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Advanced beyond-silicon electronic technology requires both channel materials and also ultralow-resistance contacts to be discovered1,2. Atomically thin two-dimensional semiconductors have great potential for realizing high-performance electronic devices1,3. However, owing to metal-induced gap states (MIGS)4–7, energy barriers at the metal–semiconductor interface—which fundamentally lead to high contact resistance and poor current-delivery capability—have constrained the improvement of two-dimensional semiconductor transistors so far2,8,9. Here we report ohmic contact between semimetallic bismuth and semiconducting monolayer transition metal dichalcogenides (TMDs) where the MIGS are 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 contact resistance of 123 ohm micrometres and an on-state current density of 1,135 microamps per micrometre on monolayer MoS2; these two values are, to the best of our knowledge, the lowest and highest yet recorded, respectively. We also demonstrate that excellent ohmic contacts can be formed on various monolayer semiconductors, including MoS2, WS2 and WSe2. Our reported contact resistances are a substantial improvement for two-dimensional semiconductors, and approach the quantum limit. This technology unveils the potential of high-performance monolayer transistors that are on par with state-of-the-art three-dimensional semiconductors, enabling further device downscaling and extending Moore’s law. Electric contacts of semimetallic bismuth on monolayer semiconductors are shown to suppress metal-induced gap states and thus have very low contact resistance and a zero Schottky barrier height.

Proving the device performance and process feasibility is imperative for the realization of two-dimensional (2D) semiconductor electronics. In this work, we have successfully adopted Tin (Sn) as the Ohmic contact metal to monolayer molybdenum disulfide (MoS2) grown by chemical vapor deposition (CVD) and demonstrated superior short channel n-type field effect transistor (nFET) performance reaching an ON-current of $480~\mu \text{A}/\mu \text{m}$ and keeping the OFF-current below 0.1 nA/ $\mu \text{m}$ at $\text{V}_{DS} = 1$ V. These efforts are close to the low power specification of Si transistors in the metrics of International Roadmap for Devices and Systems (IRDS). The performance improvement could be attributed to the re-melting behavior of Sn metal. We suggest that the Sn deposited at lower temperatures could reduce the formation of interfacial defects caused by heat, and high-melting-point capping metal also could assist the re-melting phenomenon of underlying Sn contact layer. These process modifications are helpful to form smooth Sn coverage on MoS2, thereby reducing the contact resistance to 0.84 $\text{k}\Omega \cdot \mu \text{m}$ . This work provides a practical pathway to form low-resistance metal contact on 2D semiconductors for performance improvement.

Two-dimensional (2D) semiconducting monolayers such as transition metal dichalcogenides (TMDs) are promising channel materials to extend Moore's Law in advanced electronics. Synthetic TMD layers from chemical vapor deposition (CVD) are scalable for fabrication but notorious for their high defect densities. Therefore, innovative endeavors on growth reaction to enhance their quality are urgently needed. Here, we report that the hydroxide W species, an extremely pure vapor phase metal precursor form, is very efficient for sulfurization, leading to about one order of magnitude lower defect density compared to those from conventional CVD methods. The field-effect transistor (FET) devices based on the proposed growth reach a peak electron mobility ~200 cm

One-dimensional contact (so-called edge contact) to monolayer 2D materials has been proposed for ultimate transistor scaling but reported on-state currents are much lower than those from top contact devices. Experiments in this work reveal that the fabrication processes for metal MoS2 contact strongly affect the electrical characteristics such as Schottky barrier height. Using in-situ 2D etching and metal deposition, we obtained Fermi-level pinning-free Ni-MoS2 edge contact transistor devices. Moreover, it reaches the highest on-state current among those TMDs edge contact devices reported in literatures and comparable to top-contact ones. First-principles calculation reveals the evolution of local electronic structure from strong metallization at the edge contact "interline" (1D equivalent of "interface") to semiconductor in the channel region. The short length (

Advanced beyond-silicon electronic technology requires both channel materials and also ultralow-resistance contacts to be discovered

