Electron Trapping Research Articles

Understanding the Influence of Electron Traps and Urbach States on the Kinetics of Ti3+ Persistent Luminescence in LaAlO3:Ti3.

The luminescence kinetics of Ti3+ ions, resulting from the spin-allowed 2E → 2T2 electron transition, are generally expected to be fast, within the microsecond range. However, in this study, we observed average lifetimes of up to 30 ms in nanocrystalline LaAlO3:Ti3+ powders. Our detailed analysis of the spectroscopic and thermoluminescence properties of LaAlO3:Ti3+ suggests that this prolonged Ti3+ kinetics is associated with the presence of electron traps and the proximity of the Ti3+ excited state to the conduction band, which facilitates energy transfer between them. Furthermore, the observed shift in Urbach states with an increasing Ti3+ concentration correlates with the efficiency of energy transfer between deeper traps and Ti3+ ions. This study provides a comprehensive strategy for controlling the luminescence kinetics of Ti3+ ions through electron trap engineering, induced by dopant ion concentration, which can be applied in various fields including luminescence thermometry.

Amplifying Persistent Luminescence in Heavily Doped Nanopearls for Bioimaging and Solar-to-Chemical Synthesis.

Lanthanides are widely codoped in persistent luminescence phosphors (PLPs) to elevate defect concentration and enhance luminescence efficiency. However, the deleterious cross-relaxation between activators and lanthanides inevitably quenches persistent luminescence, particularly in heavily doped phosphors. Herein, we report a core-shell engineering strategy to minimize the unwanted cross-relaxation but retain the charge trapping capacity of heavily doped persistent luminescence phosphors by confining the activators and lanthanides in the core and shell, respectively. As a proof of concept, we prepared a series of codoped ZnGa2O4:Cr, Ln (CD-Ln, Ln = Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) and core-shell structured ZnGa2O4:Cr@ZnGa2O4:Ln (CS-Ln) nanoparticles. First-principles investigations suggested that lanthanide doping elevated the electron trap concentration for enhancing persistent luminescence, but energy transfer (ET) from Cr3+ to Ln3+ ions quenched the persistent luminescence. The spatial separation of Cr3+ and Ln3+ ions in the core-shell structured CS-Ln nanoparticles suppressed the ET from Cr3+ to Ln3+. Due to the efficient suppression of deleterious ET, the optimal doping concentration of Ln in CS-Ln was elevated 50 times compared to CD-Ln. Moreover, the persistent luminescence intensity of CS-5%Ln was up to 60 times that of the original ZnGa2O4:Cr. The CS-5%Ln displayed significantly improved signal-to-noise ratios in bioimaging. Further, the CS-Ln was interfaced with the lycopene-producing bacteria Rhodopseudomonas palustris for solar-to-chemical synthesis, and the lycopene productivity was increased by 190%. This work provides a reliable solution to fulfill the potential of lanthanides in enhancing persistent luminescence and can further promote the applications of persistent luminescence phosphors in biomedicine and solar-to-chemical synthesis.

"Electron trap" modified type-I heterojunction CdS/CoSe/graphdiyne photocatalyst synergistically promotes photocatalytic hydrogen production

Modifying the carrier dynamics in heterojunction photocatalysts is a direct and effective strategy to enhance photocatalytic hydrogen production. Herein, graphdiyne (GDY) is loaded onto CdS/CoSe using a solvothermal method, and the CdS and GDY form a type-I heterojunction. In addition, the highly conductive metal-like material CoSe acts as an "electron trap" to transfer electrons from GDY to CoSe, which promoting the effective separation of photo-generated electrons and holes, further improving the performance of photocatalytic hydrogen production. The hydrogen evolution rate of CdS/CoSe/GDY (0.17mmol·h-1) is 4.25 and 1.88 times for CdS (0.04mmol·h-1) and CdS/CoSe (0.09mmol·h-1). In-situ X-ray photoelectron spectroscopy (XPS), Electron Paramagnetic Resonance (EPR) and Density functional theory (DFT) calculations and other characterizations demonstrate that the significantly improved photocatalytic performance is not only due to the fast electron transfer and separation by close contact, but also to the synergistic effect between the type-I heterojunction and the "electron trap". In conclusion, this work enriches the study of type-I heterojunction photocatalytic systems and provides new research ideas for the design of efficient photocatalysts.

