Decoupling Thermal and Electronic Effects of Metal Contacts in Bilayer MoS2 Transistors

Contact resistance remains a primary bottleneck in two-dimensional (2D) semiconductor field-effect transistors (FETs), yet the concurrent influence of metal work function, adhesion, and deposition temperature obscures the underlying mechanisms. Here, using bilayer MoS2 as a model system, we systematically benchmark four metals (In, Bi, Ti, Pd) and discover that the metal melting point, which sets the deposition thermal budget, is strongly correlated with interface integrity. Low-melting-point metals (Bi, In) preserve an intact van der Waals gap (≈0.3 nm), whereas high-melting-point metals (Ti, Pd) damage the interface and collapse the gap to ≈0.19 nm (Pd) or destroy it entirely (Ti), as revealed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Despite Fermi-level pinning rendering all devices n-type, Pd outperforms Ti in contact resistance, underscoring the primacy of interface quality over work function alignment. Remarkably, Bi, despite its higher melting point and work function than In, delivers the lowest contact resistance (≈0.14 kΩ·μm) and highest on-state current (≈525 μA·μm-1 at Lch = 100 nm), which we attribute to its semi-metallic band structure that suppresses metal-induced gap states. This work establishes a design rule of contact metals for n-type MoS2 FETs: low work function, low deposition temperature, and low density of states, which is expected to extend to other 2D semiconductor nanoelectronics and integrated circuits.