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This work aims to validate the feasibility of device-level analysis to reflect the effects of fabrication processes and operations, as contrasted with the conventional method of x-ray photoelectron spectroscopy (XPS), which is widely employed in amorphous oxide semiconductor thin-film transistors (TFTs) but analyzes film-level specimens. First, an analysis setup was introduced to determine the optimal x-ray target position for device-level XPS, where the intensity of channel components is maximized, through imaging XPS. Then, to demonstrate the effectiveness of this approach, the impact of channel composition and bias-stress was investigated through the implementation of device-level XPS on bottom-gate InGaZnO TFTs. The cationic composition ratios of the fabricated TFTs varied from 0.27:1:1.33 (In:Ga:Zn) and 0.28:1:2.21 when the subcycle of the Zn precursor increased by a factor of 1.5 in the atomic-layer deposition process. The device with a higher Zn ratio exhibited a more negative turn-on voltage and a twice larger subthreshold swing. These characteristics were validated from the comparisons in the relative amount of oxygen vacancies in O 1s of the channel and interface regions by 8.4%p and 5.6%p, respectively, between the devices. Furthermore, the electron trapping effect was verified for the devices subjected to a positive gate bias-stress of 3 MV/cm, as evidenced by the changes in the binding energy difference (0.35 eV) between the channel and gate insulator layers, in comparison to the non-stressed device. Consequently, this work demonstrates that device-level XPS can be an effective tool for understanding TFTs' characteristics in various ways beyond film-level analysis. [ABSTRACT FROM AUTHOR]

Granular metals (GMs), consisting of metal nanoparticles separated by an insulating matrix, frequently serve as a platform for fundamental electron transport studies. However, few technologically mature devices incorporating GMs have been realized, in large part because intrinsic defects (e.g., electron trapping sites and metal/insulator interfacial defects) frequently impede electron transport, particularly in GMs that do not contain noble metals. Here, we demonstrate that such defects can be minimized in molybdenum–silicon nitride (Mo–SiNx) GMs via optimization of the sputter deposition atmosphere. For Mo–SiNx GMs deposited in a mixed Ar/N2 environment, x-ray photoemission spectroscopy shows a 40%–60% reduction of interfacial Mo-silicide defects compared to Mo–SiNx GMs sputtered in a pure Ar environment. Electron transport measurements confirm the reduced defect density; the dc conductivity improved (decreased) by 104–105 and the activation energy for variable-range hopping increased 10×. Since GMs are disordered materials, the GM nanostructure should, theoretically, support a universal power law (UPL) response; in practice, that response is generally overwhelmed by resistive (defective) transport. Here, the defect-minimized Mo–SiNx GMs display a superlinear UPL response, which we quantify as the ratio of the conductivity at 1 MHz to that at dc, Δ σ ω. Remarkably, these GMs display a Δ σ ω up to 107, a three-orders-of-magnitude improved response than previously reported for GMs. By enabling high-performance electric transport with a non-noble metal GM, this work represents an important step toward both new fundamental UPL research and scalable, mature GM device applications. [ABSTRACT FROM AUTHOR]

The structural parameters, electron localization functions, electron paramagnetic resonance (EPR) parameters, formation energies, and thermodynamic transition levels of various oxygen vacancy defects in amorphous silica are comprehensively and integrally investigated by using density functional theory. The trends of changes in the oxygen vacancy defect structure and electron localization induced by the increase in distance between defective silicon atoms are clearly identified. It is shown that the dimer configuration may be the potential structure of the E δ ′ center. For the back-projected unpuckered configuration and the puckered configuration, whose EPR parameters are more consistent with the experimental values of the E γ ′ center, the unpaired electron localized on the sp3 hybridized silicon atom is a common feature. Due to the three-coordinated oxygen atom in the forward-oriented configuration, the EPR parameters are closest to those of the E α ′ center. Transformations of oxygen vacancy defects under different charge states are studied by sequentially adding and removing electrons. The thermodynamic transition level analysis reveals that the dimer and forward configurations may behave as deep traps for electron accumulation. The back-projected puckered fourfold-coordinated and fivefold-coordinated configurations are comparatively stable and may be able to function as shallow traps for electron transport. The neutral double unpuckered, neutral back-projected puckered fourfold-coordinated, and neutral back-projected unpuckered configurations are more likely to lose electrons during hole trapping. As the bias voltage is repeatedly changed, the defect density of the puckered configuration may reduce, while that of the dimer and unpuckered configuration may take an opposite trend. [ABSTRACT FROM AUTHOR]

4H-SiC/ SiO 2 interface states play a major role in the performance and reliability of modern 4H-SiC metal–oxide–semiconductor field effect transistors (MOSFETs). To gain new insights into these interface states, we developed a cryogenic measurement technique that uses photon-assisted electron depopulation to probe device performance limiting 4H-SiC/ SiO 2 interface states. This technique enables the characterization of shallow as well as deep states at the 4H-SiC/ SiO 2 interface of fully processed devices using a cryogenic probe station. Our method is performed on n-channel 4H-SiC MOSFET test structures with deposited oxide and postoxidation anneal. We identify conditions under which the electrons remain trapped at 4H-SiC/ SiO 2 interface states and trigger the controlled photon-assisted electron depopulation within a range of photon energies. This allows us to prove the presence of near interface traps, which have previously been found in thermally grown 4H-SiC MOS structures. Our results are supported by device simulations. Additionally, we study the impact of irradiation intensity and light exposure time on the photon-induced processes. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of volume traps intentionally introduced into a silicon-on-insulator (SOI) substrate by inserting a layer of polysilicon beneath buried oxide. In radio frequency applications, this type of substrate, referred to as trap-rich, is known to considerably reduce the generation of harmonics resulting from the parasitic non-linear charge dynamics introduced by the substrate handler under the buried oxide. This analysis focuses on a test vehicle in the form of an integrated coplanar waveguide on two types of substrates, namely, high-resistivity SOI substrates with and without a trap-rich layer. From a modeling point of view, a simulation methodology is implemented in order to convert the 3D simulation of the coplanar waveguide into a 2D treatment that takes into account the wave propagation effect associated with the distributed nature of the transmission line. As a first step, this modeling strategy is implemented to reproduce the effect of increasing substrate resistivity on 2nd and 3rd harmonic reductions, leading to an excellent agreement with experimental data. Building on this validation of the simulation method, we have opted to simulate the non-linear response of the transmission line on the SOI trap-rich substrate by simplifying the trap distribution model. To avoid the adoption of unverified and strongly process-dependent trap distributions across the bandgap, a midgap monovalent trap density has been introduced, either acceptor or donor density. A monovalent density of acceptor traps with a concentration of 1016 cm−3 and a carrier lifetime of 0.1 ns has been shown to reproduce the experimental data very accurately with a substantial reduction in 2nd and 3rd harmonics. A detailed analysis of the displacement current waveforms explains the beneficial role of acceptor traps compared with donor traps. [ABSTRACT FROM AUTHOR]

