The fabrication of the antireflective periodic nano-arrary structure on Si surface using nanoimprint lithography and the study on its properties

The intrinsic Fresnel reflection of Si surface, which causes more than 30% of the incident light to be reflected back from the surface, seriously influences the photoelectric conversion efficiency of Si-based semiconductor photoelectric device, such as solar cell and infrared detector. Recently, how to find a simple and efficient method, which is also suitable for mass production, aiming to suppress the undesired reflectivity and therefore improving the efficiency of the device, has become a research focus. In this work, we successfully convert a 2D nanopillar array structure into the Si surface via the nanoimprint lithography. The nanopillar has a flat surface and a paraboloid-like side wall profile. The period and the height of the hexagonal array structure are 530 nm and 240 nm, respectively. The cut-paraboloid nanopillar structure generates a relatively smooth gradient of the refractive index in the optical interface, which plays a key role in suppressing the Fresnel reflection in a wide range of wavelength. The reflectivity of the nanopillar arrayed Si surface is tested in a wavelength range from 400 to 2500 nm at an incident angle of 8° during the measurement. Compared with the unstructured Si, the structured Si has a reflectivity that significantly decreases in the test area: in a wavelength range from 400 to 1200 nm, and the reflectivity of the silicon surface is less than 10%. Specifically, the reflectivity is almost zero at a wavelength of about 1360 nm. The results are confirmed with the effective medium and rigorous coupled-wave theory.