Asymmetric junctionless nanowire TFET with built-in $${n}^{+}$$ source pocket emphasizing on energy band modification

We present a detailed study on a technique to realize a narrow and highly doped built-in \({n}^{+}\) source pocket in an asymmetric junctionless nanowire tunnel field-effect transistor (AJN-TFET). In the proposed structure, a built-in \({n}^{+}\) source pocket is created between the \({p}^{+}\) source and the channel without the need for any separate implantation or epitaxial growth. This leads to band diagram modification by providing a local minimum in the conduction band which results in tunneling width reduction at the source–channel interface in on-state. This leads to an abrupt transition between on- and off-state, improved subthreshold swing (SS) (38 mV/dec), and significant on-current enhancement (\(\sim 2000\) times) at low operating voltage compared with the conventional TFET. We further study the effect of the length of the built-in \({n}^{+}\) source pocket on the AJN-TFET characteristics. The proposed structure overcomes the difficulty in creating a narrow \({n}^{+}\) pocket and thus renders the AJN-TFET device more amenable for the future scaling trend needed in low-power applications.     

Hydrogen sensitive field-effect transistor based on germanene nanoribbon and optical properties of hydrogenated germanene

Physisorption of hydrogen molecules on armchair germanene nanoribbon (GeNR) is studied with density functional methods. The adsorption geometries, adsorption energies and transferred charge are obtained. To take the Van der Waals forces into account, the Grimme correction is added to the calculation method. The physisorption effect on the electrical properties of the ribbon is explored as a function of \(\hbox {H}_{2}\) concentration through the Green’s function techniques. Sensing features of the GeNR are investigated as a channel of a back gated field effect transistor. The optical properties of the nanoribbon are obtained for parallel and perpendicular polarizations. The results point out that, the germanene is a suitable substrate for \(\hbox {H}_{2}\) encapsulation. Moreover, \(\hbox {H}_{2}\) physisorption can improve the I–V characteristics and suppress the optical spectrum of the GeNR. The current through the nanoribbon increases by increasing \(\hbox {H}_{2}\) concentration at the same bias voltage. Also, the germanene back gated FET improve the sensing properties. The results show that the GeNR dielectric function is anisotropic and the GeNR becomes more transparent by increasing \(\hbox {H}_{2}\) density. Finally, by applying the spin-orbit coupling (SOC) effect, the obtained results are re-calculated and the changes in the results are studied. The SOC opens up the electronic band gap of the GeNR about 20 meV and increases the current slightly through the GeNR.     

Double gate graphene nanoribbon field effect transistor with electrically induced junctions for source and drain regions

In this paper a novel graphene nanoribbon transistor with electrically induced junction for source and drain regions is proposed. An auxiliary junction is used to form electrically induced source and drain regions beside the main regions. Two parts of same metal are implemented at both sides of the main gate region. These metals which act as side gates are connected to each other to form auxiliary junction. A fixed voltage is applied on this junction during voltage variation on other junctions. Side metals have smaller workfunction than the middle one. Tight-binding Hamiltonian and nonequilibrium Green’s function formalism are used to perform atomic scale electronic transport simulation. Due to the difference in metals workfunction, additional gates create two steps in potential profile. These steps increase horizontal distance between conduction and valance bands at gate to drain/source junction and consequently lower band to band tunneling probability. Current ratio and subthreshold swing improved at different channel lengths. Furthermore, device reliability is improved where electric field at drain side of the channel is reduced. This means improvement in leakage current, hot electron effect behavior and breakdown voltage. Application to multi-input logic gates shows higher speed and smaller power delay product in comparison with conventional platform.     

A novel SOI MESFET by \uppi -shaped gate for improving the driving current

This paper introduces a novel silicon-on-insulator (SOI) metal–semiconductor field-effect transistor (MESFET) with \(\uppi \) -shaped gate with triple workfunction ( \(\uppi \) -SOI MESFET) to improve the DC and radio frequency characteristics. The DC and radio frequency characteristics of the proposed structure are analyzed by 2-D ATLAS international simulator and compared with a conventional SOI MESFET (C-SOI MESFET). The simulated results show that the proposed SOI MESFET has excellent effect on the breakdown voltage and the driving current. The breakdown voltage of the \(\uppi \) -SOI MESFET structure gets 54 % enhancement compared with that of the C-SOI MESFET structure and also the driving current of the \(\uppi \) -SOI MESFET structure gets 66.66 % enhancement compared with that of the C-SOI MESFET structure. Other main characteristics such as maximum output power density, maximum oscillation frequency and maximum available gain have been evaluated and improved in the proposed structure.     

