title: Ordered arrays of dual-diameter nanopillars for maximized optical absorption.
abstract: Optical properties of highly ordered Ge nanopillar arrays are tuned through shape and geometry control to achieve the optimal absorption efficiency. Increasing the Ge materials filling ratio is shown to increase the reflectance while simultaneously decreasing the transmittance, with the absorbance showing a strong diameter dependency. To enhance the broad band optical absorption efficiency, a novel dual-diameter nanopillar structure is presented, with a small diameter tip for minimal reflectance and a large diameter base for maximal effective absorption coefficient. The enabled single-crystalline absorber material with a thickness of only 2 μm exhibits an impressive absorbance of ∼99% over wavelengths, λ = 300-900 nm. These results enable a viable and convenient route toward shape-controlled nanopillar-based high-performance photonic devices.
authors.affiliation: Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Fan
authors.forename: Rehan
authors.initials: R
authors.lastname: Kapadia
authors.forename: Paul W
authors.initials: PW
authors.lastname: Leu
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Zhang
authors.forename: Yu-Lun
authors.initials: YL
authors.lastname: Chueh
authors.forename: Kuniharu
authors.initials: K
authors.lastname: Takei
authors.forename: Kyoungsik
authors.initials: K
authors.lastname: Yu
authors.forename: Arash
authors.initials: A
authors.lastname: Jamshidi
authors.forename: Asghar A
authors.initials: AA
authors.lastname: Rathore
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Ruebusch
authors.forename: Ming
authors.initials: M
authors.lastname: Wu
authors.forename: Ali
authors.initials: A
authors.lastname: Javey