Fermi-level depinning achieved by high-work-function Au1-xSex alloy contacts for high-performance p-type WSe2 transistors

P-type contact in two-dimensional (2D) transition metal dichalcogenides (TMDs) faces more severe Fermi-level pinning (FLP) than their n-type counterparts due to the damage caused by high-work-function metal deposition. Here, we demonstrate a simple molecular beam epitaxy (MBE) contact strategy using a high-work-function (5.8 eV) Au1-xSex alloy to achieve Fermi-level depinning in monolayer WSe2 p-type transistors. The Au1-xSex alloy mitigates both defect-induced gap states (DIGS) and metal-induced gap states (MIGS) by gentle pre-deposition of selenium (Se) followed by the conversion to Au1-xSex alloy by deposition of Au at low-temperature, forming a van der Waals (vdW) interface between Au1-xSex and monolayer WSe2. Moreover, it imposes hole doping to the contacted monolayer WSe2, reducing the Schottky barrier height and enabling favorable p-type device performance. Combined experimental and theoretical analyses confirm quasi-ohmic contact behavior, yielding a contact resistance of 492 Ω·µm, an on-current of 385 µA/µm, and an on/off ratio greater than 108 for a p-FET with a 100 nm channel length. This work establishes Au1-xSex alloy contacts as a scalable solution for high-performance p-type 2D electronics. The fabrication of p-type contacts for 2D semiconductors remains an important challenge towards the industrialization of 2D electronics. Here, the authors report a low-temperature molecular beam epitaxy contact strategy using a high-work-function Au1-xSex alloy to achieve Fermi-level depinning in monolayer WSe2 and realize high-performance 2D p-type transistors.