On the Significance of the Thermoelectric Figure of Merit <Emphasis Type="Italic">Z</Emphasis>

When the electrical conductivity, σ, thermal conductivity, λ, and thermopower, S, of a material are all assumed to be constant over the temperature range of interest, then the well-known thermoelectric (TE) figure of merit, Z = σS ²/λ, arises as part of the derivation of conversion efficiency in a TE generator. However, there are an infinite number of parameter sets (σ, λ, S) that yield any given Z. So, are they truly equivalent? This paper reviews the historical basis for Z as a metric for TE quality and discusses results of simulations on three systems having different parameter sets but the same Z. The three systems exhibit different power generation capabilities, illustrating that Z is not sufficient to specify the likely performance of a TE material in a system. Instead, a systems analysis is required that incorporates, at a minimum, source and sink temperatures and thermal resistances.     

Peculiarities of finding characteristic functions of the generating process in the model of stationary linear AR(2) process with negative binomial distribution

The linear random AR(2) autoregressive process having the negative binomial distribution has been considered. It has the form ξ _t + a ₁ξ _t-1 + a ₂ξ _t-2 = ? _t , t ∈ Z, where {a ₁, a ₂ ≠ 0} are the autoregressive parameters; Z = {...,-1,0,1,...} is the sequence of integers; {ξ _t ,t ∈ Z} is the random process with discrete time and independent values having the infinitely divisible distribution law that is called generating process. The method of finding the characteristic function of the generating process for linear autoregressive process having negative binomial distribution is presented. This inverse problem is solved by using properties of the characteristic function of stationary linear autoregressive process that can be presented in the Kolmogorov canonical form and as a linear stationary autoregressive process. An example of finding the Poisson spectrum of jumps and the characteristic function for the linear second order autoregressive process (AR(2)) with negative binomial distribution has been also presented.     

Fine Structure of the long-wavelength edge of exciton-phonon absorption and hyperbolic excitons in silicon carbide of 6<Emphasis Type="Italic">H</Emphasis> polytype

The fine structure of the long-wavelength edge of the polarization spectra of exciton-phonon absorption in moderate-purity n-type 6H-SiC crystals with a concentration of uncompensated donors N_D?N_A=(1.7–2.0)×10¹⁶ cm^?3 at T=1.7 K was studied. The analysis of new special features found at the absorption edge and the reliable detection of the onset of exciton-phonon steps related to the emission of phonons from acoustical and optical branches allowed highly accurate determination of a number of important parameters such as the band gap, the exciton band gap, the exciton binding energy, and the energies of spin-orbit and crystal-field splitting of an exciton. For the first time, transitions with the emission of LA phonons to the 1S exciton state with an M₁-type dispersion law were detected in E ∥ Z(C) polarization (the electric-field vector is parallel to the optical axis of the crystal). This observation supports the previously predicted “two-well” structure of the conduction band minimum in 6H-SiC.     

Quantum Gates with Spin States in Continuous Microwave Field

The physical basis of the method of implementing quantum logical operations in a continuous microwave field in a system of two electrons with different g-factors and a constant exchange interaction is developed. A small variable additive ΔB(t) to the magnetic field is proposed as a control action. It is obtained that a simple functional dependence ΔB(t), based on harmonic functions, allows us to perform elementary quantum logical operations and their sequences. This method is adapted to the experimental conditions.     

Transport coefficients of <Emphasis Type="Italic">n</Emphasis>-Bi<Subscript>2</Subscript>Te<Subscript>2.7</Subscript>Se<Subscript>0.3</Subscript> in a two-band model of the electron spectrum

The Hall factor and thermoelectric properties of an n-Bi₂Te_2.7Se_0.3 solid solution with the roomtemperature Seebeck coefficient |S| = 212 μV/K have been studied in the temperature range 77–350 K. The observed temperature dependences demonstrate a number of specific features, which were earlier found in samples with a lower electron density N. The effect of these specific features on the thermoelectric figure of merit Z appears to be more favorable for the sample under study: this sample is most efficient in the temperature range 120–340 K, and the average value of ZT is 0.71. It is found that a rise in the density N enhances the factor responsible for the effective mass decreasing as the temperature increases. This effect appears when the analysis is carried out in terms of a single-band parabolic model with N = const(T). This finding suggests that the most probable reason for the unusual behavior of these properties is the complex structure of the electron spectrum. Temperature dependences obtained from calculations of the transport coefficients show good agreement with the experimental data for two samples of the mentioned composition with different electron densities. The calculations have been performed in terms of a two-band model and an acoustic scattering mechanism and take into account the anisotropy and nonparabolicity of the light-electron spectrum.     

