Bias Electric Field Research Articles

Resonant tunneling properties of inverted Morse double quantum barrier

We study resonant tunneling characteristics of inverted Morse double quantum barrier structures. The effect of electric bias and structure parameters is calculated by using non-equilibrium Green's function method. Results for the transmission coefficients are compared with the structure parameters. Our results show that the widths of the wells and heights of barriers have a significant effect on the transmission properties. We found that the resonant peak of the transmission coefficient decreases with increasing electric field bias. Moreover, resonant energy level increases with increasing barrier height and increasing width parameters.

Non-trivial behavior of the low temperature maximum of dielectric constant and location of the end critical point in Na0.5Bi0.5TiO3-0.06BaTiO3 lead free relaxor ferroelectrics crystals detected by acoustic emission

[001] lead free relaxor ferroelectrics crystals of Na0.5Bi0.5TiO3–0.06BaTiO3 were studied by means of dielectric and acoustic emission methods in the temperature range of 25–240 °C and under a dc bias electric field up to 0.4 kV/cm. A temperature maximum of the dielectric constant was found near 170 °C, as well as the acoustic emission bursts pointed out to both the depolarization temperature near 120 °C and the temperature, corresponding to the maximum of dielectric constant, near 170 °C. While the depolarization temperature increased linearly, the temperature of the dielectric constant maximum was shown to exhibit a V-shape behavior under an electric field: it initially decreases, reaches a sharp minimum at some small threshold electric field of 0.15 kV/cm, and then starts to increase similar to the Curie temperature of the normal ferroelectrics, as the field enhances. Acoustic emission bursts, accompanying the depolarization temperature, weakened with the enhancing field, whereas the ones accompanying the temperature of the dielectric constant maximum exhibited two maxima: near 0.1 kV/cm and near 0.3 kV/cm. The meaning of these two acoustic emission maxima is discussed.

Reducing the sensitivity of Rydberg atoms to dc electric fields using two-frequency ac field dressing

We propose a method for reducing the sensitivity of atomic ground to Rydberg transitions to stray dc electric fields, using microwave-induced dressing of Rydberg states. Calculations are presented for the Cs $\state{90S}{1/2}$ and $\state{90P}{3/2}$ states. With zero dc bias electric field, a two-frequency ac field is used to simultaneously reduce the sensitivity of both states to dc field variations. The sensitivity reduction is a factor of 95 for the $\state{90S}{1/2}$ state and a factor of 1600 for the $\state{90P}{3/2}, m_J=3/2$ state. We also show how the two-frequency ac field can be used to cancel both second- and fourth-order terms in the polarizability of a single Rydberg state. These results are relevant to improving the stability of experiments that seek to excite Rydberg atoms in the proximity of charged surfaces.

Electric-field tuning of a planar terahertz metamaterial based on strained SrTiO3 layers

We demonstrate a metamaterial exhibiting a frequency-tunable response in the terahertz domain, controlled by a bias electric field. The active part of the metamaterial consists of a periodic metallic pattern deposited on a thin epitaxially strained strontium titanate film. The role of the metallic structure is two-fold: it gives rise to the metamaterial resonance and it enables applying an electric bias to the strontium titanate layer. The strained film exhibits a pronounced dependence of its permittivity on the bias, which exerts a strong influence on the resonance. Specifically, the resonance of our structure occurs near 0.5 THz and, upon applying a bias voltage of 55 V, a relative tunability of the resonance frequency of 19% was achieved at room temperature.

Enhancement of breakdown electric field and DC bias of (In0.5Nb0.5)0.005(Ti1-xZrx)0.995O2 colossal permittivity ceramics

In, Nb, and Zr co-doped TiO2 ((In0.5Nb0.5)0.005(Ti1-xZrx)0.995O2) (x = 0–0.80) ceramics were prepared by a solid-state reaction method, and their structures, dielectric properties, and response to DC bias were studied. The solubility limit was found to be near x = 0.10, and the excess added Zr was present in the form of secondary ZrTiO4 phase. The mean grain size increased from 20.2 to 39.5 μm in the x = 0–0.10 range and then decreased to 5.2 μm for x = 0.20. Permittivity at 1 kHz exceeded 104 for the samples in the x = 0–0.20 range and then decreased to 570 for x = 0.40. For x = 0.20, the ceramic sample showed εr ≈ 104 and tanδ ≤ 0.05 (20 Hz–100 kHz), as well as good temperature (−150 to 125 °C) and DC bias (0–875 v/cm) stability. The breakdown electric field increased from 940 v/cm for x = 0 to 5770 v/cm for x = 0.20. The excellent dielectric properties are attributed to the coexistence of smaller grains and the presence of insulating ZrTiO4 in the sample.

