Monolayer and bilayer tin monoxide in edge contact with common metals: a first-principles investigation

Abstract

The high hole mobility and layer-dependent properties of two-dimensional (2D) tin monoxide (SnO) make it a promising candidate for use as a channel material in field effect transistors. However, the widely used top contact (TC) configuration in such transistors often faces high contact resistance due to weak van der Waals interaction at the interface. In contrast, the edge contact (EC) configuration offers improved charge injection efficiency through chemical bonding at the interface. This study provides a comprehensive investigation of the electronic properties of monolayer (ML) and bilayer (BL) SnO ECs with different metal electrodes (silver, aluminium, gold, copper, and nickel) via first-principles calculations. Our results show that SnO undergoes clear metallisation at the edge. Tunnelling barriers (TBs) are found within ML SnO instead of at the metal–semiconductor interface, whereas they are eliminated in BL SnO. Schottky barriers (SBs) are also observed near the TB locations. Metallisation is confined to Sn and O atoms near the interface, while distant regions remain semiconducting. The calculated Fermi level pinning factor for ML SnO ECs is 0.48, which is higher than the mean (0.31) and median (0.28) values reported in theoretical studies of ECs and TCs of 2D semiconductors. The carrier mobilities of BL SnO under ECs appear to be higher than those of its ML counterpart, as indicated by the more dispersive band structures of the former. This behaviour is likely attributed to the intrinsic layer-dependent properties of SnO. These findings offer robust guidance for the design of SnO-based EC transistors.