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 Omega cm p-type crystalline silicon. The TiO2 nanolayers were deposited by thermal atomic layer deposition at 150 degrees C and 200 degrees 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 degrees 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.