Relaxation of low mismatched semiconducting layers by misfit dislocations : models and observations

Abstract
the very first stages of the relaxation process of low mismatched systems GeSi/Si, Si/Si(As), Ge(B)/Ge and specially GaAs/Ge, are considered. X-ray topography observations are performed and allow the measurement of the critical layer thickness.Misfit dislocations first form by glide of grown-in substrate dislocations. They elongate not only in the interface but also in the neutral plane. The observed hairpin configuration reveals that plastic deformation of the substrate is involved in relaxation. GeSi/Si films metastability can be explained directly by kinetic arguments. In the case of GaAs/Ge, in addition to the kinetics of the nucleation and development of dislocations, the misfit evolution with temperature has to be taken into account. A possible mechanism for the emission of new misfit dislocations, whereby relaxation continues, can be related to stacking faults.