Molecular dynamics simulation of dipole layer formation at high-k/SiO₂ interfaces

Electric dipole layer formation at high-k/SiO₂ interface is reproduced by classical molecular dynamics simulation based on a simple two-body rigid ion model (1). The dipole layer was spontaneously formed by the migration of oxygen ions across the high-k/SiO₂ interface. In the case of Al₂O₃/SiO₂, a part of oxygen ions of Al₂O₃ penetrated into the SiO₂ side, resulting in the formation of a built-in potential of about 0.5 V. The opposite migration of oxygen ions, from SiO₂ side to high-k oxide side, is also reproduced by using different potential parameters of ionic radius and effective charge. The simulation result suggests that the dipole is not merely formed by the oxygen density difference. Rather, oxygen ions are driven by some interatomic forces at the interface. We discuss the origin of the driving force of the oxygen migration in terms of the multipole moments around cations in the oxides.