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

Abstract

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.

Antenna resonances in low aspect ratio semiconductor nanowires

“…A similar deviation toward glancing angles was found by Abujetas et al for the absorption cross section of optically thin InP nanowires [45]. Instead of the angular dispersion seen in the infinite cylinder, the mode spectrum for a finite wire consists of a well defined set of localized modes with fixed resonance frequencies.…”

“…7(g,h)). Comparison of both the mode symmetry and spectral position with the infinite cylinder case [45] shows that the a 3 2 mode coincides with the first hybrid leaky mode, HE 11 , which may explain the enhanced excitation of this particular mode toward glancing angles.…”

“…(g,h) Calculated mode profiles (both E and H fields) for selected modes a 3 2 for TM and b 9 2 for TE polarizations, for angles of incidence of 10 • and 90 • . Small shift in resonance wavelength for a 3which corresponds to the conversion of the (cylindrical) Mie resonances to the weakly damped leaky modes of a cylindrical waveguide [40,45]. In addition, the spectral resonance positions of the modes of an infinite cylinder are a function of the angle of incidence [25], resulting in a continuous evolution of the mode positions over the spectrum (angular dispersion).…”

“…Evidence of the role of longitudinal cavity modes and optical antenna effects and their relation to photon confinement within the wire was investigated in several works related to enhancement of Raman scattering [41,42] and to realizations of photonic and plasmonic lasing [43,44]. Recently, the interplay between Mie resonances and leaky modes was numerically investigated in the limit of optically thin nanowires [45]. In particular, a distinction was introduced between the cylindrical Mie resonances, which are poles at given (oblique) angle of incidence in the complex frequency plane, and leaky modes which are damped wavevector solutions at glancing angles.…”

Periodically Diameter‐Modulated Semiconductor Nanowires for Enhanced Optical Absorption

“…[ 9,10 ] Recent theoretical and experimental works have revealed that light coupling into leaky guided modes is responsible for the resonant optical absorption at grazing light incidences with respect to the nanowire axis, while Mie resonances play a critical role mostly at nongrazing incidences. [11][12][13] The leaky/guided mode resonances in simple cylindrical nanowires occur at specifi c resonance wavelengths that depend on the nanowire diameter, and the free spectral range between these resonances can be extremely large in such cylindrical nanowire resonators, resulting in the enhancement of optical absorption only in specifi c spectral regions near the resonance wavelengths. [ 14,15 ] Dual-or multiple-diameter nanowire arrays may exhibit resonances with an increased spectral density, thereby enhancing the optical absorption over a broad spectral range.…”