Graphene-based Field-effect Transistors Research Articles

Label Free DNA Detection Using Large Area Graphene-Based FET Biosensors

ABSTRACTThis work describes the fabrication of highly sensitive graphene-based field effect transistor (FET) biosensors in a cost-effective way and its application in label-free DNA detection. CVD graphene was used to achieve mass production of FET device through photolithography method. Non-covalent functionalization of graphene with 1-Pyrenebutanoic acid succinimidyl ester ensures the high conductivity and sensitivity of the device. The present device could reach the low detection limit as low as 3*10-9 M.

Doping effect on shift of threshold voltage of graphene-based field-effect transistors

A method of controllable doping by ion irradiation in reduced graphene oxide (RGO) is presented, and the threshold voltage of the RGO-based field-effect transistor can be finely tuned in the range from more than 30 V to about −20 V using this approach. Evidence of doping was also provided by Raman spectroscopy and Fourier transform infrared spectroscopy.

Scalable Synthesis of Graphene on Patterned Ni and Transfer

We present an approach to mass produce high-quality graphene on insulator substrate. Ni dots with single or few grains were achieved by annealing. Electron backscattered diffraction indicated that almost all of the Ni dots had (111) surface that is parallel to the substrate. Single-layer graphene with good crystalline quality has been grown on Ni dots. The patterned graphene films were transferred to insulating substrates by wafer bonding and etch back technique, which resulted in zero misalignment, low contamination, and high yield (>90%). Graphene-based field-effect transistors with self-aligned gate were fabricated with this method, which demonstrate the potential of this method as a candidate for mass production of graphene transistors.

Uncovering the dominant scatterer in graphene sheets onSiO2

We have measured the impact of atomic hydrogen adsorption on the electronic transport properties of graphene sheets as a function of hydrogen coverage and initial, pre-hydrogenation field-effect mobility. Our results are compatible with hydrogen adsorbates inducing intervalley mixing by exerting a short-range scattering potential. The saturation coverages for different devices are found to be proportional to their initial mobility, indicating that the number of native scatterers is proportional to the saturation coverage of hydrogen. By extrapolating this proportionality, we show that the field-effect mobility can reach $1.5 \times 10^4$ cm$^2$/V sec in the absence of the hydrogen-adsorbing sites. This affinity to hydrogen is the signature of the most dominant type of native scatterers in graphene-based field-effect transistors on SiO$_2$.

Reversible modifications of linear dispersion: Graphene between boron nitride monolayers

Electronic properties of the graphene layer sandwiched between two hexagonal boron nitride sheets have been studied using the first-principles calculations and the minimal tight-binding model. It is shown that for the $ABC$-stacked structure in the absence of external field the bands are linear in the vicinity of the Dirac points as in the case of single-layer graphene. For certain atomic configuration, the electric field effect allows opening of a band gap of over 230 meV. We believe that this mechanism of energy gap tuning could significantly improve the characteristics of graphene-based field-effect transistors and pave the way for future electronic applications.

Intrinsic doping and gate hysteresis in graphene field effect devices fabricated onSiO2 substrates

We have studied the intrinsic doping level and gate hysteresisof graphene-based field effect transistors (FETs) fabricated overSi/SiO2 substrates. It was found that the high p-doping level of graphene in some as-prepareddevices can be reversed by vacuum degassing at room temperature or abovedepending on the degree of hydrophobicity and/or hydration of the underlyingSiO2 substrate. Charge neutrality point (CNP) hysteresis, consisting of the shift of thecharge neutrality point (or Dirac peak) upon reversal of the gate voltage sweepdirection, was also greatly reduced upon vacuum degassing. However, another type ofhysteresis, consisting of the change in the transconductance upon reversal of thegate voltage sweep direction, persists even after long-term vacuum annealing at200 °C, whenSiO2 surface-bound water is expected to be desorbed. We propose a mechanismfor this transconductance hysteresis that involves water-related defects,formed during the hydration of the near-surface silanol groups in the bulkSiO2, that can act as electron traps.

