  Metal-semiconductor interface is a bottleneck for efficient transport of
charge carriers through Transition Metal Dichalcogenide (TMD) based
field-effect transistors (FETs). Injection of charge carriers across such
interfaces is mostly limited by Schottky barrier at the contacts which must be
reduced to achieve highly efficient contacts for carrier injection into the
channel. Here we introduce a universal approach involving dry chemistry to
enhance atomic orbital interaction between various TMDs (MoS2, WS2, MoSe2 and
WSe2) & metal contacts has been experimentally demonstrated. Quantum chemistry
between TMDs, Chalcogens and metals has been explored using detailed atomistic
(DFT & NEGF) simulations, which is then verified using Raman, PL and XPS
investigations. Atomistic investigations revealed lower contact resistance due
to enhanced orbital interaction and unique physics of charge sharing between
constituent atoms in TMDs with introduced Chalcogen atoms which is subsequently
validated through experiments. Besides contact engineering, which lowered
contact resistance by 72, 86, 1.8, 13 times in MoS2, WS2, MoSe2 and WSe2
respectively, a novel approach to cure / passivate dangling bonds present at
the 2D TMD channel surface has been demonstrated. While the contact engineering
improved the ON-state performance (ION, gm, mobility and RON) of 2D TMD FETs by
orders of magnitude, Chalcogen based channel passivation was found to improve
gate control (IOFF, SS, & VTH) significantly. This resulted in an overall
performance boost. The engineered TMD FETs were shown to have performance on
par with best reported till date.
