2D electrides: materials for achieving low-resistance contacts to 2D semiconductors

Layered electrides are ionic solids with loosely-bound conducting 2D electrons confined to the interstitial regions between the atomic layers, and on their surfaces when exfoliated to form 2D electrides. Because the conducting electrons are physically separated from the lattice, layered electrides display low work function which can promote charge transfer. Here, we theoretically explore a strategy using a 2D electride as an interfacial layer to achieve ultralow contact resistance to a 2D semiconductor – a major challenge that hinders their device performance. Using density functional theory we investigate the interfacial properties of a 2D semiconductor-metal contact, specifically monolayer MoS₂ (semiconductor)-monolayer Ca₂N (electride)-gold (metal). An analysis of the charge transfer, exfoliation energy, band structure and electrostatic potential demonstrates that Ca₂N donates nearly all of its surface charge resulting in the metallization of the MoS₂ and a barrier-free contact. By comparison, the monolayer MoS₂-gold contact displays a large tunneling barrier and Fermi-level pinning. These findings suggest that introducing a layered electride in 2D semiconductor-metal interfaces is a promising strategy towards achieving ohmic contacts.

We acknowledge support from SRC, NSERC, and the Digital Research Alliance of Canada.