Abstract
The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance1,2. Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited3,4,5,6,7,8,9,10,11,12. In particular, the contact resistance has not surpassed that of covalently bonded metal–semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues3,7. Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony (\(01\bar{1}2\)) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 108 and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal–oxide–semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate low variability in contact resistance, threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance13. The excellent electrical performance, stability and variability make antimony (\(01\bar{1}2\)) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon.
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Acknowledgements
This work was supported by the National Key R&D Program of China (grant numbers 2021YFA0715600, 2022YFB4400100, 2021YFA1500700, 2017YFA0204800 and 2021YFA1202903); the Leading-edge Technology Program of Jiangsu Natural Science Foundation (grant numbers BK20202005 and BK20222007); the National Natural Science Foundation of China (grant numbers T2221003, 61927808, 61734003, 61851401, 91964202, 61861166001, 51861145202, 22033002, 62204113, 62204124, 22222302, 11774153 and 11874199); the China Postdoctoral Science Foundation (grant numbers 2022M711549 and 2022T15036); Jiangsu Funding Program for Excellent Postdoctoral Talent (grant number 20220ZB63); the Natural Science Foundation of Jiangsu Province (grant number BK20220773); the Strategic Priority Research Program of Chinese Academy of Sciences (grant number XDB30000000); the Key Laboratory of Advanced Photonic and Electronic Materials, Collaborative Innovation Center of Solid-State Lighting and Energy-Saving Electronics, and the Fundamental Research Funds for the Central Universities, China.
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X.W. and Y.S. conceived and supervised the project. W.L., Z.Y., H.N., D.F., Y.X., X.T. and H.Q. contributed to the transistor fabrication, measurements and data analysis. X.G., L.M. and J.W. performed the DFT calculations. W.S. and Y.N. performed the XRD and data analysis. Ç.K. and E.P. performed the thermal analysis. S.G., P.W., T.X. and L.S. performed the TEM and data analysis. Wenfeng Wang, L.L. and T.L. performed the chemical-vapour-deposition growth of MoS2. J. Li and X.D. performed the chemical-vapour-deposition growth of WSe2. Wenhui Wang, J. Lu and Z.N. performed the Raman characterization and data analysis. W.L., Z.Y., L.M., J.W. and X.W. co-wrote the manuscript with input from other authors. All authors contributed to discussions.
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Extended data figures and tables
Extended Data Fig. 1 Electronic properties of Sb/Bi-MoS2 contacts.
a, b, The simulated band diagram and local device density of states (LDDOS) of the monolayer MoS2 with double-end Sb (\(01\bar{1}2\)) electrodes: without electron doping (zero gate bias) (a) and with 1.5 electron doping (similar to high gate bias) (b). The Fermi level is set to zero.c, d, Electrostatic potential profiles of Sb (\(01\bar{1}2\))-MoS2 (c) and Sb (0001)-MoS2 (d) contacts along the vertical direction, respectively. e, f, Atomic-projected electronic band structures of Bi (\(01\bar{1}2\))-MoS2 (e) and Bi (0001)-MoS2 (f) contacts. g, The interfacial vdW interaction between MoS2 and Bi (\(01\bar{1}2\))/Bi (0001). h, The charge transfer from Bi (0112)/Bi (0001) to MoS2 by Bader charge analysis.
Extended Data Fig. 2 The atomic-projected electronic band structures and the charge density near EF of TMDs-Sb contact.
a–f, Left panels, atomic-projected electronic band structures (left panel) of MoSe2-Sb (\(01\bar{1}2\)) (a), WS2-Sb (\(01\bar{1}2\)) (c), WSe2- Sb (\(01\bar{1}2\)) (e), MoSe2-Sb (0001) (b), WS2-Sb (0001) (d) and WSe2-Sb (0001) (f) contacts. Right panels, charge density near EF of MoSe2-Sb (\(01\bar{1}2\)) (a), WS2-Sb (\(01\bar{1}2\)) (c), WSe2- Sb (\(01\bar{1}2\)) (e), MoSe2-Sb (0001) (b), WS2-Sb (0001) (d) and WSe2-Sb (0001) (f) contacts. The corresponding isosurface level of the charge density near EF (right panel) are 1.3×10−4 e/Bohr3 for MoSe2-Sb contact (a, b), 8×10−5 e/Bohr3 for WS2-Sb (c, d) and WSe2-Sb (e, f) contact, respectively.
