MoS<sub>2</sub> Field-Effect Transistor Performance Enhancement by Contact Doping and Defect Passivation via Fluorine Ions and Its Cyclic Field-Assisted Activation
Anand Kumar, Asif A. Shah, Jeevesh Kumar, Sumana Chattaraj, Aadil Bashir Dar, Utpreksh Patbhaje, Mayank Shrivastava
Abstract
MoS 2 -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 CF 4 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 CF 4 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 CF 4 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 MoS 2, 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.