Nanostructured silicon based antireflective layers for thermal infrared optical components

We investigated the antireflective properties of nanostructured silicon layers fabricated by metal - assisted wet silicon etching. The morphological characterizations reveal that the nanostructured surface consists of holes with diameters in the range of several tens of nanometers, presenting filling factors of 0.50 and with depths in the range of 1 - 1.3 mu m. The structures configuring the silicon surface have features much smaller than that of the wavelength of the radiation in the mid - infrared spectrum domain such that the layer can be regarded as homogeneous. The FTIR spectroscopy determinations show that this layer is antireflective over a broad range of infrared wavelengths realizing efficient AR coatings for infrared optical components made on silicon.