Behind the Nature of Titanium Oxide Excellent Surface Passivation and Carrier Selectivity of c-Si

We present an expanded study of the passivation properties of titanium dioxide (TiO₂) on p-type crystalline silicon (c-Si). We report a low surface recombination velocity (16 cm/s) for TiO₂ passivation layers with a thin tunnelling oxide interlayer (SiO₂ or Al₂O₃) on p-type crystalline silicon (c-Si). The TiO₂ films were deposited by thermal atomic layer deposition (ALD) at temperatures in the range of 80-300  ̊C using titanium tetrachloride (TiCl₄) as Ti precursor and water as the oxidant. The influence of TiO₂ thickness (5, 10, 20 nm), presence of additional tunneling interlayer (SiO₂ or Al₂O₃), and post-deposition annealing temperature were investigated.
We have observed that that SiO₂ and Al₂O₃ interlayers enhance the TiO₂ passivation of c-Si. TiO2 thin film passivation layers alone result in lower effective carrier lifetime. Further annealing at 200  ̊C in N₂ gas enhances the surface passivation quality of TiO₂ tremendously.