» Back to overview
Proposing Institution

Lehrstuhl für Festkörpertheorie, Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena
Project Manager

Prof. Dr. Silvana Botti
Max-Wien-Platz 1
07743 Jena
Direct bandgap silicon has been the holy grail of the semiconductor industry for many years, since it would allow integrating both electronic and optical functionalities on a silicon platform. Possible applications include silicon-based on-chip optical interconnects and a silicon-compatible quantum light source. Recent theoretical calculations performed in our group at the University of Jena predicted that the hexagonal crystal phase SixGe1-x features a tunable direct bandgap from 1380-1800 nm, exactly coinciding with the low loss window for optical fibre communications. At the same time, our experimental partners at the Technical University of Eindhoven have recently developed a generic approach to grow defect-free hexagonal SixGe1-x with tunable composition, both as nanowire shells and as nanowire branches. We are now working together on an interdisciplinary research effort intended to demonstrate efficient light emission from direct bandgap hexagonal SiGe, followed by the development of a SiGe nanolaser. A related project entitled “Silicon Laser” has just been approved for funding in the H2020 FET-Open Research and Innovation action. The research consortium of SiLAS gathers prominent groups at the Universities of Eindhoven, Oxford, Linz, Jena, and Munich, and at IBM in Zurich. Our group in Jena is the only theoretical group in the consortium and we will provide support and guide to experiments.In this context, we will perform ab initio calculations of structural and optical properties of SiGe nanowires. We will first predict the crystal structure of the lowest-energy phases of SiGe alloys at several chemical compositions, focusing on the range that gives direct band gap materials. We will then investigate internal interfaces between different phases and effects of nanostructuring, considering how surface reconstructions affect optical properties, and what is the effect of defects, doping and impurities. Our calculations will combine (i) ab initio structural prediction using the minima hopping method and (ii) first-principles characterization of electronic and optical properties by means of density functional theory (DFT), time-dependent DFT and Green’s function approaches . The minima hopping crystal structure prediction algorithm will be used also to find the lowest-energy reconstructions at internal interfaces with secondary phases, and at hetero-interfaces between different layers composing the device. Effects of strain, quantum confinement, temperature, and doping can be directly addressed. Accurate calculations of band structures, band alignments at interfaces, light absorption and emission including the effects of defects and impurities will be performed using state-of-the-art approaches beyond density functional theory, to include electron-electron correlation in the description of excited states. All in all, this procedure allows an efficient in silico screening of phases and compositions, aimed at pre-optimizing the electronic properties of the candidate systems for the experimental realization of a direct band gap silicon nanolaser.

Impressum, Conny Wendler