Ultra-thin solar cells display high intrinsic radiation tolerance, making them interesting for space applications. This study investigates the dependence of the open-circuit voltage degradation and overall current–voltage behavior of devices with 80 nm thick GaAs absorber layers, on their absorber layer doping concentration and the radiation type used to introduce damage. The radiation types used were 1 MeV electrons and 20 keV, 100 keV, and 1 MeV protons. It is shown that the open-circuit voltage degradation rate increases with absorber layer doping concentration. This is linked to the increase in trap-assisted tunneling enhancement of the recombination rate, facilitated by the increase in electric field strength in the absorber layer with doping concentration. Trap-assisted tunneling is also found to contribute to the high local ideality factors observed in these devices, exceeding values of 2, and to be responsible for the trend of an increasing ideality factor with doping concentration. The significant role of trap-assisted tunneling in the devices is established through fitting of dark current–voltage data using a custom recombination–generation model. An open-circuit voltage degradation rate and local ideality factor curves are also shown to vary with radiation type, despite accounting for their differences in non-ionizing energy loss. This is corroborated by corresponding trends in carrier lifetime damage constants, extracted from the fitting of the dark current–voltage curves. This suggests that the introduction or behavior of radiation damage differs between ultra-thin and conventional, thicker solar cells, where non-ionizing energy loss theory tends to be reliable, especially over the studied proton energy range. [ABSTRACT FROM AUTHOR]

Loading of WS2 can greatly improve water splitting H2 generation efficiency of CdS in experiments. Here, we constructed WS2/CdS(100) and WS2/CdS(110) heterostructures with smaller mismatches and explored their interaction energy and band offset by first-principles calculations. Our calculation suggests that the WS2/CdS(100) interface with a stronger binding energy is more active in experiments, while the WS2/CdS(110) interface is metastable. The band alignment between CdS and WS2 is highly dependent on the orientation of the interfaces, and WS2/CdS(100) and WS2/CdS(110) belong to type-I and type-II band alignments, respectively. Therefore, a metal electrode and hole scavenger may be essential in experiments to help WS2/CdS(100) efficiently trap electrons, and a suitable substrate and an appropriate growth temperature are also needed to composite the CdS(110) surface to achieve a higher photocatalytic efficiency. In addition, we performed a detailed analysis of the macroscopic average potential and found that the calculated accuracy of potential difference across the heterostructures due to slab thickness is less than 80 meV at WS2/CdS interfaces. In total, our calculations not only explain the physical reasons for the increased efficiency of WS2/CdS, but also provide a detailed guideline for the design of a more efficient synergistic catalyst. [ABSTRACT FROM AUTHOR]

A ledge feature in the capacitance–voltage (CV) profiles of Ga2O3 MOS (metal–oxide–semiconductor) capacitors is investigated using UV-assisted CV measurements. A model is presented whereby the capacitance ledge is associated with carrier trapping in deep-level states at the Al2O3/Ga2O3 interface. Following UV assisted emptying of interface traps at a constant bias, a voltage ramp toward flatband results in a CV ledge when the trap recombination current becomes equal to the quasi-static sweep charging current. The ledge continues until all the traps below the corresponding pinned surface potential have been filled. Varying the UV energy varies the ledge voltage range and allows a density of states to be determined as a function of energy. A broad interface state peak with maximum density ∼8 × 1012 cm−2 eV−1 for deep trap energies lying between 2.4 and 4.1 eV below the conduction band (CB) edge is extracted. Using the conductance method, the interface trap density is also found to rise toward the CB edge in the range 0.25–0.45 eV below the CB edge, reaching a maximum density of ∼1 × 1012 cm−2 eV−1. Combining these two techniques, an interface trap distribution is estimated for almost the entirety of the bandgap of Ga2O3. This novel technique probes deep interface states where standard methods fail to quantify interface states reliably. [ABSTRACT FROM AUTHOR]

The ultra-wide bandgap of gallium oxide provides a rich plethora of electrically active defects. Understanding and controlling such defects is of crucial importance in mature device processing. Deep-level transient spectroscopy is one of the most sensitive techniques for measuring electrically active defects in semiconductors and, hence, a key technique for progress toward gallium oxide-based components, including Schottky barrier diodes and field-effect transistors. However, deep-level transient spectroscopy does not provide chemical or configurational information about the defect signature and must, therefore, be combined with other experimental techniques or theoretical modeling to gain a deeper understanding of the defect physics. Here, we discuss the current status regarding the identification of electrically active defects in beta-phase gallium oxide, as observed by deep-level transient spectroscopy and supported by first-principles defect calculations based on the density functional theory. We also discuss the coordinated use of the experiment and theory as a powerful approach for studying electrically active defects and highlight some of the interesting but challenging issues related to the characterization and control of defects in this fascinating material. [ABSTRACT FROM AUTHOR]

We present a technique for measuring the interactions between pairs of colloidal particles in two optical traps. This method is particularly suitable for measuring strongly attractive potentials, an otherwise challenging task. The interaction energy is calculated from the distribution of inter-particle separations by accounting for the contribution from the optical traps with arbitrary trap profiles. The method is simple to implement and applicable to different types of pair potentials and optical trapping geometries. We apply the method to measure dipolar pair interactions in experiments with paramagnetic colloids in external magnetic fields. We obtain consistent and accurate results in all regimes, from strongly attractive to repulsive potentials. By means of computer simulations, we demonstrate that the proposed method can be successfully applied to systems with complex pair interactions characterized by multiple attractive and repulsive regimes, which are ubiquitous in soft and biological matter. [ABSTRACT FROM AUTHOR]

We report the electrical properties, deep trap spectra, and diffusion lengths of non-equilibrium carriers in Ni Schottky diodes and NiO/Ga2O3 heterojunctions (HJs) prepared on the same n−/n+ β-Ga2O3 epi structures. The heterojunctions decrease the reverse current of Ga2O3 high-power rectifiers. In HJs, in contrast to Schottky diodes, the capacitance and AC conductance show a prominent frequency and temperature dependence, suggesting the presence of two temperature activation processes with activation energies of 0.17 and 0.1 eV. The deep trap spectra of the Schottky diodes and HJs differ by the absence in the HJ of deep electron traps E2* with level near Ec − 0.7 eV considered to be an important center of non-radiative recombination. This correlates with the observed increase in the diffusion length of non-equilibrium charge carriers in the HJs to 370 nm compared to 240 nm in the Schottky diodes. The diffusion length of charge carriers in p-NiO was found to be quite short, 30 nm. Possible reasons for the observed differences and possible origin of the minority-trap-like feature commonly reported to be present in the deep level spectra of HJs and also observed in our experiments are discussed. [ABSTRACT FROM AUTHOR]

Glow-in-the-daylight is a fascinating luminescence phenomenon displayed by certain storage phosphors that emit ultraviolet light upon being stimulated by ambient lighting. In this study, we investigate the influence of indoor lighting on the glow-in-the-daylight emission of a co-doped garnet phosphor, Y3Al5O12:Pr3+,Eu3+, known for its deep trap that effectively retains energy. Our experimental results demonstrate an interesting observation that, following x-ray radiation at room temperature, this phosphor exhibits negligible persistent luminescence in darkness but emits intense ultraviolet light peaking at 318 nm under indoor lighting conditions. This emphasizes the crucial role played by ambient lighting in releasing stored energy. Our findings not only shed light on the influence of indoor illumination dose and spectral distribution on the persistently stimulated luminescence but also expand our exploration to various ultraviolet phosphors with deep traps, with the aim of uncovering novel materials applicable in glow-in-the-daylight scenarios. [ABSTRACT FROM AUTHOR]

