Effect of external magnetic field on the instability of THz plasma waves in nanoscale graphene field-effect transistors

The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.

Realization of low contact resistance close to theoretical limit in graphene transistors

Realizing low contact resistance between graphene and metal electrodes remains a well-known challenge for building high-performance graphene devices. In this work, we attempt to reduce the contact resistance in graphene transistors and further explore the resistance limit between graphene and metal contacts. The Pd/graphene contact resistance at room temperature is reduced below the 100 Ω·μm level both on mechanically exfoliated and chemical-vapor-deposition graphene by adopting high-purity palladium and high-quality graphene and controlling the fabrication process to not contaminate the interface. After excluding the parasitic series resistances from the measurement system and electrodes, the retrieved contact resistance is shown to be systematically and statistically less than 100 Ω·μm, with a minimum value of 69 Ω·μm, which is very close to the theoretical limit. Furthermore, the contact resistance shows no clear dependence on temperature in the range of 77-300 K; this is attributed to the saturation of carrier injection efficiency between graphene and Pd owing to the high quality of the graphene samples used, which have a sufficiently long carrier mean-free-path.

Comparative Study of Monolayer and Bilayer Epitaxial Graphene Field-Effect Transistors on SiC Substrates

Monolayer and bilayer graphenes have generated tremendous excitement as the potentially useful electronic materials due to their unique features. We report on monolayer and bilayer epitaxial graphene field-effect transistors （GFETs） fabricated on SiC substrates. Compared with monolayer GFETs, the bilayer GFETs exhibit a significant improvement in dc characteristics, including increasing current density I DS, improved transconductance g m, reduced sheet resistance lion, and current saturation. The improved electrical properties and tunable bandgap in the bilayer graphene lead to the excellent dc performance of the bilayer GFETs. Furthermore, the improved dc characteristics enhance a better rf performance for bilayer graphene devices, demonstrating that the quasifree-standing bilayer graphene on SiC substrates has a great application potential for the future graphene-based electronics.

Application of graphene vertical field effect to regulation of organic light-emitting transistors

The luminescence intensity regulation of organic light-emitting transistor(OLED)device can be achieved effectively by the combination of graphene vertical field effect transistor(GVFET)and OLED.In this paper,we fabricate and characterize the graphene vertical field-effect transistor with gate dielectric of ion-gel film,confirming that its current switching ratio reaches up to 102.Because of the property of high light transmittance in ion-gel film,the OLED device prepared with graphene/PEDOT:PSS as composite anode exhibits good optical properties.We also prepare the graphene vertical organic light-emitting field effect transistor(GVOLEFET)by the combination of GVFET and graphene OLED,analyzing its electrical and optical properties,and confirming that the luminescence intensity can be significantly changed by regulating the gate voltage.

Effect of Residual Charge Carrier on the Performance of a Graphene Field Effect Transistor

The temperature-dependent effect of residual charge carrier （no）, at the Dirac point, on mobility is studied. We fabricate and characterize a graphene field effect transistor （GFET） using 7nm TiO2 as the top-gate dielectric. The temperature-dependent gate voltage-drain current and room temperature gate capacitance are measured to extract the carrier mobility and to estimate the quantum capacitance of the GFET. The device shows the mobility value of gOO cm^2 /V.s at room temperature and it decreases to 45 cm^2 /V.s for 20 K due to the increase of n0. These results indicate that the phonon scattering is not the dominant process for the unevenness dielectric layer while the coulomb scattering by charged impurities degrades the device characteristically at low temperature.

Impact of Channel Length and Width for Charge Transportation of Graphene Field Effect Transistor

The effect of channel length and width on the large and small-signal parameters of the graphene field effect transistor have been explored using an analytical approach.In the case of faster saturation as well as extremely high transit frequency,the graphene field effect transistor shows outstanding performance.From the transfer curve,it is observed that there is a positive shift of Dirac point from the voltage of 0.15 V to 0.35 V because of reducing channel length from 440 nm to 20 nm and this curve depicts that graphene shows ambipolar behavior.Besides,it is found that because of widening channel the drain current increases and the maximum current is found approximately 2.4 mA and 6 mA for channel width 2μm and 5μm respectively.Furthermore,an approximate symmetrical capacitance-voltage(C-V)characteristic of the graphene field effect transistor is obtained and the capacitance reduces when the channel length decreases but the capacitance can be increased by raising the channel width.In addition,a high transconductance,that demands high-speed radio frequency(RF)applications,of 6.4 mS at channel length 20 nm and 4.45 mS at channel width 5μm along with a high transit frequency of 3.95 THz have been found that demands high-speed radio frequency applications.

Depositing aluminum as sacrificial metal to reduce metal–graphene contact resistance

Reducing the contact resistance without degrading the mobility property is crucial to achieve high-performance graphene field effect transistors. Also, the idea of modifying the graphene surface by etching away the deposited metal provides a new angle to achieve this goal. We exploit this idea by providing a new process method which reduces the contact resistance from 597Ω ·μm to sub 200 Ω ·μm while no degradation of mobility is observed in the devices. This simple process method avoids the drawbacks of uncontrollability, ineffectiveness, and trade-off with mobility which often exist in the previously proposed methods.

