The [10-10] edge dislocation in the wurtzite structure: A high-resolution transmission electron microscopy investigation of [0001] tilt grain boundaries in GaN and ZnO

A detailed topological analysis and atomic structure investigation of [0001] tilt grain boundaries (GBs) in GaN and ZnO has been carried out using atomistic simulation and high-resolution transmission electron microscopy (TEM). The analysis of Sigma 7 asymmetric GBs in GaN, shows that they are only made of well separated a = 1/3<11<(2)over tilde>0> edge dislocations based on the three basic structural units: 4-, 8- and 57-atom rings. In this compound, the Burgers vectors adapt their orientations in order to accommodate the rotation angle of the grain boundary. However, in ZnO, the topology of such GBs is shown to comprise two types of dislocation contents: one of them follows the behavior of GaN in which individual a edge dislocations are dominant; the second is the [10 (1) over bar0] edge dislocation which comes out as a distinct structure with a large core as pointed out in the Sigma 13 (27.8 degrees/32.2 degrees) GBs. The determined low-energy configuration of this [10 (1) over bar0] dislocation is made of connected 4-8-6-atom rings in agreement with an early proposal of its possible geometrical model. The electronic structure of these GB dislocations shows the evidence of a deep state induced above the valence band edge in all the structural units comprising the 57-atom ring. In contrast to previous reports which solely ascribed such states to dangling bonds, this one is ascribed to the cooperative effect of Zn-Zn wrong bonds and broken O-O bonds inside the 57-atomic ring. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.