title: Transparent metallic fractal electrodes for semiconductor devices.
abstract: Nanostructured metallic films have the potential to replace metal oxide films as transparent electrodes in optoelectronic devices. An ideal transparent electrode should possess a high, broadband, and polarization-independent transmittance. Conventional metallic gratings and grids with wavelength-scale periodicities, however, do not have all of these qualities. Furthermore, the transmission properties of a nanostructured electrode need to be assessed in the actual dielectric environment provided by a device, where a high-index semiconductor layer can reflect a substantial fraction of the incident light. Here we propose nanostructured aluminum electrodes with space-filling fractal geometries as alternatives to gratings and grids and experimentally demonstrate their superior optoelectronic performance through integration with Si photodetectors. As shown by polarization and spectrally resolved photocurrent measurements, devices with fractal electrodes exhibit both a broadband transmission and a flat polarization response that outperforms both square grids and linear gratings. Finally, we show the benefits of adding a thin silicon nitride film to the nanostructured electrodes to further reduce reflection.
authors.affiliation: Geballe Laboratory for Advanced Materials , 476 Lomita Mall, Stanford, California 94305-4045, United States.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Afshinmanesh
authors.forename: Alberto G
authors.initials: AG
authors.lastname: Curto
authors.forename: Kaveh M
authors.initials: KM
authors.lastname: Milaninia
authors.forename: Niek F
authors.initials: NF
authors.lastname: van Hulst
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brongersma
keywords: Nanostructured transparent electrodes; Si optoelectronics; metallic gratings; space-filling fractals