Calculations of optical absorption based on a model of a single crystal containing spatially periodic compositional variations are presented. These variations can contribute a significant soure of systematic error in the analysis of composition by optical or surface techniques. The model is most appropriate for melthyphen;grown crystals and in particular for striated semiconductor crystals, and the surface concentration profile which it predicts is confined by comparison with a published xhyphen;ray topographic study of silicon. Implications of the results for optical absorption studies of impurities in silicon crystals are discussed and it is shown that significant measurement errors may occur.
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