  Metallic nanoslit arrays integrated on germanium metal-semiconductor-metal
photodetectors show many folds of absorption enhancement for
transverse-magnetic polarization in the telecommunication C-band. Such high
enhancement is attributed to resonant interference of surface plasmon modes at
the metal-semiconductor interface. Horizontal surface plasmon modes were
reported earlier to inhibit photodetector performance. We computationally show,
however, that horizontal modes enhance the efficiency of surface devices
despite reducing transmitted light in the far field.