Extended Data Fig. 3 Optical, chemical and structural characterization of Sb-MoS2 interface.
a, The Low-temperature (6 k) PL spectra of. After depositing Sb film, the main exciton peak did not show widening, and no obvious defect-related emissions were observed. This proved that the deposition of Sb was friendly to 2D materials without creating defects. The sharp peak at 1.79 eV was the photoluminescence signal from the sapphire substrate. b, High-resolution XPS spectra of 2 nm Sb deposited on monolayer MoS2/sapphire, where the absence of Sb–S bond signal from Sb2S3 indicates no chemical bond formation between Sb and MoS2. c, Cross-section HAADF-STEM image of Sb (0001)-MoS2 contact. Scale bar, 1 nm. d, Zoom-in atomic-resolution image from c. The interplane distance was 0.379 nm. Scale bar, 1 nm.
Extended Data Fig. 4 Schottky barrier extraction and small footprint MoS2 FETs.
a, The temperature-dependent Ids-Vgs transfer curves of Sb (\(01\bar{1}2\))-MoS2 FET. Vds = 0.1V. b, The Arrhenius plot at various gate bias of the same device in a. c, Gate voltage dependence of the barrier height. The deviation from the linear trend (red solid line) defines the flat band voltage and shows negative Schottky barrier height. Inset shows the linear output curves of the same FET at a low temperature of 50 K with excellent linearity. d, The temperature-dependent Ids-Vgs transfer curves of Sb (0001)-MoS2 FET. Vds = 0.1V. e, The Arrhenius plot at various gate bias of the same device in d. f, Gate voltage dependence of the barrier height. The deviation from the linear trend (red solid line) defines the flat band voltage and shows positive Schottky barrier height. g, Transfer curves of two MoS2 FETs with the same Lc = 60 nm but with contact length (Lcontact) of 60 nm and 1 μm. Vds = 0.1 V. Inset is the false-colour SEM image of the device. Scale bar, 200 nm. h–i, Output curves of the MoS2 FET with contact length of 1 μm (h) and 60 nm (i), respectively.
Extended Data Fig. 5 Extraction of low Rc from TLM devices with Sb \((01\bar{1}2)\)-MoS2.
a–e, The left is the transfer curves of TLM devices. Vds = 0.1V, and the right is the plot of Rtot versus Lc from the left devices, from which the 2Rc can be extracted from the y-axis intercepts. Symbols are experimental data and lines are linear fits at the right figure. It is noted that TLM in e contain 9 devices with Lc equal to 60 nm, 80 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1 μm and 1.5 μm. Ultralow Rc extraction from the TLM devices with sub-100-nm Lc devices further enhances confidence in ohmic contact of Sb (\(01\bar{1}2\)) -MoS2 contact. f, g, Histogram of σ (a) and R2 (b) from the linear fitting process of TLM method corresponding to the results of Sb (\(01\bar{1}2\))-MoS2 contact (115 TLMs) in Fig. 3d and e.
Extended Data Fig. 6 Comparison of MoS2 FETs with Sb (0001) and Sb \((01\bar{1}2)\) contacts.
a, Transfer characteristics of 145 MoS2 FETs (65 with Sb (0001) contact (black lines) and 80 with Sb (\(01\bar{1}2\)) contact (red lines)). Lc = 100 nm, Vds = 1V. b, The boxplot with Gaussian fitting of Ion at the same carrier density. The mean (square symbols), lower quartile (Q1, 25%), median (Q2, 50%), upper quartile (Q3, 75%), interquartile range (25%-75%) and maximum/minimum (cross symbols) are presented. The Ion of Sb (\(01\bar{1}2\)) contact is significantly improved compared with Sb (0001) contact due to the improvement of Rc.
