Universal Ohmic contacts to <b> <i>β</i> </b> -Ga2O3 using interfacial dipoles of ultra-thin MgF2 layer and related defect passivation

Abstract

We report on the role of MgF2 as an interfacial buffer layer to achieve universal Ohmic contact on polycrystalline β-Ga2O3 thin film. Polycrystalline Ga2O3 thin films were deposited using RF magnetron sputtering, followed by the growth of MgF2 through a modified approach within the same technique, enabling enhanced fluorination via trapped fluorine species. Three representative metals like Al (low work function ≈4.0 eV), and Ni, Au (high work functions ≈5.0 eV) were investigated to assess contact behavior. All three metals formed Schottky junctions with Ga2O3 in direct contact while insertion of an MgF2 interlayer resulted in a clear transition to Ohmic conduction. Interface analysis using x-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM) revealed that fluorine incorporation passivates oxygen vacancies, reducing Fermi-level pinning, while Ga–F interfacial dipoles induce downward band bending. These combined effects effectively lower the Schottky barrier height enabling universal Ohmic contacts across metals with different work functions.