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Photostimulated luminescence (PSL) is observed in BaBrCl: Eu2+ after X-ray irradiation at room temperature. It is suggested by PSL stimulation spectrum and difference absorption spectrum (DAS) that F centers are formed upon X-ray irradiation and both spectra show two bands which are centered at about 550 nm and 675 nm respectively. This enables the use of semiconductor light-emitting diodes (LED) instead of gas lasers for photostimulation. The PSL intensity increases linearly with X-ray irradiation dose increasing, and the conversion efficiency is 29% that for the standard commercial storage phosphor BaFBr:Eu from Fuji imaging plate. [ABSTRACT FROM AUTHOR]

SiC devices exhibit a number of detrimental second order effects which are caused by electrically active traps. The majority of studies into traps in SiC devices have been for SiC metal-oxide-semiconductor (MOS) devices. Other devices, such as the SiC Schottky diode, have been investigated less. However, traps can still impact SiC Schottky diodes; carrier exchange with traps can create greater-than-unity ideality factors and can cause barrier height instability. Understanding these effects is important for the continued improvement of diode performance and for device/circuit modeling purposes. Therefore, this paper reviews the state of knowledge for traps in SiC Schottky diodes. We also comment on practical impacts of these effects, techniques for detection/measurement, and alternative models where appropriate. [ABSTRACT FROM AUTHOR]

Abstract: Electrical characterizations have been performed on porous low-k SiOCH dielectric used in the 45nm technology. The present paper demonstrates that the conduction follows the Poole–Frenkel (PF) mechanism at medium and high fields. The apparent deviation from the PF mechanism at high field is explained by the trapping phenomenon due to the large amount of defects in the dielectric. This trapping deforms the band diagram and lowers the electron injection within the dielectric. A study of two key process steps is also performed and shows that the dominant conduction mechanism localization (bulk versus interface) is not necessarily at the origin of the breakdown mechanism. [Copyright &y& Elsevier]

Abstract: Dye sensitized solar cells based on annealed titanium dioxide films prepared by oblique reactive DC magnetron sputtering have been investigated in detail. Electron transport and recombination were studied using intensity-modulated photocurrent and photovoltage spectroscopy. Electron transport time as well as lifetime were found to increase upon lowering of the light intensity and to increase upon increasing the thickness of the TiO2 film. The properties are very similar to those observed for solar cells based on colloidal TiO2 films despite the morphologies being very different. In all cases, films are composed of a porous assembly of TiO2 nanocrystals. Grain boundaries with associated trap and/or energy barriers may explain the observed transport properties. [Copyright &y& Elsevier]

Three-dimensional architecture appears today to be essential for the next high-density metal-insulator-metal (MIM) capacitor generation. Thus, the classical physical vapor deposition method usually used for the electrode deposition must be replaced by more conformal deposition methods, like chemical vapor deposition (CVD) method. In this paper, trapping phenomenon of MIM capacitors using CVD-TiN for electrodes and atomic layer deposition Al2O3 for insulator is studied, when integrated in planar and in 3-D MIM devices. In particular, we demonstrate the correlation between the plasma post-treatment (PT) applied to the CVD-TiN layer to ensure its low resistivity and the charge trapping in the alumina. Moreover, while applying the Di Maria method to those MIM structures, we demonstrate that charges trapped are electrons, which are located near the metal/insulator interfaces. Based on previous paper, an explanation of the origin of this trapping phenomenon is also proposed. Finally, we demonstrate that the plasma PT does not penetrate correctly into the trenches, suggesting that CVD method for the TiN electrode deposition is not suitable for high-aspect-ratio 3-D devices. [ABSTRACT FROM PUBLISHER]

