Unraveling the Janus Role of Mie Resonances and Leaky/Guided Modes in Semiconductor Nanowire Absorption for Enhanced Light Harvesting

Light absorption from finite semiconductor nanowires is investigated through a unified theoretical picture and numerical simulations. We first show theoretically from the electromagnetic mode dispersion relation and the Mie extinction cross sections for infinite nanowires that formally equivalent (Janus) formulas yield both leaky/guided modes and Mie resonances as, respectively, complex wave vector or complex frequency solutions that, in turn, overlap only at grazing angles with respect to the nanowire axis. For finite semiconductor nanowires, the angle of incidence becomes critical: absorption is dominated by Mie resonances at incident angles perpendicular (and oblique) to the nanowire axis; by contrast, guided mode excitation (if spectrally available) governs and enhances absorption at grazing incidence. Such theoretical prediction can be exploited to optimize nanowire designs for broad band and broad angle light harvesting applications.