the In/Au–MoS2 interface showing In metal 3d5/2 (443.8 eV) and 3d3/2 (451.4 eV) peaks along with In metal loss features. f, X-ray-induced Auger spectrum showing a pristine In metal peak at 402.9 eV. In2O3 has a clear peak at 400.2 eV, which is absent in our samples. There is no sign of In2S3 (407.3 eV) and In MNN Auger spectra indicate no chemical reaction at the interface35. g, Atomic force microscopy image of CVD-grown monolayer MoS2. h, Photoluminescence of CVD-grown MoS2, with the A exciton peak at 1.84 eV and the B exciton peak at 1.97 eV clearly visible.

Extended Data Figure 2 Contact resistance and device properties of In/Au electrodes on few-layered MoS2.

a, TLM results of In/Au contacts on few-layered MoS2. b, Contact resistance RC versus carrier concentration for In/Au electrodes. Sc, Ti and Au electrodes deposited under ultrahigh vacuum (UHV, 10−9 Torr) are provided for comparison5,17. c, Comparison of contact resistance from the literature and our results for different types of electrode materials17,36,37,38,39,40,41. d, Typical output curve at room temperature shows that the highest current density is 196 µA µm−1. e, Output characteristics at low temperature, with the linearity of the output characteristics indicating the absence of a contact barrier. f, Mobility versus temperature reveals phonon-limited mobility at low temperature and acoustic phonon scattering at high temperature. g, Transfer characteristics with temperature showing the metal–insulator transition. h, Schottky barrier (ΦB) extraction indicating ideal In contacts with MoS2. The inset shows the energy band diagram of MoS2 and In.

Extended Data Figure 3 Output characteristics of WS2.

a, In contacts. b, Ti contacts.

Extended Data Figure 4 Energy-dispersive X-ray spectroscopy mapping of the contact.

a, Low-magnification cross-sectional high-angle annular dark-field (HAADF) STEM image of the MoS2 with In/Au contact. be, Elemental mapping showing the distribution of In, Au, S and O. In and Au overlap over the entire metal layer, suggesting the formation of an alloy. S is observed underneath the In and Au. O is obtained primarily from SiO2 of the substrate. f, Fast Fourier transform (FFT) pattern from metal electrode showing alloying between In and Au. Scale bar, 5 Å. The diffraction pattern is of a face-centred cubic alloy. Pure In has body-centred cubic crystal structure. a:C, amorphous carbon; dep., deposition; Z.A., zone axis.

Extended Data Figure 5

Typical transfer characteristics of the device measured immediately after fabrication and after 70 days.

Extended Data Figure 6 Topographical and scanning Kelvin probe microscopy images.

a, d, Topographical and surface potential results of the Au sample; the work function (WF) extracted is 5.09 eV, similar to the theoretical value. b, e, Topographical and surface potential results of the In/Au sample; the work function extracted is very close to that of the In work function, 4.05 eV. c, f, Topographical and surface potential results of the In/Pd sample; the work function extracted is 4.23 eV, higher than that of In/Au.

Extended Data Table 1 Literature survey of device performance

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Wang, Y., Kim, J.C., Wu, R.J. et al. Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors. Nature 568, 70–74 (2019).

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