Prediction of dislocation density in AlN or GaN films deposited on (0001) sapphire

The origin of threading dislocations (TDs) in nitride films is not completely understood but it is well established that they degrade the film properties. This work investigates the assumption that they arise from the interface between the film and sapphire substrate owing to small in-plane rotations between nitride domains. Bollmann’s formalism is first used to determine the characteristics of dislocations at the nitride film/sapphire interface that compensate both for the parametric misfit and a small in-plane rotation of the film as frequently observed. It is shown that the dislocation density and line direction depend on the rotation angle. When islands grow and coalesce in the nucleation layer, some interfacial dislocations orientate along [0001] in the boundaries between domains and transform to so-called TDs. The amount of TDs lying in the boundaries between nitride domains is calculated as a function of the rotation angle. Estimations of TD density in the nucleation layer are deduced for a range of domain sizes and compared with experimental values of the literature.