Electron Trapping Mechanism Research Articles

Reduced graphene oxide/TiO2 hybrid synergistically enhanced polyimide nanofibers with high triboelectric output and thermal charge stability

The output performance of triboelectric nanogenerators (TENGs) can drop dramatically in high temperature environments because of the thermionic emission effect. To enhance the thermal charge stability and expand the working temperature of TENG, polyimide nanofibers (PINF) were synergistically enhanced by the electron trapping mechanism of reduced graphene oxide (rGO) and interfacial polarization of TiO2. With the multiple enhancement effect of polyimide/rGO/TiO2 composite nanofibers (PRTNF) on triboelectric output, PRTNF-TENG generated an open circuit voltage of 228.26 V and a short circuit current of 5.22 μA, which were 3.80 and 3.48 times higher than those of PINF-TENG. The effective output of polymer-based TENG was investigated from 25 − 300 °C. Compared to room temperature, the PRTNF-TENG can maintain 19.45 % (44.39 V) and 18.20 % (0.95 μA) of the voltage and current at 300 °C, respectively, and still drive 50 commercial LEDs. Furthermore, PRTNF-TENGs were applied as self-powered sensors for firefighters to provide real-time motion monitoring and ambient temperature detection. This PRTNF-TENG has broad application prospects for energy harvesting and smart electronic monitor in harsh environments such as fire and space.

Physical Insights Into Electron Trapping Mechanism in the Carbon-Doped GaN Buffer in AlGaN/GaN HEMTs and Its Impact on Dynamic On-Resistance

In this work, a well-calibrated computational framework is used to probe the physical mechanisms leading to electron trapping in the carbon-doped GaN buffer in AlGaN/GaN HEMTs. Device variants having higher lateral electric field were found to exhibit a drastic increase in dynamic ON resistance beyond a critical drain stress voltage. Computations were done while considering trapping on the device surface, with and without accounting for hot electrons, as well as trapping in the GaN buffer. Detailed analysis established electron injection and trapping in the C-doped GaN buffer to be responsible for the observed dynamic ON resistance behavior. Physical insights are provided into the electron injection and trapping behavior by analyzing field evolution near the field plate edge, field-enhanced trapping, and its impact on the leakage current path within the GaN buffer. Finally, the proposed mechanism of field-enhanced electron trapping is validated by computations with device variants having field-independent trapping process and different buffer trap activation energies.

Charge Carrier Dynamics in Colloidally Synthesized Monolayer MoX2 Nanosheets

Transition metal dichalcogenides (TMDs) are nanostructured semiconductors with prospects in optoelectronics and photocatalysis. Several bottom-up procedures to synthesize such materials have been developed yielding colloidal transition metal dichalcogenides (c-TMDs). Where such methods initially yielded multilayered sheets with indirect band gaps, recently, also the formation of monolayered c-TMDs became possible. Despite these advances, no clear picture on the charge carrier dynamics in monolayer c-TMDs exists to date. Here, we show through broadband and multiresonant pump-probe spectroscopy, that the carrier dynamics in monolayer c-TMDs are dominated by a fast electron trapping mechanism, universal to both MoS2 and MoSe2, contrasting hole-dominated trapping in their multilayered counterparts. Through a detailed hyperspectral fitting procedure, sizable exciton red shifts are found and assigned to static shifts originating from both interactions with the trapped electron population and lattice heating. Our results pave the way to optimizing monolayer c-TMDs via passivation of predominantly the electron-trap sites.

Roles of Gate Voltage and Stress Power in Self-Heating Degradation of a-InGaZnO Thin-Film Transistors

Roles of gate voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) and stress power in self-heating (SH) degradation of amorphous InGaZnO thin-film transistors have been clarified. Normally observed positive threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) shift is attributed to the electron trapping mechanism, which is enhanced by both the effective V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> and stress power. The effective V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> plays a dominant role in most cases, while stress power takes control only if it is high enough. Following the positive V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shift, a second-stage negative V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> backshift is also observed and is attributed to the water-related positive charges generation mechanism. It is enhanced by both stress power and effective V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> for which stress power is found to be the dominant factor.

