Hot electron based surface plasmon resonance sensor with Au-TiO2-Ti planar micro-comb structure Schottky diodes

In this article, we present an innovative SPR sensor containing Au-TiO2-Ti planar comb-structure Schottky diodes based on Kretschmann’s configuration, and discussed the feasibility of collecting plasmon-induced hot electrons as the signal of SPR sensor instead of traditional optical measurement. Taking advantage of the intrinsic energy transition process between electromagnetic waves and electrons, i.e., Landau damping, the hot electron-hole pairs (EHPs) are excited directly where the surface plasmon waves decay into. Theoretically, the amount of EHPs is determined by the resonance state of surface plasmon, and further determined by the refractive index change in the sensing area. In this device, the effective sensing area, which is critical and limited by the propagating characters of surface plasmon, and the mean free path of EHPs, is enlarged by intensively distributed micro comb structures. We fabricated the devices on 4-inch quartz wafer with photolithography, electron-beam evaporation (EBE), and lift-off process. These fabricated devices exhibited rectified I-V relations in electrical characterization experiments. The evaluated barrier height is 0.73 eV, but series resistance and ideality factor were not ideal as expected due to fabrication defects. We measured the responsivity of 0.75 uA/mW, under illumination of a 850nm infrared laser beam through a N-BK7 prism coupler. The current response from detection of standard solutions indicated a sensitivity of 1.87×10-4 RIU/nA and a limit of detection (LoD) of 4.13×10-3 RIU. In conclusion, this article provides a feasible method to drastically simplify the conventional SPR sensing configuration with mass-produced, small, and economical comb-structure Schottky diode sensor.