Distribution of Grain Boundary Types in Multicrystalline Silicon

Grain boundary properties and dislocation density were investigated for an ingot produced in a pilot scale directional solidification furnace. The material is characteristic of traditional multicrystalline silicon, different from the current trend of producing small grained material, which has significantly lower dislocation density. Large, twinned grains were present from the bottom part of the ingot, and grain size increased as growth proceeded. While the total density of grain boundaries decreased, the fraction of all types of grain boundaries remained stable. The ingot developed extensive dislocation networks towards the top, covering large areas in the range of several cm2. Together with these regions also large regions with very low dislocation density exists. The characteristics of grain boundary types and their evolution during growth in this, former generation of multicrystalline silicon is a useful tool for evaluating product and process parameters of high performance multicrystalline silicon, although no direct comparison to such material has been performed in this work.