Strained Si was attracting attention as a new material that had high carrier mobility. Such strained Si could be produced by epitaxial growth on strain-relaxed SiGe grown on a Si substrate, because SiGe had a larger lattice constant than Si. It was important to fabricate a highly relaxed SiGe buffer layer. It was considered that the defect distribution could be controlled and that a highly-relaxed SiGe buffer could be prepared by ion implantation of the substrate. Implantation was carried out under various conditions. Then, Si0.7Ge0.3 films with a thickness of 100nm were grown at 650C onto the implanted substrates by using the solid-source molecular beam epitaxy method. The strain relaxation of SiGe films was estimated by means of Raman spectroscopy. The crystallinity was measured by transmission electron microscopy. In the case of an implantation energy of 50keV and a dose of 5 x 1013/cm2, the dislocation density was low and the relaxation was lower than 50%. In the case of 1015/cm2 or higher doses, the SiGe film became partially polycrystalline. In contrast, it was possible to form an approximately 80%-relaxed single-crystal SiGe thin film when the dose was 5 x 1014/cm2. This implied that ion implantation into the substrate before molecular beam epitaxial growth was a good method for controlling defect introduction and producing relaxed single-crystal SiGe thin films.

Strain Relaxation and Induced Defects in SiGe Thin Films Grown on Ion-Implanted Si Substrates. J.Yamanaka, K.Sawano, K.Nakagawa, K.Suzuki, Y.Ozawa, S.Koh, T.Hattori, Y.Shiraki: Materials Transactions, 2004, 45[8], 2644-6