Design and analysis of a gate-all-around CNTFET-based SRAM cell

This paper proposes a highly stable and low power 6-T static random access memory (SRAM) cell design using a gate-all-around carbon nanotube field effect transistor (GAA-CNTFET). The 6-T SRAM cell is designed and analyzed in HSPICE for different performance metrics viz. SNM, read SNM, write SNM, delay, and leakage power for both the top gate CNTFET and the GAA-CNTFET. The effect of variation of the power supply voltage on the leakage current is also presented, and it was found that the GAA-CNTFET accounts for low power dissipation at higher supply voltage. The 6-T SRAM cell is analyzed for different flat band conditions of the p-type CNTFET taking flatband of the n-type as constant, which is called a dual flat band voltage technique. Through simulations, it is found that by increasing the flatband voltage of a p-type CNTFET, the SRAM gives better performance. The dual flatband variation technique is compared with dual chirality technique, and it is observed that both techniques give the same results.     

Full Band Monte Carlo Simulation of Wurtzite AlGaN/GaN MODFETs

We present full band Monte Carlo simulations of a wurtzite Al_0.15Ga_0.85N/GaN modulation-doped field-effect transistor (MODFET). We found that without inclusion of the piezoelectric effect, the electron concentrations in the channel are much lower than obtained from experimental data. The calculated I _ds-V _ds curves show a strong negative differential resistance, which is a feature observed in experimental devices. Self-heating effects are usually believed to be the main cause of the negative differential resistance. Our simulations do not include self-heating, and this would indicate that at least part of what is observed is also caused by the drift-velocity behavior vs. electric field of the narrow conduction channel. For a 0.2 m gate MODFET, the simulations yield a maximum trans-conductance G _m 250 mS/mm with V _G = 1.0 V and V _ds = 5.0 V. When V _G = 0.0 V and V _ds = 8.0 V, we obtain a maximum cutoff frequency f _T = 180 GHz with I _d = 1159 mA/mm.     

Delta-doped tunnel FET (D-TFET) to improve current ratio ($$I_\mathrm{ON}/I_\mathrm{OFF}$$) and ON-current performance

A two dimensional (2D) analytical drain current model has been developed for a delta-doped tunnel field-effect transistor (D-TFET) that can address the ON-current issues of the conventional TFET. Insertion of a highly doped delta layer in the source region paves the way for improved tunneling volume and thus provides high drain current as compared with TFETs. The present model takes into account the effects of the distance between the delta-doping region and the source–channel interface on the subthreshold swing (SS), current ratio, and ON-current performance. The D-TFET is predicted to have a higher current ratio \(\left( {\frac{I_\mathrm{ON} }{I_\mathrm{OFF} }\cong 10^{11}} \right) \) compared with TFETs \(\left( {\frac{I_\mathrm{ON} }{I_\mathrm{OFF} }\cong 10^{10}} \right) \) with a reasonable SS \(\left( {{\sim }52\,\mathrm{mV/dec}} \right) \) and \(V_\mathrm{th}\) performance at an optimal position of 2 nm from the channel. The surface potential, electric field, and minimum tunneling distance have been derived using the solution of the 2D Poisson equation. The accuracy of the D-TFET model is validated using the technology computer aided design (TCAD) device simulator from Synopsys.     

DFT study on structural,electronic, and optical properties of cubic and monoclinic CuO

First-principles calculations were made to explore the structural, electronic, and optical properties of copper oxide (CuO) with monoclinic (m-CuO) and cubic (c-CuO) structures. We calculated the equilibrium structural parameters: lattice parameters (a, b, and c), angle \(\beta \), and volume V. The obtained results were in good agreement with the experimental data reported in the literature. The cohesive energy showed that m-CuO is more stable than c-CuO. The band structure indicated that c-CuO is an indirect band gap semiconductor with a band gap of 0.87 eV along R–G, while m-CuO has a metallic behavior. Furthermore, electrovalent and covalent bonds were observed in both c-CuO and m-CuO. The linear optical properties were calculated and analyzed along different polarization directions of the incident light. The results indicated that m-CuO possesses optical anisotropic properties. In particular, c-CuO can be used as a potential UV detector material because of its high absorption coefficient (356351.3).     

