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Determination of the minority carrier lifetime in crystalline silicon thin-film material

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ABSTRACT

The effective minority carrier lifetimes on epitaxial silicon thin-film material have been measured successfully using two independent microwave-detected photoconductivity decay setups. Both measurement setups are found to be equally suited to determine the minority carrier lifetime of crystalline silicon thin-film (cSiTF) material. The different measurement conditions to which the sample under investigation is exposed are critically analyzed by both simulations and measurements on a large number of lifetime samples. No systematic deviation between the lifetime results from different measurement setups could be observed, underlining the accuracy of the determined lifetime value. Subsequently, a method to separate the epitaxial bulk lifetime and the total recombination velocity, consisting of front surface and interface recombination between the epitaxial layer and the substrate, is presented. The method, based on different thicknesses of the epitaxial layer, is applied to all batches of this investigation. Each batch consists of samples with the same material quality but different epitaxial layer thicknesses whereas different batches differ in their material quality. In addition, the same method is also successfully applied on individual cSiTF samples. From the results, it can be concluded that the limiting factor of the effective minority carrier lifetime for the investigated solar-grade cSiTF material is the elevated recombination velocity at the interface between epitaxial layer and the substrate compared with microelectronic-grade material. In contrast, the samples cannot be classified into different material qualities by their epitaxial bulk lifetimes. Even on multicrystalline substrate, solar-grade material can exhibit high epitaxial bulk lifetimes comparable to microelectronic-grade material. Copyright © 2012 John Wiley & Sons, Ltd.

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