N on-Equilibrium Arora's Distribution Function (NEADF) is a new paradigm in performance evaluatio... more N on-Equilibrium Arora's Distribution Function (NEADF) is a new paradigm in performance evaluation of materials. Silicon is the king of electronics where NEADF has been applied successfully in assessment of CMOS and device nanostructures. With the award of 2010 Nobel Prize to Graphene as a perfect two-dimensional nanomaterial, the attention has shifted to layered semiconductors, including silicine and phosphorene. Bandgap engineering of layered semiconductors to nanowires, nanotubes, and nanoribbons has given new paradigms and new opportunities that will be discussed and new applications explored. It is shown that Ohm's law that is used in characterization breaks down on scaled down dimensions giving rise to velocity and current saturation as electric field exceeds its critical value. Ballistic and quantum transport arising from these scaled-down channels will be brought to light.
Facta universitatis. Series electronics and energetics, 2014
Starting from the graphene layer, the bandgap engineering of carbon nanotubes (CNTs) and graphene... more Starting from the graphene layer, the bandgap engineering of carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) is described by applying an appropriate boundary condition. Linear E-k relationship of graphene transforms to a parabolic one as momentum vector in the tube direction is reduced to dimensions smaller than inverse of the tube diameter of a CNT. Similar transition is noticeable for narrow width of a GNR. In this regime, effective mass and bandgap expressions are obtained. A CNT or GNR displays a distinctly 1D character suitable for applications in quantum transport.
The emerging facts from the successful organizations, including universities, indicate that the r... more The emerging facts from the successful organizations, including universities, indicate that the real source of power in a knowledge-based economy is in combining technical prowess with entrepreneurship. This paper first highlights missing links in the aptitude and attitude of an engineer in combining technical knowledge with sound decision-making and effective entrepreneurship. Second, it discusses the gaps in traditional college education and their remedies through outcome-based curricula. Third, it presents the distinction between leadership and management with reference to new models espoused in the Theory of Constraints (TOC). Fourth, it outlines the skills needed for the professional development of an individual to transform him or her from a traditional quantitative/verbal thinker to a future-oriented visionary by redirecting the whole-brain thinking. Finally, critical success factors in the development of an effective and efficient knowledge worker for the 21 st century are enumerated.
In a recent article, Serov et al. [J. Appl. Phys. 116, 034507 (2014)] claim: "This study represen... more In a recent article, Serov et al. [J. Appl. Phys. 116, 034507 (2014)] claim: "This study represents the first time that the high-field behavior in graphene on a substrate was investigated taking into account intrinsic graphene properties," ignoring the most recent anisotropic distribution function [V. K. Arora et al., J. Appl. Phys. 112, 114330 (2012)] also published in J. Appl. Phys., targeting the same experimental data [V. E. Dorgan et al., Appl. Phys. Lett. 97, 082112 (2010)]. The claim of Serov et al. of being first is refuted and many shortcomings of the hydrodynamic model for a highly quantum and degenerate graphene nanolayer are pointed out. V
Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds grea... more Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds great potential for applications in variety of sensors because of dangling π-bonds that can react with chemical elements. In spite of their excellent features, carbon nanotubes (CNTs) and graphene have not been fully exploited in the development of the nanoelectronic industry mainly because of poor understanding of the band structure of these allotropes. A mathematical model is proposed with a clear purpose to acquire an analytical understanding of the field-effect-transistor (FET) based gas detection mechanism. The conductance change in the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules is emphasized. NH 3 has been used as the prototype gas to be detected by the nanosensor and the corresponding current-voltage (I-V) characteristics of the FET-based sensor are studied. A graphene-based gas sensor model is also developed. The results from graphene and CNT models are compared with the experimental data. A satisfactory agreement, within the uncertainties of the experiments, is obtained. Graphene-based gas sensor exhibits higher conductivity compared to that of CNT-based counterpart for similar ambient conditions.
