Investigation of ionic thermocurrents in SrCl2-K crystals

Ionic thermocurrents in SrCl₂-K crystals have been investigated for the first time. Two maxima of thermally stimulated depolarization currents have been detected at T=112°K and T=210–240°K. The low-temperature maximum with a reorientation energy =0.25 eV and a frequency factor _o=7.1·10⁹ Hz is due to relaxation of impurity-vacancy dipoles. Its intensity grows linearly with the concentration of the dopand. The high-temperature maximum is due to the space charge. Its activation energy =0.46 eV coincides with the migration energy of anion vacancies associated with the potassium ions.Translated from Izvestiya Vysshikh Zavedenii, Fizika, No. 9, pp. 80–83, September, 1982.     

Thermally stimulated currents for a mixed free-carrier recombination mechanism

Analytical expressions are obtained in this paper for thermally stimulated currents in the ordinary and photoelectret modes for a mixed mechanism of free-charge-carrier recombination and a strong duplicate attachment. It is shown that in this case the same trap parameters can be determined from experimental curves for thermally stimulated currents as for bi- and monomolecular recombination; however, the majority of computation methods should be modified. Modified formulas are proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 92–97, July, 1976.The authors are grateful to A. R. Regel' for interest in the research and for useful consultation, and also to B. S. Medved' for aid in computing the curves on an electronic computer.     

Thermally stimulated currents in ice. Correction for orientational defects

The Bernal and Fowler model of ice [1] has been supplemented with modern ideas about relaxing defects arising as a result of migration of a proton along hydrogen bonds [2, 3]. We develop a theory for thermally stimulated currents (TSC) in hexagonal ice. We propose a kinetic equation taking into account relaxation of the structural defects supporting proton conductivity in the crystals. We obtain formulas qualitatively describing thermally stimulated depolarization currents and also a formula for calculating the activation energy for structural defects, allowing us to compare with experiment. Due to the unwieldiness of the calculations, we present only the derivation of the kinetic equations and analysis of the solution.Karaganda Polytechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 93–98, February, 1994.     

Negative thermally stimulated currents in ice

Using precision equipment of our own design, we measured thermally stimulated currents (TSCs) in pure crystalline ice and crystalline ice doped with HCl or NH₄OH. The conditions for heterocharge and homocharge decay under thermally stimulated depolarization (TSD) were studied. The role of proton relaxation during the formation of an electret state of the ice was determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–10, December, 1993.     

Thermally stimulated relaxation currents due to forces of nonelectrostatic origin

It is shown that unusual thermally stimulated relaxation currents can arise in the external circuit on homogeneous heating of an insulator with a polar direction that is in a thermodynamically nonequilibrium state. These currents differ from thermally stimulated depolarization currents in being observed in a specimen that is unpolarized or has been depolarized. The temperature dependence of these relaxation currents is obtained for a particular model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 32–35, July, 1982.     

Optical Properties and Structure of Electroluminescent SiOx:Tb Films

Using nondestructive optical methods (measurement of transmission spectra in the visible and IR regions and multiangular ellipsometry), we have studied the structural changes in SiO _x :Tb films subjected to high–temperature annealing in air, which are responsible for the appearance of electroluminescence in light–emitting structures based on them. It has been established that the appearance of green electroluminescence in such a film (upon annealing of the film in air at temperatures of 600–800°C) is due to the structural changes in its matrix, leading to partial disproportionation of the thermally deposited SiO _x :Tb film (as a result, the film represents a mixture of several phases – Si, SiO_x, and SiO₂). Films showing blue electroluminescence (annealing temperature 1000°C) are characterized by a higher content of oxygen, a better compactness, and a better macroscopic homogeneity in comparison with films showing green electroluminescence. It is also shown that the thermal cycling accompanying the annealing leads to the appearance of birefringence and scattering in SiO _x O:Tb films. It is anticipated that the annealing–stimulated structural changes taking place at both the micro– and the macrolevel should cause changes in the local surroundings of the luminescence center and in the conditions for heating the charge carriers exciting the luminescence centers.     

Effect of intrinsic lattice defects on excess currents of gallium arsenide tunnel diodes

Gallium arsenide tunnel diodes were irradiated with electrons of energy E = 2.0 MeV at room temperature. Secondary hump structures were observed in the region of 0.45 V and 0.65–1.1 V forward bias. The variation in the excess currents of diodes subjected to electronic bombardment is described on the basis of models including three levels; E_B + 0.25 eV, E_B + 0.55 eV, and E_C–0.5 eV. Annealing of radiation-induced defects is shown to take place in two stages at temperatures of 140–180°C and 200–240°C. Switching and memory effects are observed when the current-voltage characteristics (CVC) of tunnel diodes are measured at liquid-nitrogen temperatures in darkness.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 88–92, September, 1976.     

