Near-infrared light absorption enhancement in Ge nanostructures prepared by nanosphere lithography

Abstract

Nanosphere lithography technique has been used to get Ge nanostructures for enhancing the optical absorption in the near-infrared light region. It is proved that the morphologies of formed Ge nanostructures can be well controlled by diameter of polystyrene nanosphere as well as the etching time. A good antireflection and enhanced optical absorption characteristics have been observed in a wide spectral range, which is strongly dependent of the surface morphology. Particularly, by using the nanosphere with the diameter of 2000 nm, the reflection in the near-infrared spectral range (900–1500 nm), which cannot be efficiently utilized by Si, is suppressed and the corresponding optical absorption is enhanced significantly. The finite-difference time-domain simulation shows that, for the incident light with short wavelength, the light can only be absorbed at the surface range; but for the incident light with a long wavelength (1500 nm), the light can be efficiently absorbed in whole Ge nanostructures. Compared with the Ge nanostructure formed by using small-sized nanospheres (300 nm), the one formed by a large-sized nanosphere (2000 nm) shows the better optical absorption behaviors due to the strong Mie scattering effect.