Persistent photoconductivity in AlGaN films Grown by mocvd

ABSTRACTPhotocurrent transients due to illumination by above-bandgap and subbandgap light were studied for Si doped and undoped films of AlGaN grown by MOCVD on sapphire and having compositions ranging from 0% to 60% of Al. It is shown that in Si doped layers the decay of photoconductivity takes extremely long time (hundreds and thousands seconds, depending on temperature, composition and illumination conditions). Both the kinetics of rise and fall of photoconductivity are best described by stretched exponents. The characteristic decay times are virtually temperature independent for temperatures below 270–290K and have activation energy of 0.14–0.26 eV (depending on composition) for higher temperatures. The decay times become longer with decreased light intensity and increase when above-bandgap light excitation is replaced by subbandgap light excitation (the photocurrent values from which the decay starts being equivalent). The results cannot be quantitatively explained by the effects of changing of the quasi-Fermi level position well known for DX-centers in AlGaAs. No persistent photoconductivity could be observed in high resistivity undoped AlGaN films with 5%, 15% and 25% of Al.

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Charge Trapping by Deep Donors in Si-Doped AlxGa1-xAS

MRS Proceedings ◽

10.1557/proc-46-403 ◽

1985 ◽

Vol 46 ◽

Cited By ~ 12

Author(s):

P. M. Mooney ◽

N. S. Caswell ◽

P. M. Solomon ◽

S. L. Wright

Keyword(s):

Activation Energy ◽

Energy Range ◽

Charge Trapping ◽

Lattice Relaxation ◽

Persistent Photoconductivity ◽

Relaxation Model ◽

Thermally Activated ◽

Large Lattice ◽

Si Doped ◽

Kinetics Of

AbstractThe kinetics of charge capture by deep donors in AlxGa1-xAs have been measured. The time dependence indicates that a single energy cannot be used to describe the trap. A model assuming thermally activated capture into a resonance in the conduction band with a range of energies gives excellent fits to the data and provides a measure of the energy range for the trap. This model is consistent with the large lattice relaxation model for DX centers. The increase of the activation energy for capture as the Al mole fraction is decreased contradicts the model which attributes the decay of the persistent photoconductivity to tunneling through the heterojunction barrier in modulationdoped structures.

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Kinetics of Sulfur-Free Thiuram Vulcanization

Rubber Chemistry and Technology ◽

10.5254/1.3542900 ◽

1972 ◽

Vol 45 (4) ◽

pp. 945-954 ◽

Cited By ~ 2

Author(s):

Vratislav Ducháček

Keyword(s):

Activation Energy ◽

Induction Period ◽

Rate Equation ◽

Radical Reactions ◽

Network Chain ◽

First Order ◽

Cure Time ◽

Long Time ◽

Partial Degradation ◽

Kinetics Of

Abstract Sulfur-free thiuram vulcanization has been investigated at temperatures from 160° to 190° C over 0.5 to 600 min. Continuous measurements in a VUREMO curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. Simultaneously the values of the network chain density were calculated from swelling measurements on the vulcanizates. The cure curves show clearly an induction period (ti), then fast crosslinking, a partial degradation, a “long-time” crosslinking, and finally a slow, limited degradation. Apart from the induction period, the kinetic graphs are satisfactory represented by a rate equation assuming three independent first-order reactions: fast crosslinking, degradation, and slow crosslinking. The rate equation contains seven kinetic parameters. Over the temperature range studied, there is no difference between the values of activation energy for fast crosslinking, for degradation, for slow crosslinking, and for ti−1. Due to the presence of thiourea, the values of the induction period, the rate constant, and the extent of slow crosslinking are decreased. Simultaneously the activation energies calculated from degradation and slow crosslinking are significantly increased. On the basis of the above results, the mechanism of the sulfur-free thiuram vulcanization, in which ionic and radical reactions take place, is discussed.

