Dimensionality-Driven Contact Behaviors of van der Waals Semimetal Electrodes in 2D

Achieving low-resistance ohmic contacts at the metal–semiconductor (M–S) interface is pivotal for enhancing the performance of electronic devices. However, this remains a formidable challenge for two-dimensional (2D) semiconductors due to atomically thin nature of 2D channel materials. Van der Waal (vdW) integration has emerged as a promising alternative to mitigate FLP, offering atomically sharp and chemically inert interfaces that preserve intrinsic electronic structure and band alignment of both contact and channel materials. 2D semimetals such as graphene, VS₂, WTe₂, PtSe₂, NbS₂, ZrTe₂, and TiS₂ have gained increasing attention due to their good electrical conductivity and wide range of WFs. These 2D materials exhibit dangling-bond-free surfaces and are free from lattice-matching constraints, enabling seamless vdW integration with diverse 2D channel materials. Despite these advantages, the performance of vdW-contacted 2D devices exhibits considerable variability, even when utilizing identical 2D channel materials. This variation primarily stems from inconsistencies in the thickness and WF of these contact materials.

A critical consideration remains: when the thickness of 2D semimetallic electrodes approaches or exceeds a certain threshold, can such configuration still be classified as truly 2D contacts? The impact of contact dimensionality, particularly thickness, on modulating interfacial charge transport and overall device performance remains inadequately explored. Gaining a deeper understanding of this dimensional crossover is essential for enabling optimal vdW-contacted configurations that staightforwardly drive the development of next-generation semiconductor devices with high performance. To address this gap, our study systematically investigates the dimensional transition in semimetallic graphene spanning from monolayer, few-layer to multilayer and its impact on the contact quality and device performance of 2D MoS₂ field-effect transistors (FETs). We demonstrated that few-layer graphene (FLG) with a thickness of 2–4 nm as contact electrodes, enables MoS₂ to achieve device performance comparable to that of conventional 3D semimetal Bi with a thickness of ~ 20 nm. Our findings highlight the critical role of dimensional control in vdW-based contact electrodes for 2D FETs, , paving the way for achieving truly 2D contacts for high-performance 2D electronic devices.