Transmission spectra of epitaxial layers of Pb1 ? xEuxTe (0 ≤ x ≤ 0.37) solid solutions in the frequency range 7–4000 cm?1

The spectra of epitaxial Pb_{1 − x} Eu _x Te (0 ≤ x ≤ 0.37) solid solution layers grown on BaF₂ and Si substrates have been investigated over a wide frequency range 7–4000 cm⁻¹ at temperatures of 5–300 K. Apart from the phonon and impurity absorption lines, the absorption in a local mode in PbEuTe layers of substrates and buffer layers has been observed in the frequency range 110–114 cm⁻¹. As the temperature decreases from 300 to 5 K, the transverse phonon mode softens from 33.0 to 19.5 cm⁻¹.     

The Influence of Resistance of the Epitaxial-Film Volume on the Capacity-Voltage Characteristics of the HgCdTe/AOF and HgCdTe/SiO<Subscript>2</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> MIS Structures

The dependence of active and reactive components of the admittance of MIS structures based on heteroepitaxial Hg_0.78Cd_0.22Te produced by molecular-beam epitaxy as a function of bias voltage is experimentally studied in the frequency range 1 kHz − 1 MHz. The resistance of the epitaxial-film volume is shown to significantly affect the measured admittance in the case where the electron concentration in HgCdTe is up to 5·10¹⁴ cm^{− 3}, and this is manifested in a number of features of the capacity-voltage characteristics. The resistance of the epitaxial-film volume is found for the samples with different initial conductivity and for the samples with graded-band subsurface layers. The techniques are proposed that make it possible to avoid the influence of volume resistance on the admittance of MIS structures on the basis of heteroepitaxial HgCdTe. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 31–37, June, 2005.     

Optical properties of the ternary compound Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se:Co

We present the results of experimental studies of the optical properties of cobalt-doped Cd _x H_1−x Se (x = 0.18) single crystals with cobalt ion concentrations of NCo = 5·10¹⁸, 5·10¹⁹, and 1·10²⁰ cm⁻³ at T = 90 K and 300 K. The composition (x = 0.18) of the Cd _x Hg_1−x Se solid solution was selected so that the hypothetical resonance level is found on the bottom of the conduction band. We show that the cobalt ions in the mercury selenide can form a resonance donor level only for cobalt concentrations N_Co < 5·10¹⁸ cm⁻³. For N_Co ∼ 5·10¹⁸ cm⁻³, the cobalt ions substitute for mercury atoms, forming a solid solution and leading to an increase in the bandgap width and a change in the physical properties. The solubility of cobalt in the HgSe lattice can be greater than 5%–10%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 73–77, January–February, 2007.     

The wideband attenuation of short radio waves on mid-latitude paths during X-ray flares in January 2005

We present the results of the ionosphere oblique chirp sounding on the Cyprus—Nizhny Novgorod, Cyprus—Rostov-on-Don, and Moscow—Rostov-on-Don mid-latitude paths during X-ray flares in January 17, 19, and 20, 2005. It is found that during strong flares the blackout of short radio waves was observed over the entire frequency range of chirp sounding on the Cyprus—Nizhny Novgorod and Cyprus—Rostov-on-Don paths. Modeling of the electron-density profiles in the lower ionosphere based on absorption of short radio waves on the Moscow—Rostov-on-Don path at different stages of the decay of the X-ray radiation intensity is carried out. It is shown that at the instant corresponding to the maximum value of the flare radiation flux, the electron density in the lower ionosphere at altitudes 60–80 km increased by a factor of about 10 and 100 for flares with radiation flux densities 5·10⁻² and 3·10⁻¹ erg/(cm ²·s) in the wavelength range 0.5–4.0 Å which took place in January 19 and 20, respectively. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 1–8, January 2007.     

Spatial distribution profiles of defects in cadmium-mercury-tellurium after ion implantation

Defect spatial distributions are investigated after implantation of ions in Cd_xHg_1−xTe under various sets of conditions (radiation dose, type and energy of ions, ion current density, and dose absorption rate). Distribution profiles of electrically active radiation-induced defects are calculated with allowance for the generation of defect complexes of vacancion nature. Defect profiles are determined in experiments after implantation of hydrogen and iron ions at constant low ion current densities, and after implantation of copper, tungsten, and aluminum ions in the case of pulsed bombardment at high ion current densities. Secondary-ion mass spectrometry, electron-positron annihilation, Rutherford backscattering of ions, and differential Hall measurements are used to obtain distribution profiles of interstitial ions, vacancion and extended defects, and electrically active defects, respectively. The profiles of these defects are analyzed for various ion-implantation conditions. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 101–116, January, 1998.     