Thermoelectric figure of merit in solid solutions with phonon scattering by off-center impurities

The Seebeck coefficient and the electrical and thermal conductivities (S, σ, and κ) of ternary PbTe_1?xSe_x (x=0.1 and 0.3) and quaternary PbTe_1?2xSe_xS_x (x=0.025, 0.05, 0.1, and 0.15) solid solutions have been studied. Polycrystalline samples with an electron density of (0.5–5.0)×10¹⁸ cm^?3 were used; their quality was monitored by comparing the measured and calculated mobility values at 85 K. A considerable decrease in mobility and an anomalous trend in the σ(T) curve near 77 K were revealed in quaternary alloys with x?0.1; for x=0.15, unusual behavior of κ(T) was also found. According to estimates, the lattice thermal conductivity of this material is temperature-independent in the 80-to 300-K temperature range. This means that a reduction in phonon-phonon scattering with an increase in temperature is completely compensated by an increase in the scattering on impurities. The observed anomalies of σ(T) and κ(T) are considered assuming the possible of off-center location of sulfur atoms at the lattice sites. The thermoelectric figure of merit Z of the studied alloys has been determined in the range 80–300 K. In spite of decreasing mobility, the maximum Z was obtained in a quaternary compound with x=0.1: at 300 K, Z_max=2×10^?3 K^?1 with a carrier density of ～3×10¹⁸ cm^?3; at 175 K, Z_max=1.5×10^?3 K^?1 with the density decreasing to 5×10¹⁷ cm^?3. The obtained data indicate that the introduction of off-center impurities rises Z at T?300 K.     

Mobility of minority charge carriers in <Emphasis Type="Italic">p</Emphasis>-HgCdTe films

Temperature dependences of electron mobility in p-Hg_1?xCd_xTe films (x=0.210–0.223) grown by molecular beam epitaxy are investigated. In the temperature range 125–300 K, mobility was found by the mobility-spectrum method, and for the range 77–125 K, it was found using a magnetophotoconductivity method suggested in this study. The method is based on the measurement of the magnetic-field dependence of photoconductivity. The magnetic field is parallel to the radiation and normal to the sample surface. The electron mobility is determined using the simple expression μ _n [m²/(V s)]=1/B _H [T]. Here, B _H is the induction of the magnetic field corresponding to a half-amplitude of the photoconductivity signal under zero magnetic field. In the temperature range 100–125 K, the results obtained by the magnetophotoconductivity and mobility-spectrum methods coincide. For the samples investigated, the electron mobility at 77 K is in the range 5–8 m²/(V s).     

Universal soft demapper for <Emphasis Type="Italic">M</Emphasis>-ary PAM with reduced complexity

In this paper, we propose an efficient soft demapper for M-ary pulse amplitude modulation (PAM) schemes. The proposed demapper estimates soft decision bit information (SDBI) for any M-ary PAM symbols using a universal type of hardware structure. The proposed method performs as well as the Max-log method, without any exhaustive search process. Instead, it maps a detected PAM symbol to a specific region, with only one constellation symbol to estimate the distance. In this way, the proposed method requires approximately one distance estimation per bit. We first derive the equations to estimate SDBI for a few Gray-mapped M-ary PAM schemes, and subsequently present compact universal equations applicable to any M-ary PAM scheme. The simulation results confirm that the proposed method produces exactly the same performance as the Max-log method with greatly reduced computational complexity.     

Surface roughness and magnetic properties of Co/SiO<Subscript>2</Subscript>/Si(100) polycrystalline films deposited via DC magnetron sputtering

For polycrystalline films of cobalt that have the thickness t ≈ 1.3–133 nm and that are deposited via DC magnetron sputtering on SiO₂(0.1 μm)/Si(100) substrates, surface-roughness root-mean-square amplitude σ and surface correlation length ξ, which characterize the roughness of film surfaces, as well as saturation magnetization 4πM ₀, width of ferromagnetic-resonance line ΔH, coercitivity H _C, and saturation fields H _S, are studied as functions of film thickness t. It is shown that the behavior of dependences H _C(t) and H _S(t) coincides with the behavior of dependence σ(t)/t, whereas the behavior of 4πM ₀(t) depends on ratio t/σ(t). The dependence of the FMR line width on the film thickness, ΔH(t), is characterized by a minimum of ΔH ≈ 60 Oe present in the region of thicknesses of 30 to 60 nm. The behavior of dependence ΔH(t) is determined by ratio σ(t)/t at small thicknesses t ≤ 5 nm and by the behavior of σ(t) at t ≥ 5 nm.     

