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. 2012 Jun 19:3:906.
doi: 10.1038/ncomms1911.

Light-matter interaction in a microcavity-controlled graphene transistor

Michael Engel  1 , Mathias Steiner, Antonio Lombardo, Andrea C Ferrari, Hilbert V Löhneysen, Phaedon Avouris, Ralph Krupke
Affiliations
Free PMC article

Light-matter interaction in a microcavity-controlled graphene transistor

Michael Engel et al. Nat Commun. .
Free PMC article

Abstract

Graphene has extraordinary electronic and optical properties and holds great promise for applications in photonics and optoelectronics. Demonstrations including high-speed photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have now been reported. More advanced device concepts would involve photonic elements such as cavities to control light-matter interaction in graphene. Here we report the first monolithic integration of a graphene transistor and a planar, optical microcavity. We find that the microcavity-induced optical confinement controls the efficiency and spectral selection of photocurrent generation in the integrated graphene device. A twenty-fold enhancement of photocurrent is demonstrated. The optical cavity also determines the spectral properties of the electrically excited thermal radiation of graphene. Most interestingly, we find that the cavity confinement modifies the electrical transport characteristics of the integrated graphene transistor. Our experimental approach opens up a route towards cavity-quantum electrodynamics on the nanometre scale with graphene as a current-carrying intra-cavity medium of atomic thickness.

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Figures

Figure 1
Figure 1. Microcavity-induced optical confinement of graphene.
Visualization of a graphene layer located at the centre of a planar optical λ/2 microcavity. Optical fields with wavelength λ are confined in the direction perpendicular to the cavity mirrors with spacing L. The optical coupling is maximized if the graphene layer is oriented parallel to the cavity mirrors.
Figure 2
Figure 2. Microcavity-controlled graphene transistor and photocurrent generation.
(a) Schematic representation and electrical interconnection of the device. Inset: cross-sectional view of the device. The graphene sheet is embedded between two Ag mirrors and separated by two dielectric layers (Si3N4; Al2O3). The thickness L of the dielectric stack between the cavity mirrors determines the resonance wavelength λ of the optical microcavity. Also shown is a visualization of the intensity profile of the fundamental λ/2 cavity mode. (b) Top-view scanning electron microscope false colour image of the device; graphene sheets (yellow), Pd contacts (blue) Ag mirror (red). Scale bar, 2 μm. (c) Optical white light transmission micrograph of the device. The fundamental cavity mode is spectrally located at λcavity=585 nm, which appears green to the eye. Scale bar, 4 μm. (d) Optical transmission spectrum of the device (black line) measured with white light illumination reveals the cavity resonance at λcavity=585 nm having a cavity-Q of 20. The measured laser-induced photocurrent amplitude (red dots) samples the spectral profile of the optical cavity resonance. (e) Electrical transfer (left) and output (right) characteristics of the device; the fit (red solid line) to the transfer data (open symbols) is explained in the main text.
Figure 3
Figure 3. Electrically excited microcavity-controlled graphene thermal emitter.
(a) The schematic visualizes how thermal light emission is generated by applying a drain bias and how thermal radiation couples to the optical cavity mode. (b) Thermal near-infrared emission spectra measured for a cavity-confined (open circles) and a non-confined (filled squares) graphene transistor. The emission spectra of the cavity-controlled graphene transistor displays the optical resonance of the cavity at λcavity=925 nm. The left y-axis is the intensity of the non-confined emission (log scale), whereas the right y-axis is the intensity of the confined emission (linear scale). The indicated temperatures are derived by fitting the non-confined thermal radiation spectra to Planck's law (see Methods). (c) Simulated spectra of cavity-controlled thermal radiation (solid lines) and non-confined thermal radiation (dashed lines) modelled by assuming that the cavity resonance is spectrally located at λcavity =925 nm and has a spectral full width at half maximum of 30 nm. (d) Spectrally integrated light intensity as function of electrical power for three devices with different channel sizes (red 1×1 μm2, blue 2×2 μm2, purple 4×4 μm2). The solid lines are T3 fits assuming that the dissipated electrical power is proportional to the temperature T in the graphene sheet.
Figure 4
Figure 4. Optical confinement and electrical transport in a microcavity-controlled graphene transistor.
(a) Schematic illustration of the sample layout. (b) Normalized and integrated emitted light intensity (blue) and electrical current (red) as a function of bias voltage measured with a non-confined graphene transistor and (c) the integrated light intensity (blue) and the electrical resistance (red) plotted as a function of electrical power density. (d) Schematic illustration of the sample layout. (e) Normalized integrated emitted light intensity (blue) and electrical current (red) as a function of bias voltage measured with a microcavity-controlled graphene transistor and (f), the integrated light intensity (blue) and the electrical resistance (red) plotted as a function of electrical power density. Three regimes can be identified: (I) sub-threshold, (II) threshold and (III) above threshold, respectively.
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