Assessment of the possibility of determination of the electrophysical characteristics of CdxHg1–xTe p+–n-structures using differential hall measurements

The process of reconstuction of the distribution profile of hole concentration in the p ⁺–n structure by the method of differential Hall measurements upon implantation of ions As⁺ (Е = 190 keV, D = 3.10¹⁴ cm^-2, j = 0.025 μA/cm²) into epitaxial films Cd _x Hg_1–x Te for x ~ 0.2, with the initial electron concentration and mobility n = 10¹⁴ cm^-3 and μ = 2∙10⁵ cm²∙V^–1∙s^–1 is numerically simulated. The dependences of degree of reconstruction of the hole-concentration distribution profile on the depth of a shunting n-layer and magnitude of the magnetic field, at which the electrophysical parameters of the p ⁺–n structure are measured, are calculated. The dependence of the limiting magnetic field determining the magnetic-field range for measurements on the n-layer depth is found. It is shown that in calculations one should use the conduction values measured at the same magnetic fields as the Hall coefficients for determination of the holeconcentration distribution profile using the Petritz model.     

Dielectric properties of epitaxial Pb1−x Sn x Te layers at microwave frequencies

The dielectric properties of epitaxial Pb_1−x Sn _x Te layers are investigated at 9 GHz in a composition range betweenx=0 and 0.225. The samples are characterized by fairly low carrier concentrations between 1.4×10¹⁶ and 32×10¹⁶ cm⁻³. Data of the static dielectric constant (ε ^s ) are obtained at temperatures of 77 and 300 K. The results of ε ^s are 25% to 100% higher compared to previous measurements in bulk material from other authors. The observed higher values of ε ^s in the investigated samples may be due to the reduced number of point defects in epitaxially grown Pb_1−x Sn _x Te layers. The model of Kawamura which predicts a dependence of ε ^s on the effective band gap cannot be verified.     

Near IR laser light visualizators using nonlinear GaSe and other layered crystallites

Two methods of preparation of the devices for visualization of pulsed and continuous near-IR (near infrared) are described and the results of conversion of pulsed and continuous IR (800–1360 nm) laser radiation into the visible range of spectra (400–680 nm) by using a transparent substrate covered with the particles (including nanoparticles) of effective nonlinear materials of GaSe _x S_{1 − x} (0.2 ≤ x ≤ 0.8) are presented. Converted light can be detected in transmission or reflection geometry as a visible spot corresponding to the real size of the incident laser beam. Developed device structures can be used for checking if the laser is working or not, for optical adjustment, for visualization of distribution of laser radiation over the cross of the beam and for investigation of the content of the laser radiation. Low energy (power density) limit for visualization of the IR laser pulses with 2–3 ps duration for these device structures are: between 4.6–2.1 μJ (3 × 10⁻⁴−1 × 10⁻⁴ W/cm²) at 1200 nm; between 8.4–2.6 μJ (4.7 × 10⁻⁴−1.5 × 10⁻⁴ W/cm²) at 1300 nm; between 14.4–8.1 μJ (8.2 × 10⁻⁴–4.6 × 10⁻⁴ W/cm²) at 1360 nm. Threshold damage density is more than 10 MW/cm² at λ = 1060 nm, pulse duration τ = 35 ps. The results are compared with commercially existing laser light visualizators.     

The study of lithium fast ion conductors of Li3xLa0.67−xScyTi1−2yNbyO3 system

Perovskite-type lithium fast ion conductors of Li_3xLa_0.67−xSc_yTi_1−2yNb_yO₃ system were prepared by solid state reaction. X-Ray powder diffraction shows that perovskite solid solution form in the ranges of x=0.10, y≤0.10. AC impedance measurements indicate that the bulk conductivities and the total conductivities are of the order of 10⁻⁴ S·cm⁻¹ and 10⁻⁵ S·cm⁻¹ at 25 °C respectively. The compositions have low bulk activation energies of about 17 kJ/mol in the temperature ranges of 298 – 523 K and total activation energies of about 37 kJ/mol in the temperature ranges of 298 – 523 K.     

