Effective silicon surface passivation by atomic layer deposited Al₂O₃/TiO₂ stacks

In this work atomic layer deposition of Al₂O₃ and TiO₂ has been used to obtain dielectric stacks for passivation of silicon surfaces. Our experiments on n- and p-type silicon wafers deposited by thin Al₂O₃/TiO₂ stacks show that a considerably improved passivation is obtained compared to the Al₂O₃ single layer. For Al₂O₃ films thinner than 20 nm the emitter saturation current density decreases with increasing TiO₂ thickness. Especially the passivation of ultrathin (∼5 nm) Al₂O₃ is very effectively enhanced by TiO₂ due to a decreased interface defect density as well as an increased fixed negative charge in the stacks. Hence, the thin Al₂O₃/TiO₂ stacks developed in this work can be used as a passivation coating for Si-based solar cells.