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 (R-c) in two-dimensional material (2DM) transistors. However, the physical mechanisms occurring at the interface between 2DMs and semi-metals, which contribute to R-c 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 (R-sk) is found to be two orders of magnitude smaller than the sheet resistance of the channel (R-sh), 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 R-sk of 764 Omega/square, leading to an improvement in R-c down to 526 Omega mu m. This work provides a perspective toward the physical mechanisms beneath the semi-metal induced R-c reduction, setting a strong foundation for devising strategies to lower the R-c in 2D-based devices.