Abstract:
In recent years, a lot of scienti c research e ort has been put forth for the investigation
of Transition Metal Dichalcogenides (TMDC) and other Two Dimensional (2D) materials
like Graphene, Boron Nitride. Theoretical investigation on the physical aspects
of these materials has revealed a whole new range of exciting applications due to wide
tunability in electronic and optoelectronic properties. Transition Metal Dichalcogenides
(TMDC) and their bi-layer/tri-layer heterostructures have become the focus of intense
research and investigation in recent time due to their promising electronic and optoelectronic
applications. In this work, we have presented a rst principle simulation study
on the electronic properties of MoS2/MX2/MoS2 (M=Mo or W; X=S or Se) trilayer
heterostructure. We have investigated the e ect of stacking con guration, bi-axial compressive
and tensile strain on the electronic properties of the trilayer heterostructures.
In our study, it is found that, under relaxed condition all the trilayer heterostructures
at di erent stacking con gurations show semiconducting nature. The nature of the
bandgap, however, depends on the inserted TMDC monolayer between the top and
bottom MoS2 layers and their stacking con gurations. Like bilayer heterostructures,
trilayer structures also show semiconducting to metal transition under the application
of tensile strain. With increased tensile strain, the conduction band minima shifts to
K point in the Brillouin zone which leads to a lowering of electron e ective mass at
conduction band minima. The study on the projected density of states reveal that,
the conduction band minima is mostly contributed by the MoS2 layers and states at
the valance band maxima are contributed by the middle TMDC monolayer. In our
study, the highest bandgap was found for MoS2/WS2/MoS2 trialyer while the lowest
bandgap was found for the MoS2/WSe2/MoS2 trilayer. Besides exploring the electronic
properties, we have explored device level performance of trilayer TMDC heterostructure
(MoS2/MX2/MoS2; M=Mo or, W and X=S or, Se) MOSFETs in the quantum ballistic
regime. Our simulation shows that device `on' current can be improved by inserting
a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain
reveals a reduction in drain current which can be attributed to the lowering of carrier
e ective mass with increased tensile strain. Due to low bandgap MoS2/WSe2/MoS2
trilayer heterostrcuture MOSFETs were found to be showing high o -state leakage and
thereby high sub-threshold swing. In addition, it is found that gate underlap geometry
improves electrostatic device performance by improving sub-threshold swing. However,
increase in channel resistance reduces drain current.
