Redistribution Of Electric Field Research Articles

Device physics of perovskite light-emitting diodes

Perovskite light-emitting diodes (LEDs) have emerged as a potential solution-processible technology that can offer efficient light emission with high color purity. Here, we explore the device physics of perovskite LEDs using simple analytical and drift-diffusion modeling, aiming to understand how the distribution of electric field, carrier densities, and recombination in these devices differs from those assumed in other technologies such as organic LEDs. High barriers to electron and hole extraction are responsible for the efficient recombination and lead to sharp build-up of electrons and holes close to the electron- and hole-blocking barriers, respectively. Despite the strongly varying carrier distributions, bimolecular recombination is surprisingly uniform throughout the device thickness, consistent with the assumption typically made in optical models. The current density is largely determined by injection from the metal electrodes, with a balance of electron and hole injection maintained by redistribution of electric field within the device by build-up of space charge.

Cation-induced interface electric field redistribution and molecular orbital coupling in Co-FeS/MoS2 for boosting electrocatalytic overall water splitting

A green hydrogen economy requires efficient bifunctional electrocatalysts for simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, a mild sulfuration strategy was used to create a Co-FeS/MoS2 catalyst from metal-organic frameworks (MOFs) on foam nickel. This catalyst exhibits exceptional activity in 1 M KOH, only requiring ultralow overpotentials of 63 mV and 230 mV to achieve current densities of 10 mA cm−2 and 100 mA cm−2 for the HER and OER processes. Additionally, it achieves a low cell voltage of 1.45 V at 10 mA cm−2, surpassing reported catalysts. DFT calculations and XPS tests show that Co introduction induces high-valence Fe active sites and facilitates interface electric field redistribution. Crystal orbital Hamilton population (COHP) calculations reveal d-p orbital hybridization, enhancing conductivity and charge transfer kinetics. This research sheds light on the catalytic impacts of metal cations on transition metal sulfides to design high efficient electrocatalysts.

Engineering a Ce Promoter into a Three-Dimensional Porous Mo2C@NC Heterostructure for Hydrogen Evolution Electrocatalysis via Weakening the Mo-H Bond Strength.

The pursuit of highly efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER) is of paramount importance for water splitting. However, it is still a formidable task in Mo2C-based materials because of the agglomeration and strong Mo-H binding of Mo2C units. Herein, a novel CeOCl-CeO2/Mo2C heterostructure nesting within a three-dimensional porous nitrogen-doped carbon matrix has been designed and used for catalyzing HER via simultaneous morphology and heterointerface engineering. As expected, the optimal CeOCl-CeO2(0.2)/Mo2C@3DNC exhibits impressive HER activity, with a low overpotential of 156 mV at a current density of 10 mA cm-2 coupled with a slight Tafel slope of 62.20 mV dec-1. Introducing a Ce promoter, that is CeOCl and CeO2, would endow the interface with an internal electric field and electron redistribution between CeOCl-CeO2 and Mo2C induced by the heterogeneous work function difference. Moreover, experimental investigation and density functional calculations confirm that the CeOCl-CeO2/Mo2C heterointerface can downshift the d-band center of the active Mo center, weakening the strength of the Mo-H coupling. This proposed concept, engineering Ce-based promoters into active entities involved in the heterostructure to modulate intermediate adsorption, offers a great opportunity for the design of superior electrocatalysts for energy conversion.

Electric Field Redistribution Triggered Surface Adsorption and Mass Transfer to Boost Electrocatalytic Glycerol Upgrading Coupled with Hydrogen Evolution

