title: Near-unity broadband absorption designs for semiconducting nanowire arrays via localized radial mode excitation.
abstract: We report design methods for achieving near-unity broadband light absorption in sparse nanowire arrays, illustrated by results for visible absorption in GaAs nanowires on Si substrates. Sparse (<5% fill fraction) nanowire arrays achieve near unity absorption at wire resonant wavelengths due to coupling into 'leaky' radial waveguide modes of individual wires and wire-wire scattering processes. From a detailed conceptual development of radial mode resonant absorption, we demonstrate two specific geometric design approaches to achieve near unity broadband light absorption in sparse nanowire arrays: (i) introducing multiple wire radii within a small unit cell array to increase the number of resonant wavelengths, yielding a 15% absorption enhancement relative to a uniform nanowire array and (ii) tapering of nanowires to introduce a continuum of diameters and thus resonant wavelengths excited within a single wire, yielding an 18% absorption enhancement over a uniform nanowire array.
authors.forename: Katherine T
authors.initials: KT
authors.lastname: Fountaine
authors.forename: Christian G
authors.initials: CG
authors.lastname: Kendall
authors.forename: Harry A
authors.initials: HA
authors.lastname: Atwater