SiGe heterostructure is an important material for both electronic and optoelectronic applications due to their compatibility with existing Si technology. Recently, the growth of fully relaxed, nearly defect-free SiGe alloys has gained considerable attention. However, when the thickness of the SiGe layer exceeds a composition-dependent critical value, the strain has to be partially relaxed by the generation of misfit dislocations at the SiGe/Si interface. Consequently, a high density of threading dislocations extends into the SiGe epilayer. Two methods have been successfully realized to attain epilayers with a low density of threading dislocations, compositionally graded SiGe layers and the SiGe layer of constant composition grown on a low temperature Si buffer (typically at 400 deg C). Even in such case, the threading dislocation density may remain at 10~4-10~6 cm~(-2). Obviously, it is essential to have more or less precise models of dislocation for understanding the strain relaxation mechanism and the influence of dislocations on the properties of materials. In the present paper, the core structure of a dislocation in SiGe layer grown on low temperature Si buffer is revealed at atomic level.
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