This paper reports results of microstructural investigations of block cast multicrystalline silicon materials deliberately contaminated with iron and copper impurities from the melt. Electron microscopy techniques have been used to study interactions of grain boundaries, light element impurities such as nitrogen and oxygen, and metal impurities. The key to get access to extended defects typically present in a small density is the recently developed in-situ EBIC/FIB approach to sample preparation.
Special attention is drawn to oxygen and nitrogen containing precipitates at grain boundaries and resulting secondary defects. Strong accumulation of copper impurities is observed which is related to reduced excess carrier lifetimes in these regions. It is shown that copper silicide precipitation mainly accounts for local dislocation networks with a high recombination activity. These observations provide evidence that decoration of grain boundaries with light element contaminants leads to efficient nucleation of metal impurity precipitates. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)