Si Ge alloys: growth, properties and applications

Due to advances in epitaxial techniques, the ability to deposit high-quality epitaxial silicon-germanium alloys at lower temperature, has opened up the applications of pseudomorphicSi 1−xGe x films in advanced bipolar transistors and in novel device structures. In this review paper, the various methods of growth of Si Ge alloys are discussed, including low-temperature epitaxy by ultra-high vacuum chemical vapor deposition (UHV/CVD) and molecular beam epitaxy (MBE). The morphology of growth and the stability of the deposited films are then presented. The major application of Si Ge alloys in integrated processes has been in the bipolar transistors area. The application of these alloys to the bandgap engineering of bipolar devices is discussed, including the most recent accomplishment of 75 GHz f T heterojunction bipolar transistors using Si Ge in the base.