Highly localized electron energy loss spectroscopy was carried out by using scanning transmission electron microscopy in the energy loss regime at the band-gap, and at the N near-edge structure of cross-sectional structures. An attempt was made to determine changes in the intensity distribution and the onset energy of inelastic scattering (bandgap-related energy) of hetero-interfaces, quantum wells and dislocations. First-principles calculations, performed within the local-density approximation to density-functional theory, were used to simulate low electron energy-loss spectra. Tests in which these were compared with experimental low-loss spectra revealed good agreement of the position and shape of the spectral features. A study was made of the scattering intensity around the onset and the position of the onset energy in locations along the projection lines of isolated dislocations. Low-loss spectrum calculations of dislocated regions revealed band-gap states which were associated with all dislocation types in GaN. The related pre-bandgap scattering intensity, at 3.3eV, of the simulated spectra (for the full core screw dislocation in particular) was in qualitative agreement with experimental findings. An

absorption peak at 2.4eV, which was found in certain regions in the vicinity of dislocations was not reproduced by the calculations. It was therefore thought to be produced, not by the dislocation but by impurity segregation.

Band-Gap Related Energies of Threading Dislocations and Quantum Wells in Group-III Nitride Films as Derived from Electron Energy Loss Spectroscopy. A.Gutiérrez-Sosa, U.Bangert, A.J.Harvey, C.J.Fall, R.Jones, P.R.Briddon, M.I.Heggie: Physical Review B, 2002, 66[3], 035302 (10pp)