High-efficiency LEDs based on amorphous Ge quantum dots

In the last years strong efforts were made towards the fabrication of high-efficiency silicon-based light emitters that can be implemented into the existing silicon-based integrated mico-electronic technology. High-efficiency emitters, such as high quality light emitting diodes or lasers, are needed in order to overcome bottlenecks in the chip-to-chip and intra-chip data transfer rates and data transfer speed that are caused by the employed interconnects. This project aims at the characterization and optimization of a novel form of quantum dots, namely amorphous Ge quantum dots that can be embedded into a fully crystalline silicon matrix. The amorphization of the dots happens during their growth in a molecular beam epitaxy chamber via bombardment with positively charged Ge ions. The novel quantum dots are of great interest since they exhibit superior room temperature luminescence properties as compared to their crystalline counterparts. In order to further enhance the luminescence output of the dots it is planned to embed them into photonic structures such as micro-disk resonators, waveguides and photonic crystals. Preliminary results on not yet optimized dots already exhibit narrow, strong luminescence intensity at room temperature. To fulfill the goals aimed at within this project, the applicant has chosen the group of Prof. Oliver Schmidt at the Leibniz Institute for Solid State and Materials Research - Institute for Integrative Nanosciences in Dresden as a host. At this institution not only the necessary laboratory equipment is available to fulfill the project goals, it is also one of the leading groups dealing with the fabrication and characterization of group IV and group III-V semiconductor nanostructures and their incorporation into photonic devices. The applicant will transfer the knowledge gained in Dresden about those novel dots after two years within his return year to the Institute of Semiconductor and Solid State Physics to further strengthen the international position of the Institute of Semiconductor and Solid State Physics, University of Linz in the field of infrared optical emitters beyond the duration of the granted last funding period of the Spezialforschungsbereich (special research project) IRON (Infrared optical nanostructures).

During the course of this Erwin Schrödinger fellowship, the fabrication of a Silicon Germanium quantum dot laser was demonstrated. One can say without any doubt that the digital revolution changed our lives significantly during the last decades. This progress would have never been possible without the semiconductor material silicon, building block for about 95% of all semiconductor devices. Therefore, and because Si is the main ingredient to form concrete we life in the so-called silicon-age. Nowadays, in every mobile phone, laptop or automotive chip there are billions of silicon semiconductor devices. Within those, data is generated, transformed and transferred. On chip and inter-chip data transfer is established through electrical current in copper wires. In a single chip there are several kilometers of wires, leading to high impedances and resulting energy losses due to resistive heating. Due to the ongoing miniaturization of the semiconductor devices, more and more energy is needed worldwide and, consequently, the energy consumed by electronics increases by about twice the rate of the general worldwide energy demands. For this reason there has been intensive research efforts to enable possibilities for fast, highly efficient and energy saving on-chip and inter-chip optical data communication on silicon integrated technology devices. Hereby, the main requirement is a strong light source compatible with silicon, namely a silicon laser. However, as an indirect semiconductor, Silicon is intrinsically a not a good light emitter. Within this Project, I have demonstrated the fabrication of a nanostructure laser using partly amorphized, partly crystalline quantum dots as gain material. Those light emitters are fully compatible with the requirements of the micro and nano-electronic market. It was shown that the partial amorphisation of the quantum dots using Ge ion bombardment opens more efficient radiative carrier recombination paths and leads to enhanced light emission at room-temperature. This silicon germanium quantum dot laser is at the moment still optically pumped. In the future, realization of an electrically driven laser might lead to an important step towards embedding Si light sources as on-chip optical interconnects for faster and more efficient data transfer in modern electronics.