Simulation-based optimization of Ge-PIN-photodiodes with Al nanohole arrays for refractive index sensing

Abstract

Biosensors based on propagating surface plasmon polaritons (SPPs) or localized surface plasmon polaritons can detect molecular binding events with high sensitivity via refractive index changes. In plasmonic nanohole arrays in thin metallic films, the transmission spectra can exhibit characteristic, asymmetric peaks (Fano resonances) that are particularly sensitive to refractive index changes. We integrated Al nanohole arrays into the metallization of vertical Ge-PIN-photodiodes and observed Fano resonances in the photocurrent generated in the Ge-PIN-photodiode, thus fabricating a compact refractive index sensor that can be directly integrated with signal conditioning and wireless transmission circuits. Here, we present simulation results for our devices using finite difference time domain (FDTD) method. We investigate the influence of nanohole array parameters such as hole diameter and array pitch on Ge-PIN-photodiode response. Furthermore, we show that Ge-PIN-photodiode property can be optimized by adjusting thicknesses of the Al layer as well as the semiconductor layers of the Ge-PIN-photodiode underneath. Here, the Al thickness particularly has a large influence on optical properties of our devices. We concluded that sensors consisting of Al nanohole arrays with Ge-PIN-photodiodes can achieve high sensitivities and promising applications in refractive index sensing.