Dark shadow areas often appear in infrared images of cast monocrystalline silicon (CMC-Si) ingots. In this work, the formation of shadow and how to avoid it by optimizing the growth process are analyzed. The analysis of scanning electron microscopy & energy dispersive spectroscopy show that the shadows in CMC-Si are caused by dispersed SiC particles. These particles will further induce a great number of dislocations, subgrain boundaries, and strip-shaped grains, which decrease the quality and the minority carrier lifetime of CMC-Si. In addition, an optimized process has proposed and successfully produced a silicon ingot without any shadows. By comparing the traditional and optimized processes, the shadow formation mechanism is studied and found preventing shadow formation by keeping the liquid phase temperature gradient smooth, the maximum crystal growth rate is not more than 1.1 cm h −1 and reducing the value of G L /V below 0.235.

Photoluminescence PL imaging techniques and the minority carrier lifetime test system were employed to investigate the variation of the interstitial iron (Fe i ) concentration, the recombination activity of structural defects and the minority carrier lifetime of cast multicrystalline silicon (mc-Si) in response to the cooling rate after heating. The results showed that when the mc-Si wafers are heated to hightemperature (1000 °C) and then cooled to ambient temperature with different cooling rate, the Fe i concentration, the number of recombination active dislocations and grain boundaries increased as the cooling rate rises while the minority carrier lifetime decreased. If cast mc-Si is heated followed by faster cooling at 30 °C/s, the Fe i concentration increase by 223% and the electrical activity of grain boundaries, dislocations and intragrain increase signi cantly, that is to say, the whole wafer is heavily contaminated with metal impurities, and present extremely low minority carrier lifetime.

Physical-chemical characteristics of the band sawing dusts regarding to recovery of pure silicon from them were investigated. The experimental results show 50vol%-60vol% amorphous phases exist in the dusts, which is mostly amorphous silica. The as-received saw dusts are found to form hard agglomerates of larger than 50 microns in diameter. The iron-based inclusions collected by magnets are found to match well with the band saw material in XRD patterns. Weight loss in heating was observed by thermal gravity tests, up to 900 ℃, presumably due to reaction of the amorphous silica with carbon contaminant in the dusts. The saw dusts were variously treated to examine their physical-chemical responses, and the results were also presented.

Photoluminescence（PL）imaging techniques and the minority carrier lifetime test system were employed to investigate the variation of the interstitial iron (Fei) concentration, the recombination activity of structural defects and the minority carrier lifetime of cast multicrystalline silicon (mc-Si) in response to the cooling rate after heating. The results showed that when the mc-Si wafers are heated to high-temperature (1000 °C) and then cooled to ambient temperature with different cooling rate, the Fei concentration, the number of recombination active dislocations and grain boundaries increased as the cooling rate rises while the minority carrier lifetime decreased. If cast mc-Si is heated followed by faster cooling at 30 °C/s, the Fei concentration increase by 223% and the electrical activity of grain boundaries, dislocations and intragrain increase significantly, that is to say, the whole wafer is heavily contaminated with metal impurities, and present extremely low minority carrier lifetime.