Shallow Electron Traps Research Articles

Nature of Shallow Electron Traps in Gd<sub>3</sub>Al<sub>2</sub>Ga<sub>3</sub>O<sub>12</sub> Crystals Studied by Spectroscopy Experiments

Proceedings of the International Display Workshops Volume 27 (IDW '20),Nature of Shallow Electron Traps in Gd₃Al₂Ga₃O₁₂ Crystals Studied by Spectroscopy Experiments

The role of the disordered HfO2 network in the high-κ n-MOSFET shallow electron trapping

Current understanding of the bias temperature instability degradation usually comprises two parts: (1) shallow-level component that can recover within a short time and (2) deep level traps that the emission time of the trapped carrier is extremely long. Prevenient studies of the positive bias temperature instability degradation in the high-κ n-MOSFET indicate that oxygen vacancy (VO) is the dominant defect type that responds for the shallow electron trapping. However, recent experimental results reveal that the VO defect density required to accommodate the experimental measured recoverable threshold voltage degradation (ΔVth) is much higher than that of the reasonable atomic structure in the amorphous HfO2. On the other hand, investigations on the disordered Hf-O-Hf network in the amorphous HfO2 reveal their capabilities as charge trapping centers; therefore, in this work, atomic simulation work is performed, and our results show that the disordered Hf-O-Hf networks can act as effective electron capture centers with shallow levels near the Si conduction band. Moreover, the high density of the stretched Hf-O-Hf networks in the amorphous HfO2 also significantly enriches the shallow electron traps in the oxide.

Noble metal-modified faceted anatase titania photocatalysts: Octahedron versus decahedron

Octahedral anatase particles (OAP, with eight equivalent {101} facets) and decahedral anatase particles (DAP, with two additional {001} facets) were modified with nanoparticles of noble metals (Au, Ag, Cu). The titania morphology, expressed by the presence of different arrangements of exposed crystal facets, played a key role in the photocatalytic properties of metal-modified faceted titania. In the UV/vis systems, two-faceted configuration of DAP was more favorable for the reaction efficiency than single-faceted OAP because of an efficient charge separation described by the transfer of electrons to {101} facets and holes to {001} facets. Time-resolved microwave conductivity (TRMC) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) confirmed that distribution of electron traps (ET) and mobility of electrons were key-factors of photocatalytic activity. In contrast, metal-modified OAP samples had higher photocatalytic activity than metal-modified DAP and metal-modified commercial titania samples under visible light irradiation. This indicates that the presence of single type of facets ({101}) is favorable for efficient electron transfer via shallow ET, whereas intrinsic properties of DAP result in fast charge carriers’ recombination when gold is deposited on {101} facets (migration of “hot” electrons: Au→{101}→Au).

Effect of Surface Trap States on Photocatalytic Activity of Semiconductor Quantum Dots

Semiconductor quantum dots (QDs) are promising photocatalysts for water splitting due to the large specific area, but the influence of surface trap states on the photocatalytic activity of QDs is still not fully understood yet. To answer this question, CdSe QDs with the same morphology, diameter, crystal structure, and energy level are prepared following a hydrazine hydrate (N2H4) promoted synthesis strategy and conventional hydrothermal synthesis method. Through various characterizations and analysis, it is found that the conventional hydrothermal synthesized CdSe QDs (H-CdSe QDs) have a high concentration of Cd-involved shallow electron trap states, which seriously hinder the charge separation and transfer between CdSe and cocatalysts. In contrast, the N2H4 promoted synthesis strategy provides an energy-saving, low-cost, and facile pathway to eliminate the surface shallow electron traps, ensuring an efficient charge separation and H2 production in CdSe QDs. As a result, the N2H4-promoted synthesized CdS...

Morphology-dependent photocatalytic activity of octahedral anatase particles prepared by ultrasonication-hydrothermal reaction of titanates.

Octahedral anatase particles (OAPs) were prepared by an ultrasonication (US)-hydrothermal (HT) reaction of partially proton-exchanged potassium titanate nanowires (TNWs). The structural/physical properties of OAP-containing samples, including specific surface area, crystallinity, crystallite size, particle aspect ratio, composition and total OAP content, were analyzed. Photocatalytic activities of samples were measured under irradiation (>290 nm) for oxidative decomposition of acetic acid (CO2 system) and dehydrogenation of methanol (H2 system) under aerobic and deaerated conditions, respectively. Total density of electron traps (ETs) was measured by double-beam photoacoustic spectroscopy (DB-PAS). Mobility and lifetime of charge carriers (electrons) were investigated by the time-resolved microwave conductivity (TRMC) method. The effects of synthesis parameters, i.e., HT duration, HT temperature and US duration, on properties and photocatalytic activities of final products were examined in detail. The sample prepared with 1 h US duration and 6 h HT duration at 433 K using 267 mg of TNWs in 80 mL of Milli-Q water exhibited the highest photocatalytic activity. It was found that change in HT duration or HT temperature while keeping the other conditions the same resulted in changes in all properties and photocatalytic activity. On the other hand, duration of US treatment, before HT reaction, influenced the morphology of both the reagent (by TNWs breaking) and final products (change in total OAP content); samples prepared with various US durations exhibited almost the same structural/physical properties evaluated in this study but were different in morphology and photocatalytic activity. This enabled clarification of the correlation between morphology and photocatalytic activity, i.e., the higher the total OAP content was, the higher was the level of photocatalytic activity, especially in the CO2 system. Although the decay after maximum TRMC signal intensity (Imax) was almost constant for all samples used in this study, photocatalytic activities were roughly proportional to Imax, which tended to be proportional to total OAP content. Assuming that Imax corresponds to the product of density of electrons in mobile shallow ETs and their mobility, the results suggest that OAP particles have beneficial shallow ETs in higher density and thereby the OAP content governs the photocatalytic activities. Thus, morphology-dependent photocatalytic activity of OAP-containing particles was reasonably interpreted by density of ETs presumably located on the exposed {101} facets.

