Birgit Ryningen

The microstructure of dislocation clusters in industrial directionally solidified multicrystalline silicon

The microstructure of commonly occurring dislocation patterns in industrial directionally solidified multicrystalline silicon has been systematically studied by light microscopy, electron backscatter diffraction, and transmission electron microscopy. The work has been focused on dislocation clusters on wafers near the top of cast blocks. In near {111} grain surface, dislocation arrays parallel to {110} plane traces are lying in parallel rows of {111} planes inclined to the surface, in mainly 〈112〉30∘ orientation. The dislocation configuration suggests that the microstructure may result from a recovery process. The dislocations formed during crystal growth and cooling have undergone transformations at high temperature in order to achieve low energy configurations for minimization of dislocation and crystal energy.

On the role of stacking faults on dislocation generation and dislocation cluster formation in multicrystalline silicon

The microstructure of highly dislocated stacking fault regions (dislocation density >106 cm−2) in industrial cast multicrystalline silicon has been investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. Our observations indicate that stacking faults form strong barriers to lattice dislocation movement and to the formation of sub grain boundaries. Stepped and curved stacking fault edges appear to generate dislocations. The observations suggest that stacking faults play an important role in the plasticity as well as in the formation of the microstructure of dislocations in multicrystalline silicon.

TEM Characterization of near Sub-Grain Boundary Dislocations in Directionally Solidified Multicrystalline Silicon

A crystal is known to achieve lower energy if lattice dislocations are re-arranged in arrays forming a sub-grain boundary through a recovery process. Interaction of boundary dislocations with glide dislocations is also expected to bring about local equilibrium. In this work, dislocations localised in the vicinity of a sub-grain boundary (mis-orientation ) are studied in detail by transmission electron microscopy in order to determine their source. Contrary to the processes described above, it appears that the sub-grain boundary is the source of these dislocations, which are emitted from some locally stressed parts of the boundary. Several slip systems have been activated along the boundary resulting in high density of dislocations. It appears, further, that dislocation propagation from one or more sources is disrupted by interaction with other dislocations or other defects. The dislocations from various sources will be piled up against the obstacles of the other, resulting in the localization of the dislocations close to the sub-grain boundary