Razali Ismail

The Ultimate Ballistic Drift Velocity in Carbon Nanotubes

The carriers in a carbon nanotube (CNT), like in any quasi-1-dimensional (Q1D) nanostructure, have analog energy spectrum only in the quasifree direction; while the other two Cartesian directions are quantum-confined leading to a digital (quantized) energy spectrum. We report the salient features of the mobility and saturation velocity controlling the charge transport in a semiconducting single-walled CNT (SWCNT) channel. The ultimate drift velocity in SWCNT due to the high-electric-field streaming is based on the asymmetrical distribution function that converts randomness in zero-field to a stream-lined one in a very high electric field. Specifically, we show that a higher mobility in an SWCNT does not necessarily lead to a higher saturation velocity that is limited by the mean intrinsic velocity depending upon the band parameters. The intrinsic velocity is found to be appropriate thermal velocity in the nondegenerate regime, increasing with the temperature, but independent of carrier concentration. However, this intrinsic velocity is the Fermi velocity that is independent of temperature, but depends strongly on carrier concentration. The velocity that saturates in a high electric field can be lower than the intrinsic velocity due to onset of a quantum emission. In an SWCNT, the mobility may also become ballistic if the length of the channel is comparable or less than the mean free path.

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.

Ballistic quantum transport in a nanoscale metal-oxide-semiconductor field effect transistor

The ballistic saturation velocity in a nanoscale metal-oxide-semiconductor field effect transistor (MOSFET) is revealed to be limited to the Fermi velocity in a degenerately induced channel appropriate for the quasi-two-dimensional nature of the inverted channel. The saturation point drain velocity is shown to rise with the increasing drain voltage approaching the intrinsic Fermi velocity, giving the equivalent of channel-length modulation. Quantum confinement effect degrades the channel mobility to the confining gate electric field as well as increases the effective thickness of the gate oxide. When the theory developed is applied to an 80nm MOSFET, excellent agreement to the experimental data is obtained.

The drain velocity overshoot in an 80 nm metal-oxide-semiconductor field-effect transistor

The current at the onset of saturation in a metal-oxide-semiconductor field-effect transistor (MOSFET) is shown to be limited by the drain velocity that increases toward its saturation value with the increase in the drain voltage. The saturation of velocity crops up as randomly oriented velocity vectors in equilibrium realign themselves to become unidirectional in the presence of an extremely high electric field. The intrinsic velocity, the ultimate saturation velocity, is the function of carrier concentration and temperature, consistent with the predictions of the ballistic transport. The presence of a quantum emission either by emission of a phonon or photon lowers the saturation velocity below its intrinsic value. Channel conduction beyond the quasisaturation point enhances due to the drain velocity overshoot as a result of enhanced drain electric field as drain voltage is increased. The excellent agreement with experimental data on an 80 nm channel, without using any artificial parameters, confirms th...

Ballistic mobility and saturation velocity in low-dimensional nanostructures

Ohms law, a linear drift velocity response to the applied electric field, has been and continues to be the basis for characterizing, evaluating performance, and designing integrated circuits, but is shown not to hold its supremacy as channel lengths are being scaled down. In the high electric field, the collision-free ballistic transport is predicted, while in low electric field the transport remains predominantly scattering-limited in a long-channel. In a micro/nano-circuit, even a low logic voltage of 1V gives an electric field that is above its critical value ec (e>>ec) triggering non-ohmic behavior that results in ballistic velocity saturation. The saturation velocity is an appropriate thermal velocity for a non-degenerate and Fermi velocity for a degenerate system with given dimensionality. A quantum emission may lower this ballistic velocity. The collision-free ballistic mobility in the ohmic domain arises when the channel length is smaller than the mean free path. The results presented will have a profound influence in interpreting the data on a variety of low-dimensional nanostructures.

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.

The high-field drift velocity in degenerately-doped silicon nanowires

The charge transport in nanowires suitable for high-speed applications depends on charge carriers mobility and saturation velocity in the conducting channel. It is shown that the high mobility does not always lead to higher carrier drift velocity. The ultimate drift velocity (the intrinsic velocity) due to the high-electric-field streaming is based on the asymmetrical distribution function that converts randomness in zero-field to a streamlined one in a very high electric field. The saturation velocity limited to the intrinsic velocity is an appropriate thermal velocity for a non-degenerately doped nanowire, increasing with the temperature, but independent of carrier concentration. However, this saturation velocity is the appropriate Fermi velocity for a degenerately doped silicon nanowire, increasing with carrier concentration but independent of temperature. The results obtained are applied to the modelling of a silicon nanowire transistor.

Analytical modeling of glucose biosensors based on carbon nanotubes

In recent years, carbon nanotubes have received widespread attention as promising carbon-based nanoelectronic devices. Due to their exceptional physical, chemical, and electrical properties, namely a high surface-to-volume ratio, their enhanced electron transfer properties, and their high thermal conductivity, carbon nanotubes can be used effectively as electrochemical sensors. The integration of carbon nanotubes with a functional group provides a good and solid support for the immobilization of enzymes. The determination of glucose levels using biosensors, particularly in the medical diagnostics and food industries, is gaining mass appeal. Glucose biosensors detect the glucose molecule by catalyzing glucose to gluconic acid and hydrogen peroxide in the presence of oxygen. This action provides high accuracy and a quick detection rate. In this paper, a single-wall carbon nanotube field-effect transistor biosensor for glucose detection is analytically modeled. In the proposed model, the glucose concentration is presented as a function of gate voltage. Subsequently, the proposed model is compared with existing experimental data. A good consensus between the model and the experimental data is reported. The simulated data demonstrate that the analytical model can be employed with an electrochemical glucose sensor to predict the behavior of the sensing mechanism in biosensors.

Current-voltage characteristics of a silicon nanowire transistor

The nanowires and nanotubes are being considered as the best candidates for high-speed applications. It is shown that the high mobility does not always lead to higher carrier velocity. The ultimate drift velocity due to the high-electric-field streaming are based on the asymmetrical distribution function that converts randomness in zero-field to streamlined one in a very high electric field. The limited drift velocity is found to be appropriate thermal velocity for a nondegenerately doped sample of silicon, increasing with the temperature, but independent of carrier concentration. However, the limited drift velocity is the Fermi velocity for a degenerately doped silicon nanowire, increasing with carrier concentration but independent of temperature. The results obtained are applied to the modeling of the current-voltage characteristics of a nanowire transistor.

Correlation study between land use, water quality, and heavy metals (cd, pb, and zn) content in water and green lipped mussels perna viridis (linnaeus.) At the Johor Strait

In order to observe the variation in land use changes, satellite images from the Landsat Thematic Mapper (TM) and the Enhanced Thematic Mapper (ETM) for 1991, 2000, 2005, and 2008 were used to compare the differences between selected water quality parameters, including heavy metal (Cd, Pb, and Zn) content in both water and green mussels or Perna viridis (Linnaeus.) before and after the increase in land use activities beginning from 2006. The samples were collected at 11 points for water and 4 points for green mussels between the Second Link and the Causeway Link at the Johor Strait in 2009 and were analyzed for pH, temperature degrees Celsius), dissolved oxygen, ammoniacal nitrogen, and heavy metal (Cd, Pb, and Zn) content.