Contactless Microwave Characterization of Encapsulated Graphene p−n Junctions (original) (raw)

Non-contact method for measurement of the microwave conductivity of graphene

Applied Physics Letters, 2013

We report a non-contact method for conductivity and sheet resistance measurements of monolayer and few layers graphene samples using a high Q microwave dielectric resonator perturbation technique, with the aim of fast and accurate measurement. The dynamic range of the microwave conductivity measurements makes this technique sensitive to a range of imperfections and impurities and can provide rapid non-contacting characterisation. As a demonstration of the power of the technique, we present results for graphene samples grown by three different methods with widely differing sheet resistance values. [

Heat Confinement in Graphene Devices Using Superconducting Contacts

2013

We report on noise and thermal conductance measurements taken in order to determine an upper bound on the performance of graphene as a terahertz photon detector. The main mechanism for sensitive terahertz detection in graphene is bolometric heating of the electron system. To study the properties of a device using this mechanism to detect terahertz photons, we perform Johnson noise thermometry measurements on graphene samples. These measurements probe the electron-phonon behavior of graphene on silicon dioxide at low temperatures. Because the electronphonon coupling is weak in graphene, superconducting contacts with large gap are used to confine the hot electrons and prevent their out-diffusion. We use niobium nitride leads with a T c ≈ 10 K to contact the graphene. We find these leads make good ohmic contact with very low contact resistance. Our measurements find an electronphonon thermal conductance that depends quadratically on temperature above 4 K and is compatible with single terahertz photon detection.

Nonlinear vs. bolometric radiation response and phonon thermal conductance in graphene-superconductor junctions

Journal of Applied Physics, 2014

Graphene is a promising candidate for building fast and ultra-sensitive bolometric detectors due to its weak electron-phonon coupling and low heat capacity. In order to realize a practical graphene-based bolometer, several important issues, including the nature of radiation response, coupling efficiency to the radiation and the thermal conductance need to be carefully studied. Addressing these issues, we present graphene-superconductor junctions as a viable option to achieve efficient and sensitive bolometers, with the superconductor contacts serving as hot electron barriers. For a graphene-superconductor device with highly transparent interfaces, the resistance readout in the presence of radio frequency radiation is dominated by non-linear response. On the other hand, a graphene-superconductor tunnel device shows dominantly bolometric response to radiation. For graphene devices fabricated on SiO2 substrates, we confirm recent theoretical predictions of T2 temperature dependence of ...

Microwave Photodetection in an Ultraclean Suspended Bilayer Graphene p–n Junction

Nano Letters, 2016

We explore the potential of bilayer graphene as cryogenic microwave photodetector by studying the microwave absorption in fully suspended clean bilayer graphene p-n junctions in the frequency range of 1 − 5 GHz at a temperature of 8 K. We observe a distinct photocurrent signal if the device is gated into the p-n regime, while there is almost no signal for unipolar doping in either the n-n or p-p regimes. Most surprisingly, the photocurrent strongly peaks when one side of the junction is gated to the Dirac point (charge-neutrality point CNP), while the other remains in a highly doped state. This is different to previous results where optical radiation was used. We propose a new mechanism based on the phototermal effect explaining

Subgap states in two-dimensional spectroscopy of graphene-based superconducting hybrid junctions

Physical review, 2019

The two-dimensional nature of graphene makes it an ideal platform to explore proximity-induced unconventional planar superconductivity and the possibility of topological superconductivity. Using Green's functions techniques, we study the transport properties of a finite size ballistic graphene layer placed between a normal state electrode and a graphene lead with proximity-induced unconventional superconductivity. Our microscopic description of such a junction allows us to consider the effect of edge states in the graphene layer and the imperfect coupling to the electrodes. The tunnel conductance through the junction and the spectral density of states feature a rich interplay between graphene's edge states, interface bound states formed at the graphene-superconductor junction, Fabry-Pérot resonances originated from the finite size of the graphene layer, and the characteristic Andreev surface states of unconventional superconductors. Within our analytical formalism, we identify the separate contribution from each of these subgap states to the conductance and density of states. Our results show that graphene provides an advisable tool to determine experimentally the pairing symmetry of proximity-induced unconventional superconductivity.