Dynamics of surface electron trapping of a GaN-based transistors revealed by spatiotemporally resolved x-ray spectroscopy

Gallium nitride (GaN)-based transistors are promising for realizing ultralow latency of wireless information communications that are indispensable for smart societies. However, surface states have slow time constants of (de)trapping electrons and delay electrical signal responses of the transistors, which prevent the ultralow latency. To clarify the mechanism of surface electron trapping (SET) of GaN-based transistors, which varies spatiotemporally, we studied the dynamics of the SET by using spatiotemporally resolved x-ray spectroscopy. We directly observed that neutralization of donor-like surface states occurs only near the gate edge in the drain side just after switching off the bias. We found that the large local electric field formed by the bias application induces site- and time-specificity in the SET, which leads to the delayed responses. Our proposed mechanism will be useful for optimizing the transistor structure to achieve the ultralow latency.

Zinc Oxide with Visible Light Photocatalytic Activity Originated from Oxygen Vacancy Defects

In this study, ZnO material with oxygen defect was successfully synthesized using a hydrothermal method and interestingly, it was found to possess a remarkable photocatalytic activity under the visible light irradiation. The synthesized ZnO material was then characterized using X-ray diffraction (XRD), diffuse reflectance ultraviolet-visible (DR UV-vis), Fourier transform infrared spectroscopy (FTIR), and spectrofluorometer. Both diffraction pattern and absorption spectrum showed the characteristic of ZnO. However, the maximum emission wavelength of the synthesized ZnO was observed at 558 nm, showing that the ZnO was formed with a high concentration of oxygen vacancy. The excitation spectra also indicated that the prepared ZnO could be excited at the visible light region, which was more than 400 nm. The ZnO was evaluated for photocatalytic phenol degradation under UV and visible light. After 15 hours-reaction, the synthesized ZnO showed the ability to degrade 59.8% phenol under UV light and 39.6% phenol under visible light. This result showed a remarkable performance of ZnO under visible light, which was comparable to that performed under UV light. This study proposed that the existence of oxygen vacancy defects successfully induced the photocatalytic activity of ZnO under visible light irradiation through the electron trapping mechanism in the oxygen vacancy state.

Triode magnetron injection gun for the KIT 2 MW 170 GHz coaxial cavity gyrotron

Considering the recent understanding of the physics of electron trapping mechanisms taking place in the magnetron injection gun (MIG) region of gyrotrons and the sensitivity of the emitter ring manufacturing tolerances on the electron beam quality, a MIG has been designed and manufactured for the 2 MW, 170 GHz coaxial cavity gyrotron developed at Karlsruhe Institute of Technology. The new MIG has the following novelties: (i) the design satisfies the criteria for the suppression of the electron trapping mechanisms, (ii) a new type of emitter ring is used for the suppression of the influence of the manufacturing tolerances and misalignments on the quality of the generated electron beam, and (iii) the design was optimized to generate a good beam quality in a wide variety of magnetic field profiles to increase the flexibility. An additional important feature of the new triode MIG design is the possibility to operate with only two power supplies by using a special start-up scenario. The first experimental results of the coaxial cavity gyrotron with the new MIG are presented.

Electron trapping mechanism in a multi-level organic fet memory using lithium-ion-encapsulated fullerene as the floating gate

We report on the electron trapping mechanism in a multi-level organic field effect transistor (OFET) memory using Lithium-ion-encapsulated fullerene (Li+@C60) as the floating gate. Based on the estimation of trapped electron number per each Li+@C60 molecule when a programming voltage was applied, the active domain of the floating gate was determined to be the surface of the Li+@C60 domain. An analysis of the cyclic voltammetry indicated that each Li+@C60 molecule can trap electrons at the trapping energy level of -4.94 and -4.49 eV. The number of trapped electron was confirmed by the ultraviolet-visible spectroscopy (UV-Vis).

