Antireflective subwavelength structures on crystalline Si fabricated using directly formed anodic porous alumina masks

A simple fabrication technique for subwavelength structured (SWS) surfaces by means of anodic porous alumina masks directly formed on Si substrates was proposed and demonstrated. By this technique, SWS surfaces were fabricated on polished single-crystalline Si and chemically etched as-cut multicrystalline Si wafers. Smoothly tapered SWS surfaces with a periodicity of $100nm$ and a height of $300–400nm$ were obtained. A low reflectivity below 1% was observed from $300to1000nm$ for both of the wafers, in agreement with numerical simulation. After thermal annealing at $800°C$⁠, the reflectivity of the SWS surface increased to 3%.