M. T. Ahmadi

Modeling of graphene nano-ribbon Schottky diodes in the parabolic band structure limit

In this paper we investigate the band structure of graphene nano-ribbons and the current density. A square root approximation shows that the band energy is parabolic in the low energy limit. In this parabolic region charge transport is controlled by the saturation velocity.

CARBON NANOTUBE CAPACITANCE MODEL IN DEGENERATE AND NONDEGENERATE REGIMES

In this work, fundamental results on carrier statistics in a carbon nanotube treated as a one‐dimensional material are presented. Also the effect of degeneracy on the capacitance of the carbon nanotube channel in a carbon nan‐otube field effect transistor is discussed. A quantum capacitance as well as a classical capacitance is revealed. Furthermore it is shown that for low gate voltage, the total capacitance is equivalent to the classical capacitance but for high gate voltage it is equivalent to the quantum capacitance. We predict that in the nondegenerate regime, the total capacitance is equivalent to the classical capacitance and that the quantum capacitance can be neglected, whereas only quantum capacitance needs to be taken into account in the calculation of the total capacitance in the degenerate regime.

Electrical Property Analytical Prediction on Archimedes Chiral Carbon Nanoscrolls

Carbon nanoscrolls (CNS) with flexible exterior areas and interesting electrical and mechanical properties have gained interest in recent years, both experimentally and theoretically. These structures have been employed as ion channels, tunable water channels, molecular sensors, and gene and drug distribution systems. In this study, electrical behaviour of all types of CNS containing armchair, zigzag, and chiral CNSs band structure is investigated. In armchair CNSs, the small band gap among valence and the conduction band as a pseudo-gap are reported, which reveals a semimetallic property for some of these CNSs. This small band gap, as a result of layer interaction, has been confirmed. Also, in many other types of armchair CNSs at the Fermi level, related levels cross each other, illustrating metallic characteristics. On the other hand, our numerical results show small band gaps for zigzag types of CNSs, which means that they are semiconductors. However, it cannot be considered as a general occurrence because only in rare circumstances is a very small band gap observed that gives rise to semimetallic CNSs. In addition, the electrical properties of chiral CNSs are explored. Small band gaps between the associated valence and the conduction band reveals that chiral CNSs mainly exhibit semiconducting behaviour. Finally, all the numerical results are tabulated in the form of a CNS periodic table and a symmetric arrangement with respect to the armchair nanoscrolls and as a table diagonal data for the chiral CNSs is noticed. In addition, this investigation highlights the variations of the energy structure of chiral CNSs with respect to their length. Presented results offer significant potential for chiral CNSs as an alternative to silicon-based sensors in nanotechnology. Therefore, the band gap variations in the presence of attached materials as a sensor platform need to be explored.

Quantum confinement effect on trilayer graphene nanoribbon carrier concentration

In this study, one-dimensional vision of carrier movement based on the band structure of trilayer graphene nanoribbon in the presence of a perpendicular electric field is employed. An analytical model of ABA-stacked trilayer graphene nanoribbon carrier statistics as a fundamental parameter of field effect transistor (FET) in corporation with a numerical solution is presented in the degenerate and non-degenerate limits. The simulated results based on the presented model indicate that the model can be approximated by degenerate and non-degenerate approximations in some numbers of normalised Fermi energy. Analytical model specifies that carrier concentration in degenerate limit is strongly independent of normalised Fermi energy; however, in the non-degenerate limit, it is a strong function of normalised Fermi energy. The proposed model is then compared with other types of graphene. As a result, the developed model can assist in comprehending experiments involving trilayer graphene nanoribbon FET-based devices.

Trilayer graphene nanoribbon carrier statistics in degenerate and non degenerate limits

We present trilayer graphene nanoribbon carrier statistics in the degenerate and the nondegenerate limits. Within zero to 3kBT from the conduction or valence band edgers high concentrations of carriers sensitively depend on a normalized Fermi energy which is independent of temperature. The effect of different stacking orders of graphene multilayers on the electric field induced band gap is studied. The gap for trilayer graphene with the ABC stacking is much larger than the corresponding gap for the ABA trilayer. The gap for the different types of stacking is much larger as compared to the case of Bernal stacking. A non-monotonic dependence of the true energy gap in trilayer graphene on the charge density is investigated along with the electronic low-energy band structure of ABC stacked multilayer graphene. The band structure of trilayer graphene systems in the presence of a perpendicular electric field is obtained using a tight-binding approach.

