Electron Trapping Effect Research Articles

Suppression of Secondary Electron Emission from Nickel Surface by Graphene Composites Based on First-Principles Method.

Secondary electron emission (SEE) is a fundamental phenomenon of particle/surface interaction, and the multipactor effect induced by SEE can result in disastrous impacts on the performance of microwave devices. To suppress the SEE-induced multipactor, an Ni (111) surface covered with a monolayer of graphene was proposed and studied theoretically via the density functional theory (DFT) method. The calculation results indicated that redistribution of the electron density at the graphene/Ni (111) interface led to variations in the work function and the probability of SEE. To validate the theoretical results, experiments were performed to analyze secondary electron yield (SEY). The measurements showed a significant decrease in the SEY on an Ni (111) surface covered with a monolayer of graphene, accompanied by a decrease in the work function, which is consistent with the statistical evidence of a strong correlation between the work function and SEY of metals. A discussion was given on explaining the experimental phenomenon using theoretical calculation results, where the empty orbitals lead to an electron trapping effect, thereby reducing SEY.

Gate leakage modeling in lateral β -Ga2O3 MOSFETs with Al2O3 gate dielectric

We present a detailed model of the static and dynamic gate leakage current in lateral β-Ga2O3 MOSFETs with an Al2O3 gate insulator, covering a wide temperature range. We demonstrate that (i) in the DC regime, current originates from Poole–Frenkel conduction (PFC) in forward bias at high-temperature, while (ii) at low temperature the conduction is dominated by Fowler–Nordheim tunneling. Furthermore, (iii) we modeled the gate current transient during a constant gate stress as effect of electron trapping in deep levels located in the oxide that inhibits the PF conduction mechanism. This hypothesis was supported by a TCAD model that accurately reproduces the experimental results.

An Efficient Meshfree Numerical Technique to Solve Fractional Schamel–KdV Equation for Ion-Acoustic Solitary Waves in Dusty Plasma

The Schamel–KdV equation plays a vital role in studying the effect of electron trapping on the nonlinear interaction of ion-acoustic waves in plasma and dusty plasma. This work presents a numerical scheme-based radial basis function-finite difference (RBF-FD) method to solve the time-fractional Schamel–KdV equation. The advantages of using this method are their meshfree nature and flexibility in dealing with complex geometries. In the discretization process, a finite difference (FD) technique is used to discretize the temporal derivative, while the multiquadric (MQ) RBF is used to approximate the spatial derivatives. The theoretical convergence and stability analysis of the time-discrete scheme are also established. In addition, numerical experiments are executed through some illustrated problems, and the obtained results are compared with that acquired by the tanh method and Kudryashov method solutions to show the high accuracy and plausibility of the proposed technique. Also, the graphical representations are given to demonstrate the physical interpretation of the resulting wave structures.

Tailoring the Electron Trapping Effect of a Biocompatible Triboelectric Hydrogel by Graphene Oxide Incorporation towards Self-Powered Medical Electronics.

Triboelectric nanogenerators (TENGs) are associated with several drawbacks that limit their application in the biomedical field, including toxicity, thrombogenicity, and poor performance in the presence of fluids. By proposing the use of a hemo/biocompatible hydrogel, poly(2-hydroxyethyl methacrylate) (pHEMA), this study bypasses these barriers. In contact-separation mode, using polytetrafluoroethylene (PTFE) as a reference, pHEMA generates an output of 100.0 V, under an open circuit, 4.7 μA, and 0.68 W/m2 for an internal resistance of 10 MΩ. Our findings unveil that graphene oxide (GO) can be used to tune pHEMA's triboelectric properties in a concentration-dependent manner. At the lowest measured concentration (0.2% GO), the generated outputs increase to 194.5 V, 5.3 μA, and 1.28 W/m2 due to the observed increase in pHEMA's surface roughness, which expands the contact area. Triboelectric performance starts to decrease as GO concentration increases, plateauing at 11% volumetric, where the output is 51 V, 1.76 μA, and 0.17 W/m2 less than pHEMA's. Increases in internal resistance, from 14 ΩM to greater than 470 ΩM, ζ-potential, from -7.3 to -0.4 mV, and open-circuit characteristic charge decay periods, from 90 to 120 ms, are all observed in conjunction with this phenomenon, which points to GO function as an electron trapping site in pHEMA's matrix. All of the composites can charge a 10 μF capacitor in 200 s, producing a voltage between 0.25 and 3.5 V and allowing the operation of at least 20 LEDs. The triboelectric output was largely steady throughout the 3.33 h durability test. Voltage decreases by 38% due to contact-separation frequency, whereas current increases by 77%. In terms of pressure, it appears to have little effect on voltage but boosts current output by 42%. Finally, pHEMA and pHEMA/GO extracts were cytocompatible toward fibroblasts. According to these results, pHEMA has a significant potential to function as a biomaterial to create bio/hemocompatible TENGs and GO to precisely control its triboelectric outputs.