The emerging facts from the successful organizations, including universities, indicate that the r... more The emerging facts from the successful organizations, including universities, indicate that the real source of power in a knowledge-based economy is in combining technical prowess with entrepreneurship. This paper first highlights missing links in the aptitude and attitude of an engineer in combining technical knowledge with sound decision-making and effective entrepreneurship. Second, it discusses the gaps in traditional college education and their remedies through outcome-based curricula. Third, it presents the distinction between leadership and management with reference to new models espoused in the Theory of Constraints (TOC). Fourth, it outlines the skills needed for the professional development of an individual to transform him or her from a traditional quantitative/verbal thinker to a future-oriented visionary by redirecting the whole-brain thinking. Finally, critical success factors in the development of an effective and efficient knowledge worker for the 21 st century are enumerated.
Malaysian Journal of Fundamental and Applied Sciences, Dec 19, 2014
Nanotube Field Effect Transistor (CNTFET) and Naonowire. For each dimensionality the limitations ... more Nanotube Field Effect Transistor (CNTFET) and Naonowire. For each dimensionality the limitations on carrier drift velocity due to the high-field streaming of otherwise randomly velocity vector in equilibrium is reported. The results are based on the asymmetrical distribution function that converts randomness in zero-field to streamlined one in a very high electric field. The ultimate drift velocity for all dimensions 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 ultimate drift velocity is the Fermi velocity for degenerately doped silicon increasing with carrier concentration but independent of the temperature.
International Journal of Nanotechnology in Medicine & Engineering, 2017
A newfangled paradigm through deployment of the nonequilibrium Arora's distribution function (NEA... more A newfangled paradigm through deployment of the nonequilibrium Arora's distribution function (NEADF) for resistance surge in a carbonnanotube (CNT) ballistic conductor is presented. The experimental nonlinear I-V characteristics, when voltage across the length of aresistor is higher than its critical value, defy ohmic and ballistic transmission through a CNT. The scattering-limited lowfield restance Rois shown not to be valid when voltage is higher than its critical value Vc=IsatRo where Isat is the saturation current. Both Ro and Vc areneeded to characterize a nano resistive channel with default infinite value of Vc for an ohmic resistor. The finite value of Vc necessitates differentiation of incremental signal resistance from the direct one, bringing to focus the surge with the applied voltage. Isat is shown to be limited by the intrinsic velocity which is the Fermi velocity in a metallic CNT.
The effect of nonparabolicity of the conduction band of n-InSb type semiconductors is studied in ... more The effect of nonparabolicity of the conduction band of n-InSb type semiconductors is studied in the framework of the Arora-Peterson density-matrix formalism. To exhibit clearly the effect of nonparabolicity, only the case of elastic electron-acoustic-phonon scattering is considered. Numerical results are presented both for parabolic and nonparabolic models. The nonparabolicity enhances the magnetoresistance, the effect being larger for larger magnetic fields. The Hall coefFicient decreases slightly with the increasing magnetic field.
The theory of electron-lattice scattering is examined for a quantum-well heterostructure in the s... more The theory of electron-lattice scattering is examined for a quantum-well heterostructure in the size quantum limit when most of the electrons populate the lowest quantized subband. The acoustic-phonon scattering is found to be one of the important mechanisms of scattering at inter- mediate temperatures when donors supplying the electrons are removed in an adjacent nonconduct- ing layer.
2010 IEEE International Conference on Semiconductor Electronics (ICSE2010), 2010
The charge carriers in nanowires (NWs), carbon nanotubes (CNTs), and those confined to a very hig... more The charge carriers in nanowires (NWs), carbon nanotubes (CNTs), and those confined to a very high magnetic field have one-dimensional (1D) character as quasi-free propagation of electron waves with analog energy spectrum exists only in one direction. The energy spectrum is quantum (or digital) in other two cartesian directions where electron waves are standing waves. In the quantum limit, an electron (hole) occupies the lowest (highest) digitized/quantized state giving it a distinct 1D character. The energy E = vF | k | in carbon-based devices is linearly dependent on the wave vector k, where vF ˜ 106 m/s. This is in direct contrast to parabolic character E = h2 k2/2m* in solids with effective mass m*, for example in silicon NWs. The probability of changing wavevector from +ve to -ve direction through scattering or vice versa is greatly reduced and hence high mobility is expected, especially at low temperatures. The crucial outcome of this paper is the answer to the question: Does a higher mobility leads to a higher ultimate saturation velocity? The distribution function in a high electric field e is then naturally asymmetrical affected by the energy ±qel absorbed or emitted by a carrier of charge q during its ballistic flight in a mean free path l. The ultimate drift in response to a high electric field results in unidirectional streaming of the otherwise randomly-oriented velocity vectors in equilibrium. The highfield drift limited by the intrinsic velocity is ballistic, unaffected by scattering-limited processes. The ultimate velocity is further limited to an emission of a quantum either in the form of an optical phonon or a photon by an electron excited to a higher state by the applied electric field. The velocity does not depend on scattering parameters. Ballistic processes as a result of reduction in length of a CNT or NW below the scattering-limite--d mean free path l in the quasi-free direction are also discussed.
