Coscinodiscus diatom inspired bi-layered photonic structures with near-perfect absorptance accompanied by tunable absorption characteristics

Inspired by the morphology of Coscinodiscus species diatom, bi-layered photonic structures comprised of dielectric-filled nano-holes of varying diameters have been designed and analyzed to enhance and tune absorption characteristics of GaAs-based thin-film photonic devices. Finite difference time domain-based numerical analysis and effective medium approximation based theoretical calculations show that by adjusting diameter and areal density of the nano-holes of the two layers, the peak absorption wavelength can be tuned over a wide spectral range, while attaining a maximum peak-absorptance value of about 97% and a maximum absorption bandwidth of ∼ 190 nm. The maximum enhancement factor of the bi-layered structure is about 11% higher than the value obtained for its equivalent single-layered counterpart over the near-ultraviolet to visible regime of the spectra. High absorptance over a wide-angle for TM polarization and tunable angle-dependent absorption characteristics for TE polarization are also obtained for the proposed ultra-thin absorbers. It has been shown that instead of having misaligned pore-centers as in Coscinodiscus species diatoms, a bi-layered structure designed with layers of identical lattice constant offers significant flexibility in terms of design and practical realization of thin-film photonic devices.