Highly doped InAsSb plasmonic arrays for mid-infrared biosensing

We propose 1D periodic, highly doped InAsSb gratings on GaSb substrates as biosensing platforms applicable at the same time for surface plasmon resonance and surface enhanced infrared absorption spectroscopies. Finite-difference time-domain simulations frame array geometries (nanoribbon width and spacing), in relation to the electric field enhancement and the sensitivity on refractive index variations, for a given molecular absorption region in the mid-infrared. These optimized systems achieve sensitivities of ∼ 900 nm RIU
⁻¹
. A clear red shift of the plasmon resonance as well as the enhancement of an absorption line are presented for 2 nm thin layers. We experimentally analyze the influence of the InAsSb doping level exposing the gratings in reflection measurements to different surrounding environments. A comparison to a gold grating with equivalent optical properties in the mid-infrared is performed. Our simulations and experimental results underline the interest in the alternative plasmonic material InAsSb for highly sensitive plasmonic biosensors for the mid-infrared spectral range.