MoS2 Field-Effect Transistor Performance Enhancement by Contact Doping and Defect Passivation via Fluorine Ions and Its Cyclic Field-Assisted Activation

MoS₂-based field-effect transistors (FETs) and, in general, transition metal dichalcogenide channels are fundamentally limited by high contact resistance (R_C) and intrinsic defects, which results in low drive current and lower carrier mobilities, respectively. This work addresses these issues using a technique based on CF₄ plasma treatment in the contacts and further cyclic field-assisted drift and activation of the fluorine ions (F^-), which get introduced into the contact region during the CF₄ plasma treatment. The F^- ions are activated using cyclic pulses applied across the source-drain (S/D) contacts, which leads to their migration to the contact edges via the channel. Further, using ab initio molecular dynamics and density functional theory simulations, these F^- ions are found to bond at sulfur (S) vacancies, resulting in their passivation and n-type doping in the channel and near the S/D contacts. An increase in doping results in the narrowing of the Schottky barrier width and a reduction in R_C by ∼90%. Additionally, the passivation of S vacancies in the channel enhances the mobility of the FET by ∼150%. The CF₄ plasma treatment in contacts and further cyclic field-assisted activation of F^- ions resulted in an ON-current (I_ON) improvement by ∼90% and ∼480% for exfoliated and CVD-grown MoS₂, respectively. Moreover, this improvement in I_ON has been achieved without any deterioration in the I_ON/I_OFF, which was found to be >7-8 orders.