Low refractive index Si nanopillars on Si substrate

Low refractive index of a stalagmitelike high-aspect-ratio Si nanopillar array on Si dry etched using a self-aggregated Ni nanodot mask is demonstrated, which exhibits two minimum reflectances of 1.23 and 1.4 with corresponding refractive indices of 1.25 and 1.48 at 400 and 1200nm, respectively. Angular dependency of the transverse electrical mode reflectance at 632.8nm of the surface roughened Si nanopillar array is released, and the Brewster angle of 63° with equivalent refractive index of 1.5 is determined.