Towards high-performance p-type two-dimensional field effect transistors: contact engineering, scaling, and doping

Abstract N-type field effect transistors (FETs) based on two-dimensional (2D) transition metal dichalcogenides (TMDs) like MoS 2 and WS 2 have come closer to meeting the requirements set forth in International Roadmap for Devices and Systems (IRDS). However, p -type 2D FETs are dramatically lagging behind in meeting performance standards. Here, we adopt a three-pronged approach that includes contact engineering, channel length ( L ch ) scaling, and monolayer doping to achieve high-performance p -type FETs based on synthetic WSe 2 . Using electrical measurements backed by atomistic imaging and rigorous analysis, Pd was identified as the favorable contact metal for Wse 2 owing to better epitaxy, larger grain size, and higher compressive strain leading to lower Schottky barrier height. While the ON-state performance of Pd-contacted WSe 2 FETs was improved by ~10× by aggressively scaling L ch from 1 µm down to ~ 20 nm, ultra-scaled FETs were found to be contact limited. To reduce the contact resistance, monolayer tungsten oxyselenide (WO x Se y ) obtained using self-limiting oxidation of bilayer WSe 2 was used as p -type dopant. This led to ~ 5× improvement in the ON-state performance and ~ 9× reduction in the contact resistance. We were able to achieve a median ON-state current as high as ~ 10 µA/µm for ultra-scaled and doped p -type WSe 2 FETs with Pd contacts. We also show the applicability of our monolayer doping strategy to other 2D materials, like MoS 2 , MoTe 2 , and MoSe 2 .