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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

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Document pages: 24 pages

Abstract: We present a detailed topological analysis and atomic structure investigation on [0001] tilt grain boundaries (GBs) in GaN and ZnO using atomistic simulation and high-resolution transmission electron microscopy (TEM). Through analysis of ∑7 asymmetric GBs in GaN, GBs are only made of well-separated a=1 3<11‾20> edge dislocations based on the three basic structure units: 4-, 8- and 57-atom rings; and it shows that the Burgers vectors adapt their orientations in order to accommodate the rotation angle of the GBs. In ZnO, the topology of GB is shown to comprise two types of dislocation contents in coincidence site lattice (CSL) formalism: one of them follows the behaviour of GaN in which individual a edge dislocations are dominant; besides the [10‾10] edge dislocation comes to be a distinct structural unit to exhibit a large core while reconstructing the ∑13 (27.8° 32.2°) GBs. The determined low-energy configuration of this [10‾10] dislocation is made of adjacent 4-8-6-atom rings in a clear agreement with a very early proposal of its possible geometrical model. The investigation of electronic structure of all the structural units based on the lowest energy core structures points out that a deep state induced above the valence band edge mainly results from the constituent of 57-atom ring. In contrast to previous report which ascribed it only to the dangling bond, it may come from the cooperative effect of Zn-Zn wrong bonds and broken O-O bonds inside the 57-atomic ring.

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