Slow Trap Research Articles

Charge Carrier Dynamics in Bandgap Modulated Covellite-CuS Nanostructures.

Copper Sulfide (CuS) semiconductors have garnered interest, but the effect of transition metal doping on charge carrier kinetics and bandgap remains unclear. In this study, the interactions between dopant atoms (Nickel, Cobalt, and Manganese) and the CuS lattice using spectroscopy and electrochemical analysis are explored. The findings show that sp-d exchange interactions between band electrons and the dopant ions, which replace Cu2+, are key to altering the material's properties. Specifically, these interactions result in a reduced bandgap by shifting the conduction and valence band edges and increasing carrier concentration. It is observed that undoped CuS nanoflowers exhibit a carrier lifetime of 2.16 ns, whereas Mn-doped CuS shows an extended lifetime of 2.62 ns. This increase is attributed to longer carrier scattering times (84 ± 5 fs for Mn-CuS compared to 53 ± 14 fs for CuS) and slower trapping (∼1.5 ps) with prolonged de-trapping (∼100 ps) rates. These dopant-induced energy levels enhance mobility and carrier lifetime by reducing recombination rates. This study highlights the potential of doped CuS as cathode materials for sodium-ion batteries and emphasizes the applicability of metal sulfides in energy solutions.

Magnetically induced perfect absorption and slow light trapping in a double-cavity structure with strontium atoms

Magnetically induced perfect absorption and slow light trapping in a double-cavity structure with strontium atoms

A Physics-Based Model for Slow Gate-Induced Electron Trapping in GaN HEMTs

A Physics-Based Model for Slow Gate-Induced Electron Trapping in GaN HEMTs

Dependence of Positive Bias Stress Instability on Threshold Voltage and Its Origin in Solution-Processed Aluminum-Doped Indium Oxide Thin-Film Transistors.

The initial electrical characteristics and bias stabilities of thin-film transistors (TFTs) are vital factors regarding the practical use of electronic devices. In this study, the dependence of positive bias stress (PBS) instability on an initial threshold voltage (VTH) and its origin were analyzed by understanding the roles of slow and fast traps in solution-processed oxide TFTs. To control the initial VTH of oxide TFTs, the indium oxide (InOx) semiconductor was doped with aluminum (Al), which functioned as a carrier suppressor. The concentration of oxygen vacancies decreased as the Al doping concentration increased, causing a positive VTH shift in the InOx TFTs. The VTH shift (∆VTH) caused by PBS increased exponentially when VTH was increased, and a distinct tendency was observed as the gate bias stress increased due to a high vertical electric field in the oxide dielectric. In addition, the recovery behavior was analyzed to reveal the influence of fast and slow traps on ∆VTH by PBS. Results revealed that the effect of the slow trap increased as the VTH moved in the positive direction; this occured because the main electron trap location moved away from the interface as the Fermi level approached the conduction band minimum. Understanding the correlation between VTH and PBS instability can contribute to optimizing the fabrication of oxide TFT-based circuits for electronic applications.

Effects of Varying Annealing Ambient towards Performance of Ternary GaxCeyOz Passivation Layers for Metal-Oxide-Semiconductor Capacitor

In this work, different annealing ambient (nitrogen-oxygen-nitrogen (N2-O2-N2), forming gas-oxygen-forming gas (FG-O2-FG), and argon-oxygen-argon (Ar-O2-Ar)) were explored to investigate the feasibility of employing the annealed ternary GaxCeyOz passivation layer (PL) for development of Si-based metal-oxide-semiconductor (MOS) capacitors. The impact of nitrogen and/or hydrogen in hindering the growth of silicon dioxide (SiO2) interfacial layer (IL) was quantitatively evaluated. The combination of effects brought by nitrogen attached to oxygen vacancies, nitrogen-silicon bonding, and nitrogen accumulation at the GaxCeyOz/Si interface effectively minimized the formation of SiO2 IL. Consequently, among all the samples, the GaxCeyOz PL annealed in N2-O2-N2 ambient exhibited superior MOS characteristics in terms of low effective oxide charge, slow trap density, interface trap density, and interface state density, which have translated into good leakage current density-electric field characteristics.

