STRAIN TUNING OF NEXT-GENERATION GROUP-IV LIGHT EMITTERS /
"STRONG LIGHT"

This LIT Seed project aims at providing the stepping stone for exploiting the recently theoretically predicted benefits of in-situ and ex-situ strain-tuning of defect-enhanced group-IV quantum dots (DEQDs) on their light-emission. Epitaxial Ge on Si quantum dots (QDs), into which intentionally Ge split-interstitial defects are introduced, have been demonstrated to be extraordinary and Si technology compatible room-temperature light-emitters. In particular, signs for optically-pumped lasing of DEQDs in micro-resonators and light emitting diodes containing DEQDs that are efficiently operating up to 100°C imply their potential towards Si-based data communication. However, recent theoretical calculations based on density functional theory suggest that the so-far employed and up to 4% biaxially compressively strained Ge QDs are far from being the ideal host matrices for these light emitting defects and that a reduction of the compressive strain leads to significantly enhanced
oscillator strength and directness of the involved optical transitions. In this proposal, we aim to change the strain-status of DEQDs by either changing the QD strain during growth using deposition of diluted SiGe alloys on Si, and growth of Ge DEQDs on virtual SiGe substrates of by ex-situ strain tuning. The latter will allow us to strain-optimize the optical properties of these semiconductor nanomaterials by their integration onto piezoelectric actuators.

Implications on technology, industrial relevance and implications for other fields of research:
Light emission from Si and Si-compatible materials is regarded as a highly important step towards higher data transfer speed and rates in Si integrated technology. Time will tell if other approaches, such as strained Ge or GeSn, will succeed as materials for reliable lasing operation at RT and even above. The method of light-emission from group-IV nanostructures that were modified by Ge ion bombardment has the potential to succeed in this race. Having excellent RT light-emitters in a fully crystalline, dislocation-free Si matrix is certainly an advantage over many other processes that need micrometer-thick graded SiGe buffer layers that are full of dislocations. Another advantage of the DEQDs is based on the ease of doping the DEQD structures. Thus, we are confident that the DEQDs might cause a paradigm change in the aim to implement electrically driven light emitters with Si electronics for future integrated technology. Potential long term high-gain outcomes upon the realization of this project and major follow-on project includes faster data transfer at the on-chip- and datacenter-level. The project outcome can also provide an excellent starting point for very different future on-chip applications using DEQDs, e.g. the implementation of novel sensing functionalities on a chip,35-37, thus merging the field of lab-on-a-chip with the integrated technology benefits of Si-based microelectronics. The work on DEQD-membranes will also open the route to integration of optoelectronic devices on flexible substrates for wearable electronic applications.

Funded by: Linz Institute of Technology (LIT), JKU Linz

PI: Assist.-Prof. Dr. Moritz Brehm

Duration: 01.06.2020-31.05.2022