Ultrasensitive detection of methamphetamine by antibody-modified transistor assay

Effective detection of methamphetamine(Met)requires a fast,sensitive,and cheap testing assay.However,commercially available methods require expensive instruments and highly trained operators,which are time-consuming and labor-intensive.Herein,an antibody-modified graphene transistor assay is developed for sensitive and minute-level detection of Met in complex environments.The anti-Met probe captured charged targets within 120 s,leading to a p-doping effect near the graphene channel.The limit of detection reaches 50 aM(5.0×10^(-17)M)Met in solution.The graphene transistor would be a valuable tool for Met detection effective prevention of drug abuse.

Computational Model of Edge Effects in Graphene Nanoribbon Transistors

We present a semi-analytical model incorporating the effects of edge bond relaxation,the third nearest neighbor interactions,and edge scattering in graphene nanoribbon fi eld-effect transistors(GNRFETs)with armchair-edge GNR(AGNR)channels.Unlike carbon nanotubes(CNTs)which do not have edges,the existence of edges in the AGNRs has a signifi cant effect on the quantum capacitance and ballistic I V characteristics of GNRFETs.For an AGNR with an index of m=3p,the band gap decreases and the ON current increases whereas for an AGNR with an index of m=3p+1,the quantum capacitance increases and the ON current decreases.The effect of edge scattering,which reduces the ON current,is also included in the model.

Graphene field effect transistor-based terahertz modulator with small operating voltage and low insertion loss

In this work, we report a broadband terahertz wave modulator based on a top-gate graphene field effect tran- sistor with polyimide as the gate dielectric on a PET substrate. The transmission of the terahertz wave is modulated by controlling the Fermi level of graphene via the polyimide as the top-gate dielectric material instead of the traditional dielectric materials. It is found that the terahertz modulator can achieve a modulation depth of ~20.9% with a small operating gate voltage of 3.5 V and a low insertion loss of 2.1 dB.

A silicon-graphene-silicon transistor with an improved current gain

In history,semiconductor-metal-semiconductor transistor(SMST)was proposed for frequency improvement.However,a general fabrication method is still missing due to the unsolved technological problem of deposition of a general crystalline semiconductor on metal,and a thinner metal base is also difficult to be fabricated with high quality.Recently,due to the atomic thickness of graphene,the concept of semiconductor-graphene-semiconductor transistor(SGST)has emerged which leads to the renaissance of SMST,however the experimental study is in its infancy.In this letter,SMST and SGST are fabricated using Si membrane transfer.It is found the common base current gain can be improved from about 0.5%in a Si-Au-Si transistor to about 1%in a Si-Gr-Ge one,and to above 10%in a Si-Gr-Si one,which is attributed to both the ultra-thin thickness and the quantum capacitance effect of graphene.

A method to transfer an individual graphene flake to a target position with a precision of sub-micrometer

Graphene field-effect transistors have been intensively studied.However,in order to fabricate devices with more complicated structures,such as the integration with waveguide and other two-dimensional materials,we need to transfer the exfoliated graphene samples to a target position.Due to the small area of exfoliated graphene and its random distribution,the transfer method requires rather high precision.In this paper,we systematically study a method to selectively transfer mechanically exfoliated graphene samples to a target position with a precision of sub-micrometer.To characterize the doping level of this method,we transfer graphene flakes to pre-patterned metal electrodes,forming graphene field-effect transistors.The hole doping of graphene is calculated to be 2.16×10^12cm^-2.In addition,we fabricate a waveguide-integrated multilayer graphene photodetector to demonstrate the viability and accuracy of this method.A photocurrent as high as 0.4 μA is obtained,corresponding to a photoresponsivity of 0.48 mA/W.The device performs uniformly in nine illumination cycles.

Construction of highly accessible single Co site catalyst for glucose detection

The development of high-performance glucose sensors is an urgent need, especially for diabetes mellitus diagnosis. However, the glucose monitoring is conventionally operated in an invasive finger-prick manner and their noninvasive alternatives largely suffered from the relatively poor sensitivity, selectivity, and stability, resulted from the lack of robust and efficient catalysts. In this paper, we design a concave shaped nitrogen-doped carbon framework embellished with single Co site catalyst(Co SSC) by selectively controlling the etching rate on different facet of carbon substrate, which is beneficial to the diffusion and contact of analyte. The Co SSC prompts a significant improvement in the sensitivity of the solutiongated graphene transistor(SGGT) devices, with three orders of magnitude better than those of SGGT devices without catalysts. Our findings expand the field of single site catalyst in the application of biosensors, diabetes diagnostics and personalized health-care monitoring.

Sentaurus~based modeling and simulation for GFET's characteristic for ssDNA immobilization and hybridization

The graphene field effect transistor （GFET） has been widely studied and developed as sensors and functional devices. The first report about GFET sensing simulation on the device level is proposed. The GFET＇s characteristics, its responding for single strand DNA （ssDNA） and hybridization with the complimentary DNA （cDNA） are simulated based on Sentaurus, a popular CAD tool for electronic devices. The agreement between the simulated blank GFET feature and the reported experimental data suggests the feasibility of the presented simulation method. Then the simulations of ssDNA immobilization on GFET and hybridization with its cDNA are performed, the results are discussed based on the electron transfer （ET） mechanism between DNA and graphene.