The degradation of ballistic mobility in a metal-oxide semiconductor field-effect transistor is a... more The degradation of ballistic mobility in a metal-oxide semiconductor field-effect transistor is attributed to the nonstationary ballistic injection from the contacts as the length of a channel shrinks to the length smaller than the scattering-limited mean free path. Apparent contradiction between the rise of magnetoresistance mobility and fall of drift mobility with increasing channel concentration is attributed to scattering-dependent magnetoresistance factor. The ballistic mean free path of injected carriers is found to be substantially higher than the long-channel drift mean free path. Excellent agreement with the experimental data on length-limited ballistic mobility is obtained.
Exact analytical expressions for the switching delay of an inverter driving an RC load, taking in... more Exact analytical expressions for the switching delay of an inverter driving an RC load, taking into account the velocity saturation, are obtained. Modified expressions to include theeffectofsource resistance arethen presented.Owing to the limitation on switching current imposed by the velocity saturation mechanism, the switching delay is substantially increased for identical width-io-length ratios of the MOSFET in a complementary MOS logic circuit. Obviously, it is important to increase the saturation velocity by miniband engineering or otherwise to improve the performance. However, it is found that the improvements in the time delay are marginal after a saturation velocity of 2.4 x lO'cm s-' is reached. The effect of technologies aimed at circumventing the hot-electron and other deleterious effects is a longer delay time of the circuit due to increased series resistance. However, the effect of increased series resistance is substantially damped due to velocity safuration. These results are particularly important in designing CMOS circuits with submicrometre MOSFET dimensions
Numerical evaluation of energy spectrum and carrier statistics for nanostructure device applicati... more Numerical evaluation of energy spectrum and carrier statistics for nanostructure device application is presented. The low-dimensional energy spectrum was successfully derived for the respective quasi 3D, 2D and 1D system that invoked the effect of quantum confinement (QCE) comparable to the De Broglie wavelength (×’D =a·‰ 10nm). For non-degenerately (ND) doped samples the Fermi-Dirac (FD) integral is well approximated by Boltzmann statistics. However, in degenerate doped quasi 3D, 2D and 1D device, the FD integral is found to be approximated by order one-half, zero and minus one-half respectively. The Fermi energy is revealed to be a weak (logarithmic) function of carrier concentration, but varies linearly with temperature in the ND regime. However, for strongly degenerate statistics, the Fermi energy is independent of temperature and is a strong function of carrier concentration.
The carriers in a carbon nanotube (CNT), like in any quasi-1-dimensional (Q1D) nanostructure, hav... more 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 streamlined 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.
Comparative benchmarking of a graphene nanoribbon field-effect transistor (GNRFET) and a nanoscal... more Comparative benchmarking of a graphene nanoribbon field-effect transistor (GNRFET) and a nanoscale metal-oxide-semiconductor field-effect transistor (nano-MOSFET) for applications in ultralarge-scale integration (ULSI) is reported. GNRFET is found to be distinctly superior in the circuit-level architecture. The remarkable transport properties of GNR propel it into an alternative technology to circumvent the limitations imposed by the silicon-based electronics. Budding GNRFET, using the circuit-level modeling software SPICE, exhibits enriched performance for digital logic gates in 16 nm process technology. The assessment of these performance metrics includes energy-delay product (EDP) and power-delay product (PDP) of inverter and NOR and NAND gates, forming the building blocks for ULSI. The evaluation of EDP and PDP is carried out for an interconnect length that ranges up to 100 μm. An analysis, based on the drain and gate current-voltage (Id-VdandId-Vg), for subthreshold swing (SS),...