Critical current densities of high pressure oxygen sputtered thin films of YBa2Cu3O7−x by non-resonant rf absorption method

The critical current densities (J _c) have been measured at 77K in high pressure oxygen sputtered thin films of YBa₂Cu₃O_7−x superconductor using the non-resonant rf absorption technique. High values ofJ _c (∼ 10⁵ A/cm²) are observed in these relatively large area (∼ 1·2 cm²) films.     

Carrier mobility in nonstoichiometric n-Bi2Te3−x Sex solid solutions

A study has been made of the thermoelectric and galvanomagnetic properties of n-Bi₂Te_3−x Se_x solid solutions (x=0.3 and 0.36) in the temperature range 80–300 K. The lowest carrier concentrations, (0.8–1)×10¹⁸ cm⁻³, were obtained by displacing the solid solution from the stoichiometric to a Te-rich composition. At such carrier concentrations, the second subband in the conduction band of n-Bi₂Te_3−x Se_x is not filled, which results in a growth of mobility because of the absence of interband scattering, and brings about an increase of thermoelectric efficiency in the 80–120-K range. Fiz. Tverd. Tela (St. Petersburg) 39, 483–487 (March 1997)     

Dielectric properties of (1−x)[0.7PbZrO3·0.3K0.5Bi0.5TiO3]·xSrTiO3 solid solutions in the vicinity of phase transitions

The dielectric properties of polycrystalline (1−x)[0.7PbZrO₃·0.3K_0.5Bi_0.5TiO₃]·xSrTiO₃ solid solutions, where x=0–0.7, are studied in the temperature range 150–600 K. Systematic spreading of the ferroelectric phase transition with increasing strontium titanate content is discovered. The dispersion of the dielectric constant at frequencies from 10⁻¹ to 10⁶ Hz is investigated for a composition with x⋍0.7. The existence of two relaxation processes characterized by diffuse relaxation time spectra, which broaden with decreasing temperature, is established. It is postulated that a transition to a glasslike state takes place in the material with x⋍0.7. Zh. Tekh. Fiz. 69, 35–38 (March 1999)     

Changes in 8–12 μm CdxHg1?xTe photodiode arrays caused by fast neutron irradiation

We have measured the current-voltage characteristics of the long-wavelength infrared (LWIR) photodiode array, formed on the epitaxial Cd_xHg_1−xTe film (x = 0.21–0.23) with a high concentration of the Shockley-Read-Hall centres, before and after irradiating it with fast neutrons (energy 1 MeV, dose 5×10¹³ cm⁻²) at room temperature. Residual changes in current-voltage characteristics, persisting after 20 days, have been identified. Model calculations indicate that the Shockley-Read-Hall centre concentration increases 2–4 times, and the carrier lifetime decreases 2–5 times after the irradiation.     

Enhancement of minority carrier lifetime in GaAs1? x P x ( x =0.4; 0.65) by nitrogen implantation

Minority carrier lifetimes in nitrogen implanted GaAs_1-x P _x (x=0.4; 0.65) were measured at 77K by an optical phase shift method as a function of nitrogen dose and annealing temperature in order to investigate the dependence of the lifetime on the concentration of nitrogen isoelectronic traps. A large increase in the lifetime was observed after nitrogen implantation followed by annealing at and above 800°C. The maximum lifetimes were 22ns for GaAs_0.35P_0.65 and 6.7 ns for GaAs_0.6P_0.4. They were obtained by implantation to a dose of 5×10¹³ cm⁻² in GaAs_0.35P_0.65 and 10¹³ cm⁻² in GaAs_0.6P_0.4. The lifetime after nitrogen implantation followed by annealing was longer by a factor of 6–7 than that of the unimplanted sample.     

Structural and electrical characterisation of strontium zirconate proton conductor co-sputter deposited coatings

SrZr_1−x Y _x O₃ coatings were co-sputtered from metallic Zr–Y (84–16 at.%) and Sr targets in the presence of a reactive argon–oxygen gas mixture. The structural and chemical features of the film have been assessed by X-ray diffraction and scanning electron microscopy. The electrical properties have been investigated for different substrates by Complex Impedance Spectroscopy as a function of crystalline state, temperature and atmosphere. The as-deposited coatings are amorphous and crystallise after annealing at 673 K for 2 h under air. The stabilisation of the perovskite structure is a function of the nominal composition. The films are dense and present a good adhesion on different substrates. Crystallisation and mechanical stresses are detected by alternating current (AC) impedance spectroscopy. Significant ionic conductivity in the 473–823 K temperature range is evidenced in air. Two different conduction regimes in the presence of steam are attributed to a modification of the charge carrier nature. In spite of low conductivity values (σ ~10⁻⁶ S.cm⁻¹ at 881 K), the activation energies are in agreement with that of Y-doped strontium zirconate ceramics (~0.7 eV in air).     

