X-ray topography contrast from edge dislocations in ZnGeP2 single crystals

Abstract

X-ray topography images in the form of contrast rosettes from edge dislocations of the \{ {\bar 110} \}\langle {110} \rangle slip system in ZnGeP2 single crystals, obtained under different diffraction conditions, are identified and interpreted. To analyze and model the dislocation images, a semi-phenomenological theory of contrast is applied. The simulation of images of edge dislocations under Borrmann effect conditions was carried out in cases when the diffraction vector was parallel or perpendicular to the slip plane of the dislocation. In both cases, the main part of the experimental image is formed because of waveguiding of Bloch waves in the regions of tension and compression of the lattice on either side of the slip plane. Additional image details arise through relaxation of stresses at the exit surface. Since the color of all lobes of the contrast rosette is related to the sign of the deformation, the location of the dislocation half-plane is unambiguously determined. Thus, from the form of the rosette image, it is possible to obtain the slip plane, the magnitude and sign of the Burger's vector, and the direction of the dislocation line.