Ultrathin titanium dioxide nanolayers by atomic layer deposition for surface passivation of crystalline silicon

We demonstrate a low surface recombination velocity of 14 cm/s with only 1.5 nm thin titanium dioxide (TiO₂) layers on undiffused 10 Ωcm p-type crystalline silicon. The TiO₂ nanolayers were deposited by thermal atomic layer deposition at 150 °C and 200 °C substrate temperatures using tetrakis-dimethyl-amido titanium as the Ti precursor and water as the oxidant. The influence of a post-deposition anneal in forming gas at different temperatures was investigated. We have observed that a subsequent anneal in forming gas at 350 °C enhances the surface passivation quality of the TiO₂ layers tremendously. Increasing the thickness of the TiO₂ layers leads to a reduction of the surface passivation quality. Introducing a thin interfacial layer of silicon oxide (1.6 nm) grown by rapid thermal oxidation underneath the TiO₂ layer improves the surface passivation of thicker TiO₂ layers (5.5 and 15 nm). These results show that ultrathin TiO₂ layers with a thickness of only 1.5 nm can be used to effectively passivate the c-Si surface.