Morphology-dependent high antireflective surfaces via anodic aluminum oxide nanostructures

High density honeycombed nano-pattern of anodic aluminum oxide (AAO) is of great use to various high-performance optoelectronic devices due to its non-lithographic and excellent sub-wavelength structure (SWS) anti-reflection (AR) properties. In this paper, we introduce an ultra-thin AAO based bilayer polydimethylsiloxane (PDMS) scheme to simply replicate and obtain regular triangle-like surface nano-pillar array with a period of 125 nm, which shows a 5% to 27% AR enhancement under the light wavelength ranging from 250 nm to 850 nm. In order to investigate the intrinsic property of AAO nano-structure based light extraction properties, gallium nitride (GaN) light-emitting models are built. Compared to the bare GaN, the maximum AR enhancements of low ordered AAO array, regular array and high ordered AAO array are respectively 20.2%, 22.0% and 23.5%. Grain size effect is found to further improve the AR performance of the high ordered AAO array and the effective refractive index based thin film model demonstrates a success in AAO pattern-dependent surface AR analysis. Besides, by tailoring the side-wall profile, a further AR enhancement (e.g. 39.1%) can be obtained because of a smoothly changing of the refractive index along the height direction.