Electron trapping mechanism in a multi-level organic fet memory using lithium-ion-encapsulated fullerene as the floating gate

We report on the electron trapping mechanism in a multi-level organic field effect transistor (OFET) memory using Lithium-ion-encapsulated fullerene (Li+@C60) as the floating gate. Based on the estimation of trapped electron number per each Li+@C60 molecule when a programming voltage was applied, the active domain of the floating gate was determined to be the surface of the Li+@C60 domain. An analysis of the cyclic voltammetry indicated that each Li+@C60 molecule can trap electrons at the trapping energy level of -4.94 and -4.49 eV. The number of trapped electron was confirmed by the ultraviolet-visible spectroscopy (UV-Vis).

Photoluminescence and thermoluminescence properties of ZnGa2O4 prepared by a microwave assisted solid state reaction

A novel microwave assisted solid state chemical reaction was used to synthesize ZnGa2O4, from stoichiometric amounts of ZnO and Ga2O3 that were calcined at 1100 °C for 8 h under the assistance of 1200 W microwave power. The formation of a single phase was confirmed by X-ray diffractometry (XRD). The optical properties were probed using UV–Vis–NIR absorption, photoluminescence (PL) and Thermoluminescence (TL) spectroscopic techniques. The energy band gap of the compound was approximated to 4.68 eV from diffuse reflectance spectrum using the Kubelka-Munk model. The displayed greenish emission was centred at 528 nm, and the thermoluminescence measurements proved that the electron trapping and de-trapping mechanisms followed second-order kinetics. The variable heating rate (VHR) and initial rise (IR) methods were used to determine the depth of the electron trapping centres.

Synthesis of MnNiO3/Mn3O4 nanocomposites for the water electrolysis process

The hydrothermal method was optimized to produce highly efficient, novel MnNiO3/Mn3O4 nanocomposites for water electrolysis. The predominant peak observed at 36.6° corresponds to the X-ray crystal plane orientation of (1−10) and confirmed rhombohedral phase MnNiO3. The other well-resolved peaks were attributed to MnNiO3/Mn3O4 nanocomposites. Vibrational properties and metal oxygen vibrations were revealed in Fourier transform infrared profile around ~570–620 cm−1. The oxygen vacancies and electron trapping mechanism were exposed from photoluminescence spectra. The combined morphology of nanorods and distinguished nanopetals was determined for highly active MnNiO3 nanocatalyst. The band structure and modification was thoroughly studied by employing UV-visible diffuse reflection spectra and the observed band gap was 2.8 eV for MnNiO3/Mn3O4 nanocomposites. Cyclic voltammogram and linear sweep voltammogram study were used to investigate the redox behavior and water oxidation nature of the novel MnNiO3/Mn3O4 nanocomposites. A higher OER activity of 274 mA/g at 10 mV/s was achieved for the electrode loaded with optimized electrocatalysts. The excellent conductivity and ionic mobility were confirmed by electrochemical impedance spectra. The 72-h stability test was carried out and long-time durability was reported for the optimized electrocatalysts. Thus, the present study completely dealt with the preparation of novel combinations of MnNiO3/Mn3O4 nanocomposites by using controlled synthesis techniques and the exploration of optimized candidates for efficient water electrolysis process.

Electrical transport properties of sensitized PbSe thin films for IR imaging sensors

Electrical transport properties of sensitized PbSe thin films for IR imaging applications were investigated. PbSe thin films were deposited by Chemical Bath Deposition (CBD) method. To sensitize the film, oxidation at 460 °C and iodization at 350 °C were performed successively. As-grown PbSe thin films showed p-type conduction due to Se-rich condition with carrier concentrations, mobility of and electrical resistivity of PbSe thin film after oxidation, the carrier density, mobility and resistivity values were and However, the carrier type was still p-type after oxidation. After sensitization (oxidation and iodization), PbSe thin film showed p-type behavior with carrier concentration of mobility of and resistivity of Iodine-rich PbI2 phase is formed on the top part of the film after iodization. Therefore, this I-rich PbI2 phase still generates p-type conduction without any carrier inversion. A PbI2/PbSe thin film structure showed pp isotype heterojunction characteristics after sensitization. No photoluminescence (PL) signal was observed from as grown thin films and oxidized PbSe thin film showed a peak at 285 meV. After sensitization, a significantly intense IR fluorescence peak from the band gap at 291 meV was observed. The peak height from sensitized PbSe thin film is 12 times higher than that of oxidized PbSe possibly the recombination of photo-generated electron-hole pairs was effectively suppressed. In addition, dark current as a function of temperature in as-grown, oxidized and sensitized PbSe was investigated and results showed the grain boundary activation energy values of 31 meV, 57 meV and 96 meV respectively, which may act as a sensitizing center for electron trapping. In summary, electrical properties data for as grown, oxidized and sensitized PbSe thin films are presented and temperature dependence studies indicates electron trapping mechanism for photoconductivity.

