Bioinspired broadband midwavelength infrared antireflection coatings on silicon

Abstract

Silicon has been extensively used in manufacturing refractive infrared optics due to its high refractive index and excellent transmission over a very broad range of infrared wavebands. However, the high refractive index of silicon leads to large reflection loss which greatly limits the performance of the final optoelectronic devices. Here, the authors report a simple and scalable templating nanofabrication technology for making subwavelength-structured, broadband antireflection coatings on crystalline silicon wafers, targeting the midwavelength infrared (MWIR) waveband (3–8 μm), which has important implications for various civilian and military purposes. Periodic arrays of silicon nanopillars with tapered shapes, which mimic the microstructured cornea of nocturnal moths, can be patterned on both surfaces of silicon wafers using self-assembled monolayer silica colloidal crystals as structural templates. The resultant moth-eye gratings can greatly enhance optical transmission for the entire MWIR region. Finite-difference time-domain simulations have also been performed and the theoretical predictions agree reasonably well with the experimental optical measurements.