Individual threading dislocations were identified in relaxed compositionally graded structures by means of simultaneous topographic and photo-response imaging. The threading dislocations were associated with shallow depressions in surface morphology and with a 5 to 10% reduction in photo-response as compared with defect-free regions. The average spatial extent of the reduction in photo-response was 0.66; which was larger than the associated morphology. The results also demonstrated the applicability of near-field scanning optical microscopy to the characterization of electrically active defects. The spatial resolution was 10 times higher than that of conventional optical techniques.

J.W.P.Hsu, E.A.Fitzgerald, Y.H.Xie, P.J.Silverman: Applied Physics Letters, 1994, 65[3], 344-6