High-performance multilayer WSe2 p-type field effect transistors with Pd contacts for circuit applications

WSe2 is thought to be one of the best emerging p-type transition metal dichalcogenide (TMD) materials for potential low-power complementary metal oxide semiconductor (CMOS) circuit applications. However, the contact barrier and the interface quality hinder the performance of p-type field effect transistors (FETs) with WSe2 films. In this work, metals with different work functions—Pd, Pt, and Ag—were systematically investigated as contacts for WSe2 to decrease the contact resistances at source/drain electrodes and potentially improve transistor performance. Optimized p-type multilayer WSe2 FETs with Pd contacts were successfully fabricated, and excellent electrical characteristics were obtained: a hole mobility of 36 cm2V−1 s−1; a high on/off ratio, over 106; and a record low sub-threshold swing, SS = 95 mV/dec, which may be attributed to the small Schottky barrier height of 295 meV between Pd and WSe2, and strong Fermi-level pinning near the top of the valence band at the interface. Finally, a full-functional CMOS inverter was also demonstrated, consisting of a p-type WSe2 FET together with a normal n-type MoS2 FET. This confirmed the potential of TMD FETs in future low-power CMOS digital circuit applications.