Abstract: The photoreactivity of TSP, a microporous titanosilicate with the pharmacosiderite structure consisting of nanoclusters of titania octahedra linked through silicate tetrahedra, has been studied by EPR spectroscopy. UV irradiation of TSP in the presence of O2 produces the EPR signal of holes trapped at oxide ion sites (O−). This is attributed to the scavenging of electrons by O2. The trapped holes in TSP are much more stable than the corresponding species in TiO2. Reaction of O2 with O− to form is also observed. Trapped holes can be seen as well when TSP is irradiated in the presence of adsorbed CO2, which can also act as an electron scavenger. [Copyright &y& Elsevier]

Electron trapping in high- gate dielectrics under constant voltage stress is investigated. It is suggested that the electron trapping occurs through a two-step process: resonant tunneling of the injected electron into the preexisting defects (fast trapping) and thermally activated migration of trapped electrons to unoccupied traps (slow trapping). Characteristics of the electron traps extracted based on the proposed model are in good agreement with the calculated properties of the negatively charged oxygen vacancies. The model successfully describes low-temperature threshold voltage instability in NMOS transistors with /TiN gate stacks. [ABSTRACT FROM PUBLISHER]

We describe our recent work on all-optical serial-to-parallel converters (SPCs), from the all-optical switches employed in the SPCs to the application of the SPCs for packet processing. The ability to handle ultrafast optical signals is enabled by types of surface-normal optical switches employing different switching mechanisms: one is based on rapid electron trapping in low-temperature-grown Be-doped quantum wells, and the other is based on differential spin-excitation. With these switches, 1:16 SPCs are demonstrated for 40-Gbit/s, 100-Gbit/s, and 1-Tbit/s optical packets. In addition, the SPC is compact, low power, polarization insensitive, exhibits extremely high on/off ratios, and generates a simultaneous parallel output, and thus, provides a promising interface device allowing the processing of ultrafast, asynchronous optical packets in a highly functional complementary metal-oxide-semiconductor (CMOS) processor. As an application, an optical label swapper that integrates the SPC with a CMOS processor is also demonstrated for 40-Gbit/s asynchronous optical packets [ABSTRACT FROM PUBLISHER]

A Penning trap consisting of concentric ring electrodes on a substrate and a magnetic field perpendicular to the substrate plane has been loaded with electrons. In order to demonstrate the performance of the trap we have measured the motional frequencies of the trapped electrons. Frequencies, line shape and width agree well with simulations. Miniaturization of the device is at hand which opens novel possibilities for application in quantum computing. [ABSTRACT FROM AUTHOR]

A radial inhomogeneous magnetic field produced by counter-propagating currents in anti-Helmholtz configuration coils has been superimposed to a Penning trap. The confinement properties of electrons in such a trap have been studied experimentally. Without the radial B-field we find a number of operating conditions where instabilities occur, arising from higher order contributions to the quadrupolar trapping field. When we apply the radial field the trap properties remain essentially unchanged until the strength of this field at the boundary of the electron cloud is of the same order as the homogeneous Penning field. Then a sudden breakdown in the confinement appears. The experiments have been performed in low magnetic fields. The equations of motions of the trapped particles can be cast in a dimensionless form and our results can be considered as independent of the field strength. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Ge surface nitridation on Ge/HfO2/Al MOS capacitors has been studied. Low-frequency measurements indicated the presence of significant interface states in surface nitrided devices. As temperature decreased from 300 to 140 K, electron trapping increased monotonically in both nitrided and nonnitrided devices, but the interface state density didn't show a major fluctuation in nitrided devices as compared to nonnitrided devices. A constant voltage stress was applied on both samples to test their behavior under stress. Electron trapping was dominant in nonnitrided devices at lower stress voltages. After relaxation, detrapping was observed as devices recovered to their original state. Nitrided devices showed hole trapping after stress, but further device deterioration was observed after relaxation [ABSTRACT FROM PUBLISHER]

