Progress on the Pseudo-Binary (Al2O3)3(TiO2)2-System for Surface Passivation of P-Type Silicon

We have reported before on the use of (Al₂O₃)₃(TiO₂)_1-x pseudo-binary alloys, deposited by spin coating and thermally treated, for field-induced surface passivation of p-type silicon. These layers show fixed negative charge densities in the order of 10¹² cm ^-2 and yield low surface recombination velocities, but the passivating properties are degrading with time. It was found now that a treatment at high temperature (720degC-1000degC) in oxygen substantially reduces this degradation. The influence of temperature, oxygen flow and duration of the treatment on the effective lifetime is studied, as are effects occuring at the PBA/Si interface. A first optimization of this process leads to surface recombination velocities below 150 cm/s on low-resistivity FZ material and around 300 cm/s on CZ months after deposition. Experiments on the exact nature of the degradation mechanism are ongoing