Silicon material quality and throughput: the high and the low, the fast and the slow

The author examines the factors that influence the material quality and throughput of silicon produced by various methods. Particular emphasis is placed on the minority-charge carrier lifetime tau as an indicator of material quality. Purity, rate of growth, cooling rate, microdefect, and macrodefect effects on tau are enumerated. The concept of the tau .T (where T is throughput) product as a measure of process viability is qualitatively introduced. Most of the PV (photovoltaic) silicon work in the last decade has focused on trying to improve the quality ( tau ) of perceived low-cost (high-T) material generation processes. Another avenue for increasing tau .T is to relax intrinsically high- tau processes to improve T. The approaches under development for PV silicon in the US are reviewed with respect to quality and throughput characteristics supplied by their practitioners. They span the entire range of quality/throughput combinations, and a number of them show potential for silicon/based PV power generation systems.<
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