Formation of thermally stable low-resistance Ti/W/Au ohmic contacts on n-type GaN

A Ti(12 nm)/W(20 nm)/Au(50 nm) metallization scheme has been investigated for obtaining thermally stable low-resistance ohmic contacts to n-type GaN (4.0×10¹⁸ cm^-3). It is shown that the current–voltage (I–V) characteristics of the samples are abnormally dependent on the annealing temperature. For example, the samples that were annealed at temperatures below 750 °C for 1 min in a N₂ ambient show rectifying behavior. However, annealing the samples at temperatures in excess of 850 °C results in linear I–V characteristics. The contact produces a specific contact resistance as low as 8.4×10^-6 Ω cm² when annealed at 900 °C. It is further shown that the contacts are fairly thermally stable even after annealing at 900 °C; annealing the samples at 900 °C for 30 min causes insignificant degradation of the electrical and structural properties. Based on glancing angle X-ray diffraction and Auger electron microscopy results, the abnormal temperature dependence of the ohmic behavior is described and discussed. PACS 72.80.Ey; 73.40.Cg; 73.20.At; 79.60Bm; 73.40.Gk     

Positron annihilation and Hall effect in electron irradiatedn-InP crystals

Positron annihilation and Hall effect inn-InP crystals as a function of electron irradiation up to 1 · 10¹⁹ cm^–2 and post-irradiated isochronal annealing up to 550 °C have been studied. It is concluded that in irradiatedn-InP samples positrons interact with negatively charged acceptor-type defect with level atE _c –0.33 eV, probablyV _In (primary defect). In post-irradiated isochronal annealed (up to 330 °C) samples ofn-InP positron trapping occurs preferably in secondary defects-vacancy clusters, which are formed in the temperature range (150–300 °C). Inn-InP crystals containing radiation induced defects the trapping rate was found to decrease with temperature in the range (300–77) K.     

Thermal ionization of impurity centers in Fe-doped Bi12SiO20 and Bi12GeO20 crystals

The spectral and temperature dependence of the optical absorption and thermally stimulated depolarization currents in Fe-doped Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀ crystals are investigated in the photon energy range 1.36–3.46 eV and temperature 85–750 K. The results show thermally induced electron redistribution between donor and acceptor levels and defect association-dissociation processes and are discussed using the configuration-coordinate model. Fiz. Tverd. Tela (St. Petersburg) 41, 1006–1011 (June 1999)     

Aerosol Synthesis of Fullerene Nanocrystals in Controlled Flow Reactor Conditions

Fullerene nanocrystals in the size range 30–300 nm were produced starting from atomized droplets of C₆₀ in toluene. The experiments were carried out under well-controlled conditions in a laminar flow reactor at temperatures of 20–600°C. Particle transformation and crystallization mechanisms of polydisperse and monodisperse (size classified) fullerene aerosol particles were studied. The results show that fullerene particles are roughly spherical having pores and voids at temperatures of 300°C and below. Particles are already crystalline and likely fine-grained at 20°C and they are polycrystalline at temperatures up to 300°C. At 400°C monodisperse particles evaporate almost completely due to their low mass concentration. Polydisperse particles are crystalline, but sometimes heavily faulted. At 500°C most of the particles are clearly faceted. In certain conditions, almost all particles are hexagonal platelets having planar defects parallel to large (111) faces. We suggest that at 500°C fullerene particles are partially vaporized forming residuals with lamellar defects such as twins and stacking faults, which promote crystal growth during synthesis. Subsequently fullerene vapor is condensed on faces with defects and hexagonal particles are grown by a re-entrant corner growth mechanism. At 600°C particles are single crystals, but they have a less distinct shape due to higher vaporization of fullerene. The final size and shape of the particles are mainly determined at the reactor outlet in the short time when the aerosol cools.     

The reaction process of the Bi-Sr-Ca-Cu-O system and the forming mechanism of the 2212 superconducting phase

The reaction process and the reaction behavior of each component in the Bi-Sr-Ca-Cu-O system are presented in this paper. It reveals that the reaction is carried out in three different stages: forming of an insulating interphase at 680°C–790°C, forming of the 2212 superconducting phase at 790°C–860°C and forming often semiconducting phases in the presence of the liquid phase at 860°C–970°C. It is also confirmed that the 2212 superconducting phase (T _c=85 K) is formed by the reaction of a trinary interphase together with CuO, SrO and CaO. A new two-step method is presented to prepare the 2212 superconducting phase by a presynthesized interphase.     

