InGaN nanoinclusions in an AlGaN matrix

GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80–300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective.     

Phase states and magnetic structure of superconducting lead inclusions in a narrow-gap PbTe semiconducting host

Samples of the narrow-gap semiconductor PbTe with n-and p-type conductivities are investigated using a SQUID magnetometer in the temperature range 1.7–20 K and in magnetic fields up to 1 kOe. It is shown that there are microscopic inclusions of superconducting lead with minimum dimensions ～1300 Å containing ～(1?5)×10¹⁸ lead atoms/cm³ in the lead telluride matrix and that the samples undergo a phase transition that is characteristic of type-II superconductors.     

Optical reflection from the Bragg lattice of AsSb metal nanoinclusions in an AlGaAs matrix

The optical properties of metal-semiconductor metamaterials based on an AlGaAs matrix are studied. The specific feature of these materials is that there are As and AsSb nanoinclusion arrays which modify the dielectric properties of the material. These nanoinclusions are randomly arranged in the medium or form a Bragg structure with a reflectance peak at a wavelength close to 750 nm, corresponding to the transparency region of the matrix. The reflectance spectra are studied for s- and p-polarized light at different angles of incidence. It is shown that (i) As nanoinclusion arrays only slightly influence the optical properties of the medium in the wavelength range 700–900 nm, (ii) chaotic AsSb nanoinclusion arrays cause strong scattering of light, and (iii) the spatial periodicity in the arrangement of AsSb nanoinclusions is responsible for Bragg resonance in the optical reflection.     

Intrinsic defect states in PbTe single-crystal films grown by laser-modulated epitaxy

The electrical properties of PbTe/KCl(KBr) layers grown by infrared-laser-modulated epitaxy and their dependences on conditions of fabrication (power density of the laser beam W, substrate temperature T _s ) have been investigated. It is established that the R _H (T) dependences can be explained within the framework of a two-level model in which one of the levels (E _d1) is in the conduction band and the second level E _d2 is in the band gap. The positions of the energy levels and their density of states depend on the conditions of growth. Fiz. Tekh. Poluprovodn. 32, 47–49 (January 1998)     

Features of vanadium impurity states in lead telluride

Temperature dependences of resistivity, magnetic susceptibility, and charge-carrier concentration and mobility in single-crystalline PbTe:V samples with a varied impurity content are investigated. It is shown that vanadium forms a donor level located ∼20 meV below the conduction-band bottom. The electron mobility is as high as 10⁵ cm² V⁻¹ s⁻¹ in the samples with N _V ≤ 0.21 at % and proves to be more than an order of magnitude higher in the samples with the highest vanadium content N _V = 0.26 at %. In the same samples, the real part of the conductivity is characterized by a pronounced frequency dependence. An increase in vanadium concentration is accompanied by a decrease in the effective magnetic moment of impurity atoms. The features of electron transport in PbTe:V may be caused by a variable vanadium valence and by the effect of interimpurity correlations.     

Arrangement of arsenic atoms in the PbTe lattice

Mössbauer emission studies based on the ⁷³As(⁷³Ge) isotope showed arsenic impurity atoms in the PbTe lattice to be localized in both the anion and the cation sublattices, with the ⁷³Ge atoms formed in the radioactive decay of ⁷³As being electrically inactive in both positions.     

Bragg resonance in a system of AsSb plasmonic nanoinclusions in AlGaAs

The optical reflection from periodic structures based on a semiconductor AlGaAs matrix containing 2D arrays of plasmonic AsSb nanoinclusions is studied. The number of nanoinclusion layers is 12 or 24, and the nominal spatial periods are 100 or 110 nm, respectively. In the experimental spectra of the optical reflection coefficient at normal incidence, we observe resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm (1.64 or 1.60 eV), depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reach 22 and 31% for the systems of 12 and 24 AsSb–AlGaAs layers, while the volume fraction of the nanoinclusions is much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifts according to Wulff–Bragg’s law. Numerical simulation of the optical reflection spectra is performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers.     

Donorlike behavior of rare-earth impurities in PbTe

The Hall coefficient, thermoelectric power, and electrical conductivity in PbTe doped with La, Pr, Sm, and Gd are investigated in the temperature range (77–700) K. The impurity atoms act as donors with an electrical activity that increases with temperature until the fraction of electrically active lanthanide atoms (Ln) reaches values close to or slightly more than half of their total number. A decrease in the electron mobility and a change in the thermoelectric power relative to their values in PbTe〈I〉 are also noted. At low temperatures, the Seebeck coefficient in PbTe〈Ln〉 is found to be higher than in PbTe〈I〉, while at high temperatures it is lower. The data are interpreted by invoking a band of impurity resonant states, whose energetic position and number are functions of composition and temperature. The experimental data imply that when La and Pr dope PbTe, the electrical activity of the compound is dominated by intrinsic donorlike defects that form when Ln is incorporated in the ratio LnTe. Fiz. Tekh. Poluprovodn. 32, 806–810 (July 1998)     

Energy of impurity resonance states in lead telluride with different contents of thallium impurity

The Hall factor in PbTe is calculated with regard to resonance scattering of holes at thallium impurity. At low temperatures (T ≈ 77 K) and relatively low Tl content (N _Tl ≈ 0.5 at %), the calculated value substantially differs from unity. Using the corrected Hall factor, the energy of resonance levels is refined. In contrast to the results obtained previously, the energy of the impurity resonance states appeared independent of thallium concentration up to 2 at %.     