Poisson–Nernst–Planck model for an ionic transistor based on a semiconductor membrane

In this paper we developed a Poisson–Nernst–Planck model of an ionic current flowing through a nanopore in a layered solid-state membrane made of a single highly-doped \(n\) -Si layer sandwiched between two thick oxide layers which we call the ionic transistor. We studied this layered membrane for a range of source-drain voltages while keeping the gate (the semiconductor membrane) voltage fixed at a certain value, which was later varied too. We find that for this ionic transistor to be effective in controling the ion fluxes through the nanopore, the gate voltage must be kept relatively large. Another solution could be to increase the surface negative charge on the membrane or to replace the outer oxide layers with the semiconductor material, such as the \(p\) -Si material. The developed model can be applied to study ionic filtering and separation properties of membranes of different composition and nanopore geometries.     

The Mott Transition Field Effect Transistor: A Nanodevice?

A field effect transistor device (FET), consisting of a nonlinear Mott Insulator channel material, and a high dielectric-constant gate oxide, is explored as a nanoscale device. Experimental functionality of a large scale prototype (5 m channel length) has been demonstrated. The underlying physics of the device is analyzed and modeled using a time-dependent Hartree approach. Timing estimates suggest a relatively short switching time.     

Output universality in maximum efficiency linear power amplifiers

A general linear passive termination is considered for a typical field effect power transistor such that the first m odd harmonics, excluding the fundamental frequency, are open circuited with the remaining harmonics short‐circuited. Under this termination, with the appropriate resistive termination at the fundamental frequency, it is shown that an optimum maximum efficiency of is universally achieved independent of non‐linearities in the transistor. Furthermore, where higher ordered harmonics are terminated in finite reactive impedances, which is the case with any realizable network, it is shown that the same maximum efficiency is obtained with the correct complex termination at the fundamental frequency. A prototype network is then defined including the output capacitance of the transistor and synthesized in a lowpass form which, when terminated in a shunt resonant circuit and load resistor, will provide the correct impedances at the fundamental and all of the harmonics. Remarkably, this optimum network has a simple formula for the element values in the general (2m+1) th degree network and a rigorous proof is presented in the appendix. Copyright © 2003 John Wiley & Sons, Ltd.     

Generalized optical gain analysis in nonparabolic semiconductor laser

A simple generalized theory is developed for optical gain of nonparabolic semiconductor lasers based on the three‐band model of Kane, by taking into account the wave‐vector () dependence of the optical matrix element. The gain in laser of nonparabolic semiconductors is demonstrated, by taking InAs, InSb, Hg_1−xCd_xTe and In_1−xGa_xAs_yP_1−y lattice matched to InP as examples, and it has been found that the peak of the gain spectra for a given carrier density is higher in the three‐band model of Kane than those with parabolic energy band approximations in all the cases. The difference between the peak of gain spectra for three‐band model and the parabolic band model is greater for laser of narrow band gap materials in comparisons with that of laser of wide band gap materials, thereby reveals the necessity for inclusion of the nonparabolicity in modeling lasers of small band gap materials. The well‐known results for wide band gap materials having parabolic energy bands has also been obtained from our generalized formulation under certain limiting condition. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel symmetrical 4H–SiC MESFET: an effective way to improve the breakdown voltage

In this paper, a novel symmetrical structure (SS) of 4H–SiC metal semiconductor field effect transistor (MESFET) as an effective way to improve the breakdown voltage is presented. The key idea in this work is to improve the breakdown voltage, maximum output power density, and frequency parameters of the device using a symmetrical structure with recessed gate. The SS-MESFET modifies the electric field in the drift layer significantly. The influence of the SS-MESFET on the saturation current, breakdown voltage \((\hbox {V}_{\mathrm{BR}})\), and small-signal characteristics of the SS-MESFET are studied by numerical device simulation. Using two-dimensional device simulation, we demonstrate that the breakdown voltage \((\hbox {V}_{\mathrm{BR}})\) improved by factors 2.5 and 3.3 in comparison with an asymmetrical conventional MESFET structure (AC-MESFET) and a symmetrical conventional MESFET structure (SC-MESFET), respectively. Also, the maximum output power density \((\hbox {P}_{\mathrm{max}})\) improved about by 93 and 250 % in comparison with the AC-MESFET and SC-MESFET structures, respectively. So, the SS-MESFET shows the superior maximum available gain (MAG), unilateral power gain (U), and current gain \((\hbox {h}_{12})\) which is presenting the proposed structure is more suitable device for high power microwave applications.     