Extended Data Fig. 7 Stability of Sb \((01\bar{1}2)\)-MoS2 contact.
a, Thermal stability of Ion for Sb and Bi contact measured at different time in 125 °C nitrogen environment. b, Transfer characteristics of a typical Sb-contact MoS2 FET measured Lc = 100 nm, Vds = 1V. c, d, The output characteristics of the same device in the initial state (c) and after 24 h (d). From bottom to up, Vgs = −2 V to 10 V with 2 V step. e, Transfer characteristics of a typical Bi-contact MoS2 FET measured at different time in 125 °C nitrogen environments. Lc = 100 nm, Vds = 1V. f, g, The output characteristics of the same device at 125 °C in the initial state (f) and after 24 h (g). From bottom to up, Vgs = −2 V to 10 V with 2 V step.
Extended Data Fig. 8 Short-channel MoS2 FETs with Sb \((01\bar{1}2)\)-contact.
a, Transfer characteristics of a MoS2 FET with Lc = 40 nm under Vds = 0.2 V and 1 V. Inset shows the corresponding SEM image. Scale bar, 500 nm. b, The output characteristics of the same devices in a. From bottom to up, Vgs = −2 V to 10 V with 2 V step. The solid and dotted lines are the results of the DC and pulse I-V measurements, respectively. c, Transfer characteristics of a MoS2 FET with Lc = 20 nm under Vds = 0.2 V and 1 V. Inset shows the corresponding SEM image. Scale bar, 500 nm. d, The output characteristics of the same devices in c. From bottom to up, Vgs = −2 V to 10 V with 2 V step. The solid and dotted lines are the results of the DC and pulse I-V measurements, respectively.
Extended Data Fig. 9 The steady-state temperature distribution of the short-channel MoS2 FET in Fig. 4b, c by finite-element method simulation.
a, Steady-state distribution of temperature rises across the centre cross-section of the device along the current direction, for Vds = 1 V and Ids = 1.23 mA/μm. Only half of the geometry is shown, x = 0 (halfway between the drain and source contacts) serving as the symmetry plane. A contact resistance of 100 Ω·μm is assumed in order to determine the fraction of the power dissipated at the contacts. b, The temperature rise above ambient in MoS2 (black) and the contact just above MoS2 (red) plotted as a function of position along the direction of current flow.
Extended Data Fig. 10 Ambipolar monolayer WSe2 FETs with Sb \((01\bar{1}2)\) contact.
a, Transfer curves of n-type TLM devices with Sb (\(01\bar{1}2\)) contact. Vds = 0.1 V. b, Plot of Rtot versus Lc from n-type TLM devices with Sb (\(01\bar{1}2\)) contact (red symbols) and Ti contact (blue symbols), from which the 2Rc can be extracted from the y-axis intercepts. Symbols are experimental data and lines are linear fits at b. c, d, Performance comparison of n-type monolayer WSe2 FETs with Sb (\(01\bar{1}2\)) contact (red) and Ti contact (blue). Lc = 100 nm. c shows the transfer curves at Vds = 0.1 V. d shows the output curves at Vgs from 0 V to 40 V with 4 V step with the same devices at c. e, Transfer curves of p-type TLM devices with Sb (\(01\bar{1}2\)) contact. Vds = −0.1 V. f, Plot of Rtot versus Lc from p-type TLM devices with Sb (\(01\bar{1}2\)) contact (red symbols) and Ti contact (blue symbols), from which the 2Rc can be extracted from the y-axis intercepts. Symbols are experimental data and lines are linear fits at f. g, h, Performance comparison of p-type monolayer WSe2 FETs with Sb (\(01\bar{1}2\)) contact (red) and Ti contact (blue). Lc = 100 nm. g shows the transfer curves. Vds = −0.1 V. h shows the output curves at Vgs from 0 V to −50 V with −5 V step with the same devices at g.
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Li, W., Gong, X., Yu, Z. et al. Approaching the quantum limit in two-dimensional semiconductor contacts. Nature 613, 274–279 (2023). https://doi.org/10.1038/s41586-022-05431-4
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DOI: https://doi.org/10.1038/s41586-022-05431-4
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