Optimizing effective phase modulation in coupled double quantum well Mach–Zehnder modulators**Project supported by the National Natural Science Foundation of China (Grant No. 11474106), the Natural Science Foundation of Guangdong Province, China (Grant No. 2016A030313439), and the Science and Technology Program of Guangzhou City, China (Grant No. 201707010403).

We report optimal phase modulation based on enhanced electro–optic effects in a Mach–Zehnder (MZ) modulator constructed by AlGaAs/GaAs coupled double quantum well (CDQW) waveguides with optical gain. The net change of refractive indexes between two arms of the CDQW MZ modulator is derived by both the electronic polarization method and the normal-surface method. The numerical results show that very large refractive index change over 10−1 can be obtained, making the phase modulation in the CDQW MZ modulator very highly efficient. It is desirable and important that a very small voltage-length product for π phase shift, Vπ × L0 = 0.0226 V⋅mm, is obtained by optimizing bias electric field and CDQW structural parameters, which is about seven times smaller than that in single quantum-well MZ modulators. These properties open an avenue for CDQW nanostructures in device applications such as electro–optical switches and phase modulators.

The Electrocaloric Effect in BaTiO3–SrTiO3 Solid Solution

We have studied the electrocaloric effect in 0.68BaTiO3–0.32SrTiO3 solid solution, as well as the dielectric, pyroelectric, and piezoelectric properties of this compound in the vicinity of the first-order phase transition in a bias electric field. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.

Электрокалорический эффект в твердом растворе BaTiO-=SUB=-3-=/SUB=--SrTiO-=SUB=-3-=/SUB=-

AbstractWe have studied the electrocaloric effect in 0.68BaTiO_3–0.32SrTiO_3 solid solution, as well as the dielectric, pyroelectric, and piezoelectric properties of this compound in the vicinity of the first-order phase transition in a bias electric field. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.

Analysis of temperature effect in dielectric response of electrostrictive polymers for pseudo-pyroelectric operations

Thanks to their flexibility and easy processability, electroactive polymers have gained a lot of attention over the last decades. More specifically, dielectric electrostrictive polymers have been demonstrated to provide interesting ways for mechanical actuation and energy harvesting or for electrocaloric applications. This Letter aims at presenting an additional application potential of such materials, showing their ability in terms of converting thermal energy into electrical energy. More particularly, it is shown that such materials, once polarized through the application of a bias electric field, allow a polarization variation with the temperature, yielding the so-called pseudo-pyroelectric effect. Theoretical analysis, supported by experiments, therefore demonstrates that such a material can exhibit pseudo-pyroelectric activity that can be tuned with the applied electric field.

Fabrication of spiral inter-digitated terminal (IDT) structure of electroplated gold on quartz substrate and progressive microplasma generation

This paper discussed about the progressive microplasma generation in planar spiral inter-digitated terminal (IDT) structure. The IDT structures (with separation between two adjacent spiral electrodes varied progressively from 30 to 33 µm) are fabricated on quartz wafer by 5 µm thick gold electroplating. The onset of microplasma is witnessed around 580 V applied bias (Electric field: ~ 193 kV/cm). Initially, the microplasma is observed nearby the central area of the spiral IDT structure. Thereafter, the microplasma started spreading out other regions and finally engulfs the whole IDT with an intense glow. Although the bias is applied continuously, the microplasma generation in the spiral IDT structure is found to be discontinuous. It seems to be due to the discharge of the energy stored in the metal-air-metal capacitor (spiral IDT) during micro-plasma generation and thus reduces the resultant electric field below the threshold of microplasma generation. When the micro-plasma stops, the voltage at the IDT capacitors is again restored to its threshold value and microplasma is being observed again.

Contributions of intrinsic and extrinsic polarization species to energy storage properties of Ba0.95Ca0.05Zr0.2Ti0.8O3 ceramics

Ba0.95Ca0.05Zr0.2Ti0.8O3 ceramics were prepared at different sintering temperatures by citrate precursor and solid-state reaction methods, respectively. The crystal structure and microstructure of the specimens were characterized. In view of energy storage capacitor utilizations, the dielectric properties of the specimens were investigated at room temperature as a function of frequency and applied electric field. Moreover, the nature of mobile charge carriers in the specimens was diagnosed by complex impedance spectroscopy at elevated temperatures. While the dielectric constants of the specimens prepared by different methods are quite different (4.4 × 103–2.2 × 104 at 10 kHz) at zero electric field, the energy storage densities at an identical strong electric field are similar (e.g. 0.32–0.41 J/cm3 at 120 kV/cm). The dielectric constants under bias electric field were fitted to a multipolarization mechanism model to resolve the contributions of intrinsic and extrinsic polarization mechanisms. It turned out that the extrinsic contributions fade out within low electric field range (<20 kV/cm) and thereby the intrinsic lattice polarization governs the overall dielectric responses at higher fields. Based on the fitting result, the energy storage properties of the specimens were interpreted.

