Site-specific focussed ion-beam milling was used to prepare cross-sectional transmission electron microscopic sample foils from a range of epitaxial thin films. The high threading-defect densities which were associated with hetero-epitaxial GaN/sapphire samples prohibited the unambiguous identification of hillock nucleation events. However, inversion domains were identified at the core of hillocks which formed on chemical vapour-grown GaN on N-polar bulk GaN substrates. It was concluded that residual contamination which arose from KOH chemomechanical polishing was responsible for inversion-domain nucleation.

A Transmission Electron Microscopy Investigation of Buried Defect Sources within Epitaxial GaN. P.D.Brown: Journal of Physics - Condensed Matter, 2000, 12[49], 10195-203