Au–Si Diffusion Effects on Surface Plasmon Resonance Sensor Using Internal Photoemission at Metal/Si Schottky Barrier

Surface plasmon resonance sensors based on Schottky barriers have been extensively studied for their potential to enable compact, high-performance chemical sensing. These sensors utilize gold periodic structures on n-type silicon to couple surface plasmon resonance and convert it into electrical signals via internal photoemission at the gold/silicon (Au/Si) Schottky interface. However, stability over time remains challenging, as such sensors exhibit performance degradation. In this study, we investigate the mechanisms underlying performance degradation in surface plasmon resonance sensors utilizing a Au/Si Schottky barrier, with a particular focus on atomic diffusion at the interface. Rigorous 10-day continuous measurements of a conventional Au/Si sensor demonstrated silicon atom migration to the Au surface, hindering the device operation with a drop in responsivity of over 46%. An alternative design incorporating a molybdenum diffusion barrier layer to mitigate atomic diffusion effectively suppresses both the shift in the surface plasmon resonance angle and the degradation of responsivity over time, as confirmed by SPR response measurements and spectroscopy analysis. These findings address the crucial role of Si diffusion in resonance angle shifts and performance degradation.