AbstractElectrocatalytic glycerol oxidation reaction (GOR) stands out as an economical and prospective technology to replace oxygen evolution reaction for co‐producing high‐valued chemicals and hydrogen (H2). Regulating the adsorption of glycerol (GLY) and hydroxyl (OH) species is of great significance for improving the GOR performance. Herein, a hierarchical p–n heterojunction by combining Co‐metal organic framework (MOF) nanosheets with CuO nanorod arrays (CuO@Co‐MOF) is developed to realize the optimization on GOR. Specifically, CuO@Co‐MOF electrode exhibits superior performance with a conversion of 98.4%, formic acid (FA) selectivity of 87.3%, and Faradaic efficiency (FE) of 98.9%. The flow‐cell system with the bifunctional CuO@Co‐MOF electrode for pairing GOR with the hydrogen evolution reaction (HER) reveals better energy conversion efficiency. Experimental results and theoretical calculations unravel the redistributed electric field by introducing Co‐containing species that contribute to the improved performance, which not only enhances the OH adsorption but also modulates the excessive GLY adsorption of CuO, thus reducing reaction energy barriers of FA desorption. Simultaneously, finite element analysis reveals that the novelty hierarchical structure can increase the concentration of OH− and facilitate the mass transfer of OH− in the solution.

Optimized energy storage performance in bilayer heterogeneous films

Film-based dielectric capacitors featured with small size, high breakdown field, and high energy storage density enable the application for integrated and miniatured electronic devices. So far, kinds of dielectrics have been explored for higher energy storage performance. Linear-like dielectrics can endure a high breakdown field but the polarization is too small. Conversely, ferroelectrics have high polarization but a low breakdown field, limiting their further performance optimization. Herein, we designed bilayer dielectric film capacitors that combined the linear-like dielectric layer and the ferroelectric layer, which brings in a redistribution of electric field owing to the different capacitance of each layer, thus improving the breakdown field and delaying the polarization saturation. Consequently, a high energy density of 57 J cm−3 with an efficiency of 88% was achieved. In addition, the bilayer film also exhibited excellent anti-fatigue and temperature-invariant characteristics, showing great potential for future applications in dielectric energy storage.

Ultrahigh energy density and high thermal stability in novel bilayer-structured nanocomposites with surface-decorated TiO2@BaTiO3 nanoparticles

Despite the need to implement renewable energy, it is still hampered by the difficulty of storing and effectively utilizing energy on demand. Herein, for dielectric energy storage application, inaugurally, novel surface-decorated TiO2@BaTiO3 nanoparticles were incorporated in various weight percentage ratios in P(VDF-HFP)-P(VDF) blended polymer and synthesized in new heterogenous bilayer-designed nanocomposite films that contained PEI as its bottom layer. The top layer acted as a polarization layer, the bottom layer operated as an insulation layer, and TiO2@BaTiO3 nanoparticles enhanced polarizability as well as breakdown strength (Eb). The XRD and SEM analysis demonstrated the successful preparation of TiO2@BaTiO3 nanoparticles and bilayer nanocomposite film. Additionally, the ideal bilayer nanocomposite film comparatively demonstrated higher permittivity, lower tangent loss, highest Eb, highest discharge energy density, and optimum charge-discharge efficiency of 11.8, 0.019, 500 MV/m, 14.7 J/cm3, and 76 %, respectively. Also, the TGA analysis revealed enhanced thermal stability by incorporating novel nanoparticles. Moreover, the finite element simulation revealed effective electric field redistribution around TiO2@BaTiO3 nanoparticles and in each layer of bilayer nanocomposites, a mandatory parameter for higher Eb values and energy storage properties. Overall, this work demonstrates that bilayered heterogeneous nanocomposites with TiO2@BaTiO3 surface-decorated nanofillers can be utilized in pulsed power systems and advanced dielectrics.

Bending-induced isostructural transitions in ultrathin layers of van der Waals ferrielectrics