Beam-driven electron-acoustic waves in auroral region of magnetosphere with superthermal trapped electrons

The propagation characteristics of nonlinear electron-acoustic (EA) waves are studied in a four-component magneto-plasma, containing inertial cold electrons, warm drifting beam electrons, trapped superthermal hot electrons, and static ions. A linear dispersion relation for EA waves is derived to analyze the impact of electron superthermality on the ω−k relation. For nonlinear analysis, a reductive perturbation formalism is adopted to solve the set of model equations in the form of a trapped Zakharov–Kuznetsov (tZK) equation. The latter is analyzed to determine the solitary structures in terms of phase portraits and exact soliton solutions showing the impact of electron trapping efficiency (γ), hot electron superthermality (κ), drifting speed, temperature and density of beam electrons, and temperature and density of cold electrons, using typical parameters from the short-duration burst of broad-band electrostatic noise emissions observed by the Viking spacecraft in the auroral region. The solitary structures propagate as positive potential pulses and become modified with superthermal trapped electrons, leading to hole (hump) in cold (hot) electron density excitations. The electric field structures of the EA waves are found to be in exact agreement with the observed solitary structures in the auroral region. It is observed that electric field strength associated with these waves decreases as the magnetic field increases. The present model can be used to understand the transport of energy and momentum between plasma particles and to comprehend magnetic reconnection region in magnetopause, where two-temperature electrons and large-amplitude parallel electrostatic waves have been reported by magnetopause multiscale observations.

Defect suppression and optoelectronic property investigation of a self-powered β-Ga2O3/p-Si photodetector grown by pulsed laser deposition

Abstract The pulsed laser deposition method is recognized for its ability to minimize defects in semiconductors by carefully controlling gas pressure and temperature during deposition. This study discusses the presence of defect states in β-Ga2O3/p-Si heterojunction created using pulsed laser deposition at different oxygen pressures through deep-level transient spectroscopy (DLTS). When the oxygen pressure rises from 0 to 25 mTorr, the electron trap at EC −1.21 eV associated with an oxygen vacancy vanished, resulting in a 1.6 fold decrease in the total defect density. A gallium vacancy hole trap located at EV + 0.57 eV was identified when the oxygen pressure reached 55 mTorr. The presence of this hole trap suggested that β-Ga2O3 was grown in an oxygen-rich environment. The photoluminescence findings are outstanding and in agreement with DLTS data. The β-Ga2O3/p-Si device showed its peak photoresponsivity at 25 mTorr (330 mA W−1). This shows that carrier transport is improved because defects are reduced. Our discovery provides a possible path for enhancing the high optoelectronic properties of β-Ga2O3/p-Si devices.

Characterizing hole trap production due to proton irradiation in germanium cross-strip detectors

We present an investigation into the effects of high-energy proton damage on charge trapping in germanium cross-strip detectors with the goal of accomplishing three important measurements. First, we calibrated and characterized the spectral resolution of a spare COSI-balloon detector in order to determine the effects of intrinsic trapping, finding that electron trapping due to impurities dominates over hole trapping in the undamaged detector. Second, we performed two rounds of proton irradiation of the detector in order to quantify, for the first time, the rate at which charge traps are produced by proton irradiation. We find that the product of the hole trap density and cross-sectional area, [nσ]h, follows a linear relationship with the proton fluence, Fp, with a slope of (5.4±0.4)×10-11cm/p+. Third, by utilizing our measurements of physical trapping parameters, we performed calibrations which corrected for the effects of trapping and mitigated degradation to the spectral resolution of the detector.

Local Polarization Piezoelectric Electric Field Promoted Water Dissociation for Hydroxyl Radical Generation under Ambient Humidity Condition.

