Band bending and effective index in the engineered Mach–Zehnder interferometer-based electrolytic sensor

We studied a Mach–Zehnder Interferometer (MZI)-based electrolytic sensor on a silicon-on-insulator (SOI) platform. First, the Si waveguide, integrated with the dielectric layer (SiO₂) and operating under varying pH, is designed using commercial software Nextnano. The impact of the band bending in the SiO₂ integrated with the Si waveguide is presented. Parameters obtained using Nextnano from the designed Si waveguide structure, under varying pH values of electrolytic solutions, were adopted to design an MZI-based electrolytic sensor. We also present a simple strategy for experimental verification of liquid electrolyte’s effects on the optical properties of SiO₂/p-Si using spectroscopic ellipsometry. Two different schemes of MZI-based electrolytic sensors were numerically investigated using the Finite Difference Eigenmode method. A rib waveguide-based sensor demonstrates increased sensitivity compared to a strip waveguide-based sensor. This work contributes to developing robust and waveguide integrated sensors for applications in next-generation electrolytic and biosensors.