Electron Trap Depth Research Articles

Impact of SiN Composition Variation on SANOS Memory Performance and Reliability Under nand (FN/FN) Operation

Despite significant advances in structure and material optimization, poor erase (E) speeds and high retention charge loss remain the challenging issues for charge trap flash (CTF) memories. In this paper, the dependence of SANOS memory performance and reliability on the composition of silicon nitride (SiN) layer is extensively studied. The effect of varying the Si:N ratio on program (P)/E and retention characteristics is investigated. SiN composition is shown to significantly alter the electron and hole trap properties. Varying the SiN composition from N-rich (N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) to Si-rich ( Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) lowers electron trap depth but increases hole trap depth, causing lower P state saturation but significant over erase, resulting in an enhanced memory window. During retention, P state charge loss depends on thermal emission followed by the tunneling out of electrons mostly through tunnel dielectric, which becomes worse for Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> SiN. Erase state charge loss mainly depends on hole redistribution under the influence of internal electric fields, which improves with Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> SiN. This paper identifies several important performances versus reliability tradeoffs to be considered during the optimization of SiN layer composition. It also explores the option for CTF optimization through the engineering of SiN stoichiometry for multilevel cell NAND flash applications.

Relationship between Electric Potential Distribution and Trap Depth in Polymeric Materials

The relationship between a three dimensional electric potential distribution and electron trap depth in polymeric material was discussed. A semi-empirical method of molecular orbital is applied to calculate the distribution of electric potential distribution in simple molecule models for the polymers after determining the configurations of orbital electron and proton. Furthermore the electron trap depth was calculated from difference between an electron affinity and conduction level for each polymers. As the model of polar polymers, Polycarbonate (PC), Polyethyleneterephthalate (PET), Polyethylenenaphthalate (PEN) and Polyimide (PI) are chosen. The relationships were also investigated on the simulated models of Polyethylene (PE), Polytetrafluoro-ethylene (PTFE), Polypropylene (PP) and Polystyrene (PS) as typical non-polar polymers. In the case of polar polymers, it is found that the electron traps were basically consisted of carbonyl group and benzene ring, and the trap depth equals to electron affinity which is always positive polarity. In the case of non-polar polymers, the conduction level equals to the electron affinity of PE and the trap depth equals to the difference between the conduction level and each electron affinity of polymer.

Trapping and Evolution Dynamics of Ultracold Two-Component Plasmas

We demonstrate the trapping of a strongly magnetized, quasineutral ultracold plasma in a nested Penning trap with a background field of 2.9 T. Electrons remain trapped in this system for several milliseconds. Early in the evolution, the dynamics are driven by a breathing-mode oscillation in the ionic charge distribution, which modulates the electron trap depth. Over longer times scales, the electronic component undergoes cooling. Trap loss resulting from E x B drift is characterized.

Study of blue colour in ancient mosaic tesserae by means of thermoluminescence and reflectance measurements

The colouring effects of cobalt and copper ions in glass have been investigated by means of thermoluminescence and reflectance measurements. The two techniques have been used to characterise the colour centres of ancient blue glass mosaic tesserae, in comparison with standard modern colourless and blue glass. Thermoluminescence measurements allowed us to characterise the colour centres in the glass network and to evaluate the electron trap depth in ancient and modern samples. In ancient samples there is evidence of three electron traps, at the same temperatures of crystalline quartz, perhaps due to a partial re-crystallisation of the lattice. On the contrary, in modern samples, the continuum of trapping levels typical of amorphous silica is evident.

The dynamic characteristics of sulfur sensitization centers in T-grain AgBrI microcrystals

The microwave absorption dielectric-spectrum technique was used to study the decay kinetics of the free photoelectrons and shallow-trapped electrons in the sulfur-sensitized T-grain AgBrI crystals prepared under different sensitization times. It was found that, from the dependence of the kinetic behavior of photoelectrons in the sensitized T-grain AgBrI emulsions, the optimal sensitization time was 45min. With an increase of the sensitization time, the trap effect of the sulfur sensitization centers varies from the hole trap to shallow electron trap, and to deep electron trap, corresponding to the sulfur sensitization centers in the forms of a monomer, dimmer, and cluster of Ag2S, respectively. The range of the shallow electron trap depth traps was determined to be 0.26–0.27eV.