Two-in-One Electrons Trapped Fe-BiOCl-Vo Nanosheets for Promoting Photocatalytic-Fenton Degradation Performances of Phenol

Fe-BiOCl-Vo nanosheets with electron-capture centers of doped Fe and surface oxygen vacancies (Vo) for enhanced photocatalytic-Fenton performances were conducted. Compared with pristine BiOCl nanosheets, the band gap of the resulting Fe-BiOCl-Vo nanosheets was narrowed, and defective bands were introduced due to the Fe doping and Vo. Furthermore, the integrated electron trapping effect of Vo and doped Fe can efficiently drive charge transfer and separation. As a result, the photocatalytic-Fenton performances of phenol over Fe-BiOCl-Vo nanosheets were enhanced. The photocatalytic-Fenton performances of Fe-BiOCl-Vo nanosheets were enhanced two-fold and four-fold, respectively, as compared with the photocatalytic performances of Fe-BiOCl-Vo and pristine BiOCl nanosheets. During the photocatalytic-Fenton process, the multiple reactive species referring holes (h+), superoxide radicals (●O2−), and hydroxyl radicals (●OH) induced by the efficiently separated charge carriers and Fenton reaction played synergetic roles in phenol degradation and mineralization. This work provides a sophisticated structure design of catalysts for efficient charge transfer and separation, promoting photocatalytic-Fenton performance.

Insight into over Repair of Hot Carrier Degradation by GIDL Current in Si p-FinFETs Using Ultra-Fast Measurement Technique

In this article, an experimental study on the gate-induced drain leakage (GIDL) current repairing worst hot carrier degradation (HCD) in Si p-FinFETs is investigated with the aid of an ultra-fast measurement (UFM) technique (~30 μs). It is found that increasing GIDL bias from 3 V to 4 V achieves a 114.7% VT recovery ratio from HCD. This over-repair phenomenon of HCD by UFM GIDL is deeply discussed through oxide trap behaviors. When the applied gate-to-drain GIDL bias reaches 4 V, a significant electron trapping and interface trap generation of the fresh device with GIDL repair is observed, which greatly contributes to the approximate 114.7% over-repair VT ratio of the device under worst HCD stress (-2.0 V, 200 s). Based on the TCAD simulation results, the increase in the vertical electric field on the surface of the channel oxide layer is the direct cause of an extraordinary electron trapping effect accompanied by the over-repair phenomenon. Under a high positive electric field, a part of channel electrons is captured by oxide traps in the gate dielectric, leading to further VT recovery. Through the discharge-based multi-pulse (DMP) technique, the energy distribution of oxide traps after GIDL recovery is obtained. It is found that over-repair results in a 34% increment in oxide traps around the conduction energy band (Ec) of silicon, which corresponds to a higher stabilized VT shift under multi-cycle HCD-GIDL tests. The results provide a trap-based understanding of the transistor repairing technique, which could provide guidance for the reliable long-term operation of ICs.

