Thermally Stimulated Currents in Si〈P,Au〉: Analysis of Rate Equations

Thermally stimulated currents (TSCs) in semiconductors were analyzed theoretically in terms of a single-level model. The rate equations describing TSCs in the single-level model were solved numerically for various process parameters, which made it possible to assess the effect of each parameter on the TSC curve. The effects of physical and instrumental parameters were analyzed: the former characterize the material and cannot be changed during measurements, and the latter can be varied readily during experiment (applied voltage, excitation intensity, etc.). By adjusting the instrumental parameters, one can control the shape of the TSC curve and, eventually, assess the parameters of trap levels. The slow and fast retrapping approximations were examined for an arbitrary heating profile and constant-rate heating followed by isothermal holding until complete detrapping. The effect of excitation wavelength on the TSC in SiP,Au was studied. It was shown that, using resonance photoexcitation, one can identify the type (electron or hole) of the traps and evaluate their ionization energy. A new approach to TSC data processing was proposed: cleaning of a higher temperature peak from the lower temperature peak by storing the preilluminated material in the dark at the relaxation temperature of the lower temperature peak. The depths and capture cross sections of three trapping centers in SiP,Au were evaluated.     

Analysis of Differential Equations of Thermally Stimulated Currents in Semiconductors: Arbitrary Heating Profile

The thermally stimulated current (TSC) rate equations are solved for an arbitrary heating profile. The equations are analyzed for fast and slow retrapping regimes in the case when the sample is rapidly heated at a constant rate to the set temperature and held there until the current fully decays.     

Thermally Stimulated Currents in MnGaInS4 Single Crystals

Thermally stimulated current measurements indicate that MnGaInS₄ single crystals contain fast trapping centers. The trap depths, concentrations, and capture cross sections are determined. The results obtained by the thermal cleaning method demonstrate that the band gap of MnGaInS₄ contains two trapping levels with exponential energy distributions: 0.05–0.20 and 0.16–0.25 eV.     

Deep-trap discharge in semiconductors in response to concurrent heat and light flows

We have numerically solved differential equations describing the detrapping kinetics of impurity traps during heating (thermally stimulated conductivity) under illumination (induced impurity photoconductivity) with arbitrary trap parameters. An algorithm has been formulated for determining parameters of impurity traps in semiconductors (ionization energy, photon capture cross section, and concentration) from isothermal detrapping curves measured under illumination.     

Studies of thermally stimulated currents and surface charge in polystyrene thin films

A careful study was undertaken of the initial charge developed on the non-metallized surface and of short-circuit thermally stimulated currents (TSCs) in unilaterally metallized polystyrene (PS) films 25 microm thick. The films had been negatively charged by Townsend breakdown at a voltage of −5 kV at various temperatures ranging from 90 to 130°C. The surface charge densities observed were of the order of 10^-8 C cm^-2, corresponding to full trap densities of the order of 10¹⁴ cm⁻³. The short-circuit TSC spectra of newly charged samples show a single peak at a temperature between 98 and 102°C. The thermal activation energy associated with this peak was found to be 1.2 eV. An analysis of TSCs indicates that electrons are subject to fast retrapping in PS. The ratio of the mean charge depth to the sample thickness is found to increase from 0.069 to 0.12 with the increase in the temperature of polarization, indicating a higher charge accommodation at higher temperatures of polarization. The trap-modulated mobility values for electrons at the TSC peak temperatures are the order of 10⁻¹² cm² V⁻¹s⁻¹. Such low mobility values at peak temperatures are considered to indicate the excellent charge storage properties of PS.     

Trapping parameters of repulsive centers in SbSI single crystals

Charge trapping centers in antimony sulphide iodide (SbSI) single crystals have been investigated by the use of thermally stimulated current (TSC) technique. The TSC spectrum consists of only one apparent peak which is found to be associated with a single trapping level. Those traps are experimentally found to obey the monomolecular kinetics. The trapping parameters as the energy depth, temperature dependent frequency factor and capture cross section together with the concentrations of the corresponding discrete trapping level are determined. The TSC signal is found to be strongly dependent on illumination temperature of the sample and this is explained by the model in which the traps are considered to be surrounded by repulsive potential barriers.     

Evaluation of Impurity Concentration in Semiconductors from the Relaxation of Thermally Stimulated Currents

The rate equations of thermally stimulated currents due to isothermal detrapping are analyzed. The results demonstrate that, at small trap population, isothermal detrapping follows an exponential law, independent of the trapping rate: fast, slow, or intermediate (the trapping time is comparable to the recombination time). Expressions are derived for determining the density of charged traps in the course of detrapping and assessing the trap density from known trap parameters and thermally stimulated current spectra.     

