Multilayer thin-film coatings boost graphene absorption from 2.3% to 50%

Graphene is finding its way into photonic components and systems because of its electro-optical and other properties, which are usually a function of the optical, semiconductor, or other structure that it is integrated into. As for its intrinsic optical properties, though, undoped graphene is quite simple: no matter what the wavelength in the visible or infrared spectrum, graphene has a constant 2.3% absorption of light. While this property is interesting because of its frequency independence, the 2.3% figure is quite low—increasing graphene’s absorption would widen its applicability in, for example, some photodetector designs. Some ways to increase graphene’s absorptance have been developed, but they typically involve adding complex structures.

Now, researchers at Tohoku University (Sendai, Japan) have come up with a more straightforward way to boost absorptance of graphene at a chosen arbitrary frequency: add a quarter-wave thin-film dielectric stack to each side of a graphene film, with the graphene acting as the plane of symmetry. The stacks, consisting of alternating layers of two materials with differing refractive indices (the materials are unspecified in the theoretical study), cause interference and a boost to the electric field in proximity to the graphene, which in turn causes absorption from joule heating of the graphene. The resulting absorption reaches to 50%. The researchers hope to experimentally test their idea soon. Reference: S. A. Nulli et al., Appl. Phys. Lett., 112, 073101 (2018).