Electric Field Dependence Research Articles

Dielectric and piezoelectric properties of 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with sodium niobate

In this paper, we present the dielectric and piezoelectric properties of tetragonal 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with NaNbO3 ((1-x)[0.8Na0.5Bi0.5TiO3-0.2BaTiO3]-xNaNbO3). Our experimental study has revealed that the ferroelectric phase in these compositions is suppressed with the increase of sodium niobate concentration. A broad anomaly, resembling relaxor ferroelectrics, appears in the 325–450 K temperature interval. The investigation of the electric field dependence of polarization has indicated that the double hysteresis loop behaviour is characteristic of the modified compositions, which is associated with the 1st order phase transition under the applied electric field. The experiments below room temperature have revealed that the range of stability of the ferroelectric phase is shifted to lower temperatures upon the increase of sodium niobate concentration. The electromechanical displacement in the modified compositions shows a similar maximum displacement in the whole concentration range. The electromechanical response in 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 solid solutions is due to the piezoelectric effect, while, in the mixed compositions, it is related to the jump-like change of the lattice constants in the vicinity of electric fieldinduced 1st order phase transition.

Bias dependent dipolar electric field at self-assembled monolayer (SAM)/organic interface determines the hole drift mobility

The room-temperature current-voltage data of hole transport in ITO/PFB(400 nm)/Al organic diode (Khodabakhsh et al., 2004) where PFB is polyfluorene copolymer, and the related 5 devices of different self-assembled monolayer (SAM) with permanent molecular dipole moments chemisorbed onto the indium-tin-oxide (ITO) electrode are investigated. It is shown that the intrinsic hole mobility, μmax, within the diode is Ea independent but it is strongly dependent on the magnitude and the orientation of the SAM´s permanent molecular dipole moments. The current-density data jointly with the reported values of 4 SAM’s molecular dipole moments and their orientation with respect to the ITO normal at the contact enable to provide an estimate of the PEDOT:PSS, as well as pristine ITOP/PFB molecular dipole moments and their orientations. The dipolar electric field that is induced at the ITO/SAM/PFB interface, Eint, turns out to be a linear function of the applied field Ea of approximately SAM`s independent slope. The current-density induced dipolar electric field occurs even at the pristine ITO/PFB interface. The intrinsic hole mobility, μmax, multiplied by the given algebraic function of the Ea dependent interfacial electric field, Eint, combine into the Ea dependent hole drift mobility, μd, Influenced jointly by the dipolar and interfacial effects, it is the parameter that is amenable in the current-density-voltage measurements. The relevance of the stated findings to the current switching mechanism in the self-assembled supramolecular ferroelectric organic semiconductor diode is also briefly discussed.

Revisiting the Dielectric Breakdown in a Polycrystalline Ferroelectric: A Phase‐Field Simulation Study

AbstractTo understand the dielectric breakdown in a polycrystalline ferroelectric, a thorough phase field simulation has been performed by introducing a new degradation function. Time and position evolution of breakdown path, electric field dependence of breakdown time, and the effect of several parameters such as grain orientation, dielectric constant of grain and grain‐boundaries (GBs), thickness of GBs (), and grain size () on the threshold breakdown electric field, , are investigated. The results indicate that is improved with decreasing dielectric constant. The dependence of on grain size and GB's thickness obeys a power function () and (), respectively. The results help to engineer the grains and GBs properties and achieve a high breakdown electric field, which is very important in energy‐storage applications.

Delocalization and insulator to metal transition in PEDOT:PSS

Charge transport in poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS), with systematic increase in the percentages of dimethyl sulfoxide (DMSO) and ethylene glycol (EG), is investigated as a function of temperature and electric field down to 4.2 K. The conductivity in pristine PEDOT:PSS (1.4 S cm−1) increased to 1070 S cm−1 with 10% of DMSO, and to 565 S cm−1 with 6% of EG. The conductivity ratio () is substantially reduced to 2.5 in 10% DMSO sample. This gradual transition from insulator (variable range hopping) to disordered metal (T 1/2 fit), with an intermediate critical regime (power law), is observed by small variations in the volume fractions of these solvents. The temperature dependence of the ratio of hopping length to localization length ( is rather weak for samples (2D & 4EG) near the transition. As the delocalization increases in more conducting samples, larger electric field dependence of conductivity is observed at lower fields (0.1 V cm−1). The real part of impedance decreases at higher frequency and the peak in the imaginary part of impedance shifts to higher frequency as the sample conductivity increases.