Electronic properties of graphyne nanotubes filled with small fullerenes: a density functional theory study

The encapsulation of small fullerenes into graphyne nanotubes was studied to investigate the possibility of band gap engineering in these nanotubes. The electronic properties of zigzag (4,0) and (5,0) graphyne nanotubes filled with small \(\hbox {C}_{20}\) and \(\hbox {C}_{30}\) fullerenes were studied using density functional theory. It was found that the zigzag (4,0) and (5,0) graphyne nanotubes were semiconductors. These graphyne nanotubes filled with \(\hbox {C}_{20}\) and \(\hbox {C}_{30}\) fullerenes were shown p-type and n-type semiconducting properties, respectively. The energy band gap was dependent on the number of the encapsulated fullerenes. Our results demonstrated the ability of band gap engineering through the encapsulation of small fullerenes into graphyne nanotubes.     

Analysis and modeling of unipolar junction transistor with excellent performance: a novel DG MOSFET with $${N}^{+}{-}{P}^{-}$$ junction

We propose herein a new dual-gate metal–oxide–semiconductor field-effect transistor (MOSFET) with just a unipolar junction (UJ-DG MOSFET) on the source side. The UJ-DG MOSFET structure is constructed from an \({N}^{+}\) region on the source side with the rest consisting of a \({P}^{-}\) region over the gate and drain, forming an auxiliary gate over the drain region with appropriate length and work function (named A-gate), converting the drain to an \({N}^{+}\) region. The new structure behaves as a MOSFET, exhibiting better efficiency than the conventional double-gate MOSFET (C-DG MOSFET) thanks to the modified electric field. The amended electric field offers advantages including improved electrical characteristics, reliability, leakage current, \({I}_{\mathrm{ON}}/I_{\mathrm{OFF}}\) ratio, gate-induced drain leakage, and electron temperature. Two-dimensional analytical models of the surface potential and electric field over the channel and drain are applied to investigate the drain current in the UJ-DG MOSFET. To confirm their accuracy, the MOSFET characteristics obtained using the 2D Atlas simulator for the UJ-DG and C-DG are analyzed and compared.     

Dual material gate junctionless tunnel field effect transistor

This paper proposes a junctionless tunnel field effect transistor (JLTFET) with dual material gate (DMG) structure and the performance was studied on the basis of energy band profile modulation. The two-dimensional simulation was carried out to show the effect of conduction band minima on the abruptness of transition between the ON and OFF states, which results in low subthreshold slope (SS). Appropriate selection of work function for source and drain side gate metal of a double metal gate JLTFET can also significantly reduce the subthreshold slope (SS), OFF state leakage and hence gives improved I _ON/I _OFF.     

Effect of band parameters on interband optical absorption in quantum wire structure of low band gap III–V semiconductors

A generalized theory is presented to study the effect of band parameters on inter band optical absorption in quantum wire structure of III–V compound semiconductors considering the wave-vector ( $\vec{k}$ ) dependence of the optical transition matrix element (OME). The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted to calculate the inter band optical absorption coefficient (IOAC) for a wide range of III–V compound semiconductors like, InAs, InSb, Hg_1?x Cd _x Te and In_1?x Ga _x As _y P_1?y lattice matched to InP, having varied split-off energy band compared to their energy band gap. It has been found that IOAC for quantum wires (QWRs) increases in oscillatory manner with increasing incident photon energy and the positions of peaks of oscillation of the coefficient are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of band energy constants. This effect of band parameters is better revealed from the study of light polarization dependence of the absorption coefficient.     

