Face-dependent Schottky barrier modulation and asymmetric pinning at Metal/Janus-MoSSe contacts: a first-principles study

High interfacial contact resistance induced by Fermi-level pinning (FLP) limits the performance of two-dimensional (2D) van der Waals (vdW) field-effect transistors (FETs). Although symmetric 2D materials often face a trade-off between suppressing FLP and preserving carrier injection efficiency, symmetry-broken Janus structures provide a structural route to overcome this limitation. Here, using first-principles density functional theory calculations, we systematically investigate the interfacial coupling in Metal/Janus-MoSSe junctions. For conventional metal contacts, stronger FLP is found on the S-face than on the Se-face. Strikingly, this face-dependent pinning asymmetry is reversed upon replacing the conventional metals with 2D metallic vdW contacts: the SMoSe contact then approaches the Schottky-Mott limit much more closely, owing to suppressed chemical interactions and metal-induced gap states. This polarity-driven, face-dependent reversal introduces a new physical degree of freedom for designing high-performance, directionally tunable 2D FETs with tailorable contact properties.