NUCLEATION, GLIDE VELOCITY AND BLOCKING OF MISFIT DISLOCATIONS IN SIGE SI/

Relaxation of strained layer systems is still not well understood. It is time dependent and changes considerably for samples with different growth history. This has to be discussed in terms of nucleation, glide velocity and blocking of misfit dislocations. We have investigated th ese phenomena at samples with SiGe layer thicknesses ranging from 60 n m up to 120 nm grown by molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) by means of X-ray topography. The samples were annea led at temperatures between 500 degrees and 600 degrees C. Nucleation of misfit dislocations is heterogeneous and the rate is obviously depe ndent on layer strain and thickness. A quantified nucleation rate was not yet accessible, mainly due to the preferential formation of disloc ation bundles. The propagation velocities of misfit dislocation segmen ts were measured during annealing by means of synchrotron radiation pl ane wave topography (reflection geometry). The values agree well with theory and there is no evidence that they depend on growth regime. It is shown that the interaction of propagating misfit dislocations with crossing ones may lead to blocking or cross slip in different glide sy stems. These results are corroborated by investigations with atomic fo rce and transmission electron microscopy.