Electron Trap Parameters Research Articles

Variation of luminescence sensitivity, characteristic dose and trap parameters of quartz from rocks and sediments

We investigated the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of quartz from sediments and parent rocks across South America. OSL and TL sensitivities were compared with the characteristic dose of dose response curves. Additionally, we estimated electron trap parameters of quartz from sediments with contrasting OSL sensitivities. Our results show that the natural sensitivities of quartz OSL (initial 0.8 s) and TL (110 °C peak) are positively correlated and range over six and four orders of magnitude respectively. The corresponding characteristic doses range from around 30 Gy–3000 Gy for dose response curves described by a single exponential function. Quartz from igneous and metamorphic rocks and Andean short-transported sediments report low-sensitivity OSL and high characteristic dose. The studied initial OSL signal has significant contribution of medium and slow components in quartz from rocks and Andean short-transported sediments, while in quartz from Brazilian long-transported sediments, the initial OSL signal is dominated by the fast component. The trend of sensitivity increase and characteristic dose decrease is attributed to the relative contribution of medium and low components to the initial OSL emission. Regarding the electron trap parameters, high, medium and low sensitivity quartz has statistically similar values of the activation energy and the frequency factor, but both parameters have larger variations in medium and low sensitivity quartz.

Thermoluminescence study of pellets prepared using NaCl from Khewra Salt Mines in Pakistan.

In this study, the thermoluminescence characteristics of naturally occurring salt (NaCl) were assessed for the development of a radiation dosimeter. For this purpose, mined crystalline samples of salt were procured directly from Khewra salt mines in Pakistan. The samples were hand crushed, sieved, and compressed to pellets comparable in size to standard TLD chips, and irradiated to gamma radiation doses in the range of 5mGy and 5000mGy. Thermoluminescence (TL) response showed three main peaks in the glow curve around 115-130°C, 150-170°C, and 220-240°C. A linear TL response was observed for the dose range of 5-100mGy. The TL response became supra-linear for the dose ranges of 100-1000mGy and 1000-5000mGy. The Tm-Tstop method was applied to identify the overlapping peaks of the glow curve. Computerized glow curve deconvolution (CGCD) was then employed for the characterization of electron trap parameters such as frequency factor (s), activation energy (E), and the kinetic order (b), using General Order (GO) kinetics. The figure-of-merit (FOM) was found to be 1.08%, 0.94%, 0.77%, and 0.75%, at 500mGy, 1Gy, 2Gy, and 5Gy, respectively. The TL intensity faded by 20% within the first 24h after irradiation and finally stabilized after two weeks. In addition, structural, morphological, and elemental analyses, were also performed using various analytical techniques. X-ray diffraction (XRD) showed that the salt crystallizes in a face-centered cubic structure. Scanning electron microscope (SEM) micrographs indicated that the crystallites are closely packed and cubic-shaped with non-uniform size, and mostly found in the agglomerated form. Similarly, the elemental analysis confirmed the presence of impurities such as Mg, Sr, S, K, O, and Ca, in the samples. The present study concludes that the pellets made from salt samples from Khewra mines have a potential for use as radiation dosimeters.

Determination of electron trapping parameters: A revisit to Urbach’s formula

Determination of electron trapping parameters in insulating as well as semi-insulating (SI) solids has remained an interesting rewarding field of research in solid state physics. The earliest formula for determination of the trap-depth (E)-the key parameter-was given by Urbach in 1948. Despite being one of the simplest formula that has its own limitations, it is used even today. In this work we revisit the relevance of the formula at a time when whole curve fitting method has been the accepted method not only for evaluation of trap depth (E) but also other trap parameters like the frequency factor (s) and the order of kinetics (b). On the finer aspect of the work we test the historical formula for ZnO based phosphors and provide some insight into thermally stimulated processes (TSPs) as a whole. Finally, we present the philosophical implications of the historical formula by comparing the electron trap parameter (E) obtained by both the methods (Urbach and whole curve fitting).

