Silicon-Enhanced Nanocavity: From Narrow Band Color Reflector to Broadband Near-Infrared Absorber

Abstract: Subwavelength-scale light absorbers and reflectors have gained significant attention for their potential in photonic applications. These structures often utilize a metal-insulator-metal (MIM) architecture, similar to a Fabry-Perot nanocavity, using noble metals and dielectric or semiconductor spacers for narrow-band light absorption. In reflection mode, they function as band-stop filters, blocking specific wavelengths and reflecting others through Fabry-Perot resonance. Efficient color reflection requires asymmetric Fabry-Perot cavities, where metals with differing reflectivities and extinction coefficients enable substantial reflection for non-resonant wavelengths and near-perfect absorption at resonant ones. Unlike narrowband techniques, broadband absorption does not rely on a single resonance phenomenon. Recent developments show that integrating an asymmetric Fabry-Perot nanocavity with an anti-reflection coating achieves near-unity absorption across a broad wavelength range. This study introduces an asymmetric Fabry-Perot nanocavity with a dielectric-semiconductor-dielectric spacer, enabling near-unity color reflection. By incorporating silicon, the reflected color can be tuned with just a 5 nm thickness variation, while achieving broadband absorption over 70% in the 800-1600 nm range. The addition of an anti-reflection coating extends broadband absorption to near unity with minimal impact on reflected color. The planar, nanopattern-free design holds promise for display technologies with better color fidelity and applications in thermal photovoltaics.