Observation of dislocations in strain-relaxed silicon-germanium thin films with flat surfaces grown on ion-implanted silicon substrates

Strained Si grown on a relaxed SiGe layer is an attractive material because of its potential for high carrier mobility. We considered that the ion-implantation technique is useful in order to form the relaxed SiGe because the distribution of lattice defects can be accurately controlled. We implanted Ar ion into Si substrates and then grew 100-nm-thick Si _0.8Ge _0.2 at 500°C by the solid source molecular beam epitaxy method. Next we annealed specimens at 900°C. The microstructure of SiGe/Si was investigated by transmission electron microscopy, and the strain relaxation by Raman spectroscopy and X-ray diffractometry. When the Ar-ion implantation energy and ion dose were 25keV and 1 × 10 ¹⁵ cm ^-2, respectively, we succeeded in forming highly relaxed SiGe thin film with a dislocation-free flat surface. It was revealed that dislocations, which are necessary for stress relaxation, formed loops and were localized around the interface of the SiGe and the Si substrate.