Near-field scanning optical microscopy imaging of individual threading dislocations on relaxed GexSi1−x films

We have identified individual threading dislocations on relaxed, compositionally graded GexSi1−x structures through simultaneous imaging of topography and photoresponse. The threading dislocations show shallow depressions in surface morphology and a 5%–10% reduction in photoresponse compared with the defect-free regions. The average spatial extent of the reduced photoresponse is (0.66±0.16) μm, which is larger than the associated morphology. This study further demonstrates the application of near-field scanning optical microscopy to characterization of electrically active defects. The spatial resolution is ten times higher than conventional optical techniques.