Strong anisotropy of electric field effects on uniaxial relaxor ferroelectric Sr0.75Ba0.25Nb2O6 crystals proved by acoustic emission

[001] oriented Sr0.75Ba0.25Nb2O6 uniaxial relaxor ferroelectric crystals have been studied by acoustic emission in the temperature range of 20÷200 °C and under an external electric field up to 1 kV/cm. Under the application of an electric field the temperature of a dielectric maximum exhibits a nontrivial behavior: it remains constant at first, secondly steep decreases down to some threshold field, and thirdly starts to increase as a field enhances, whereas the same temperature of a dielectric maximum under a bias electric field to [100] oriented Sr0.75Ba0.25Nb2O6 crystals exhibits a smoothed minimum before the start to increase as a field enhances (E. Dul'kin et al., J. Appl. Phys. 110, 044106 (2011)). Such a difference of electric field effects in c- and a-cut crystals is discussed from the viewpoint of random-bond-random-field model of relaxor ferroelectrics. By the comparison between experimental and theoretical data, a dipole moment of the PNR was estimated to be 0.1 (C cm).

Debye-like relaxation behavior and electric field induced dipole re-orientation of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic

Mechanisms of the dielectric relaxation and electric field induced dipole re-orientation process in the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic have been investigated by a combination of experiments and simulations. Using the modified Debye relaxation theory, the observed strong relaxation is related to the evolution of the distribution of relaxation times with increasing temperatures. The increased freezing temperature under dc bias electric fields indicates that the nonlinear dielectric behavior has positive contributions to the total polarization. In relaxor state, the dielectric response of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic shows a maximum value with the increasing external fields, which is attributed to two main polarization mechanisms, lattice phonon polarization and re-orientation of polar clusters. The contribution of these two polarization mechanisms is separated by the multi-polarization model, indicating that the re-orientation of polar clusters is responsible for the increase of the dielectric constant. At last, Monte Carlo method is performed to simulate the dipole re-orientation process, and the simulated results are consistent with experimental findings. This study provides a different perspective to investigate the relaxor materials with isolated polar clusters.

Comparison on the Synchronization of Two Parallel GaAs Photoconductive Semiconductor Switches Excited by Laser Diodes

In this letter, the synchronization of GaAs photoconductive semiconductor switches in two electrically driven configurations for laser diodes excitation is investigated. Comparisons on the synchronization are carried out by varying the bias electric field and optical excitation energy. The optimum synchronization of 296 ps is achieved at 1.2 kV with optical excitation energy of 1.9 μJ. The results demonstrate the relationship between the synchronization and transient carriers' population ratio among the intervalley.

Interactions between self-accelerating beams in photorefractive media.

We investigate interactions between in-phase or out-of-phase Airy beams and nonlinear accelerating beams in photorefractive crystals by means of direct numerical simulations. Since self-accelerating beams possess infinite energy, we evaluated the propagation of two shifted counter beams by truncating the oscillating tails. The numerical results show that the external bias electric field has a profound effect on the propagation dynamics and the solitons shed from the Airy beam. We also found that during interactions between two nonlinear accelerating beams, single solitons, soliton pairs, and bound breathing solitons were produced. When the nonlinear accelerating beam collides with a soliton beam, the main lobe continues accelerating while the soliton intensity fluctuates with the lobes.

