Polarization Field Effects Research Articles

Estimating seismometer component orientation of the Brazilian seismographic network using teleseismic P-wave particle motion analysis and directional statistics

Seismometer component orientation is one of the most critical parameters for seismology, especially for methods that take wave field polarization effects into account, such as receiver functions, seismic anisotropy, surface wave dispersion and seismic tomography. Using P-wave particle motion combined with directional statistics, we estimated the orientation for 90 stations of the Brazilian Seismographic Network (RSBR), corresponding to 105 seismometers. The difference between the number of stations (90) and seismometers (105) is due to instrument replacement during station operation. We observed that 81 seismometers have an orientation of ±5° and 19 seismometers greater than ±5°. Only one seismometer has an orientation greater than 90° (BOAV station). ON and BR are the subnetworks of RSBR with the largest number of seismometers with orientation errors bigger than ±10° (6 for each one) and NB is the only subnetwork with no misoriented station. All the estimated orientations were close to the measured in the field, which is evidence that our approach is more accurate to detect misoriented stations than previous studies that analyzed the orientation of RSBR stations. The Watson's U2 statistical test indicated that the back azimuth deviations for Precambrian Basement and Phanerozoic Cover were significantly different, suggesting that the regional geology could affect back azimuth estimates.

Ordinary light induced polarization zones in Tutton salt crystal

Ordinary light wave passing through a low symmetry crystal along an off optic -axis direction gets split into ordinary and extra-ordinary waves. If the beam size is large, the two polarized waves could overlap covering a large volume within the medium. It is realized that overlapping ordinary and extra-ordinary waves, result in creation of alternate polarization regions with different fluctuating crystalline fields inside a low - symmetry hydrated crystal. If suitable ions are doped in an experimental crystal, their optical absorption spectra could reflect the effect of alternate polarization fields and creation of ordinary light induced periodic polarization (OLIPP) effect inside a low symmetry hydrated crystal.

Electronic and optical properties of boron-containing GaN alloys: The role of boron atom clustering

Boron (B) containing III-nitride materials, such as wurtzite (wz) (B, Ga)N alloys, have recently attracted significant interest due to their ability to tailor the electronic and optical properties of optoelectronic devices operating in the visible and ultraviolet spectral range. However, the growth of high quality samples is challenging and B atom clustering is often observed in (B, Ga)N alloys. To date, a fundamental understanding of the impact of such clustering on the electronic and optical properties of these alloys is sparse. In this work, we employ density functional theory (DFT) in the framework of the meta-generalized gradient approximation [modified Becke Johnson (mBJ) functional] to provide insight into this question. We use mBJ DFT calculations, benchmarked against state-of-the-art hybrid functional DFT, on (B, Ga)N alloys in the experimentally relevant B content range of up to 7.4%. Our results reveal that B atom clustering can lead to a strong reduction in the bandgap of such an alloy, in contrast to alloy configurations where B atoms are not forming clusters, thus not sharing nitrogen (N) atoms. We find that the reduction in bandgap is linked mainly to carrier localization effects in the valence band, which stem from local strain and polarization field effects. However, our study also reveals that the alloy microstructure of a B atom cluster plays an important role: B atom chains along the wz c axis impact the electronic structure far less strongly when compared to a chain formed within the c-plane. This effect is again linked to local polarization field effects and the orbital character of the involved valence states in wz BN and GaN. Overall, our calculations show that controlling the alloy microstructure of (B, Ga)N alloys is of central importance when it comes to utilizing these systems in future optoelectronic devices with improved efficiencies.

