An ideal light-absorbing surface is able to collect light energy from wide ranges of wavelengths and angles of incidence. It has been reported that photonic structures can manipulate and couple light on the nanoscale surface. These photonic nanostructures can enhance light absorption and improve solar energy conversion also have been expected. In this article, we will describe how to calculate the optical properties of photonic nanostructures, especially for the biomimetic antireflecting structures on semiconductor substrates. The optical properties of biomimetic nanostructures were been analyzed using finite difference time domain (FDTD) calculations. Our FDTD simulation results show that the antireflecting structures utilize design parameters of spacing/wavelength and length/spacing, which could be expected exhibiting ∼99% optical absorption over wavelength from UV-vis region and angle of incidence up to 60° in high-index semiconductor materials.