Trapping Centers Research Articles

1/f noise in semiconductors arising from the heterogeneous detrapping process of individual charge carriers

Abstract We propose a model of 1 / f noise in semiconductors based on the drift of individual charge carriers and their interaction with the trapping centers. We assume that the trapping centers are homogeneously distributed in the material. The trapping centers are assumed to be heterogeneous and have unique detrapping rates. We show that uniform detrapping rate distribution emerges as a natural consequence of the vacant trap depths following the Boltzmann distribution, and the detrapping process obeying Arrhenius law. When these laws apply, and if the trapping rate is low in comparison to the maximum detrapping rate, 1 / f noise in the form of Hooge’s relation is recovered. Hooge’s parameter, α H, is shown to be a ratio between the characteristic trapping rate and the maximum detrapping rate. The proposed model implies that 1 / f noise arises from the temporal charge carrier number fluctuations, not from the spatial mobility fluctuations.

Ion crystal size and structure in Paul traps.

This article presents a relationship between the size of an ion crystal in a Paul trap and the radio frequency potential applied on the central ring electrode. Using a simple and elegant derivation it has been shown that the distance of an ion in the crystal from the trap center is proportional to power of the applied radio frequency voltage. The validity of this power law has been demonstrated on ion crystals having up to 13 ions. A spring-mass model has been presented to predict structure of ion crystals in Paul traps operating in the Dehmelt regime. Structures are obtained by minimizing the total potential energy stored in an ion ensemble. The total potential energy is taken to be the sum of the electrostatic potential due to ion-ion interaction and the potential energy stored in the springs. Structures of crystals having up to 13 ions predicted by our model have been verified by comparing them with results obtained by direct numerical simulations.

Charge Carrier Dynamics of SnO2 Electron‐Transporting Layers in Perovskite Solar Cells

Perovskite solar cells (PSCs) have demonstrated remarkable increase in their photovoltaic efficiencies over the past several years. Charge carrier properties including charge selectivity, extraction, and transport play key roles in device performances. Therefore, a comprehensive insight into the charge carrier dynamics and mobility within the bulk materials and at the interface is of great importance for the future development of this cutting‐edge technology. This review discusses the recent advances that have been made in SnO2 electron‐transporting layers and their limitations, followed by outlining the key development of novel strategies in improving SnO2 films through surface defect engineering, interface modification, and doping approaches. In addition, the recent developments are highlighted for identifying the origin of defect and trap center, and promoting SnO2 electron extraction and transporting capacity in PSCs. Importantly, the novel approaches are also discussed for studying photogenerated charge carrier dynamics of the devices. In conclusion, the own prospectives and outlooks are presented for the development of SnO2‐based PSCs, with a particular focus on addressing current difficulties in SnO2 and providing in‐depth understanding on the relationships between materials and devices.

Linkage engineered poly(heptazine imide) optimizes charge transfer for efficient photocatalytic H2O2 production: Regulating oxygen reduction pathway

Photocatalytic H2O2 production via oxygen reduction reaction (ORR) is of great interest. However, the inferior charge transfer efficiency and the low 2e− ORR selectivity grossly constrain this process. Herein, we incorporated pyrimidine (PM) groups as linkers between heptazine units into the poly(heptazine imide) (PHI-PM). There was an augmented in-plane built-in electric field leading to elevated charge separation and transfer capabilities. Additionally, the incremental electron sink effect by PM groups prolonged the charge lifetime and fostered an efficient transfer of electrons from PM groups (electron trapping center) to −C≡N groups (oxygen adsorption center), significantly improving the activity and selectivity of 2e− ORR. Results indicated that the optimization of charge transfer greatly increased the proportion of two-step single-electron ORR, accelerating the reaction kinetics. Meanwhile, side-reaction 4e− ORR was inhibited attributed to the selective generation of •O2−. This work paved new avenues for regulating the pathway of photocatalytic ORR for H2O2 production.

Thermoluminescence characteristics of UV-irradiated natural hackmanite

Hackmanite has received extensive attention from scholars in recent years. However, there is still no report on the thermoluminescence properties of natural hackmanites under UV irradiation, as well as its relative electron trap and luminescence center. In this paper, the structural defects and thermoluminescence spectroscopic properties of hackmanite are comprehensively characterized by XRD, TL spectroscopy, SEM, EPR, XPS and Raman spectroscopy. The traps depth of TL peaks are calculated by computerized glow curve deconvolution (CGCD) techniques. And the charge transition energy levels of intrinsic defects in Na8Al6Si6O24(Cl,S)2 are calculated by spin-polarized density-functional theory (DFT) in VASP. It shows that the low-temperature TL peaks of hackmanite are associated with Cl vacancies and photochromic properties. The high-temperature peak is caused by marginal oxygen vacancies. The results are conducive to deepening the understanding of structural defects of the hackmanites and linking the thermoluminescence with the phototropy.