Combining piezocatalysts with mechanical ball milling for dissociating water to generate hydroxyl radicals (·OH) offers unprecedented opportunities for energy conversion and environmental remediation. However, the in-depth insights into the relationship between water and local polarization piezoelectric electric field (LPPEF) are currently lacking, in particularly, the ·OH formation mechanism in ball milling driven piezocatalyst system is not systematically elucidated. To this end, the present work constructs a ball milling driven piezoelectric solid/liquid interface between piezoelectric Pb2B5O9Cl (PBOC) and different contents of water to investigate LPPEF initiated catalytic reaction. Results show that PBOC exhibits an excellent Tetrabromobisphenol A (TBBPA) degradation efficiency with a 68.94 and 12.43 times faster rate constant than traditional SiO2 and BaTiO3, respectively. Under ambient humidity condition, the lower energy barrier of water dissociation (0.23eV) endows ·OH generation more energetically favorable than under the water-oversaturated condition (0.66eV), and trace water magnifies the polarizability of [BO3] and [BO4] units in PBOC to initiate an enhanced LPPEF, thus it enhances the trapping of lone pairs electrons in trace adsorbed water by holes to contribute a higher yield of ·OH. This study constructs a highly correlated field-initiated electron transfer system that provides opportunities for promoting the performance of piezocatalytic materials.

Structural and electronic properties of interstitial oxygen defect in amorphous indium gallium oxide (IGO) semiconductors: a theoretical study

Abstract We elucidate the role of gallium (Ga) in the structural and electronic properties of amorphous indium gallium oxide(a-IGO) for different Ga concentrations with oxygen interstitial defects by using hybrid density functional methods. Ab initio molecular dynamic simulations reveal that Ga substitution significantly affects the structural characteristics and that Ga-O coordination is particularly sensitive to changes in oxygen stoichiometry. The electronic structure indicates the formation of an O-O dimer in the neutral state. The stability of this dimer upon capturing electrons is influenced by the local atomic structure around the dimer. When the bond breaks, the dimer's antibonding defect level is significantly lowered from the conduction band, approaching the valence band. This makes it more energetically advantageous for the dimer to capture two electrons. We statistically studied the Ga concentration dependence on the impact of O2 dimer generation in a-IGO. Formation transition energy indicates that O-O bond is broken easily with more Ga, which acts as an electron trap identifying the origin of positive bias stress (PBS) observed in the transistor behavior.

Defects Calculation and Accelerated Interfacial Charge Transfer in a Photoactive MOF-Based Heterojunction.

Photocatalytic hydrogen production is currently considered a clean and sustainable route to meet the energy and environmental issues. Among, heterojunction photocatalysts have been developed to improve their photocatalytic efficiency. Defect engineering of heterojunction photocatalysts is attractive due to it can perform as electron trap and change the band structure to optimize the interfacial separation rate of photogenerated electron-hole pairs. Here, the MOF-based heterojunction photocatalysts with theoretically high reduction and oxidation abilities are successfully synthesized, denoted ZrO2/Pt/Zr-MOF-X, with tuned linker defectivity through an in situ electrochemical route. The defectivity are rationally calculated from the TG and 1H NMR results. A positive correlation is found between the defectivity and photocatalytic activity, and ZrO2/Pt/Zr-MOF-6 with the optimized defectivity of ca. 35% exhibits the highest hydrogen production rate of up to 2923 µmol g-1 h-1, illustrating the importance of structural defects in heterojunction photocatalysts. Ultrafast transient absorption spectroscopy and electron spin resonance results unveil the highest carrier concentration and charge separation efficiency in the defected heterostructure of ZrO2/Pt/Zr-MOF-6 through a direct Z-scheme contact, leading to its efficient photocatalysis through the high redox power.

Integrated analysis of cellulose structure and properties using solid-state low-field H-NMR and photoacoustic spectroscopy

