A Design Strategy for High-performance p-type Two-dimensional Field Effect Transistors

Abstract Doping plays a critical role in tailoring the characteristics of semiconducting materials and electronic devices. Specifically, in the context of field-effect transistors (FETs), degenerate doping in the silicon channel beneath the source and drain regions has become essential for achieving high-performance n- and p-type devices, as well as significantly reducing contact resistance (R_C). In contrast, two-dimensional (2D) semiconductors have mainly relied on metal work-function engineering to lower R_C. While this approach has proven successful for n-type 2D FETs due to the natural tendency of the metal Fermi level to align near the conduction band edge, it has been challenging to achieve the same for p-type 2D FETs. To address this, we demonstrate that degenerate p-type doping can be accomplished in few-layer (>3) MoSe2 and WSe2 through substitutional doping of transition metal with V, Nb, and Ta. However, this substitutional doping leads to weakened electrostatic gate control, resulting in a poor on/off current ratio in multilayer p-type 2D FETs. Interestingly, at the monolayer limit, the doping effectiveness is significantly reduced due to strong quantum confinement effects, thereby restoring the electrostatic gate control. Based on this observation, we designed a FET structure where the channel is constructed using monolayer 2D material, while the contact regions consist of degenerately doped multilayers, allowing us to achieve both low R_C and high on/off current ratio. This doping and device design strategy is equally applicable for n-type FETs and can also redirect the large-area synthesis approach, emphasizing the production of doped multilayers to advance 2D FET technology.