Graphene, a two-dimensional layer of carbon atoms, is a promising material for optoelectronic devices due to its strong light-matter interactions and optical non-linearity. For example, the use of graphene in photodetectors, saturable absorbers, and optical switches has been demonstrated. Application of graphene as a light source still remains a challenge because its gapless nature prevent the interband radiative recombination. Another emission process in graphene, known as Raman scattering, has been widely used to investigate the graphene properties. In particular, G’ Raman scattering in monolayer graphene is stronger than graphite. Coupling of the Raman scattering to the nanocavity is one possible pathway for increasing light emission from graphene.

In this work, we demonstrate enhancements of Raman scattering from monolayer graphene on two-dimensional photonic crystals using double resonances, which originate from simultaneous enhancements by a localized guided mode and a cavity mode. The double resonance can be tuned to the G’ Raman scattering by engineering the hole diameter and lattice constant of the photonic crystal.

We measure the excitation wavelength dependence and observe that the Raman intensity increases when the G’ mode is tuned to the double resonance. Spatial imaging measurements confirm that the enhancement is localized at the photonic crystal cavity, and we obtain an enhancement of the Raman intensity by a factor of 60 compared to that on un-patterned silicon substrate.

To learn more about this work, please refer to:
W. Gomulya, H. Machiya, K. Kashiwa, T. Inoue, S. Chiashi, S. Maruyama, Y. K. Kato Enhanced Raman scattering of graphene using double resonance in silicon photonic crystal nanocavities Appl. Phys. Lett. 113, 081101 (2018).