Antirefiection subwavelength gratings at near-infrared wavelengths fabricated by self-organized nanoparticles

We design subwavelength gratings (SWGs) in 1.55 μm wavelength range used for optical communication devices or solar cells. Also, we propose a novel fabrication technique of SWGs using self-organized nanoparticles, for the large-area and low-cost fabrication. In the fabrication, SiO₂ particles with the diameters of 170 nm are spin-coated on a silicon substrate. Then, a 170-nm-period SiO₂ particle pattern is formed on the substrate. Using the SiO₂ particles as a mask, the silicon substrate is etched by a dry etching machine. A 170-nm-period SWG with tapered profile is fabricated. The SWG height is approximately 820 nm. Reflectivity of the SWG is decreased to be -18.7 dB (1.3%) from -3.39 dB (45.8%) of a Si mirror surface at a wavelength of 1550 nm. Calculated reflectivity of the SWG at a wavelength of 1550 nm is -18.3 dB (1.5%), which almost agrees with the measured value.