The electron trap parameter extraction-based investigation of the relationship between charge trapping and activation energy in IGZO TFTs under positive bias temperature stress

Experimental extraction of the electron trap parameters which are associated with charge trapping into gate insulators under the positive bias temperature stress (PBTS) is proposed and demonstrated for the first time in amorphous indium-gallium-zinc-oxide thin-film transistors. This was done by combining the PBTS/recovery time-evolution of the experimentally decomposed threshold voltage shift (ΔVT) and the technology computer-aided design (TCAD)-based charge trapping simulation. The extracted parameters were the trap density (NOT) = 2.6×1018 cm−3, the trap energy level (ΔET) = 0.6 eV, and the capture cross section (σ0) = 3 × 10−19 cm2.Furthermore, based on the established TCAD framework, the relationship between the electron trap parameters and the activation energy (Ea) is comprehensively investigated. It is found that Ea increases with an increase in σ0, whereas Ea is independent of NOT. In addition, as ΔET increases, Ea decreases in the electron trapping-dominant regime (low ΔET) and increases again in the Poole–Frenkel (PF) emission/hopping-dominant regime (high ΔET). Moreover, our results suggest that the cross-over ΔET point originates from the complicated temperature-dependent competition between the capture rate and the emission rate. The PBTS bias dependence of the relationship between Ea and ΔET suggests that the electric field dependence of the PF emission-based electron hopping is stronger than that of the thermionic field emission-based electron trapping.

Definition of curve fitting parameter to study tunneling and trapping of electrons in Si/ultra-thin SiO 2/metal structures

The tunneling of electrons through metal–oxide–silicon (MOS) structures with ultra-thin oxide is modeled using a linear model for the electron potential energy, an approach which simplifies the computation of both the interface potential and the field penetration distance in the substrate. The one-particle quantum problem is split into finding the metastable states induced by the internal field penetration in the substrate and the running states in the gate region. The two states are assumed to be connected by the condition for the continuity of the probability density at the substrate–dielectric interface. The electron probability current and the total gate current density are obtained for different gate voltages. As the model yields excellent fittings with experimental current–voltage ( I– V) data for MOS structures, it was further applied to constant current stressing analysis in order to obtain values for important electron trapping parameters in the oxide. The resultant estimates of the electron trapping cross-section fall in the range of other independent determinations in the literature.

Determining the Parameters of Electron Traps in Inhomogeneous Layers by Method of Thermionic Emission

Quasi-stationary nonlinear variation of the density of filled electron traps in the course of thermionic emission from the surface oxide layer on a metal cathode is theoretically described. Expressions for the electron affinity, energy, and density of electron traps in this dielectric layer are obtained. Numerical estimates of the electron trap parameters are obtained based on the results of measurements of the temperature dependence of thermionic emission from the porous surface oxide layer of an iron-nickel alloy.

X-radiation response of SIMOX buried oxides: influence of the fabrication process

X-ray induced electron and hole trapping properties have been investigated in SIMOX buried oxides of different processes, including standard and supplemental implantation oxides, as well as new thin and ultra-thin oxides. The effect of the substrate bias applied during irradiation is studied, and then used to extract both hole and electron trapping parameters. The results demonstrate that varying the oxygen implantation conditions has very little effect on the radiation induced behavior of the material. They show that the charge trapping properties of the buried oxide are related to the ultra high temperature anneal performed on the confined oxide layer, and confirm that the post implantation anneal is the most critical part of the SIMOX process.

A study of high field conduction and electron trapping in buried oxides produced by SIMOX technology

Low Fowler-Nordheim barrier heights measured at SIMOX interfaces are attributed to points of field intensification causing preferential injection and an associated reduced injection area. This was taken into account in the analysis of constant voltage stress (CVS) experiments from which oxide electron trapping parameters were derived. Comparison of parameters from CVS and avalanche injection experiments indicate the efficacy of the CVS technique in identifying trap species for SOI.

