Abstract
This paper presents an comprehensive study of light trapping and absorption enhancement in graphene through metallic plasmonic structures and shows a strategy to realize both ultrabroadband and strong absorption enhancement. Three different plasmonic absorber designs are investigated by numerical simulations. The excitation of localized plasmons in the metallic structures significantly enhances the interactions between graphene and light at the resonances. By employing a splitted cross design for plasmonic resonant antennas and integrating two types of sub-antennas with different sizes, more than 30% of optical absorption in monolayer graphene is realized in a ultrabroad spectral range from 780 to 1760 nm. This enhancement functionality can be translated to any wavelength band from ultraviolet to terahertz ranges by modifying the geometric design of the plasmonic structure and can be applied for other two dimensional materials and their heterogeneous structures. It may significantly improve the efficiency of optical devices such as broadband photodetectors and solar cells based on graphene and other two-dimensional materials.
Highlights
In the past few years, graphene and other two-dimensional materials have emerged as promising materials for optics and optoelectronics[1,2,3]
The metallic structures consist of arrays of periodical metallic crosses backed by a metallic mirror, which is a well-known design for plasmonic perfect absorbers[39]
By employing a splitted cross design for plasmonic resonant antennas, dual resonances can be obtained in the studied spectral range
Summary
In the past few years, graphene and other two-dimensional materials have emerged as promising materials for optics and optoelectronics[1,2,3]. Graphene shows very high carrier mobility and exhibits a nearly wavelength-independent absorption of about 2.3% in the visible and near infrared range which is related to the fine structure constant[14,15]. These properties make graphene a novel material for high speed and broadband photodetectors with a couple of exciting demonstrations having been made recently[16,17]. At short wavelengthes in the visible and near infrared range, localized plasmons of metallic nanostructures have been exploited for light trapping and absorption enhancement in graphene[34,35,36,37]. The enhanced absorption is more than one order higher than that by a freestanding graphene film without enhancement
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