Two-Dimensional 2H-TaS₂ Contact for Fermi-Level Pinning-Free P-Type WSe₂ Field-Effect Transistors

Two-dimensional (2D) transition metal dichalcogenides (TMDs), represented by WSe₂, have exhibited considerable promise in complementary metal-oxide-semiconductor and optoelectronic device applications due to their tunable bandgap and the prospect of compatibility with conventional silicon-based processes. However, the precise control of p-type transport characteristics in 2D TMDs has been challenging due to the Fermi-level pinning effect at the interface with evaporated metal electrodes, resulting in most TMDs exhibiting a single n-type conductivity and significantly impeding the achievement of p-type and n-type contacts by using homogeneous materials. Here, we present Fermi-level pinning-free WSe₂ field-effect transistors via 2D van der Waals 2H-TaS₂ contacts, establishing an exceptionally clean and atomically flat interface between the WSe₂ semiconductor and the 2H-TaS₂ metal. Such contacts enable the Schottky barrier height to closely match the work function of the 2H-TaS₂ electrodes, as evidenced by a pinning factor of 0.95, conforming to the Schottky-Mott rule. The integration of TaS2 as contacts in WSe₂ field-effect transistors results in p-type polarity, predominantly driven by hole transport, without the need for external doping, demonstrating a hole mobility of 23.74 cm² V^-1 s^-1 and an on/off current ratio of 1 × 10⁷. Our findings further reveal that the p-type polarity achieved through this interface engineering strategy exhibits robustness, regardless of the thickness of WSe₂, thereby offering a promising application opportunity for next-generation logic electronics utilizing 2D materials.