Nanowires (NWs) composed of 2,4-bis[(4-diethylamino)-2-hydroxyphenyl] squaraine were prepared by evaporation-induced self-assembly (EISA). NWs were ∼560 nm wide (aspect ratios: 10–90). X-ray diffraction analysis indicated polymorphism (monoclinic/triclinic). Optical data reported the triclinic phase with energetic disorder. Given the favorable alignment of the Au work function and squaraine HOMO energy, symmetric, unipolar metal–insulator–metal devices were formed by the EISA of NW meshes on inter-digitated Au electrodes. Room temperature DC I–V characteristics displayed hysteretic I–V loops, indicating memristive behavior. At low bias, data indicated Ohmic transport with carrier extraction facilitated by thermionic emission. At high biases, devices exhibited space-charge-limited conduction in the presence of shallow traps. At 77 K, data indicated Ohmic transport at low bias with carrier extraction by thermionic emission while, at high biases, trap-limited space-charge-limited conduction in the presence of traps distributed in energy, with carrier extraction by Fowler–Nordheim tunneling, was observed. The I–V hysteresis was eliminated at 77 K and attenuated by fast scan rates at room temperature, suggesting that carrier trapping/de-trapping underpinned the hysteresis. In impedance measurements, the device response fitted a Randles equivalent circuit indicating purely electronic conduction. By applying voltage waveforms, I–V hysteresis and analog resistive switching (memristive) functionality were observed. Device conductance could be increased sweep by sweep, giving conductance tuning through distinct states, with wait time- or voltage-erase options, consistent with trap filling/emptying effects. Repeated erase–write–read of multiple distinct states over many voltage cycles during continuous use in air was demonstrated. Finally, synaptic functions, e.g., pulse-dependent plasticity, and short- to long-term memory transition, were successfully emulated. [ABSTRACT FROM AUTHOR]

Photomultiplication-type organic photodetectors (PM-OPDs) have been stimulating more and more researchers' interest owing to their extremely high external quantum efficiency (EQE). To prepare high-performance PM-OPDs with a broadband spectral response range from visible to near-infrared and investigate the role of energy levels of the donor and acceptor on its responsiveness, the non-fullerene acceptor Y6 was added into the P3HT:PC71BM system in this work. The photomultiplication phenomenon with the highest EQE has been achieved under both forward and reverse bias when the ratio of Y6 in two acceptors approaches 80 wt. %. The introduction of Y6 not only promotes the formation of moderate hole traps in the active layer but also results in an appropriate amount of low injection barriers to allow more electron injection from the external circuit. Therefore, the spectral response of the device with 80 wt. % Y6 has been broadened from 750 to 950 nm, and the champion EQE of 15 691% at 10 V and 7639% at −20 V at 850 nm was achieved. This work reveals the importance of hole-trapping ability determined by the energy level difference between the donor and the acceptor for the selection of the multiplication system and provides a scheme for the design of high-performance broadband PM-OPDs. [ABSTRACT FROM AUTHOR]

Hafnium oxide (HfO2) has been explored as high-κ gate dielectrics in scaled CMOS devices, artificial synapses to be used in neuromorphic computing to achieve brain-like functionalities, a storage layer in memory devices, a piezoelectric energy harvester, and a photodetector. In this article, the origin of a native defect present in the HfO2 thin films on silicon is experimentally probed using deep level transient spectroscopy (DLTS) technique. It was realized that defects (predominantly oxygen vacancies) in HfO2 segregate near the Si/HfO2 interface. The interfacial and bulk HfO2 trap charges are communicating through the tunneling/ hopping, and, finally, they are emitted to the respective bands of silicon depending on the silicon used. We have observed four prominent defect states, and we believe that all these belong to oxygen vacancies in different charge states. The activation energies of trap states are in the range of 1.22–2.02 eV from the HfO2 conduction band edge, and they fall in front of the Si bandgap in the band alignment of the Al/HfO2/Si gate stack. The capture cross sections of these traps are measured with insufficient filling DLTS and found to be of the order of 10−19 cm2. The results provide valuable insights into realizing the behavior of oxygen vacancy-related deep defects in HfO2 and guide their possible impact on the device performance. [ABSTRACT FROM AUTHOR]

Most semiconductors exhibit a saturation of free carriers when heavily doped with extrinsic dopants. This carrier saturation or "doping limit" is known to be related to the formation of native compensating defects, which, in turn, depends on the energy positions of their conduction band minimum and valence band maximum. Here, we carried out a systematic study on the n-type doping limit of GaAs via ion implantation and showed that this doping limitation can be alleviated by the transient process of pulsed laser melting (PLM). For n-type doping, both group VI (S) and amphoteric group IV (Si and Ge) dopants were implanted in GaAs. For comparison, p-type doping was also studied using Zn as the acceptor. Implanted dopants were activated by the PLM method, and the results are compared to rapid thermal annealing (RTA). Our results reveal that for all n-type dopants, while implantation followed by the RTA results in a similar saturation electron concentration of 2–3 × 1018 cm−3, the transient PLM process is capable of trapping high concentration of dopants in the substitutional site, giving rise to a carrier concentration of >1019 cm−3, exceeding the doping limit of GaAs. However, due to scatterings from point defects generated during PLM, the mobility of n-type GaAs after PLM is low (∼80–260 cm2/V s). Subsequent RTA after PLM (PLM + RTA) is able to remove these point defects and recover the mobility to ∼1000–2000 cm2/V s. The carrier concentrations of these PLM + RTA samples are reduced but are still a factor of 3 higher than RTA only GaAs. This can be understood as the dopants are already incorporated in the substitutional site after PLM; they are less likely to be "deactivated" by subsequent RTA. This work is significant to the understanding of doping mechanisms in semiconductors and provides a means for device applications, which require materials with ultra-high doping. [ABSTRACT FROM AUTHOR]

Using the novel process of hot N+-ion implantation at 800 °C into Si quantum dots (Si-QDs) with approximately 3.2 nm fabricated by hot Si+-ion implantation into an SiO2 layer and post-Ar annealing, we experimentally demonstrated that the photoluminescence intensity (IPL) of the Si-QDs increased with increasing N+-ion dose (D N + ). Post-N2 high-temperature annealing without hot N+-ion implantation, as a reference process, also increased the IPL of Si-QDs, because N atoms trapped within Si-QDs, which was evaluated by secondary ion mass spectrometry, terminate the dangling bonds within Si-QDs and at the Si/SiO2 interface. Additionally, the IPL of Si-QDs showed the maximum value at the optimal D N + of 5 × 1015 cm−2, which was 1.4-fold higher than that observed without hot N+-ion implantation. With a short post-annealing time (<60 min), the increase in IPL owing to N+-ion implantation was considerably larger than that caused by N2 annealing, which is likely due to the efficiency of the termination of the dangling bonds of the Si-QDs by the N+-ions. This is an advantage of the hot N+-ion implantation technique. Forming gas annealing after furnace annealing also induced a larger IPL than that observed before forming gas annealing. However, the maximum IPL observed after forming gas annealing was completely independent of the conditions of furnace annealing and D N + . This suggests that the perfect termination of the dangling bonds of the Si-QDs may be realized via forming gas annealing after furnace annealing. [ABSTRACT FROM AUTHOR]