Sulphide centres on (111) AgBr surfaces: energy levels and computer simulated sensitometry

Sensitometric and spectroscopic techniques are used to characterize sensitizer centres produced by sulphur sensitization of AgBr octahedra. Activation energies for long-wavelength sensitivity were independent of thiosulphate concentration for the single-sulphide centres (550 nm), but showed a concentration dependence for the multiple-sulphide centres (700 nm). The achievement of maximum photographic speed is associated with the production of the multiple-sulphide centres. Using activation energies for long-wavelength sensitivity, with the lowest one for the multiple-sulphide centres being taken as closest to reality, an energy level scheme was constructed for the two sulphide centres. The single-sulphide centres are estimated to have an electron trap depth between 0 and 0.1 eV, whereas the multiple-sulphide centres have trap depths between 0.25 and 0.45 eV. Deconvolution of thiosulphate-induced absorption spectra suggested that only 65 per cent of the converted thiosulphtate is photographically active and that the single-sulphide centres are the predominant sulphide species. Computer simulated sensitometry based on these ideas was consistent with experimental sensitometry. Computer simulation of the sensitometry for the optimum thiosulphate concentration required a small concentration of the multiple-sulphide centres. Attempts to simulate the sensitometry of the oversensitized emulsion were less successful. Computer simulations based on the single-sulphide centres acting as hole traps were inconsistent with the experimental data.

Selenide versus sulphide centres on (100) AgIBr surfaces: characterization and energy levels

Sensitometric and spectroscopic techniques are used to characterize sensitizer centres produced by sulphur and selenium sensitization of AgIBr cubes. Sulphur sensitization primarily affects the long-wavelength sensitivity in three spectral regions—550, 700 and 800 nm. For selenium sensitization only the 550 and 800 nm spectral regions were affected, along with a weak effect at 650 nm. The concentration dependence of the long wavelength sensitivity showed the 550 nm region to be associated with single-chalconide centres. The other spectral regions are assumed to be multiple-chalconide species, but concentration-dependent activation energies for long-wavelength sensitivity precluded a more definitive assignment. A prominent 480–490 nm peak is observed in diffuse reflectance spectroscopy of these emulsions sensitized with either sulphur or selenium that is not observed in the long-wavelength sensitivity measurements. This peak is assigned to a product of the chemical sensitization that is not photographically active. An energy level scheme was constructed based on the activation energies and photon absorption energies. This scheme indicated that all chalconide centres are poor hole traps, but their electron trap depth increases with increasing absorption wavelength. The speed advantage of selenium over sulphur sensitization is suggested to be due to fewer but slightly deeper traps created by the former sensitization.

Sulphide centres on AgIBr (100) surfaces: characterization and energy levels

Sensitometric and spectroscopic techniques are used to characterize sensitizer centres produced by sulphur sensitization of AgIBr cubes. Sulphur sensitization primarily affects the long-wavelength sensitivity in three spectral regions: 550, 700 and 800 nm. The concentration dependence of the long-wavelength sensitivity in these spectral regions shows the first to be associated with single-sulphide centres. The other two spectral regions are attributed to multiple-sulphide species, but thiosulphate concentration-dependent activation energies for long-wavelength sensitivity precluded a more definitive assignment. A prominent 480–490 nm peak is observed in diffuse reflectance spectroscopy of these emulsions that is not observed in the long-wavelength sensitivity measurements. This peak is assigned to a product of the sulphur sensitization that is not photographically active. An energy level scheme was constructed on the basis of the activation energies and photon absorption energies. This scheme showed that all three sulphide centres are poor hole traps, but their electron trap depth increases with increasing absorption wavelength.

The Effect of Trap Depth on Latent-Image Formation in an AgBr Tabular Grain: A Computer Simulation Study

Computer simulation is used to study how electron trap depth affects the efficiency of latent-image formation. These traps, modeled as products of chemical sensitization, are located at the corners of a 1.0 &#xD7; 0.2 &#x3BC;m tabular &#x201C;grain.&#x201D; Comparisons are made with uniformly distributed 0.2 eV traps and irreversible traps located at the grain corners. For a minimum developable size of three atoms, there is no clear advantage of the corner traps over that for the uniformly distributed trap case, even though the trapping radius in the former is 2&#xD7; that in the latter. For a minimum developable size of four atoms, there is some efficiency advantage of the corner traps, particularly at high irradiance. Some decrease in efficiency for the deeper traps was noted. This behavior is due to enhanced free-hole/trapped-electron recombination at these traps.