Charge trapping characterization of MOCVD HfO 2/p-Si interfaces at cryogenic temperatures

The paper focuses on the study of charge trapping processes in high- k MOS structures at cryogenic temperatures. It was shown, that there is extremely strong trapping in shallow electron and hole traps, localized in the high- k dielectrics. Concentration of shallow electron traps is as much as 10 13 cm −2, while abnormal small capture cross-sections (4.5–8 × 10 −24 cm 2 for different samples, accordingly) suggests localization of shallow emitting electron traps in transition layer “high- k dielectric/Si”, more, than at the interface. Shallow hole traps with concentration near 10 12 cm −2 are separated from silicon valence band with energy barrier in the range 10–39 meV for different samples.

Electronic trap effect of spectral sensitizing dye adsorbed on the surface of silver chloride

Using spectral sensitizing technology，silver halide microcrystals can be sensitized to the visible light region. The spectral sensitizing technology is important to the modern information recording and storage，solar energy transfer and storage, and the photoelectronic devices. The photoelectron decay characteristic of silver chloride microcrystals，which is adsorbed with green sensitizing cyanine dye，is studied by microwave absorption and dielectric spectrum detection technology. The model of photoelectron decay is set up. Electron trap effect of the dye in the silver halide surface is analyzed based on the photoelectron decay model and the photoelectron decay characteristic. The results show that when the mono-molecular dye is adsorbed on the surface，shallow electron traps are created; when the J-aggregated dye is adsorbed on the surface，deep electron traps are created. The critical dose of dye that seperates the shallow electron trap and deep electron trap effects is 0.2ml of dye (with concentration of 5.0mg/ml) per 40g AgCl emulsion.

DECAY PROCESS OF PHOTOELECTRONS RELATED TO SHALLOW ELECTRON TRAP IN SILVER HALIDE MICROCRYSTAL

Combining the microwave absorption dielectric spectrum experiment with computer simulation, the decay process of free photoelectrons related to shallow electron trap in silver halide microcystal is investigated. It is found that when shallow electron traps exist in silver halide, the free photoelectron decay will be sped up at the beginning, and then slowed down in the subsequent process. Shallow electron traps like a reservoir can store up photoelectrons temporarily, and then release them tardily? which results in lengthening free photoelectron lifetime or decay time and enhancing the efficiency of latent image formation.

Characteristics of Shallow Electron Traps in Cubic AgClMicrocrystals Doped with K4Fe(CN)6

A model is proposed to describe the photoelectron decay process atroom temperature in cubic AgCl microcrystals homogeneously doped withK4Fe(CN)6. By combining calculation of thekinetic equations resulted from the model with a microwave absorptiondielectric-spectrum measuring technique, the capture cross-section andthe trap depth of shallow electron traps induced by[Fe(CN)6]4- at room temperature are obtained,which are 3.560×10-17cm2 and 0.115 eV,respectively. Based on the two parameters, the optimal doping amount ofK4Fe(CN)6 is easily gained to be 2 ppm by computercalculation.

The kinetics simulation of trap depths and capture cross sections of SETs in AgC l microcrystals doped with ［Fe(CN)6］4- complex

To describe the photoelectron rise and decay process of AgCl microcrystals doped with ［Fe(CN)6］4-, a kinetics model composed of three in trinsic centres and a shallow electron traps(SETs)is set up, and further more, a set of differential equations is deduced. By solving the differential equations, photoelectron decay curve and photoelectron lifetime that is in accord with the transient microwave photoconductivity experimental data are obtained. Adjusting related simulation parameters, the SET depths and capture cross sections at room temperature for ［Fe(CN)6］4- are obtained and they are 0.115eV and 2 .136×10-17cm2, respectively.

