Boron-related minority-carrier trapping centers in p-type silicon

Photoconductivity-based measurements of recombination lifetimes in multicrystalline silicon are often hampered by carrier trapping effects, which cause a characteristically large relative increase in the photoconductance. Single-crystal p-type float-zone wafers of varying resistivities were cross contaminated with multicrystalline wafers that exhibited such trapping. A proportion of the impurities present in the multicrystalline samples was found to effuse into the float-zone wafers, where they act as both recombination centers and trapping centers. By the application of a simple theoretical model, the trap density in the float-zone samples was determined, and found to be directly proportional to the boron-dopant concentration. These results suggest that the trapping centers are caused by boron-impurity pairs.