Properties of Silver Clusters Adsorbed to Silver Bromide

Density functional calculations of the structure and electronic properties of silver clusters interacting with a fragment of silver bromide that is embedded within a polarizable representation of the AgBr crystal are presented. Flat (001) surfaces and kinked surfaces are considered. The optimized geometry of the silver clusters is nearly planar for the clusters up to four atoms that are considered. We examined the degree to which different surface defect sites could modulate the properties of the adsorbed silver cluster. The positive kink site is unique in providing a location where the neutral cluster can capture photoelectrons. This effect can be rationalized by electrostatic arguments and is consistent with this site functioning as a location for photolytic silver formation. Other kink sites of neutral or partial negative charge do not permit electron trapping at neutral silver clusters. These sites could act as locations for chemically produced silver clusters. Calculations are presented showing that some geometries of Ag3+ adsorbed at the negative kink can trap electrons in accord with a proposal by Tani. The calculations are used to compare different mechanisms for photolytic formation of silver clusters. They can be compared to gas-phase calculations adjusted for the interaction with a polarizable surface to show that both calculations agree that cationic silver clusters are unstable with respect to dissociation except on the negative kink. The calculations show a deep electron trap depth for the silver atom consistent with its participation in the nucleation phase of silver cluster growth during photolysis. A sulfide ion substituted for bromide at a positive kink is shown to provide a means of coupling the electron to the crystal ions.

The use of positron lifetime measurements in a study of electron scavenging by a range of radiosensitizer compounds

Abstract Positron lifetime measurements were made in aqueous solutions of a number of radiosensitizer compounds in order to measure the o -Ps inhibition and quenching constants. By making measurements in the presence and in the absence of perchloric acid, the inhibiting effects on the o -Ps yield due to epithermal and trapped electrons could be determined on the basis of the spur model. Inhibition constants relating to the scavenging by the sensitizer molecule of epithermal electrons. ( K 1 ) and traped electrons, ( K 2 ) were found for eight basic nitroimidazoles. The results are also discussed in terms of electron trap depth which is here taken to be equivalent to the one-electron redox potential, E 1 7 . It is concluded that o -Ps lifetime measurements alone are not capable of determining the finer details of these spur reactions. Estimates of the respective yields of RS - and OH . species in oxygen and R—NO 2 compounds show that these are not able to explain the large differences in sensitizing efficiency.

High-field electron capture and emission in nitrided oxides

High-field, constant current injection has been used to study electron trapping and reemission processes in ammonia-annealed (nitrided) silicon dioxide. The gate voltage during injection versus injected charge exhibits two rates. The first provides the capture cross section and trap density information. The second provides information on reemission of trapped charge by tunneling. From the tunneling data, the electron trap depth can be estimated to be 3.5–4 eV below the insulator conduction band. Nitrogen annealing reduces the density of these traps.

Recombination ina−Si:H: Defect luminescence

A study of defect photoluminescence in $a\ensuremath{-}\mathrm{Si}:\mathrm{H}$ is presented. In both doped and undoped samples we observe a broad defect-related transition peaking at 0.9 eV with a width of \ensuremath{\sim}0.35 eV. The line shape, temperature dependence, and excitation energy dependence of this luminescence are described. The recombination is interpreted as a transition between an electron in a doubly occupied dangling bond, and a valence-band tail hole. We estimate that the electron trap depth is \ensuremath{\sim}0.5 eV and involves a distortion energy of about 0.1 eV. The relation between the luminescence data and light-induced electron spin resonance is also discussed.

The trap depth in evaporated polypropylene from measurements of thermally stimulated currents

Abstract The occurrence of thermally stimulated currents in thin evaporated films of polypropylene was demonstrated and an analysis of the curves gave an electron trap depth of 0.33 eV in this material.

The reactivity of allyl and propargyl alcohols with solvated electrons: temperature and solvent effects

The rate constants k1 for the reaction of solvated electrons with allyl alcohol in a number of hydroxylic solvents differ by up to two orders of magnitude and decrease in the order tert-butyl alcohol &gt; 2-propanol &gt; 1-propanol ≈ ethanol &gt; methanol ≈ ethylene glycol &gt; water. In methanol and ethylene glycol the rate constants (7 × 107 M−1 s−1 at 298 K) and activation energies (16 kJ/mol) are equal, in spite of a 32-fold difference in solvent viscosity (0.54 and 17.3 cP, respectively) and 3-fold difference in its activation energy (11 and 32 kJ/mol, respectively). The reaction in tert-butyl alcohol is nearly diffusion controlled and has a high activation energy that is characteristic of transport in that liquid (E1 = 31 kJ/mol, Eη = 39 kJ/mol). The activation energies in the other alcohols are all 16 kJ/mol, and it is 14 kJ/mol in water. They do not correlate with transport properties. The solvent effect is connected primarily with the entropy of activation. The rate constants correlate with the solvated electron trap depth. When the electron affinity of the scavenger is small, a favorable configuration of solvent molecules about the electron/scavenger encounter pair is required for the electron jump to take place. The behavior of the rate parameters for propargyl alcohol is similar to that for allyl alcohol, but k1, A1, and E1 are larger for the former. The ratio k(propargyl)/k(allyl) at 298 K equals 10.5 in water and decreases through the series, reaching 1.3 in tert-butyl alcohol. Rate parameters for several other scavengers are also reported.