ИЗМЕРЕНИЯ ЭЛЕКТРОННЫХ РЕЛАКСАЦИОННЫХ ПРОЦЕССОВ В МАРГАНЦЕВЫХ ФЕРРИТАХ

The measurements of magnetic loss factor in the system Mn _x Fe_3–x O_4+y for 0.62x1.66 are described. The temperature range used was 2°K to 360°K and four fixed frequencies 75, 150, 300, and 600 kHz were employed. The results show, that three distinct processes were found with various dependences upon composition. The corresponding maxima in tg vsT curves are situated at 2°K, 10°–50°K, and 90°–350°K respectively. The connection of these processes with electron transport and/or reorientation of distortions surrounding octahedrally coordinated Mn³⁺ ions is used as a basis for an interpretation already proposed earlier.     

Switching processes and the electronic subsystem in ferroelectric ceramic of the barium-lead niobate type

This paper is devoted to the study of the relation between switching processes and the states of the electronic subsystem in a ferroelectric ceramic. Experimental observations of the dielectric hysteresis loops at 5·10^–3 Hz, thermally stimulated currents, the relaxation of the conductivity, and the temperature dependence of the stationary conductivity in the temperature range 280–423 K were performed. Formulas are proposed for calculating the hysteresis loop and the coefficient of dielectric viscosity from the parameters of the hysteresis loop. It is established that for a ferroelectric ceramic of the BLN type charge carriers localized at the levels 0.18, 0.25, 0.27, and 0.37 eV play the determining role in the formation of the equilibrium ferroelectric state far from the phase-transition point. It is shown that the coefficient of dielectric viscosity for polycrystalline samples is determined by the relaxation time of the electronic subsystem and the orientation of the internal field in the sample.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 9–14, February, 1989.In conclusion we thank V. P. Kamentsev and A. V. Nekrasov for a useful discussion of this work.     

Electrophysical and photoelectric properties of (CdSe)1−x(CuInSe2)x solid solutions

The results are given of measurements of the electrophysical properties in the interval of temperatures 300–900°K and of the photoelectric properties at 300°K of (CdSe)_1–x–(CuInSe₂)_x solid solutions. It is shown that the electrophysical and photoelectric properties of the solid solutions depend on the composition and temperature. The forbidden-band widths calculated from the temperature dependence of the conductivity and from the photoconductivity spectrum, respectively, vary from 1.68 and 1.77 eV for initial compound CdSe to 1.25 and 1.18 eV for the solid solution Cu_0.1Cd_0.9In_0.1Se_1.1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 41–43, January, 1992.     

Temperature dependence of the stationary photocurrent in doped sillenite type crystals

The temperature dependence of the photocurrent in doped sillenite-type crystals is investigated in the temperature range 80–300°K. In the region of low temperatures thermally activated photocurrent is observed, while at high temperatures quenching is observed. In a number of specimens the temperature quenching section is absent. The results are explained within the framework of a multilevel recombination model involving slow and fast recombination centers as well as capture levels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 85–89, June, 1985.     

Electric and tensoelectric study of radiation defects in GaAs

The electric and tensoelectric properties are studied for GaAs crystals which have been irradiated by electrons (2.3 Mev) at 300°K with integrated fluxes of up to 2·10¹⁵ –1·10¹⁹ cm^–2. On the basis of the electrical neutrality equation, including seven energy levels (E1–E5, H0, H1) of the radiation defects, the specific resistivity and the strain sensitivity coefficient are quantitatively analyzed as a function of exposure. The pressure coefficients for the E1–E5 levels with respect to the _c ⁶ point are determined to be (0, 9.6, 11.0, 11.6, 11.6)·10^–6 eV/bar, respectively, at 300°K.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–87, October, 1986.     

Electrical behaviour of thermally diffused silicon solar cells submitted to rapid annealing

Conventional thermally diffused silicon solar cells have been submitted to subsequent rapid thermal annealing (1–10 s) in the temperature range 600–1000 °C, in order to investigate the effects of such treatments on the electrical behaviour. It appears that a decrease of the minority carrier diffusion length in the base region of the device is produced due to the generation of microscopic defects (as measured by DLTS) induced by the rapid high temperature cycling.     

Determination of the quasicontinuous defect-energy distribution for a disordered insulator by thermally stimulated depolarization

A method is described for determining the quasicontinuous energy distribution of the electrically active defects in a disordered insulator from a family of thermally stimulated depolarization-current curves as measured for various polarization temperatures. It is shown that the method is comparable in informativeness with the method of fractional thermally stimulated depolarization while it is technically simpler to operate. Results are presented from a study on the defect energy distributions in amorphous films of silicon monoxide.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 71–75, December, 1981.     

Photoconductivity of thin films of modifications of zinc sulfide

Fine structure in the spectral response in the 300–340 nm range is reported for polycrystalline films at 90 ° and 293 ° K. The response spectrum is compared with the absorption and reflection spectra; peaks in absorption correspond to minima in the photocurrent. The detailed spectrum is dependent on the modification and on the structure defects.