Comparative study of effect of add layer on the field and reflectance parameters of plasmonic structure

In this research article, we have theoretically studied the effects of add layer on the reflectance spectra and field-dependent performance parameter of considered surface plasmon resonance (SPR) sensor structure. First, we optimized the thickness of considered metal thin-film layer. After that, we have added ten different add layers, one at a time, (PTTE, LiF, MgO, Si₃N_4, TiO_2, LiNbO_3, GaN, BaTiO_3, GaS, and GaP) over metal thin film at optimized the thickness. The conventional and four-layered SPR sensors structure are simulated using COMSOL Multiphysics software. Furthermore, we analysed the obtained reflectance spectra parameter, i.e., resonance angle (θ_r), change in resonance angle (∆θ_r)_, full beam width (FBW), sensitivity (S), quality factor (Q), and figure of merit (FoM) as well as field-dependent performance parameters, i.e., penetration depth (PD) and field intensity at different interfaces, i.e., metal–sample (M–S), metal–dielectric (M–D) and dielectric–sample (D–S). We found that ∆θ_r is maximum for GaP and GaN, i.e., 1.60° among all the considered add layer which signifies the higher sensitivity of the four layer. After that FBW is maximum for four-layer structure with GaP as an add layer, i.e., 15.43°, detection accuracy is maximum for four-layer SPR sensor with GaN as add layer, i.e., 1053 × 10^–4 and FoM is also maximum for four-layer SPR sensor with LiNbO₃ as an add layer, i.e., 7.288 (a.u./RIU). Furthermore, PD is maximum for four-layer considered structure with LiF as an add layer, i.e., 185.14 nm. Moreover, at constant thickness of the considered add layer, sensitivity, detection accuracy, quality factor, and FoM increases with the refractive index of the add layer, whereas PD decreases. After that, field intensity at M–D interface is higher than D–S interface for all considered SPR sensor structure. Furthermore, at constant thickness of add layer, the field intensity at interfaces increases with the refractive index of add layer. The presented comparative study will help to choose add layer over metal thin film in an SPR sensor.