Linear modulation optically stimulated luminescence and thermoluminescence techniques in Al2O3:C

An analysis of the linear modulation-OSL (LM-OSL) peak and the main TL peak from irradiated Al2O3:C is presented. Data are presented indicating that the LM-OSL peak is composed of three overlapping components originating from populated traps with optical cross sections of 10(-18) - 10(-20) cm2. Studies of the main TL peak before and after LM-OSL measurement indicate that the first two LM-OSL components, corresponding to traps with the largest optical cross sections, originate from traps which also contribute to the low temperature side of the TL peak and that the third component, corresponding to the traps with smallest optical cross section, are due to traps that contribute to the high temperature side of the TL peak. Some consequences for dosimetry are discussed.     

Thermally Stimulated Currents in Sillenite Crystals

Thermally stimulated currents in nominally undoped, doped, and vacuum-annealed Bi₁₂TiO₂₀, Bi₁₂SiO₂₀, and Bi₁₂GeO₂₀ crystals were measured between 80 and 300 K. The results were used to assess the depth and concentration of trapping centers.     

Kinetic modelling of the optically stimulated conversion of peaks 5a and 5 to peak 4 in LiF:Mg,Ti (TLD-100)

The TC/LC conversion model for peaks 4, 5a and 5 in LiF:Mg,Ti (TLD-100) has been studied by solution of the coupled differential equations describing the charge carrier traffic following optical stimulation. Aspects of the model investigated were (i) the two-component exponential decay of the composite peak 5 TL intensity following the bleach, (ii) the role of retrapping during bleaching, (iii) the hole nature of peak 4 and (iv) the conversion of peak 5a traps to peak 4 traps. The high conversion efficiency is naturally explained due to the absence of conduction band competitive mechanisms in the optical ionisation of the electron in the e-h occupied structure corresponding to peak 5a and thereby leading to the hole-only occupied TC/LC leading to peak 4.     

A new technique to study transient conductivity under pulsed monochromatic light in Cr-doped GaAs using acoustoelectric voltage measurement

The transient conductivity of high-resistivity, Bridgman grown, Cr-doped GaAs under pulsed monochromatic light is monitored using transverse acoustoelectric voltage (TAV) at 83 K. Keeping the photon flux constant, the height and transient time constant at the TAV are used to calculate the energy dependence of the trap density and its cross section, respectively. Two prominent trap profiles with peak trap densities of approximately 10(17) cm(-3) eV(-1 ) near the valence and the conduction bands are detected. These traps have very small capture cross sections in the range of 10(-23 )-10(-21 )cm(2). A phenomenon similar to the persistent photoconductivity with transient time constants in excess of a few seconds (in some cases, a few hundred seconds) in high-resistivity GaAs at T=83 K is also detected using this technique. These long relaxation times are readily explained by the spatial separation of the photo-excited electron-hole pairs and the small capture cross section and large density of trap distribution near the conduction band. The technique is nondestructive and, because of the dependence of the polarity of the acoustoelectric voltage on the carrier type, it yields information about the charge of the transient carriers and the type of deep traps involved in the release or trapping of these carriers.     

Simultaneous Thermoluminescence and Thermally Stimulated Current in Polyamide

We have obtained simultaneous thermoluminescence (TL) and thermally Stimulated current (TSC) spectra in two types of polyamide film, such as nylons 6 and 11 under study of electron detrapping and recombination. There are three main relaxation peaks or regions, designated γ,β and α in order of increasing temperature in the TSC spectra, in contrast, a high temperature relaxation peak in TL spectra disappears. The centers or peaks of these relaxation regions are located at near 180, 230 and 310 K, respectively, deviating±10 K. However. we also observed two anomalous phenomena: first, a very large, short-circuited, thermally stimulated discharge current (TSDC) up to 10-8 A, but reversible in direction for non-polarized nylons 6 and 11, even after several times repeatedly; secondly, no TL signal except for non-polarized nylon 6 film.     

Ionization and drift characteristics of electrons in copper vapor in electric field

The ionization and drift characteristics (Townsend coefficient, drift velocity, mean energy) of electrons in copper vapor occurring in a homogeneous electric field have been numerically simulated. Copper is of interest by offering an example of element with the peak excitation cross section being significantly greater than the ionization cross section. A two-branch curve of electron loss is constructed, which separates the region of effective electron multiplication and the region of significant runaway (from which electrons leave the discharge gap without multiplication). Owing to the large excitation cross section of copper, the upper and lower branches of the electron leaving curve are closer to each other for this metal vapor than for usual gases.     

Effect of Inorganic Filler on Thermally StimulatedCurrent in Low-density Polyethylene

By measuring the thermally stimulated current (TSC) spectra at various fields in low-density polyethylene with inorganlc filler (f LDPE) and comparing with those in LDPE, we found that thelr TSC spectra shew slgnificant distinction. in virtue of analysing change of peak current,peak temperature and activation enew with pollng field, it can be depicted that the TSC in f-LDPE specimen comes from dipole relaxation of residual silanol groups on surface of filler, but the injected electrons in very high 6elds, no doubt, are captured in deeper traps, and they can not be released even near 100"C. The filler (kaolin) plays a key role in changing the TSC spectra through deep and interfacial traps existing between the filler and the polymer matrix. Whereas,the TSC spectra of LDPE specimen possess marked characteristics of electron release from traps in amorphous-crystalline or crystalline region.     

