Electron microscope samples were prepared in cross-sectional and plan-view geometry, and investigations were carried out in a dedicated cold field emission scanning transmission electron microscope. The relative dislocation signal strength in both orientations was considered on the grounds of geometrical considerations and, from a comparison with experimental signals, it was deduced that the scattering cross-sections for bulk and dislocation related scattering in the core loss energy regime were similar. The low-loss results suggested that the scattering cross-sections for dislocation-related scattering in the band-gap regime were significantly smaller than that for bulk scattering processes. Also, the localization of scattering events in this energy regime was an order of magnitude less than that in core loss spectroscopy. The experimental low-loss spectra provided evidence for dislocation-related energy states below the band edge, in accordance with the predictions of calculated low-loss spectra. Core excitation losses exhibited dislocation-related changes in the s–pz hybridized states. A peak in the energy range around 2.5eV, which was not related to energy states introduced by the dislocation cores but was presumably due to point defects, increased in strength for measurements towards the thin film surface, and in the vicinity of dislocations.

Electron Energy Loss Studies of Dislocations in GaN Thin Films. U.Bangert, A.Gutiérrez-Sosa, A.J.Harvey, C.J.Fall, R.Jones: Journal of Applied Physics, 2003, 93[5], 2728-35