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Persistent Photoconductivity And Thermal Recovery Kinetics Of Low Energy Ar + Bombarded GaAs

MRS Proceedings ◽

10.1557/proc-223-203 ◽

1991 ◽

Vol 223 ◽

Author(s):

A. Vaseashta ◽

L. C. Burton

Keyword(s):

Deep Level Transient Spectroscopy ◽

Deep Level ◽

Thermal Recovery ◽

Low Energy ◽

Persistent Photoconductivity ◽

Transport Parameters ◽

Excellent Correlation ◽

Proposed Model ◽

Transient Spectroscopy ◽

Kinetics Of

ABSTRACTKinetics of persistent photoconductivity, photoquenching, and thermal and optical recovery observed in low energy Ar+ bombarded on (100) GaAs surfaces have been investigated. Rate and transport equations for these processes were derived and simulated employing transport parameters, trap locations and densities determined by deep level transient spectroscopy. Excellent correlation was obtained between the results of preliminary simulation and the experimentally observed values. The exponential decay of persistent photoconductivity response curve was determined to be due to metastable electron traps with longer lifetime and is consistent with an earlier proposed model.

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Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19821780 ◽

1982 ◽

Vol 47 (7) ◽

pp. 1780-1786 ◽

Cited By ~ 2

Author(s):

Rostislav Kudláček ◽

Jan Lokoč

Keyword(s):

Experimental Data ◽

Activation Energy ◽

Liquid Phase ◽

Ionizing Radiation ◽

Oxide Catalyst ◽

Absorbed Dose ◽

Hydrogenation Rate ◽

Solution Composition ◽

Mixed Catalyst ◽

Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

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On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

Journal of Elastomers & Plastics ◽

10.1177/00952443211020330 ◽

2021 ◽

pp. 009524432110203

Author(s):

Sudhir Bafna

Keyword(s):

Mechanical Properties ◽

Activation Energy ◽

Weight Loss ◽

Oxygen Consumption ◽

Dwell Time ◽

Room Temperature ◽

Elevated Temperatures ◽

Degradation Mechanism ◽

Kinetics Of ◽

Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

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Fluoride Leaching of Titanium from Ti-Bearing Electric Furnace Slag in [NH4+]-[F−] Solution

Metals ◽

10.3390/met11081176 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1176

Author(s):

Fuqiang Zheng ◽

Yufeng Guo ◽

Feng Chen ◽

Shuai Wang ◽

Jinlai Zhang ◽

...

Keyword(s):

Activation Energy ◽

Electric Furnace ◽

Kinetic Equations ◽

Surface Chemical ◽

Leaching Rate ◽

Surface Chemical Reaction ◽

Mechanism And Kinetics ◽

Semi Empirical ◽

Kinetics Of ◽

Furnace Slag

The effects of F− concentration, leaching temperature, and time on the Ti leaching from Ti-bearing electric furnace slag (TEFS) by [NH4+]-[F−] solution leaching process was investigated to reveal the leaching mechanism and kinetics of titanium. The results indicated that the Ti leaching rate obviously increased with the increase of leaching temperature and F− concentration. The kinetic equation of Ti leaching was obtained, and the activation energy was 52.30 kJ/mol. The fitting results of kinetic equations and calculated values of activation energy both indicated that the leaching rate of TEFS was controlled by surface chemical reaction. The semi-empirical kinetics equation was consistent with the real experimental results, with a correlation coefficient (R2) of 0.996. The Ti leaching rate reached 92.83% after leaching at 90 °C for 20 min with F− concentration of 14 mol/L and [NH4+]/[F−] ratio of 0.4. The leaching rates of Si, Fe, V, Mn, and Cr were 94.03%, 7.24%, 5.36%, 4.54%, and 1.73%, respectively. The Ca, Mg, and Al elements were converted to (NH4)3AlF6 and CaMg2Al2F12 in the residue, which can transform into stable oxides and fluorides after pyro-hydrolyzing and calcinating.