The multifield regulation on resistance of PbPd0.9Co0.1O2/PMN-PT(001) laminate film

Spin gapless semiconductor (SGS) presents abundant electric and magnetic properties and is highly sensitive to external factors, such as current, electric field, magnetic field, and stress. This paper reports on a PbPd0.9Co0.1O2/PMNPT(001) laminate thin film with the “SGS/ferroelectrics” structure, which exhibits significant current-induced resistance (I-ER) effect. More importantly, the colossal static electric-field-induced resistance (E-ER) effect in such a laminate film was observed for the first time. The introduction of lattice defects (Pb vacancies) induces a local electric field, electron spin ordering state, and ferroelectric polarization field effect to explain the excellent physical properties. The reported laminate thin film composite exhibits promising application potential in spintronic devices, composite sensor units, storage systems, and other low-energy semiconductor electronic device fields. This work proposes an alternative way to investigate the novel properties for spin gapless semiconductors and expand the research fields of multi-field modulation effect in magnetoelectric composites.

Field dipole interaction and polarization effects in light-sheet optical fluorescence microscopy

Polarization plays a crucial role in understanding the interaction of fluorescent molecules in a light field. We report the study on the effect of a field–dipole interaction under polarization light-sheet fluorescence microscopy using the vectorial theory of light. The molecule is suitably modeled as a radiating electric dipole in a polarized electric field (both linear and random), and the system point spread function (PSF) is determined for different orientations of the dipole (both fixed and random). PSF analysis and contour plots suggest distinct nature of a field distribution in each case, indicating the importance of a field–dipole interaction for high-quality fluorescence imaging. The analysis suggests that the field spreads gradually along the polarization axis at a high numerical aperture (NA) of the objective lens, whereas it is more isotropic and homogeneous at low NA. Moreover, fast changes are not observed at low NA (i.e., far from the central lobe in the field contour plots), suggesting the absence of high-frequency components. However, sidelobes are prominent for linear polarized (along x) light. On the other hand, rapid variations are evident for randomly polarized light, depicting the presence of high spatial frequencies in the system optical transfer function. The other significant observation is the distinct frequency spectrum (both kx and ky) for random and fixed dipoles, indicating the significance of dipole orientation in a light-sheet field. Compared to the point-illumination-based fluorescence microscopy, sheet based polarization technique provides a high signal-to-noise ratio, a uniform field, an order large field of view, and critical information (related to the micro-environment of a dipole and its short-range interactions). The study is expected to facilitate polarization-sensitive investigation of large biological specimens (both fixed and live).

Critical Importance of Nonuniform Polarization and Fringe Field Effects for Scaled Ferroelectric FinFET Memory

The ferroelectric field-effect transistor (FEFET) is an emerging nonvolatile memory technology that can offer ultra-scalability, fast operation, and reduced power consumption. However, a limited understanding of FEFET physics poses challenges for optimum device design. In this article, we provide physical insights into the operation of FinFET-based FEFETs (FEFinFETs) using a phase-field framework built on time-dependent Landau–Ginzburg (TDGL) thermodynamic theory. We exploit the source–drain fringing field to stabilize a monodomain configuration in the OFF state of short channel FEFinFETs. Based on recent experiments, we first analyze the switching dynamics of FEFinFETs with low remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) and high coercive field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) hafnium zirconium oxide (HZO) FE. We find that the switching in these FEFinFETs occurs via domain nucleation and growth from the gate metal edges at the source–drain spacers. We also show that a non-zero drain bias can be used for dynamically modulating the memory window (MW) of FEFinFET to lower its power consumption. Furthermore, we find the spacer permittivity to be a crucial design parameter to control the MW and show that a lower spacer permittivity can significantly increase the MW. Finally, we show that the commonly held idea that a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> leads to a large MW is not always valid. For a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> , the formation of multiple domains in the FE layer can lead to a significant reduction in the MW. In addition, these devices can suffer from low write endurance due to exposure of the interfacial oxide layer to high electric fields.

GW Quasiparticle Energies and Bandgaps of Two-Dimensional Materials Immersed in Water.

