Surface Passivated Porous Silicon-Based Antireflective Coating

This paper reports a surface passivated porous silicon-based technique for realization of ultra-band infrared optical components applicable in thermal imaging and infrared spectroscopy. The functionalized Si-surface consists of light-trapping (islet-like) structures and a porous silicon (PSi) multilayer structure forming lambda/4 layers underneath. The combined macro- and nanostructures are created by electrochemical etching processes with different etchant concentrations, current densities, and etching times in which the nanostructures are created in a self-organized process at suitable anodization conditions. The long-term stability of the manufactured optical component is obtained by an effective 2-step-oxidation surface stabilization process. The influence of this stabilisation process on the optical performance is almost negligible. The surface stability is proven by additional thermal annealing steps up to 1000deg C and 10 h. The samples maintained the almost perfect black body characteristic in a wavelength range from 1.5 micrometer to about 20 micrometer (MIR).