A STUDY ON THE PROPERTIES OF SiO2 THIN FILM THERMALLY NITRIDED IN AMMONIA AND ITS INTERFACE

The properties of thermally nitrided SiO2 thin film and its interface have been studied. It is found that the chemical composition, refractive index, electron trap parameters, surface mobility, fixed charge and interfacial state densities are dependent obviously on the annealing condition in ammonia. The mechanism of nitridation, anti-oxidation, and the effect of nitridation on interfacial characteristics are discussed.

Admittance spectroscopy of traps in AuInSe Schottky cells

The electron trap parameters in InSe single crystals have been obtained through measurements of conductance and capacitance as a function of temperature, frequency and reverse bias voltage on their Schottky junctions. The results agree with the theoretical model of Roberts and Crowell and the theoretical model of Losee. One trap at about 1 eV from the conduction band edge has been revealed by the minima in the capacitance and/or conductance-reverse bias voltage characteristics, while one trap at about 0.1 eV has been revealed by the maxima in the conductance-temperature characteristics.

Significance of the electron trap parameters of glow curves of photosynthetic membranes

AbstractSeveral methods are available to determine the electron trap parameters such as activation energy E, preexponential frequency factor s, and the lifetime τ of the electrons in the trap states in photosynthesis. These parameters are also related by the Arrhenius expression which helps in calculating the E values without any assumptions regarding the particular order of kinetics applicable or the values of preexponential factors. Subsequent calculation then yields the values for s and τ in a straightforward manner. However, application of these methods (as well as the Arrhenius expression) to some of the experimental data has recently yielded such values that give rise to some questions regarding the meaning attributable to these parameters. The significance of these findings are discussed in view of the correlation of thermoluminescence and delayed light emission studies in photosynthetic membranes.

Electron traps in CdS single crystals obtained by admittance spectroscopy on the hetero- and Schottky junctions

The electron trap parameters in semiconducting CdS single crystals were obtained by admittance spectroscopy on its hetero- and Schottky junctions, and the trap depths obtained were 0.065, 0.09, 0.15 0.20, and 0.40 eV. The capture cross-section of the shallowest trap on the Cd-face of the crystals was about 10−19 cm2, one order smaller than that of the bulk crystal. The resolving power of the employed method was about 50 meV to distinguish the two traps with different depths.

Properties of the Room-Temperature Electron Trap in Rutile

By a combination of thermoluminescence, thermally stimulated current, and photocurrent measurements, the electron trapping parameters of the room-temperature trap in rutile were obtained. The photon-capture cross section and the electron-frequency factor were determined. The values of the electron-capture cross section, the trap density, and the ratio of optical to thermal ionization energies of the trap were calculated. The relation of the trapping center to the photocurrent decay is discussed.

The evaluation of thermally stimulated current curves

A method of evaluating experimentally determined thermally stimulated current curves by a process of successive approximation is described. The method is essentially one of curve fitting and an excellent fit is eventually obtained between the theoretical and experimental curves. The process of curve fitting serves to determine the electron-trapping parameters. The technique can be used for the two extreme cases of trap emptying: emptying with no retrapping and emptying with fast retrapping. The technique is illustrated by its application to some experimental results obtained from CdS crystals.

Determination of Electron Trapping Parameters

A detailed investigation of different methods for determining electron trap parameters has been made on crystals of CdS-CdSe. The principal techniques involved are decay of photoconductivity and thermally stimulated conductivity (TSC). Direct evidence of a quasicontinuous trap distribution with total density of 5×1015 cm−3, trap depth range of 0.1–0.7 eV, and capture cross sections of the order of 10−16 cm2 is obtained, for which correct values of the parameters can be calculated from Fermi-level analysis of either decay or TSC data. In the same crystals a discrete trap level with density of 2×1014 cm−3, depth of 0.73 eV, and apparent cross section of 10−14 cm2 is also found. In spite of the large value of cross section derived from the freeing of trapped electrons, these traps exactly obey monomolecular kinetics. A temperature threshold at 180°K is found, below which it is not possible to fill these traps. Examination of a number of possibilities favors the proposal that these traps are characterized by a Coulomb-repulsive barrier.