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New µ-PCD Based Method for Sorting Boron and Gallium Doped Feedstock Material
F. Korsós, G. Paráda, D. Fátay
Carrier Lifetime, Light Induced Degradation (LID), Gallium Doping, Iron-Acceptor Pairs
Wafer-based Silicon Solar Cells and Materials Technology
Subtopic: Silicon Feedstock, Crystallisation and Wafering
Event: 26th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2BV.4.10
1817 - 1820
ISBN: 3-936338-27-2
Paper DOI: 10.4229/26thEUPVSEC2011-2BV.4.10
0,00 EUR
Document(s): paper


A fast, non-destructive, non-contact and preparation free measurement method is introduced which is capable of distinguishing between boron and gallium doped PV silicon bulk feedstock materials (slugs, ingots or uneven shaped material pieces). The method consists of high-injection minority carrier lifetime measurement and high intensity laser treatment. The microwave photoconductance decay method is applied as a high injection carrier lifetime measurement. The boron or gallium dopant species can be determined from the polarity of the carrier lifetime change caused by the applied laser treatment sequence. All boron doped samples show negative carrier lifetime change, while the laser treatment increases the lifetime of most gallium doped pieces. The negative lifetime change of boron doped silicon is caused by the formation of boron-oxygen LID defects. Dissociation of iron-acceptor pairs is found to be responsible for the lifetime increase in the gallium doped samples. The dynamics of lifetime change caused by the laser treatment is discussed in detail, optical dissociation of irongallium pairs is found to be much slower than in the case of iron-boron pairs, while light induced degradation shows the expected dynamics.