ABSTRACT
We analyse the core structure of a-type threading dislocations in GaN by transmission electron microscopy. For image simulation we use essentially four different core structures (the full core, open core, Ga-vacancy and N-vacancy structure), which have been calculated by an ab-initio density functional theory based method. The comparison of through focus series with image simulations indicates a Ga-vacancy core structure to be present in samples grown under N-rich growth conditions. Spatially and spectrally resolved cathodoluminesence in the transmission electron microscope shows these dislocations to act as non-radiative recombination centres.
