Effect of Diffusion at the AU/N-SI Schottky Interface in Current Detection Surface Plasmon Resonance Sensors

We investigated the causes of performance degradation in surface plasmon resonance (SPR) sensors. Schottky-based photodetectors employ Au, which generates SPR and detects induced currents via internal photoemission at the Au/Si interface, which promoted the development of compact SPR-based chemical sensors. However, Si atoms progressively diffuse into the Au layer, leading to sensor response degradation and induced deviations in the optical responses. Here, we introduced a Mo diffusion barrier layer at the Au/Si interface to inhibit Si diffusion and evaluated its effectiveness through rigorous continuous measurements. Whereas conventional devices presented over 40% drop in responsivity, the diffusion barrier effectively suppressed performance degradation, confirmed by SPR response measurements and spectroscopy analysis. Further, it mitigated surface oxidations and significantly suppressed SPR absorption peak shifts while maintaining responsivity. We reduced the SPR resonance angle shift by 93% and limited the decrease in responsivity, a measure of light sensitivity, by 75%. These findings improve the performance of thin-film SPR sensors, paving the way for practical, compact, label-free sensor applications.