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Prospects of Zero Schottky Barrier Height in a Graphene Inserted MoS2-Metal Interface

A low Schottky barrier height (SBH) at source/drain contact is essential for achieving high drive current in atomic layer MoS2 channel based field-effect transistors. Approaches such as choosing metals with appropriate work functions and chemical doping are employed previously to improve the carrier injection from the contact electrodes to the channel and to mitigates the SBH between the MoS2 and metal. Recent experiments demonstrate significant SBH reduction when graphene layer is inserted between metal slab (Ti and Ni) and MoS2. However, the physical or chemical origin of this phenomenon is not yet clearly understood. In this work, density functional theory (DFT) simulations are performed, employing pseudopotentials with very high basis sets to get insights of the charge transfer between metal and monolayer MoS2 through the inserted graphene layer. Our atomistic simulations on 16 different interfaces involving five different metals (Ti, Ag, Ru, Au and Pt) reveal that: (i) such a decrease in SBH is not consistent among various metals, rather an increase in SBH is observed in case of Au and Pt (ii) unlike MoS2-metal interface, the projected dispersion of MoS2 remains preserved in any MoS2-graphene-metal system with shift in the bands on the energy axis. (iii) a proper choice of metal (e.g., Ru) may exhibit ohmic nature in a graphene inserted MoS2-metal contact. These understandings would provide a direction in developing high performance transistors involving hetero atomic layers as contact electrodes.