Advanced beyond-silicon electronic technology requires discoveries of both new channel materials and ultralow-resistance contacts 1,2 . Atomically thin two-dimensional (2D) semiconductors have great potential for realizing high-performance electronic devices 1,3 . However, because of metal-induced gap states (MIGS) 4-7 , energy barriers at the metalsemiconductor interface, which fundamentally lead to high contact resistances and poor current-delivery capabilities, have restrained the advancement of 2D semiconductor transistors to date 2,8,9 . Here, we report a novel ohmic contact technology between semimetallic bismuth and semiconducting monolayer transition metal dichalcogenides (TMDs) where MIGS is sufficiently suppressed and degenerate states in the TMD are spontaneously formed in contact with bismuth. Through this approach, we achieve zero Schottky barrier height, a record-low contact resistance (R C ) of 123 Ω μm, and a recordhigh on-state current density (I ON ) of 1135 µA µm -1 on monolayer MoS 2 . We also demonstrate that excellent ohmic contacts can be formed on various monolayer semiconductors, including MoS 2 , WS 2 , and WSe 2 . Our reported R C values are a significant improvement for 2D semiconductors, and approaching the quantum limit. This technology unveils the full potential of high-performance monolayer transistors that are on par with the state-of-the-art 3D semiconductors, enabling further device down-scaling and extending Moore's Law.The electrical contact resistance at a metal-semiconductor (M-S) interface has been an increasingly critical, yet unsolved issue for the semiconductor industry, hindering the ultimate

The performance and reliability of large-area graphene grown by chemical vapor deposition are often limited by the presence of wrinkles and the transfer-process-induced polymer residue. Here, we report a transfer approach using paraffin as a support layer, whose thermal properties, low chemical reactivity and non-covalent affinity to graphene enable transfer of wrinkle-reduced and clean large-area graphene. The paraffin-transferred graphene has smooth morphology and high electrical reliability with uniform sheet resistance with ~1% deviation over a centimeter-scale area. Electronic devices fabricated on such smooth graphene exhibit electrical performance approaching that of intrinsic graphene with small Dirac points and high carrier mobility (hole mobility = 14,215 cm2 V−1 s−1; electron mobility = 7438 cm2 V−1 s−1), without the need of further annealing treatment. The paraffin-enabled transfer process could open realms for the development of high-performance ubiquitous electronics based on large-area two-dimensional materials.

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The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters.ABSTRACT: Lateral heterostructures with planar integrity form the basis of two-dimensional (2D) electronics and optoelectronics. Here we report that, through a twostep chemical vapor deposition (CVD) process, highquality lateral heterostructures can be constructed between metallic and semiconducting transition metal disulfide (TMD) layers. Instead of edge epitaxy, polycrystalline monolayer MoS 2 in such junctions was revealed to nucleate from the vertices of multilayered VS 2 crystals, creating one-dimensional junctions with ultralow contact resistance (0.5 kΩ·μm). This lateral contact contributes to 6-fold improved field-effect mobility for monolayer MoS 2 , compared to the conventional on-top nickel contacts. The all-CVD strategy presented here hence opens up a new avenue for all-2D-based synthetic electronics. See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. Corresponding SEM images. Inset in panel f is the zoomed-in SEM image of a lateral VS 2 −MoS 2 interface (scale bar 2 μm). (g, h) Raman and PL spectra on the central VS 2 region and the surrounding MoS 2 region (blue and red curves, respectively) for the MoS 2 −VS 2 heterostructures. (i) Schematic illustration of MoS 2 growth on presynthesized multilayered VS 2 .

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