Using Landau-Ginzburg-Devonshire (LGD) phenomenological approach we analyze the bending-induced re-distribution of electric polarization and field, elastic stresses and strains inside ultrathin layers of van der Waals ferrielectrics. We consider a CuInP2S6 (CIPS) thin layer with fixed edges and suspended central part, the bending of which is induced by external forces. The unique aspect of CIPS is the existence of two ferrielectric states, FI1 and FI2, corresponding to big and small polarization values, which arise due to the specific four-well potential of the eighth-order LGD functional. When the CIPS layer is flat, the single-domain FI1 state is stable in the central part of the layer, and the FI2 states are stable near the fixed edges. With an increase of the layer bending below the critical value, the sizes of the FI2 states near the fixed edges decreases, and the size of the FI1 region increases. When the bending exceeds the critical value, the edge FI2 states disappear being substituted by the FI1 state, but they appear abruptly near the inflection regions and expand as the bending increases. The bending-induced isostructural FI1-FI2 transition is specific for the bended van der Waals ferrielectrics described by the eighth (or higher) order LGD functional with consideration of linear and nonlinear electrostriction couplings. The isostructural transition, which is revealed in the vicinity of room temperature, can significantly reduce the coercive voltage of ferroelectric polarization reversal in CIPS nanoflakes, allowing for the curvature-engineering control of various flexible nanodevices.

Total-Ionizing-Dose Radiation-Induced Electric Field Redistribution Model and Hardening Method for SGT MOSFET

Total-Ionizing-Dose Radiation-Induced Electric Field Redistribution Model and Hardening Method for SGT MOSFET

High-temperature polymer dielectric films with excellent energy storage performance utilizing inorganic outerlayers

The optimization of high-temperature polymer capacitors is critical to the development of power electronics in harsh environments. The conduction loss of polymers increases dramatically at high temperatures, leading to a decrease in energy density and charge/discharge efficiency, which is a major impediment for capacitor applications. In this work, polyetherimide (PEI) composite films with trilayer structures are designed, in which the boron nitride nanosheet (BNNS) outer layers are optimized for charge blocking effect at multiple interfaces. The modulation of the inorganic layers not only increases the barrier height for charge injection from the electrodes, but also creates a PEI layer/BNNS layer interface that facilitates the formation of traps, thus effectively suppressing further carrier transport. Experiment and simulation verify that the construction of the trilayer structure promotes electric field redistribution, which significantly enhances high-temperature energy storage performance. At 200 °C, the energy density of the trilayer composite film is 3.81 J cm−3 with a charge/discharge efficiency >90 %, which is 766 % higher than PEI film (0.44 J cm−3 with a charge/discharge efficiency >90 %). Notably, the energy storage performance of trilayer composite film at high temperature is far superior to the reported high-temperature polymer dielectric films. This work demonstrates the promising potential of multilayer structures applied to dielectric polymer composite films at high temperatures.

Influence of Rain on the Support Insulation Electrical Strength

The article presents the results of studying the influence of artificial rain on the electrical strength of an extra high voltage support insulation column containing insulators of different heights when subjected to positive polarity switching impulses. It has been found that, in general, rain has an adverse effect on the support insulation discharge characteristics, which is associated with the occurrence of cascading overlaps from the screen fittings along the insulation structure components. The adverse effect caused by rain tends to aggravate with increasing the column upper element structural height, the switching impulse front time, and rainwater conductivity. As a result, the support insulation electrical strength may drop by as much as 40%. The reason for such a significant effect is the external electric field redistribution along the columns. On the one hand, the presence of a relatively high conductivity water film on the insulator surface when subjected to impulses with a front time of several milliseconds leads to an almost uniform distribution of voltage across insulation structural elements. On the other hand, sharp field strength spikes of the opposite polarity arise on the water droplets and trickles formed at the edges of neighboring sheds, which facilitates the occurrence of spark overlaps across a number of shed spacing distances, weakening of air insulation, and a decrease of structural discharge voltage. Measures to increase the support insulation electrical strength under rain conditions are proposed.

Potential and electric field analysis of field plated AlGaN/GaN HEMT for high voltage applications using 2-D analytical approach

A physics-based 2-D analytical model is developed for field plated AlGaN/GaN high electron mobility transistor (HEMT) and the effect of field plate on potential and electric field is analyzed. The complete generalized theory developed includes the dependence of electric field and electric potential distribution on (i) different dielectric materials and (ii) dielectric thickness below the field plate. An extensive study of the effect of various non-field plate parameters such as doping concentration in the AlGaN layer, drain source voltage, and gate source voltage has also been carried out. It is observed that with the introduction of field plate, primary peak of electric field gets reduced and redistribution of electric field occurs in a better way with the introduction of much smaller secondary electric field peak. This leads to improved breakdown voltage thus making the device suitable for high voltage applications. The analytical results are also compared with the simulated results extracted with ATLAS 2D device simulation. The good agreement validates the analytical approach.

