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Anti-reflection high-index metasurfaces combining Mie and Fabry-Pérot resonances
摘要： Minimizing reflection losses is required for the efficient operation of a wide range of optical components. Anti-reflection coatings supporting Fabry-Pérot resonances are commonly used to solve this problem and can be applied on an industrial scale. Recent work has shown that reflections can also be reduced by placing an array of high-index nanostructures on a surface. In such coatings, anti-reflection is achieved by tailoring the scattering by optical Mie resonances. Here, we design and fabricate Si metasurfaces that combine both Fabry-Pérot and Mie resonances in a single metasurface to realize a multi-resonant broadband anti-reflection response. We optically characterize the metasurfaces demonstrating 4.1% AM1.5–averaged reflectance across the visible spectrum (425–900 nm). Our metasurface design strategy is generally applicable to different materials and frequency ranges, making our approach relevant for a broad variety of applications.
关键词： Mie resonators,Metasurface,Effective Medium,Anti-Reflection Coating (ARC),Fabry-Pérot resonances
更新于2025-09-23 15:23:52
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Resonant Metagratings for Spectral and Angular Control of Light for Colored Rooftop Photovoltaics
摘要： We design semi-transparent metagrating supercells that enable control over the spectrum and directivity of incident light for applications in photovoltaics with tailored angular appearance. The building block of the supercells is a 110-120 nm wide and 175 nm tall silicon nanowire that shows a strong Mie resonance around λ= 650 nm. By arranging the resonant Mie scatterers into metagratings of increasing pitch (675-1300 nm) we create a Lambertian-like scattering distribution over an angular range of choice. The millimeter-sized metasurfaces were fabricated using electron beam lithography and reactive ion etching. The fabricated metasurface nearly fully suppress specular reflection on resonance while 10% of the incoming light around the resonance is scattered into the angular range between 30-75°, creating a bright red appearance over this specific range of angles. Off-resonant light in the blue, green and near-infrared is efficiently transmitted through the metasurface and absorbed in the underlying photovoltaic cell. The implemented silicon heterojunction solar cells with integrated metagrating supercells show a reduction in external quantum efficiency matching the resonant scattering spectral range. The short circuit current is reduced by 13% due to the combined effects of resonant scattering, reflection from the high-index substrate and absorption in the Si nanowires. In addition, to efficient colorful photovoltaics with tailored angular appearance, the metagrating concept can find application in many other light management designs for photovoltaics and other opto-electronic devices.
关键词： light management,metasurface,Mie resonators,BIPV,silicon nanoparticles,colored photovoltaics,transparent metagratings,solar cells
更新于2025-09-19 17:13:59
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Nanoscale characterization of photonic metasurface made of lens-like SiGe Mie-resonators formed on Si (100) substrate
摘要： 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 °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.
关键词： SiGe,metasurfaces,photonic properties,Mie resonators,Raman microscopy
更新于2025-09-16 10:30:52