An energy-dependent electro-thermal response model of CUORE cryogenic calorimeter

The Cryogenic Underground Observatory for Rare Events (CUORE) is the most sensitive experiment searching for neutrinoless double-beta decay (0νββ) in 130Te. CUORE uses a cryogenic array of 988 TeO2 calorimeters operated at ∼10 mK with a total mass of 741 kg. To further increase the sensitivity, the detector response must be well understood. Here, we present a non-linear thermal model for the CUORE experiment on a detector-by-detector basis. We have examined both equilibrium and dynamic electro-thermal models of detectors by numerically fitting non-linear differential equations to the detector data of a subset of CUORE channels which are well characterized and representative of all channels. We demonstrate that the hot-electron effect and electric-field dependence of resistance in NTD-Ge thermistors alone are inadequate to describe our detectors' energy-dependent pulse shapes. We introduce an empirical second-order correction factor in the exponential temperature dependence of the thermistor, which produces excellent agreement with energy-dependent pulse shape data up to 6 MeV. We also present a noise analysis using the fitted thermal parameters and show that the intrinsic thermal noise is negligible compared to the observed noise for our detectors.

Unveiling the role of ethylene glycol for enhanced performance of PEDOT:PSS/Silicon hybrid solar cells

Recently, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and n-silicon (n-Si) based hybrid solar cells (HSCs) are given significant attentions owing to their cost-effective processing and promising photovoltaic performances. Pristine PEDOT:PSS, however, due to its limited electrical conductivity, cannot yield highly efficient HSCs. Doping of ethylene glycol (EG) in PEDOT:PSS boosts its electrical properties. However, role of EG on the formation, working mechanism of PEDOT:PSS/n-Si heterojunction and the performance of the HSCs are rarely explained. Herein, influence of EG on the optical, structural, electrical, and passivation properties of PEDOT:PSS along with polymer/n-Si heterojunction formation is investigated. HSCs with significantly enhanced power conversion efficiency (by ∼3.5 fold) is achieved for an optimal EG concentration (as compared to pristine PEDOT:PSS) on micro-engineered thin n-Si wafers even in the simplest device design. Optimal EG induces a strong inversion layer (p+-n junction) in n-Si at the polymer/Si interface enabling efficient separation and transportation of photo-carriers and hence enhanced solar cell performances. Formation of EG dependent strong electric field at polymer/n-Si interface is confirmed by the results of minority carrier lifetime, J-V characteristics, quantum efficiency, electrochemical impedance and C-V measurements of the HSCs. Role of EG in making an efficient PEDOT:PSS/n-Si solar cell is explained which may pave the way for further advancement of the cost-effective hybrid solar cell technology.

Analysis of the electric field dependence on the electrocaloric properties on BaHf0.11Ti0.89O3 ferroelectric ceramics

Analysis of the electric field dependence on the electrocaloric properties on BaHf0.11Ti0.89O3 ferroelectric ceramics

Calibrating the scintillation and ionization responses of xenon recoils for high-energy dark matter searches

Liquid xenon-based direct detection dark matter experiments have recently expanded their searches to include high-energy nuclear recoil events as motivated by effective field theory dark matter and inelastic dark matter interaction models, but few xenon recoil calibrations above 100 keV are currently available. In this work, we measured the scintillation and ionization yields of xenon recoils up to 426 keV. The experiment uses 14.1 MeV neutrons to scatter off xenon in a compact liquid xenon time projection chamber and produce quasi-monoenergetic xenon recoils between 39 keV and 426 keV. We report the xenon recoil responses and their electric field-dependence for recoil energies up to 306 keV; due to the low event statistics and the relatively mild field dependence, the yield values at higher energies are reported as the average of xenon responses for electric fields between 0.2-2.0 kV/cm. This result will enable xenon-based dark matter experiments to significantly increase their high energy dark matter sensitivities by including energy regions that were previously inaccessible due to lack of calibrations.

