Competitive gettering of iron in silicon photovoltaics: Oxide precipitates versus phosphorus diffusion

Abstract

Experiments have been conducted to understand the behaviour of iron in silicon containing oxide precipitates and associated defects (dislocations and stacking faults), which is subjected to phosphorus diffusion gettering. Injection-dependent minority carrier lifetime measurements are analysed to provide quantitative information on the degree to which the precipitates and associated defects are decorated with iron impurities. These data are correlated with bulk iron measurements based on the photodissociation of FeB pairs. Iron in the vicinity of oxide precipitates in samples with relatively low levels of bulk iron contamination (< 5 × 1012 cm−3) can be gettered to some extent. Higher levels of bulk iron contamination (> 1.2 × 1013 cm−3) result in irreversible behaviour, suggesting iron precipitation in the vicinity of oxide precipitates. Bulk iron is preferentially gettered to the phosphorus diffused layer opposed to the oxide precipitates and associated defects.