  Finite-difference time-domain method is employed to investigate the optical
properties of semiconductor thin films patterned with circular holes. The
presence of holes enhances the coupling of the incident plane wave with the
thin film and greatly enhances the absorption performance. For a typical 100 nm
thin film, the optimal hole pattern is achieved when the hole radius is 180 nm
and volume fraction is about $30\%$. Disorderness can alter the absorption
spectra and has an impact on the broadband absorption performance. The
non-uniform radius of holes can slightly broaden the absorption peaks and
enhance the integrated absorption. Random hole position can completely change
the shape of the absorption spectra and the averaged integrated absorption
efficiency is slightly smaller than the optimized ordered nanohole pattern.
Compared to random positioned nanoholes or ordered nanohole, amorphous
arrangement of nanoholes will result in a much better absorption performance.
However, it is also found that the absorption enhancement of amorphous pattern
over an ordered pattern is weak when the incident angle departures from normal
or when the intrinsic material absorption is strong.
