Deciphering the Critical Role of Doping on P-Type Ohmic Contact Formation in MoS₂ FETs

The formation of p-type Ohmic contacts in 2D material-based field-effect transistors (FETs) remain challenging due to the Schottky barriers induced by Fermi-level pinning effect. This study investigates the impact of p-type doping on MoS2 FET contacts using a hybrid approach combining TCAD device simulations with first-principles calculations. The device transfer curves underscore that p-type conduction with a steep subthreshold slope and high on-current requires a small Schottky barrier for hole injection. The barrier thinning effect, modulated by doping and gate bias, primarily adjusts the threshold voltage. While in multilayer MoS2 FETs with lower doping concentrations, it becomes the dominant mechanism facilitating current transport via tunneling. In contrast, in few-layer MoS2 FETs, the barrier-lowering effect is essential to regulate device polarity and current conduction. Atomistic simulations reveal that p-type doping reduces the Schottky barrier height by inducing an interfacial dipole via dopant ionization. This dipole generates a potential shift that governed by the Poisson equation and aligns the metal Fermi level to the MoS2 valence band, thereby lowering the barrier. These findings differentiate the distinct roles of doping-induced barrier lowering and barrier thinning in controlling MoS2 FET polarity, underscoring heavy doping as an effective strategy for achieving barrier-free Ohmic contacts in p-type MoS2 FETs.