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ECN publication
Distribution of iron in multicrystalline silicon ingots
Kvande, R.; Geerligs, L.J.; Coletti, G.; Arnberg, L.; Di Sabatino, M.; Ovrelid, E.J.; Swanson, C.
Published by: Publication date:
ECN Solar Energy 17-9-2008
ECN report number: Document type:
ECN-W--08-003 Article (scientific)
Number of pages:

Published in: Journal of Applied Physics (American Institute of Physics), , 2008, Vol.104, p.064905-.

The distribution of iron in multicrystalline silicon ingots for solar cells has been studied. A p- and a n-type multicrystalline ingot were intentionally contaminated by adding 53 ppm wt  g/g of iron to the silicon feedstock and compared to a reference p-type ingot produced from ultrapure silicon feedstock. The vertical total iron distribution was determined by neutron activation analysis and glow discharge mass spectrometry. For the intentionally Fe-contaminated ingots, the distribution can be described by Scheil’s equation with an effective distribution coefficient of 210-5. The interstitial iron concentration was measured in the p-type ingots. In the Fe-contaminated ingot, it is almost constant throughout the ingot and constitutes about 50% of the total concentration, which is in conflict with the previous studies. Gettering had a large impact on the interstitial iron levels by reducing the concentration by two orders of magnitude. Considerable trapping was observed at crystal defects on as-cut wafers from the same ingot. The trapping was suppressed by gettering. The back diffusion of iron from the ingot top after complete solidification was modeled and found to affect the iron concentration up to a distance of approximately 17 mm into the ingot. The interstitial as well as the total iron concentration of the reference ingot were extremely low and difficult to measure accurately.

Copyright (2008) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

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