Correlation between the defect structure and the residual stress distribution in ZnO visualized by TEM and Raman microscopy

A deep understanding of the appearance and distribution of residual stresses in ZnO is of high importance as mechanical stresses directly influence its electrical and optical properties. In this paper we investigate the correlation between residual stresses and the plastic deformation below a micro indent placed on a prism plane of a ZnO single crystal. The residual stress field was mapped by means of confocal Raman microscopy. A cross section was studied by transmission electron microscopy and cathodoluminescence to visualize defect structures. In the Raman measurement bands of residual stresses were observed. The analysis of the defect structure showed that the residual stress distribution corresponds to crystallographic directions which are known to be the preferred directions for plastic deformation. The preparation of lamellae by FIB strongly alters both the residual stress state as well as the defect density caused by plastic deformation.