Electron microscopy of nanoledges at the (001)InAs/(001)GaAs interface for an approximate orientation relationship

The structure of the InAs/GaAs(001) epitaxial heterointerface is observed by high resolution electron microscopy (HREM) along [110] when there is a slight long range angular misorientation between the two crystals around the common observation direction. The lattice misfit and the local misorientation (ε = 6.9%, Δθ = 1.5°) are simultaneously accommodated via a non planar and non pseudoperiodic distribution of defects involving usual 90° and 60° dislocation cores and yet unreported nanoledges with exotic Burgers vector contents. One of these nanoledges is five (001) planes high and has a total Burgers vector content equal to (1/6)[331]. Its local elastic field has been analysed in terms of ribbon-like Somigliana dislocations. It depends on ε, Δθ and its nanoledge height. Comparisons between the experimental and calculated tunnel positions between atom columns are given to appreciate the validity of the model.