Dielectric and multiferroic behavior in Sm2BaNiO5, a Haldane spin-chain compound

The Haldane spin-chain (S = 1) insulating compound, Sm2BaNiO5, which has been proposed to order antiferromagnetically around (TN = ) 55K, was investigated for its complex dielectric permittivity, magnetodielectric and pyrocurrent behavior as a function of temperature (T). In order to enable meaningful discussions, the results of ac and dc magnetization and heat-capacity studies are also reported. We emphasize on the following findings: (i) There is a pyrocurrent peak near TN, but it is shown not to arise from ferroelectricity, but possibly due to ‘thermally stimulated depolarization current’, unlike in many other members of this rare-earth series in which case ferroelectric features were reported at or above TN; (ii) however, the pyrocurrent measured in the presence of a bias electric field (after cooling in zero electric field) as well as dielectric constant reveal a weak peak with increasing T around 22K–the temperature around which population of the exchange-split excited state of Kramers doublet has been known to occur. This finding suggests that this compound presents a novel situation in which multiferroicity is induced by an interplay between crystal-field effects and exchange interaction. No multiglass features could be observed down 2K unlike in many other members of this family.

Efficient two-step photocarrier generation in bias-controlled InAs/GaAs quantum dot superlattice intermediate-band solar cells

We studied the effects of the internal electric field on two-step photocarrier generation in InAs/GaAs quantum dot superlattice (QDSL) intermediate-band solar cells (IBSCs). The external quantum efficiency of QDSL-IBSCs was measured as a function of the internal electric field intensity, and compared with theoretical calculations accounting for interband and intersubband photoexcitations. The extra photocurrent caused by the two-step photoexcitation was maximal for a reversely biased electric field, while the current generated by the interband photoexcitation increased monotonically with increasing electric field intensity. The internal electric field in solar cells separated photogenerated electrons and holes in the superlattice (SL) miniband that played the role of an intermediate band, and the electron lifetime was extended to the microsecond scale, which improved the intersubband transition strength, therefore increasing the two-step photocurrent. There was a trade-off relation between the carrier separation enhancing the two-step photoexcitation and the electric-field-induced carrier escape from QDSLs. These results validate that long-lifetime electrons are key to maximising the two-step photocarrier generation in QDSL-IBSCs.

Field-driven electro-optic dynamics of polar nanoregions in nanodisordered KTa1−xNbxO3 crystal

Polar nano-regions (PNRs) are considered to be responsible for giant electro-optic (EO) and piezoelectric effects, but the PNR response mechanism remains unclear. For our further understanding of the PNR field-driven dynamics, we investigate quadratic and linear EO effects in nanodisordered KTa1−xNbxO3 at (Tc + 2 °C) under various ac and (ac + dc) electric fields. The large EO effects exhibit a strong electric field dependence. Our results show that non-ergodic PNRs have vibrational and reorientational field-driven dynamics that jointly contribute to the dynamic EO characteristics. Further, macroscopic symmetry breaking under a bias electric field induces the intrinsic linear EO effect. This understanding of the dynamic EO characteristics and field-driven dynamics of PNRs will be valuable for photonic device development and provide a basis for exploring the origin of giant EO and piezoelectric effects in disordered ferroelectrics and relaxors.

High Efficient THz Emission From Unbiased and Biased Semiconductor Nanowires Fabricated Using Electron Beam Lithography

Besides having perfect control on structural features, such as vertical alignment and uniform distribution by fabricating the wires via e-beam lithography and etching process, we also investigated the THz emission from these fabricated nanowires when they are applied DC bias voltage. To be able to apply a voltage bias, an interdigitated gold (Au) electrode was patterned on the high-quality InGaAs epilayer grown on InP substrate by molecular beam epitaxy. Afterwards, perfect vertically aligned and uniformly distributed nanowires were fabricated in between the electrodes of this interdigitated pattern so that we could apply voltage bias to improve the THz emission. As a result, we achieved enhancement in the emitted THz radiation by ∼four times, about 12 dB increase in power ratio at 0.25 THz with a DC biased electric field compared with unbiased NWs.

Adjustability of resonance frequency by external magnetic field and bias electric field of sandwich magnetoelectric PZT/NFO/PZT composites

Sandwich magnetoelectric composites of PZT/NFO/PZT (PNP) have been prepared by laminating PZT5, NiFe2O4, and PZT5 ceramics in turn with polyvinyl alcohol (PVA) paste. A systematic study of structural, magnetic and ferroelectric properties is undertaken. Structural studies carried out by X-ray diffraction indicate formation of cubic perovskite phase of PZT5 ceramic and cubic spinel phase of NiFe2O4 ceramic. As increasing the content of PZT5 phase, ferroelectric loops and magnetic loops of PNP composites showed increasing remnant electric polarizations and decreasing remnant magnetic moments separately. Both external magnetic fields and bias voltages could regulate the basal radial resonance frequency of the composites, which should be originated with the transformation and coupling of the stress between the piezoelectric phase and magnetostrictive phase. Such magnetoelectric composite provides great opportunities for electrostatically tunable devices.