Low-temperature strain relaxation in SiGe/Si heterostructures implanted with Ge+ ions

Pseudomorphic Si0.76Ge0.24/Si heterostructures grown by molecular beam epitaxy were implanted with Ge+ ions at 400 °C in such a way that an ion-damaged region was located below the SiGe/Si interface. The effect of Ge+-ion irradiation on strain-relaxation rate and defect structure in the heterostructures was studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and low-temperature photoluminescence (PL). It was found that annealing at a temperature as low as 600 °C resulted in very high degree of strain relaxation, while density of threading dislocations was low (<105 cm−2). The enhanced strain relaxation was attributed to the fact that complexes of point defects produced by the heavy-ion implantation at the elevated temperature acted as nucleation sites for dislocations. The obtained results allowed us to propose a method for preparation of thin highly relaxed SiGe layer with low threading dislocation density and good surface morphology.