An improved chaos sparrow search algorithm for UAV path planning

This study suggests an improved chaos sparrow search algorithm to overcome the problems of slow convergence speed and trapping in local optima in UAV 3D complex environment path planning. First, the quality of the initial solutions is improved by using a piecewise chaotic mapping during the population initialization phase. Secondly, a nonlinear dynamic weighting factor is introduced to optimize the update equation of producers, reducing the algorithm's reliance on producer positions and balancing its global and local exploration capabilities. In the meantime, an enhanced sine cosine algorithm optimizes the update equation of the scroungers to broaden the search space and prevent blind searches. Lastly, a dynamic boundary lens imaging reverse learning strategy is applied to prevent the algorithm from getting trapped in local optima. Experiments of UAV path planning on simple and complex maps are conducted. The results show that the proposed algorithm outperforms CSSA, SSA, and PSO algorithms with a respective time improvement of 22.4%, 28.8%, and 46.8% in complex environments and exhibits high convergence accuracy, which validates the proposed algorithm's usefulness and superiority.

Customer churn classification through a weights and structure determination neural network

In today's corporate world, acquiring and keeping clients are the most important priorities. Every business’s market is expanding quickly, which is increasing the number of subscribers. Because neglect could result in a drop in profitability from a major standpoint, it has become imperative for service providers to limit churn rates. These days, identifying which customers are most likely to leave a business requires a lot less work thanks to machine learning. Taking this into account, a novel weights and structure determination (WASD) neural network has been built to meet the aforementioned challenge of customer churn classification, as well as to handle its unique characteristics. Motivated by the observation that WASD neural networks outperform conventional back-propagation neural networks in terms of slow training speed and trapping in a local minimum, we enhance the WASD algorithm's learning process with a new activation function for best adapting to the customer churn model. Superior performance and flexibility to problems are demonstrated in an experimental investigation using a dataset from a telecommunications provider.

Growth of gallium cerium oxide passivation layer on 4H-Silicon carbide substrate and its metal-oxide-semiconductor characteristics

Gallium cerium oxide (GaxCeyOz) passivation layer was successfully grown on 4H-silicon carbide (SiC) through postdeposition annealing at 800 °C in nitrogen-oxygen-nitrogen (N2–O2–N2) ambient. The gracing incident X-ray diffraction and ultraviolet–visible spectrophotometer measurements have confirmed the successful incorporation of Ga3+ cation into the CeO2 lattice to form the ternary GaxCeyOz passivation layer. In addition, the thicknesses of GaxCeyOz passivation layer and silicon dioxide (SiO2) interfacial layer (IL) were determined using field-emission scanning electron microscopy and X-ray reflectivity characterizations. A high dielectric constant (k) value of 24.11 was attained for the investigated Al/GaxCeyOz/4H–SiC/Al metal-oxide-semiconductor (MOS) structure attributable to the nitrogen ions accumulating at the interface that have retarded the growth of SiO2 IL. Besides, the effective oxide charge, slow trap density, interface trap density, interface state density, as well as leakage current density-electric field characteristic of the investigated GaxCeyOz passivation layer on 4H–SiC substrate was presented in this work.

Interface and oxide trap states of SiO2/GaN metal–oxide–semiconductor capacitors and their effects on electrical properties evaluated by deep level transient spectroscopy

The relationship between the electrical properties and the carrier trap properties of the SiO2/GaN metal–oxide–semiconductor (MOS) capacitors was investigated using electrical measurements and deep level transient spectroscopy (DLTS). The capacitance–voltage (C–V) measurement showed that the frequency dispersion of the C–V curves became smaller after an 800 °C annealing in O2 ambient. DLTS revealed that before the annealing, the interface trap states, in a broad energy range above the midgap of GaN, were detected with the higher interface state density at around 0.3 and 0.9 eV below the conduction band minimum (EC) of GaN. Moreover, the oxide trap states were formed at around 0.1 eV below the EC of GaN, plausibly indicating a slow electron trap with a tunneling process. Although both trap states affect the electrical reliability and insulating property of the SiO2/GaN MOS capacitors, they were found to drastically decrease after the annealing, leading to the improvement of the electrical properties.

Analysis and Classification of Charge Trapping States in β-Ga2O3 Mosfets Using I-V and C-V in Dark and Illumination Conditions