Effects of trapped electrons on the sheath at the boundary of a dusty plasma

In the present paper, the characteristic behaviors of the sheath in an unmagnetized dusty plasma that contained trapped electrons, cold ions, and variable-charged dusts are investigated, based on the Sagdeev potential approach. The result shows that both the formation and structure of the sheath are modified by the trapped electrons. At the sheath edge, the critical ion Mach number decreases as the trapping parameter β increases. It is noted that the effect of electron trapping on the ion-entering-sheath-velocity is indirect, and closely related to the dust charge variation. In the sheath, the increased β leads to the enlargement of the sheath thickness and the absolute value of electrostatic potential, which results in the redistribution of particle densities. Moreover, the results of the Maxwellian case are essentially recovered when β = 1. As expected, the present results can give more insight into the interaction processes that happened on the plasma-wall interface.

Research Process of Carbon Dots in Memristors

AbstractThe explosive growth of digital communication promotes advanced memory and computing devices in Big Data and artificial intelligence era. In particular, memristors hold great promise for in‐memory computing and artificial synapses, expected to break through restrictions on hardware computational power and storage capacity caused by the von Neumann bottleneck and declining Moore's Law. The memristance controllability is vital to memristors, in which functional layer materials are key. As novel functional layer materials, carbon dots (CDs) are expected to overtake silicon‐based materials due to their satisfactory modulation effects on memristance and distinguished memristive performances. The combination of CDs and matrix materials may carry out multimode sensation memristors for interactive intelligent systems. This review first gives a brief introduction to memristors and their functional layer materials, especially different CDs and their relations with memristance. Then the modulation effects of CDs on memristance are highlighted, mainly including the local electric field enhancement effect, the electron trapping and detrapping effect, and the photosensitization effect, accompanied by applications of CDs‐based memristors (CDMs). Lastly, challenges and perspectives of CDMs are pointed out. This work is rewarding to understand the role of CDs in memristors, to guide relevant research about CDMs, and to promote implementation for intelligent memory and computing.

Charge Trapping and Emission Properties in CAAC-IGZO Transistor: A First-Principles Calculations.

The c-axis aligned crystalline indium-gallium-zinc-oxide field-effect transistor (CAAC-IGZO FET), exhibiting an extremely low off-state leakage current (~10-22 A/μm), has promised to be an ideal candidate for Dynamic Random Access Memory (DRAM) applications. However, the instabilities leaded by the drift of the threshold voltage in various stress seriously affect the device application. To better develop high performance CAAC-IGZO FET for DRAM applications, it's essential to uncover the deep physical process of charge transport mechanism in CAAC-IGZO FET. In this work, by combining the first-principles calculations and nonradiative multiphonon theory, the charge trapping and emission properties in CAAC-IGZO FET have been systematically investigated. It is found that under positive bias stress, hydrogen interstitial in Al2O3 gate dielectric is probable effective electron trap center, which has the transition level (ε (+1/-1) = 0.52 eV) above Fermi level. But it has a high capture barrier about 1.4 eV and low capture rate. Under negative bias stress, oxygen vacancy in Al2O3 gate dielectric and CAAC-IGZO active layer are probable effective electron emission centers whose transition level ε (+2/0) distributed at -0.73~-0.98 eV and 0.69 eV below Fermi level. They have a relatively low emission barrier of about 0.5 eV and 0.25 eV and high emission rate. To overcome the instability in CAAC-IGZO FET, some approaches can be taken to control the hydrogen concentration in Al2O3 dielectric layer and the concentration of the oxygen vacancy. This work can help to understand the mechanisms of instability of CAAC-IGZO transistor caused by the charge capture/emission process.

Enhanced sensing response of the first polyoxometalate electron acceptor modified MoS2 for NO2 gas detection at room temperature

Here, we introduce polyoxometalate (POMs) electron acceptor into a classical 2-D gas sensing material, MoS2. The MoS2 @PW12 composite nanohydrangeas are prepared by hydrothermal and soaking methods. Then we explore the effect of POMs on sensing property of MoS2 gas sensor for the first time. The research results prove that the sensitivity to 100 ppm NO2 can be effectively promoted to 38.0% via introducing PW12, which is 3.42 times that of pristine MoS2. The promotion can be due to the formation of p-n heterojunction between MoS2 and PW12 and the shallow electron trapping effect of PW12, which can promote carriers migration and restrain their recombination. This work provides a novel thought to develop MoS2-based gas sensors with enhanced sensing sensitivity by the means of utilizing polyoxometalates as electron acceptors.

