Defects in Epitaxially Grown Silicon Wafers Causing Lifetime Patterns

Epitaxially grown silicon wafers (EpiWafers) have the potential of gaining high electrical quality while production costs can be significantly reduced compared to conventional wafers. High efficiencies are already reported for solar cells made of EpiWafers yet defects originating from the specific production sequence are limiting their quality. Photoluminescence imaging shows line patterns of high recombination activity. A further reduced lifetime is visible in square shaped features often positioned at crossing points of the lines. Those features correspond mainly to stacking faults with polycrystalline inclusions, similar square shaped features beside lines to regular stacking faults. Micro photoluminescence measurements reveal that the lines consist of agglomerations of spots with high recombination activity. In the areas with those spots threading dislocations can be found on defect etched samples in a number exceeding the number of spots. We explain all observations by dislocation mediated impurity aggregation and precipitation.