High-dielectric loss black silicon decorated with multi-nanostructure for wide-band mid-infrared absorption

Because of the excellent light-trapping ability of black silicon, it has emerged as a versatile substrate for photothermic applications. In this paper, multi-nanostructured black silicon with wide-band mid-infrared absorption properties for application in pyroelectric detectors is reported. Black silicon is fabricated on a substrate surface masked by Ag nanoparticle arrays using single-step etching of C₄F₈ and SF₆ plasma. The low absorption of black silicon in the mid-infrared region is improved when a secondary nanostructure with Pt nanoparticles and SiO₂ thin films is deposited on the surface of the prepared black silicon by microelectromechanical system (MEMS) processes. Electrons are scattered at particle boundary, resulting in dielectric loss to incident infrared (IR) region. Compared to single black silicon, the structure decorated with the multi-nanostructure can achieve higher infrared absorption, which is contributed to the high-dielectric loss properties of the Pt nanoparticles. Simulations and experiments show that the thickness of black silicon and number of layers of platinum particles contribute to mid-infrared absorption, with wavelength ranging from 2.5 to 20.0 μm, and the absorption reaches ~ 90%. The proposed absorber provides a promising solution for thermal detectors.