Improved Charge Transfer and Barrier Lowering across a Au-MoS2 Interface through the Insertion of a Layered Ca2N Electride

Abstract

Transition-metal dichalcogenides (TMDCs) are a family of layered semiconductors with great potential to impact the upcoming field of two-dimensional (2D) electronics. In particular, MoS2 is a TMDC with a desirable band gap for the construction of transistors, solar cells, and biochemical sensors. Despite immense promise, use of TMDCs in electronics applications is hindered by the difficulties in forming effective metal contacts with low resistance, as required in any practical device. Although to varying degrees, transition metals spanning the entire d-block of the periodic table fail to form proper ohmic contact with MoS2 . In this work, we propose insertion of a two-dimensional electride [Ca2N]+(e-), an electron rich material, at a metal–TMDC interface to establish proper electrical contact. As a proof-of-concept, we study a Au–Ca2N–MoS2 heterostructure and compare it to a Au–MoS2 heterostructure within a density-functional theory framework using the exchange-hole dipole moment dispersion model. We choose Au since it is a common metal and its interface with MoS2 leads to a van der Waals gap that is known to exhibit strong Fermi-level pinning, as well as forming high Schottky and tunneling barriers. Calculations predict nearly complete charge transfer from the electride surface states, resulting in a cationic [Ca2N]+ monolayer at the interface and metalization of the negatively doped MoS2 . Thus, formation of the Au–Ca2N–MoS2 heterostructure eliminates both the tunneling and Schottky barriers, indicating that inserting a single 2D electride layer at metal–TMDC interfaces is a viable strategy to achieve proper ohmic contacts in device manufacture.