Localized interlayer excitons in MoSe2–WSe2 heterostructures without a moiré potential

Interlayer excitons (IXs) in MoSe2–WSe2 heterobilayers have generated interest as highly tunable light emitters in transition metal dichalcogenide (TMD) heterostructures. Previous reports of spectrally narrow (<1 meV) photoluminescence (PL) emission lines at low temperature have been attributed to IXs localized by the moiré potential between the TMD layers. We show that spectrally narrow IX PL lines are present even when the moiré potential is suppressed by inserting a bilayer hexagonal boron nitride (hBN) spacer between the TMD layers. We compare the doping, electric field, magnetic field, and temperature dependence of IXs in a directly contacted MoSe2–WSe2 region to those in a region separated by bilayer hBN. The doping, electric field, and temperature dependence of the narrow IX lines are similar for both regions, but their excitonic g-factors have opposite signs, indicating that the origin of narrow IX PL is not the moiré potential.

Defects in poly(vinylidene fluoride)-based ferroelectric polymers from a molecular perspective

As the most intensively investigated ferroelectric polymers, poly(vinylidene fluoride) and its co-/ter-polymers enable major breakthroughs in a wide range of applications. Since defects play a vital role in tuning a spectrum of physical properties of poly(vinylidene fluoride)-based ferroelectric polymers, defect engineering has become an ingenious and robust strategy in the design of high-performance ferroelectric polymers. In this Review, we summarize the physical insights into the role of defects induced by various monomers at the molecular level on the physical properties and the structure–property relationship of defect-modified ferroelectric polymers. We focus on the fundamentals of the different structural defects on tailoring the dielectric, ferroelectric, electromechanical, and electrocaloric properties, along with the device performance enhancement in capacitors, actuators, and solid-state cooling. The influence of defects on the electric field dependence of the electrostriction and electrocaloric response is highlighted. The role of chiral defects in driving the emergent relaxor properties and morphotropic phase boundary behavior of ferroelectric polymers is discussed. Finally, we offer insightful perspectives on the challenges and opportunities in this rapidly evolving field. The underlying mechanisms revealed in the article are anticipated to guide future fundamental and applied studies of ferroelectric polymers that capitalize on defect engineering for electronic and energy applications.

Laplace DLTS study of defects introduced in GaAs during sputter deposition of Au Schottky contacts

The RF sputter deposition was used to fabricate Au Schottky barrier diodes on Si-doped n-type GaAs with two different carrier densities (1 × 1015 cm−3, 1 × 1016 cm−3 and partially 8 × 1016 cm−3) at a power of 150 W. Deep-level transient spectroscopy (DLTS) and Laplace DLTS were used to measure the electrical properties of the sputter-induced defects near the surface of the GaAs. By using DLTS, we found that the samples contained six defects (S1 (0.046 eV), S2 (0.22 eV), S3 (0.30 eV), S4 (0.55 eV), S5 (0.56 eV) and S6 of which three (S1, S3 and S5) were metastable and one (S4) was highly dopant concentration dependent. S6 was observed close to where the EL2 was expected, but had different properties and two components which could be resolved by Laplace DLTS: S6a (0.83 eV) and S6b (0.84 eV). The depth profile showed a difference in depth distribution of the defects in the samples which shows by increasing depth, a rapid decay of defect concentration. The electric field dependence of the S3 defect could be explained by a combination of Poole-Frenkel and phonon-assisted tunnelling mechanisms while for the S4 and S5 defects the emission of carriers indicate the phonon-assisted tunnelling. True capture cross-section measurements were done, and the S3 defect had a much lower capture cross-section than the S4 and S5 defects and the real capture cross-section of S3 and S4 defects is in the range of Auger mechanism while for the S5 defect indicates multiphonon emission. Finally, measurements as to the effect of annealing on I–V characteristics were carried out on the sputtered samples as well.

