Evolution Diagram of Transistor Scaling. Cross-sectional STEM images demonstrating key technology nodes: the 22-nm FinFET (C.-H. Jan et al., IEDM, pp. 3.1.1–3.1.4, 2012), the 3-nm FinFET (W. Hafez et al., VLSI Symp., pp. 1–2, 2024) and the GAAFET (N. Loubet et al., VLSI Symp., pp. T230–T231, 2017). Credit: Du et al.

In recent years, electronics engineers have been trying to identify semiconducting materials that could substitute for silicon and enable the further advancement of electronic devices. Two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS₂), have proved to be among the most promising solutions, as their thinness and resistance to short-channel effects could yield highly performing and smaller electronics.

To create transistors and other electronic components based on 2D materials, however, engineers need to be able to attach electrical connections to them and reliably form ohmic contacts, which allow electrical current to flow freely through the resulting devices. As devices get smaller, however, they also require smaller contacts that have proved to be very difficult to attach to 2D semiconductors.

Researchers at Nanjing University and other institutes in China recently introduced a new strategy to reliably grow ultra-short and low-resistance semimetallic antimony crystal contacts directly on MoS₂.

Their approach, outlined in a paper published in Nature Electronics, allowed them to create ultra-small and high-performance transistors based on a 2D semiconducting material.

"Scaling 2D semiconductor transistors to and beyond a 1-nanometer node has remained elusive, despite a lot of work and wide anticipation from academia and industry," Xinran Wang, senior author of the paper, told Tech Xplore.

"Previous works on device scaling mostly focused on channel scaling, but it is the contact that really limits device performance. One of the main challenges is large contact resistance Rc at extreme contact length. The Rc scales with contact length Lc as , where the transfer length LT stands for the length scale at which carriers can be injected from metal to semiconductor.

"1 nm node requires that LT is smaller than 20 nm, which is very difficult for van der Waals contacts that are typically in 2D semiconductors."

Ultra-small MoS2 transistor with intimate Sb(011 ̅2) crystal contacts. Credit: Du et al. (Nature Electronics, 2025).

A strategy to deposit antimony contacts on MoS₂

The primary objective of the recent research by Wang and his colleagues was to develop contacts that retain an ultra-low resistance even when they are significantly reduced in size. In addition, they set out to reliably attach these contacts to 2D materials, creating transistors that perform remarkably well while meeting size targets within the field (i.e., 1nm node, with a contacted gate pitch below 40 nm).

The researchers made their contacts out of crystalline semimetallic antimony and directly grew them onto a monolayer MoS₂ film via molecular beam epitaxy (MBE). This is a technique used to grow ultra-thin layers of crystals atom by atom and with high precision onto a desired substrate.

"We used MBE in ultra-high vacuum to deposit crystalline antimony ohmic contacts," explained Weisheng Li, co-first author of the paper.

"The process begins by heating the substrate while depositing antimony atoms at a precisely controlled rate, giving atoms sufficient time to settle into the lowest energy state. This enables antimony atoms to spontaneously arrange into a specific Sb(012) crystal orientation, forming an intimate contact interface with MoS₂."

The MBE-based strategy proposed by the researchers has significant advantages over other widely used thin-film deposition techniques that rely on evaporation. Most notably, it was found to yield high-quality, nearly phase-pure Sb(012) crystals with grain sizes that were greater by two orders of magnitude.

"Due to this high quality, the contact resistance shows little degradation down to 18 nm, while in the electron-beam evaporated Sb contacts start to degrade at 60 nm," said Li. "The extracted LT ~13 nm, which is, to our knowledge, the only 2D semiconductor contact technology that meets the 1nm node target."

Informing the development of 2D material-based electronics

The recent efforts by Wang, Li and their collaborators highlight the potential of MBE for the creation of smaller, high-performance transistors based on 2D semiconductors. Using their proposed film deposition strategy, the researchers realized what could be the smallest high-performance 2D material-based transistor developed to date.

"Previously, people believed that 2D transistors could be useful but there was no experimental demonstration of their performance at such scaled device lengths," said Wang.

"We believe that this work will accelerate the lab-to-fab transition of 2D semiconductors. In 2025, IMEC released its device roadmap and 2D semiconductors are the end-of-map options for transistor scaling. Our work brings this vision closer to reality."

The results achieved by these researchers could open new possibilities for the advancement of electronic devices, enabling their further miniaturization and potential performance gains. Other research groups could soon draw inspiration from this work and devise similar strategies for the fabrication of ultra-small transistors based on 2D materials.

"In the area of 2D transistor technology, much still needs to be done," added Wang. "We now plan to prioritize optimizing the reliability and manufacturability of this contact technology for mass production. Another important problem is p-type contact (with, for example, WSe2), which currently lags behind the n-type counterpart.

"Doping strategies and gate stack also need to be developed with low interface trap density. Design-Technology Co-Optimization (DTCO) will be very important moving forward."

Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.

More information: Mingyi Du et al, Scaled crystalline antimony ohmic contacts for two-dimensional transistors, Nature Electronics (2025). DOI: 10.1038/s41928-025-01500-4

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