Graphene field-effect transistors with self-aligned gates

We present a device fabrication process that produces graphene-based field-effect transistors with self-aligned gates. This process utilizes the inherent nucleation inhibition of atomic-layer-deposited films with the graphene surface to achieve electrical isolation of the gate electrode from the source/drain electrodes while maintaining electrical access to the graphene channel. Self-alignment produces access lengths of 15–20 nm, which allows for improved device stability, performance, and a minimal normalized contact resistance of 540 Ω μm.

Ambipolar Behavior in Epitaxial Graphene-Based Field-Effect Transistors on Si Substrate

In this research, ambipolar behavior, which is one of graphene's unique characteristics, is studied for the epitaxial graphene formed on 3C-SiC grown on a Si substrate. The graphene channel is believed to be unintentionally p-type-doped at Dirac-point voltages of approximately +0.11 to +0.12 V. However, as drain voltage negatively increases, Dirac point voltage shifts. The drain current in the p-channel mode of operation saturates at a lower level than that in the n-channel mode of operation. These behaviors are caused by asymmetric carrier transport throughout channel-substrate heterojunctions (i.e., graphene, thin n-type SiC layer, and p-type Si substrate) and source/drain Schottky metal contacts. The interface between the p-type Si substrate and n-type SiC has a significant effect on transport in graphene channels. The results may be helpful for understanding transport in the device and for suppressing ambipolar operation, leading to a unipolar FET operation.

Tunable graphene system with two decoupled monolayers

The use of two truly two-dimensional gapless semiconductors, monolayer and bilayer graphene, as current-carrying components in field-effect transistors (FETs) gives access to special types of nanoelectronic devices. Here, we report on the development of graphene-based FETs containing two decoupled graphene monolayers manufactured from a single one folded during the exfoliation process. The transport characteristics of these devices differ markedly from those manufactured from a single-crystal bilayer. By analyzing Shubnikov–de Haas oscillations, we demonstrate the possibility to independently control the carrier densities in both layers using top and bottom gates, despite there being only a nanometer scale separation between them.

Graphene-Based Organic Field-Effect Transistors Fabricated by Using a Thermally-Treated Exfoliation Technique

Graphene-Based Organic Field-Effect Transistors Fabricated by Using a Thermally-Treated Exfoliation Technique

Free-standing graphene at atomic resolution

Research interest in graphene, a two-dimensional crystal consisting of a single atomic plane of carbon atoms, has been driven by its extraordinary properties, including charge carriers that mimic ultra-relativistic elementary particles. Moreover, graphene exhibits ballistic electron transport on the submicrometre scale, even at room temperature, which has allowed the demonstration of graphene-based field-effect transistors and the observation of a room-temperature quantum Hall effect. Here we confirm the presence of free-standing, single-layer graphene with directly interpretable atomic-resolution imaging combined with the spatially resolved study of both the pi --> pi* transition and the pi + sigma plasmon. We also present atomic-scale observations of the morphology of free-standing graphene and explore the role of microstructural peculiarities that affect the stability of the sheets. We also follow the evolution and interaction of point defects and suggest a mechanism by which they form ring defects.

Substrate-induced band gap in graphene on hexagonal boron nitride:Ab initiodensity functional calculations

We determine the electronic structure of a graphene sheet on top of a lattice-matched hexagonal boron nitride $(h\text{\ensuremath{-}}\mathrm{B}\mathrm{N})$ substrate using ab initio density functional calculations. The most stable configuration has one carbon atom on top of a boron atom, and the other centered above a BN ring. The resulting inequivalence of the two carbon sites leads to the opening of a gap of $53\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at the Dirac points of graphene and to finite masses for the Dirac fermions. Alternative orientations of the graphene sheet on the BN substrate generate similar band gaps and masses. The band gap induced by the BN surface can greatly improve room temperature pinch-off characteristics of graphene-based field effect transistors.

Electrons in bilayer graphene

Electrons in bilayer graphene possess an unusual property: they are chiral quasiparticles characterized by Berry phase 2 π . We review the tight-binding model of bilayer graphene which determines the band structure and low-energy quasiparticle properties of this material and we describe the optical manifestation of the existence of a pair of split-bands and low-energy branches in the bilayer spectrum. Then, we analyze the stability of a bilayer with respect to a ferroelectric transition and we model the self-consistent control of the interlayer asymmetry gap induced by a transverse electric field in a graphene-based field-effect transistor.