In this paper, we report an analysis of reverse current mechanisms observed in GaN Schottky barrier diodes leading to hysteretic behavior of the I–V curves at low temperature. By means of DC measurements from 33 to 475 K, we demonstrate the presence of two leakage mechanisms when comparing the experiments with the results obtained using a unified model to predict the ideal reverse current of the diode. Poole–Frenkel emission is the dominant mechanism for temperatures above 200 K, while trap-assisted tunneling prevails for lower temperatures, where also, hysteresis cycles are revealed by means of DC dual-sweep voltage measurements. The energy of the corresponding traps has also been determined, being around 0.2 and 0.45 eV, respectively. The hysteresis phenomenon is attributed to the bias-induced occupancy of the energy states originating the leakage-current processes, which leads to the reduction of the reverse current after a high negative voltage is applied to the diode. [ABSTRACT FROM AUTHOR]

We have analyzed and modeled the reverse-biased gate leakage current in a Schottky-gate AlGaN/GaN high electron mobility transistor. While the Poole–Frenkel emission current along conductive threading dislocations dominates at low negative gate bias, the trap-assisted tunneling of thermally energized electrons and the thermal emission of electrons from threading dislocations aided by dislocation-related states at multiple energy levels within the AlGaN bandgap are dominant at moderate to large reverse bias. Additionally, deep trap levels of high density localized near the gate/AlGaN interface cause significant leakage at 473 K at low to moderate reverse bias, which could be specific to the device we have analyzed. We extracted about 10 12 cm − 2 traps near the AlGaN/GaN interface from the difference of the barrier layer electric field profile obtained from the experimental high-frequency capacitance–gate voltage and the one needed for final matching. The thermionic- and the thermionic field-emission currents are considerably low; the latter, however, dominates in the defect-free case. Finally, the simulation framework we developed here helped us identify various conduction mechanisms contributing to the reverse-biased gate leakage and the density and electronic structure of the responsible defects. [ABSTRACT FROM AUTHOR]

Strain plays an important role in the performance and reliability of AlGaN/GaN high electron mobility transistors (HEMTs). However, the impact of strain on the performance of proton irradiated GaN HEMTs is yet unknown. In this study, we investigated the effects of strain relaxation on the properties of proton irradiated AlGaN/GaN HEMTs. Controlled strain relief is achieved locally using the substrate micro-trench technique. The strain relieved devices experienced a relatively smaller increase of strain after 5 MeV proton irradiation at a fluence of 5 × 1014 cm−2 compared to the non-strain relieved devices, i.e., the pristine devices. After proton irradiation, both pristine and strain relieved devices demonstrate a reduction of drain saturation current (Ids,sat), maximum transconductance (Gm), carrier density (ns), and mobility (μn). Depending on the bias conditions the pristine devices exhibit up to 32% reduction of Ids,sat, 38% reduction of Gm, 15% reduction of ns, and 48% reduction of μn values. In contrast, the strain relieved devices show only up to 13% reduction of Ids,sat, 11% reduction of Gm, 9% reduction of ns, and 30% reduction of μn values. In addition, the locally strain relieved devices show smaller positive shift of threshold voltage compared to the pristine devices after proton irradiation. The less detrimental impact of proton irradiation on the transport properties of strain relieved devices could be attributed to reduced point defect density producing lower trap center densities, and evolution of lower operation related stresses due to lower initial residual strain. [ABSTRACT FROM AUTHOR]

This study explores the nature, dynamics, and reactivity of the photo-induced charge separated excited state in a Fe3+-doped titanium-based metal organic framework (MOF), xFeMIL125-NH2, as a function of iron concentration. The MOF is synthesized with doping levels x = 0.5, 1 and 2 Fe node sites per octameric Ti-oxo cluster and characterized by powder x-ray diffraction, UV-vis diffuse reflectance, atomic absorption, and steady state Fe K-edge X-ray absorption spectroscopy. For each doping level, time-resolved X-ray transient absorption spectroscopy studies confirm the electron trap site role of the Fe sites in the excited state. Time scan data reveal multiexponential decay kinetics for the charge recombination processes which extend into the microsecond range for all three concentrations. A series of dye photodegradation studies, based on the oxidative decomposition of Rhodamine B, demonstrates the reactivity of the charge separated excited state and the photocatalytic capacity of these MOF materials compared to traditional heterometal-doped semiconductor photocatalysts. [ABSTRACT FROM AUTHOR]

Bipolar gradual resistive switching was investigated in ITO/InGaZnO/ITO resistive switching devices. Controlled intrinsic oxygen vacancy formation inside the switching layer enabled the establishment of a stable multilevel memory state, allowing for RESET voltage control and non-degradable data endurance. The ITO/InGaZnO interface governs the migration of oxygen ions and redox reactions within the switching layer. Voltage–stress-induced electron trapping and oxygen vacancy formation were observed before conductive filament electroforming. This device mimicked biological synapses, demonstrating short- and long-term potentiation and depression through electrical pulse sequences. Modulation of post-synaptic currents and pulse frequency-dependent short-term potentiation were successfully emulated in the InGaZnO-based artificial synapse. The ITO/InGaZnO/ITO memristor exhibited spike–amplitude-dependent plasticity, spike–rate-dependent plasticity, and potentiation–depression synaptic learning with low energy consumption, making it a promising candidate for large-scale integration. [ABSTRACT FROM AUTHOR]

The formation of electron and hole traps in semiconductors via atomistic defects is the fundamental microscopic mechanism for tuning the electronic and photonic properties of these materials. Here we find in experiments that bismuth atoms doped into anatase TiO2 as substituents can appear as paired diatomic defects. Through first-principles density functional theory calculations, we reveal that the observed bismuth pair is separated by a medium distance of 6.37 Å through a delicate balance of Pauli repulsion and effective attractive interaction. We further clarify that the effective attractive interaction is related to the exchange coupling between the two bismuth defect states, which also leads to the formation of a spin singlet electronic state of the two unpaired electrons. Our study brings up a new type of defect state in TiO2, and motivates further experimental and theoretical studies of multi-electronic states in materials. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal chalcogenides (2D TMCs) like MoS2, WS2 etc., have established significant dominance in the field of nanoscience and nanotechnology, owing to their unique properties like strong light–matter interaction, high carrier mobility, large photo-responsivity etc. Despite the widespread utilization of these binary TMCs, their potential in the advancement of the optoelectronic research is limited due to the constraints in band tuning and charge carrier lifetime. To overcome these limitations, ternary transition metal chalcogenides have emerged as promising alternatives. Although, the optical properties of these materials have never been explored properly. Herein, we have investigated one such promising member of this group, Cu2MoS4 (CMS) using both steady state and time-resolved spectroscopic techniques. The material exhibits a broad range of visible light absorption, peaking at 576 nm. Photoluminescence spectroscopy confirmed the presence of both band gap emission and trap state-mediated emissions. Transient absorption spectroscopy unraveled the excited state charge carrier dynamics of CMS in sub-ps timescale, upon irradiation of visible light. We found significant influence of the trap mediated recombination, while Auger process being dominant at high charge density. We extended our study in a wide temperature range (5–300 K), which reveals the impact of electron-phonon coupling strength on the band gap and charge carrier dynamics of this material. This detailed study would draw more attention toward the unexplored optical properties of ternary 2D chalcogenides and will open new avenues for the construction of 2D material-based optical devices. [ABSTRACT FROM AUTHOR]

