Large Responsivity of Graphene Radiation Detectors With Thermoelectric Readout: Results of Simulations

Simple estimations show that the thermoelectric readout in graphene radiation detectors can be extremely effective even for graphene with modest charge-carrier mobility ∼ 1000 cm 2 /(Vs). The detector responsivity depends mostly on the residual charge-carrier density and split-gate spacing and can reach competitive values of ∼ 10 3 - 10 4 V/W at room temperature. The optimum characteristics depend on a trade-off between the responsivity and the total device resistance. Finding out the key parameters and their roles allows for simple detectors and their arrays, with high responsivity and sufficiently low resistance matching that of the radiation-receiving antenna structures

Temperature distribution in a large Bi2Sr2CaCu2O8+δ mesa

Joule heating in large Bi2Sr2CaCu2O8+delta mesas was numerically analyzed while taking into account typical thermal conductivities and their temperature dependences of all the materials involved in heat dissipation and removal. Such mesas are used in experiments on THz-range radiation. The analysis shows that the temperature increases with bias current and is distributed unevenly along the mesas. The temperature of the mesa's middle part can even exceed T-c at sufficiently high bias. The overall current-voltage characteristics are also calculated self-consistently, showing a negative differential conductance in a wide range of currents

Detection of graphene microelectromechanical system resonance

We present an experimental setup for fast detection of resonances of graphene microelectromechanical structures of different quality. The relatively simple technique used to read-out of the resonance frequency is the main advantage of the proposed system. The resolution is good enough to detect vibrations of the graphene resonator with the quality factor of ∼24 and resonance frequency of 104 MHz

Cleaning graphene using atomic force microscope

We mechanically clean graphene devices using an atomic force microscope (AFM). By scanning an AFM tip in contact mode in a broom-like way over the sample, resist residues are pushed away from the desired area. We obtain atomically flat graphene with a root mean square (rms) roughness as low as 0.12 nm after this procedure. The cleaning also results in a shift of the charge-neutrality point toward zero gate voltage, as well as an increase in charge carrier mobility

Family of graphene-based superconducting devices

A family of highly sensitive devices based on a graphene nanobridge and superconducting electrodes has been developed, manufactured, and examined. These devices can be used to create a graphene-based integral receiver. A cold-electron bolometer prototype with superconductor-insulator-normal metal tunnel junctions has been studied. Its response to a change in the temperature and external microwave radiation has been measured. A superconducting quantum interferometer with a graphene strip as a weak coupling between superconducting electrodes has been examined. The corresponding modulation of the voltage by a magnetic field at a given current has been measured. The effect of the gate voltage on the resistance of graphene has been analyzed for these samples. To confirm that graphene is single-layer, measurements with the reference samples were performed in high magnetic fields, displaying the half-integer quantum Hall effect

High mobility graphene on EVA/PET

Transparent conductive film on a plastic substrate is a critical component in low cost, flexible and lightweight optoelectronics. CVD graphene transferred from copper- to ethylene vinyl acetate (EVA)/polyethylene terephthalate (PET) foil by hot press lamination has been reported as a robust and affordable alternative to manufacture highly flexible and conductive films. Here, we demonstrate that annealing the samples at 60\ua0∘C under a flow of nitrogen, after wet etching of copper foil by nitric acid, significantly enhances the Hall mobility of such graphene films. Raman, Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the morphology and chemical composition of the graphene

Graphene bolometer with thermoelectric readout and capacitive coupling to an antenna

We report on a prototype graphene radiation detector based on the thermoelectric effect. We used a split top gate to create a p-n junction in the graphene, thereby making an effective thermocouple to read out the electronic temperature in the graphene. The electronic temperature is increased due to the AC currents induced in the graphene from the incoming radiation, which is first received by an antenna and then directed to the graphene via the top-gate capacitance. With the exception of the constant DC voltages applied to the gate, the detector does not need any bias and is therefore very simple to use. The measurements showed a clear response to microwaves at 94 GHz with the signal being almost temperature independent in the 4-100 K temperature range. The optical responsivity reached ∼700 V/W

Current-induced enhancement of photo-response in graphene THz radiation detectors

Thermoelectric readout in a graphene terahertz (THz) radiation detector requires a p-n junction across the graphene channel. Even without an intentional p-n junction, two latent junctions can exist in the vicinity of the electrodes/antennas through the proximity to the metal. In a symmetrical structure, these junctions are connected back-to-back and therefore counterbalance each other with regard to rectification of the ac signal. Because of the Peltier effect, a small dc current results in additional heating in one and cooling in another p-n junction, thereby breaking the symmetry. The p-n junctions then no longer cancel, resulting in a greatly enhanced rectified signal. This allows simplifying the design and controlling the sensitivity of THz radiation detectors

Unusual thermopower of inhomogeneous graphene grown by chemical vapor deposition

We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone

Chiral charge pumping in graphene deposited on a magnetic insulator

We demonstrate that a sizable chiral charge pumping can be achieved at room temperature in graphene/Yttrium Iron Garnet (YIG) bilayer systems. The effect, which cannot be attributed to the ordinary spin pumping, reveals itself in the creation of a dc electric field/voltage in graphene as a response to the dynamic magnetic excitations (spin waves) in an adjacent out-of-plane magnetized YIG film. We show that the induced voltage changes its sign when the orientation of the static magnetization is reversed, clearly indicating the broken spatial inversion symmetry in the studied system. The strength of effect shows a non-monotonous dependence on the spin-wave frequency, in agreement with the proposed theoretical model.Comment: 8 pages, 5 figure