A numerical study on the relationship between the doping and performance in P3HT:PCBM organic bulk heterojunction solar cells

In this study, we perform a simulation analysis to investigate the influence of p-type and n-type doping concentration in BHJ SCs using the drift-diffusion model. Specifically, we investigate the effect of doping on the charge carrier transport and calculate the above-mentioned device parameters. We show that doping the active layer can increase the cell characteristic parameters, that the results are in an excellent agreement with the experimental results previously reported in the literature. We also show that doping causes space charge effects which subsequently lead to redistribution of the internal electric field in the device. Our results reveal that higher doping levels lead to screening the electrical field in the P3HT:PCBM active region. This in turn forces the charge carrier transport to be solely dominated by the diffusion, consequently decreasing the performance of the device. We also show that doping of the active layer to an optimum level can effectively improve the charge transport. Moreover, we show that doping can create an Ohmic contact between the organic and cathode interface. Additionally, the charge carrier concentration profile shows that by increasing the dopant concentration, the J_{sc} can be improved remarkably. Upon doping the active layer, this indicates that illumination can simply reduce the series resistance in the device.

Single-event burnout hardening evaluation with current and electric field redistribution of high voltage LDMOS transistors based on TCAD Simulations

—A single-event burnout (SEB) hardened design based on high voltage lateral double-diffused metal-oxide-silicon (LDMOS) devices with an optimal partial buried oxide (BOX) layer and a N-buffer layer is firstly proposed in this paper. By analyzing the response of surface electric field and transient current, the optimal parameters of hardened layers are selected. Simulation results reveal that an optimal buffer layer can suppress the peak electric field from 4.5 MV/cm to 2 MV/cm, recreate the position of peak electric field and an optimal BOX layer can reconstruct the path of electron and hole currents, reducing the risk of parasitic bipolar-junction-transistor (BJT). By contrast, the SEB triggering voltage can be improved from 197 V to 396 V, with an increase of 100%. And the ratio of safe operating area (SOA) with SEB to breakdown voltage (BV) can be increased from 30% to 69%. In the case of heavy-ions with different energies, the SEB hardened LDMOS also has better performance than the conventional one.

Enhanced energy storage performance of polyetherimide-based sandwich-structured dielectric films in elevated temperature range via using cyanoethyl cellulose layer

In order to satisfy the application of electronic device in the harsh environment, polymer-based dielectrics should have high discharge energy density (Ud) and high-temperature resistance synchronously. Herein, a series of sandwich-structured polymer films consisting of cyanoethyl cellulose (CEC) and polyetherimide (PEI) were fabricated by the solution casting method. The PEI-based sandwich-structured dielectric films showed high dielectric constant because of highly polarized CEC layer and the macroscopical interfacial polarization. In addition, the polymer films displayed the improved breakdown strength owning to the insulating PEI, barrier effect of the interface, and electric field redistribution. As a result, the maximal Ud of a positive sandwich-structured P–5C–P film with outer PEI layer and central CEC layer reached 6.8 J/cm3 (151% of pure PEI) along with charge-discharge efficiency of 80%. More importantly, at 100 °C and 150 °C, a high Ud of 5.5 J/cm3 and 3.0 J/cm3 were achieved in the P–5C–P film due to both high glass transition temperature (Tg) of PEI and CEC, which was 1.72 times and 1.36 times than that of pristine PEI, respectively. This work provides a new method for the preparation of high-performance sandwich-structured polymer dielectrics via selecting highly polarized central polymer layer with high Tg.

