Octahedral voids were found in the bulk of wafer samples by using infra-red tomography. These voids were often of twin type and were about 100nm in size. A 2nm-thick layer existed on the side-walls of the void defects. It was suggested that this 2nm-thick layer consisted of SiOx. It was concluded that the void structure formed via the agglomeration of vacancies during ingot growth.

T.Ueki, M.Itsumi, T.Takeda: Applied Physics Letters, 1997, 70[10], 1248-50