Mismatch Dislocation Nucleation and Propagation in Si/Si1−xGex Heterostructures

Abstract

AbstractMismatch dislocation nucleation mechanisms have been studied in the Si/Si1−xGex materials system using the simple application of a selective, defect revealing chemical etch, followed by standard Nomarski optical microscopy. The onset of mismatch dislocation formation was found to occur at a point just above the equilibrium critical thickness limit set by Matthews and Blakeslee (he). However, the bulk of the material remained coherently strained until it reached a metastable critical thickness (hm), where hm >> he. Nomarski micrographs clearly show the initiation of the mismatch dislocation network and the major dislocation multiplication processes that occur at hm. At low levels of relaxation the individual mismatch dislocation half loops can be identified, and we show, for the first time, the evolution and propagation of these dislocations from nucleation sites in the epilayer. A dramatic decrease in hm has been observed for epilayers that contain a large number of intrinsic dislocations.The mismatch dislocations were found to nucleate at extended defects and further relaxation occurred by dislocation multiplication at these sites. This gave rise to a non-uniform distribution of mismatch dislocations, with patches of highly relaxed material surrounded by material that was still coherently strained.