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ABSTRACT The deteriorated area of the multicrystalline silicon (mc-Si) ingots grown by directional solidification, commonly known as the Red Zone, is usually removed before wafering. This area, characterized by poor minority carrier lifetime, is located on the sides, at the top, and the bottom of the mc-Si ingots. In this study, the effect of internal gettering by oxygen precipitates and structural defects has been investigated on the bottom zone of a mc-Si ingot. Nucleation and growth of oxygen precipitates as well as low temperature annealing were studied. Photoluminescence imaging, lifetime mapping, and interstitial iron measurements performed by μ-PCD reveal a considerable reduction of the bottom Red Zone. An improvement of lifetime from below 1 µs to about 20 µs and a reduction of interstitial iron concentration from 1.32 × 1013 at/cm3 to 8.4 × 1010 at/cm3 are demonstrated in this paper. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Metallurgical purification routes to solar grade silicon have gained a respectable success for the manufacture of standard multicrystalline solar cells. However, gas phase chemically refined silicon (commonly designated as polysilicon) remains unchallenged for semiconductor applications and for the manufacture of monocrystalline solar cells, particularly the most popular high efficiency cell architectures. Therefore, in the medium term future virgin polysilicon should keep a predominant share of the silicon feedstock to electronic and photovoltaic wafers. For photovoltaic to meet the grid parity cost target, significant efforts have been deployed during the past years aiming at drastically reducing the cost of polysilicon. This has been achieved not only through massive capacity expansions but also through simplifying the process as well as developing new gas/solid purification and deposition processes. The replacement of the historical Siemens by the Fluidized Bed Reactor is the most accomplished example of such attempts. Worth noting is also the replacement of chlorine by other halogens in the volatile silicon bearing compound or hydrogen by metal in the deposition/reduction process. However, such cost efficient progress might have been on the expense of the ultimately desirable purity. This contribution will review the most accomplished and promising attempts to develop the polysilicon process. The potential and the limitations of the emerging polysilicon products will be illustrated with respect to their ability to produce high quality wafers for semiconductor or high efficiency solar cells (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]