Wideband anti-reflective micro/nano dual-scale structures: fabrication and optical properties

This Letter reports the fabrication and optical characteristics of large-area wideband anti-reflective micro/nano dual-scale (MNDS) structures. Microstructures, including inverted pyramids and V-shaped grooves, with controllable geometry sizes (e.g. width, pitch and depth) are fabricated by anisotropic wet etching of silicon. Highly dense arrays of high-aspect-ratio nanostructures are then formed atop those microstructures by an improved maskless deep-reactive ion etching process. Compared with the black silicon surface made of nanostructures only, these MNDS structures further reduce the optical reflectance to less than 0.6%, and the total light absorption has almost reached 95%. More importantly, by combining the light trap of microstructures and the anti-reflectance of nanostructures, these MNDS structures can efficiently suppress the reflectance of incident light at a wideband range of wavelengths from the ultraviolet, through the solar spectrum, to the near-infrared region (i.e. from 200 to 2500%nm).