P. Werner, G. Cirlin, V. Talalaev, and N.D. Zakharov
The application of silicon for optical devices/circuits suffers from the disadvantage that this material has an indirect optical transitions related to its specific band structure. Promising results were achieved by applying nanostructures in a Si matrix, such as nanoparticles, quantum wells and quantum dots. Our approach: Si/Ge superlattices (SL) are of particular interest due to the possibility to create a direct band gap in the Si-based system. The SL consists of a stack of alternating numbers of Si and Ge monolayers. To generate such a SL molecular beam epitaxy (MBE) was applied. Holes are confined in the flat Ge islands, electrons are located in the Si spacer layers between them. Concerning the electronic structure of a Si/Ge –SL, a miniband can be generated caused by the overlapping of electron wave functions in real and k- space. The results: Stronger luminescence (PL, EL) with faster transition. Such a p-n-heterostructure can be used as an infrared emitter working at RT. Si/Ge QD-SL is a promising system for Si-based optoelectronics. European patents as well as US patents covering there light-emitting Si/Ge nanostructures have been granted.