Interlayer-Engineered Schottky Barrier and Rectification at Metal/β-Ga₂O₃ Interfaces from First Principles

Using DFT-NEGF simulations with the TB-mBJ exchange potential, we investigate Schottky barrier formation and carrier transport in metal/β-Ga₂O₃(100) contacts. For Ni, Ti, Ag, and Au contacts at a donor concentration of 1 × 10¹⁹ cm^-3, Au exhibits pronounced forward rectification, while Ag, Ti, and Ni display degraded or reversed rectification due to metal-induced gap states (MIGS) that enhance Fermi-level pinning and tunneling. Inserting a monolayer hexagonal boron nitride (h-BN) interlayer into the Ag contact suppresses MIGS, shifting the dominant transport mechanism from quantum tunneling to thermionic emission and restoring forward rectification. In contrast, a polar Janus WSSe interlayer creates an interfacial built-in electric field that yields reverse rectification relative to the h-BN-interlayered contact. However, the Janus-interlayered contact exhibits a small current. Reversing the WSSe orientation to WSeS changes the transport response, but the effect is not a simple mirror image. These results provide design rules for choosing metals, doping levels, and 2D interlayers to suppress MIGS and tailor Schottky rectification in ultra-wide-bandgap β-Ga₂O₃ electronics.