Carbon-based Materials have been extensively researched for their prospect in the fields of environment and energy, especially for graphene oxide (GO). In this work, a novel sodium dodecyl sulfate (SDS)-assisted synthesis of BiOBr/Bi2WO6/GO ternary composite has been synthesized successfully by a handy hydrothermal method. Photoluminescence, Photocurrent, Electrochemical Impedance Spectroscopy, surface photovoltage and transient photovoltage measurements illustrate that construction of p-n BiOBr/Bi2WO6 heterojunction leads to the obviously enhancement of charge separation efficiency, and the photogenerated electrons trapped by GO can effectively inhibit the recombination process of photogenerated charge, resulting in the improvement of charge separation efficiency and the longer lifetime of photogenerated carriers for BiOBr/Bi2WO6/GO. The characterization of structure and morphology indicate that role of GO can also improve the visible light absorption range, and the SDS-assisted synthesis can reduce the size of particle in the composite and enhances the specific surface area of the composite by regulating the particle size and agglomeration. Under optimal conditions, BiOBr/Bi2WO6/GO (SDS) has the outstanding photocatalytic degradation performance and the degradation rate constants for oxytetracycline, tetracycline hydrochloride, methylene blue and rhodamine are 0.056, 0.057, 0.103 and 0.414 min−1, respectively. Notably, the degradation rate constants obtained by BiOBr/Bi2WO6/GO (SDS) are more ten times higher than that of pure BiOBr and Bi2WO6. The possible mechanism of photocatalytic degradation was suggested for BiOBr/Bi2WO6/GO based on the dynamic properties of photogenerated charge and reactive oxidation species results. Surprisingly, the recyclability of the BiOBr/Bi2WO6/GO (SDS) composite obtained from the cyclic experiments has laid a foundation for the study of efficient and stable photocatalysts. [ABSTRACT FROM AUTHOR]

The ab initio path integral Monte Carlo (PIMC) method is one of the most successful methods in statistical physics, quantum chemistry and related fields, but its application to quantum degenerate Fermi systems is severely hampered by an exponential computational bottleneck: the notorious fermion sign problem. Very recently, Xiong and Xiong [J. Chem. Phys. 157, 094112 (2022)] have suggested to partially circumvent the sign problem by carrying out simulations of fictitious systems guided by an interpolating continuous variable ξ ∈ [−1, 1], with the physical Fermi- and Bose-statistics corresponding to ξ = −1 and ξ = 1. It has been proposed that information about the fermionic limit might be obtained by calculations within the bosonic sector ξ > 0 combined with an extrapolation throughout the fermionic sector ξ < 0, essentially bypassing the sign problem. Here, we show how the inclusion of the artificial parameter ξ can be interpreted as an effective penalty on the formation of permutation cycles in the PIMC simulation. We demonstrate that the proposed extrapolation method breaks down for moderate to high quantum degeneracy. Instead, the method constitutes a valuable tool for the description of large Fermi-systems of weak quantum degeneracy. This is demonstrated for electrons in a 2D harmonic trap and for the uniform electron gas (UEG), where we find excellent agreement (∼ 0.5 %) with exact configuration PIMC results in the high-density regime while attaining a speed-up exceeding 11 orders of magnitude. Finally, we extend the idea beyond the energy and analyze the radial density distribution (2D trap), as well as the static structure factor and imaginary-time density–density correlation function (UEG). [ABSTRACT FROM AUTHOR]

The luminescence properties of green Ba4Si6O16:Eu2+, rare-earths (RE) (RE = Sc, Y, La and Lu except Pm) phosphors are reported. Their long-lasting phosphorescence is discussed in view of trap depths and concentrations determined from thermally stimulated luminescence experiments. A second emission band centered at 439 nm was evidenced at low temperatures, which stems from the substitution of Eu2+ in the two non-equivalent Ba2+ sites of Ba4Si6O16. The mechanoluminescence properties of Ba4Si6O16:Eu2+, RE phosphors are described, and a new mechanoluminescence mechanism is proposed, in the case where RE = Ho3+, involving a trap distribution from 0.694 to 0.924 eV. Mechanical loading (post UV irradiation) induces a decrease in depth of the trap distribution, leading to an increase of the luminescence intensity, whereas a drop of the luminescence intensity is observed upon unloading, following the faster release of the charge carriers. [ABSTRACT FROM AUTHOR]

Halide perovskite, Bridgman grown single crystals have shown excellent performance for high energy radiation detectors. CsPbBr3 perovskite detectors with 1.4% energy resolution have been demonstrated. These detectors demonstrate a wide range of operations from −2 to 70 °C. Semiconductor hard radiation detectors have been used for applications in defense, medicine, and bioelectronics. In most of these applications, there is a need for the detectors to operate at room temperature and above. Previous hard radiation detector devices have used the material cadmium zinc telluride for room temperature operation [Luke et al., IEEE Trans. Nucl. Sci. 48, 282 (2001)]. There are now other semiconductors that show considerable promise. These include the halide perovskite compound semiconductors with a formula CsPbX3, where X = Cl, Br, I [Liu et al., Proc. SPIE 8852, 88520A (2013); Peters et al., J. Lumin. 243, 118661 (2022)]. These materials are also being developed for other device applications, including light-emitting diodes, lasers, solar cells, and photodetectors. It is claimed that these semiconductors are defect-tolerant, although the reason for this behavior is not well understood. Thermally stimulated current spectroscopy was used to detect electron traps in these materials to improve their performance. The halide compound cesium lead bromide has a bandgap of 2.25 eV, which makes it suitable for room temperature operation and above. They also have high permittivity. These halide perovskite semiconductors have shown room temperature detector device performance. Recently, we demonstrated hard radiation detectors using CsPbBr3 as the device platform. The detectors had 1.4% energy resolution for high-energy γ rays [He et al., Nat. Photonics 15, 36 (2021)]. The detectors demonstrate a wide temperature region from −2 to 70 °C for stable operations. [ABSTRACT FROM AUTHOR]

Indium phosphide is widely used in electronics and photovoltaic devices due to its high electro-optical conversion efficiency, high electron mobility, and good radiation resistance. Defects are the main limitation for the performance of InP devices. In this work, based on hybrid functional with finite size correction, electronic properties of intrinsic and H-related defects have been investigated in InP. We found that PIn defect is the most stable intrinsic defect with the lowest formation energy. Defect signals detected experimentally are defined by our calculated results. Experimentally observed electron traps with the energy level of EC −0.66 eV and EC −0.68 eV are ascribed to the transition level ɛ(−1/−2) and ɛ(−2/−3) of In vacancies. The hydrogenated vacancies in InP have been systematically reported in the present work. Formation energies of H-related defects indicate that hydrogen atoms prefer to bind to In vacancy than P vacancy. The formation energy of In vacancy decreases with the addition of H, while that of P vacancy increases. For hydrogenated In vacancies, it captures fewer electrons than bare In vacancies when the Fermi level is close to CBM. Especially for the VIn −3H structure, it is 0 charge state in all Fermi levels so that it will not tend to capture electron or hole. Our work is helpful to explain experimental phenomena and radiation-induced damages and improve the performance of InP devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The demand for reliable memory devices capable of operating in harsh environments, such as space and vehicles, necessitates the development of high-temperature-resistant technologies. In this study, we propose a novel ferroelectric domain wall (DW) memory utilizing BiFeO3 thin films, which exhibit exceptional retention and fatigue properties at 135 °C. Achieving this performance was made possible through precise control of the oxygen vacancy density in the epitaxial thin films induced by a post-annealing procedure conducted under an appropriate oxygen pressure of 10 Pa. Initially, prototype nano-memory devices lacking post-annealing treatment demonstrated resistive switching behavior at room temperature, with a current rectification ratio of 100:1, achieved by manipulating the uncompensated DW induced by polarization switching. With the additional annealing procedure in lower oxygen pressure, the wall current magnitude of the devices increased significantly, indicating the critical role of the oxygen vacancies in modulating the DW conductivity. Moreover, the nanodevices exhibited improved polarization retention due to oxygen vacancy-mediated charge injection that can be further enhanced at the elevated temperature. The electrons trapped deeply at the artificial DW were found to stabilize the switched polarization at the expense of reduced DW conductivity, emphasizing the importance of precise control over oxygen vacancy density for achieving a balance between high DW conductivity and excellent polarization retention. [ABSTRACT FROM AUTHOR]