Dual Light Temporal Coding Modes Enabled by Nanoparticle-Mediated Phototransistors via Gate Bias Modulation for Brain-Inspired Visual Perception.

The core integration and cooperation of the retina, neurons, and synapses in the visual systems enable humans to effectively sense and process visual information with low power consumption. To mimic the human visual system, an artificial sensory nerve, along with optical sensing─a paired-pulse ratio (PPR) of the light pulse stimulated currents─and neural coding has been developed. For performing the artificial visual perception functions, we consistently reveal the positive and negative correlations between the PPR index and light pulse time interval by applying two consecutive light stimuli with gate voltages of -10 and 5 V, respectively, to a phototransistor. This phototransistor contains a heterostructured channel layer composed of zinc-oxide nanoparticles (ZnO NPs) interconnected with a solution-processed zinc-tin oxide (ZTO) film. The oxygen adsorption and desorption on the ZnO NP surface under light illumination are responsible for the positive-sloped PPR; the electron trapping effect at the ZnO NP/SiO2 interface is attributed to the negative-sloped PPR. The various accountable light power densities and number of surface trap states are considered to be directly realizing these spike-timing interval-dependent characteristics. The actual benefit of these characteristics is the dual temporal coding modes based on multiplicative operation using a ZTO/ZnO NP phototransistor realized via the active gate voltage modulation. The contrary tendency of the PPR index and temporal coding─a major biological neural coding─is well demonstrated by the potential of ZTO/ZnO NP phototransistors to be implemented in sensor networks for an artificial visual perception.

Improved photoelectrocatalytic performances over electrochemically reduced WO3: implications of oxygen vacancies.

The introduction of rich oxygen vacancies into the WO3 lattice has been achieved through a facile and environmentally friendly route of electrochemical reduction. It has been shown that the electrochemical reduction treatment significantly increases the charge separation efficiency from 37.44% to 65.44% at 0.74 V vs. NHE, and charge injection efficiency from 15.06% to 58.20% at 0.74 V vs. NHE, leading to enhanced PEC performances for synergetic 4-CP degradation and H2 evolution. Various characterization results well demonstrated that the formation of W5+ species resulting from the introduction of oxygen vacancies in the WO3 lattice raises the Fermi level closer to the energy level of oxygen vacancies. The raised Fermi level achieves the substantial electron trap effect of the oxygen vacancies and further bends upward the band at the semiconductor/electrolyte interface, both of which play dominant roles in the effective interfacial transfer and separation of the photogenerated charges for enhanced PEC performances.

Rational construction of S-scheme BN/MXene/ZnIn2S4 heterojunction with interface engineering for efficient photocatalytic hydrogen production and chlorophenols degradation

Achieving structural optimization and component modulation in ZnIn2S4-based photocatalysts while performing photocatalytic hydrogen evolution and degradation performance is a great challenge. In this work, a BN/MXene/ZnIn2S4 S-scheme photocatalytic heterojunction was obtained by growing the etched BN/MXene on the ZnIn2S4 nanosheets directly. Among them, introducing a special electron trapping effect of MXene successfully avoids the photocatalytic inferiority caused by the broader band gap of BN with weak conductivity and poor photocatalytic response activity. Therefore, a stable photocatalytic heterojunction can be constructed by adding MXene. The S-scheme heterojunction was identified by UPS, EPRS, VB-XPS and Mott-Schottky measurements. The bifunctional composite heterojunction photocatalyst exhibited excellent hydrogen production performance (∼1455 μmol·g−1·h−1) and 4-chlorophenol (4-CP) degradation ability (90 %) with good stability compared to the that of pure BN/MXene and the ZnIn2S4 samples. In particular, the formation of a built-in electric field at the interface between BN/MXene and ZnIn2S4 n-type semiconductors provides directional acceleration of effective separation of the photogenerated charges and preserves excellent redox capability of the semiconductors. With the excellent hydrogen production performance and 4-CP degradation efficiency of the constructed bifunctional BN/MXene/ZnIn2S4 heterojunction, this work provides a feasible strategy for constructing an S-scheme heterojunction for energy and environmental remediation.

