Ab initio study of symmetric tilt boundaries in ZnO - art. no. 045410

The atomic and electronic structure of the [0001]/((12) over bar 30) Sigma = 7 symmetric tilt boundary in ZnO has been investigated by an ab initio pl ane-wave pseudopotential method within the local-density approximation. Two types of equilibrium geometries are obtained with similar boundary energie s. Atomic arrangement is largely reconstructed to vanish dangling bonds in one configuration, whereas the other shows small bond distortion but has da ngling bonds at the boundary core. The balance between the energies for def orming atomic arrangements and vanishing dangling bonds should be significa nt in determining the boundary energies. The electronic structure of the gr ain boundaries is discussed with a special interest in the relationship wit h the bond disorder. Owing to the bond distortion and/or the presence of th e dangling bonds, localized states form mainly at the lower valence band an d the bottom of the upper valence band. On the other hand, the electronic s tates in the vicinity of the band gap are not significantly affected by the bond disorder. Deep electronic states are not generated in the band gap ev en for the configuration with dangling bonds. This behavior can be generall y explained by the band structure intrinsic to ZnO.