The contacts between two-dimensional materials and metal electrodes

The advent of two-dimensional (2D) materials has ushered in a new era for electronic and optoelectronic devices. However, their atomic-scale thickness presents a fundamental contact interface challenge: the formation of a Schottky barrier at the 2D material–metal contact interface, which often leads to Schottky barrier and high contact resistance (R_C). While detrimental for conventional transistor scaling, this inherent Schottky barrier is also a critical functional element, actively harnessed in devices like photodetectors. This duality defines the central theme of contact interface engineering in 2D electronics. This review comprehensively examines recent advances in understanding and engineering these critical interfaces. We first elucidate the core physical principles governing contact formation, including Fermi level (E_F) pinning (FLP), charge transfer, and Schottky barrier modulation. We then distinguish strategic pathways for engineering contacts: routes toward ultralow-resistance Ohmic contacts (van der Waals (vdW) integration, interfacial doping, and edge contacts) and methods for tailoring Schottky contacts through barrier-height tuning. Insights from advanced characterization techniques and theoretical models for extracting Schottky barrier height (SBH) and R_C are also integrated. Finally, we outline unresolved challenges and future directions, providing a roadmap toward rationally designed 2D contact interfaces for unlocking full device potential.