Tuning work functions to convert schottky to ohmic contacts in ZnMN2 (M = Si, Ge)-based van der waals interfaces

The Schottky barrier at the interface between two-dimensional (2D) semiconductors and metal electrodes critically limits the performance of nanoelectronic devices. Replacing conventional bulk metals with 2D metals in van der Waals contacts suppresses Fermi-level pinning, while work-function matching offers a route to Ohmic contact. Using first-principles calculations, we systematically investigate the contact properties of six van der Waals heterostructures composed of monolayer ZnSiN 2 or ZnGeN 2 and three 2D electrodes with distinct work functions: graphene (Gr), NbS 2 , and NbSe 2 . The global minimum-energy stacking configuration for each heterostructure is determined by optimizing the interlayer distance and in-plane displacement. Projected band structures confirm that ZnSiN 2 /NbS 2 , ZnGeN 2 /NbS 2 and ZnGeN 2 /NbSe 2 form p-type Ohmic contacts. Analysis of plane-averaged charge-density differences and electrostatic potentials reveals the mechanism: the high work function (>6.0 eV) of NbS 2 shifts the Fermi level toward the valence band maximum (VBM) of ZnMN 2 , giving rise to p-type Ohmic contacts. Among all systems, ZnSiN 2 /NbS 2 exhibits favorable Ohmic behavior and a relatively high ultraviolet absorption coefficient, highlighting its potential for high-performance photodetectors. This work demonstrates that work-function engineering effectively modulates the contact type in ZnMN 2 -based van der Waals heterostructures, providing theoretical guidance for electrode selection in this material system.