Fast, Multi-Bit, and Vis-Infrared Broadband Nonvolatile Optoelectronic Memory with MoS2 /2D-Perovskite Van der Waals Heterojunction.

Nonvolatile optoelectronic memory (NVOM) integrating the functions of optical sensing and long-term memory can efficiently process and store a large amount of visual scene information, which has become the core requirement of multiple intelligence scenarios. However, realizing NVOM with vis-infrared broadband response is still challenging. Herein, the room temperature vis-infrared broadband NVOM based on few-layer MoS2 /2D Ruddlesden-Popper perovskite (2D-RPP) van der Waals heterojunction is realized. It is found that the 2D-RPP converts the initial n-type MoS2 into p-type and facilitates hole transfer between them. Furthermore, the 2D-RPP rich in interband states serves as an effective electron trapping layer as well as broadband photoresponsive layer. As a result, the dielectric-free MoS2 /2D-RPP heterojunction enables the charge to transfer quickly under external field, which enables a large memory window (104V), fast write speed of 20 µs, and optical programmable characteristics from visible light (405nm) to telecommunication wavelengths (i.e., 1550nm) at room temperature. Trapezoidal optical programming can produce up to 100 recognizable states (>6 bits), with operating energy as low as 5.1 pJ per optical program. These results provide a route to realize fast, low power, multi-bit optoelectronic memory from visible to the infrared wavelength.

First Demonstration of Ferroelectric Tunnel Thin-Film Transistor Nonvolatile Memory With Polycrystalline-Silicon Channel and HfZrO Gate Dielectric

In this work, the nonvolatile memory constructed on the tunnel thin-film transistors (tunnel-TFTs) using polycrystalline-silicon channel featuring ferroelectric HfZrOx layer is demonstrated for the first time. When the pulse voltages of program (PG) and erase (ER) are, respectively, 3.5 and −2 V with the pulsewidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 ~\mu \text{s}$ </tex-math></inline-formula> , the threshold voltage modulation amount of the ferroelectric tunnel-TFT can reach −0.524 and 0.496 V, respectively. In addition, the endurance behaviors of the ferroelectric tunnel-TFT exhibit a strong PG/ER pulsewidth dependence. The wake-up effect of the ferroelectric layer becomes more pronounced as increasing the PG/ER pulsewidth. Moreover, the increase of the PG/ER pulsewidth also causes the ferroelectric tunnel-TFT to be subjected to the electrical dynamic stress effect, leading to the degradation of the subthreshold swing (SS) and the electron trapping effect. When the pulsewidth is 100 ns, the endurance is mainly dominated by the fatigue effect of the ferroelectric layer and the degradation of the SS. When the pulsewidth increases to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 ~\mu \text{s}$ </tex-math></inline-formula> , the endurance is mainly dominated by the electron trapping effect of the ferroelectric layer in addition to the fatigue effect. The retention of the ferroelectric tunnel-TFT exhibits stable behavior at 50 °C. Consequently, the ferroelectric tunnel-TFT exhibits sufficient electrical performance and can be integrated with display panels and various sensor systems on smart wearable devices for edge computing applications.

Fundamental Identification of Defect‐Related Electron Trap in Hf1−xZrxO2 Alloy Gate Dielectric on Silicon: Oxygen Vacancy versus Hydrogen Interstitial

Hf1−x Zr x O2 alloy is recently employed as gate dielectric in complementary metal–oxide semiconductor (CMOS) devices because of its relatively low carrier trapping ability, low threshold voltage shift, and good reliability. Experimentally it is found that as the Zr concentration x increases, the device reliability caused by the defect‐related electron trapping would be improved. However, the trap nature in Hf1−x Zr x O2 alloy is still not yet well understood. Herein, using first‐principles hybrid‐functional calculations, the transition energies of some possible defects tending to occur in the experimental process for Hf1−x Zr x O2 alloys are discussed. The results show that, differing from previous studies suggesting that the oxygen vacancy (VO) is the main defect of electron trapping, the hydrogen interstitial (Hi), which can successfully explain the experimental observations of a reduction of the electron trapping ability as the Zr concentration increases, is more likely to be the origin responsible for the electron trapping in Hf1−x Zr x O2 dielectric. This work, therefore, broadens the understanding of electron trapping effect in high‐k dielectrics and gives guidance on improving the reliability in microelectronics.