2012 Third International Conference on Intelligent Systems Modelling and Simulation, 2012
Numerical evaluation of energy spectrum and carrier statistics for nanostructure device applicati... more Numerical evaluation of energy spectrum and carrier statistics for nanostructure device application is presented. The low-dimensional energy spectrum was successfully derived for the respective quasi 3D, 2D and 1D system that invoked the effect of quantum confinement (QCE) comparable to the De Broglie wavelength ( D 10nm). For non-degenerately (ND) doped samples the Fermi-Dirac (FD) integral is well approximated by Boltzmann statistics. However, in degenerate doped quasi 3D, 2D and 1D device, the FD integral is found to be approximated by order one-half, zero and minus one-half respectively. The Fermi energy is revealed to be a weak (logarithmic) function of carrier concentration, but varies linearly with temperature in the ND regime. However, for strongly degenerate statistics, the Fermi energy is independent of temperature and is a strong function of carrier concentration.
Charge transfer mechanism in carbon nanotubes (CNTs) from the scattering-limited Ohmic transport ... more Charge transfer mechanism in carbon nanotubes (CNTs) from the scattering-limited Ohmic transport to high-field-initiated ballistic transport is studied. It is shown that the electrons changes their motion from randomness (in equilibrium) to streamlined one (in non-equilibrium) when high electric field is applied. The intrinsic velocity is discussed in non-parabolic semiconducting limits considering the nondegenerate and degenerate situations. The results obtained are significant in extracting carrier transport properties from experimental data on CNTs and in understanding the fundamental processes controlling the charge transport in nanoscale devices.
The transient switching delay in a micro/nano-scale circuit containing resistive and reactive ele... more The transient switching delay in a micro/nano-scale circuit containing resistive and reactive elements are sternly affected by the surge in the resistance arising from sub-linear current-voltage (I-V) characteristics limited by the velocity and current saturation. The saturation arises due to the realignment of randomly oriented velocity vectors to the unidirectional streamlined ones in a high electric field when voltage applied across a resistor exceeds its decreasing critical value with reduced channel length. The frequency response f = 1/2pt t is affected by a transit time delay t t is lower than that predicted from the application of Ohm's law. The resistance surge dramatically boosts the RC time constant and switching delay and attenuates the L/R time constant and switching delay
N on-Equilibrium Arora's Distribution Function (NEADF) is a new paradigm in performance evaluatio... more N on-Equilibrium Arora's Distribution Function (NEADF) is a new paradigm in performance evaluation of materials. Silicon is the king of electronics where NEADF has been applied successfully in assessment of CMOS and device nanostructures. With the award of 2010 Nobel Prize to Graphene as a perfect two-dimensional nanomaterial, the attention has shifted to layered semiconductors, including silicine and phosphorene. Bandgap engineering of layered semiconductors to nanowires, nanotubes, and nanoribbons has given new paradigms and new opportunities that will be discussed and new applications explored. It is shown that Ohm's law that is used in characterization breaks down on scaled down dimensions giving rise to velocity and current saturation as electric field exceeds its critical value. Ballistic and quantum transport arising from these scaled-down channels will be brought to light.
Facta universitatis. Series electronics and energetics, 2014
Starting from the graphene layer, the bandgap engineering of carbon nanotubes (CNTs) and graphene... more Starting from the graphene layer, the bandgap engineering of carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) is described by applying an appropriate boundary condition. Linear E-k relationship of graphene transforms to a parabolic one as momentum vector in the tube direction is reduced to dimensions smaller than inverse of the tube diameter of a CNT. Similar transition is noticeable for narrow width of a GNR. In this regime, effective mass and bandgap expressions are obtained. A CNT or GNR displays a distinctly 1D character suitable for applications in quantum transport.
The emerging facts from the successful organizations, including universities, indicate that the r... more The emerging facts from the successful organizations, including universities, indicate that the real source of power in a knowledge-based economy is in combining technical prowess with entrepreneurship. This paper first highlights missing links in the aptitude and attitude of an engineer in combining technical knowledge with sound decision-making and effective entrepreneurship. Second, it discusses the gaps in traditional college education and their remedies through outcome-based curricula. Third, it presents the distinction between leadership and management with reference to new models espoused in the Theory of Constraints (TOC). Fourth, it outlines the skills needed for the professional development of an individual to transform him or her from a traditional quantitative/verbal thinker to a future-oriented visionary by redirecting the whole-brain thinking. Finally, critical success factors in the development of an effective and efficient knowledge worker for the 21 st century are enumerated.