Novel Stacked Passivation Structure for AlGaN/GaN HEMTs on Silicon With High Johnson’s Figures of Merit

We present a high-performance AlGaN/GaN high electron mobility transistors (HEMTs) on silicon substrate with novel stacked passivation layer (HfO2/SiO2). The stacked passivation structure can effectively modulate the electric field and reduce the electric field peak on the gate side, thus improving the breakdown voltage of the device. The prepared device with a gate length of 450 nm has a unit current gain cutoff frequency (fT) of 31.5 GHz, a maximum oscillation frequency (fMAX) of 46.3 GHz, and a three-terminal OFF-state breakdown voltage (BVgd) of 140 V at the gate-drain distance of 2.3 μm. The estimated Johnsonfs figure of merit (J-FOM=BVgd×fT) is 4.4 THz∙V, which is three and five times higher than that of the device with single HfO2 passivation layer and single SiO2 passivation layer, respectively. Furthermore, a significant suppression of the current collapse ( 5.7%) is observed due to the electric field redistribution near the drain region. The results show that the AlGaN/GaN HEMTs with stacked passivation layer proved to be a promising candidate for high-performance radio frequency (RF) power device applications.

Organic/Inorganic Hybrid Top-Gate Transistors with Ultrahigh Electron Mobility via Enhanced Electron Pathways

The top-gate structure is currently adopted in various flat-panel displays because of its diverse advantages such as passivation from the external environment and process compatibility with industries. However, the mobility of the currently commercialized top-gate oxide thin-film transistors (TFTs) is insufficient to drive ultrahigh-resolution displays. Accordingly, this work suggests metal-capped Zn-Ba-Sn-O transistors with top-gate structures for inducing mobility-enhancing effects. The fabricated top-gate device contains para-xylylene (PPx), which is deposited by a low-temperature chemical vapor deposition (CVD) process, as a dielectric layer and exhibits excellent interfacial and dielectric properties. A technology computer-aided design (TCAD) device simulation reveals that the mobility enhancement in the Al-capped (Zn,Ba)SnO3 (ZBTO) TFT is attributed not only to the increase in the electron concentration, which is induced by band engineering due to the Al work function but also to the increased electron velocity due to the redistribution of the lateral electric field. As a result, the mobility of the Al-capped top-gate ZBTO device is 5 times higher (∼110 cm2/Vs) than that of the reference device. These results demonstrate the applicability of top-gate oxide TFTs with ultrahigh mobility in a wide range of applications, such as for high-resolution, large-area, and flexible displays.

Toward a theory of ‘stepped-leaders’ in lightning

An unresolved issue in the physics of lightning is an explanation for lightning proceeding to the ground by successive luminous steps separated by ‘dark’ times of many microseconds. There is also no explanation of the structure of the dark column connecting the streamer step with the cloud that can be km in length, is electrically conducting, yet has a very low sustaining electric field. It is proposed that these two processes can be explained by the accumulation of singlet delta metastable oxygen molecules excited in the corona pulses of lightning. The step time is necessary for the excitation of large metastable densities to produce significant metastable detachment of electrons from negative ions. The detached electrons form a highly conducting step, initially luminous, that causes a redistribution of electric fields and an increase in the potential and electric fields at the end of the step to make possible a further step by ionization. These features are supported by calculations of densities of electrons, positive ions, negative ions and singlet delta metastable oxygen molecules for the first 7 μs of a discharge chosen to be initiated by a 50 cm sphere of charged hail particles. The calculated corona streamers produce metastable densities of 1017 cm−3 near the corona source. These metastables, by electron detachment, produce a conducting cylinder 10 m long with a radius of 1 cm and an electron density ∼1012 cm−3 that is attributed to being the first step and a lightning ‘leader’. These conducting regions develop within them very low electric fields. Successive steps are likely to combine to form the long conductive columns of lightning that exist before the return stroke. Electron densities in the leader and the column are an equilibrium between electron production by metastable detachment and electron loss by attachment to neutral oxygen molecules, requiring no electric field.

Dark Current Modeling for a Polyimide-Amorphous Lead Oxide-Based Direct Conversion X-ray Detector.

