Effect Of Transverse Electric Field Research Articles

(Invited, Digital Presentation) Interface Charge Trapping and Scattering in SiC MOSFET Channels

The channel conductivity of SiC MOSFETs is severely limited by charge trapping at interface states and mobility limiting scattering processes. In this talk, the status of interface state passivation for both n- and p-channel 4H-SiC MOSFETs will be presented. First, results from capacitance-based methods to extract interface state density (Dit) across the entire 4H-SiC band gap for thermally grown nitrided silicon dioxide gate dielectrics will be presented, emphasizing the critical importance of the SiO2(N)/SiC interface composition and nitrogen bonding. Next, the scattering mechanisms for channel electrons and holes in these devices will be analyzed and contrasted by Hall measurements. [1] The transport will be characterized as a function of temperature and substrate-bias within an effective transverse electric field model. The final part of the talk will focus on latest development on deposited dielectrics for 4H-SiC. Deposited dielectrics are an attractive alternative to thermal oxidation as it minimizes the release of carbon and the perturbation of surface crystal structure and opens the possibility of ‘high-k’ dielectrics with higher permittivity than SiO2. Herein, the key importance of 4H-SiC surface control prior to dielectric deposition will highlighted using results obtained for atomic layer deposition (ALD) of Aluminum Oxide (Al2O3) [2]. To this end, a systematic variation of SiC surface termination with processes involving oxygen, hydrogen and nitrogen will be presented. The composition of the deposited films and the interfacial bonding will be characterized for various deposition processes and correleated with electrical measurements . It will be demonstrated that surface nitridation followed by H2 annealing prior to ALD results in a factor of 2 higher channel mobility than typical NO annealed thermal SiO2. This is due to the formation of stable sub-nm SiON layers that passivates the surface and enables the formation of high-quality interfaces between SiC and deposited dielectric. In addition, the results indicate that clean Si-H terminated surfaces formed by hydrogen etching and annealing, prior to dielectric deposition leads to uniform nucleation of Al2O3. The reduction of Dit is also accompanied by improvements in oxide charge trapping and bias instability, but dielectric leakage current is significantly higher for Al2O3 compared to SiO2 due to bulk trap-assisted tunneling in Al2O3. The reliability is a significant challenge that need to be overcome to exploit the enhanced mobilities and make deposited dielectrics competitive with traditional nitrided SiO2.Acknowledgments: The authors acknowledge support from the US Army Research Laboratory (grant ARMY-W911NF-18-2-0160) and US Department of Energy (subcontracted to National Renewable Energy Laboratory, grant NREL-AHL-9-92632-01). The authors also acknowledge the support Dr. Leonard C. Feldman (Auburn, Rutgers) and Mr. Hengfei Gu (Rutgers) for help with XPS measurements. The authors also deeply thank Ms. T Isaacs-Smith, Ms. Lu Wang (Auburn), Dr. K. Ramadoss and Dr. D. Morisette (Purdue Univ.) for useful discussions and help with fabrication.[1] S. Das et al., J. Appl. Phys. 130, 225701, (2021).[2] I. U. Jayawardhena et al., J. Appl. Phys. 129, 75702, (2021) Figure 1

Electrically switchable giant Berry curvature dipole in silicene, germanene and stanene

The anomalous Hall effect in time-reversal symmetry broken systems is underpinned by the concept of Berry curvature in band theory. However, recent experiments reveal that the nonlinear Hall effect (NHE) can be observed in non-magnetic systems without applying an external magnetic field. The emergence of NHE under time-reversal symmetric conditions can be explained in terms of non-vanishing Berry curvature dipole (BCD) arising from inversion symmetry breaking. In this work, we availed realistic tight-binding models, first-principles calculations, and symmetry analyses to explore the combined effect of transverse electric field and strain, which leads to a giant BCD in the elemental buckled honeycomb lattices—silicene, germanene, and stanene. The external electric field breaks the inversion symmetry of these systems, while strain helps to attain an asymmetrical distribution of Berry curvature of a single valley. Furthermore, the topology of the electronic wavefunction switches from the band inverted quantum spin Hall state to normal insulating one at the gapless point. This band gap closing at the critical electric field strength is accompanied by an enhanced Berry curvature and concomitantly a giant BCD at the Fermi level. Our results predict the occurrence of an electrically switchable nonlinear electrical and thermal Hall effect in a new class of elemental systems that can be experimentally verified.

