Monolithic Mixed-Dimensional Contact Engineering for High-Performance Ambipolar Transport in Two-Dimensional WS2 Transistors

Abstract

The development of ambipolar two-dimensional (2D) field-effect transistors (FETs) based on transition metal dichalcogenides is hindered by Fermi-level pinning and the intrinsic trade-offs in using a single-contact geometry for both carrier types. Herein, a monolithic mixed-dimensional contact scheme is presented in which a one-step metallization seamlessly integrates one-dimensional high-work-function (Pd) edge contacts and 2D low-work-function (Ti) surface contacts. This architecture allows the spatial separation of hole and electron injection pathways on a WS2 ambipolar channel, enabling independent contact optimization without a complex doping process. The resulting WS2 FETs exhibit highly symmetric ambipolar characteristics, with on/off ratios exceeding 107, comparable field-effect carrier mobilities of 182.5 (holes) and 159.0 cm2<middle dot>V-1<middle dot>s-1 (electrons), and Schottky barrier heights below 20 meV for both carrier types. Structural and temperature-dependent electrical analyses confirm the high crystallinity of the channel layer, which has a highly symmetrical contact resistance for both hole and electron carriers. Furthermore, the architecture enables the fabrication of complementary logic circuits, as demonstrated via a low-power WS2-based inverter with a robust voltage transfer behavior. This mixed-dimensional contact scheme addresses the fundamental bottleneck in 2D device engineering and offers a scalable complementary metal-oxide-semiconductor-compatible route for ambipolar logic and reconfigurable electronics.