In this study, we explore the structural intricacies of cellulose, a polymer composed of glucose monomers arranged in a linear chain, primarily investigated through solid-state NMR techniques. Specifically, we employ low-field proton nuclear magnetic resonance (H-NMR) to delve into the diverse hydrogen atom types within the cellulose molecule. The low-field H-NMR technique allows us to discern these hydrogen atoms based on their distinct chemical shifts, providing valuable insights into the various functional groups present in cellulose. Our focus extends to the examination of anomeric protons of glucose units and protons linked to carbon atoms engaged in glycosidic linkages within cellulose chains, which exist in diverse crystalline and amorphous forms. Solid-state low-field H-NMR spectroscopy aids in characterizing the crystallinity degrees and amorphous regions within cellulose, revealing time-dependent changes in free induction decay (FID) signals. Complementing this, we investigate the photo-absorption properties of cellulose fibers under both continuous and modulated irradiation using reversed double-beam photoacoustic spectroscopy (RDB-PAS). This photoacoustic approach allows us to observe ultraviolet- and visible light-induced processes, including electron trap filling and reductive changes on the fiber surface. Our findings suggest that RDB-PAS is a feasible method for estimating the electron trap distribution, serving as a potential measure of the density of crystalline cellulose defects. This integrated approach of combining solid-state low-field H-NMR and RDB-PAS techniques offers a comprehensive understanding of cellulose structure and properties, enhancing our ability to characterize its diverse features.

Modeling of Composition and Channel Length-Dependent Transient Characteristics in Short-Channel IGZO Field-Effect Transistors.

In this study, we analyze the characteristics of fast transient drain current (ID) in IGZO-based field-effect transistors (FETs) with different composition ratios (device O: ratio of 1:1:1 for In, Ga, Zn, device G: ratio of 0.307:0.39:0.303) for reliable operations. Overshoot currents, which can cause device degradation, are caused by fast transients and are attributed to the trapping of electrons in the energy band. As the lateral electric field (Elat) of the IGZO channel is increased, the overshoot drain current difference (ΔIOS) is increased for both devices. It is also found that the increase in ΔIOS with decreasing L is less pronounced in device G compared with that for device O. While device G yields larger ΔIOS values than device O in long channels (L = 5, 10 μm), it yields smaller ΔIOS in short channels (L = 0.5, 1 μm). This phenomenon is explained using three physical parameters (nOS, Ever, and NOT), based on Technology Computer-Aided Design (TCAD) simulation modeling. Device G has stronger immunity against ΔIOS in a short-channel region; this can be attributed to the lower concentration of oxygen vacancies in device G that suppresses dopant diffusion effects within IGZO layer. These results experimentally demonstrate that the short-channel effects on fast-transient ID can be improved by controlling the Ga composition ratio of IGZO.

Defect-mediated electron–phonon coupling in halide double perovskite

Optically active defects often play a crucial role in governing the light emission as well as the electronic properties of materials. Moreover, defect-mediated states in the midgap region can trap electrons, thus opening a path for the recombination of electrons and holes in lower energy states that may require phonons in the process. Considering this, we have probed electron–phonon interaction in halide perovskite systems with the introduction of defects and investigated the thermal effect on this interaction. Here, we report Raman spectroscopic study of the thermal evolution of electron–phonon coupling, which is tunable with the crystal growth conditions, in the halide perovskite systems Cs2AgInCl6 and Cs2NaInCl6. The signature of electron–phonon coupling is observed as a Fano anomaly in the lowest frequency phonon mode (51 cm−1), which evolves with temperature. In addition, we observe a broad band in the photoluminescence (PL) measurements for the defect-mediated systems, which is otherwise absent in defect-free halide perovskite. The simultaneous observation of the Fano anomaly in the Raman spectrum and the emergence of the PL band suggests the defect-mediated midgap states and the consequent existence of electron–phonon coupling in the double perovskite.

Structural modification of defective WO3 by g-C3N4 for photocatalytic gold recovery from non-cyanide-based plating effluent

A set of nCN/WO3 − x composites was synthesized through a simple thermal treatment for gold recovery from the simulated effluent of a non-cyanide-based plating bath. The obtained results exhibited that all nCN/WO3 − x composites demonstrated a higher photocatalytic activity for gold recovery than their pristine components due to the formation of nanocomposites which paved a convenient pathway for charge transfer. Among all synthesized composites, the 5.0CN/WO3 − x composite exhibited the highest photocatalytic activity, recovering around 69.4% of gold within 120 min under UV-vis light irradiation at an intensity of 3.45 mW/cm² and a catalyst loading of 1.0 g/L, in the absence of hole scavenger. This result can be ascribed to the presence of an optimal number of defects, which can act as electron trapping sites and thereby reduce the recombination rate of charge carriers. Gold recovery increased with repeated reuse, attributed to the decorated gold, which enhances light absorption and decreases the recombination rate of charge carriers. The feasible application of used CN/WO3 − x were also explored for H2 production, dye degradation and gold recovery. The obtained results provide a new insight about the photocatalytic recovery of gold from industrial wastewater and also shed light on the application of gold-decorated CN/WO3 − x as a catalyst for other photocatalytic applications.

