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.

The emerging two-dimensional (2D) materials exhibit strong exciton effects with rich exciton types, dominating their optical and optoelectronic properties. The modulation of the interlayer van der Waals (vdW) gap in 2D materials significantly influences interlayer coupling, enabling the manipulation of the excitonic binding energy (E_B), electronic band structure, etc. However, the impact of the vdW gap between 2D materials and their substrates on excitonic behavior is seldom explored, and the physical mechanism remains unclear. Here, we experimentally demonstrate the vdW gap between 2D materials and substrates can effectively tune the excitonic E_B and electronic bandgap, owing to the change in the local dielectric environment and the Coulomb screening effect. The vdW gap between monolayer WS₂ and SiO₂/Si substrate reduced from ~ 6 to 3 nm by the simple annealing process enhances the Coulomb screening effect, decreases the excitonic E_B by ~ 20 meV, redshifts the bandgap by ~ 14 meV and thus strongly suppresses the trion formation. Our findings elucidate the underlying physical interaction mechanisms between 2D materials and substrates, offering valuable insights for designing and optimizing optical and optoelectronic devices by utilizing these supported 2D materials.