Impact-ionization-stimulated electroluminescence in isotype <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-AlGaAsSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb heterostructures

We have studied electroluminescence in n-GaSb/n-AlGaAsSb/n-GaInAsSb heterostructures with isotype heterojunctions, in which the quantum efficiency of emission is increased due to the additional production of electron-hole pairs as a result of the impact ionization that takes place near the heterointerface. The impact ionization in such heterostructures is possible due to the presence of deep wells in the energy band structure.     

Speed of sound in <Emphasis Type="Italic">n</Emphasis>-hexane, <Emphasis Type="Italic">n</Emphasis>-octane, <Emphasis Type="Italic">n</Emphasis>-decane,and <Emphasis Type="Italic">n</Emphasis>-hexadecane in the liquid state

This paper describes an improved experimental facility for measuring the speed of sound in liquids with an accuracy of up to 0.1%. Measurements of the speed of sound in liquid n-hexane, n-octane, n-decane, and n-hexadecane at temperatures of 298–433 K and pressures of 0.1–100 MPa have been made. It has been shown that in the possible comparison range the obtained values of the speed of sound are in good agreement with the literature data. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 732–736, July–August, 2008.     

Long-wavelength photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures

Photodiodes sensitive in the wavelength ranges 1–2.5 μm and 1–4.8 μm at room temperature have been created on the basis of n-GaSb/n-GaInAsSb/p-AlGaAsSb double-junction heterostructures of two types. The broadband photosensitivity of the diode structures of both types is indicative of the complete separation of photogenerated electron-hole pairs in the staggered n-p heterojunction (n-GaInAsSb/p-AlGaAsSb). The noise characteristics of photodetectors based on the proposed diode structures have been studied. Prospects of the use of these devices in thermophotovoltaic cells for low-temperature radiation sources are considered.     

Acoustic and thermodynamic properties of the binary liquid system <Emphasis Type="Italic">n</Emphasis>-dodecane+<Emphasis Type="Italic">n</Emphasis>-hexadecane

By the method of direct measurement of the pulse-passage time, the velocity of sound in a binary liquid mixture n-dodecane+n-hexadecane has been investigated in the temperature range 298–433 K and in the pressure range 0.1–100.1 MPa. The maximum measurement error is 0.1%. Experimental data on the velocity of sound for the investigated mixture have been obtained for the first time. On the basis of the data on the velocity of sound, we have determined the density, the isobaric expansion coefficient, the isobaric and isochoric heat capacities, and the isothermal compressibility coefficient of a mixture of three compositions in the 298–433 K temperature range and in the 0.1–100.1 MPa range of pressures. The coefficients of the Tate equations in the above range of parameters have been calculated. A table of thermodynamic properties of the mixture is presented.     

Inference with progressively censored <Emphasis Type="Italic">k</Emphasis>-out-of-<Emphasis Type="Italic">n</Emphasis> system lifetime data

A system with n independent components which works if and only if a least k of its n components work is called a k-out-of-n system. For exponentially distributed component lifetimes, we obtain point and interval estimators for the scale parameter of the component lifetime distribution of a k-out-of-n system when the system failure time is observed only. In particular, we prove that the maximum likelihood estimator (MLE) of the scale parameter based on progressively Type-II censored system lifetimes is unique. Further, we propose a fixed-point iteration procedure to compute the MLE for k-out-of-n systems data. In addition, we illustrate that the Newton–Raphson method does not converge for any initial value. Finally, exact confidence intervals for the scale parameter are constructed based on progressively Type-II censored system lifetimes.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions in ZnO implanted with group V ions

n-Type ZnO〈Ga〉 films were implanted with 150-keV N⁺ (As⁺) ions to a dose of 7 × 10¹⁵ cm⁻² and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm²/(V s), and carrier concentration of ∼10¹⁸ cm⁻³. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.     

Thermodiffusion Coefficient Analysis of <Emphasis Type="Italic">n</Emphasis>-Dodecane /<Emphasis Type="Italic">n</Emphasis>-Hexane Mixture at Different Mass Fractions and Pressure Conditions

In this study, the thermodiffusion coefficient of n-dodecane/n-hexane binary mixture at 25 ^°C mean temperature was determined for several pressure conditions and mass fractions. The experimental technique used to determine the thermodiffusion coefficient was the thermograviational column of cylindrical configuration. In turn, thermophysical properties, such as density, thermal expansion, mass expansion and dynamic viscosity up to 10 MPa were also determined. The results obtained in this work showed a linear relation between the thermophysical properties and the pressure. Thermodiffusion coefficient values confirm a linear effect when the pressure increases. Additionally, a new correlation based on the thermodiffusion coefficient for n C₁₂/n C₆ binary mixture at 25 ^°C temperature for any mass fraction and pressures, which reproduces the data within the experimental error, was proposed.     

