Strain relaxation induced by He-implantation at the Si1−xGex/Si(100) interface investigated by positron annihilation

Relaxation of 110 nm thick Si0.72Ge0.28 epitaxial layers grown on Si (100) substrate by molecular beam epitaxy have been studied by a variable energy slow positron beam. He-implantation at 18 keV energy and 2–3×1016 ions cm−2 fluence and subsequent annealing has been used to create a defect zone with large cavities in the substrate, at approximately 180–240 nm from the surface, in order to enhance strain relaxation in the SiGe layer. Positrons detected a significant difference in the cavity profile between single implantations with 2×1016 and 3×1016 ions cm−2 fluence. e+ trapping in the SiGe layer and at the interface was found to be below the limit of the resolution of the slow positron technique.