Dual roles of oxygen vacancy in hafnium oxide for passivating silicon surface defects

Oxygen vacancy (VO) defects serve as the primary electron traps, addressing the limited out-of-plane carrier transport in HfO2-passivated Si-based heterojunction devices, while their roles in passivating Si surface defects have seldom been studied before. In this work, HfO2 thin films with various VO defect densities were grown via the atomic layer deposition method by simply varying the H2O dosage during the growth procedure. The results suggest that introducing VO defects into HfO2 thin films degrades the overall surface passivation efficiency on N-type Si. Further studies suggest that VO defects are the primary source of fixed positive charges in HfO2 thin films, which induce remarkable field-effect passivation. In contrast, introducing VO defects into HfO2 degrades the chemical passivation by suppressing the interfacial layer formation. This work demonstrates dual roles of VO defects in HfO2 thin films in passivating Si surface defects, offering clues to optimize the HfO2 passivation layer by carefully modulating and positioning VO defects to achieve both efficient interfacial passivation and effective interfacial transport in HfO2-passivated Si-based devices in the future.