First-Principles Study of Oxygen Vacancy Defects in Amorphous HfO₂/Si Interfaces

Understanding the impact of oxygen vacancy defects on the amorphous HfO2/Si interfaces is crucial for improving the performance of Si-based devices. In this study, we combine first-principles calculations with molecular dynamics simulations to investigate the electronic structure, defect states, and carrier transport properties of the amorphous HfO2/Si interfaces. The constructed amorphous HfO2/Si interface is an indirect-gap semiconductor, with the conduction and valence band edges primarily contributed by the Si side. The introduction of oxygen vacancies affects both the size and the nature of the band gap. Specifically, the VO2 defect reduces the band gap by 0.128 eV, while the VO3 defect induces a transition from an indirect to a direct band gap. Hydrogen passivation effectively eliminates defect states, reduces the band gap, and restores the energy band alignment to that of the perfect interface. At low defect concentrations (<1 × 1020 cm–3), the mobility remains stable, exhibiting typical band-like transport characteristics. However, at high defect concentrations, defect-induced lattice distortions and stress concentrations further exacerbate polar optical phonon scattering, leading to a sharp decline in mobility. These findings emphasize the key role of oxygen vacancy defect engineering and passivation in optimizing interface properties, providing theoretical guidance for the design of high-performance Si-based MOS devices.