Beta-gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor for high power applications. Its breakdown electric field of 8 MV cm-1, a Baliga figure of merit 3-10 times larger than that of SiC and GaN, and the ability to be grown from the melt make it highly attractive for the semiconductor industry. Significant improvements have been made in β-Ga2O3 device performance for both high power and high frequency operation. Currently, aluminum oxide (Al2O3) is the preferred gate dielectric for β-Ga2O3 transistors due to its electron and hole barriers, and similar atomic structure. Process optimizations to improve the interface quality has been explored by chemical treatments1 to the β-Ga2O3 surface before dielectric deposition, during the deposition of Al2O3, and with post-deposition annealing. Therefore, there is a desire to understand and classify defects at and near the Al2O3/β-Ga2O3 interface. Here, we report on a study of the Al2O3/β-Ga2O3 interface and border traps in planar depletion-mode β-Ga2O3 MOSFETs using DC I-V and C-V measurements in dark and under illumination with wavelengths from 730 nm (1.7 eV) to 230 nm (5.4 eV). The MOSFETs are fabricated on a 50 nm Si-doped epitaxial layer with a target doping concentration of 2.4 x 1018 cm-3 grown on a (010) semi-insulating β-Ga2O3 substrate. A Ti/Al/Ni/Au metal stack is deposited and annealed to form the Ohmic contacts. Plasma-assisted atomic layer deposition (PE-ALD) is used to deposit the 20 nm Al2O3 gate dielectric. The fabricated transistor structures have a LG of 1.94 µm, LS of 0.5 µm, and LD varying from 0.5 µm, 5.5 µm, and 10.5 µm. Measurements were performed at room temperature. Most FETs exhibited a threshold voltage of approximately -4 V, high linearity, and ION/IOFF ratios between 107 – 109. Using the conductance method, we extract an interface trap state density, Dit, of 3 x 1011 eV-1 cm-2 up to 0.44 eV below the conduction band. Illumination is used to obtain deep trap concentration and behavior. We observe little to no change in IV and CV curves for wavelengths above 365 nm but see a significant voltage shift in the CV curves for illumination wavelengths between 365 nm (3.4 eV) to 230 nm (5.4 eV), indicating significant activated traps from 3.4 eV below the conduction band. We will present the analysis of photo-assisted CV and stress-CV curves at various wavelengths to obtain densities of fixed, fast, and slow trap states and discuss their impact on device performance.

Gas–Water Characteristics of Tight Sandstone in Xihu Sag, East China Sea Basin under Different Charging Models

The Xihu sag has two main oil−gas fields: Huagang Gas Field and Pinghu Oil Field. The Huagang formation is the reservoir of the Huagang Gas Field in the Central Tectonic Zone, while the Pinghu formation is the reservoir of the Pinghu Oil Field in the Western Slope Zone. In this paper, which mainly focusses on the Huagang formation, we conducted gas-driven water displacement–magnetic resonance imaging (GWD-MRI) experiments to simulate the charging characteristics of the sandstone migration layer, centrifugal magnetic resonance (Cen-NMR) experiments to simulate the short-term rapid trap charging process, and semi-permeable baffle (SPB) charging experiments to simulate the slow trap accumulation process. The results indicate that a start-up pressure exists for migration layer charging, where the start-up pressure for a core with a permeability of 0.3 mD is about 0.6 MPa. Our experimental simulations confirm that a planar front of changing water saturation exists, which has a width of about 1–1.5 cm. Migration layer charging is mainly influenced by two actions: the drive effect and the carrying effect. The drive effect can reduce the water saturation to 70–80%, while the carrying effect can further reduce the water saturation by 5–10%. The water saturation in the rapid charging scenario is mainly affected by the petrophysical characteristics of the rock: if the porosity is high, the water saturation is low. The water saturation decreases significantly with the increase in centrifugal force when the centrifugal force is small; however, when the centrifugal force is greater than 0.8 MPa, the water saturation decreases slowly. In the slowly charging trap experiment, the water saturation was basically stable at 40–50%, which matched the measured water saturation of the airtight cores well (ranging from 40–55%), and the petrophysical characteristics of the rock did not have a significant effect on the final water saturation.

β-cyclodextrin-scaffolded crosslinked poly(ionic liquid)s for ultrafast removal of multiple pollutants: Insight into adsorption performance and mechanism

The design of highly rapid and efficient cross-linked polymer materials is essential for developing adsorption of pollutant methods based on cyclodextrin to replace currently used slow trapping activated carbons. It is rarely possible to achieve rapid and complete adsorption at high concentrations, even though available adsorbents have developed high adsorption capacity. Herein, a beta-cyclodextrin cross-linked poly(ionic liquid) adsorbents (CD-PILs), was facilely fabricated through one-pot radical polymerization for fast, high-capacity and selective removal of pollutants from water, including organic dyes, pharmaceutical and personal care products, heavy metal ions as well as microbial contamination. It could be completely removed from water within a short period ranging from seconds to minutes at a wide range of high-load anionic dyes (1 mM). Theoretical maximum adsorption capacity of CD-PILs for CR, MO, DS, SD, K2Cr2O7, and CA is 2058.2, 1338.6, 903.7, 1661.4, 878.2, and 343.6 mg/g, respectively. The adsorption rate of ionic CD-PILs superior than those of most of reported synthetic adsorbent materials with the highest adsorption capacity so far, especially for heavy metals. Moreover, after being regenerated five times, the water-remediation performance of CD-PILs remained almost the same as fresh ones, demonstrating the great potential of CD-PILs in industrial water remediation.

