Surface dipole induced Ohmic contact in two-dimensional Sc2CTT’/graphene heterostructures

Abstract

Schottky electrical contact occurs at the metal–semiconductor heterstructures (MSHs) that are comprised of metallic graphene eletrode and most of two-dimensional (2D) semiconductors, which seriously degrades the electronic devices’ performance. Herein, we proposed a family of 2D Sc₂CTT’ semiconductors through eliminating the surface electrons of Sc₂C electride. We exploited these Sc₂CTT’ as channel materials to construct graphene-based MSHs and achieved their Ohmic contacts with low contact resistance. The Sc₂CClH/graphene form a p-type Schottky contact (Shc) with a tiny SBH (∼0.1 eV), the Sc₂CHCl/graphene exhibits a p-type Ohmic contact (Ohc), and the Sc₂CClOH/graphene favors an intrinsic n-type Ohc. These excellent electric contacts are owing to the intrinsic and distinctive electronic characters where the band edge electronic states reside in the inner Sc₂C layer while the outer H (or OH) and Cl layers only act as encapsulation layers. Furthermore, the p-type Shc easily transforms into the p-type Ohc for Sc₂CClH/graphene, and the Ohc of Sc₂CHCl/graphene and Sc₂CClOH/graphene are well retained under perpendicular electric fields. This can be explained by the counteraction between external electric fields and intrinsic built-in electric fields. This study demonstrates that the surface dipole of 2D semiconductors with asymmetric bonding can greatly impact the interface contact properties.