Electrical and photoelectric properties of electrodeposited <Emphasis Type="Italic">n</Emphasis>-Si/<Emphasis Type="Italic">n</Emphasis>-Cd<Subscript>1 - <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>x</Subscript>S heterojunctions

n-Si/n-Cd_{1 - x} Zn_xS heterojunctions are produced by electrodepositing Cd_{1 - x} Zn_xS (0 x 0.6) films on silicon substrates, and their electrical and photoelectric properties are studied. The results demonstrate that the spectral response of the heterojunctions depends strongly on the film composition and heat-treatment conditions. The highest photosensitivity is achieved at x = 0.6 by heat treatment at 350°C for 7 min: V _OC = 0.5 V and I _SC = 3.8 mA/cm² under illumination of 1500 lx at 300 K.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 276–280.Original Russian Text Copyright © 2005 by Mamedov, Gasanov, Amirova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

The Activation Energy <Emphasis Type="Italic">U</Emphasis>(<Emphasis Type="Italic">T</Emphasis>,<Emphasis Type="Italic">H</Emphasis>) in Y-based Superconductors

Based on the Arrhenius equation, a method to calculate the activation energy from the resistance transition is proposed for high temperature superconductors. This method is applied to the Y-based superconductors. The activation energy is found to be U(T,H)∼(1−T/T _c )^4.8(H/H ₀)^−3.8 of YBCO crystal, and U(T,H)∼(1−T/T _c )^3.3(H/H ₀)^−2.2 of Er doped MTG YBCO crystal, respectively. With the obtained activation energy U(T,H), the lower part of the experimental curve ρ(T,H) and its derivative can be reproduced.      

<Emphasis Type="Italic">p</Emphasis>-AgCoO<Subscript>2</Subscript>/<Emphasis Type="Italic">n</Emphasis>-ZnO heterojunction diode grown by rf magnetron sputtering

P-type transparent semiconducting AgCoO₂ thin films were deposited by rf magnetron sputtering of sintered AgCoO₂ target. The AgCoO₂ films grown by rf sputtering were highly c-axis oriented showing only (001) reflections in the X-ray diffraction pattern unlike in the case of amorphous films grown by pulsed laser deposition (PLD). The bulk powder of AgCoO₂ was synthesized by hydrothermal process. The optical bandgap was estimated as 4·15 eV and has a transmission of about 50% in the visible region. The temperature dependence of conductivity shows a semiconducting behaviour. The positive sign of Seebeck coefficient (+220 μVK⁻¹) indicates p-type conductivity. Transparent p-n heterojunction on glass substrate was fabricated by rf magnetron sputtering of p-AgCoO₂ and n-type ZnO: Al thin films. The structure of the diode was glass/ITO/n-ZnO/p-AgCoO₂. The junction between p-AgCoO₂ and n-ZnO was found to be rectifying.     

Synthesis and characterization of <Emphasis Type="Italic">n</Emphasis>-ZnO:Al/CoPc/<Emphasis Type="Italic">p</Emphasis>-Si structures

Photosensitive structures of the n-ZnO:Al/CoPc/p-Si type were synthesized for the first time using vacuum sublimation of cobalt phthalocyanine (CoPc) and magnetron sputtering of a ZnO:Al target. The maximum photoresponse is observed when the structure is illuminated from the side of the ZnO layer and amounts to ?400 V/W at T = 300 K. Mechanisms of current transfer and peculiarities of the photosensitivity spectrum are considered. It is suggested that the new photosensitive structures can be used in multiband photoconverters of natural radiation with a broad working spectral range.     

Understanding the effect of <Emphasis Type="Italic">n</Emphasis>-type and <Emphasis Type="Italic">p</Emphasis>-type doping in the channel of graphene nanoribbon transistor

In this paper, device performance of graphene nanoribbon field effect transistor (GNRFET) with different doping concentrations in different parts of the channel is reported. The study is performed by using atomistic simulations based on self-consistent solution of Schrodinger’s and Poisson’s equation within the non-equilibrium Green’s function formalism. The transfer and output characteristics suggest that device performance with n-type doping in the channel is better with smaller supply voltage compared to higher supply voltage. On increasing the n-type doping concentration, we obtained better on-current and output characteristics in comparison with undoped and p-type doped channel GNRFET. Further, we introduced step-doping profile in the graphene nanoribbon (GNR) channel and found that the device gives better on-current and good saturation condition when compared to undoped or uniformly-doped channel.     

