Nanoscale characterization of photonic metasurface made of lens-like SiGe Mie-resonators formed on Si (100) substrate

Submicrometer-sized high-index Mie resonators attract significant interest in photonic applications due to their capabilities to manipulate light. 2-dimensional metamaterials or metasurfaces consisting of arrays of such resonators on a device surface can be used in the flat optics, sensors, and other applications. Here, we report on the comprehensive nanoscale characterization and optical properties of nearly regular SiGe Mie resonator arrays on a Si surface fabricated using a simple and low-cost method. We achieved control on the surface morphology by depositing Ge on the Si(100) surface at elevated temperatures 890-960 degrees C and obtained arrays of submicrometer/micrometer low-Ge-content SiGe lenslike islands via dewetting when the Ge content was >4%. At the lower Ge content, we observed the formation of a continuous SiGe film via wetting. We used Raman microscopy not only for the Ge content and stress control but also for studying photonic properties of the islands and their coupling with the Si substrate. In contrast to the elastic light scattering, we clearly distinguished visible light Raman signals from the islands themselves and from the substrate areas under the islands enhanced compared to the signal from the open substrate. Calculation of the light electric field distribution in the islands and the substrate demonstrate how the islands trap the light and forward it into the high-index substrate. This explains the island-induced reflection suppression and Si substrate Raman enhancement, which we observe experimentally. Such an SiGe-island array is a promising metasurface for the improvement of Si photosensors and solar-energy device performance.