Substitutional Doping Strategies for Fermi Level Depinning and Enhanced Interface Quality in WS2-Metal Contacts

Addressing contact resistance challenges at the interface between metals and transition-metal dichalcogenides (TMDs) remains a complex task due to the persistent Fermi level pinning (FLP) effect near the conduction band minima. Various methods have been explored to mitigate FLP by reducing the chemical interaction between metals and semiconductors. However, these approaches often lead to undesirable consequences, such as reduced adhesion and increased tunneling resistance, ultimately resulting in poor interface quality. A promising solution to overcome these limitations lies in the use of substitutionally doped semiconductor/metal interfaces. We conducted a thorough investigation using first-principles calculations, focusing on S-substituted WS2-metal interfaces involving commonly used metals such as Ag, Au, Cu, Pd, Pt, Sc, and Ti. Additionally, we explored the incorporation of nonmetallic dopants, including C, Cl, N, F, O, and P, into the WS2 surface. Our analysis revolved around several critical parameters, including adhesion strength, Schottky barrier height (SBH), tunnel barrier, charge transfer across the interface, and interface dipole formation. Our study demonstrated that substitutionally doped interfaces can undergo Fermi level depinning while maintaining an enhanced adhesion strength and lower tunneling barrier at the interface. This finding marks a departure from existing methods and offers a promising avenue for inducing p-type contact polarity and addressing contact resistance challenges in TMDs.