Laser based methods for enhancement of the photoluminescence of Si quantum dots by coupling to plasmonic particles

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Silicon nanostructures (quantum dots) like Si nanocrystals (Si-NC) or amorphous Si clusters with particle diameters < 10 nm are – in contrast to bulk silicon – efficient light emitters and absorbers in the visible and infrared spectral range. This is, amongst others, attributed to quantum confinement. Therefore, Si quantum dots (Si-QD) are of great interest as integrated active emitters in Si photonics. Regarding applications in photovoltaics and data storage, such Si quantum dots have also great potential: previously inefficiently used spectral portions of the sunlight may be better utilized in Si-NC containing solar cells. In spite of numerous achievements, the efficiency of light absorption and emission of Si-QD is still not sufficient for many applications. The aim of this project is therefore to show that this efficiency can be enhanced by coupling the Si-QD to plasmonic (metallic) nanoparticles. Specifically, gold nanoparticles (Au-NP) will be implanted by means of laser radiation into a Si-QD containing oxide matrix. Here, implantation refers to the insertion of gold originally coated on the surface into a region beneath the surface in form of nanoparticles. The Si-QD are generated by thermal annealing of a SiOx-film (x < 2). The generation of Si-QD by laser irradiation will also be examined. By controlling the distance between regularly ordered Si-QD and Au-NP, the efficiency of absorption and emission will be enhanced and their radiation characteristics will be adjusted. Generally, completely different process technologies are used for structuring gold and silicon. Therefore, such combinations have rarely been treated so far. The various material modifications (local heating, phase separation, dewetting, particle formation, implantation) which can be caused by laser radiation in both the metal and the semiconductor components enable processes which are still almost unexplored in this context. The approach pursued here is especially promising, because the characteristics of metallic nanoparticles are simultaneously exploited in two ways: on the one hand, they serve as local heaters for the generation of Si-QD, so that the otherwise observed complications of the laser based generation of Si-QD are overcome. On the other hand, these Au-NP act as antennas for the enhanced and directional absorption and emission of the Si-QD. These antennas themselves will be optimized by shape forming (elongate particles or rows of particles) and arrangement (two dimensional arrays). We expect that the results will be transferable to other material combinations and therefore will be of general importance.