Electrically Tunable Coherent Optical Absorption in Graphene with Ion Gel

    Authors

    V. Thareja; J. H. Kang; H. T. Yuan; K. M. Milaninia; H. Y. Hwang; Y. Cui; P. G. Kik;M. L. Brongersma

    Comments

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    Abbreviated Journal Title

    Nano Lett.

    Keywords

    Coherent absorption control; graphene; Salisbury screen; differential; reflectance; transfer matrix; ionic gel; QUANTUM CAPACITANCE; PHOTODETECTOR; PLASMONICS; TRANSPORT; Chemistry, Multidisciplinary; Chemistry, Physical; Nanoscience &; Nanotechnology; Materials Science, Multidisciplinary; Physics, Applied; Physics, Condensed Matter

    Abstract

    We demonstrate electrical control over coherent optical absorption in a graphene-based Salisbury screen consisting of a single layer of graphene placed in close proximity to a gold back reflector. The screen was designed to enhance light absorption at a target wavelength of 3.2 mu m by using a 600 nm-thick, nonabsorbing silica spacer layer. An ionic gel layer placed on top of the screen was used to electrically gate the charge density in the graphene layer. Spectroscopic reflectance measurements were performed in situ as a function of gate bias. The changes in the reflectance spectra were analyzed using a Fresnel based transfer matrix model in which graphene was treated as an infinitesimally thin sheet with a conductivity given by the Kubo formula. The analysis reveals that a careful choice of the ionic gel layer thickness can lead to optical absorption enhancements of up to 5.5 times for the Salisbury screen compared to a suspended sheet of graphene. In addition to these absorption enhancements, we demonstrate very large electrically induced changes in the optical absorption of graphene of similar to 3.3% per volt, the highest attained so far in a device that features an atomically thick active layer. This is attributable in part to the more effective gating achieved with the ion gel over the conventional dielectric back gates and partially by achieving a desirable coherent absorption effect linked to the presence of the thin ion gel that boosts the absorption by 40%.

    Journal Title

    Nano Letters

    Volume

    15

    Issue/Number

    3

    Publication Date

    1-1-2015

    Document Type

    Article

    Language

    English

    First Page

    1570

    Last Page

    1576

    WOS Identifier

    WOS:000351188000019

    ISSN

    1530-6984

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