Theoretical Exploration of Two-Dimensional Electrenes for Low-Resistance Metal-2D Semiconductor Contacts

Transition-metal dichalcogenides (TMDCs), including MoS₂, have great potential in electronic applications. However, achieving low-resistance metal contacts is a challenge that impacts their performance in nanodevices, due to strong Fermi level pinning and the presence of a tunnelling barrier. As a solution, we explore a strategy utilizing two-dimensional (2D) alkaline-earth sub-pnictide electrenes with a general formula of M₂X (M = Ca, Sr, Ba; X = N, P, As, Sb) as an intermediate material between the 2D TMDC and metal. Electrenes possess one excess electron per formula unit resulting in the formation of 2D sheets of charge on their surfaces. This charge can be readily donated when interfaced with a TMDC semiconductor, thereby lowering its conduction band below the Fermi level and eliminating Schottky and tunnelling barriers. Density-functional theory calculations were performed on metal-electrene-MoS₂ heterojunctions for all stable M₂X electrenes, and both Cu and Au metals. To identify the material combinations that provide the most effective Ohmic contact the charge transfer, band structure and electrostatic potential, among other quantities, were analyzed. In all cases, a linear correlation was found between the charge donated to the MoS₂ and the electrene surface charge. The electride Ca₂N is found to be most promising for achieving an Ohmic metal-MoS₂ contact, due to its high surface charge density.<br/><br/>This research was supported by SRC.