Suppressing Polaronic Defect-Photocarrier Interaction in Halide Perovskites by Pre-distorting Its Lattice.

In halide perovskites, photocarriers can have strong polaronic interactions with point defects. For iodide-deficient MAPbI3, we found that the Fermi level can shift significantly by 0.6-0.7 eV upon light illumination. This energy level shift is accompanied by the formation of deep electron traps. These experimental observations are consistent with the formation of a Pb-Pb dimer when photoexcited electrons are trapped at an iodide vacancy. Interestingly, we found that this polaronic interaction is suppressed when a portion of MA+ cations is replaced by smaller Cs+ ions. Density functional theory calculations reveal that Cs-doping can reduce the distance between two Pb atoms across an iodide vacancy, even without electron trapping. The predistortion of the lattice induced by cation replacement resembles the Pb-Pb dimer formed by electron trapping at the defect site, which explains the suppression of light-induced effects observed in the experiment. Our finding unveils a counterintuitive strategy to enhance the photostability of halide perovskites by preintroducing distortions into its lattice.

Interface Characterization of Plasma‐Treated InAs Electrodes for Resistive Random‐Access Memories Using Capacitance–Voltage Methods

InAs nanowires have been used as selectors and electrodes in a one‐transistor one‐resistor resistive random‐access memory (RRAM) configuration for increased memory scalability. Such oxide‐based memories not only show promise both in conventional memory technology but also as analog memories for neural networks. The small areas of the oxide elements, however, result in challenges for electrical characterization of the oxide–semiconductor interface. By analyzing larger test structures, it is possible to perform impedance spectroscopy on the oxide–InAs interface. In this article, HfO2‐based RRAMs on InAs are fabricated using plasma‐enhanced atomic layer deposition. The effect of the plasma‐length is investigated using capacitance–voltage and DC measurements. It is found that an increased plasma‐length results not only in a higher total electron trapping but also in the formation of a more stable interfacial oxide, possibly related to the stoichiometry of the complex InAs oxide. The findings give us a better understanding of the noise‐ and switching‐performance of scaled nanowire devices.

Terahertz Saturable Absorption across Charge Separation in Photoexcited Monolayer Graphene/MoS2 Heterostructure.

Unveiling the nonlinear interactions between terahertz (THz) electromagnetic waves and free carriers in two-dimensional materials is crucial for the development of high-field and high-frequency electronic devices. Herein, we investigate THz nonlinear transport dynamics in a monolayer graphene/MoS2 heterostructure using time-resolved THz spectroscopy with intense THz pulses as the probe. Following ultrafast photoexcitation, the interfacial charge transfer establishes a nonequilibrium carrier redistribution, leaving free holes in the graphene and trapping electrons in the MoS2. When probed with intense THz pulses exceeding 34 kV/cm in a peak electric field, significant THz saturable absorption is observed over a period of 20 ps. Furthermore, the photoinduced change in the transmitted THz waveform, linked to the THz-driven nonlinear current, manifests as a substantial self-phase modulation. These nonlinear responses can be attributed to the competition between rapid carrier heating and slow carrier cooling via electron-electron and electron-phonon scattering in the charge-transfer-induced hole system of the graphene layer. This work demonstrates an integration of advantages arising from robust nonlinear absorption in graphene and enhanced photocarrier harvesting in transition metal dichalcogenides by exploiting heterostructure construction.

