Strain-relaxation mechanisms of SiGe layers formed by two-step growth on Si(0 0 1) substrates

We have investigated the relationship between strain-relaxation behaviors and dislocation structures in SiGe layers on Si(0 0 1) substrates grown by the two-step stain-relaxation procedure. From the plan-view transmission electron microscopy (TEM) observation, three kinds of dislocation structures at the SiGe/Si interface can be observed, reflecting the propagation process of 60 deg. dislocations in the SiGe layer. Threading dislocations in the strain-relaxed SiGe layer observed in the plan-view TEM image show the correspondence to pit morphologies formed on the surface detected by atomic force microscopy. In samples after the two-step growth, the degree of strain-relaxation measured by X-ray diffraction is found to be larger than that estimated from dislocation separations at the SiGe/Si interface measured from the TEM images and the [1 1 0] edge component of Burgers vector of the 60 deg. dislocation. This indicates that additional factors other than the [1 1 0] edge component of Burgers vector of the 60 deg. dislocation also play a role in relaxing the strain along the [1 1 0] direction in the SiGe buffer layer