(Invited) Strain Engineering of Si/Ge Heterostructures on Ge-on-Si Platform

Si/Ge heterostructures with high Ge contents have attracted increasing interests for last few decades because of their various high potential applications in the microelectronics industry. Strain engineering is an additional key technology not only for electronic devices with enhanced carrier mobilities but also for photonic devices since efficient light emission can be made possible via strain-induced direct band transition. In addition to the conventional (100) orientation, Si/Ge with a (111) orientation is very attractive owing to the higher electron mobility and applicability to spintronic devices via lattice matched epitaxial growth of high-quality ferromagnetic materials. As well known, however, it is a challenging issue to grow high-quality Ge-rich SiGe layers on the Si platform due to the large lattice mismatch between Si and Ge. Hence, strain engineered Si/Ge heterostructures with high Ge contents have to be created on Ge-on-Si virtual substrates, whereas strain states and crystallinities of the SiGe are expected to be highly influenced by those of the Ge-on-Si. Here, we show recent studies on heteroepitaxy of various Si/Ge heterostructures on Ge-on-Si with various surface orientations and discuss their strain states, stabilities, critical thickness and crystal qualities. Furthermore, their applications to optoelectronic and spin devices are overviewed.