ABSTRACT
Graphene is ideally suited for optoelectronics. It offers absorption at telecom wavelengths, high-frequency operation and CMOS-compatibility. We show how high speed optoelectronic mixing can be achieved with high frequency (~20 GHz bandwidth) graphene field effect transistors (GFETs). These devices mix an electrical signal injected into the GFET gate and a modulated optical signal onto a single layer graphene (SLG) channel. The photodetection mechanism and the resulting photocurrent sign depend on the SLG Fermi level (EF). At low EF (<130 meV), a positive photocurrent is generated, while at large EF (>130 meV), a negative photobolometric current appears. This allows our devices to operate up to at least 67 GHz. Our results pave the way for GFETs optoelectronic mixers for mm-wave applications, such as telecommunications and radio/light detection and ranging (RADAR/LIDARs.).
ABSTRACT
Correction for 'Transport mechanisms in a puckered graphene-on-lattice' by T. Xu et al., Nanoscale, 2018, 10, 7519-7525.
ABSTRACT
Understanding the fundamental properties of graphene when its topography is patterned by the use of a compliant substrate is essential to improve the performances of graphene sensors. Here we suspend a graphene monolayer on SiO2 nanopillar arrays to form a puckered graphene-on-lattice and investigate the strain and electrical transport at the nanoscale. Despite a nonuniform strain in the graphene-on-lattice, the resistivity is governed by thermally activated transport and not the strain. We show that the high thermal activation energy results from a low charge carrier density and a periodic change of the chemical potential induced by the interaction of the graphene monolayer with the nanopillars, making the use of graphene-on-lattice attractive to further increase the electrical response of graphene sensors.
ABSTRACT
We investigate the magneto-transport properties of epitaxial graphene single-layer on 4H-SiC(0001), grown by atmospheric pressure graphitization in Ar, followed by H2 intercalation. We directly demonstrate the importance of saturating the Si dangling bonds at the graphene/SiC(0001) interface to achieve high carrier mobility. Upon successful Si dangling bonds elimination, carrier mobility increases from 3 000 cm(2)V(-1)s(-1) to >11 000 cm(2)V(-1)s(-1) at 0.3 K. Additionally, graphene electron concentration tends to decrease from a few 10(12) cm(-2) to less than 10(12) cm(-2). For a typical large (30 × 280 µm(2)) Hall bar, we report the observation of the integer quantum Hall states at 0.3 K with well developed transversal resistance plateaus at Landau level filling factors of ν = 2, 6, 10, 14... 42 and Shubnikov de Haas oscillation of the longitudinal resistivity observed from about 1 T. In such a device, the Hall state quantization at ν = 2, at 19 T and 0.3 K, can be very robust: the dissipation in electronic transport can stay very low, with the longitudinal resistivity lower than 5 mΩ, for measurement currents as high as 250 µA. This is very promising in the view of an application in metrology.
ABSTRACT
Trilayer graphene is of particular interest to the 2D materials community because of its unique tunable electronic structure. However, to date, there is a lack of fundamental understanding of the properties of epitaxial trilayer graphene on silicon carbide. Here, following successful synthesis of large-area uniform trilayer graphene, atomic force microscopy (AFM) showed that the trilayer graphene on 6H-SiC(0001) was uniform over a large scale. Additionally, distinct defects, identified as flower-shaped domains and isolated wrinkle structures, were observed randomly on the surface using scanning tunneling microscopy and spectroscopy (STM/STS). These carbon nanostructures formed during growth, has different structural and electronic properties when compared with the adjacent flat regions of the graphene. Finally, using low temperature STM/STS at 4K, we found that the isolated wrinkles showed an irreversible rotational motion between two 60° configurations at different densities of states.
ABSTRACT
We have investigated the energy loss of hot electrons in metallic graphene by means of GHz noise thermometry at liquid helium temperature. We observe the electronic temperature T â V at low bias in agreement with the heat diffusion to the leads described by the Wiedemann-Franz law. We report on T â âV behavior at high bias, which corresponds to a T(4) dependence of the cooling power. This is the signature of a 2D acoustic phonon cooling mechanism. From a heat equation analysis of the two regimes we extract accurate values of the electron-acoustic phonon coupling constant Σ in monolayer graphene. Our measurements point to an important effect of lattice disorder in the reduction of Σ, not yet considered by theory. Moreover, our study provides a strong and firm support to the rising field of graphene bolometric detectors.
