Quantification of the sheet resistance between two-dimensional semiconductors and semi-metals by a contact-end-resistance method

Semi-metal presents an extremely promising method for establishing an ohmic contact with near-quantum-limit contact resistance (Rc) in two-dimensional material (2DM) transistors. However, the physical mechanisms occurring at the interface between 2DMs and semi-metals, which contribute to Rc reduction, are not yet well understood. Leveraging on the contact-end-resistance model applied to the transfer length method structure, we conduct a quantitative and comprehensive characterization of the molybdenum disulfide (MoS2) contact interface with various contact metals. The sheet resistance beneath the semi-metal contact (Rsk) is found to be two orders of magnitude smaller than the sheet resistance of the channel (Rsh), validating the electron doping effect of semi-metals on MoS2 contact areas. Among semi-metals studied, including bismuth (Bi), antimony (Sb), and their alloy, Bi results in the highest electron doping density and the lowest Rsk of 764 Ω/◻, leading to an improvement in Rc down to 526 Ω μm. This work provides a perspective toward the physical mechanisms beneath the semi-metal induced Rc reduction, setting a strong foundation for devising strategies to lower the Rc in 2D-based devices.