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A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Ceramics ◽

10.3390/ceramics4020025 ◽

2021 ◽

Vol 4 (2) ◽

pp. 331-363

Author(s):

Eugeniy Lantcev ◽

Aleksey Nokhrin ◽

Nataliya Malekhonova ◽

Maksim Boldin ◽

Vladimir Chuvil'deev ◽

...

Keyword(s):

Activation Energy ◽

Solid Phase ◽

Continuous Heating ◽

Diffusion Creep ◽

Hard Alloys ◽

Fine Grained ◽

Plasma Sintering ◽

Spark Plasma ◽

The Impact ◽

Kinetics Of

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

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Multifaceted phase ordering kinetics of an antiferromagnetic spin-1 condensate

Scientific Reports ◽

10.1038/s41598-021-88454-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Joanna Pietraszewicz ◽

Aleksandra Seweryn ◽

Emilia Witkowska

Keyword(s):

Scaling Laws ◽

Study Phase ◽

One Dimensional ◽

Phase Domain ◽

Ordering Kinetics ◽

Domain Coarsening ◽

Long Time ◽

Phase Ordering ◽

Kinetics Of ◽

Antiferromagnetic Spin

AbstractWe study phase domain coarsening in the long time limit after a quench of magnetic field in a quasi one-dimensional spin-1 antiferromagnetic condensate. We observe that the growth of correlation length obeys scaling laws predicted by the two different models of phase ordering kinetics, namely the binary mixture and vector field. We derive regimes of clear realization for both of them. We demonstrate appearance of atypical scaling laws, which emerge in intermediate regions.

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Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

Rubber Chemistry and Technology ◽

10.5254/1.3542149 ◽

1960 ◽

Vol 33 (2) ◽

pp. 335-341

Author(s):

Walter Scheele ◽

Karl-Heinz Hillmer

Keyword(s):

Activation Energy ◽

Physical Properties ◽

Chemical Kinetics ◽

Kcal Mole ◽

First Order ◽

Equilibrium Swelling ◽

Kinetics Of ◽

Kinetics Of Vulcanization ◽

Limiting Value ◽

Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

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Magnetic Properties, Nanostructure, and Ordering Kinetics of Nb Additive FePtCu Films

Materials Science Forum ◽

10.4028/www.scientific.net/msf.638-642.1743 ◽

2010 ◽

Vol 638-642 ◽

pp. 1743-1748

Author(s):

G.J. Chen ◽

Y.H. Shih ◽

Jason S.C. Jang ◽

S.R. Jian ◽

P.H. Tsai ◽

...

Keyword(s):

Heat Treatment ◽

Activation Energy ◽

Magnetic Properties ◽

Heating Rates ◽

Fept Alloy ◽

Ordering Kinetics ◽

Nb Content ◽

Kinetics Of ◽

Nb Addition ◽

Microstructure And Magnetic Properties

In this study,the (FePt)94-xCu6Nbx (x=0, 2.87, 4.52, 5.67) alloy films were prepared by co-sputtering. The effects of Nb addition content and heat treatment on the microstructure and magnetic properties of the polycrystalline FePtCu films are reported. Our previous experiments showed that the ordering temperature of the (FePt)94Cu6 films reduced to 320 °C, which is much lower than that of the FePt alloy. However, the grain growth after heat treatment limited the practical application in recording media. By adding the Nb content in the (FePt)94Cu6 film, the grain sizes of the films can be adjusted from 50 to 18nm, even for the films annealed at temperature as high as 600°C. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, revealed that the addition of Nb enhanced the activation energy of ordering from 87 kJ/mol to 288 kJ/mol for the (FePt)94-xCu6Nbx (x=0 and 2.87, respectively) films. The reduction of the grain size and the corresponding increase in the activation energy of the Fe-Pt-Cu-Nb films might result from the precipitation of the Nb atoms around the ordering FePt phase. The (FePt)94-xCu6Nbx (x=2.87) film showed a coercive force of 13.4 kOe and the magnetization of 687 emu/cc.

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