07 - Scattering Interfaces with Tailored Disorder

Light scattering interfaces play an importance role in many applications of optics and photonics. For example, in photovoltaics they enhance light trapping and thus the efficiency of solar cells. In particular, stochastic interfaces have proven advantageous due to their spectrally broadband and efficient performance. Nevertheless, light scattering abilities of state-of-the-art interfaces remain limited. Particularly, tailoring the surface topography and with that the ability to scatter light is severely restricted by the fabrication methods considered thus far. Due to a lack of suitable techniques, it can be safely assumed that the full potential of disordered scattering interfaces has not been fully explored yet. In this project we desire to explore a promising approach to solve this issue. We aim to fabricate and investigate disordered interfaces with well-controlled topographies. Control over topography enables us to control the interaction of light with these systems as well. Our approach facilitates the fabrication of sample systems with scattering properties on demand. This concerns far-field properties, such as a predefined angular distribution of the scattered light for a specific spectral range, as well as near-field properties, such as luminescence enhancement of quantum emitters located in the vicinity of the interface. The key of our approach is to use a polydisperse colloidal solution as the starting point to fabricate the interface. The solution contains spheres with sizes ranging from several tens of nm to a few µm. It is deposited onto a substrate on which the spheres will form a dense monolayer. The exact position of each sphere and their arrangement is random.

However, the size distribution of the colloidal solution determines the topographical parameters of the surface, e.g. correlation length and average height. The deposited monolayer provides the referential topography that is subsequently transformed into an interface, e.g. using adapted thin-film deposition techniques. This final interface shall feature the desired scattering properties. The size distribution of the colloidal solutions here is the central lever: By carefully tailoring the size distribution, the topography of the interfaces is managed easily and fast. Identifying suitable size distributions to control the scattering properties upon request is one major challenge of our project. Exemplary application cases for our interfaces chosen here are simplified sample systems. On the one hand, we want to increase the light absorption in thin Si films. On the other hand, we aim at enhancing the luminescence of integrated quantum emitters. But our approach is not limited to these applications. Further application areas not addressed here are, e.g., random lasing or imaging of objects behind diffusive media. Beyond that, our proposed system constitutes an ideal platform to investigate fundamental physical phenomena, such as Anderson localization.