Design of mid-infrared photodetectors enhanced by surface plasmons on grating structures

We propose to exploit the unique properties of surface plasmons to enhance the signal-to-noise ratio of mid-infrared photodetectors. The proposed photodetector consists of a slit in a metallic slab filled with absorptive semiconductor material. Light absorption in the slit is enhanced due to Fabry-Perot resonances. Further absorption enhancement is achieved by surrounding the slit with a series of periodic grooves that enable the excitation of surface plasmons that carry electromagnetic energy towards the slit. Using this scheme, we design and optimize a photodetector operating at lambda(0) = 9.8 mu m with a roughly 250 times enhancement in the absorption per unit of volume of semiconductor material compared to conventional photodetectors operating at the same wavelength.