Theory of slow traps and random telegraph signals in ultra-small planar MOSFETs

It is shown that ultra-small MOSFETs with heavily doped substrates contain a significant concentration of slow traps in their space-charge regions. Such a trap arises due to random doping fluctuations and is created if a few shallow impurities form a small-scale cluster, resulting in a high binding energy of the ground state of the particle on this multiply charged “nucleus.” Inside the space-charge region, this “nucleus” is surrounded by a high potential barrier, which turns it into a slow trap with capture and emission times not too different from each other. Since a multiply charged trap scatters free carriers much more than a singly charged trap, it generates an easily observable random telegraph signal (RTS) when it captures or emits a free carrier. Such traps, located near the silicon–dielectric interface, generate high-amplitude RTSs that interfere with the normal operation of ultra-small MOSFETs. The probability of their formation depends very sharply on the doping profile near the interface. Therefore, if it can be proven that the slow traps generating the observed RTSs are in silicon, this will provide a clue to reducing this probability. This paper develops a theory describing why a multiply charged silicon slow trap can generate a high-amplitude random telegraph signal, how to reliably distinguish whether the observed RTS is generated by a silicon or oxide trap, and what experimental data are required for this. An analysis of the relevant published data for the RTSs observed in such a MOSFET shows that they are generated by slow traps located in silicon rather than in oxide. The developed theory is in qualitative and reasonable quantitative agreement with the analyzed data.

Quantitative Analysis of Channel Width Effects on Electrical Performance Degradation of Top-gate Self-aligned Coplanar IGZO Thin-film Transistors under Self-heating Stresses

In this study, a quantitative analysis was conducted on the effects of channel width on electrical performance degradation induced by self-heating stress (SHS) in top-gate self-aligned coplanar indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). From the transfer and capacitance-voltage curves obtained before and after SHS, we revealed that the electrical performance of the TFT was nonuniformly degraded along the channel length direction and the degree of this degradation was more significant in TFTs with a wider channel width. The threshold voltage shift (ΔVSUBTH/SUB) under SHS in the fabricated IGZO TFT was mainly attributed to the increase in the density of shallow donor states and acceptor-like deep states in the IGZO active region and electron trapping into the fast and slow traps in the SiOSUBX/SUB gate dielectric. In addition, we conducted a decomposition of the SHS-induced ΔVSUBTH/SUB originated from each degradation mechanism using the subgap density of states-based ΔVSUBTH/SUB decomposition technique for TFTs with different channel widths. Although every ΔVSUBTH/SUB from each degradation mechanism increased as the channel width increased, increased electron trapping into the slow trap in the SiOSUBX/SUB gate dielectric was the dominant reason for the larger ΔVSUBTH/SUB under SHS in IGZO TFTs with a wider channel width.

DYSCALCULIA, a Venus flytrap mutant without the ability to count action potentials

The Venus flytrap Dionaea muscipula estimates prey nutrient content by counting trigger hair contacts initiating action potentials (APs) and calcium waves traveling all over the trap.1,2,3 A first AP is associated with a subcritical rise in cytosolic calcium concentration, but when the second AP arrives in time, calcium levels pass the threshold required for fast trap closure. Consequently, memory function and decision-making are timed via a calcium clock.3,4 For higher numbers of APs elicited by the struggling prey, the Ca2+ clock connects to the networks governed by the touch hormone jasmonic acid (JA), which initiates slow, hermetic trap sealing and mining of the animal food stock.5 Two distinct phases of trap closure can be distinguished within Dionaea's hunting cycle: (1) very fast trap snapping requiring two APs and crossing of a critical cytosolic Ca2+ level and (2) JA-dependent slow trap sealing and prey processing induced by more than five APs. The Dionaea mutant DYSC is still able to fire touch-induced APs but does not snap close its traps and fails to enter the hunting cycle after prolonged mechanostimulation. Transcriptomic analyses revealed that upon trigger hair touch/AP stimulation, activation of calcium signaling is largely suppressed in DYSC traps. The observation that external JA application restored hunting cycle progression together with the DYSC phenotype and its transcriptional landscape indicates that DYSC cannot properly read, count, and decode touch/AP-induced calcium signals that are key in prey capture and processing.

