Climb/glide dislocation sources at low-misfit Gex Si1-x -Si(001) interfaces
Detailed analysis of Burgers vectors and line directions has been carried out on three types of dislocation defect (called X, Y and single loops) formed in lowmisfit GexSi1-x/Si(001) heterostructures, grown under conditions of planar interface growth. The X and Y defects originate from small prismatic vacancy half-loops nucleated at visible precipitates at the strained-layer-Si substrate interface. The single-loop defects also originate from small vacancy character half-loops usually nucleated at the interface but also sometimes within the strained layer. After growth, none of the dislocations lies in glide planes, and all three dislocation structures have to be transformed into glissile configurations before they can generate strain-relieving dislocations. The mechanism controlling this sessile/glissile transformation is climb by vacancy absorption. This corresponds to the nucleation stage for the generation of misfit dislocations observed by Houghton and is consistent with the experimental results of Stirpe et al. who found a reduction in thenucleation rates during rapid thermal anneals after Si irradiation at room temperature of the as-grown samples. The paper discusses the driving forces controlling the formation of the observed structures, and their sessile-glissile transformation.