The reduction of the dark current (DC) to a tolerable level in amorphous selenium (a-Se) X-ray photoconductors was one of the key factors that led to the successful commercialization of a-Se-based direct conversion flat panel X-ray imagers (FPXIs) and their widespread clinical use. Here, we discuss the origin of DC in another X-ray photoconductive structure that utilizes amorphous lead oxide (a-PbO) as an X-ray-to-charge transducer and polyimide (PI) as a blocking layer. The transient DC in a PI/a-PbO detector is measured at different applied electric fields (5–20 V/μm). The experimental results are used to develop a theoretical model describing the electric field-dependent transient behavior of DC. The results of the DC kinetics modeling show that the DC, shortly after the bias application, is primarily controlled by the injection of holes from the positively biased electrode and gradually decays with time to a steady-state value. DC decays by the overarching mechanism of an electric field redistribution, caused by the accumulation of trapped holes in deep localized states within the bulk of PI. Thermal generation and subsequent multiple-trapping (MT) controlled transport of holes within the a-PbO layer governs the steady-state value at all the applied fields investigated here, except for the largest applied field of 20 V/μm. This suggests that a thicker layer of PI would be more optimal to suppress DC in the PI/a-PbO detector presented here. The model can be used to find an approximate optimal thickness of PI for future iterations of PI/a-PbO detectors without the need for time and labor-intensive experimental trial and error. In addition, we show that accounting for the field-induced charge carrier release from traps, enhanced by charge hopping transitions between the traps, yields an excellent fit between the experimental and simulated results, thus, clarifying the dynamic process of reaching a steady-state occupancy level of the deep localized states in the PI. Practically, the electric field redistribution causes the internal field to increase in magnitude in the a-PbO layer, thus improving charge collection efficiency and temporal performance over time, as confirmed by experimental results. The electric field redistribution can be implemented as a warm-up time for a-PbO-based detectors.

Sandwich-structured polymer dielectric composite films for improving breakdown strength and energy density at high temperature

Polymer dielectric capacitor have attracted much attention in the field of electronic power systems recently due to high power density and high breakdown strength. However, with the development of miniaturization and integration, further demands have been set on the higher energy storage density as well as better temperature resistance for dielectric polymers. Up to now, hierarchical structure provides an effective way to meet these requirements. Herein, we report a sandwich-structured all-organic composite via inserting polymethyl methacrylate/poly(vinylidene fluoride) (PMMA/PVDF) blend layer into polyetherimide layers. Increasing temperature increases the permittivity of the middle layer and the addition of PMMA makes the permittivity increase faster with temperature than pure PVDF middle layer. The capacitor series model and finite element simulation confirmed that the change of the middle layer permittivity realized the electric field redistribution to self-adapt to the temperature, preventing premature breakdown at elevated temperature. At 100 °C, optimized composite exhibits a high breakdown strength of 486.05 MV/m along with high polarization. Eventually, a high discharge energy density of 8.65 J/cm3 is obtained, which is 229.44% of pure PEI. The high polarization at high temperature was realized by utilizing the permittivity of PMMA/PVDF rising with temperature, thereby increasing the energy density at elevated temperature.

Temperature-Dependent Characteristics of HgCdTe Mid-Wave Infrared E-Avalanche Photodiode

This paper presents the characteristics of HgCdTe mid-wavelength infrared (MWIR) electron-initiated avalanche photodiodes (e-APDs) as a function of temperature under different biases. The devices show a low dark current density of the order of <inline-formula><tex-math notation="LaTeX">${10^{ - 7}} \text{A/cm}^2$</tex-math></inline-formula> at 80 K when the reverse bias voltage is below 4 V, with an exponential gain above 100 at &#x2212; 8 V. Low excess noise factor of around 1.2 is also demonstrated for the devices at 80 K. The dark current and gain characteristics at different temperatures are analyzed, along with the device simulation results. A varied-temperature impact ionization model for MWIR e-APD devices is adopted based on the experimental results. In addition, a significant increase of the dark current in the APD device is observed at high temperature under large reverse bias, which can be associated with the local electric field redistribution due to the accumulation of holes in the depletion region at high temperatures. The analysis presented in this work paves the way to achieve a high operating temperature (HOT) of the HgCdTe APD with further optimization.