Progress in Light Emission from Silicon and Germanium Nanostructures

Light emission from silicon and germanium nanostructures has been of great interest for some time now owing to the need for silicon-based light sources for applications in silicon optoelectronics and photonics. Both silicon and germanium possess indirect band gaps, which makes them very inefficient light emitters. Band gap engineering employing quantum wells, wires, or dots has been proposed as one way to overcome this limitation and, in the past, Si/Ge, Si/SiO2, or Si/SiGe-alloy thin-multilayer nanostructures grown on Si have been produced on this principle, and although light emission with greatly improved efficiency has been obtained at low temperatures the emission at room temperature is still very weak, because of exciton dissociation. Recent advances in band gap engineering technology have resulted in the development of new systems incorporating one-, two-, and three-dimensionally confined Si-Ge nanostructures that produce bright light in the near infrared. Here, the novel optical properties of recently-investigated various such nanostructures are reviewed.