Computational simulations have become of major interest to screen potential photocatalysts for optimal band edge positions which straddle the redox potentials. Unfortunately, these methods suffer from a difficulty in resolving the dynamic solvent response on the band edge positions. We have developed a computational method based on the GW approximation coupled with an implicit solvation model that solves a generalized Poisson equation (GPE), that is, GW-GPE. Using GW-GPE, we have investigated the band edge locations of (quasi) 2D materials immersed in water and found a good agreement with experimental data. We identify two contributions of the solvent effect, termed a "polarization-field effect" and an "environmental screening effect", which are found to be highly sensitive to the atomic and charge distribution of the 2D materials. We believe that the GW-GPE scheme can pave the way to predict band edge positions in solvents, enabling design of 2D material-based photocatalysts and energy systems.

Effect of strain-induced polarization field on band structure of MoS2 nanoribbon

Single-layered transition metal dichalcogenides (TMDs) materials show intriguing device application potential due to their superior adjustability under various mechanisms. External strain can produce huge polarization fields inside two-dimensional piezoelectric semiconductor materials to modulate the relevant properties. In this paper, the strain-induced polarization field in monolayer zigzag MoS2 nanoribbon is specifically discussed. For comparison, we also study the deformation potential by means of the strain-modified bond lengths and hopping energies. The edge states and band gap indicate a distinct change due to polarization field. This work can put forward feasible perspectives for designing low-dimensional materials-based devices.

Comparative investigation into key optoelectronic characteristics of semipolar InGaN blue laser diodes: A strategy to mitigate quantum-confine stark effect

In recent years, semipolar InGaN-based blue laser diodes (LDs) have raised indescribable appeal within solid-state lighting industry as promising alternatives for currently available polar c-plane LDs due to reduction in internal polarization field and related quantum-confined stark effect. However, any comparative study in terms of energy band gap, optical emission profile, power output (P) and forward bias response (I-V) etc. between semipolar-oriented InGaN blue LDs is inherently unattainable. This work aims to demonstrate the impact of internal polarization field on aforementioned key optoelectronic parameters of In0.17Ga0.83N/GaN double quantum well (DQW) blue LD along semipolar (101-2), (112-2), (101-1), (202-1), (303-1-), (202-1-) and (101-1-) crystal orientations by figuring out six-band k.p Hamiltonian at the brillouin zone center aided from Euler’s tensor transformation method. Three-level rate equations based LD analogous circuit model and state-space matrix are employed here to obtain P-I-V and frequency characteristics. Radiative as well as non-radiative recombination mechanisms for LD systems are portrayed by addressing modified ABC model. Our numerical investigation illustrates that best hole effective mass, optical gain, lasing power, threshold current and forward voltage can be attained from (112-2)-oriented InGaN blue LD due to insignificant presence of spontaneous plus piezoelectric (PZ) polarization charge. In addition with these, the inspection of bode plot and relevant optical power gain (dB) confirms the stability and superiority of this semipolar blue LD system for achieving high-speed visible-light communications at relatively low current densities.

Effect of ferroelectric polarization field on different carrier migration in photoanode

Spontaneous polarization field in ferroelectric can improve the oxidation kinetics and photocurrent of a photoanode in photoelectrochemical water splitting. But the impact of ferroelectric polarization field on the migration of different charge carriers which have different mobility and diffusion length is still unknown. In this work, we synthesized tetragonal BaTiO3 nanoparticles by solvothermal method successfully and fabricated the hybrid photoanode composed by monoclinic WO3 and BaTiO3 for solar water oxidation. Density functional theory calculations showed that the mobility of electron was faster than that of the hole in WO3, and had a longer diffusion length. We demonstrated that the polarization field of ferroelectric had a greatly impact upon holes migration compared with electrons, thus the thin hybrid photoanode after poling by bias presented a significant improvement of photocurrent (210.5%) under the back-side illumination, and a remarkable augment of charge separation efficiency (94%) and oxidation kinetics (69%) at 1.23 V. Our work provided a deeper understanding of how ferroelectric polarization field affected the photoelectrochemical water oxidation and a general pathway towards enhancing minority carrier collection in photoanode.