Formalizing REST APIs for web-based communication and SIP interworking

This paper proposes an instantaneous recovery route design scheme using multiple coding-aware link protection scenarios to achieve higher link cost reduction in the network. In this scheme, two protection scenarios, namely, (i) traffic splitting (TS), and (ii) two sources and a common destination (2SD) are used to integrate multiple sources and a common destination. The proposed scheme consists of two phases. In the first phase, the proposed scheme determines routes for 2SD and TS scenarios of all possible source-destination pairs to minimize the total link cost. In this phase, the network coding is applied to the common path within each scenario, individually. In the second phase, network coding is applied to the common path between two scenarios (or a scenario pair) in order to enhance the resource saving. This phase develops conditions that select the most appropriate combination of scenario pairs, such as TS–TS, 2SD–2SD, and 2SD–TS for network coding, including their proofs. Using these conditions, a heuristic algorithm is introduced in order to select the most appropriate combination of scenario pairs for further enhancing of resource saving. Simulation results show that the proposed scheme outperforms the conventional 1 + 1 protection scheme, the TS scenario, and the 2SD scenario in terms of link cost reduction in the network.     

Electronic Processes in CdIn<Subscript>2</Subscript>Te<Subscript>4</Subscript> Crystals

The results of investigations of electrical, optical, and photoelectric properties of CdIn₂Te⁴ crystals, which were grown by the Bridgman method are presented. It is shown that electrical conductivity is determined mainly by electrons with the effective mass m_n = 0.44m₀ and the mobility 120–140 cm²/(V s), which weakly depends on temperature. CdIn₂Te₄ behaves as a partially compensated semiconductor with the donor-center ionization energy E_d = 0.38 eV and the compensation level K = N_a/N_d = 0.36. The absorption-coefficient spectra at the energy hν < E_g = 1.27 eV are subject to the Urbach rule with a typical energy of 18–25 meV. The photoconductivity depends on the sample thickness. The diffusion length, the charge-carrier lifetime, and the surface-recombination rate are determined from the photoconductivity spectra.     

Thermoelectric figure of merit of Ag<Subscript>2</Subscript>Se with Ag and Se excess

In the temperature range of 100–300 K, the electric (σ) and thermoelectric (α₀) properties of Ag₂Se with an excess of Ag as high as ～0.1 at. % and Se as high as ～1.0 at. %, respectively, are investigated. From the data on σ, α₀, and χ_tot (thermal conductivities), the thermoelectric power α ₀ ² σ and the figure of merit Z are calculated. It is found that α ₀ ² σ and Z attain the peak values at room temperature and the electron concentration n ≈ 6.5 × 10¹⁸ cm^?3.     

Efficient Techniques for Fault Detection and Correction of Reversible Circuits

It is very important to detect and correct faults for ensuring the validity and reliability of reversible circuits. Test vectors play an important role to detect as well as correct the faults in the circuits. The optimum number of test vector implies the more capabilities for detecting several types of faults in the circuits. In this paper, we have proposed an algorithm for generating optimum test vectors. We have shown that the proposed algorithm generates optimum test vectors with the least complexity of time as compared to existing methods, i.e., we have proved that the proposed algorithm requires O(log ₂ N) time, whereas the best known existing method requires O(N. log ₂ N) time, where N is the number of inputs. We have also proposed another algorithm for detecting faults using the generated test vectors. This proposed method can detect more faults than existing ones. We have proved that the proposed fault detection algorithm requires least time complexity as compared to the best known existing methods, i.e., the proposed algorithm requires O(d. 1/N) time, whereas the best known existing methods require O(d. N) time, where N is the number of inputs and d is the number of gates in a reversible circuit. Finally, we have proposed another algorithm for correcting the detected faults. We have also proved that the proposed methods require the least time complexity as compared to the best known existing methods. In addition, the experimental results using benchmark circuits show the efficiency of the proposed methods.     

Computationally Efficient Motion Estimation Algorithm for HEVC

In this paper, we present a novel computationally efficient motion estimation (ME) algorithm for high-efficiency video coding (HEVC). The proposed algorithm searches in the hexagonal pattern with a fixed number of search points at each grid. It utilizes the correlation between contiguous pixels within the frame. In order to reduce the computational complexity, the proposed algorithm utilizes pixel truncation, adaptive search range, sub-sampling and avoids some of the asymmetrical prediction unit techniques. Simulation results are obtained by using the reference software HM (e n c o d e r_l o w d e l a y_P_m a i n and e n c o d e r_r a n d o m a c c e s s_m a i n profile) and shows 55.49% improvement on search points with approximately the same PSNR and around 1% increment in bit rate as compared to the Test Zonal Search (TZS) ME algorithm. By utilizing the proposed algorithm, the BD-PSNR loss for the video sequences like B a s k e t b a l l P a s s_416 × 240@50 and J o h n n y_1280 × 720@60 is 0.0804 dB and 0.0392 dB respectively as compared to the HM reference software with the e n c o d e r_l o w d e l a y_P_m a i n profile.     