Outlook of the Superconducting Maglev

The superconducting maglev has been developed as an ultra-high speed mass transport system. It makes use of modern superconducting magnets (SCMs), which enable a large gap electro-dynamic suspension and an efficient linear motor propulsion. Running tests have been conducted smoothly on the 18.4-km-long Yamanashi Maglev Test Line since 1997 and reaped the harvests such as the maximum speed of 581 km/h, relative speed of 1026 km/h on two trains' passing test and on-board high temperature SCM running tests. In March 2005 the Committee under the Ministry of Land, Infrastructure and Transport appreciated that “all the technologies of the Superconducting Maglev necessary for the future revenue service were established.” Based on this situation, JR Central has decided to expand the existing test line as well as renew the existing facilities and equipment into those of the future revenue service level. Furthermore, the company has decided to promote the Tokaido Shinkansen Bypass project utilizing the superconducting maglev system.      

Analysis of the solidus lines for PbTe and SnTe

Experimental valúes of p-n, P_{Te 2}, and T along the solidus lines of PbTe and SnTe, and for compositions within the homogeneity range of SnTe are fit using the simple model of a nondegenerate semiconductor compound containing fully-ionized native defects. As a result values for the intrinsic material parameters of these compounds at high temperature are obtained as well as some indication of the uncertainty in these.     

Electrophysical properties of solid solutions of silver in PbTe

The thermopower coefficient α₀ and the electrical conductivity σ of Pb_{1 − x} Ag _x Te solid solutions, where x = (0–0.007), are measured at T = 300 K. The hole concentration p is calculated. All samples are of the p type. With increasing silver content, α₀ decreases, while p and σ increase. For undoped crystals, α₀ = 251.0 μV/K, p = 1.1 × 10¹⁸ cm⁻³, and σ = 165 Ω⁻¹ cm⁻¹. At the silver-solubility limit for x = 0.007, α₀ = 193.8 μV/K, p = 2.3 × 10¹⁸ cm⁻³, and σ = 216 Ω⁻¹ cm⁻¹. The hole concentration in all samples is much lower than the concentration of introduced silver atoms. The hole gas in Pb_{1 − x} Ag _x Te solid solutions is weakly degenerate in the entire silver-concentration range.     

Calculation of the optimum vapor pressure for stoichiometry in PbTe and PbSnTe

Optimum vapor pressure for stoichiometry in growth of PbTe and PbSnTe has been calculated. The result is in a good agreement with the experimentally obtained ones for vapor pressure controlled Bridgman growth and liquid phase epitaxy. The procedure of calculation follows that performed earlier for GaAs, which assumed the equality of the chemical potentials of the volatile element in gas, liquid and solid phases. Also it is pointed out that the nonequilibrium reactions of interstitial Te atoms with Pb vacancies forming anti-site Te, as well as Te precipitations, take place at the highest applied Te vapor pressure region.     

High thermoelectric figures of merit in PbTe quantum wells

High-quality Pb_1−xEu_xTe/PbTe multiple quantum wells (MQWs) have been grown by molecular beam epitaxy. The measured 300K thermoelectric properties have been compared with that of the best bulk PbTe. This experimental investigation is the first detailed study of MQW structures designed to improve ZT of thermoelectric materials and has resulted in a breakthrough in the decades-long ZT ≅ 1 barrier for a room-temperature thermoelectric material. A value of Z_2DT >1.2 has been achieved for these PbTe quantum wells.     

Nonuniformity of electrical properties for the PbTe single crystals in the growth direction

It is established that nonuniformity of electrical parameters conditioned by a nonuniform distribution of excess Te exists along the single-crystal PbTe ingot. In addition to the shallow acceptor and donor levels, deep acceptor levels with activation energy of ～0.1 eV exist in the band gap of the PbTe single crystals. These levels are not associated with excess Te and manifest themselves in the samples with a low concentration in the shallow levels at relatively high temperatures.     

Defect formation in PbTe under the action of a laser shock wave

Mechanisms of the defect formation in PbTe thin films on BaF₂ substrates under shock-wave action are studied, and the kinetics of the annealing of the resulting nonequilibrium crystal defects at room temperature is analyzed. The respective roles of the first-and second-order annealing reactions in settling of the equilibrium state of the defects are estimated. The contributions of Frenkel pair annihilation in both sublattices and migration of interstitials to sinks to a change in the total concentration of nonequilibrium defects at different stages of annealing are considered.     

Mobility of charge carriers in double-layer PbTe/PbS structures

The method of hot-wall epitaxy is used to grow epitaxial heterostructures of p-PbTe/n-PbS on BaF₂ substrates. Hall-effect measurements are analyzed in order to obtain the dependence of the effective carrier mobility on thickness and temperature in the ranges 0.1–2 μm and 100–300 K, respectively. It is found that this mobility depends on the thickness of the sample and on the individual thicknesses of its constituent layers. The effective mobility is calculated under the assumption that charge carriers are scattered by the surface of the structure and by dislocations that form at the heterojunction boundary. Fiz. Tekh. Poluprovodn. 32, 1064–1068 (September 1998)     

高温超导微波器件在电子战接收机中的应用

高温超导微波器件同常规微波器件相比,具有非常明显的优势;本文回顾了高温超导微波器件的特点,探讨了电子战接收机对高温超导微波器件的应用要求及在系统中的应用可行性;开展了初步的应用试验,并提出了工程应用中需要解决的问题。     

超导热管在沥青加热中的应用

本文首先阐述了超导热管这种加热形式在沥青加热过程中的运用,对沥青加热过程中采用这种形式的必要性和急迫性,以及其可操作性进行了解析。规划了对沥青供应点和公路站沥青加热设备展开更新的方案,思考了当前这一技术实施中存在的几个问题。