Atomic structures of twin boundaries in GaN

The atomic structures of (1011), (1012), and (1013) twins in the wurtzite gallium nitride have been studied by atomic computer simulation using an empirical interatomic potential of the Stillinger-Weber type. Distinct reference structures have been considered with respect to the type planes of the two adjacent crystals. The atomic structure of the twin boundaries was found to be dependent on these starting configurations. The lowest energy structure of the (1013) boundary is composed by 6-coordinated channels whereas the (1012) twin boundary can present three distinct structures composed by either 4-, 8-, or 5/7-coordinated channels separated by 6-coordinated channels. In both cases there is a mirror symmetry relating the two crystals. In the (1011) twin the two structures of low energy do not exhibit mirror symmetry and present corrugated boundary planes.