Direct experimental observation of the local electronic structure at threading dislocations in metalorganic vapor phase epitaxy grown wurtzite GaN thin films

The electronic structure of pure edge threading dislocations in metalorgani c vapor phase epitaxy grown wurtzite GaN thin films has been studied direct ly by atomic resolution Z-contrast imaging and electron energy loss spectro scopy in a scanning transmission electron microscope. Dislocation cores in n-type samples grown in N-rich conditions show no evidence for the high con centration of Ga vacancies predicted by previous theoretical calculations. Nitrogen K-edge spectra collected from edge dislocation cores show a sudden and significant increase in the intensity of the first fine-structure peak immediately above the edge onset compared to the bulk spectra. The origin of this increase is discussed. (C) 2000 American Institute of Physics. [S00 03-6951(00)03404-5].