QUANTUM CAPACITANCE EFFECT ON ZIG-ZAG GRAPHENE NANOSCROLLS (ZGNS) (16, 0)

Miniaturization of electronic devices carries them to the quantum limits which mean quantum effect will be dominant in nano-size device characterization. A first band analytical model of the quantum capacitance for (16, 0) zig-zag graphene nanoscroll (ZGNS) is presented. The behavior of the quantum capacitance within the degeneracy limits is approximated using the Maxwell–Boltzmann approximation within a range of E - EF > 3KBT. The quantum capacitance is subsequently derived from the carrier density of the ZGNS due to its significance within one-dimensional (1D) devices by employing the Taylors series expansion for parabolic energy band structure approximation. Additionally, the quantum capacitance analytical derivation in term of ZGNS physical form considering the Archimedean spiral-type structure is modeled. Because of its unique geometry structure which provides high area for intercalation, it is expected that ZGNS structure (length and interlayer distances) will alter the quantum capacitance. We also report that at first sub-band of (16, 0) ZGNS the quantum capacitance reach degenerate limit at approximately of ≅ 0.49 × 10-10F/m @ 49 pF/m.

A review on carbon-based materials as on-chip interconnects

Interconnect wires are major technology components of modern high-speed integrated circuits. To overcome the latters degradation caused by increasing miniaturization, there is an urgent need to look for alternative technologies. Since carbon based materials generate promising results, this paper focuses on describing the electrical properties of carbon based materials, in particular the use of graphene nanoribbon (GNR) as well as trilayer graphene nanoribbon (TGN) as next generation interconnects: since the conductance of TGN is less affected by external fields compared to GNR, it forms an improved choice for on-chip interconnects. The conductance model of TGN is derived and discussed in detail.

Strain effect on graphene nanoribbon carrier statistic in the presence of non-parabolic band structure

The effect of tensile uniaxial strain on the non-parabolic electronic band structure of armchair graphene nanoribbon (AGNR) is investigated. In addition, the density of states and the carrier statistic based on the tight-binding Hamiltonian are modeled analytically. It is found that the property of AGNR in the non-parabolic band region is varied by the strain. The tunable energy band gap in AGNR upon strain at the minimum energy is described for each of n-AGNR families in the non-parabolic approximation. The behavior of AGNR in the presence of strain is attributed to the breakable AGNR electronic band structure, which varies the physical properties from its normality. The linear relation between the energy gap and the electrical properties is featured to further explain the characteristic of the deformed AGNR upon strain.

The effect of width on graphene nanoribbon density of state under uniaxial strain

In this paper, an analytical density of states modeling and simulation study was performed for 3m, 3m+1 and 3m+2 armchair-edge graphene nanoribbon under smaller tensile uniaxial strain. It has been discovered that the irregular variation in DOS as a function of energy when the tensile uniaxial strain is increased from 0% to 3%. In addition, despite to be reduced in terms of energy gap, 3m+1-AGNR is reported to have higher DOS compared to the other families of AGNR while the energy gap opening is confirmed to behave according to its familys behavior.

The impact of germanium in strained Si/relaxed Si1−xGex on carrier performance in non-degenerate and degenerate regimes

The impact of the fraction of germanium on the carrier performance of two-dimensional strained silicon, which embraces both the non-degenerate and degenerate regimes, is developed. In this model, the Fermi integral of order zero is employed. The impact of the fraction of germanium on the relaxed Si1−xGex substrate (x), carrier concentration and temperature is reported. It is revealed that the effect of x on the hole concentration is dominant for a normalized Fermi energy of more than three, or in other words the non-degenerate regime. On the contrary, the x gradient has less influence in the degenerate regime. Furthermore, by increasing x there is an increase in the intrinsic velocity, particularly with high carrier concentration and temperature.