Suppression of the hole trap for high-quality amino-phosphine based InP quantum dots

InP quantum dots (QDs) have emerged as promising nanomaterials in various fields due to their exceptional optical properties. However, its wide emission linewidth limits further application. In this study, we synthesized high-quality InP/ZnSe/ZnS QDs by suppressing hole defects. The unreacted In precursors during nucleation easily enter ZnSe in the subsequent shelling process, forming a hole trapping center that adversely affects the photo-excitons radiative recombination. Our results demonstrate that the presence of In ions in ZnSe shell enhances exciton-phonon coupling, broadens the fluorescence emission spectrum, and weakens exciton binding energy. The optimized InP QDs exhibit a line width of 44 nm and 90% PLQY at 630 nm. Furthermore, our investigation into the interaction between shell hole defects and core exciton function provides valuable insights for designing and preparing another high-performance core-shell heterojunction QDs.

Improved synthetic method for the color-tunable LiYGeO4:Tb3+ persistent phosphor toward information storage

Efficient and stable persistent phosphors play a crucial role in the fields of energy storage, anti-counterfeiting, and biomedical fields. Here, we present an improved synthetic method for preparing a series of color-tunable LiYGeO4:Tb3+ persistent phosphor. The increased Tb3+ concentration in the improved method enhances the persistent luminescent intensity at 20 s by ∼ 2.96 times. This enhancement is due to the dual roles of Tb3+ as both emitters and trap centers within LiYGeO4. By simply increasing the doping concentrations, the persistent color can be adjusted from blue to green. LiYGeO4:Tb3+ exhibits no loss of persistent luminescent intensity even after exposure to water at 80 °C for 72 hours, surpassing the commercial green persistent phosphor. Furthermore, information storage was successful demonstrated by using LiYGeO4:Tb3+ with various doping concentrations. This study represents a significant advancement in optimizing the properties of persistent luminescent materials, where dopants simultaneously serve as emitters and trap centers.

Formation of a combined electron-hole emission state in the LiRbSO4 – Eu phosphor

In the irradiated phosphor 4 LiRbSO Eu , the mechanisms of formation of the induced or combined electron-emitting state at 3.1-2.94 eV were studied using optical and thermal activation spectroscopy methods. It has been shown experimentally that the combined electron-emitting state of the phosphor is formed from the electron states of impurity and intrinsic electron and hole trapping centers of 24Eu SO   and 34 4 SO SO . Electron and hole trapping centers are created by irradiating the phosphor with photons exceeding the width of the forbidden band of the matrix, where free electrons are created in the conduction band and a hole in the valence band. The trapping center is formed by the capture of free electrons by impurities and anionic complexes according to the reaction 3 2 Eu e Eu      ,2 34 4 SO e SO    . In one process with electron centers, holes in the form of 24SO are localized. Thus, impurity and intrinsic 2 4Eu SO   and 34 4 SO SO  electron-hole trapping centers are formed. Similarly, trapping centers are formed as a result of charge transfer from the excited anion of the 24SO complex to the 3Eu  impurities and to the neighboring 2 4 SO anions according to the reaction ( 2 3 O Eu   ) and ( 2 24O SO  ), and localized holes are also formed in one act along with it. Combined electron-emitting states consisting of impurity and intrinsic electron states are excited by photons with energies of ~4.0 eV and ~4.5 eV.

Low temperature recombination luminescence of Mg3Y2Ge3O12:Tb3+

A study was conducted to examine the recombination processes in persistent phosphor Mg3Y2Ge3O12:Tb3+ garnet at low temperatures. Photoluminescence (PL), recombination luminescence (RL), electron paramagnetic resonance (EPR), and EPR detected by PL or RL were measured.In samples with low Tb3+ concentration, a broad PL and RL band around 400–450 nm and characteristic Tb3+ lines were observed. However, in samples with high Tb3+ concentration, only Tb3+ lines were present. Both the broad-band and the line components exhibit long-lasting tunneling luminescence with hyperbolic decay. After 263 nm UV irradiation signals of intrinsic electron (F-type) and hole (V-type) trapping centres were observed in the EPR spectra. Such signals were also observed in RL-detected EPR spectra, indicating that the broad RL band at low Tb3+ concentrations originates from tunneling recombination between these intrinsic traps. At high Tb3+ concentrations, the RL-EPR spectrum was not observed, suggesting that intrinsic electron and Tb-related hole trapping centres probably participate in the tunneling recombination.

