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 (TiO ₂ ) layers on undiffused 10 Ωcm p-type crystalline silicon. The TiO ₂ 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 TiO ₂ layers tremendously. Increasing the thickness of the TiO ₂ 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 TiO ₂ layer improves the surface passivation of thicker TiO ₂ layers (5.5 and 15 nm). These results show that ultrathin TiO ₂ layers with a thickness of only 1.5 nm can be used to effectively passivate the c-Si surface.