Variations in dislocation density with length in web silicon

We have examined the influence of crystal length on dislocation density in web silicon. The observed variations in dislocation density do not show a consistent pattern. However, the changes do not appear to be cumulative and may be largely determined by the local thermal conditions during growth. We have argued that the majority of dislocations are not replicated during ribbon growth, resulting in non-accumulation. A variety of dislocation configurations are observed by X-ray topography. We have rationalized the preceding observations in terms of dislocation glide caused by thermal gradient-induced stresses.