Strain relaxation and induced defects in SiGe thin films grown on ion-implanted Si substrates

Strained Si has been attracting attention as a new material that has high carrier mobility. Such strained Si can be produced by epitaxial growth on strain-relaxed SiGe grown on a Si substrate, because SiGe has a larger lattice constant than Si. It is important to fabricate a highly relaxed SiGe buffer layer. We consider that defect distribution can be controlled and that the highly relaxed SiGe buffer can be prepared by ion implantation into the substrate. We carried out ion implantation under several conditions. Then, Si0.7Ge0.3 films with a thickness of 100 nm were grown at 650degreesC on the implanted substrates by the solid-source molecular beam epitaxy method (MBE). The strain relaxation of SiGe films was estimated by Raman spectroscopy. The crystallinity was observed by transmission electron microscopy. In the case of an implantation energy of 50 keV and an ion dose of 5 x 10(13) cm(-2), the dislocation density was low and the relaxation was lower than 50%. In the case of 1 x 10(15) cm(-2) or a higher ion dose, the SiGe film became partially polycrystall line. In contrast, we succeeded in forming an approximately 80%-relaxed single-crystal SiGe thin film when the ion dose was 5 x 10(14) cm(-2). This means that ion implantation into the substrate before MBE growth is a good method of controlling defect introduction and producing relaxed single-crystal SiGe thin films.