Abstract
We theoretically investigated the enhancement of light intensity in a semiconductor near the surface by
metal gratings with a coupled-mode method, focusing on the enhancement under the metal opening (slit).
Although the enhancement peaks at the Fabry-Perot resonance wavelengths, dark lines appear in it under
the slit at wavelengths slightly longer than the diffraction’s onset called the Rayleigh wavelength. By
inspecting the reflection coefficient at the slit’s exit interface, we clarified that the disappearance of the
enhancement is caused by the boundary conditions at the interface and is a general feature of metal
gratings.
