Dislocation contrast imaged by weak reflections and the complete determination of the Burgers vector

The properties of dark-field diffraction contrast of a dislocation imaged by weak reflections are analysed by experiment and dynamical calculation. Near the centre of the contour of a weak reflection g, the contrast of a dislocation appears as a multiple image and the number of the images is directly related to the magnitude of the inner product g.b (b is the Burgers vector). When departing from the centre of the reflection contour, the main contrast of the dislocation shifts to one side of the real dislocation line depending on the sense of g.b . These properties provide a new method for determining g.b and the Burgers vector, including both its direction and its magnitude. For the first time, multiple images of a single dislocation in a GaAs semiconductor when g.b=1,2,3,4,5 and 6 are observed systematically and the complete Burgers vector is identified by diffraction contrast experiments.