Electron mobilities and ranges in methyl substituted pentanes through the liquid and critical regions

Density normalized penetration ranges bGPd of secondary electrons and mobilities μe of thermal electrons vary in similar manners as the temperature of the solvent hydrocarbon is increased toward the critical. These quantities pass through maxima in 3,3-dimethylpentane, 2,2,4-trimethylpentane, and 2,2,4,4-tetramethylpentane, but not in 3-methylpentane. In 2,3-dimethylbutane μe has a small maximum just below the critical point while bGPd reaches a short plateau. As the molecules in a series become more spherelike, the maxima grow and the temperature at which they occur moves farther below the critical. Changes of the range and mobility are caused by changing scattering properties of the fluids. The decrease of μe on the high temperature side of the maximum is attributed to a decrease of mobility in the conduction band μ0h rather than to an increase in electron trap depth that might have been caused by the greater density fluctuations that occur as the critical region is approached. The results support the earlier conclusion that the major part of the secondary electron range bGP is attained while the electron has only a few tenths of an eV energy and is skittering through the liquid in the conduction band. The mobilities in all the liquids are independent of field strength up to 30 kV/cm, except in 2,2,4,4-tetramethylpentane under conditions where the drift velocity exceeds 14 km/s. The mobilities in the five critical fluids are all between 19 and 31 cm3/V s, a factor of 1.6, whereas those in the liquids at 293 K range over a factor of 130. This demonstrates the importance of short range forces in governing electron behavior in dense matter.

Some electrical properties of evaporated polypropylene

The occurrence of thermally stimulated currents in thin evaporated films of polypropylene was demonstrated and an analysis of the curves gave an electron trap depth of 0.33 eV in this material.

Temperature dependence of the recombination fluorescence of photoionized indole and N,N,N',N'-tetramethyl-p-phenylenediamine in organic glasses. Consequences of electron tunneling and diffusion

The recombination fluorescence seen when TMPD is photoionized in methylcyclohexane, 3-methylhexane, and 2-methyltetrahydrofuran glasses and when indole is photoionized in 2-propanol and ethanol glasses has been investigated. The initial intensity and decay rate of the recombination fluorescence decreases as the UV irradiation temperature is increased from temperatures below the glass transition temperature T/sub g/ of the matrix. This is interpreted in terms of electron tunneling to the cation in which the tunneling barrier height or electron trap depth increases slightly (0.05 to 0.2 eV) with increasing irradiation temperature. By considering how the matrix polarity affects the degree of electron trap deepening as well as the electron trap depth relative to the excited singlet level of the solute, we are able to understand the difference in magnitudes and their changes for the initial decay rate and the initial recombination fluorescence. At temperatures 10 to 30 K above T/sub g/, depending on the matrix polarity, diffusive recombination dominates tunneling recombination and produces a peak in the recombination fluorescence unless the electron trap depth has dropped below the excited singlet of the solute. Thus, this type of experiment offers a simple diagnostic for distinguishing tunneling and diffusive recombination of electrons with cations inmore » disordered matrices.« less

On the temperature dependence of the recombination fluorescence of photoionized tryptophan in aqueous glasses: Consequences of electron tunneling

The recombination fluorescence seen when tryptophan in ethylene glycol/water and 9M LiCl frozen aqueous glasses is photoionized has been investigated. It is found that the intensity as well as the initial decay rate of this recombination fluorescence decreases as the uv irradiation temperature increases from 77 K. This is interpreted in terms of a tunneling process in which the electron trap depth increases slightly with increasing irradiation temperature. This causes the tunneling rate constant to decrease, and as the trap depth drops below the lowest singlet level of tryptophan, an increasing fraction of the recombination events will lack the energy necessary to generate recombination fluorescence.

Influences of Heat-treatment upon Cadmium Sulphide Single Crystals

Ionization energies and electron trap depths in cadmium sulphide single crystals heat-treated in vacuum or in oxygen were obtained by measuring the dark conductivity as a function of the temperature and the thermally stimulated current, respectively. It was found that, in the case of crystals heat-treated in vacuum, the ionization energies were 0.04 eV, 0.7 eV, 1.0 eV and 1.4 eV, and the major electron trap depth was 0.50 eV below the conduction band, and the dark conductivities and the concentrations of the electron traps were reduced as the crystals were heat-treated in oxygen. And when the crystals were heat-treated in vacuum or in oxygen, it was found that the sensitivity of photocurrent at about 600 mµ was increased.