Unsteady electromagnetohydrodynamic flow of couple stress fluid through a microchannel: A theoretical analysis

In this work, we investigate the transient electromagnetohydrodynamic (EMHD) flow of non-Newtonian fluid in a narrow/micro-fluidic channel. We consider the couple stress fluid (CSF) model to characterize non-Newtonian behaviour. We present an analytical solution for electric potential and temporal EMHD flow velocity by applying the standard Laplace transform method using physically relevant boundary conditions. We demonstrate the excellent agreement between the present analytical solution for fluid flow with the CSF model and previously reported results for a Newtonian fluid. We analyse the transient flow velocity and volume flow rate for a wide range of flow governing parameters. We notice that the steady-state flow velocity magnitude is higher for magnetic parameter/ Hartmann number values than for the couple stress parameter values, which characterizes the flow’s viscous resistance. We demonstrate that the contribution of couple stresses in the fluid medium is prominent in the combined pressure, magnetic and electroosmotic force to increase the volume flow rate, which contrasts with the EMHD flow of Newtonian fluid. We observe that the critical Hartmann number attains a fixed value (about 1.3) for higher values of the couple stress parameter due to the transverse electric field effect. The present work hold the key towards explaining non-Newtonian behaviour impersonating bio-fluid transport in the narrow/micro-fluidic channel under the combined effect of electromagnetic force and pressure gradient. The results anticipated from the present attempt are useful to develop efficient electro-magneto-mechanical and micro-bio-fluidic devices.

The spin-polarized edge states of blue phosphorene nanoribbons induced by electric field and electron doping

Edge states of various two-dimensional materials such as graphene are intrinsically spin-polarized. In other materials, electric field and charge doping are required for introducing magnetism to their edges. In this work, by using first-principles calculations, we studied the effects of transverse electric field on the edge states of the armchair blue phosphorene nanoribbon (ABPNR), and found that a transverse electric field drives the edge electronic state occupied and at the same time spin-polarized. We also doped electrons to the ABPNR and found that these additional electrons occupy and spin-polarize the electronic states of both edges of the nanoribbon.

Analytical Model to Study Hard Turn-off Switching Dynamics of SiC mosfet and Schottky Diode Pair

Fast switching transient of SiC mosfet may lead to prolonged oscillations, spurious turn on, large device stress, and high amount of electromagnetic interference generation. For an optimal layout and gate driver design, study of switching dynamics is important. This article presents an analytical model that captures the turn-off switching dynamics of SiC mosfet and SiC Schottky barrier diode (SBD) pair using parameters obtained from device and gate driver datasheets and the values of external circuit parasitics. Unlike linear approximation, a detailed model of channel current is considered that captures the gradual transition from ohmic to saturation region and the transverse electric field effect. A comprehensive model of the transfer capacitance is used and the effect of external gate-drain capacitance is considered. This results in a better estimation of switching transition time, actual loss incurred, (dv/dt), (di/dt), and transient overvoltage. The behavioral simulation and experimental results confirm the accuracy of the presented analytical model over a range of operating conditions for two 1.2-kV discrete SiC mosfet and SBD pairs of different current ratings.

Nonlinear optical properties of lens-shaped core/shell quantum dots coupled with a wetting layer: effects of transverse electric field, pressure, and temperature

In this study, we numerically determined the intra-band transition lifetime of carriers as well as, the linear, nonlinear, and total absorption coefficients fro lens-shaped core/shell quantum dot structures. Our computations considered the combined effects of the wetting layer, pressure, applied transverse electric field, temperature, and core/shell sizes. By using suitable choices for these parameters, we found that a red or blue shift in the energy of the absorption spectrum could be achieved. In addition, the largest absorption coefficient was obtained when an intense transverse electric field was applied along the diagonal of the cross section of the structure considered. Hence, the magnitude of the absorption coefficient increased by 50%. Moreover, our results showed that the transition lifetime of the carriers decreased as the temperature increased, whereas it increased as the pressure increased. Comparative analysis of a semi-spherical core/shell quantum dot system showed that the transition lifetime was shorter than that of the lens-shaped core/shell quantum dot structure, which was 255 ns.

First-principles study of electric field effect and spin-polarization transport properties of zigzag α-2 graphyne nanoribbons

Combining the density functional theory with the non-equilibrium Green's function, we have investigated the external transverse electric field effect of the electronic structures and spin-polarization transport properties within zigzag α-2 graphyne nanoribbons (zα-2GYNRs). The external transverse electric field can induce remarkable spin-polarized and half-metallicity behaviors in our system when the electric field is lower than 0.4 V/Å with the anti-ferromagnetic state. Particularly, we find that a nonmagnetic semiconductor feature can be obtained when the electric field is larger than 0.5 V/Å. Furthermore, analyzing the current-voltage characteristics of the zα-2GYNRs device, some interesting phenomena such as the excellent spin filtering and negative differential resistance have been found. Our results indicate that the external transverse electric field is a practical method for band modulation of the α-2 graphyne, and the design of spin-resolved devices based on zα-2GYNRs can realize multifunctional spin-dependent transport features.

