Anti-reflective surfaces: Cascading nano/microstructuring

The creation of anti-reflective surfaces is reliant on the engineering of the surface textures and patterns to enable efficient trapping or transmission of light. Here we demonstrate anti-reflective layers composed of hierarchical nano/microscale features that are prepared on Si using a combination of wet and dry etching processes, and which are both scalable and affordable. The performance of the structured surfaces was tested through optical measurements of the reflectance, transmittance, and scattering spectra from the visible to mid-infrared wavelength regions, and the results were verified using numerical simulations to identify the performance of the textured anti-reflective layers. The anti-reflective properties of the layers were shown to be dramatically improved by the composite nanostructured surfaces over a broad spectral range, which thus provides a basis for the design rules that are essential for the progress towards effective anti-reflector fabrication. At normal incidence, the hierarchical surfaces achieve reflectances that are 10-80 times lower than that of conventional single-etch nano-microstructures. Portions of the absorbed, transmitted, scattered, and reflected light in the visible-IR spectrum are presented to illustrate the results.