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 (RC) 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 RC 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 (ION)
improvement by ∼90% and ∼480% for exfoliated and CVD-grown
MoS2, respectively. Moreover, this improvement in ION has been achieved without any deterioration
in the ION/IOFF, which was found to be >7–8 orders.