Interfacial atomic structure and electrical activity of nano-facetted CSL grain boundaries in high-performance multi-crystalline silicon

The interfacial structure of coincidence site lattice grain boundaries in multi-crystalline silicon plays a decisive role in their electrical behavior as revealed by high-resolution (scanning) transmission electron microscopy investigations. Considering only the global misorientation of the adjacent grains can lead to a false correlation between the structural and electrical properties of a grain boundary. The grain boundary habit plane as well as local deviations in the orientation and misorientation that induce additional structural defects need to be analyzed. Indeed, a Sigma 9 {221} grain boundary, presenting a perfect coincidence and periodicity at the atomic scale, appears electrically non-active. However, a grain boundary also identified as Sigma 9 {221} at the mesoscale is found to be composed of nano-sized triangular structures involving Sigma 3 {111} and Sigma 3 {112} facets at the nano-scale. This leads to the formation of grain boundary kinks and triple junctions that induce additional structural defects and turn the overall grain boundary interface electrically active. The possible origin of such a grain boundary dissociation, as well as its impact on the electrical activity, is discussed.