Samples which were grown by means of selective area epitaxy and subsequent lateral overgrowth exhibited sharply peaked anisotropic structures which were in the form of hexagonal pyramids and ridges. A study of radiation which was centered on 550nm (the yellow band) indicated that the emission arose mainly from the apex regions of the pyramids and ridges. Transmission electron microscopy showed that the apex region was nearly dislocation-free, and that dislocations clustered at the vertical growth core region. The spatial separation of the dislocations and optical emissions indicated that the yellow-band emission had no direct relationship to dislocations. The observation of yellow-band emission which was strongly localized in the apical regions of both types of structure, and the tendency of impurity species to concentrate in these areas, suggested that it arose from impurity states. The most likely candidate was a complex which comprised a vacancy, VGa, plus Si or O.

Impurity States were the Origin of Yellow-Band Emission in GaN Structures Produced by Epitaxial Lateral Overgrowth X.Li, P.W.Bohn, J.J.Coleman: Applied Physics Letters, 1999, 75[26], 4049-51