Interference-enhanced absorption of visible and near-infrared radiation in ultrathin film coatings

We report the interference-enhanced absorption of electromagnetic radiation in two-layer lossy coatings on metal substrates. The conditions for the complete absorption of monochromatic radiation are described in comparison with those in previously studied single-layer coatings. Proof-of-principle measurements of the interference-enhanced absorption in the near-infrared range are presented for silicon-on-germanium coatings on aluminum substrates. We also provide various examples of materials that can be used to create similar light-absorbing coatings for visible and near-infrared ranges. The proposed design can be applied to optical filters, optoelectronic devices, photodetectors, and light-emitting devices.