Facile and thermally-stable Al₂O₃ passivation by using in-situ TiO₂ as a capping layer for boron emitter of N-type silicon

Al₂O₃/TiO₂ stacks formed by atomic layer deposition are known to provide a high level of passivation for boron-doped silicon. In previous works, the TiO₂ layer was deposited on a pre-annealed Al₂O₃ layer, however this stack showed passivation degradation after post-deposition annealing. This work presents an alternative to using the as-deposited Al₂O₃ for the Al₂O₃/TiO₂ stack, which shows no degradation of passivation after post-deposition annealing up to 400 °C. This approach simplifies the processing, allowing continuous layer deposition, and eliminates the undesirable vacuum breaking. This simplified processing leads to better thermal stability of the Al₂O₃/TiO₂ stacks and a low emitter saturation current density. In order to understand the underlying mechanism of surface passivation, an investigation on the effect of thermal SiO₂ on the passivation of the Al₂O₃/TiO₂ stack was performed, which indicates that the TiO₂ capping layer enhances the field-effect passivation for both the Si/Al₂O₃ and SiO₂/Al₂O₃ structures.