Spin Dynamics in the Bi-Directional Charge Density Wave State of High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

In this paper, we investigate the dynamical spin susceptibility in the bi-directional charge density wave (BCDW) state by adopting a random-phase approximation. In the BCDW state, we find that no spin resonance exists and only a broad commensurate peak appears for the frequency dependence of the dynamical spin susceptibility at Q = (π,π), though a low-energy spin gap feature can also be found as in the superconducting state. While the “hourglass” type of the dispersion for the BCDW state bears some similarities with that in the superconducting state, the momentum distribution of Im χ ^+?(Q,ω) is just the opposite with the incommensurate peaks lying along the diagonal direction for the energy below ω _c and along the axial direction above ω _c . In the coexistence of SC and BCDW, the frequency dependence of the dynamical spin susceptibility at Q = (π,π) generally shows the two-peak structure, reflecting two energy scales of the spin excitations. These unique features may serve as signatures to verify whether or not the BCDW state is responsible for the formation of the Fermi arcs.     

Specific features of technology of electron irradiation of large-area <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> silicon structures

We have studied the influence of irradiation by 4-MeV electrons via flat metal screens on the main electrical characteristics of high-power silicon diodes intended to operate at currents up to 600 A. The electron irradiation was performed via metal masks, which led to the formation of enhanced recombination zones (ERZs) in the base region of p ⁺-n-n ⁺ silicon structures. It is shown that the local irradiation of a large-area diode structure improves (as compared to the total irradiation) the relationship been the reverse recovery time (t _rr ) and energy loss in the conducting state (U _f ), while decreasing the temperature sensitivity of the reverse current (I _R ). It is established that the relationships between t _rr , U _F , and I _R in locally irradiated structures depends on the experimental conditions (ERZ size).     

Modification of radiation hardness of silicon <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junction photodiodes by hydrogen plasma treatment

The influence of treatment by a low energy hydrogen ions on degradation of the spectral response, diffusion length of minority carriers (L_D) and efficiency (η) of silicon p-n junction photodiodes (solar cells without antireflective coatings) under the effect of electron irradiation has been investigated. Evaluation of the radiation hardness was made by subjecting the unhydrogenated and hydrogenated photodiodes to 1 MeV electron irradiation with doses of (0.1÷3) × 10¹⁵ cm^-2. The measurements have shown that pre-hydrogenation of the silicon p-n junction devices significantly decreases the degradation rate of L_D and η thereby improving their radiation hardness.     

Project of laser-pumped quantum <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">X</Emphasis></Subscript> magnetometer

The possibility of creating a new scheme of a laser-pumped quantum magnetometric device based on a double-beam M _X magnetometer is considered. The proposed system ensures the simultaneous measurement of the modulus of the Earth’s magnetic field vector (with an absolute accuracy of 0.02 nT) and two angles of deviation of this vector with an absolute accuracy and sensitivity of not worse than 0.4″ (0.1 nT) at a measurement time of τ = 1 s. In contrast to the known analogous systems, the proposed scheme does not require generating additional magnetic fields.     

Nernst Signal in High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

The time-dependent Ginzburg–Landau equation with thermal noise is used to calculate the Nernst signal e _N , describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree–Fock method. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The values of e _N are in good quantitative agreement with experimental data for temperature close to T _c on Bi₂Sr₂CaCu₂O_8+δ and Bi₂Sr₂Ca₂Cu₃O_10+δ .     

The search for novel superhard and incompressible materials on the basis of higher borides of <Emphasis Type="Italic">s</Emphasis>, <Emphasis Type="Italic">p</Emphasis>, <Emphasis Type="Italic">d</Emphasis> metals

The state of the art in the search for novel superhard and (or) incompressible materials on the basis of higher borides of s, p, d metals has been briefly reviewed. The information has been considered about experimental and theoretical studies of the following groups of borides: diborides of 4d, 5d heavy metals (Tc, Ru, Rh, Re, Os, and Ir), hexagonal tetraborides with the WB₄-type structure, and AMB₁₄ borides (where A, M are s, p metals) as well as of a number of related systems.     

The sound velocity in liquid binary mixtures of <Emphasis Type="Italic">n</Emphasis>-alkanes

The method of direct measurement of the time of pulse transmission is used for investigating the sound velocity in liquid binary mixtures of n-alkanes, namely, n-hexane + n-hexadecane, n-octane + n-hexadecane, and n-decane + n-hexadecane in the range of temperatures from 298 to 433 K and pressures from 0.1 to 100.1 MPa. The maximal error of measurements is 0.1%. It is for the first time that experimental data for mixtures of n-octane + n-hexadecane and n-decane + n-hexadecane are obtained.     

The Boundary Effect on the Energy Gap of High <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconductors

Spatial dependence of the pairing potential across the thickness of the superconducting CuO₂ planes in high T _c superconductors (HTSC) copper oxides is found by using the Ginzburg-Landau-Gor’kov (GLG) theory. The potential turned out to be significantly suppressed due to an effect of non-superconducting layers, which separate the CuO₂ planes. The effect leads also to the reduction of the critical temperature of these superconductors. The temperature dependence of the effective energy gap was calculated in this work.