Si nanowires arrays fabricated by wet chemical etching for antireflection and self-cleaning

Here we report a simple and cost effective fabrication technique, which created large area vertical Si nanowires (diameter in similar to 200 nm) by means of silver induced wet chemical etching on single crystalline Si substrates. By this technique, Si nanowires were fabricated on single crystalline in aqueous 5M HF and 0.02M AgNO3 solution at room temperature. The scanning electron microscope (SEM) images indicate that etched silicon wafers consist of dense and nearly vertically aligned one-dimensional nanostructures. Length of Si nanowires was found to increase linearly with etching time (0-300 min). The mechanism of vertical nanowires formation can be understood as being a self-assembled Ag induced selective etching process based on the localized microscopic electrochemical cell model. A low reflectivity averaged similar to 1.7% from 450 to 790 nm was observed. The nanometer scale rough surface can make water droplet either in the so-called Wenzel or the Cassie regime, which can increase contact angle (CA). High CA makes the surface hydrophobicity and self-cleaning. Water CA (150 degrees) was observed on the etched Si surface. Such antireflection (AR) and self-cleaning surface may have potential applications for silicon solar cells.