Fabrication of shaddock peel biochar mediated Cd0.8Zn0.2S nanocomposite and synergistic adsorptive-photocatalytic performance for pollutant removal

Developing inexpensive, eco-friendly and efficient catalysts is the key to photocatalytic removal of organic pollutants from wastewater. In this paper, a novel pre-treatment activated shaddock peel biochar mediated hexagonal Cd0.8Zn0.2S composite photocatalyst (CZS/BC) was fabricated by hydrothermal method and comprehensively characterized. The photocatalytic performance was assessed by degradation of Rhodamine B (RhB) in aqueous solution under visible light irradiation. Compared with the pristine Cd0.8Zn0.2S (CZS), the doping of shaddock peel biochar (BC) not only significantly reduces the band gap energy (Eg) of the CZS, but also significantly improves the adsorption and photocatalytic performance. Under the synergistic action of adsorption and photocatalysis, the optimal CZS/BC-0.3 sample exhibited the best removal performance, and could almost completely eliminate RhB pollutant within 50min with good stability, possessing great application potential in practical environmental remediation. The removal efficiency was 6.4 folds higher than pristine CZS. Studies on photocatalytic mechanism showed that photocatalysis was mainly predominated by •O2- and h+ induced pathways, and the enhancement of photocatalytic performance can be attributed to the formation of hexagonal CZS, with biochar as an electron bridge and trap, the photogenerated carrier can be separated more effectively, thus enhancing the photocatalytic performance. This work provides a new idea for constructing new composite photocatalysts using BC as electron transport bridge.

One-step fabrication of high energy storage polymer films with a wide bandgap and high melting temperature induced by the fluorine effect for high temperature capacitor applications with ultra-high efficiency.

The development of polymer dielectrics with both high energy density and low energy loss is a formidable challenge in the area of high-temperature dielectric energy storage. To address this challenge, a class of polymers (Parylene F) are designed by alternating fluorinated aromatic rings and vinyl groups in the polymer chain to confine the conjugating sequence and broaden the bandgap with the fluorine effect. The target films with desired thickness, ultra-high purity, and a wide bandgap are facilely fabricated by a one-step chemical vapor deposition (CVD) technique from monomers. The symmetric and bulky aromatic structures exhibit high crystalline performance and excellent stability at high temperature. The presence of strongly electronegative fluorine atoms effectively enhances bandgap and electron trapping capability, which effectively reduces the conduction loss as well as the possibility of breakdown at high temperatures. CVD technology avoids the post-processing film-forming process, ensuring the fabrication of thin films with high quality. These benefits allow Parylene F films to effectively store electrical energy at temperature up to 150 °C, exhibiting a record discharged energy density of 2.92 J cm-3 at charge-discharge efficiency exceeding 90%. This work provides a new idea for the design and synthesis of all-organic polymer dielectric films for high temperature applications.

Surfactants govern the fabrication of sulfur-enriched heterojunction catalysts for highly selective photocatalytic conversion of toluene

Photocatalytic selective oxidation of toluene represents a milder and more environmentally friendly strategy for the synthesis of benzaldehyde. In order to enhance catalytic performance, efficient carrier separation and transport are crucial in the photocatalytic process. This study focused on the preparation of ZnS@ZnIn2S4 with sulfur vacancies and heterostructures, combining the advantages properties of ZnS and ZnIn2S4 in photocatalysis. The effects of ZnS and surfactants on the catalytic properties of the composites were studied in depth. Characterization tests revealed that surfactant-modified ZnS@ZnIn2S4 exhibited a higher concentration of sulfur defects, which facilitated electron trapping and promoted photogenerated carrier separation and utilization. Additionally, the present study also demonstrated that the incorporation of ZnS and surfactants could reduce the crystal size of ZnIn2S4, thereby facilitating the exposure of additional active sites. The synergistic effect of the aforementioned advantages enabled toluene to undergo oxidation at a conversion rate of 39% in the presence of oxygen, resulting in the production of benzaldehyde with an exceptional selectivity of 92%. This finding offers valuable insights for future endeavors in designing photocatalytic C-H bond oxidation catalysts.

Ultrahigh detectivity of near-infrared organic phototransistor assisted by additional electron trap sites in a dielectric layer

This study introduced an additional electronic traps (ZnO nanoparticles) into the dielectric layer of the organic phototransistor, obtaining a high Ilight/Idark and an ultra-high detectivity while keeping the response time unchanged.