The evolution of surface roughness and the subsequent plastic relaxation mechanisms have been studied by transmission electron microscopy (TEM) as a function of the thickness of highly strained In0.30Ga0.70As layers on GaAs(001). The following stages have been observed: formation of coherent islands, coalescence of islands, and nucleation of dislocations at the troughs of the surface ripples. Dislocations are thus systematically generated where the highest stress concentrations are expected, according to recent theoretical predictions. It is the first time such a plastic relaxation mechanism has been observed in highly strained semiconductor heterostructures.

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