Analysis of [0001] tilt grain boundaries in GaN

transmission electron microscope studies of GaN epitaxial layers on sapphire show a very high density of threading dislocations forming grain boundaries. The atomic structure of <0001> tilt grain boundaries was analysed by high resolution transmission electron microscopy (HREM). Energetics calculations were also performed with the modified Stillinger-Weber potential to take into account the wrong bonds Ga-Ga and N-N in the core of the defects. Low-angle and high-angle grain boundaries may form and their atomic structures have been analysed by HREM. Energetics calculations have been performed on <0001> tilt grain boundaries described in terms of structural units. The construction of the grain boundary is based on the coincidence site lattice (CSL) model, which states that a CSL grain boundary may be described with regularly spaced dislocations. HREM experiments were carried out along the [0001] zone axis using a Topcon 0002B electron microscope operating at 200 kV with a point to point resolution of 0.18 nm.