Ultrathin Titanium Dioxide Nanolayers by Atomic Layer Deposition for Surface Passivation of Crystalline Silicon

• Published in: IEEE journal of photovoltaics 2016-05, Vol.6 (3), p.649-653
• Main Authors: Gad, Karim Mohamed, Vossing, Daniel, Richter, Armin, Rayner, Bruce, Reindl, Leonhard M., Mohney, Suzanne E., Kasemann, Martin
• Format: Article
• Language: English
• Subjects: Annealing; Atomic layer deposition (ALD); Crystal structure; Forming; Nanostructure; Passivation; Photovoltaic cells; Silicon; surface passivation; Temperature measurement; Thickness; Titanium; Titanium dioxide; ultrathin titanium dioxide (TiO2) nanolayers
• ISSN: 2156-3381; 2156-3403
• DOI: 10.1109/JPHOTOV.2016.2545404

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.