In-situ observations of misfit dislocation motion in AlSb/GaSb dislocation filter layer structures

The dislocation dynamics in epitaxially strained GaSb/AlSb/GaSb heterostructures grown on a Si(001) substrate via molecular beam epitaxy have been studied by means of scanning transmission electron microscopy. The 100 nm-thick AlSb layer – intentionally inserted as dislocation filter – is partially relaxed by bending pre-existing threading dislocations of the GaSb buffer into the interface with AlSb, creating a complex network of misfit dislocations. In addition to the expected misfit dislocation lines along the orthogonal <110> directions, irregular curved lines are also detected. Plan-view lamellae of the as-grown heterostructure were annealed in-situ in the microscope at temperatures well above the growth temperature to observe the propagation and interaction of the dislocations in real time. It was found that the (thermally activated) motion of misfit dislocations occurs independently of their Burgers vectors within the interface plane, which is not one of the primary slip systems of zinc-blende crystal structure, and without affecting the threading dislocation configuration in the filter layer. This unusual dislocation motion at this later stage of plastic relaxation (already 50% of lattice mismatch is relieved in the as-grown heterostructure AlSb layer) can only be explained by a non-conservative dislocation climb process on the one hand, and a vacancy-assisted slip on the other hand as it was recently discovered using molecular dynamics modeling. The results provide deeper insights into the thermal activation of dislocations in epitaxially strained systems and reveal potential for re-examining the conditions of those epi-layers as dislocation filters .