High-Contrast Fano Resonances in Single Semiconductor Nanorods

Fano resonances in plasmonics have received widespread attention for their distinctly narrow asymmetric line shapes. A variety of configurations have been considered, either requiring complex metallic nanostructures or being extremely faint if originated in simple single nanoparticles. Here we report on the emergence of high-contrast, strongly asymmetric Fano line shapes in the light scattered from semiconductor nanorods. Numerical calculations are carried out for the scattering cross sections of finite semiconducting nanorods, with dimensions such that the lowest-order (transverse) Mie resonances coexist with the lowest-order guided modes. Such intense narrow Fano resonances are strongly/weakly asymmetric in TE/TM polarization and overlap with the Mie-like background. A physical interpretation is presented stemming from the (strong or weak) interference of the far-field angular patterns of Mie resonances (indeed, of both magnetic and dielectric dipole character) with narrow Fabry–Perot (guided mode) resonances, the latter calculated through a 1D line current model. A quasi-analytical expression is developed for the scattering cross sections that reproduce fairly well the Fano numerical line shapes, along with a generalized Fano formula, with fitting factors confirming their high asymmetry and contrast. These high-contrast, strongly asymmetric Fano resonances herein obtained could be potentially exploited in nanophotonics and sensing in the visible and near-IR, eased by simplified fabrication requirements of shape (nanorod) and material (semiconductor)