Considerations on the Effect of Interstitial and Precipitated Fe in Intentionally Fe-Doped mc-Silicon
In this work laboratory scale multicrystalline silicon ingots were grown which have been intentionally contaminated with iron in the range between 10 to 400 ppmw by adding FeSi2 to the silicon feedstock. It is shown that an iron contamination at these high levels does not result in a structural breakdown of the columnar grain growth regime because constitutional supercooling could be avoided by strong mixing of the melt in the present crystal growth experiments. The minority carrier lifetime mappings are dominated by the iron contamination and show the distribution of the impurity over the ingot height. The measured values of the specific electrical resistivity show a significant drop from 40 to below 20 Ωcm for a contamination level of 10 ppmw Fe probably due to interactions of iron with thermal donors. At higher contamination levels the specific resistivity increases significantly with increasing iron concentration compared to the 10 ppmw ingot. Above 400 ppmw iron the specific resistivity drops below the initial value for nominally iron free material. These results indicate that interstitial iron shows a donor-like behavior in multicrystalline silicon and precipitated iron decreases the specific resistivity.
Hiroshi Yamada-Kaneta and Akira Sakai
M. Azizi et al., "Considerations on the Effect of Interstitial and Precipitated Fe in Intentionally Fe-Doped mc-Silicon", Materials Science Forum, Vol. 725, pp. 145-148, 2012