Abstract
Quarter-wavelength cavity, as a classical structure for preventing wave reflection, presents an effective way to enhance the interaction between light and material of ultrathin thickness. In this paper, we propose a method to control the bandwidth of graphene’s enhanced absorption in quarter-wavelength cavity. By varying the spacing distance between graphene and a metallic reflecting plane, which equals to an odd number of quarter-wavelengths, fundamental and higher order cavity modes are excited, whose fields couple to graphene with different spectral bandwidths, leading to bandwidth-controllable absorption in graphene. Absorption efficiencies of 9% and 40% are measured for graphene monolayer at 15° and 85° incident angles, respectively. Its absorption bandwidth varies between 52% and 10% of the central wavelength when the spacing distance between graphene and metallic reflecting plane increases from a quarter wavelength to seven quarter wavelengths. Our findings pave a way in engineering graphene for strong absorption with a controllable bandwidth, which has potential applications in tailoring spectral response of graphene-based optoelectronic devices.
Highlights
As an emerging two-dimensional material, graphene has attracted considerate interest due to its remarkable properties such as large electron mobility, electrostatic tuning, wideband photoresponse, and strong plasmonic effect.[1]
A 300 nm-thick Cu was deposited by electron beam evaporation onto a silicon wafer, and SiO2 spacer layers with four different thickness of 0.295 μm, 0.935 μm, 1.57 μm and 2.21 μm were grown using plasma enhanced chemical vapor deposition (PECVD) growth, which correspond to approximately d=λ/4n, 3λ/4n, 5λ/4n, 7λ/4n, respectively
Its absorption bandwidth could be varied between 10% and 52% of the central wavelength
Summary
As an emerging two-dimensional material, graphene has attracted considerate interest due to its remarkable properties such as large electron mobility, electrostatic tuning, wideband photoresponse, and strong plasmonic effect.[1]. An alternative approach for increasing absorption of graphene is to use graphene or hybrid graphene/metal nanostructures,[12,13,14,15,16,17,18,19] whose plasmonic resonance effectively intensifies the near-field and thereby enhances the interaction with graphene. A variety of plasmonic structures such as graphene nanodisks and microribbons have been proposed to achieve nearly perfect absorption in graphene,[12,13,19] which depends critically on the actual carrier mobility in graphene.[20] Recently, Fang and Jang et al have demonstrated a strong graphene absorption of 30% in arrayed graphene disks and ribbons in mid-infrared
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