title: Effective method to extract optical bandgaps in Si nanowire arrays.
abstract: A simple method to extract the optical bandgap of Si nanowire (SiNW) arrays that utilizes the reflection spectra of freestanding SiNW arrays is presented in this Letter. At a fixed nanowire diameter, three different wire lengths reproducibly formed a cross point in their reflectance curve plots. The cross point wavelength corresponded to the optical bandgap, as verified by the classical Tauc's model. The optical bandgap of the SiNW arrays (112 nm in average diameter) was measured to be ~1.19 eV, which is larger than the ~1.08 eV bandgap of bulk Si. Further decreasing the wire diameter to 68 nm caused an increase of the bandgap to ~1.24 eV, which is closer to the optimal bandgap (~1.40 eV) required to achieve the highest conversion efficiency in single-junction photovoltaic devices. Our method suggests that the multijunction tandem structure can be realized via control of the diameter of SiNW arrays.
authors.affiliation: Department of Chemical Engineering, Hanyang University, Ansan, Kyounggi 426-791, South Korea.
authors.forename: Jin-Young
authors.initials: JY
authors.lastname: Jung
authors.forename: Keya
authors.initials: K
authors.lastname: Zhou
authors.forename: Han-Don
authors.initials: HD
authors.lastname: Um
authors.forename: Zhongyi
authors.initials: Z
authors.lastname: Guo
authors.forename: Sang-Won
authors.initials: SW
authors.lastname: Jee
authors.forename: Kwang-Tae
authors.initials: KT
authors.lastname: Park
authors.forename: Jung-Ho
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000042:Absorption; D053770:Nanowires; D055620:Optical Phenomena; D012825:Silicon / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D012825:Silicon