The accelerated development of the strained Sil-xGex/Si(001) arises from its fortuitous material properties. A completely miscible Si/Ge alloy with a moderate lattice mismatch to Si provides the additional advantages of heterostructure devices—a concept with tremendous success in group III/V optoelectronics and high-speed devices and circuits. SiGe alloys and heterojunctions extend the performance of future Si-based devices. The strain because of the incorporated Ge in the pseudomorphic Sil-xGex limits the thickness of the film that can be developed without the generation of misfit dislocations, which are detrimental to device performance. Consequently, this poses a severe design constraint and limits its potential device applications. The Sil-xGex on the Si(001) system exhibits some severe limitations, such as the existence of a critical thickness for perfect pseudomorphic growth that depends on the amount of germanium. To use carbon-containing layers for device applications, one of the key parameters is the carrier mobility in the new epitaxial materials.
