Wide angle and broadband antireflection properties for a siliconnanotip array

摘要

Biomimetic structures provided important clues for nano-synthesis in pursuit of enhanced performances. Here, wereport a wide angle and broadband antireflection is observed on a 6-inch silicon nanotip array (SiNTs) substratefabricated using a single step electron cyclotron resonance plasma etching technique. This subwavelength structureconsists of the SiNTs with apex and bottom diameter of 5 nm and 200 nm, respectively, length of1600 nm anddensity of 10~9/cm~2. This aperiodic array of SiNTs with geometry designed in the sub-wavelength level to demonstrate alow hemispherical reflectance of < 1% in the ultraviolet to infrared region. The antireflection property holds good for awide angle of incidence and both, s and p, forms of polarizations of light. The effective refractive index distributionrelated to the structure of SiNTs is built. The equivalent three-layered thin films with gradient refractive index can beapplied in interpretation of the low reflection phenomenon. The equivalent admittance of the system is shown to be nearthat of air even the wavelength is varied from 400 nm to 800 nm (or angle of incidence is varied from 25 to 70 degree).The configuration to have broadband and wide-angle antireflection is different from the previous design because theequivalent rare film adjacent to air in our case is much thinner than the requirement proposed by J. A. Dobrowolski. Thisnear ideal antireflection property suggests enhanced performances in renewable energy, and electro-optical devices indefense applications.