Electro-physical properties of cadmium-silicon diarsenide irradiated by H<Superscript>+</Superscript> ions

The effect of proton irradiation (E = 5 MeV, D = 2 · 10¹⁷ cm⁻²) on electro-physical properties of p-CdSiAs ₂ crystals is studied. The irradiation resulted in semi-insulating CdSiAs ₂ samples with the Fermi-level position in the proximity of E_g/2. The energy position of a “neutral” point is calculated for CdSiAs ₂, and thermal stability of radiation defects is investigated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 12–15, August, 2007.     

Magnetic and electrical properties of Mg1−x CuxO solid solutions and magnetic shielding in Cu-Mg1−x CuxO structures

Mg_1−x Cu_xO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg_1−x Cu_xO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ ⁻¹(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ _eff=1.9 μ _B, close to the 1.73 μ _B of a Cu²⁺ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10⁻⁴ eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg_1−x Cu_xO at T=300 K is ≈10⁻¹¹–10⁻¹² Ω⁻¹ cm⁻¹ for x=0 and increases to 10⁻⁵–10⁻⁶ Ω⁻¹ cm⁻¹ for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg_1−x Cu_xO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999)     

Defects and transport in SrFe1−xCoxO3−δ

The non-stoichiometry and chemical diffusion coefficient of SrFe_1−xCo_xO_3-δ have been measured by steady state and transient thermogravimetry in the temperature range 750–1200 °C at different oxygen partial pressures. At high oxygen partial pressures, the chemical diffusion coefficient was in the range 1·10⁻⁴ – 7·10⁻⁴ cm²/s. This, combined with high concentration of disordered vacancies make these materials perhaps the fastest solid oxygen ion diffusers known at high temperatures and high oxygen partial pressures. However, due to the high concentration of defects in SrFe_1−xCo_xO_3-δ the compound transforms from a cubic (disordered) perovskite to a brownmillerite type of structure under reduced oxygen partial pressures below approx. 900 °C. Due to this phase transition, the mobility of oxygen vacancies in SrFe_1−xCo_xO_3-δ decreases up to about an order of magnitude at 850 °C. We also observe an ordering effect at 1000 °C, although smaller in size, and this is suggested to be due to short range ordering of four-coordinated polyhedra of Fe. For possible use as oxygen separation membranes, phase stability against sulphur and carbon containing atmospheres is also discussed with respect to the formation of carbonates and sulphates. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Free carrier concentration and conductivity in chlorine doped lead telluride

Plasma resonance in the IR reflection spectra is used to measure the concentration and relaxation time of free charge carriers along with the conductivity in PbTe_{1 − x} Cl _x solid solutions. It is found that with increasing the chlorine concentration, the electron concentration and conductivity increase and reach saturation at x = 0.03 (n = 5.5 × 10¹⁹ cm⁻³, σ = 3750 Ohm⁻¹ · cm⁻¹). The relaxation time decreases with increasing the chlorine concentration and reaches the minimum value of 2.2 × 10⁻¹⁴ s at x = 0.03; then, it almost does not change.     

Influence of atomic ordering on the magnetic properties of FePd,FePt, and Fe<Subscript>50</Subscript>Pd<Subscript>50−<Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloy films

The phase composition, crystal structure, and magnetic properties of films of the ordered alloys FePd, FePt, and Fe₅₀Pd_{50 − x} Pt _x , where x = 1–10 at %, were analyzed. The spectral dependences of the magnetic rotation and optical absorption were taken. The effect of heat treatment on the crystal structure, magnetization, and coercive field strength of the ordered alloy films was studied. The influence of the degree of atomic ordering on the perpendicular magnetic anisotropy was investigated. It was shown that films of ordered FePd and FePt alloys of equiatomic composition and films of Fe₅₀Pd_{50 − x} Pt _x , where x = 1–10 at %, can serve as media for magnetic and thermomagnetic data recording and storage.