Topic scientific community in science: a combined perspective of scientific collaboration and topics

Scientific communities are clusters of researchers and play important roles in modern science. Studying different forms of scientific communities that either physically or virtually exist is a feasible way to disclose underlying mechanisms of science. From the perspective of complex networks, topology-based communities and topic-based communities reflect scientific collaboration and topical features of science respectively. However, the two features are not isolated but intertwined in scientific practice. This study proposes an approach to detect Topical Scientific Communities (TSCs) with both topology and topic features by applying machine learning techniques and network theory. As an example, the TSCs of the informetrics field are detected, and then the characteristics of these TSCs are analyzed. It is shown that collaboration patterns on the topic level can be revealed by analyzing the static network structure and dynamics of TSCs. Furthermore, cross-topic collaborations at multiple levels could be investigated through TSCs. In addition, TSCs can effectively organize researchers in terms of productivity. Future work will further explore and generalize characteristics of TSCs, and the applications of TSCs to other tasks of studying science.     

Thermally stimulated currents in organic monomolecular layers

The polarization phenomenon in metal/organic monomolecular layer/metal devices has been studied by thermally stimulated currents (TSCs). The thermal current peaks for various experimental conditions (temperature, electric field, polarization time, dielectric thickness) show that the polarization in orthophenanthroline with three stearic chains is due to local charge displacements between two potential wells. We found that these charge displacements vary as the thickness increases, which implies that the dielectric structure changes when the number of monolayers increases.The high values of the activation energies (1.1–3.4 eV) determined from the current peaks suggest that the moving charges are ions. In orthophenanthroline multilayers at room temperature we have not observed a notable space charge phenomenon due to ion displacements from one electrode to the other.     

The Heating of Electrons in Magnetic Traps of Low-Pressure Electron-Cyclotron-Resonance Microwave-Frequency Reactors

Methods are analyzed of maintaining plasma in low-pressure electron-cyclotron-resonance reactors in which the ionization is caused by fast electrons blocked in traps developed by permanent magnets. The key part played by zones of electron-cyclotron heating of electrons by the electric field of the wave is treated. The mathematical simulation of the electron motion in magnetic traps is used to investigate the effect of the size of magnetic traps on the efficiency of heating, and the principles of designing electron-cyclotron-resonance plasma MW (microwave-frequency) reactors are formulated.     

Thermally stimulated discharge currents in iodine-doped polystyrene films

Studies were made of the thermally stimulated discharge (TSD) current in iodine-doped polystyrene (PS) films (20 μm thick) as a function of the iodine concentration and the temperature of polarization. Unpolarized doped films were observed to give TSD currents. This is attributed to the formation of charge transfer complexes (CTCs) between iodine and the main molecular chain of PS. Doping PS with iodine lowers the temperáture at which the current peak occurs and enhances the peak current. An increase in the temperature of polarization increases the TSD current and shifts its maximum to a higher temperature while an increase in the concentration of iodine lowers the activation energy of the discharge process. The thermally assisted detrapping of carriers is suggested as a possible mechanism.     

Trapping centers and their distribution in Tl2InGaSe4 single crystals by thermally stimulated luminescence

Thermoluminescence (TL) measurements in Tl₂InGaSe₄-layered single crystals have been carried out in the temperature range of 10–200 K at various heating rates (0.2–1.0 K s^?1) to get information about the characteristics of traps. Two TL overlapping glow peaks related to defect levels have been clearly observed. Thermal cleaning procedure was applied to the glow curves to separate overlapped peaks. Initial rise, peak shape, and heating rate methods were used to calculate the activation energies of the revealed traps. The energy values of 5 and 28 meV were evaluated for the peaks observed at low and high temperatures, respectively. Moreover, heating rate dependence and traps distribution analysis were also investigated on the curve obtained after thermal cleaning. The activation energies of the distributed trapping centers were found to be increasing from 29 to 151 meV with increasing the illumination temperature from 42 to 80 K.     

An investigation of the heating of electrons in multipolar magnet systems and design of low-pressure electron-cyclotron-resonance microwave-frequency reactors

The problem is treated of sustaining plasma in low-pressure electron-cyclotron-resonance plasma reactors in which the main source of ionization is provided by fast electrons blocked in magnetic traps of multipolar magnet systems. The electron-cyclotron heating of electrons by the electric field of a microwave is analyzed. The numerical simulation of the electron motion in magnet systems of various configurations and statistical processing of the calculation results are used to simulate the high-energy part of the electron energy distribution function. It is demonstrated that the main factor defining the electron loss in magnetic traps in the collisionless limit is the departure of fast electrons from magnetic traps to the boundaries of the structure among other things. Comparison is made of different multipolar magnet systems, and the principles of designing optimal electron-cyclotron-resonance MW reactors are formulated.