Effect of oxygen-related defects on the performance of seed-end wafers in Ga-doped recharged Czochralski silicon: Thermal donors

Abstract

Ga-doped recharged Czochralski silicon (Ga-RCZ) is now becoming mainstream in the current photovoltaic market because of the enhanced production efficiency and reduced costs. It also hardly suffers from light-induced degradation (LID) due to the absence of boron-oxygen complexes. However, the performance deterioration of the seed-end wafers universally exists in industrial Ga-RCZ production, even if no ring-like defects are found there. Considering the severe enrichment of oxygen in the seed-end part due to crucible corrosion and oxygen segregation, oxygen-related defects like oxygen precipitates (OPs) and thermal donors (TDs) are easy to generate and may account for this deterioration. In this paper, comprehensive characterization methods including resistivity, minority carrier lifetime (MCL), and Fourier Transform Infrared Spectroscopy (FTIR) were used to identify the true reason for the deterioration in three randomly selected industrial Ga-RCZ ingots with different interstitial oxygen concentrations ([Oi]). The results showed that no OPs were observed but TDs were produced even up to 6.87 × 1014 cm−3 in the samples. It reveals that TDs should be the culprit for the performance degradation at seed-end wafers in Ga-RCZ.