Band-gap modulation of carbon nanotubes with Haeckelite structure under a transverse electric field: A first principle study

We have addressed the effect of transverse electric field on chiral carbon nanotubes with two types of Haeckelite structure. We have successfully verified that chiral (10, 5) carbon nanotube with different types of Haeckelite structure react quite differently in response to a transverse electric field. The band gap varies quadratically for small electric fields and becomes monotonically linear upon increasing the transverse electric filed. Two main interesting phenomena were observed when a transverse electric field applied on the nanotubes with Haeckelite structures. First of all, the semiconductor-metal transition existed regardless Haeckelite structure type; although some variations in the band-gap between the pristine nanotubes and nanotubes with both types of Haeckelites structure. This variation is an indication for strong effect caused by introducing this special type of defects to the nanotube surface. Second, the variations in the band-gap for the pristine nanotube and the two nanotubes with Haeckelite structure have the same trend, even though each type of defects have distinct band gap values under various strengths of the external transverse electric field.

Effect of transverse electric field on polariton reflectance spectra of wide quantum wells

AbstractExcitonic waves propagating in thick GaAs/AlGaAs quantum wells form an interference pattern, which is observed as oscillations in the reflectance spectra. Oscillations in the spectra of wide GaAs quantum wells should reveal a non-trivial behavior as a function of the external uniform electric field as it is found in the theory developed in the present work. The oscillations are suppressed as the electric field increases and then reappear again with an opposite phase at the further rise of the field.

Effective Channel Mobility of AlGaN/GaN-on-Si Recessed-MOS-HFETs

We have investigated the channel mobility of AlGaN/GaN-on-Si recessed-metal-oxide-semiconductor-heterojunction field-effect transistors (recessed-MOS-HFET) with SiO 2 gate oxide. Both field-effect mobility and effective mobility for the recessed-MOS channel region were extracted as a function of the effective transverse electric field. The maximum field effect mobility was 380 cm 2 /V·s near the threshold voltage. The effective channel mobility at the on-state bias condition was 115 cm 2 /V·s at which the effective transverse electric field was 340 kV/cm. The influence of the recessed-MOS region on the overall channel mobility of AlGaN/GaN recessed-MOS-HFETs was also investigated.

Effect of transverse electric field on the longitudinal current–voltage characteristic of graphene superlattice

The current density induced along the axis of graphene superlattice in the presence of ac and dc electric fields has been calculated. The dc electric field vector is assumed to have both transverse and longitudinal components with respect to the superlattice axis. The constant component of the current density is shown to oscillate with a change in the ac field amplitude. The longitudinal current–voltage characteristic of graphene superlattice contains a portion with negative differential conductivity. The maximum of the longitudinal current–voltage characteristic shifts to larger values of the longitudinal component of dc field with an increase in the transverse component of electric field.

Effect of transverse electric field and temperature on light absorption in GaAs/AlGaAs tunnel-coupled quantum wells

The photoluminescence and intersubband absorption spectra are studied in GaAs/AlGaAs tunnel- coupled quantum well structures. The peak positions in the photoluminescence and absorption spectra are consistent with the theoretically calculated energies of optical carrier transitions. The effect of a transverse electric field and temperature on intersubband light absorption is studied. It is caused by electron redistribution between the size-quantization levels and a variation in the energy spectrum of quantum wells. The variation in the refractive index in the energy region of observed intersubband transitions is estimated using Kramers–Kronig relations.

Helicoidal graphene nanoribbons: Chiraltronics

We present a calculation of the effective geometry-induced quantum potential for the carriers in graphene shaped as a helicoidal nanoribbon. In this geometry the twist of the nanoribbon plays the role of an effective transverse electric field in graphene and this is reminiscent of the Hall effect. However, this effective electric field has a different sign for the two iso-spin states and translates into a mechanism to separate the two chiral species on the opposing rims of the nanoribbon. Iso-spin transitions are expected with the emission or absorption of microwave radiation which could be adjusted to be in the THz region.

Field-enhanced electronic specific heat of carbon nanotubes

The tight-binding model including curvature effects is used to study the effect of transverse electric field on the low-temperature electronic specific heat (Cv) for armchair and zigzag carbon nanotubes (ACNTs and ZCNTs). Electric field could effectively modulate energy dispersions of CNTs and cause a shift of electronic states toward the Fermi energy. As field strength reaches to a critical value (Fc), it induces special structures in the density of states near the Fermi energy and thus the giant specific heat. At Fcs, Cv has a value comparable to that of the phonon specific heat and reveals strongly non-linear dependence on temperature. The critical field strength and giant specific heat are closely related to nanotube's geometry. Moreover, under Fcs, the extra longitudinal magnetic flux could cause a re-enhancement in Cv for ZCNTs, whereas Cv is always diminished for ACNTs.