Atomistic analysis of piezoelectric potential fluctuations in zinc-blende InGaN/GaN quantum wells: A Stillinger-Weber potential based analysis

In this paper we investigate strain and local polarization field effects in zinc-blende indium gallium nitride (InGaN) alloys and quantum wells. To do so we parametrize and establish a Stillinger-Weber potential with parameters fitted to hybrid functional density functional theory data. The developed model gives very good agreement with quantities to which it has not been fitted, such as Kleinman parameters of cubic III-N materials or the composition dependence of the lattice constant in InGaN alloys. Equipped with this model, we extract the composition dependence of elastic constants ${C}_{11}$ and ${C}_{12}$ in InGaN alloys, including bowing parameters for these quantities, which may form input for continuum-based calculations. Furthermore, applying this model to InGaN alloys and wells reveals that random alloy fluctuations can lead to strong local strain field fluctuations. Building on this information, we present a model that allows for the calculation of connected local built-in field fluctuations at the microscopic level, accounting for first- and second-order piezoelectric effects. The approach is general and can be applied to any zinc-blende III--V alloy or heterostructure investigated in the frame of semiempirical models (e.g., valence force field models) targeting strain fields on an atomistic level. Here, building on our Stillinger-Weber potential we show that local strain fluctuations in zinc-blende InGaN quantum wells can lead to strong piezoelectric built-in field fluctuations. This contribution has been widely overlooked in previous theoretical studies of these systems. Finally, we briefly discuss the impact of these polarization field fluctuations on carrier localization effects in such quantum well systems.

Dynamics of moving electron vortices and magnetic ring in laser plasma interaction

Moving electron vortices have been observed in laser interaction with non-uniform near-critical-density plasma by multi-dimensional Particle-in-Cell simulations. In two dimensional geometry, there are two vortices with opposite magnetic polarity, moving perpendicularly to the plasma density gradient direction. The field distribution and particle motion composing such a moving structure have been clearly observed in simulations, which explains the vortex motion. Two components of loop currents are formed around each electron vortex, which dominate the vortex motion. The moving velocity can be as large as a 0.2c level, forming relativistic vortices inside the plasma. Laser plasma conditions such as intensity, polarization, density profile, and external magnetic field effects on the vortex motion and evolution are also studied. In three dimensions, the structure appears as an expanding magnetic ring with an internal magnetic field up to 1000 Tesla. Such vortex structures suggest an interesting way of energy (with more than 5% of the laser energy) transportation to ambient plasmas as far as 50 μm away from the laser-plasma interaction region, which may have applications in laser plasma-based inertial confinement fusion and laboratory astrophysics.

Magnetic-field-induced splitting and polarization of monolayer-based valley exciton polaritons

Atomically thin crystals of transition metal dichalcogenides are ideally suited to study the interplay of light-matter coupling, polarization and magnetic field effects. In this work, we investiagte the formation of exciton-polaritons in a MoSe2 monolayer, which is integrated in a fully-grown, monolithic microcavity. Due to the narrow linewidth of the polaritonic resonances, we are able to directly investigate the emerging valley Zeeman splitting of the hybrid light-matter resonances in the presence of a magnetic field. At a detuning of -54.5 meV (13.5 % matter constituent of the lower polariton branch), we find a Zeeman splitting of the lower polariton branch of 0.36 meV, which can be directly associated with an excitonic g factor of 3.94\pm0.13. Remarkably, we find that a magnetic field of 6T is sufficient to induce a notable valley polarization of 15 % in our polariton system, which approaches 30% at 9T. Strikingly, this circular polarization degree of the polariton (ground) state exceeds the polarization of the exciton reservoir for equal magnetic field magnitudes by approximately 50%, as a consequence of enhanced relaxation of bosons in our monolayer-based system.