In a recent article, Serov et al. [J. Appl. Phys. 116, 034507 (2014)] claim: "This study represen... more In a recent article, Serov et al. [J. Appl. Phys. 116, 034507 (2014)] claim: "This study represents the first time that the high-field behavior in graphene on a substrate was investigated taking into account intrinsic graphene properties," ignoring the most recent anisotropic distribution function [V. K. Arora et al., J. Appl. Phys. 112, 114330 (2012)] also published in J. Appl. Phys., targeting the same experimental data [V. E. Dorgan et al., Appl. Phys. Lett. 97, 082112 (2010)]. The claim of Serov et al. of being first is refuted and many shortcomings of the hydrodynamic model for a highly quantum and degenerate graphene nanolayer are pointed out. V
Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds grea... more Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds great potential for applications in variety of sensors because of dangling π-bonds that can react with chemical elements. In spite of their excellent features, carbon nanotubes (CNTs) and graphene have not been fully exploited in the development of the nanoelectronic industry mainly because of poor understanding of the band structure of these allotropes. A mathematical model is proposed with a clear purpose to acquire an analytical understanding of the field-effect-transistor (FET) based gas detection mechanism. The conductance change in the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules is emphasized. NH 3 has been used as the prototype gas to be detected by the nanosensor and the corresponding current-voltage (I-V) characteristics of the FET-based sensor are studied. A graphene-based gas sensor model is also developed. The results from graphene and CNT models are compared with the experimental data. A satisfactory agreement, within the uncertainties of the experiments, is obtained. Graphene-based gas sensor exhibits higher conductivity compared to that of CNT-based counterpart for similar ambient conditions.
The emerging facts from the successful organizations, including universities, indicate that the r... more The emerging facts from the successful organizations, including universities, indicate that the real source of power in a knowledge-based economy is in combining technical prowess with entrepreneurship. This paper first highlights missing links in the aptitude and attitude of an engineer in combining technical knowledge with sound decision-making and effective entrepreneurship. Second, it discusses the gaps in traditional college education and their remedies through outcome-based curricula. Third, it presents the distinction between leadership and management with reference to new models espoused in the Theory of Constraints (TOC). Fourth, it outlines the skills needed for the professional development of an individual to transform him or her from a traditional quantitative/verbal thinker to a future-oriented visionary by redirecting the whole-brain thinking. Finally, critical success factors in the development of an effective and efficient knowledge worker for the 21 st century are enumerated.
Malaysian Journal of Fundamental and Applied Sciences, Dec 19, 2014
Nanotube Field Effect Transistor (CNTFET) and Naonowire. For each dimensionality the limitations ... more Nanotube Field Effect Transistor (CNTFET) and Naonowire. For each dimensionality the limitations on carrier drift velocity due to the high-field streaming of otherwise randomly velocity vector in equilibrium is reported. The results are based on the asymmetrical distribution function that converts randomness in zero-field to streamlined one in a very high electric field. The ultimate drift velocity for all dimensions 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 ultimate drift velocity is the Fermi velocity for degenerately doped silicon increasing with carrier concentration but independent of the temperature.
International Journal of Nanotechnology in Medicine & Engineering, 2017
A newfangled paradigm through deployment of the nonequilibrium Arora's distribution function (NEA... more A newfangled paradigm through deployment of the nonequilibrium Arora's distribution function (NEADF) for resistance surge in a carbonnanotube (CNT) ballistic conductor is presented. The experimental nonlinear I-V characteristics, when voltage across the length of aresistor is higher than its critical value, defy ohmic and ballistic transmission through a CNT. The scattering-limited lowfield restance Rois shown not to be valid when voltage is higher than its critical value Vc=IsatRo where Isat is the saturation current. Both Ro and Vc areneeded to characterize a nano resistive channel with default infinite value of Vc for an ohmic resistor. The finite value of Vc necessitates differentiation of incremental signal resistance from the direct one, bringing to focus the surge with the applied voltage. Isat is shown to be limited by the intrinsic velocity which is the Fermi velocity in a metallic CNT.
