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Title:
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Behaviour of natural and implanted iron during annealing of multicrystalline silicon wafers
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Author(s):
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Published by:
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Publication date:
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ECN
Solar Energy
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1-5-2005
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ECN report number:
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Document type:
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ECN-RX--05-099
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Conference Paper
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Number of pages:
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Full text:
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5
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Download PDF
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Presented at: Gadest 2005, XIth Gadest Conference, Giens, France, 25-30 september 2005.
Abstract:
Changes in the concentration of interstitial
iron in multicrystalline silicon wafers after high temperature annealing
(900ºC)
have been monitored by carrier lifetime measurements. Two cooling rates
were investigated. The first was considered ?fast?, meaning the interstitial
Fe had no time to diffuse to precipitation sites, and should therefore
be frozen-in, despite being far above the solubility limit at lower
temperatures. A second ?slow? cool down to 650ºC allowed ample time for the Fe to reach
the surfaces or other internal precipitation sites. Surprisingly, in
both cases the Fe remained in a supersaturated state. This indicates
the precipitation process is not diffusion-limited, and that another
energetic barrier to precipitate formation must be present. Since the
slow cooling used here is similar to the cooling rate experienced by
multicrystalline ingots after crystallisation, this precipitate-impeding
mechanism is probably responsible for the surprisingly high interstitial
Fe concentrations often found in as-grown multicrystalline silicon wafers.
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