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Diffusion length from spatial resolution of photoluminescence in silicon

: Daub, E.; Klopp, P.; Kugler, S.; Würfel, P.; Schindler, R.; Warta, W.

12th European PV Solar Energy Conference '94. Proceedings
European PV Solar Energy Conference <12, 1994, Amsterdam>
Fraunhofer ISE ()

Values of the diffusion length of minority carriers in unprocessed single crystalline or polycrystalline silicon are obtained from the variation of the photoluminescence intensity as a function of the distance of an illuminating laser spot from a plane of high recombination by Light Beam Induced Luminescence (LBIL). The luminescence intensity which under low injection conditions is proportional to the minority carrier density, is modeled in a 3-dimensional analysis considering recombination in the bulk, at the front and back surfaces and at an edge or a grain boundary.
This contact-free method is demonstrated on an unprocessed bare polycrystalline silicon wafer, for which an image of the luminescence intensity shows the distribution of the minority carriers. The spatial variation of the luminescence is in excellent agreement with LBIC-results of a solar cell, which had been processed from an adjacent wafer of the same polycrystalline silicon block exhibiting the same pattern of grains and grain boundaries.