Phototransferred thermoluminescence (PTTL) induced from natural calcite using 470, 525, and 405 nm illumination is reported. We consider the measurement and analysis of time-response profiles, the dependence of PTTL intensity on the sample temperature during illumination to induce phototransfer, the role of deep electron traps, and discuss mechanisms for phototransfer in calcite. The conventional TL glow curve is a complex collection of closely overlapping glow peaks, but there are three stand-out ones near 90, 210, and 330 °C, denoted as I–III. These are reproduced under phototransfer. The dependence of PTTL intensity on illumination can be properly described by systems of acceptors and donors, where the number of the latter depends on the preheating temperature. The systems have been analyzed by phenomenological and kinetics models. The intensity of the PTTL is influenced by the illumination temperature, and the attendant thermal assistance and thermal quenching have been quantified. Electronic processes relevant to the PTTL of calcite are thought to involve the relaxation of (CO3)2− and Mn2+ ions. An anomalous increase in PTTL induced from deep electron traps has been deduced to be a possible result of quantum tunneling of charge between (CO3)3− stabilized close to Mn3+ cations. [ABSTRACT FROM AUTHOR]

This document is a collection of research papers on wide- and ultrawide-bandgap electronic semiconductor devices. It focuses on the progress and challenges in developing devices made from wide-bandgap materials like GaN, AlGaN, AlN, Ga2O3, BN, and diamond for power, rf, and photonic applications. The papers cover topics such as improving GaN power devices, exploring new wide bandgap materials, and investigating gate insulator properties. Additionally, there are papers on defect detection, new concepts for wide bandgap devices, and the growth and properties of different materials. The research provides valuable insights for researchers interested in using these materials in electronic devices. [Extracted from the article]

A set of new millimeter-wave diagnostics will deliver unique measurement capabilities for National Spherical Torus Experiment-Upgrade to address a variety of plasma instabilities believed to be important in determining thermal and particle transport, such as micro-tearing, global Alfvén eigenmodes, kinetic ballooning, trapped electron, and electron temperature gradient modes. These diagnostics include a new integrated intermediate-k Doppler backscattering (DBS) and cross-polarization scattering (CPS) system (four channels, 82.5–87 GHz) to measure density and magnetic fluctuations, respectively. The system can access reasonably large normalized wavenumbers kθρs ranging from ≤0.5 to 15 (where ion sound gyroradius ρs = 1 cm and kθ is the binormal density turbulence wavenumber). The system addresses the challenges for making useful DBS/CPS measurements with a remote control of launch polarization (X- or O-mode), probed wavenumber, polarization match of the launch beam with the edge magnetic field pitch angle, and beam steering of the launched beam for wave-vector alignment. In addition, a low-k DBS system consisting of eight fixed frequencies (34–52 GHz) and four tunable frequencies (55–75 GHz) for low-k density turbulence and fast ion physics will be located at a nearby port location. The combined systems cover the near LCFS and pedestal regions (34–52 GHz), the pedestal or mid-radius (50–75 GHz), and core plasmas (82.5–87 GHz). [ABSTRACT FROM AUTHOR]

An edge-confined single-species plasma will relax to create a potential energy hill that climbs from the boundary. This hill represents a potential well for species of the opposite sign and can be a means to confine the second species. With this ultimate application in mind, we have studied the relation between the plasma temperature, the number of confined particles, and the electrostatic potential well that forms in a fully non-neutral plasma of electrons in a trapping volume with an artificially structured boundary (ASB). An ASB is a structure that produces periodic short-range static electric and magnetic fields for confining a plasma. To perform a detailed analysis on this topic, simulations using a particle-in-cell code have been performed. By varying the configurational elements of the ASB, such as the bias on the boundary electrodes and the internal radius of the structure, coupled with a course thermalization process and a prescribed threshold for particle leakage, potential well values were determined for a range of plasma temperatures and confinement conditions. Maximum well depths were observed below a threshold plasma temperature in each configuration. This study gives insight into the limitations of primary particle confinement with this type of structure and optimal conditions for the formation of a potential well that might be utilized to confine a second species. [ABSTRACT FROM AUTHOR]

This work demonstrates a high-performance monolithically integrated GaN inverters platform, which incorporates enhancement-mode (E-mode) and depletion-mode (D-mode) GaN high-electron-mobility transistors (HEMTs) simultaneously using an Al:HfOx-based charge trapping layer. The developed E-mode HEMT exhibits a positive threshold voltage of 2.6 V, a high ON–OFF current ratio of 1.9 × 108, a current density of 376 mA/mm, and an ON-resistance of 15.31 Ω·mm. Moreover, the direct-coupled field-effect-transistor logic (DCFL) GaN inverter was characterized with and without D-mode device threshold voltage (VTH) modulation, demonstrating improved output swing and switching threshold shift by proposed VTH modulation. The optimized DCFL GaN inverter manifests a switching threshold of 2.34 V, a logic voltage output swing of 4.98 V, and substantial logic-low and logic-high noise margins of 2.16 and 2.49 V, respectively, at a supply voltage of 5 V. These results present a promising approach toward realizing monolithically integrated GaN logic circuits for power IC applications. [ABSTRACT FROM AUTHOR]

HgTe nanocrystals (NCs) have unique properties that make them suitable for optoelectronic devices in the mid-wave infrared (MWIR) and short-wave infrared regions. However, electrically active defects can trap charge carriers, reducing their mobility and diffusion length, which degrades the NCs' optical and electrical properties. In this study, we used the thermal admittance spectroscopic (TAS) method to analyze defects in HgTe NC-based photovoltaic devices. The ITO/HgTe/Al device structure was used to study the defect levels in HgTe nanocrystals and the effect of these traps on transport properties. Using low-temperature I–V measurements, we calculated the trap activation energy as 0.14 eV, and the transport was found to occur mainly through these trap states. From the TAS measurements, the trap activation energy obtained was 0.14 eV, and the concentration of trap level was 3.16 × 10 16 cm − 3 eV − 1 . We have also fabricated ITO/ TiO 2 /HgTe/Au and fluorine doped tin oxide/ TiO 2 /HgTe/ MoO 3 /Au devices and did TAS measurements to understand the effect of adding electron and hole extraction layer on the formation of defect levels. Intriguingly, a distinct reversal in the capacitance–frequency (C–F) behavior is observed at different temperatures, leading to positive slopes in the Arrhenius plot. This peculiar phenomenon is attributed to the size-dependent doping effects within the HgTe nanocrystals. The outcomes of this study shed light on the significance of understanding and quantifying electrically active defects in HgTe nanocrystals for the advancement of NC-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Defects in nanostructures play a pivotal role in determining their properties and performance in the desired applications. Herein, the defect states and structural properties of the bi-metal oxide composite of ZnO and α-Fe2O3 (ZF-W) are varied by annealing the composite at different temperatures. The changes in defects, structures, and phase are evaluated thoroughly using transmission electron microscopy, x-ray diffraction, photoluminescence, and Mössbauer spectroscopy techniques. The defect-rich ZF-W composite is found to be composed of defect-deficient ZnFe2O4 attaining the equilibrium state when as-synthesized ZF-W is annealed at 500 °C [ZF-W(500)]. Further annealing at 1000 °C, ZF-W(1000), a non-stoichiometric and highly defected ZnFe2O4 is evidenced in the composite. The changes in the composite with the annealing temperature are correlated with the cationic migration and evolution of defect states. Moreover, the transition associated with the vacancy defects, which trapped the excited electron and dispel the free electrons, thereby inhibiting fast electron–hole pair recombination, is corroborated from the photoluminescence spectra. When implemented for methyl blue adsorption/degradation without the assistance of any external sources, the degradation efficiency of ZF-W, ZF-W(300), ZF-W(500), and ZF-W(1000) is found to be 86%, 84%, 68%, and 82%, respectively. The prepared samples are highly stable and can be used repeatedly without losing effectiveness. The simultaneous evolution of defects and structural properties of the composite are attributed for the variation in methyl blue adsorption/degradation. The present study reveals the importance of defects present in the mixed metal oxide composite in obtaining high-performance dye degradation/adsorption properties for sustainable wastewater treatment. [ABSTRACT FROM AUTHOR]

