Unraveling the Fe/β-Ga2O3(100) Interface through a combined XPD and DFT+U study of strain-induced interdiffusion

The atomic-scale structure of the Fe/ β -Ga 2 O 3 (100) interface is investigated through a combined experimental and theoretical approach using X-ray photoelectron diffraction (XPD) and density functional theory with Hubbard correction (DFT+U). The clean β -Ga 2 O 3 (100) surface is shown to be dominated by the B-termination, characterized by a nearly coplanar arrangement of the outermost atomic layers, as confirmed by XPD and supported by DFT calculations. Deposition of Fe results in significant outward relaxation at the vacuum interface, with interplanar expansions up to +27% relative to bulk Fe. While the DFT coherent interface model predicts strong interfacial strain due to lattice mismatch, experimental XPD data indicate that strain is not accommodated elastically. Instead, multiple-scattering simulations and DFT+U calculations reveal that strain relaxation occurs via Fe–Ga interdiffusion. Substitutional incorporation of Fe into the Ga sublattice reduces the R-factor and is energetically favorable, with an activation barrier of 1.76 eV determined via CI-NEB calculations. This barrier is lower than the demarcation energy of the annealing treatment (2.63 eV), confirming the kinetic feasibility of the process. These findings demonstrate that cationic substitution is one mechanism for plastic relaxation at the Fe/ β -Ga 2 O 3 (100) interface, providing new insights into the structural and chemical evolution of metal contacts on ultra-wide bandgap semiconductors.