Theoretical simulation of dielectric breakdown by molecular dynamics and tight-binding quantum chemistry methods

A novel methodology is addressed and employed to simulate dielectric breakdown process of the amorphous SiO₂ (a-SiO₂) under high electric fields, as well as the role of hydrogen and oxygen vacancy in the breakdown process. This methodology is based on classical molecular dynamics in conjunction with our original tight-binding quantum chemical molecular dynamics method. It is shown from the electronic structure that gap of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for a-SiO₂ under no electric field at 300 K is calculated to be 7.5 eV and the orbital contributions to the valence band and conduction band are in line with experimental data. We have evaluated the electric field dependence of breakdown for a-SiO₂ at 300 K and found that the insulator property shifts to conductor when electric field reached to a very high value of 5 × 10¹⁰ V/m. The result of this process can be ascribed to the decreasing of band gap induced by the destruction of geometry of a-SiO ₂ under very high electric field. Our results reveal that the conductivity of a-SiO₂ increases with the increase of hydrogen or oxygen vacancy concentration in the oxide structure under the electric field. This supports the fact that defects play an important role in triggering breakdown process. Finally, a complex model has been build and used to simulate the influence of interface structure of Si and SiO₂ under high electric field.