We demonstrate the highest nFET current of 390 μA/μ $m$ at VDS = 1 V based on CVD Mos2 mono layers without intentional doping. The transistor exhibits good subthreshold swing of 109 m V/ decade, large $\mathrm{I}_{\mathrm{ON}}/\mathrm{I}_{\mathrm{OFF}}$ ratio of 4 × 10 8 , and nearly zero DIBL. The high on-current achieved in monolayer Mos2 nFET is mainly attributed to the thin EOT ~ 2 nm of HfO x gate oxide, short gate length of 100 nm, and low contact resistance ~ 1.1 kω- μm.

High performance carbon nanotube (CNT) network transistors with on-resistance (R on ) of DDQ ) and have the comparable active power (P ACTIVE ) consumption under the same operation frequency as compared to the operation without the power gating CNT transistors. The fabrication of CNT devices in the BEOL is verified to cause no performance degradation in the underlying FEOL Si CMOS devices. This study has successfully demonstrated heterogeneous integration of advanced Si logic circuits with low-cost and high-mobility CNT transistors in the BEOL fabricated at low, BEOL-compatible temperatures (250 °C).

In this work, graphene-methylammonium lead iodide (MAPbI3) perovskite hybrid phototransistors fabricated by sequential vapor deposition are demonstrated. Ultrahigh responsivity of 1.73 × 107 A W−1 and detectivity of 2 × 1015 Jones are achieved, with extremely high effective quantum efficiencies of about 108% in the visible range (450–700 nm). This excellent performance is attributed to the ultra-flat perovskite films grown by vapor deposition on the graphene sheets. The hybrid structure of graphene covered with uniform perovskite has high exciton separation ability under light exposure, and thus efficiently generates photocurrents. This paper presents photoluminescence (PL) images along with statistical analysis used to study the photo-induced exciton behavior. Both uniform and dramatic PL intensity quenching has been observed over entire measured regions, consistently demonstrating excellent exciton separation in the devices.

We developed a polymer-free (PF) transfer method and examined the optimum annealing temperature and time for the polymer-free graphene to improve the graphene–metal contact. To further tune the work function of graphene to reduce contact resistance, we report solution doping combined with the PF method, and by using P-doped graphene, the contact resistance is markedly reduced to 24 Ω µm, which is an extremely low value in recent research. Photoemission spectroscopy was used to investigate the graphene/Au interface to explain the results of our contact resistance measurements, and the highest FET mobility of these low-contact devices was 14400 cm2 V−1 s−1 for intrinsic graphene in this study.

In this work, we report a simple method for solution-processed organic light emitting devices (OLEDs), where single-layer graphene acts as the anode and the hexa-peri-hexabenzocoronene exfoliating agent (HBC-6ImBr) provides surface modification. In SEM images, the PEDOT:PSS solution fully covered the graphene electrode after coating with HBC-6ImBr. The fabricated solution-processed OLEDs with a single-layer graphene anode showed outstanding brightness at 3182 cd/m2 and current efficiency up to 6 cd/A which is comparable to that of indium tin oxide films, and the OLED device brightness performance increases six times compared to tri-layer graphene treated with UV-Ozone at the same driving voltage. This method can be used in a wide variety of solution-processed organic optoelectronics on surface-modified graphene anodes.

Achieving low contact resistance between graphene and metals is crucial to the further development of high-performance graphene field effect transistors. Increasing the number of conduction modes is the key issue in improving the contact between graphene and metals. This study characterized the work function between graphene and metal contacts using in situ thermal evaporation and ultraviolet photoelectron spectroscopy. Silver produces weak n-type doping and gold produces heavy p-type doping in graphene. The use of a polymer-free transfer method and a double electrode contact structure produced gold contacts with a resistance value of 352.8 Ω µm, which is 2.7 times lower than that obtained using conventional methods. This method also produced silver contacts with a resistance value of 958.6 Ω µm, which represents a 180% improvement over conventional methods.