Electronic and optical properties of AlAs/Al<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As(110) superlattices

Electronic states in the conduction band of (AlAs)_M(Al_xGa_1?xAs)_N(110) superlattices are investigated for various M and N. It is shown that electronic properties of these structures are mainly determined by electrons of two pairs of valleys, namely, either Γ-X ^Z or X ^X –X ^Y . Calculations based on the developed model of joining the envelope functions were carried out. Miniband spectra, symmetry, and localization of wave functions, as well as probabilities of miniband-to-miniband infrared absorption, are determined and analyzed. It is shown that, in the case of the X ^X –X ^Y pair of valleys, the absorption probabilities are high not only for polarization of light along the growth axis of the superlattice but also for the normal incidence of an optical wave on the structure surface.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

Structurally complex two-hole and two-electron slow traps with bikinetic properties in <Emphasis Type="Italic">p</Emphasis>-ZnTe and <Emphasis Type="Italic">n</Emphasis>-ZnS crystals

Thermal-activation and photoactivation methods were used to ascertain the existence of two-hole traps in p-ZnTe crystals and two-electron traps in n-ZnS. It was found that these traps have a large number of energy states that are grouped in two series of levels: E_V+(0.46–0.66) eV and E_V+(0.06–0.26) eV in p-ZnTe and E_C?(0.6–0.65) eV and E_C?(0.14–0.18) eV in n-ZnS. Both the hole and the electron traps belong to the class of slow traps with bikinetic properties. These traps feature normal kinetic properties in the state with a single trapped charge carrier and feature anomalous kinetic properties in the state with two charge carriers. Multiple-parameter models allowing for a relation of traps in p-ZnTe and n-ZnS to the vacancy-impurity pairs distributed according to their interatomic distances and localized in the region of microinhomogeneities with collective electric fields that repel the majority charge carriers are suggested. The main special features of behavior of electron and hole traps are explained consistently using the above models.     

A Modified 8<Emphasis Type="Italic">f</Emphasis> Geometry with Reduced Optical Aberrations for Improved Time Domain Terahertz Spectroscopy

We present a modified 8f geometry for time domain terahertz (THz) spectroscopy (TDTS) experiments. We show, through simulations and data, that a simple rearranging of the off-axis parabolic mirrors, which are typically used to focus and direct THz radiation in TDTS experiments, results in a nearly 40 % reduction in the THz focal spot diameter. This effect stems from significant reduction of the principle optical aberrations which are enhanced in the conventional 8f geometry but partially compensated in the modified 8f experimental setup. We compare data from our home-built TDTS spectrometer in the modified 8f geometry to that of previous iterations that were designed in the conventional 8f geometry to demonstrate the effect.     

Electrical and thermoelectric properties of <Emphasis Type="Italic">p</Emphasis>-Ag<Subscript>2</Subscript>Te

Temperature dependences of the Hall coefficient R, electrical conductivity σ, and thermopower α₀ are investigated in the range of 4–300 K. The specific features observed in temperature dependences R(T), σ(T), and α₀(T) are interpreted in the context of a model with two types of charge carriers.     

Special features of radiation-defect annealing in silicon <Emphasis Type="Italic">p-n</Emphasis> structures: The role of Fe impurity atoms

Deep-level transient spectroscopy is used to study the formation of complexes that consist of a radiation defect and a residual impurity atom in silicon. It is established that heat treatment of the diffused Si p⁺-n junctions irradiated with fast electrons lead to the activation of a residual Fe impurity and the formation of the FeVO (E_0.36 trap) and FeV₂ (H_0.18 trap) complexes. The formation of these traps is accompanied by the early (100–175°C) stage of annealing of the main vacancy-related radiation defects: the A centers (VO) and divacancies (V₂). The observed complexes are electrically active and introduce new electron (E_0.36: E _t ^e =E _c -0.365 eV, σ _n =6.8×10^?15 cm²) and hole (H_0.18: E _t ^h =E _v +0.184 eV, σ _p =3.0×10^?15 cm²) levels into the silicon band gap and have a high thermal stability. It is believed that the complex FeVO corresponds to the previously observed and unidentified defects that have an ionization energy of E _t ^e =E _c ?(0.34–0.37) eV and appear as a result of heat treatment of irradiated diffused Si p⁺-n junctions.