External electric field-dependent photoinduced charge transfer in non-fullerene organic solar cells

Based on Marcus theory, the photoinduced electron transfer properties of D-A type non-fullerene acceptor organic solar cells (OSCs) under the dependence of external electric field (Fext) were investigated. The research results shown that the charge transfer mode under different Fext intensities changes with certain regularity. Focusing on the important parameters (ΔG, λ, and VDA) that affect the charge transfer rate, it was found that both charge separation (|ΔGCS|>λ(1.3019 vs 0.8275 eV at Fext = 0) and charge recombiation (|ΔGCR|>λ, (1.9633 vs 0.8275 eV)) processes occur in the Marcus inverted region. The ΔGCS is relatively sensitive to Fext, and the calculated ΔGCS at different Fext intensities yields an increment of 0.0073 eV, which is also the main reason for the increase in the rate of charge separation. The ΔGCR ranges between −1.9633 and −1.9637 eV, is insensitive to Fext, and ΔGCR is significantly smaller than ΔGCS, which makes the charge recombination rate significantly smaller than the charge separation rate. For VDA, it is found that VDA will transition to a new level only when the Fext intensity reaches a certain intensity, which also enables to obtain a faster charge separation rate. By studying the charge transfer parameters in different polar solvents, it is found that polar solvents can indeed increase the charge transfer rate. To a certain extent, our results also demonstrate that the addition of Fext can further improve the performance of non-fullerene acceptor OSCs.

Modeling of ferroelectric tunnel junctions based on the Pt/BaTiO3/Nb:SrTiO3 stack

In this paper, we report a comprehensive modeling investigation of the Pt/BaTiO3/Nb:SrTiO3 stack designed to operate as a Ferroelectric Tunnel Junction (FTJ). The analysis accounts for some specific features of the materials in the stack that are typically overlooked, such as the electric field dependence of the dielectric constant of Nb:SrTiO3 and the dependence of the dielectric constant of BaTiO3 on its thickness. Modeling results are validated through a systematic and consistent comparison with experimental data for the current–voltage characteristics of devices with different stack parameters, at different temperatures. From that, the resistive memory window of an FTJ based on the Pt/BaTiO3/Nb:SrTiO3 stack is then explored over its design space. Results allow to comprehensively assess the ultimate performance of the device, providing hints for the successful development of next-generation FTJ-based memory technologies.

Multiferroic Properties of Pure and Ion‐Doped BiCrO3 Bulk and Thin Films

The multiferroic properties of BiCrO 3 (BCO) bulk and thin films are investigated for the first time using a microscopic model. The influence of ion doping on the multiferroic properties of BCO is also studied because the doping process changes the physical properties and can be used for potential applications in magnetoelectronic devices. The magnetization M increases by Mn and decreases by Ga-ion doping whereas the Néel temperature T N decreases in both cases. There are some discrepancies by polarization whether it is ferroelectric or antiferroelectric. It is shown that bulk pure BCO is antiferroelectric because the electric field dependence of polarization P shows a double hysteresis loop and the dielectric constant has no anomalies at T N . In Ga-, Mn- or Ti-doped BCO a ferroelectric polarization appears. The specific heat shows a peak at T N for BCO. By Ga doping, this peak vanishes with increasing x. The multiferroic behavior of BCO is demonstrated in the magnetic field dependence of the dielectric constant. In BCO thin films, ferroelectric and ferromagnetic behavior is observed.

Cluster-type analogue memristor by engineering redox dynamics for high-performance neuromorphic computing

Memristors, or memristive devices, have attracted tremendous interest in neuromorphic hardware implementation. However, the high electric-field dependence in conventional filamentary memristors results in either digital-like conductance updates or gradual switching only in a limited dynamic range. Here, we address the switching parameter, the reduction probability of Ag cations in the switching medium, and ultimately demonstrate a cluster-type analogue memristor. Ti nanoclusters are embedded into densified amorphous Si for the following reasons: low standard reduction potential, thermodynamic miscibility with Si, and alloy formation with Ag. These Ti clusters effectively induce the electrochemical reduction activity of Ag cations and allow linear potentiation/depression in tandem with a large conductance range (~244) and long data retention (~99% at 1 hour). Moreover, according to the reduction potentials of incorporated metals (Pt, Ta, W, and Ti), the extent of linearity improvement is selectively tuneable. Image processing simulation proves that the Ti4.8%:a-Si device can fully function with high accuracy as an ideal synaptic model.

Electric field dependence of thermal conductivity in bulk systems and nanosystems with charged mobile defects

In systems with charged mobile defects, application of an external electric field modifies the spatial distribution of defects. We obtain the corresponding dependence of the thermal conductivity on the electric field due to the redistribution of defects, both in bulk systems (heat transfer described by Fourier’s law) and in nanosystems (heat transfer described by phonon hydrodynamics). We consider the electric field transverse to the heat flux as well as the electric field parallel to the heat flux; in the latter case, we consider a superlattice composed of alternating layers with defects and without defects. For transverse electric fields, the effective thermal conductivity is increased in bulk systems and decreased in nanosystems. This dependence on the field would allow us to control heat transport in an easy and reversible way without modifying the material.

