Silicon–Germanium: properties, growth and applications

Silicon–germanium is an important material that is used for the fabrication of SiGe heterojunction bipolar transistors and strained Si metal–oxide–semiconductor (MOS) transistors for advanced complementary metal—oxide–semiconductor (CMOS) and BiCMOS (bipolar CMOS) technologies. It also has interesting optical properties that are increasingly being applied in silicon-based photonic devices. The key benefit of silicon–germanium is its use in combination with silicon to produce a heterojunction. Strain is incorporated into the silicon–germanium or the silicon during growth, which also gives improved physical properties such as higher values of mobility. This chapter reviews the properties of silicon–germanium, beginning with the electronic properties and then progressing to the optical properties. The growth of silicon–germanium is considered, with particular emphasis on the chemical vapour deposition technique and selective epitaxy. Finally, the properties of polycrystalline silicon–germanium are discussed in the context of its use as a gate material for MOS transistors.