Density functional plane-wave pseudopotential calculations were performed on two high-angle grain boundaries in ZnO which were decorated with various quantities of Bi. The results showed that both grain boundaries, which had significantly different structures, could accommodate up to about 30% of substitutional Bi in qualitative agreement with experimental observations. The segregation of Bi to the boundaries results in local charge accumulation which was localized within Bi-Bi bonds or on Bi atoms. The charge accumulation in both boundaries results in fluctuations in potential across the interface and the formation of a barrier to electron transport. However, there was no evidence for a deep acceptor level usually associated with the Schottky barrier model. The present results suggested an alternative mechanism in which electrons were trapped in Bi-Bi bonds and depleted in an external field. However, defect states had not been ruled out and it was suggested that if they exist they were caused by more complex defects than those considered here.

Charge Accumulation and Barrier Formation at Grain Boundaries in ZnO Decorated with Bismuth. H.S.Domingos, J.M.Carlsson, P.D.Bristowe, B.Hellsing: Journal of Physics - Condensed Matter, 2002, 14[48], 12717-24