Temperature dependent electrical studies on Cu/AlGaN/GaN Schottky barrier diodes with its microstructural characterization

The performance of the AlGaN/GaN heterostructure based devices depends largely upon electrical behavior of Schottky contact which controls the current flowing through the channel. In this work, electrical behavior of Copper (Cu) Schottky diodes on Al0.25Ga0.75N/GaN heterostructures grown on Silicon have been investigated using temperature dependent current-voltage (I-V) and capacitance-voltage (C-V) techniques. An ideality factor (η) of 1.3 at room temperature (RT) signified that the forward current is dominated by thermionic emission process for current flow in the Schottky diode. The strong polarization field effects with in the barrier layer of the strained AlGaN/GaN heterostructure were considered for evaluating the barrier height using C-V measurements. The barrier height from such analysis was found to be 1.66 eV at RT which is significantly higher than theoretically predicted barrier height for Cu/AlGaN/GaN Schottky diodes. This observation of high barrier height is attributed to the presence of an ultra-thin Cu2O layer between Cu and AlGaN layer as revealed from scanning transmission electron microscopy. The temperature dependence of the barrier height suggests inhomogeneous nature of the Cu/AlGaN/GaN interface with different level of barrier inhomogeneities in different temperature ranges. Further, frequency-dependent C-V measurements were used to electrically characterize surface traps at Cu/AlGaN/GaN interface. Present study highlights the potential of Cu as a Schottky contact on AlGaN/GaN heterostructures for achieving high barrier height which is of utmost importance in GaN based device technology.

The electrical properties of single-crystalline Z-cut LiNbO3 thin films fabricated by crystal-ion-slicing technique

Single-crystalline Z-cut lithium niobate (LiNbO3, LN) thin film with a thickness of ~ 878 nm situated between top and bottom electrodes is fabricated depending on crystal-ion-slicing (CIS) technique and SiO2 bonding method. Microstructure characteristics indicate that the LN thin film has a good crystalline quality and there is no obvious defects on the surface. Moreover, ferroelectric performances are intensively analyzed by the ferroelectric hysteresis loop measurements, which express a glorious rectangularity in spite of shifting to the forward electric field under the effect of internal polarization field. And when external electric field increases the polarization intensity approximates saturation at 900 kV/cm and the value is around 58 μC/cm2. The great ferroelectric performances make it potential for the tunable filters based on the CIS-fabricated LN thin film in other cut directions. The leakage current is also measured in different direction bias and the conduction mechanism is further analyzed, which is dominated by Schottky emission mechanism and has no effect of bulk defects.

A full palette: Crystal chemistry, polymorphism, synthetic strategies, and functional applications of lanthanide oxyhalides

Ionic compounds wherein lanthanide cations are arrayed alongside anions adopt a wide range of crystal structures as a result of the variation of ionic radii and electronic configurations across the lanthanide series. Owing to the constricted nature of 4f orbitals, local coordination environments and structural preferences in such compounds are primarily dictated by electrostatic interactions and steric considerations with the primary driving force being the minimization of the crystal lattice energy. In this review, we examine a broad class of dianionic rare-earth compounds, lanthanide oxyhalides that present a multidimensional design space for tuning of functional properties by dint of the possibilities for extensive alloying on cationic and anionic sublattices; the considerable span of ionic radii and hardness across the lanthanide series and down the halide group, respectively; a large tolerance window for point defects such as oxide and halide vacancies; as well as multiple accessible polymorphs. In addition to their structural versatility, control over functional properties is accessible based on alteration of microstructure and surface chemistry. Synthetic strategies for accessing atomistic, nanoscale, and mesoscale control are discussed using illustrative examples placing particular emphasis on non-hydrolytic sol—gel processes that provide access to well-defined solid-solution nanocrystals. The reactivity and post-synthetic modification of these compounds is further delineated. Methods for defining color centers within these compounds, cooperativity of the optical response of the color centers with the host lattice (determined by overlap integrals specific to each structure type and the polarization and ligand field effects of different halide ions) and adjacent color centers (reliant on energy transfer schema), and their practical application in phosphors are further detailed. Mechanisms facilitating down- and up-conversion of energy absorbed from incident electromagnetic radiation or high-energy particles are delineated with particular emphasis on X-ray and electron-beam excitation. The accessible energy conversion mechanisms, efficacious radiative recombination channels, and opportunities for systematically tuning color through compositional modulation have led to the emergence of these materials as potential candidates for phosphors. These materials have potential applications in solid-state lighting, radiation detection, and as the active elements of imaging devices. The tolerance towards large concentrations of anion vacancies and the facile diffusivity of anions in these compounds further underpins the function of lanthanide oxyhalides as ion conductors, gas sensors, and heterogeneous catalysts. Increasing interest has focused on utilization of well-defined color centers for quantum information science and multiplexed sensing in biological systems. Such applications require additional control of the positioning of dopant atoms and understanding of their interactions with the host lattice and other dopant atoms.

