SPATIALLY RESOLVED LIFETIME INVESTIGATIONS OF Al- AND P-GETTERING IN COMBINATION WITH REMOTE HYDROGEN PLASMA PASSIVATION IN EFG RIBBON SILICON

摘要

In defect containing silicon minority charge carrier lifetimes can be improved by gettering and passivation techniques in order to reach sufficient solar ceil efficiencies. Consequently, such processing steps should be investigated. This has partly been done in this study, where the impact of P- and Al-gettering and their combination with a remote hydrogen plasma passivation on Edge-defined Film-fed Growth (EFG) silicon ribbons was examined. But in contrast to previous studies of other groups the mapping microwave detected photoconductance decay technique was applied for the measuring of lifetimes. As a consequence not just integral lifetime values but spatially resolved lifetime mappings have been obtained. This turned out to be essential for a detailed investigation of processing steps applied to EFG silicon material, as it was found that regions of comparable starting lifetimes can react very differently on the various processing steps. Therefore, the results of integral measurements depend strongly on the nature of regions incorporated in the specific sample. Moreover, it was found that the impact of the different processing steps on the various wafer areas also depends strongly on their starting quality. In good regions bulk lifetimes of about 280 μm have been reached.