Grating-Based Surface Plasmon Resonance Sensor for Visible Light Employing a Metal/Semiconductor Junction for Electrical Readout

In this study, we proposed an electrical readout surface plasmon resonance (SPR) chemical sensor coupled with visible light to avoid significant light absorption of water. A gold (Au) diffraction grating with a submicrometer pitch, designed using the rigorous coupled-wave analysis (RCWA) method to have a submicrometer pitch and 30-nm-tall Au grating, was fabricated on an n-type silicon (n-Si) substrate by nanofabrication/microfabrication. The hot electrons generated by SPR on the grating are converted to photocurrent at the Schottky barrier at the Au/n-Si interface. The Schottky barrier height was estimated based on the <inline-formula> <tex-math notation="LaTeX">$I-V$ </tex-math></inline-formula> characteristics of the device to be <inline-formula> <tex-math notation="LaTeX">$q{\Phi}_{\mathrm{B}} = 0.72$ </tex-math></inline-formula> eV. The peak shift of photocurrent was observed to be consistentwith the SPR theory when the concentration of glucose aqueous solution changed the refractive index on the Au grating. Assuming that the incident wavelength and angle were fixed, a noise analysis revealed a refractive index resolution of <inline-formula> <tex-math notation="LaTeX">$3.4-4.0 \times 10^{-5}$ </tex-math></inline-formula> refractive index unit (RIU). Since this structure eliminated bulky optics in SPR experiments, it would contribute to the realization of a thin single-chip label-free chemical sensor.