Zaharah Johari

Graphene nanoribbon conductance model in parabolic band structure

Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR) with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel.

Modelling of graphene nanoribbon fermi energy

Graphene nanoribbon (GNR) is a promising alternative to carbon nanotube (CNT) to overcome the chirality challenge as a nanoscale device channel. Due to the one-dimensional behavior of plane GNR, the carrier statistic study is attractive. Research works have been done on carrier statistic study of GNR especially in the parabolic part of the band structure using Boltzmann approximation (nondegenerate regime). Based on the quantum confinement effect, we have improved the fundamental study in degenerate regime for both the parabolic and nonparabolic parts of GNR band energy. Our results demonstrate that the band energy of GNR near to the minimum band energy is parabolic. In this part of the band structure, the Fermi-Dirac integrals are sufficient for the carrier concentration study. The Fermi energy showed the temperature-dependent behavior similar to any other one-dimensional device in nondegenerate regime. However in the degenerate regime, the normalized Fermi energy with respect to the band edge is a function of carrier concentration. The numerical solution of Fermi-Dirac integrals for nonparabolic region, which is away from the minimum energy band structure of GNR, is also presented.

Carbon nanotube conductance model in parabolic band structure

Fermi dirac integral is applied to study the parabolic band structure of Carbon Nanotube (CNT) which is in the range of minimum band energy. In this letter electronic transport property of one dimensional carbon nanotube with parabolic band structures near the charge neutrality point is investigated. The temperature dependent conductance model which shows minimum conductance near the charge neutrality point and decreases by decreasing the temperature is presented. CNTs with micrometer length exhibit nondegenerate behavior on fundamental band structure similar to the conventional long channel devices.

Effective mobility model of graphene nanoribbon in parabolic band energy

In this letter, we investigate the transport properties of one-dimensional semiconducting Graphene nanoribbons (GNRs) with parabolic band structure near the Dirac point. The analytical model of effective mobility is developed by using the conductance approach, which differs from the conventional method of extracting the effective mobility using the well-known Matthiessen rule. Graphene nanoribbons conductance model developed was applied in the Drude model to obtain the effective mobility, which then gives nearly close comparison with the experimental data.

BILAYER GRAPHENE NANORIBBON CARRIER STATISTICS IN THE DEGENERATE REGIME

In this paper we discuss the energy band structure of bilayer graphene nanoribbons (BGNRs) near the Fermi level between zero and 3kBT away from the conduction and valence bands. BGNRs can be used as the channel in field effect transistors (FETs). A FET can be created using graphene bilayers with the gate voltage perpendicular to the layers. We focus on carrier statistics in the degenerate regime and the density of states, and consider them to be fundamental properties of BGNRs. The model presented indicates that the normalized Fermi energy in the degenerate regime strongly depends on carrier concentration and is independent of temperature.

DRIFT VELOCITY AND MOBILITY OF A GRAPHENE NANORIBBON IN A HIGH MAGNITUDE ELECTRIC FIELD

We study the high‐field transport behavior of a graphene nanoribbon in the degenerate and nondegenerate regimes by incorporating a previous low field mobility calculation modified for a high electric field in both regimes. The drift velocity model presented predicts that the transport behaviour is different in each regime when subject to an electric field. Our theoretical results are comparable with experimental data. The Fermi velocity (for the degenerate regime) and thermal velocity (for the nondegenerate regime) coupled with optical phonon emission have a large influence on the drift velocity leading to a velocity saturation preceded by a monotonic increase with increasing electric field.

Band energy effect on carrier velocity limit in graphene nanoribbon

Many studies on low-energy limit indicate that band energy of graphene nanoribbon research (GNR) is linear while it illustrates parabolic characteristic with square root approximation model near the Fermi point (k = 0) and non-parabolic characteristic when wave vector is far away from Fermi point . We report that in parabolic and non-parabolic conditions charge transport is controlled by the saturation velocity similar to the conventional one-dimensional device. Also, we claim that at narrower bandwidth the intrinsic velocity approaches saturation faster because wider widths have lighter effective mass, which leads to higher average velocity. The intrinsic velocity is approximated to be thermal velocity in nondegenerate regime and Fermi velocity in degenerate regime, which depends on carrier concentration. Even in very high electric field, because of quantum emission, the saturation velocity can be lower than the intrinsic velocity.

Low-field mobility model on parabolic band energy of graphene nanoribbon

The carrier mobility in low-field specifically in parabolic energy region of one-dimensional graphene nanoribbon (GNR) band energy is presented in this work. Low-field mobility model describe the carrier transport and its dependency factors when dealing with degenerate and non-degenerate principals. The result shows that the low-field mobility strongly depends on the temperature in the non-degenerate regime in which it sharply decreases with increasing temperature in the range of 10–250 K but the mobility is less affected by the temperature above 250 K. The effect of varying the GNR width to the mobility is also demonstrated in this work. In addition, it is also shown that the mobility depends on the carrier concentration in degenerate domain in which it increases at higher carrier concentrations.

Atomistic simulation of stone-wales defect position in armchair graphene nanoribbon field-effect transistor

Graphene continues to fascinate the research community due to its excellent physical and electrical properties. In this study, the electronic and transport characteristics of armchair graphene nanoribbon (AGNR) with a Stone-Wales (SW) defect is investigated. The SW defects are located at three different locations on the AGNR device; underneath the metal gate, near the drain and near the source. The band structures, density of states and transmission spectra are analyzed. The current-voltage characteristics are then extracted and the performance of pristine AGNR and AGNR incorporated with the SW defects is analyzed. From the simulation, it is found that the SW defect alters the electronic and transport properties of the AGNR. Remarkably, the SW defect increases the amount of energy bandgap, while decreasing the drain current. Most notable, the drain current of AGNR FET with SW defect near its source had decreased by almost 60 % compared to the perfect AGNR FET, while the defect at the center caused the drain current to decrease by only 4.13 %. The outcome of this study suggests that defects present on AGNR are not unreasonable and may be useful to enhance the transport properties of AGNR FET. The position of SW defect on the AGNR conducting channel plays an important role to enhance the electrical characteristics of the AGNR FET.

Performance evaluation of dual-channel armchair graphene nanoribbon field-effect transistor

Graphene has become a potential successor to silicon in electronic devices. In this paper, the performance of dual-channel armchair graphene nanoribbon field-effect transistor (AGNR FET) is investigated. Both physical and electrical properties of dual-channel AGNR FET are simulated using Atomistic Tool Kit from Quantum Wise. Their band structures and transmission spectra are analyzed. Current-voltage characteristic is then extracted and the performance of single and dual-channel AGNR FETs is compared. From the simulation, it is found that dual-channel AGNR FET exhibits significant improvement in ON current over two fold. Results obtained will give insight in the implementation of dual-channel AGNR FET for performance enhancement in future electronic devices.