Silicane nanoribbons: electronic structure and electric field modulation

We present electronic band structure, Gibbs free energy of formation, and electric field modulation calculations for silicane nanoribbons (NRs), i.e., completely hydrogenated or fluorinated silicene NRs, using density functional theory. We find that although the completely hydrogenated silicene (H-silicane) sheet in the chair-like configuration is an indirect-band-gap semiconductor, a direct band gap can be achieved in the zigzag H-silicane NRs by using Brillouin-zone folding. Compared to H-silicane NRs, the band gaps of completely fluorinated silicene (F-silicane) NRs reduce at least by half. For all silicane NRs considered here, the Gibbs free energy of formation is negative but shows different trends by changing the ribbon width for H-silicane NRs and F-silicane NRs. Furthermore, by analyzing the effect of transverse electric fields on the electronic properties of silicane NRs, we show that an external electric field can make the electrons and holes states spatially separated and even render silicane NRs self-doped. The tunable electronic properties of silicane NRs make them suitable for nanotechnology application.

Effects of transverse electric fields on Landau subbands in bilayer zigzag graphene nanoribbons

The magneto-electronic properties of quasi-one-dimensional zigzag graphene nanoribbons are investigated by using the Peierls tight-binding model. Quasi-Landau levels (QLLs), dispersionless Landau subbands within a certain region of -space, are resulted from the competition between magnetic and quantum confinement effects. In bilayer system, the interlayer interactions lead to two groups of QLLs, one occurring at the Fermi level and the other one occurring at higher energies. Transverse electric fields are able to distort energy spectrum, tilt two groups of QLLs, and cause semiconductor-metal transition. From the perspective of wave functions, the distribution of electrons is explored, and the evolution of Landau states under the influence of electric fields is clearly discussed. More interestingly, the band mixing phenomena exhibited in the energy spectrum are related to the state mixing, which can be seen by the wave functions. The density of states, which could be verified through surface inspections and optical experiments, such as scanning tunneling spectroscopy and absorption spectroscopy, is provided at last.

Analysis on effects of transverse electric field in an injector cavity of compact-ERL at KEK

For a future synchrotron light source based on a linac, e.g. an X-ray free electron laser and an energy recovery linac (ERL), an injector is a key component to generate a high brightness electron beam. For the acceleration and transportation of the electron beam in the injector, the adjustment of beam orbit inside the cavity is important to avoid the deterioration of the beam quality due to the transverse electric field of it, which causes the transverse emittance growth. To adjust the beam orbit, an investigation of the electromagnetic center of the cavity is required in the beam operation. This paper shows a new method for measuring the electromagnetic center of the cavity, and describes an analytical model of emittance growth due to a combination of transverse electric field and orbit offset. The validation of the method was confirmed by the emittance measurement in the compact ERL (cERL) injector at KEK.

Modulation of electric field on persistent current of carbon nanotubes

Abstract We use tight-binding model including curvature effects to study the effect of transverse electric field on the persistent currents of armchair and zigzag carbon nanotubes (ACNTs and ZCNTs) threaded by longitudinal magnetic field. With increasing field strength, ZCNTs could undergo zero-gap transitions, whereas metallic ACNTs are not affected. The current amplitude, without electric field, in a ( m , m ) ACNT is inversely proportional to m 2 . However, for a ( m , 0 ) ZCNT, it is determined by the modulus of m with respect to three. Electric field could enhance the current amplitude of an ACNT, but could not change its magnetism. As for a ZCNT, both electric-field-distorted electronic states and zero-gap transitions determine a change in magnetism that is pronouncedly related with nanotube's geometry.

Effect of electric field on persistent current of boron nitride nanotubes

We study the effect of transverse electric field on persistent currents of armchair and zigzag boron nitride nanotubes (ABNNTs and ZBNNTs) threaded by longitudinal magnetic field within the tight-binding model. In the absence of electric field, the persistent current of (m,m) ABNNTs has a weak amplitude decaying exponentially with nanotube׳s radius and shows paramagnetism. For (m,0) ZBNNTs, the current amplitude and magnetism are determined by the modulus of m with respect to three. Electric field could enhance the current amplitude of both ZBNNTs and ABNNTs, but could not change the magnetism of ABNNTs. However, for ZBNNTs, electric field could further change the magnetism and the symmetry in the current–flux curves that is pronouncedly associated with nanotube׳s geometry.

Increasing the viewing angles in displays based on liquid crystals Review^∗ This review uses some materials of an invited report delivered at the International Conference in Calcutta on “Trends in Optics and Photonics,” 12/7–9/2011

This paper discusses modern principles of constructing displays based on liquid crystals, which provide high-contrast images at large viewing angles. The characteristics of displays based on the twist and supertwist effects and the transverse electric-field effect are considered, along with optical compensator films and multidomain vertically oriented structures. Displays with controllable field-of-view angles are described.