ACS Photon. http://doi.org/ck72 (2018)

The ability to engineer the absorption of light is important, especially for devices such as solar cells and photodetectors, for example. An epsilon-near-zero (ENZ) material, which has a permittivity that approaches zero near a specific wavelength of light, can exhibit very strong absorption but only in a narrowband region around this wavelength. Now, Joshua Hendrickson and colleagues in Ohio and Alabama, have found a way to increase the absorption bandwidth of an ENZ material by an order of magnitude, achieving a 240-nm-wide band with >98% absorption centred at the telecom 1,550 nm wavelength. This broadband behaviour was enabled by coupling the ENZ mode to a gap plasmon resonance in a structure that consists of (from the bottom up) a TiN metal ground plane, SiO2 dielectric spacer layer, indium tin oxide (ITO) nanofilm, and finally, an array of gold squares. The authors also emphasize that the idea can be tailored to other spectral regions by structural scaling and appropriate choice of ENZ material.

Credit: American Chemical Society