A practical Tamm plasmon sensor based on porous Si

We report the fabrication and characterization of a new type of porous Si sensor using the Tamm plasmon resonance. The sensor consists of a photonic crystal created by periodic electrochemical anodization of crystalline Si, followed by partial thermal oxidation. The photonic crystal is transferred to a Au-coated glass substrate to allow optical measurements of surface modes at the metal/porous Si interface. This configuration greatly simplifies sensing since an analyte can be introduced in the pores from the opposite side of the metal layer without disrupting the optical path. The fabricated device exhibits a Tamm plasmon resonance within the photonic bandgap at a wavelength of 794 nm with a quality factor of 25. We observe a wavelength shift of the resonance when the nanosized pores are infiltrated with different concentrations of a toluene/ethanol solution. The measured sensitivity reaches 139 nm/RIU, in agreement with scattering matrix simulations and more than twice larger than those previously reported for Tamm plasmons. The quality factor and sensitivity yield a sensor figure of merit of 4. We also show that the electric field within the Tamm device is confined within a mode volume twice smaller than within a Fabry–Pérot resonator of comparable size according to calculations.