Graphene is a very attractive material for broadband photodetection in hyperspectral imaging and sensing systems. However, its potential use has been hindered by tradeoffs between the responsivity, bandwidth, and operation speed of existing graphene photodetectors. Here, we present engineered photoconductive nanostructures based on gold-patched graphene nano-stripes, which enable simultaneous broadband and ultrafast photodetection with high responsivity. These nanostructures merge the advantages of broadband optical absorption, ultrafast photocarrier transport, and carrier multiplication within graphene nano-stripes with the ultrafast transport of photocarriers to gold patches before recombination. Through this approach, high-responsivity operation is realized without the use of bandwidth-limiting and speed-limiting quantum dots, defect states, or tunneling barriers. We demonstrate high-responsivity photodetection from the visible to infrared regime (0.6 A/W at 0.8 μm and 11.5 A/W at 20 μm), with operation speeds exceeding 50 GHz. Our results demonstrate improvement of the response times by more than seven orders of magnitude and an increase in bandwidths of one order of magnitude compared to those of higher-responsivity graphene photodetectors based on quantum dots and tunneling barriers.
We investigate metadevices working in microwave frequencies by integrating passive metamaterials with active graphene devices.
Graphene as transparent electrode for direct observation of hole photoemission from silicon to oxide Appl. Phys. Lett. 102, 123106 (2013) Temperature dependent thermal conductivity of a free-standing graphene nanoribbon Appl. Phys. Lett. 102, 111911 (2013) Directional quantum transport in graphyne p-n junction J. Appl. Phys. 113, 073710 (2013) Charge transport in lightly reduced graphene oxide: A transport energy perspective J. Appl. Phys. 113, 063710 (2013) Effect of chiral property on hot phonon distribution and energy loss rate due to surface polar phonons in a bilayer graphene J. Appl. Phys. 113, 063705 (2013) Additional information on J. Appl. Phys. Shubnikov-de Haas (SdH) and Hall effect measurements performed in a temperature range between 1.8 and 275 K, at an electric field up to 35 kV m À1 and magnetic fields up to 11 T, have been used to investigate the electronic transport properties of monolayer graphene on SiC substrate. The number of layers was determined by the use of the Raman spectroscopy. The carrier density and in-plane effective mass of electrons have been obtained from the periods and temperature dependencies of the amplitude of the SdH oscillations, respectively. The effective mass is in good agreement with the current results in the literature. The two-dimensional (2D) electron energy relaxations in monolayer graphene were also investigated experimentally. The electron temperature (T e ) of hot electrons was obtained from the lattice temperature (T L ) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss indicate that the energy relaxation of electrons is due to acoustic phonon emission via mixed unscreened piezoelectric interaction and deformation-potential scattering.
An approach for obtaining one-way transmission in the beaming regime is suggested that is based on the directional radiation of surface plasmons in nonsymmetric metallic gratings with a single slit. In contrast to the various nonsymmetric one-way diffraction gratings that have recently been proposed, the possibility of obtaining of narrow beams is demonstrated. Strong directional selectivity can appear a wide range of the observation angles, while the angle of incidence is retained. © 2010 Optical Society of America OCIS codes: 050.2770, 240.6690.Achieving optical isolation has been the focus of interest for a long time. Within the passive framework, it can be obtained using anisotropic [1,2] or nonlinear [3] materials. Recently, several grating structures have been proposed for freely propagating waves, which enable the realization of the regimes with strong directional selectivity, that are not the same but similar in some features to the conventional isolation [4][5][6]. They all only contain isotropic constituents, and therefore no transformation of the initially linear polarization of the incident wave occurs.In particular, it has been shown for the branched slit metallic gratings with different periods of the front-and back-side interfaces (nonsymmetric gratings) at normal incidence, θ ¼ 0, that higher-order transmittance can be either zero or nonzero, depending on whether the larger-period or smaller-period interface is illuminated [4]. In contrast to the slit gratings, in those based on the photonic crystals with nonisotropic dispersion, the zero order cannot be coupled to a Floquet-Bloch wave in the vicinity of θ ¼ 0, so transmittance is zero in one direction and nonzero in the opposite direction, while θ is retained. Furthermore, a similar effect can be obtained at θ ≠ 0 in case of isotropic dispersion with the effective index of refraction as 0 < n eff < 1, for example, in the gratings containing low-permittivity layers [6], and in the photonic crystal gratings [5]. If only zero order is coupled to a wave propagating inside a grating, the interfaces are isolated from each other in the sense that the numbers of higher diffraction orders, which contribute to transmission and reflection, are determined only by the period of the corresponding interfaces. The common features of the approaches in [4][5][6] are that at least one higher order is propagating and that they operate with wide beams.At the same time, beaming is known to be obtainable in metallic gratings with slits, owing to surface plasmons [7][8][9][10][11]. For example, a plane or corrugated interface between a Drude metal and dielectric medium can support surface plasmons [12]. Since the skin depth of the plane metallic surfaces in the microwave regime approaches zero, they cannot be supported. Pendry et al. theoretically showed that the metallic surfaces, which can be thought of as perfect electric conductors in microwave regime, can support surface-plasmon-like waves, known as designer surface plasmons, when the surface has subwavelength hol...
Cataloged from PDF version of article.Strong directional selectivity is theoretically predicted and experimentally validated at the microwave frequencies in the beaming regime for a single subwavelength slit in nonsymmetric metallic gratings with double-side corrugations. The operation regime can be realized at a fixed angle of incidence when the surface-plasmon assisted transmission is significant within a narrow range of observation angles, if illuminating one of the grating interfaces, and tends to vanish for all observation angles, if illuminating the opposite interface. The studied effect is connected with asymmetry (nonreciprocity) in the beaming that occurs if the surface plasmon properties are substantially different for the two interfaces being well isolated from each other. (c) 2011 American Institute of Physics
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