Performance of field-effect transistors based on Nb_xW_1-xS₂ monolayers

The Schottky barrier has been detected in many field-effect transistors (FETs) based on transition metal dichalcogenide (TMD) semiconductors and has seriously affected the electronic properties of the devices. In order to decrease the Schottky barrier in WS₂ FETs, novel Nb doping in WS₂ monolayers has been performed and p-FETs based on Nb-doped WS₂ (Nb_xW_1-xS₂) monolayers as the active channel have been fabricated for the first time. The monolayer Nb_0.15W_0.85S₂ p-FET has a drain current of 330 μA μm^-1, an impressive I_ON/I_OFF of 10⁷, and a high effective hole mobility of ∼146 cm² V^-1 s^-1. The novel Nb doping in monolayer WS₂ has eliminated the ambipolar behavior and reduced the Schottky barrier in WS₂ FETs. The reduction of the Schottky barrier is ascribed to the hybridization between W 5d, Nb 4d and S 3p states near the E_F and to the enhancement of the metallization of the contact between the Pd metal and monolayer Nb_xW_1-xS₂ after Nb doping.