The effect of nonparabolicity of the conduction band of n-InSb type semiconductors is studied in ... more The effect of nonparabolicity of the conduction band of n-InSb type semiconductors is studied in the framework of the Arora-Peterson density-matrix formalism. To exhibit clearly the effect of nonparabolicity, only the case of elastic electron-acoustic-phonon scattering is considered. Numerical results are presented both for parabolic and nonparabolic models. The nonparabolicity enhances the magnetoresistance, the effect being larger for larger magnetic fields. The Hall coefFicient decreases slightly with the increasing magnetic field.
The theory of electron-lattice scattering is examined for a quantum-well heterostructure in the s... more The theory of electron-lattice scattering is examined for a quantum-well heterostructure in the size quantum limit when most of the electrons populate the lowest quantized subband. The acoustic-phonon scattering is found to be one of the important mechanisms of scattering at inter- mediate temperatures when donors supplying the electrons are removed in an adjacent nonconduct- ing layer.
2010 IEEE International Conference on Semiconductor Electronics (ICSE2010), 2010
The charge carriers in nanowires (NWs), carbon nanotubes (CNTs), and those confined to a very hig... more The charge carriers in nanowires (NWs), carbon nanotubes (CNTs), and those confined to a very high magnetic field have one-dimensional (1D) character as quasi-free propagation of electron waves with analog energy spectrum exists only in one direction. The energy spectrum is quantum (or digital) in other two cartesian directions where electron waves are standing waves. In the quantum limit, an electron (hole) occupies the lowest (highest) digitized/quantized state giving it a distinct 1D character. The energy E = vF | k | in carbon-based devices is linearly dependent on the wave vector k, where vF ˜ 106 m/s. This is in direct contrast to parabolic character E = h2 k2/2m* in solids with effective mass m*, for example in silicon NWs. The probability of changing wavevector from +ve to -ve direction through scattering or vice versa is greatly reduced and hence high mobility is expected, especially at low temperatures. The crucial outcome of this paper is the answer to the question: Does a higher mobility leads to a higher ultimate saturation velocity? The distribution function in a high electric field e is then naturally asymmetrical affected by the energy ±qel absorbed or emitted by a carrier of charge q during its ballistic flight in a mean free path l. The ultimate drift in response to a high electric field results in unidirectional streaming of the otherwise randomly-oriented velocity vectors in equilibrium. The highfield drift limited by the intrinsic velocity is ballistic, unaffected by scattering-limited processes. The ultimate velocity is further limited to an emission of a quantum either in the form of an optical phonon or a photon by an electron excited to a higher state by the applied electric field. The velocity does not depend on scattering parameters. Ballistic processes as a result of reduction in length of a CNT or NW below the scattering-limite--d mean free path l in the quasi-free direction are also discussed.
The degradation of ballistic mobility in a metal-oxide semiconductor field-effect transistor is a... more The degradation of ballistic mobility in a metal-oxide semiconductor field-effect transistor is attributed to the nonstationary ballistic injection from the contacts as the length of a channel shrinks to the length smaller than the scattering-limited mean free path. Apparent contradiction between the rise of magnetoresistance mobility and fall of drift mobility with increasing channel concentration is attributed to scattering-dependent magnetoresistance factor. The ballistic mean free path of injected carriers is found to be substantially higher than the long-channel drift mean free path. Excellent agreement with the experimental data on length-limited ballistic mobility is obtained.
Exact analytical expressions for the switching delay of an inverter driving an RC load, taking in... more Exact analytical expressions for the switching delay of an inverter driving an RC load, taking into account the velocity saturation, are obtained. Modified expressions to include theeffectofsource resistance arethen presented.Owing to the limitation on switching current imposed by the velocity saturation mechanism, the switching delay is substantially increased for identical width-io-length ratios of the MOSFET in a complementary MOS logic circuit. Obviously, it is important to increase the saturation velocity by miniband engineering or otherwise to improve the performance. However, it is found that the improvements in the time delay are marginal after a saturation velocity of 2.4 x lO'cm s-' is reached. The effect of technologies aimed at circumventing the hot-electron and other deleterious effects is a longer delay time of the circuit due to increased series resistance. However, the effect of increased series resistance is substantially damped due to velocity safuration. These results are particularly important in designing CMOS circuits with submicrometre MOSFET dimensions
Numerical evaluation of energy spectrum and carrier statistics for nanostructure device applicati... more Numerical evaluation of energy spectrum and carrier statistics for nanostructure device application is presented. The low-dimensional energy spectrum was successfully derived for the respective quasi 3D, 2D and 1D system that invoked the effect of quantum confinement (QCE) comparable to the De Broglie wavelength (×’D =a·‰ 10nm). For non-degenerately (ND) doped samples the Fermi-Dirac (FD) integral is well approximated by Boltzmann statistics. However, in degenerate doped quasi 3D, 2D and 1D device, the FD integral is found to be approximated by order one-half, zero and minus one-half respectively. The Fermi energy is revealed to be a weak (logarithmic) function of carrier concentration, but varies linearly with temperature in the ND regime. However, for strongly degenerate statistics, the Fermi energy is independent of temperature and is a strong function of carrier concentration.