Interface Characterization of All-Perovskite Oxide Field Effect Heterostructures

All-oxide devices consisting of Niobium-doped Strontium Titanate (Nb:STO)/Strontium Titanate (STO)/Lanthanum Strontium Cuprous Oxide (LSCO) heterostructures were fabricated and characterized electrically for their interface properties through capacitance-voltage (C-V) and current-voltage (I-V) techniques, in the context of electric field effect studies. The C-V studies establish the occurrence of charge modulation in the LSCO channel. Absence of hysteresis in the C-V characteristic when the voltage is retraced suggests the absence of mobile ions in the gate oxide and slow interface traps. This is further corroborated by the absence of drift in the C-V characteristic and shift in the flat band voltage (V _FB) when the device is subjected to temperature-bias aging. The interface state density obtained from V _FB is 10¹²/cm². The uncompensated hole concentration in the LSCO channel calculated from the measured room temperature C-V data is 10²⁰/cm³ and is in good agreement with the expected hole concentration in LSCO. Current-time and current-voltage plots are invariant with respect to the polarity of the applied voltage up to 5 V. This, in a structure with asymmetric interfaces, indicates that the electrical contacts to STO are non-blocking and the conduction through STO is bulk-limited in this voltage regime. Thickness dependent current and capacitance studies also corroborate the bulk-limited nature of conduction through the device in this voltage regime. However, I-V characteristic shows a rectifying nature beyond 8 V indicating that the mechanism in this voltage regime could be interface limited.     

Feld- und Schubkraftverlauf des magnetischen Schweifes beim Kurzstator-Linearmotor

Übersicht Die Beschreibung des Feldverhaltens wie die Bestimmung der dabei wirksamen Bremskräfte am Ende eines Kurzstator-Linearmotors ist mit Hilfe der Ausgleichswellen recht einfach möglich. Die freie Ausgleichswelle des magnetischen Schweifes erfährt aber durch das Ende der Eisenkontur eine starke änderung. So kann das Wellenverhalten der Schiene in freier Luft durch einen schlupfabhängig vergrößerten Luftspalt dargestellt werden. Der Übergangsbereich läßt sich durch eine übliche lineare Luftspaltaufweitung unter 51° berücksichtigen. Auch dieser Übergangsbereich kann mit Hilfe einer Vielzahl von Störstellen getreppt dargestellt und berechnet werden. Die häufige Reflexion der Wellen führt zu einer in den Motorbereich zurücklaufenden Welle. Es bildet sich durch die Aufweitung eine Bremskraft aus, die von den Linearmotorberechnungsmethoden, die diese Luftspaltaufweitung benutzen, nicht einwandfrei erfaßt wird. Es ist zweckmäßig die Feld- wie Bremskraftbestimmung separat durchzuführen und dem Verhalten bei konstantem Luftspalt zu überlagern, denn der aufgeweitete magnetische Schweif ist vom Motorbereich entkoppelt zu betrachten.

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Distribution of field and thrust in the magnetic tail of a short-primary linear motor

Contents The determination of the magnetic field distribution at the end of a short-primary linear motor and the braking forces caused by the end effect can be quite easy by using the balancing wave method. The free balancing wave of the magnetic tail, however, is modified by the end of the stator core. To take this effect into account, the field outside the stator can be calculated if we consider the reaction rail facing an enlarged air gap. The transition region between the active part of the motor and the field around the rail in free air can be represented by letting the air gap width increase linearly. The field in this region may, however, also be calculated by assuming the width of the air gap to increase stepwise. The repeated reflection of the balancing waves results in a wave moving backward into the active part of the motor. The end effect described above generates a braking force which is not determined correctly by calculation methods based on the enlargement of the air gap. It is useful to determine the field and thrust for an air gap of constant width, and the effect due to the end of the stator core separately, adding the results afterwards, because the magnetic field tail in the enlarged air gap is to be considered unrelated to the field in the active region of the motor.

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Verwendete Symbole A Strombelag - a ₀ Wellenzahl der Grundwelle - a Wellenzahl der Ausgleichswelle - B magnetische Induktion - F Schubkraft - I _sl Seitenleiterstrom - l Maschinenbreite - l _ü Schienenüberstand - m ₀ Korrekturgröße zur Berücksichtigung des Seitenleiterwiderstandes - P Leistung - rey₀ magnetische Reynoldszahl der Maschinenpolteilung - s Schlupf - S Abklingstrecke der Ausgleichswelle - v Geschwindigkeit - v ₀ Synchrongeschwindigkeit - v Phasengeschwindigkeit der Ausgleichswelle - x Längenkoordinate - y _l Schienendicke - Luftspalt - ₀ Permeabilität der Luft - spezifische Schubkraft - _p0 Polteilung der Maschine - _pw Polteilung der Ausgleichswelle - Jochfluß - ₀ Kreisfrequenz - , verwendete Phasenwinkel Indices m mitlaufende Komponente - g gegenlaufende Komponente