Light-Induced Degradation and Regeneration in n-Type Silicon

Whereas n-type silicon wafers are used for many high-efficiency cells concepts, the unfavourable segregation coefficient of phosphorus leads to significant resistivity variation along the ingot. Crystals grown by counter doping with boron or from umg silicon feedstock might offer a solution, but these materials suffer from light-induced degradation due to the boron oxygen defect. In this manuscript, we demonstrate the application of a curing process to B-P compensated n-type Cz silicon. Significant charge carrier lifetime improvements are achieved and a high degree of stability is proven with extensive light soaking experiments. The observation of slight lifetime changes during light soaking is attributed to incompleteness of the curing due to not optimized process parameters. We demonstrate stable lifetimes exceeding 1 ms in wafers with high boron and interstitial oxygen concentrations. Similar top-type silicon the illumination intensity and process temperature are found to be crucial for the regeneration process in n-type silicon as well. Furthermore the influence of different diffusion conditions is studied and we attribute the results to an influence of diffusion peak temperature rather than thermal budget. Thus, we can report an illumination-stable high-lifetime state of the BO-defect in compensated n-type silicon and provide further insight to the phenomenon of light-induced degradation.