Abstract: We investigate secondary electron emission (SEE) of hydrogenated diamond films subjected to incident electron irradiation at energies between 5 and 20 eV. For the hydrogenated films it was found that the SEE intensity decays under continuous electron irradiation. This effect is explained as due to electron trapping by resonance electron attachment into C–H (ads) bonds in the near-surface region of the hydrogenated diamond films resulting in the formation of a depletion layer and upward surface band bending. The SEE intensity decay rate from the hydrogenated diamond surface was measured as a function of incident electron energy and compared to the H− desorption cross section by dissociative electron attachment. Both were found to display a peak at ∼9 eV. The similar dependence of these two phenomena with incident electron energy suggests that the main mechanism of electron trapping is by resonant electron attachment of incident electrons onto C–H bonds present within the near-surface region of the hydrogenated diamond films. Increasing the surface temperature results in an enhanced electron emission and less efficient surface charging. [Copyright &y& Elsevier]

A model is developed to explain a hysteresis observed experimentally in nanotube field-effect transistors. The model explains the hysteresis through trapping of electrons in an oxide layer. The Fowler-Nordheim tunneling mechanism is held responsible for the electron injection. The influence of different parameters such as the sweeping rate or the range of the gate voltage on the hysteresis is studied and compared with experimental results. [ABSTRACT FROM PUBLISHER]

Kinetics of photoinduced process is studied in a new photosensitive material for volume hologram recording which is a photo-thermo-refractive glass (PTRG). A system of balance equations is derived which describes the processes of generation of electrons in a conduction band of these glass matrix by photoionization of Ce3+ and trapping of electrons by both silver ions Ag+ and hole centers (Ce3+)+. The main approach for the system solution is a calculation of low quasistationary concentration of free electrons in a conduction band, while concentrations of generated electron and hole centers are expected to be variable. A general solution of a system is found as a combination of exponential and hyperbolic functions. It is shown that an exponential solution is the result of the absence of a re-trapping of electrons, while a pure hyperbolic solution occurs in the case of equal probability of trapping and re-trapping. The approach developed for the first stage of photo-thermo-refractive process which is photoionization and trapping, is applied for the modeling of the final result of the whole process of photo-thermo-induced refractive index transformation in glass. It is found that the refractive index increment in PTRG is better described by hyperbolic function compare to the exponential one. Kinetic parameters of induced refraction in PTRG are determined. [Copyright &y& Elsevier]

BaV10O15 can be regarded as a Ba-doped V2O3 in which the Ba2+ ions substitute in the O2− close-packed layers. The Ba2+ ions order within these layers and direct the occupation of the octahedral sites by V2+ and V3+ ions resulting in a structure with subtle differences from that of V2O3 which can be described in Cmca at room temperature. Magnetic susceptibility data show evidence for two phase transitions at 135 and 40 K. The higher temperature transition at 135 K is shown to be structural in origin to another orthorhombic form, Pbca. The structural transition temperature, Ts, decreases with decreasing V2+ content to a minimum value of 105 K. Crystallographic and DSC data support a first-order transition driven by partial bond formation which results in a 7% reduction in the distance between two of the five crystallographically distinct V atoms. There is no conclusive crystallographic evidence for V2+/V3+ charge ordering in either the Cmca or Pbca forms. Electrical conductivity data show semiconducting behavior above Ts which can be fitted to a small polaron hopping model for the most reduced samples (Ts=135 K). The same sample shows a sharp but not discontinuous decrease in conductivity below Ts, consistent with carrier removal due to bond formation. More oxidized materials with Ts=105 K show a more subtle anomaly. Evidence for correlated (Efros-Shklovskii) variable-range hopping at low temperatures is seen in the Ts=105 K sample from analysis using a Hill-Zabrodski (log dE vs. log T) plot. Thermopower data on the Ts=135 K material show an anomalously small value of S∼+1 μV/K at room temperature which increases to >+200 μV/K upon cooling to 90 K. Plots of dS/dT show evidence for the Ts=135 K phase transition. These results are not consistent with a simple one carrier model for small polaron hopping assuming that the V2+ ions are the carriers, which would predict S∼−100 μV/K, but seem to demand a two carrier model with n∼p at room temperature for which n-type carriers are trapped as a result of bond formation at the phase transition as temperature is lowered. The lower temperature phase transition near 40 K is magnetic in origin and will be discussed in a subsequent publication. [Copyright &y& Elsevier]