Enhanced Field Modulation Sensitivity and Anomalous Polarity-Dependency Emerged in Spatial-Confined Manganite Strips.

An anomalous polarity-dependent electrostatic field modulation effect, facilitated by spatial confinement, is found in an oxide-based field-effect prototype device with a spatial-confined Pr0.7(Ca0.6Sr0.4)0.3MnO3 channel. It is revealed that the dominant field modulation mode under a small bias field varies from a polarity-independent strain-mediated one to a nonvolatile polarity-dependent one with enhanced modulation sensitivity as the channel width narrows down to several micrometers. Specially, in the structure confined to length scales similar to that of the phase domains, the field modulation exhibits a greatly increased modulation amplitude around the transition temperature and an anomalous bias-polarity dependence that is diametrically opposite to the normal one observed in regular polarization field-effect. Further simulations show that a large in-plane polarization field is unexpectedly induced by a small out-of-plane bias field of 4 kV/cm in the narrow strip (up to 790 kV/cm for the 3 μm strip). Such large in-plane polarization field, facilitated and enhanced by size reduction, drives phase transitions in the narrow channel film, leading to the reconfiguration of percolation channel and nonvolatile modulation of transport properties. Accordingly, the accompanied polarity relationship between the induced in-plane polarization field and the applied vertical bias field well explains the observed anomalous polarity-dependence of the modulation. Our studies reveal a new acting channel in the nanoscale control of lateral configurations of electronic phase separation and macroscopic behaviors by a small vertical electric bias field in spatial-confined field-effect structures. This distinct acting mechanism offers new possibilities for designing low-power all-oxide-based electronic devices and exploiting new types of multifunctionality to other strongly correlated materials where electronic phase competition exists.

Publisher’s Note: “Degradation effect of Auger recombination and built-in polarization field on GaN-based light-emitting diodes” [AIP Advances 8, 015005 (2018)

First Page

Degradation effect of Auger recombination and built-in polarization field on GaN-based light-emitting diodes

In this work, theoretical investigation of the influence of Auger recombination coefficient and built-in polarization field on the internal quantum efficiency (IQE) in terms of lateral-vertical single quantum well (SQW) as well as multiquantum well (MQW) GaN-based blue light-emitting diodes are presented. The degradation effect of the built-in polarization field on the IQE of vertical light-emitting diodes is used to strengthening the Auger recombination coefficient in comparison to lateral light-emitting diodes. This result has been found consistent in both single-as well as multi-quantum well structures. In addition, when Auger recombination coefficient has been included in the analysis, vertical multiquantum well structure shows more degradation in the IQE in comparison to the lateral structures. The effect has been dominant in vertical MQW case.

Effects of electric field and light polarization on the electromagnetically induced transparency in an impurity doped quantum ring

We theoretically investigated the effects of the impurity position, in-plane electric field, intensity and polarization of the probe and control lasers on the electromagnetically induced transparency (EIT) in GaAs/GaAlAs disc shaped quantum ring. Our study reveals that, depending on the impurity position, the quantum system presents two specific configurations for the EIT occurrence even in the absence of the external electric field, i.e. ladder-configuration or V-configuration, and changes the configuration from ladder to V for specific electric field values. The polarization of the probe and control lasers plays a crucial role in obtaining a good transparency. The electric field controls the red-shift (blue-shift) of the transparency window and modifies its width. The system exhibits birefringence for the probe light in a limited interval of electric field values.