A bio-inspired weights and structure determination neural network for multiclass classification: Applications in occupational classification systems

<abstract><p>Undoubtedly, one of the most common machine learning challenges is multiclass classification. In light of this, a novel bio-inspired neural network (NN) has been developed to address multiclass classification-related issues. Given that weights and structure determination (WASD) NNs have been acknowledged to alleviate the disadvantages of conventional back-propagation NNs, such as slow training pace and trapping in a local minimum, we developed a bio-inspired WASD algorithm for multiclass classification problems (BWASDC) by using the metaheuristic beetle antennae search (BAS) algorithm to enhance the WASD algorithm's learning process. The BWASDC's effectiveness is then evaluated through applications in occupational classification systems. It is important to mention that systems of occupational classification serve as a fundamental indicator of occupational exposure. For this reason, they are highly significant in social science research. According to the findings of four occupational classification experiments, the BWASDC model outperformed some of the most modern classification models obtainable through MATLAB's classification learner app on all fronts.</p></abstract>

Photophysical Study of Electron and Hole Trapping in TiO2 and TiO2/Au Nanoparticles through a Selective Electron Injection

The photophysics surrounding the electron and hole trapping in TiO2 do not have a scientific consensus. Herein, we studied the steady-state photoluminescence and time-resolved spectroscopy features from TiO2 and TiO2/Au nanoparticles (NPs). In TiO2/Au NPs, time-resolved photoluminescence indicates that the electrons from bandgap excitation decay slower (∼30 ps) than in TiO2 (<24 ps). We conclude this as a result of the band bending passivation effect on the surface electron traps. Meanwhile, electron trapping is proved as the dominant surface depopulation process because of the easy-fill characteristics of surface hole traps even under low excitation density, which also interprets the slow surface hole trapping (∼2 ns) in TiO2. Through plasmon-assisted electron injection, we distinguished the electron and hole behaviors at varied photon fluences and then obtained the intrinsic bulk trapping of electrons and holes in the ∼50 and ∼400 ps time range, respectively.

Three-phase co-assembly of compositionally tunable WO3/TiO2 inverse opal photoelectrodes

Heterostructured WO3/TiO2 photonic crystal films in the form of three-dimensional macroporous inverse opals were developed by single-step, three-phase co-assembly of colloidal templates with water soluble precursors enabling simultaneous growth of both metal oxides into a firmly interconnected periodic pore framework whose skeletal walls consisted of uniformly distributed nanoscale type II WO3-TiO2 heterojunctions. A marked size- and composition-dependence of the binary WO3/TiO2 inverse opal properties was evidenced by controlling the W/Ti molar ratio and macropore diameter that allowed Fermi level and photonic band gap engineering according to optical and photoelectron spectroscopies supplemented by electrochemical measurements. Compositional tuning along with the reduction of WO3 nanocrystallite size and the concomitant W5+ defect growth with increasing TiO2 phase content were explored for the optimization of photocurrent generation by WO3/TiO2 inverse opal photoanodes combining reduced charge carrier recombination and optimal slow light trapping. One step co-assembly of mixed metal oxides is concluded as a promising route for the development of heterostructured inverse opal networks with tailored electronic properties and improved solar light harvesting for photo-induced applications.

Effect of high-pressure D2 and H2 annealing on LFN properties in FD-SOI pTFET

Tunneling field-effect transistors (TFETs) are a promising candidate for the next generation of low-power devices, but their performance is very sensitive to traps near the tunneling junction. This study investigated the effects of high-pressure deuterium (D2) annealing and hydrogen (H2) annealing on the electrical performance and low-frequency noise (LFN) of a fully depleted silicon-on-insulator p-type TFET. Without high-pressure annealing, the typical noise power spectral density exhibited two Lorentzian spectra that were affected by fast and slow trap sites. With high-pressure annealing, the interface trap density related to fast trap sites was reduced. The passivation of traps near the tunneling junction indicates that high-pressure H2 and D2 annealing improves the electrical performance and LFN properties, and it may become a significant and necessary step for realizing integrated TFET technology in the future.

Simultaneous slow light and sound rainbow trapping in phoxonic crystals.

In this paper, we use a phoxonic crystal (PxC) which can control the topological states of light and sound by breaking inversion symmetry and thus make it possible to achieve rainbow trapping of light and sound simultaneously. It is shown that topologically protected edge states can be obtained at the interfaces between PxCs with different topological phases. Thus, we designed a gradient structure to realize the topological rainbow trapping of light and sound by linearly modulating the structural parameter. In the proposed gradient structure, the edge states of light and sound modes with different frequencies are respectively trapped at different positions, owing to near zero group velocity. The topological rainbows of light and sound are simultaneously realized in one structure, which open a new, to the best of our knowledge, view and provide a feasible platform for the application of the topological optomechanical devices.