Role of Shallow Electron Traps in the Fast Transient Optical Phenomena of Alkali Halide Crystals

We present additional evidences that the same shallow electron traps-atomic alkali impurity centres [M + ] c 0 e - are responsible for both classes (A and B) of the transient IR-absorption bands: (A) bands with maximum at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps or bound polarons) and (B) bands with maximum at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, KBr:I, RbCl:I and RbBr:I (due to on-centre STE or on-centre STE localised at iodine dimer). Both classes of the IR bands have the same location, similar shape (both exactly coincide for KCl:I and KCl at 10 or 80 K), half-width, vibration structure. It is established that the same Mollwo-Ivey plot curves E o =a/d n (d is the nn anion-cation distance, n is the exponent, a is the constant) take place for both IR band classes, if we plot instead of the IR band peak energy values the more definite values of the IR band zero-phonon line energy E 0 (for NaCl, KCl, KBr, RbCl and KCl:I) and/or the IR band low-energy edge E 0 (±0.03 eV) values (for NaBr, NaI, NaCl:I, KBr:I, RbCl:I and RbBr:I). Two types of the [M + ] c 0 e - centres are predominant: (i) [Na + ] c 0 e - in KX and RbX host crystals, for which the relation E 0 ≃6.15/d 2.74 is valid, and (ii) [Li + ] c 0 e - in NaX host crystals for which the relation E 0 ≃29.4/d 4.72 is valid. The Mollwo-Ivey relation E 0 ≃18.36/d 2.70 is valid as well for the F' band in NaCl, KCl, KBr, KI, RbCl, RbI, if we use the F' centre optical binding energy E o values. Under irradiation at 77 or 4.2 K the shallow trapped electron centres ([M + ] c 0 e - and F' centres) and their associations with the V k -type centres, i.e., dipolar pairs {[M + ] c 0 e - …V k } and {F'…V k } are created. Such a quasi-molecular electronic transients have a very wide lifetime spectrum (τ ≥ 1 ns) and can play a great role in the intense pulse excitation experiments.

Defects and the photographic process

The high imaging efficiency of today's color negative film depends on the unique defect properties of silver halides. We have chosen two important defect topics to highlight: defect-induced anisotropic crystal growth, and shallow electron trapping at surface defects and transition metal dopant sites. High imaging efficiency depends on the ability to concentrate photoelectrons and thereby to form a single latent image center per crystallite. This requires electron localization at a partially-charged, shallow electron trap at the surface followed by a shallow—deep transition to a metastable atom state. Subsequent ionic and electronic trapping processes that build the latent image occur only at this site. In some cases, doping the bulk of the microcrystal with extrinsic shallow electron traps can improve latent image formation efficiency. Electron concentration does not occfur at these dopant sites since they are not partially charged. Magnetic resonance and photoconductivity studies of the dynamics of shallow trapping by dopants and of the shallow-deep transition at surface sites are presented.

Transient photoconductivity study of shallow electron traps in [Ru(CN)6]4− doped AgCl microcrystals: effects of doping concentration and position

Cubic AgCl microcrystals doped with K4Ru(CN)(, were studied by transient microwave photoconductivity (TMPC) in X-band. The dopant was introduced in either the core, the subsurface shell or the outer shell of the microcrystals and its concentration was varied between 0 and 100 ppm. [Ru(CN)6]4− increases strongly the photoelectron response time at both room temperature (RT) and 120 K, the increase being smaller when the doping level decreases and when the doping position is closer to the surface of the microcrystals. This can be semiquantitatively explained by a model in which [Ru(CN)6]4− introduces shallow electron traps (SETs), the density of which increases with the doping level. Within this model, the photoelectron response time is controlled by competitive trapping processes in the doping area and at the surface. Evidence is presented showing that [Ru(CN)6]4− related centres may interact at higher local concentrations. The knowledge obtained from this study may be useful for practical microcrystal design making use of SETs introduced by dopants in AgX (X = C1, Br). Finally, good agreement with experimental results obtained by other techniques, e.g. Q-band TMPC at RT and electron paramagnetic resonance at low temperature, will be demonstrated.

Reduction of charge trappings and electron tunneling in SIMOX by supplemental implantation of oxygen

The reduction of excess-silicon related defects in SIMOX (separation by implantation of oxygen) by the supplemental implantation of oxygen is examined. The supplemental implant is 6% of the oxygen dose used to form the buried oxide, and is followed by a 1000 degrees C anneal, in contrast to the >1300 degrees C anneal used to form the buried oxide layer of SIMOX. The defects examined include shallow electron traps, deep hole traps, and silicon clusters. The radiation-induced shallow electron and deep hole trapping is measured by cryogenic detrapping and isothermal annealing techniques. The low-field (3 to 6 MV/cm) electron tunneling is interpreted as being due to a two-phase mixture of stoichiometric SiO/sub 2/ and Si clusters at a few nm in size. Single and triple SIMOX samples have been examined. All of the defects are reduced by the supplemental oxygen processing. Shallow electron trapping is reduced by an order of magnitude. The low-field electron tunneling due to Si clusters is also significantly reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>