Superconducting quantum interference devices with graphene junctions

Bulletin of the American Physical Society, 2017

A series of five dc superconducting quantum interference devices ͑SQUIDs͒ have been operated as microstrip amplifiers at frequencies ranging from 2.2 to 7.4 GHz. In these devices, the signal is connected between the SQUID washer and coil, which acts as a microstrip resonator. The gain measured at 4.2 K ranged from 12Ϯ1 to 6Ϯ1 dB. The noise temperature of three devices at 4.2 K in the frequency range 2.2-4 GHz was between 1 and 2 K, and the saturation temperature was between 150 and 250 K. Applications of these devices include readout for axion detectors, and intermediate-frequency amplifiers for superconductor-insulator-superconductor and hot-electron bolometer mixers.

Graphene Gas Sensing using a Non-Contact Microwave Method

Nanotechnology, 2017

We report a non-contact CVD graphene gas sensing method that utilises a high Q microwave dielectric resonator perturbation technique. A graphene sample is coupled to the evanescent field of a dielectric resonator whereupon nitrogen dioxide (NO2), a p-doping gas, is detected by monitoring the change in the linewidth and frequency of the resonant mode. The resonant peak shape is dependent on the number of carriers in the graphene sheet. Therefore, the linewidth perturbation can be converted to a measurement of the graphene sheet resistance. To demonstrate the strength of this technique, sensor response curves for NO2 at different concentrations and temperatures are measured showing sub ppm sensitivity. This technique eliminates interactions between the trace gas and metal contacts that otherwise effect the sensor response of the graphene device.

Microwave method for high‐frequency properties of graphene

IET Circuits, Devices & Systems, 2015

Graphene is a remarkable material, which is yet to make the transition from unique laboratory phenomenon to useful industrial material. One missing element in the development process is a quick method of quality control of the electrical properties of graphene which may be applied in, or close to, the graphene growth process on an industrial scale. In this study, the authors describe a non-contact method using microwave resonance which potentially solves this problem. They describe the technique, consider its limitations and accuracy and suggest how the method may have future take up.

Surface conductance of graphene from non-contact resonant cavity

Measurement, 2016

A method is established to reliably determine surface conductance of single-layer or multi-layer atomically thin nano-carbon graphene structures. The measurements are made in an air filled standard R100 rectangular waveguide configuration at one of the resonant frequency modes, typically at TE 103 mode of 7.4543 GHz. Surface conductance measurement involves monitoring a change in the quality factor of the cavity as the specimen is progressively inserted into the cavity in quantitative correlation with the specimen surface area. The specimen consists of a nanocarbon-layer supported on a low loss dielectric substrate. The thickness of the conducting nanocarbon layer does not need to be explicitly known, but it is assumed that the lateral dimension is uniform over the specimen area. The non-contact surface conductance measurements are illustrated for a typical graphene grown by chemical vapor deposition process, and for a high quality monolayer epitaxial graphene grown on silicon carbide wafers for which we performed non-gated quantum Hall resistance measurements. The sequence of quantized transverse Hall resistance at the Landau filling factors ν = ±6 and ±2, and the absence of the Hall plateau at ν = 4 indicate that the epitaxially grown graphene is a high quality mono-layer. The resonant microwave cavity measurement is sensitive to the surface and bulk conductivity, and since no additional processing is required, it preserves the integrity of the conductive graphene layer. It allows characterization with high speed, precision and efficiency, compared to transport measurements where sample contacts must be defined and applied in multiple processing steps.

Bolometric response in graphene based superconducting tunnel junctions

Applied Physics Letters, 2012

We fabricate graphene-TiOx-aluminum tunnel junctions and characterize their radio frequency response. Below the superconducting critical temperature of aluminum and when biased within the superconducting gap, the devices show enhanced dynamic resistance which increases with decreasing temperature. Application of radio frequency radiation affects the dynamic resistance through electronic heating. The relation between the electron temperature rise and the absorbed radiation power is measured, from which the bolometric parameters, including heat conductance, noise equivalent power, and responsivity, are characterized.