Dielectric relaxation currents in SiO2 /Al2O3 and SiO2 /HfO2 high-κ dielectric stacks are studied in this paper. We studied the thickness dependence, gate voltage polarity dependence and temperature dependence of the relaxation current in high-κ dielectric stacks. It is found that high-κ dielectric stacks show different characteristics than what is expected based on the dielectric material polarization model. By the drain current variation measurement in n-channel MOSFET, we confirm that electron trapping and detrapping in the high-κ dielectric stacks is the cause of the dielectric relaxation current. From substrate injection experiments, it is also concluded that the relaxation current is mainly due to the traps located near the SiO2/high-κ interface. As the electron trapping induces a serious threshold voltage shift problem, a low trap density at the SiO2/high-κ interface is a key requirement for high-κ dielectric stack application and reliability in MOS devices. [ABSTRACT FROM AUTHOR]

At DSRI, in collaboration with the cyclotron facility at Copenhagen University Hospital, we have performed a study of radiation effects exposing a 2.7 mm thick CZT drift strip detector to 30 MeV protons. The detector characteristics were evaluated after exposure to a number of fluences in the range from 2×108 to 60×108 p+/cm2. Even for the highest fluences, which had a dramatic effect on the spectroscopic performance, we were able to recover the detectors after an appropriate annealing procedure. The radiation damage was studied as a function of depth inside the detector material. A numerical model that emulates the physical processes of the charge transport in the CZT detector was used to derive the charge trapping parameter, μτe (the product of charge mobility and trapping time) as a function of fluence. The analysis showed that the electron trapping increased proportionately with the proton dose. The radiation contribution to the electron trapping was found to obey the following relation: (μτe−1)rad=(2.5±0.2)×10−7×Φ (V/cm)2 with the proton fluence, Φ in p+/cm2. The trapping depth dependence, however, did not agree well with the damage profile calculated using the standard Monte Carlo simulations, TRIM , for the proton-induced radiation effects. The present results suggest that proton-induced nuclear reactions contribute significantly to the radiation damage. Further work will elaborate on these effects. [Copyright &y& Elsevier]

Experiments on dye-sensitized (DS) photoelectrochemical cells made from SnO2, ZnO and comparison with similar cells based on TiO2 gives much insight into the nature of charge separation, transport and recombinations. It is shown that the trap mediated recombinations are sensitive to the effective electron mass and therefore explains difference between the cells made from TiO2 and SnO2 or ZnO. Considering the trap mediated electron leakage from nanocrystallites, a theoretical model is constructed to explain quantitatively the effect of trapping on static and transient behavior of the cells. The model clearly demonstrate that trapping seriously affects the performance of the cell, when the electron leakage from traps is significant. The predictions of the model are compared with experimental data on transient measurements. The paper will also comment on the problem of recombinations in DS solid-state cells. [Copyright &y& Elsevier]

The energy positions relative to the host valence and conduction bands of the 5d excited states and 4f ground states of Ce3+ in CaS were determined from photoluminescence and photoconductivity measurements. The determination was based on the observation that the 5d electrons of Ce3+ are trapped after transport in the conduction band only when they were excited to the upper 5d-state (Eg), which, therefore, must lie above the minimum of the conduction band of CaS. [Copyright &y& Elsevier]

