  In this work, doping-defect interactions relevant to self-compensation in
p-type GaN were investigated using atom probe tomography. The 3D visualization
of ion distribution revealed the formation of spherical Mg-rich clusters and
the segregation of Mg dopant towards dislocations in MOCVD-grown GaN:Mg.
Impurities related to self-compensation, such as oxygen and hydrogen, were
identified and detected adjacent to Mg-rich dislocations. Crystal stoichiometry
around the defect regions was investigated to understand how the defects can
serve as traps and influence dopant diffusion. Non-stoichiometric regions of
N:Ga were found adjacent to Mg-rich dislocations and overlapping with some
Mg-rich clusters, indicating potential traps. Variations in N:Ga were not
proportional to the Mg content, suggesting that the microfeatures (clusters and
dislocations) interact differently with local chemistry. Techniques for
defining the quality of an APT experiment through invalidation of artifacts are
also demonstrated. Mg-rich defects and variations in N:Ga were found to be
independent of artifacts related to the evaporation field in APT.
