Studies of electrically active defects in relaxed GeSi films using a near-field scanning optical microscope

We study the electrical activity of threading dislocation defects in relaxed GeSi films with a novel, high-resolution optical technique. A near-field scanning optical microscope is used to measure spatially resolved photoresponse while simultaneously imaging the surface topography. We have convincingly established that shallow topographic depressions in these films are electrically active threading dislocations. The apparent sizes of the dislocations in the photovoltage images are in agreement with estimates based on the junction geometry and the near-field optical excitation spot size. We can clearly observe photoresponse changes at ≤100 nm lateral scale, a tenfold improvement from far-field optical techniques. This higher resolution is due to reduction of the excitation volume and of the carrier lifetime near defects.