Numerical study of m = 2/n = 1 neoclassical tearing mode stabilized by the Ohkawa-mechanism-dominated current drive of electron cyclotron waves

This paper reports a numerical study of the 2/1 neoclassical tearing mode (NTM) stabilized by the Ohkawa-mechanism-dominated current drive (OKCD) of electron cyclotron (EC) waves, and the results are compared with those of the traditional Fisch–Boozer mechanism dominated EC current drive (ECCD). The peak values, radial positions and radial widths of the driven current profiles by EC waves are passed to the modified Rutherford equation to study the effect of OKCD/ECCD on the 2/1 NTM. Well-localized current density profiles and large driven current can be achieved for 2/1 NTM stabilization in a low-aspect-ratio tokamak (R/a ∼ 2.7) by using OKCD. The optimal minimum EC powers are calculated for both OKCD and ECCD to fully stabilize the 2/1 NTM. We compare our results with those of ECCD to stabilize the 2/1 NTM, when the choices of magnetic field strength and gyrotron frequency are such that off-axis deposition on the high-field side is not practical to generate localized current effectively, so that the electron trapping effect is large and important. In this paper, we show that it is better to use lower gyrotron frequencies optimized for the Ohkawa mechanism to obtain a higher current drive efficiency for 2/1 NTM stabilization.

Low Buffer Trapping Effects above 1200 V in Normally off GaN-on-Silicon Field Effect Transistors.

We report on the fabrication and electrical characterization of AlGaN/GaN normally off transistors on silicon designed for high-voltage operation. The normally off configuration was achieved with a p-gallium nitride (p-GaN) cap layer below the gate, enabling a positive threshold voltage higher than +1 V. The buffer structure was based on AlN/GaN superlattices (SLs), delivering a vertical breakdown voltage close to 1.5 kV with a low leakage current all the way to 1200 V. With the grounded substrate, the hard breakdown voltage transistors at VGS = 0 V is 1.45 kV, corresponding to an outstanding average vertical breakdown field higher than 2.4 MV/cm. High-voltage characterizations revealed a state-of-the-art combination of breakdown voltage at VGS = 0 V together with low buffer electron trapping effects up to 1.4 kV, as assessed by means of substrate ramp measurements.

All-fluorescence white organic light-emitting diodes with record-beating power efficiencies over 130 lm W‒1 and small roll-offs

Improving power efficiency (PE) and reducing roll-off are of significant importance for the commercialization of white organic light-emitting diodes (WOLEDs) in consideration of energy conservation. Herein, record-beating PE of 130.7 lm W−1 and outstanding external quantum efficiency (EQE) of 31.1% are achieved in all-fluorescence two-color WOLEDs based on a simple sandwich configuration of emitting layer consisting of sky-blue and orange delayed fluorescence materials. By introducing a red fluorescence dopant, all-fluorescence three-color WOLEDs with high color rendering index are constructed based on an interlayer sensitization configuration, furnishing ultrahigh PE of 110.7 lm W−1 and EQE of 30.8%. More importantly, both two-color and three-color WOLEDs maintain excellent PEs at operating luminance with smaller roll-offs than the reported state-of-the-art WOLEDs, and further device optimization realizes outstanding comprehensive performances of low driving voltages, large luminance, high PEs and long operational lifetimes. The underlying mechanisms of the impressive device performances are elucidated by host-tuning effect and electron-trapping effect, providing useful guidance for the development of energy-conserving all-fluorescence WOLEDs.

Effect of driving frequency on new filament generation in atmospheric-pressure pulsed radio-frequency discharges

Side discharges as well as filament clusters in atmospheric pressure pulsed radio-frequency dielectric barrier discharges were manipulated by varying the driving frequency, monitored with voltage and current probes, imaged with a slow camera, and quantified by gray-value analysis. Results show that the way of producing a new filament varies with the driving frequency. Based on the side discharge and filament-cluster structure, the key factors influencing the variation are discussed in terms of the electron trapping effect, activation-inhibition effect, and electric field distribution.