The carriers in a carbon nanotube (CNT), like in any quasi-1-dimensional (Q1D) nanostructure, hav... more 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 streamlined 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.
Comparative benchmarking of a graphene nanoribbon field-effect transistor (GNRFET) and a nanoscal... more Comparative benchmarking of a graphene nanoribbon field-effect transistor (GNRFET) and a nanoscale metal-oxide-semiconductor field-effect transistor (nano-MOSFET) for applications in ultralarge-scale integration (ULSI) is reported. GNRFET is found to be distinctly superior in the circuit-level architecture. The remarkable transport properties of GNR propel it into an alternative technology to circumvent the limitations imposed by the silicon-based electronics. Budding GNRFET, using the circuit-level modeling software SPICE, exhibits enriched performance for digital logic gates in 16 nm process technology. The assessment of these performance metrics includes energy-delay product (EDP) and power-delay product (PDP) of inverter and NOR and NAND gates, forming the building blocks for ULSI. The evaluation of EDP and PDP is carried out for an interconnect length that ranges up to 100 μm. An analysis, based on the drain and gate current-voltage (Id-VdandId-Vg), for subthreshold swing (SS),...
2012 Third International Conference on Intelligent Systems Modelling and Simulation, 2012
Numerical evaluation of energy spectrum and carrier statistics for nanostructure device applicati... more Numerical evaluation of energy spectrum and carrier statistics for nanostructure device application is presented. The low-dimensional energy spectrum was successfully derived for the respective quasi 3D, 2D and 1D system that invoked the effect of quantum confinement (QCE) comparable to the De Broglie wavelength ( D 10nm). For non-degenerately (ND) doped samples the Fermi-Dirac (FD) integral is well approximated by Boltzmann statistics. However, in degenerate doped quasi 3D, 2D and 1D device, the FD integral is found to be approximated by order one-half, zero and minus one-half respectively. The Fermi energy is revealed to be a weak (logarithmic) function of carrier concentration, but varies linearly with temperature in the ND regime. However, for strongly degenerate statistics, the Fermi energy is independent of temperature and is a strong function of carrier concentration.
Charge transfer mechanism in carbon nanotubes (CNTs) from the scattering-limited Ohmic transport ... more Charge transfer mechanism in carbon nanotubes (CNTs) from the scattering-limited Ohmic transport to high-field-initiated ballistic transport is studied. It is shown that the electrons changes their motion from randomness (in equilibrium) to streamlined one (in non-equilibrium) when high electric field is applied. The intrinsic velocity is discussed in non-parabolic semiconducting limits considering the nondegenerate and degenerate situations. The results obtained are significant in extracting carrier transport properties from experimental data on CNTs and in understanding the fundamental processes controlling the charge transport in nanoscale devices.
The transient switching delay in a micro/nano-scale circuit containing resistive and reactive ele... more The transient switching delay in a micro/nano-scale circuit containing resistive and reactive elements are sternly affected by the surge in the resistance arising from sub-linear current-voltage (I-V) characteristics limited by the velocity and current saturation. The saturation arises due to the realignment of randomly oriented velocity vectors to the unidirectional streamlined ones in a high electric field when voltage applied across a resistor exceeds its decreasing critical value with reduced channel length. The frequency response f = 1/2pt t is affected by a transit time delay t t is lower than that predicted from the application of Ohm's law. The resistance surge dramatically boosts the RC time constant and switching delay and attenuates the L/R time constant and switching delay
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Papers by Vijay Arora