Abstract
Misfit dislocations have been observed in some AlGaAs/GaAs/AlGaAs thick double-heterostructures grown by molecular beam epitaxy, and analysed using X-ray reflection topography. In some cases, only pure edge segments have been observed in a particular 〈110〉 direction parallel to the interface plane. These observations emphasize the role of dislocation sources for strain relaxation. A model of edge dislocation formation is proposed, based on the existence of particular sources located at an interface and able to generate simultaneously two dislocation half-loops in two different {111} glide planes.