Understanding of the charge transport and recombination mechanisms of dye-sensitized solar cells based on semiconductor nanostructures is essential for the improvement of their performance. A great deal of information on these systems have been obtained from studies on a single material (mostly TiO2 and to a lesser extent ZnO and SnO2). We have conducted extensive measurements on composite dye-sensitized nanosturctures and found that the composite systems possess unusual properties. Dye-sensitized photoelectrochemical cells made from nanocrystalline films of some materials (e.g., SnO2) yield comparatively small open-circuit voltages and energy and quantum conversion efficiencies, despite excellent dye-semiconductor interaction. However, on deposition of ultra-thin shells of insulators or high band gap semiconductors on the crystallites, a dramatic increase in the above parameters is observed. Outer shells were found to have insignificant or in most cases a negative effect on TiO2 films. We explain the above findings on the basis of vast differences in the leakage rates of trapped electrons in different materials which is sensitive to the effective electron mass. Electrons injected to the conduction band in dye-sensitization enter into shallow traps from which they get thermally reemitted to the conduction band. The building up of the electron quasi-fermi level and transport depends on this process. The spread of the hydrogenic wave function of a trapped electron increases inverse exponentially with the effective mass so that the electron leakage and their recombination with acceptors ‘outside’ become severe when the crystallite size is comparable to the Bohr radius of the trapped electron. Such recombinations are effectively suppressed by deposition of thin films on the crystallites. Excited dye molecules anchored to the outer shell injects electrons to the conduction band via tunneling. [Copyright &y& Elsevier]

Ion acoustic waves (IAWs) are studied for degenerate trapped electron and non-degenerate ion plasma in the presence of quantizing magnetic field in the Tsallis framework. The presence of a magnetic field induces a trapping effect on degenerated electrons, which is studied using the generalized form of the Fermi–Dirac in the non-extensive framework. An appropriate new electron density is reformulated and reexamined in this statistics. The new expression for electron density is used to study the propagation of ion acoustic waves. The linear dispersion relation for IAWs is derived in the presence of the quantizing magnetic field and a small finite temperature in the framework of q-statistics, there influence on the propagation characteristics of the linear ion acoustic wave is discussed. In arbitrary amplitude, we use the Sagdeev potential showing that rarefactive and compressive ion acoustic solitary wave can exist simultaneously under certain conditions of temperature T, quantizing magnetic field η and the entropic index q. In addition, to study the dynamics of small but finite amplitude ion Acoustics solitary waves. Using the reductive perturbation technique the Korteweg de-Vries equation is established. Our results show that both rarefactive and compressive solitary waves may coexist in a certain range of plasma parameters. [ABSTRACT FROM AUTHOR]

We apply the gated Hall method to obtain the density of trap distribution, \textD\mathrm {it} (E), at the insulator/III-N interface of a heterostructure field effect transistor. It is shown that \textD\mathrm {it} is proportional to the difference between the steady-state and the high-frequency prediction of the gate-induced two-dimensional electron gas concentrations. The \textD\mathrm {it} profile at the SiNx/GaN interface in the energy range of 1.2–2.3 eV below the GaN conduction band is obtained as a demonstration of the method. [ABSTRACT FROM AUTHOR]

BiVO 4 is one of the most promising photoanode candidates to achieve high-efficiency water splitting. However, overwhelming charge recombination at the interface limits its water oxidation activity. In this study, we show that the water oxidation activity of the BiVO 4 photoanode is significantly boosted by the TiO 2 overlayer prepared by atomic layer deposition. With a TiO 2 overlayer of an optimized thickness, the photocurrent at 1.23 V RHE increased from 0.64 to 1.1 mA·cm -2 under front illumination corresponding to 72% enhancement. We attribute this substantial improvement to enhanced charge separation and suppression of surface recombination due to surface-state passivation. We provide direct evidence via transient photocurrent measurements that the TiO 2 overlayer significantly decreases the photogenerated electron-trapping process at the BiVO 4 surface. Electron-trapping passivation leads to enhanced electron photoconductivity, which results in higher photocurrent enhancement under front illumination rather than back illumination. This feature can be particularly useful for wireless tandem devices for water splitting as the higher band gap photoanodes are typically utilized with front illumination in such configurations. Even though the electron-trapping process is eliminated completely at higher TiO 2 overlayer thicknesses, the charge-transfer resistance at the surface also increases significantly, resulting in a diminished photocurrent. We demonstrate that the ultrathin TiO 2 overlayer can be used to fine tune the surface properties of BiVO 4 and may be used for similar purposes for other photoelectrode systems and other photoelectrocatalytic reactions.