m-Line Frank–Shockley Partial Dislocations in Wurtzite GaN: Atomistic Calculations and High Resolution Electron Microscopy Imaging

High Resolution Image Download MS PowerPoint Slide Frank–Shockley partial dislocations, with lines parallel to the ⟨101̅0⟩ direction, were studied in wurtzite GaN using atomistic calculations, based on density functional theory, and high resolution scanning transmission electron microscopy. Two types of dislocations were considered, that is, mixed 55° and 73°, with core configurations in their vacancy and interstitial variants of both gallium or nitrogen polarity. The core configurations of the mixed 55° dislocation have a structure with a 7-atom ring, involving both gallium and nitrogen dangling bonds, associated with shallow gap states. The core configurations of the mixed 73° dislocation with gallium polarity have a 3/5-atom ring structure, whereas those with nitrogen polarity have a structure with a 6-atom ring. These core configurations were found to be associated with both shallow and deep gap states, where the latter are due to either Ga–Ga bonds or interacting nitrogen dangling bonds. It was demonstrated that a direct discrimination between vacancy and interstitial core variants of the same partial dislocation, in a high resolution transmission electron microscopy observation, is impossible along the m- direction, unless the sample is rotated by ± 30° around the ⟨0001⟩ axis. This rotation reveals the I1 basal stacking fault, enabling its location to be determined in relation to the extra half-plane associated with the c /2 component. It also allows the core variant of the partial dislocation to be determined. Knowledge of the core structures of the m -line Frank–Shockley partial dislocation allowed for the decryption of the dissociation of the a + c edge dislocation, observed by high-resolution scanning transmission electron microscopy, which is involved in the relaxation of strain at the technologically relevant InGaN/GaN interfaces.