Study of thermoluminescence characteristics of quartz for high radiation doses (>1kGy): Implications for extending the luminescence dating range

Quartz is an omnipresent abundant natural mineral, used for luminescence dating. Lately, quartz optically stimulated luminescence (OSL) technique is widely used to estimate the equivalent doses (De) for dating geological events (up to 250 Gy, limited by saturation). Some works report thermoluminescence (TL) saturation around ∼ (10–40) kGy. Still dose estimates for such high radiation dose (HRD) range are not achieved. Significant research exists about luminescence response for low dose ranges (<250 Gy) but limited studies are done for HRDs (>1 kGy). This work characterizes the luminescence response of quartz for HRDs (1–21 kGy) to improve existing understanding of luminescence mechanism. Results show that the characteristics of the trap (<200 °C) differ significantly at HRDs than low doses. TL in multi-spectral detection (UV–Visible) band suggest an increase in 340–380 °C peak intensity up to 11 kGy dose. The measurements of saturation dose suggest that it depends on the trapping centres but is independent of recombination centres for the samples used for study. The traps are found bleachable by sunlight, reducing TL signal to residual levels in 1 h. Further, the bleachability is found to be anti-correlated with luminescence emission wavelength. At HRDs luminescence sensitivity is influenced by dose given in previous cycle which is difficult to correct by routine normalization procedures. The work also explores the various normalization methods to find appropriate method for HRD estimation and recommends the use of mass normalization as other normalization methods do not correct the sensitivity changes at HRDs adequately.

Lead-Free Perovskite With Efficient Tellurium Ion Activation for Multifunctional Applications.

Lead-free perovskite materials have received extensive attention due to their non-toxicity, super environmental stability and adjustable photoelectric properties. However, the inherent problems of low luminous efficiency and low photoluminescence quantum yields (PLQYs) limit its development in multifunctional applications. Here, Te4+ doped Cs2ZrCl6 with high luminous efficiency and stability for multifunctional applications are developed. Te4+ ions are used as emission centers to improve the optical properties of Cs2ZrCl6 to make efficient and stable single-component white light-emitting diodes (WLEDs), and can be used as scintillator materials to improve scintillation performance to achieve high-resolution and low-dose X-ray imaging detection. In addition, it is found for the first time that Te4+ ions can be introduced into the trap center, so that the Cs2ZrCl6:Te4+ perovskite material exhibits excellent persistent luminescence (PersL) and mechanoluminescence (ML) after X-ray radiation, which has potential applications in the fields of delayed imaging and stress sensing. This work provides a method for designing lead-free perovskites with high optical performance and scintillating properties, as well as developing multifunctional applications.

Time-Responsive Visualization of Cryogenic Detection Based on the Dynamic Optical Signals of CaZnOS.

Cryogenic detection technology is essential to ensure safety and effectiveness in fields such as medical refrigeration, cold chain transport, and cryogenic bioengineering. In this paper, a time-responsive visual cryogenic detection strategy is developed based on the storage properties of CaZnOS: Pb2+, Pr3+ phosphors with shallow traps. Since the carrier release rate from the trap center receives the influence of ambient temperature and storage time, the storage time of the temperature-sensitive product can be determined by the different optical signals of CaZnOS: Pb2+, Pr3+ phosphors obtained under 980 nm laser irradiation. In addition, CaZnOS: Pb2+, Pr3+ phosphors with multimode luminescence enable time-responsive visual detection of ambient temperature under extreme conditions. This work not only demonstrates the potential of CaZnOS: Pb2+, Pr3+ phosphors for visual detection of temperature and time but also paves the way for the development of various applications relying on cryogenic monitoring.

Long-lived carriers-promoted photocatalytic deuteration of halides with D2O as the deuterium source over Cu doped quantum dots