The energy band structure is crucial for solid insulation research. The traditional thermally stimulated current is used mostly for direct trap estimation but has some limitations, which can be overcome by the space charge decay method. With the help of a modified pulsed-electro acoustic system, we perform the test under different low temperatures and obtain a more comprehensive band spectrum including shallow traps and different polarities. This study chooses isotactic polypropylene (PP) to investigate in a temperature range of −120 to 20 °C. Signal processing and recovery are considered. Two basic trap estimation methods are compared and the one based on the modified isothermal relaxation current theory is used here. The electron and hole trap densities near different electrode interfaces are considered in the experiment. In the preliminary results, it is found that the traps tend to move toward a shallow direction with a decrease in temperature. A model of the retrapping process caused by phonon scattering is put forward to explain the results. The retrapping possibility is, therefore, assumed to follow a power relation with temperature. An attempt to rectify the trap depth is performed on such a model by numerical approximation and reaches the result that the retrapping possibility may be dependent upon the second power of temperature. Finally, the broadband energy spectrum is calculated after correction. In the normalized coordinate system, the traps in PP are mainly distributed in a deep range; few shallow traps are found maybe because the space charge density is low. [ABSTRACT FROM AUTHOR]

High-flux capable semiconductor x-ray detectors are essential in various applications, but the detrimental effects of detector polarization limit their use in many cases. Here, we studied the polarization of perovskite CsPbBr3 semiconductor detectors using ultrahigh flux synchrotron x rays (106–1012 photons s−1 mm−2 at 58.61 keV). The CsPbBr3 detectors did not show immediate polarization prominently until a flux higher than 1010 photons s−1 mm−2. Using the pump-and-probe technique, we visualized the spatial and temporal effects of polarization. The polarized region, represented by reduced photocurrent, extended beyond the area under direct irradiation, and the reduced photocurrent persisted after potential de-polarization treatments. We found that stronger applied electric fields and fewer carrier traps can mitigate polarization, represented by less photocurrent deficit. By examining the detectors' current response under controlled ambient light, low, and high-flux x rays, we studied the trap filling and release behavior of CsPbBr3. We discovered that the polarization is caused by partial detector damage due to deep defects generated by ultrahigh flux x-ray irradiation. Our work provides insight into CsPbBr3 polarization under extremely intense x-ray radiation and shows that reducing crystal defects and increasing detector bias voltage are effective solutions. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots (QDs) are efficient organic photoredox catalysts due to their high extinction coefficients and easily tunable band edge potentials. Despite the majority of the surface being covered by ligands, our understanding of the effect of the ligand shell on organic photocatalysis is limited to steric effects. We hypothesize that we can increase the activity of QD photocatalysts by designing a ligand shell with targeted electronic properties, namely, redox-mediating ligands. Herein, we functionalize our QDs with hole-mediating ferrocene (Fc) derivative ligands and perform a reaction where the slow step is hole transfer from QD to substrate. Surprisingly, we find that a hole-shuttling Fc inhibits catalysis, but confers much greater stability to the catalyst by preventing a build-up of destructive holes. We also find that dynamically bound Fc ligands can promote catalysis by surface exchange and creation of a more permeable ligand shell. Finally, we find that trapping the electron on a ligand dramatically increases the rate of reaction. These results have major implications for understanding the rate-limiting processes for charge transfer from QDs and the role of the ligand shell in modulating it. [ABSTRACT FROM AUTHOR]

The optical properties of non-toxic indium phosphide (InP) quantum dots (QDs) are impinged by the existence of characteristic deep trap states. Several surface engineering strategies have been adopted to improve their optical quality, which has promoted the use of InP QDs for various technological applications. An antithetical approach involves the effective utilization of the deep trap states in InP QDs to modulate back electron transfer rates. Here, we explore the influence of the core-size of InP on their In-to-P stoichiometry and charge transfer dynamics when bound to an acceptor molecule, decyl viologen (DV2+). The mechanism of interaction of InP and DV2+ based on the quenching sphere model established the presence of (i) a 1:1 complex of DV2+ bound on InP and (ii) immobile quenchers in the quenching sphere, depending on the concentration of DV2+. While the forward electron transfer rates from photoexcited InP to bound DV2+ does not substantially vary with an increase in core size, the back electron transfer rates are found to be retarded. Findings from inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) reveal that the In to P ratio is higher for QDs with larger core size, which further brings about increased carrier trapping and a decreased rate of charge recombination. Furthermore, long-lived charge-separated states in DV2+ bound to InP, extending to hundreds of milliseconds, are obtained by varying the number of DV2+ in the quenching sphere of the QDs. [ABSTRACT FROM AUTHOR]

Besides being impacted by quantum confinement effects, the channel electrostatics of ultra-thin-body silicon-on-insulator (SOI) MOS devices, with channel thicknesses less than 10 nm, are also likely to be impacted by interface trap states. In this work, we comprehensively investigated the effect of band edge energy (surface passivation energy) on the band structure of the silicon channel. We propose to utilize this band edge energy (Δ E e d g e ) to study the effect of interface traps on device electrostatics, which is generally used to passivate the channel/oxide interface. First, by using s p 3 d 5 s ∗ semi-empirical tight-binding methodology with a fully passivated interface (Δ E e d g e > --> 5 eV) and by including suitable bandgap correction for different device temperatures, the band structure is obtained, which is solved self-consistently with Poisson's equation to accurately determine the channel electrostatics, without the effect of trap states. Interface trap states are now seen in the band structure through suitably varying the edge energy (− 5 eV < Δ E e d g e < 5 eV) based on which the interface trap density (D i t ) and the interface trap charge density (Q i t ) are determined. Through incorporating Q i t in the boundary condition for solving Poisson's equation self-consistently with the band structure, channel electrostatics is recomputed to analyze the effect of traps for a wide range of device conditions. Finally, the degradation in the integrated charge density due to interface traps is accurately modeled for different SOI channel thickness and device temperatures. [ABSTRACT FROM AUTHOR]

