Silicon light emitters based on defect-enhanced quantum dots

Silicon, a group-IV element in the periodic table of elements, is the dominating material of our digital world, simply because all integrated device technology (computer chips) is silicon-based. In the upcoming years, this digitalization which is driven by silicon electronics will face clear boundaries that are induced by limited data transfer rates and strongly increasing energy consumption of electronic devices. Due to the ongoing miniaturization of single devices, the length of the currently used copper interconnects is ever increasing while their cross-section is continuously decreasing, leading to pronounced Joule heating. Thus, in recent years the search for data transfer on chips using optical means started to be a heavily pursued research topic. Unfortunately, silicon itself is a very poor light emitter which is caused by specific material properties, namely the indirect energy band gap of this semiconductor. In the framework of this project, we will investigate an entirely novel approach of obtaining efficient light emission from silicon-compatible group-IV materials, such as germanium. The material class that we aim to exploit is based on epitaxially grown germanium quantum dots, i.e. few atomic layers high strain-induced material accumulations. Into such quantum dots, we intentionally implant heavy ions, leading to distortions of the crystal structure (defects). Our preliminary results indicate that the optical properties of these group-IV nanostructures can be drastically enhanced, especially at room temperature and light emitting diodes working efficiently up to 100C were demonstrated. However, an electrically pumped laser operating at room temperature and above will be needed in order to successfully merge these light emitters in the future with silicon-based electronics. Furthermore, the material system itself, e.g. possible atomic arrangements of different defect structures and their interplay with the chemical and optoelectronic properties of the quantum dots was barely investigated so far. Thus, the main goals of the project can be formulated as follows: (1) The system quantum dot/defect will be investigated experimentally, support by additional theory. In this way, the structural, electronic and optical properties will be investigated to determine e.g. non-radiative recombination mechanisms and provide strategies for their reduction. (2) We will vary fabrication parameters of defect enhanced quantum dots in order to find the most promising ones and thus increase their light emission yield. (3) The work in (1) and (2) are necessary to reach the main goal of the project, the demonstration of an electrically pumped laser-diode that is compatible with silicon technology. The success of this project could be an important step towards the implementation of silicon-based light sources into modern semiconductor devices.