title: Six-fold hexagonal symmetric nanostructures with various periodic shapes on GaAs substrates for efficient antireflection and hydrophobic properties.
abstract: We fabricated various periodic nanostructures with a six-fold hexagonal symmetry on gallium arsenide (GaAs) substrates using simple process steps, together with a theoretical analysis of their antireflective properties. Elliptical photoresist (PR) nanopillars, which are inevitably generated by the asymmetric intensity distribution of the laser interference, were converted to rounded lens-like patterns by a thermal reflow process without any additional complex optic systems, thus leading to an exact six-fold hexagonal symmetry. Various shaped periodic nanostructures including nanorods, cones, truncated cones, and even parabolic patterns were obtained under different etching conditions using the rounded lens-like PR patterns formed by the reflow process. For the parabolic structure, the calculated lowest average reflectance of ∼ 2.3%  was obtained. To achieve better antireflection characteristics, an aluminum-doped zinc oxide (AZO) film was deposited on the GaAs parabolas, which forms an AZO/GaAs parabolic nanostructure. The structure exhibited a low average reflectance of ∼ 1.2%  over a wide wavelength region of 350-1800 nm and a hydrophobic surface with a water contact angle of θ(c) ∼ 115°. The calculated reflectances were reasonably consistent with the measured results.
authors.affiliation: Department of Electronics and Radio Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do, Republic of Korea.
authors.forename: Jung Woo
authors.initials: JW
authors.lastname: Leem
authors.forename: Young Min
authors.initials: YM
authors.lastname: Song
authors.forename: Jae Su
authors.initials: JS
authors.lastname: Yu