Optimization of Fully Integrated Al Nanohole Array-Based Refractive Index Sensors for Use With a LED Light Source

Plasmonic nanohole arrays that are directly structured into the top metallization of vertical Ge-on-Si PIN photodiodes can be used to sense refractive index changes. This concept can pave the way to fully integrated biosensors with small footprint and high sensitivities. Here, we show that by optimizing the layer structure of the Ge-on-Si PIN photodiode as well as the geometry of the nanohole arrays, we can achieve high and narrow optical responsivity peaks with Fano-resonance lineshapes. We used an iterative, simulation-based approach in order to optimize the photodiode layer structure as well as the nanohole geometry and compared the predictions to measurement results obtained from fabricated devices. Our fabricated device shows large peak shifts upon changes in the superstrate refractive index. Finally, we argue that the improved device setup can have potential applications in a sensor system that uses an LED light source and estimate the limit of detection to be 2.2·10 −5 RIU.