Diffraction contrast and Bragg reflection determination in forescattered electron channeling contrast images of threading screw dislocations in 4H-SiC

Abstract

The experimental diffraction parameters and contrast features associated with electron channeling contrast imaging (ECCI) are determined by the study of threading screw dislocations (TSDs) in 4H-SiC. The images are recorded by forescatter diode detectors mounted on a commercial electron backscatter diffraction system. ECCI of TSDs penetrating the (0001) surface reveals dark-to-light contrast, the direction of which depends on the acting Bragg reflection, the deviation from the Bragg condition, and the dislocation Burgers vector. Burgers vector identification is confirmed through observations of the rotational direction of atomic step spirals associated with various screw dislocations. Dark “twin-lobed” features are observed when the incoming electron beam exactly satisfies the Bragg condition for various Bragg reflections. The experimentally observed behavior of channeling contrast features for screw dislocations in this study is found to be consistent with transmission electron microscopy diffraction contrast mechanisms.