Study of TL kinetic parameters of UV and γ rays irradiated ATiO3:Eu2+, Yb2+ (A = Ca, Ba, Sr) phosphors

The paper discusses the structural studies and TL kinetics analyses of UV and γ rays irradiated ATiO3:Eu2+, Yb2+ (A = Ca, Ba, Sr) phosphors synthesized by conventional solid state reaction technique. The impurity ion concentration of Eu2+, Yb2+ ions varies from 0 to 2 mol% for each. The study of crystal structure, phase and lattice parameters is done by XRD analysis. The morphological and topographical studies set forth the irregularity of shape and size of particles in synthesized phosphors along with agglomeration. The thermoluminescent spectral study of UV and gamma irradiated phosphors reveals crucial TL kinetics and electron trapping mechanism. The phosphors possess second order kinetics with very high value of activation energy (~ 3 eV). This confirms the trapping of electrons in trap centers with high traps depth. The gamma irradiated phosphors possess low fading characteristics than UV irradiated phosphors. The incorporation of divalent impurity ions in the perovskite host lattice attributes to formation of more number of defects and vacancies. These defects and vacancies act as electron trapping sites or trap centers. These phosphors confirm their competence for sensing and TL mapping applications.

Overview on recent progress in magnetron injection gun theory and design for high power gyrotrons

The magnetron injection gun (MIG) is one of the most critical subcomponents in gyrotrons. The electron beam, which has the primary role on the gyrotron operation, is generated and configured at this part of the tube. The electron beam properties determine the excitation mode in the cavity, the power of the generated microwaves and the gyrotron efficiency. The operation of MIGs could be influenced by several factors such as trapped electrons, manufacturing tolerances, roughness of the emitter ring, emitter temperature inhomogeneity, electron beam neutralization effect, etc. The influence of many of these factors on the electron beam quality has been systematically investigated during the last years. Several novelties have been proposed in order to limit the influence of these factors on the gyrotron operation. In particular, new design criteria have been proposed for the suppression of electron trapping mechanisms, a new type of the emitter ring has been proposed to minimize the influence of the manufacturing tolerances and edge effects on the beam quality, alternative MIG design approaches have been proposed, etc. An overview of all these works will be presented here.

Two-step degradation of a-InGaZnO thin film transistors under DC bias stress

A unified explanation is proposed to consistently explain the two-step degradation of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) under DC positive bias temperature instability (PBTI) stress without or with different drain stress voltages (Vds). For PBTI stress without stress Vds, this initial negative Vth shift is believed to be induced by donor-like defect states corresponding to H2O molecule and intrinsic defects, while for PBTI stress with stress Vds, the negative shift is believed to be induced by donor-like defect states corresponding to oxygen vacancies. The gate-bias-induced electron trapping mechanism is responsible for positive Vth shift. These transitions from negative to positive Vth shift are resulted from the competition between the donor-like states creation and electron trapping.

Highly-luminescent Eu,Sm,Mn-doped CaS up/down conversion nano-particles: application to ultra-sensitive latent fingerprint detection and in vivo bioimaging.