Deuterium labeling is a highly valuable yet challenging subject of research in various scientific fields. Conventional deuteration methods often involve harsh reaction conditions and suffer from limited reactivity and selectivity. Herein, we report a visible light–driven C–X (X = halogen) to C–D (D = deuterium) exchange strategy over copper-doped cadmium sulfide quantum dots (Cu-CdS QDs) under mild conditions, eliminating the need for noble metal catalysts and expensive deuterium sources. The conversion of aryl halides into deuterated products using Cu-CdS QDs reaches up to 99%, which is four times higher than that achieved using pristine CdS QDs. The substantial enhancement in the photocatalytic activity of the QDs can be primarily attributed to the generation of long-lived charge carriers (approximately 6 μs) induced by Cu doping. Mechanistic studies reveal that the Cu dopants considerably retard the recombination of photoinduced carriers by creating intermediate energy levels that serve as hole trapping centers in CdS QDs, thereby improving the electron utilization efficiency in energetically demanding photoreduction reactions. Additionally, the introduction of Cu increases the energy offset between the conduction band of CdS QDs and molecular acceptors, facilitating the electron transfer process. Upon visible light irradiation, a series of aryl halides can be efficiently converted into the desired deuterated compounds using D2O as the deuterium source. This work demonstrates that regulating charge carrier dynamics in ultrasmall QD-based photocatalysts is a promising strategy for promoting organic transformations.

White afterglow achieved in Eu2+, Ce3+, Dy3+co-doped LiSr4(BO3)3 phosphor

In prior study by our team, orange-yellow afterglow was observed in Eu2+ and Dy3+ co-doped LiSr4(BO3 )3 phosphor due to the emission from Eu2+ center. In this study, further incorporation of Ce3+into the phosphor lead to the observation of white afterglow due to the mixed result of blue light from Ce3+ and orange-yellow light from Eu2+ centers. Upon ultraviolet excitation, the phosphor displays a spectrum characterized from blue emission of Ce3+ at 462nm and orange-yellow emission of Eu2+ at 632nm. Fine-tuning the concentration of Ce3+ enabled the realization of white luminescence in LiSr4(BO3)3: Eu2+, Ce3+ and Dy3+phosphor with chromaticity coordinates of (0.3979, 0.2939). The photoluminescence intensities of the samples could be modulated by incorporating varying amounts of Ce3+ ions, with a critical quenching concentration identified with 0.16 Ce3+. White afterglow is also observed after the removal of the light illumination due to the existence of suitable electron traps with optimal trap depth created by the co-doped Dy3+. The underlying mechanism proposes that the white afterglow is generated by the mixed lights of blue and orange-yellow that are created by the recombination of heat-released electrons from the trap centers with pre-existing holes in the Ce and Eu emission sites.

Preparation of porous composite coatings to suppress surface charge movement and reduce electrical resistivity

In this work, Cr2O3/TiO2 composite coatings were prepared on α-Al2O3 insulating ceramic matrix surface by screen printing and solid phase sintering methods to yield an average film thickness of about 14.10 μm. Scanning electron microscopy (SEM) revealed changes in the pore structures of the coatings at different TiO2 contents. The atomic force microscopy (AFM) analysis of the coating surface roughness suggested a TiO2 content of 0.025 mol to yield the best surface roughness and pore structure of the coating. The calculation showed an increase in the energy level of the deep trap center on the surface from 1.506 eV to 1.547 eV, reaching a maximum. The surface resistivity of insulating ceramics decreased from 1016 Ω to 1012 Ω. The formation of deep surface traps and the decrease in surface resistivity promoted charge dispersion and suppressed the formation of flashover channels, effectively improving the surface flashover voltage of the ceramics.

Peroxymonosulfate-assisted photocatalysis system enhanced magnetic Fe3O4@P-C3N4 treatment of tetracycline wastewater: Multi-pathways mediated electrons migration to generate reactive species

Photocatalytic wastewater purification is essential for environmental remediation, but rapid carrier recombination and limited oxidative capacity hinder progress. This study proposes an innovative strategy by integrating homogeneous and heterogeneous electron acceptors into a g-C3N4−based photocatalytic system, significantly enhancing the multipath utilization of photogenerated electrons. A novel Fe3O4@P-C3N4 was developed to activate an advanced peroxymonosulfate−assisted photocatalysis (PAP) system, achieving complete degradation and significant mineralization of tetracycline (TC) in real water environments, outperforming others reported in the last five years. Phytic acid, as a key precursor, modifies the hollow tubular morphology and introduces phosphorus (P) heteroatoms as electronic trapping centers, enhancing the visible light response and carrier separation, thereby promoting the Fe2+/Fe3+ cycle and the formation of reactive species. Density functional theory (DFT) calculations pinpointed TC’s vulnerable sites and synergically identified reactive species, revealing almost non-toxic degradation processes. Moreover, the recyclable magnetic Fe3O4@P-C3N4/PAP system demonstrates practical application potential and leaching stability in cyclic and continuous testing. This study offers unique insights into the strategic design of photocatalysts and catalytic environments, potentially advancing practical wastewater remediation.

