Electronic Properties of Strained Si/SiGe and Si 1ℒy C y Alloys

This chapter presents a review of the electronic properties of strained silicon–germanium (SiGe), strained silicon (Si) on relaxed SiGe, and a brief introduction to strained Si1–_yC_y/Si heterostructures. Perhaps the most well-known electronic property of SiGe alloys is the reduction in the indirect energy bandgap compared to that of Si as Ge is added to the alloy. The band alignment for strained SiGe on Si is such that almost all of the bandgap difference appears in the valence band. This material is thus ideally suited for the fabrication of npn Si/SiGe/Si heterojunction bipolar transistors, as well as for applications such as p-channel field-effect transistor where confinement of holes in the SiGe layer is desired. The high Ge content in the buried layer is made possible in part by the relaxed SiGe layer that reduces the overall mismatch. Strain plays a critical role in determining the energy band structure and the lineup of the bands at strained SiGe/Si and strained Si/SiGe heterojunctions.