Due to their unique properties, rare-earth doped upconversion luminescence (UCL) nanomaterials are of considerable scientific interest. Meanwhile, alkaline-earth sulfide materials based on a completely different electron trapping (ET) mechanism demonstrate extremely high UCL efficiencies, which are several dozens of times more than those of conventional fluoride UCL nanomaterials. However, the large particle size, easy hydrolysis, and difficulty in achieving uniform dispersion have precluded bioassay applications. Herein, we have synthesized super-bright Eu,Sm,Mn-doped CaS nanoparticles of ∼30 nm average particle size using a reverse microemulsion technique. The UCL quantum yield was up to nearly 60%. Modification of the nanoparticles with an organic layer allows their stable dispersion throughout aqueous solutions without significant loss of the fluorescence intensity. We demonstrate the application of the novel UCL materials to latent fingerprint detection, deep tissue imaging, and in vivo bioimaging.

Electron trapping induced electrostatic adsorption of cations: a general factor leading to photoactivity decay of nanostructured TiO2

In this work, a mechanism of electron trapping induced electrostatic adsorption of electrolyte cations (ETIEA) is proposed to explain the general photoactivity decay of nanostructured TiO2 electrodes, usually occurring during the initial several minutes of photoelectrochemical (PEC) processes.

Electron trapping mechanisms in magnetron injection guns

A key parameter for the gyrotron operation and efficiency is the presence of trapped electrons. Two electron trapping mechanisms can take place in gyrotrons: (i) the adiabatic trap and (ii) the magnetic potential well. Their influence on the gyrotron operation is analyzed. Two gun design criteria are then proposed to suppress both mechanisms in order to minimize the risk of possible problems. Experimental results of three high power gyrotrons are presented and their performance is correlated to the presence of populations of trapped electrons. Finally, some very general gun design principles are presented for the limitation of harmful electron trapping.

Trap-clearing Spectroscopy in Perylene Diimide Derivatives

Perylene diimide (PDI) derivatives are important components of organic circuits and photovoltaic systems, but the electron trapping mechanism(s) in higher-LUMO PDIs (−3 to −4 eV, where radical anions are expected to react with atmospheric water and oxygen) are not well characterized. Here, we examine the spatial distribution of traps in transistors made from PDIs with these higher LUMO levels and measure trap-clearing spectra in n-type organic materials using time- and wavelength-resolved frequency-modulated Kelvin probe force microscopy (FM-KPFM). We find that the rate of trap-clearing under visible light does not follow a LUMO-level trend, and we observe spectral evidence for different trapping mechanisms on bare versus HMDS-treated SiO2.

KINETIC SIMULATIONS OF THERMOLUMINESCENCE DOSE RESPONSE: LONG OVERDUE CONFRONTATION WITH THE EFFECTS OF IONISATION DENSITY.

The reader will time-travel through almost seven decades of kinetic models and mathematical simulations of thermoluminescence (TL) characteristics based on the band-gap theory of the solid state. From post-World-War II, ideas concerning electron trapping mechanisms to the highly idealised one trap-one recombination (OTOR) model first elaborated in 1956 but still in 'high gear' today. The review caresses but purposely avoids in-depth discussion of the endless stream of papers discussing the intricacies of glow peak shapes arising from first-order, second-order, mixed-order and general-order kinetics predominantly based on non-interacting systems, and then on to the more physically realistic scenarios that have attempted to analyse complex systems involving ever greater numbers of interacting trapping centres, luminescent centres and non-luminescent centres. The review emphasises the difficulty the band-gap models have in the simulation of dose response linear/supralinear behaviour and especially the dependence of the supralinearity on ionisation density. The significance of the non-observation of filling-rate supralinearity in the absorption stage is emphasised since it removes from consideration the possibility of TL supralinearity arising from irradiation stage supralinearity. The importance of the simultaneous action of both localised and delocalised transitions has gradually penetrated the mindset of the community of kinetic researchers, but most simulations have concentrated on the shape of glow peaks and the extraction of the glow peak parameters, E (the thermal activation energy) and s (the attempt-to-escape frequency). The simulation of linear/supralinear dose response and its dependence on ionisation density have been largely avoided until recently due to the fundamental schism between the effects of ionisation density and some basic assumptions of the band-gap model. The review finishes with an in-depth presentation and discussion of the most recent nanoscopic-localised/delocalised kinetic model that promotes an ice-breaking solution to bridge the schism.