Identification of shallow trap centers in InSe single crystals and investigation of their distribution: A thermally stimulated current spectroscopy

Identification of trap centers in semiconductors takes great importance for improving the performance of electronic and optoelectronic devices. In the present study, we employed the thermally stimulated current (TSC) method within a temperature range of 10–280 K to explore trap centers in InSe crystal—a material with promising applications in next-generation devices. Our findings revealed the existence of two distinct hole trap centers within the InSe crystal lattice located at 0.06 and 0.14 eV. Through the leveraging the Tstop method, we offered trap distribution parameters of revealed centers. The results obtained from the experimental methodology employed to investigate the distribution of trap centers indicated that one of the peaks extended between 0.06 and 0.13 eV, while the other spanned from 0.14 to 0.31 eV. Notably, our research uncovers a remarkable variation in trap density, spanning one order of magnitude, for every 10 and 88 meV of energy variation. The results of our research present the characteristics of shallow trap centers in InSe, providing important information for the design and optimization of InSe-based optoelectronic devices.

Exploring the suppression methods of helium-induced damage in tungsten by investigating the interaction between beryllium and helium

Abstract Helium (He)-induced damage is a sensitive concern for the performance of tungsten plasma facing materials (W-PFMs). Recent experiments have revealed that trace impurities in He plasma can effectively prevent the formation of He bubbles and fuzz on W surfaces. To explore its plausibility and underlying mechanism, we performed a multiscale computational study that combines density functional theory calculations and object kinetic Monte Carlo simulations to investigate the effects of a small quantity of beryllium (Be) on the evolution of He bubbles. It is found that there is a strong attractive interaction between He and Be, which can be attributed to the decrease in electron density and the lattice distortion induced by embedded Be atoms. Therefore, the co-implantation of Be continuously introduces trapping centers for He. Due to the low implantation depth and high migration energy of Be, the Be atoms are located close to the surface, leading to the trapping of the majority of He within the near-surface region and the development of a shielding layer for He permeation. The presence of Be facilitates the dispersion of the trapped He, skewing the He clusters into smaller sizes. More importantly, the Be trapping centers bring the He clusters closer to the surface, significantly increasing the probability of bubble bursting and the release of He back to the vacuum. This ultimately leads to a lower retention of He in the case of He + Be co-irradiation, compared with the case of He-only irradiation. Consequently, our findings elucidate the suppressive effect of a low flux of Be atoms on the growth of He bubbles, highlighting the need to focus on synergetic effects between plasma species.

Oxygen vacancy-mediated activation of Zn-O bonds at the S-scheme heterostructure interface for efficient uranium collection and resistance to biological contamination

Efficient reduction of U(VI) to U(IV) during seawater uranium extraction remains a challenge. Here, cerium dioxide quantum dots were bonded to the surface of indium zinc sulfide (ZIS) to form ZIS composite cerium dioxide quantum dots (ZIS/QDs-Ce). The oxygen vacancies are able to activate the Zn-O bonds at the ZIS and QDs-Ce interfaces, thus enabling the constructed S-scheme heterojunction to show great potential in facilitating the separation and transfer of photogenerated carriers. ZIS/QDs-Ce exhibited high anti-bio-pollution activity by generating biotoxic free radical reactive oxygen species (ROS). The photo-induced reduction of uranium by ZIS/QDs-Ce in 10 ppm uranium spiked simulated seawater reached 99.6 %. Oxygen vacancies cause distortions in the crystal field, and the Zn-O bond activation process triggers the movement of ZIS/QDs-Ce from the singlet low-spin state to the stable triplet state, resulting in free-carrier trapping centers and optimized electronic energy band structures. ZIS/QD-Ce has superior uranium extraction capabilities and is highly recommended for uranium extraction from seawater.

Al–O–Al defect complexes as possible candidates for channel electron mobility reducing trapping centers in 4H-SiC metal–oxide–semiconductor field-effect transistors

The deep-level drain current transient spectroscopy (Id-DLTS) measurements of Al-doped SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) strongly suggest that the reduction in the channel mobility at low temperatures is related to a shallow trap detectable at 70 K. Using the Shockley–Reed–Hall (SRH) theory, the level of this trap has been extracted to be around 0.15 eV below the conduction band minimum of SiC. Density functional theory (DFT) calculations of AlSiNCAlSi and AlSiOCAlSi defect complexes have found one configuration of the AlSiOCAlSi complex, which has a charge transition level within the SRH extracted trap level range. Therefore, we suggest that these AlSiOCAlSi defects are likely candidates for traps responsible for the channel mobility reduction.