Absorption enhancement in nanostructured silicon fabricated by self-assembled nanosphere lithography

In this work, we give a detailed experimental and theoretical analysis of a nano cone array on silicon wafer, which can greatly enhance the absorption compared with the polished silicon. The experimental absorptance can reach 98.7% in the wavelength ranging from 400 nm to 1100 nm. The mechanism of absorption enhancement is attributed to the nano cone array that can suppress the reflection by building a grade index from air to silicon surface. Moreover, an ultrathin 13 nm thickness gold film was sputtered on the nano cone array, by which surface plasmon can be excited and the absorption in the near-infrared region can be greatly enhanced. We also give a deep comprehending on the physics mechanism of such high absorption. This kind of nano cone array can be fabricated by a simple and low-cost colloidal sphere lithography and reactive ion etching, which makes it a more appropriate candidate for photovoltaics, spectroscopy, photodetectors, sensor, especially for the silicon-based application in the near-infrared region.