Giant Stark Effect in Two-Dimensional Hittorf’s Phosphorene

The electric field tunable band gap and optical properties in low-dimensional materials (quantum-confined Stark effect) are very useful in applications of optoelectronics. In this paper, based on the many-body perturbation method, we investigate the evolution of the quasiparticle electronic structure, exciton, and optical properties of two-dimensional (2D) Hittorf's phosphorene under an out-of-plane electric field. Compared to other 2D monolayers, the relatively large thickness of Hittorf's phosphorene leads to a significant reduction in the quasiparticle band gap when an electric field is applied along the quantum confinement direction. The unique bilayer structure, on the other hand, guarantees a well spatial separation of photon-excited electron-hole pairs and, consequently, reduced exciton binding energy under an out-of-plane electric field. These combined effects lead to an almost fixed exciton energy and optical absorption edge at low applied electric fields. However, when the field is larger than 0.1 V/\AA{}, substantial reductions in the exciton energy and optical absorption edge are identified. For the higher-order exciton states, the involvement of more complex band-to-band electron-hole pair formation results in a nonmonotonic electric field dependence. The effective optical modulation accompanied with these giant Stark effects shows potential applications of Hittorf's phosphorene in 2D optoelectronic devices.

Simulation of Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes.

Al0.85Ga0.15As0.56Sb0.44 is a promising avalanche material for near infrared avalanche photodiodes (APDs) because they exhibit very low excess noise factors. However electric field dependence of ionization coefficients in this material have not been reported. We report a Simple Monte Carlo model for Al0.85Ga0.15As0.56Sb0.44, which was validated using reported experimental results of capacitance-voltage, avalanche multiplication and excess noise factors from five APDs. The model was used to produce effective ionization coefficients and threshold energies between 400-1200 kV.cm-1 at room temperature, which are suitable for use with less complex APD simulation models.

An ultrahigh sensitivity three-dimensional electric-field sensor with barium titanate crystal waveguides

The high-speed development and applications of modern automation production, high-capacity high-speed telecommunications, and aerospace are promoting the detection and sensing of various electric fields. In this article, we investigate a three-dimensional high-frequency electric-field sensor with a barium titanate (BaTiO3) crystal film waveguide due to an extremely high electrooptic (EO) coefficient, r51 = r42. First, the dependences of the lowest electric field, namely, the sensitivity of the sensor to the electric field and the most sensitive direction, are modeled through the nonlinear EO modulation equation of the EO coefficient, r51, and birefringence, beo, with an embedded waveguide/electrode regime. Then, for the given r51/beo values, broad dependences of device sensitivities are numerically simulated with a broad design of electrodes. Thus, as a result, for a given BaTiO3 crystal thin-film having an EO coefficient value of r51 = ≥500 pm/V and an absolute beo value of ≤0.01, the lowest electric field of tens of kilovolt/m level and the electric-field direction could also be detected with a sensing length of millimeters. Meanwhile, the frequency dependence of a scattering parameter of the microwave sensor antenna, S11, is simulated and the frequency point of 2.15 GHz for the highest gain antenna is found.

Hyperbolic-tan graded composition InxGa1-xAs layers for THz radiation emitters

The growth and characterization of InxGa1-xAs layers with hyperbolic tangent In concentration profiles is presented. Along the growth the molecular beam fluxes of Ga and In, and the substrate temperature were varied. Since the concentration of In is varied during growth process the strain is expected to increase monotonically, and eventually be relaxed via dislocation formation. Positively, reordering of the ternary alloy and the improvement of its crystal quality were propitiated by annealing the samples. The gradual In concentration propitiated along the thickness of the film conduced to variations of the near-surface band bending. The THz emission from GaAs, InAs, and graded samples was investigated by femtosecond laser pumping excitation. The band-bending from hyperbolic-tan graded composition InxGa1-xAs layers causes depth dependence of effective mass and built-in electric fields modifying accordingly the THz emission.