Rolled-up nanomembrane electrodes are used to prepare optically transparent Au / TiO 2 Schottky diodes suitable for deep level transient photocapacitance spectroscopy. It is demonstrated that both the binding energy and the capture cross section of the oxygen vacancy can be extracted from the photocapacitance transients using a rate equation model. The values are consistent with those obtained from conventional deep level transient spectroscopy, taken from the same sample. Furthermore, information about the capture process can be extracted. [ABSTRACT FROM AUTHOR]

Here, glancing angle deposition is employed to synthesize the undoped GeO2 and Mg-doped (0.4 and 0.8 at. %) GeO2 nanowires (NWs) on a Si substrate. The microscopic images show the formation of the NW-like morphology of the grown materials. The gradual decrease in the average ratio of length to diameter depicts the worsening of the formation of NWs with the incorporation of Mg into the GeO2 host lattice. This also affects the crystallinity characteristics of the materials, which have been demonstrated from the selected area electron diffraction (SAED) pattern of the materials. The polycrystallinity nature of undoped GeO2 NWs changes to amorphous due to the introduction of Mg, which has been confirmed from both the obtained SAED and x-ray diffraction patterns of the samples. The presence of Mg was confirmed from the obtained broad bands at 473 and 437 cm−1 in the Fourier transmission spectrum of the doped samples. The increasing conductance with the temperature of Au/undoped GeO2 devices can be explained by the thermionic emission process, whereas the Mg-GeO2 device shows an overall decrease in conductance with increasing temperature. We have ascribed the origin of this abnormal conductance as the positive temperature coefficient of resistance, which is one of the first reports, due to the generation of random grain boundaries and enormous electron trapping at the Au/Mg-GeO2 NW junction. Furthermore, the undoped GeO2 NW device shows good temperature-dependent conductivity as well as stability compared to the doped one. [ABSTRACT FROM AUTHOR]

Impacts of spatial charge inhomogeneities on carrier transport fluctuations and premature breakdown were investigated in Schottky ampere-class Ga2O3 power diodes. Three prominent electron traps were detected in Ga2O3 epilayers by a combination of the depth-resolved capacitance spectroscopy profiling and gradual dry etching. The near-surface trap occurring at 1.06 eV below the conduction band minimum (EC), named E3, was found to be confined within a 180 nm surface region of the Ga2O3 epilayers. Two bulk traps at EC − 0.75 eV (E2*) and at EC − 0.82 eV (E2) were identified and interconnected with the VGa- and FeGa-type defects, respectively. In the framework of the impact ionization model, employing the experimental trap parameters, the TCAD simulated breakdown characteristics matched the experimental breakdown properties well, consistently with inverse proportionality to the total trap densities. In particular, the shallowest distributed E3 trap with the deepest level is responsible for higher leakage and premature breakdown. In contrast, Ga2O3 Schottky diodes without E3 trap exhibit enhanced breakdown voltages, and the leakage mechanism evolves from variable range hopping at medium reverse voltages, to the space-charge-limited conduction at high reverse biases. This work bridges the fundamental gap between spatial charge inhomogeneities and diode breakdown features, paving the way for more reliable defect engineering in high-performance Ga2O3 power devices. [ABSTRACT FROM AUTHOR]

Stimulated Brillouin scattering (SBS) has complex dependence on the plasma electron temperature via the Landau damping, particle trapping, and consequent nonlinear frequency shift. It is found from our numerical simulation that the SBS reflectivity in its saturation stage tends to increase with the plasma electron temperature within a certain range, although the linear growth rate of SBS normally reduces with the increasing electron temperature. This is because the phase velocity of an ion acoustic wave (IAW) increases with the electron temperature, which tends to reduce the Landau damping of the IAWs and hence reduce ion trapping. In the nonlinear saturation stage, ion trapping will modify the ion distribution function and induce a negative frequency shift in the IAW. This nonlinear frequency shift will break the three-wave coupling, thereby causing saturation of the SBS. With further increase in the electron temperature, however, electron trapping will dominate over ion trapping, which induces a positive frequency shift in the IAW and can lead to the SBS saturation as well. As a result, the SBS reflectivity first increases and then decreases with increase in the electron temperature. At around the peak of the SBS reflectivity, the positive frequency shift of IAW induced by electron trapping roughly offsets the negative frequency shift induced by ion trapping. [ABSTRACT FROM AUTHOR]

Degradation and trap evolution in NiO/β-Ga2O3 heterojunction pn diodes under on-state electrical stress were investigated in this work using deep-level transient spectroscopy measurements and density functional theory (DFT) calculations. The decrease in turn-on voltage and forward current appears to correlate with an increase in the concentration of the compensating acceptor-like traps. From the energy level of EV + 1.3 eV, the corresponding acceptor-like traps can be attributed to the Ga vacancy complex with hydrogen (VGa-H). Interestingly, accompanied by the increase in VGa-H concentration, the self-trapped holes (STH) originally passivated by H may gradually recover. DFT calculations show a monotonous decrease in energy, suggesting the spontaneous diffusion of hydrogen from STH passivated sites to the adjacent VGa, which are generated under stress. This phenomenon leads to the recovery of STH and the generation of VGa-H. This investigation offers new insights into the degradation mechanisms of β-Ga2O3-based devices under electrical stress. [ABSTRACT FROM AUTHOR]

The generation of abrasive particles is an unavoidable consequence of sliding electrical contact wear in conductive slip rings (SRs). The adhesion of abrasive particles to the insulators may lead to a decrease in flashover voltage, posing a risk to satellite power transmission. In this paper, the effect of abrasive particles on flashover is first studied. Surface abrasive particles can distort the surface electric field of the dielectric, absorb scattered electrons, and then re-emit them, thereby accelerating the development and formation of secondary electron avalanches. Flashover test results indicate that surface abrasive particles lead to a significant reduction in flashover voltage. To mitigate the impact of particle adhesion on flashover, a method of constructing particle traps on the surface of insulators is proposed. The location and structural parameters of the particle trap are further optimized and determined. The flashover test results using planar dielectric samples and SR insulator samples both demonstrate that the optimized particle trap can significantly improve the flashover voltage. The dielectric maintains high electrical strength even when particles are trapped in particle traps. The physical details of the impact of particles on flashover and the effect of particle traps are analyzed utilizing an electron movement simulation, corroborating the experiment from a microscopic aspect. [ABSTRACT FROM AUTHOR]

Trapped ions for quantum information processing have been an area of intense study due to the extraordinarily high fidelity operations that have been reported experimentally. Specifically, barium trapped ions have been shown to have exceptional state-preparation and measurement fidelities. The 133Ba+ (I = 1/2) isotope in particular is a promising candidate for large-scale quantum computing experiments. However, a major pitfall with this isotope is that it is radioactive and is thus generally used in microgram quantities to satisfy safety regulations. We describe a new method for creating microgram barium chloride (BaCl2) ablation targets for use in trapped ion experiments and compare our procedure to previous methods. We outline two recipes for the fabrication of ablation targets that increase the production of neutral atoms for isotope-selective loading of barium ions. We show that heat-treatment of the ablation targets greatly increases the consistency at which neutral atoms can be produced, and we characterize the uniformity of these targets using trap-independent techniques such as energy dispersive x-ray spectroscopy and neutral fluorescence collection. Our comparison between fabrication techniques and the demonstration of consistent neutral fluorescence paves a path toward reliable loading of 133Ba+ in surface traps and opens opportunities for scalable quantum computing with this isotope. [ABSTRACT FROM AUTHOR]