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 (<i>R</i>_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 <i>R</i>_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>I</i>_ON) improvement by ∼90% and ∼480% for exfoliated and CVD-grown MoS₂, respectively. Moreover, this improvement in <i>I</i>_ON has been achieved without any deterioration in the <i>I</i>_ON/<i>I</i>_OFF, which was found to be >7–8 orders.