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.     

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.     

Truncation Error Bound for the Kravchenko–Kotelnikov Series

The truncation error of the Kravchenko–Kotelnikov series, which is a generalization of the Whittaker–Kotelnikov–Shannon series, is studied. The basis functions of the Kravchenko–Kotelnikov series are the spectra F_a(t) of the atomic function h_a(x), linearly transformed with respect to the argument. In this case, the function F_a(t) is defined by an infinite product. Two theorems on the truncation error bound for the Kravchenko–Kotelnikov series are proven. A practically important case in which the infinite product F_a(t) is replaced by a partial one is considered. A comparative analysis of the obtained formulae is carried out.     

Work Function Tuning and Doping Optimization of 22-nm HKMG Raised SiGe/SiC Source–Drain FinFETs

The basic requirements on process design of extremely scaled devices involve appropriate work function and tight doping control due to their significant effect on the threshold voltage as well as other critical electrical parameters such as drive current and leakage. This paper presents a simulation study of 22-nm fin field-effect transistor (FinFET) performance based on various process design considerations including metal gate work function (WF), halo doping (N _halo), source/drain doping (N _sd), and substrate doping (N _sub). The simulations suggest that the n-type FinFET (nFinFET) operates effectively with lower metal gate WF while the p-type FinFET (pFinFET) operates effectively with high metal gate WF in 22-nm strained technology. Further investigation shows that the leakage reduces with increasing N _halo, decreasing N _sd, and increasing N _sub. Taguchi and Pareto analysis-of-variance approaches are applied using an L₂₇ orthogonal array combined with signal-to-noise ratio analysis to determine the best doping concentration combination for 22-nm FinFETs in terms of threshold voltage (V _t), saturation current (I _on), and off-state current (I _off). Since there is a tradeoff between I _on and I _off, the design with the nominal-is-best V _t characteristic is proposed, achieving nominal V _t of 0.259 V for the nFinFET and ?0.528 V for the pFinFET. Pareto analysis revealed N _halo and N _sub to be the dominant factor for nFinFET and pFinFET performance, respectively.     

Study of the electrical properties of Cd<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

On the basis of the temperature and field dependences of the Hall coefficient R _H , it was found that samples with a low electron density are, as a rule, compensated, and the degree of compensation changes upon thermal conversion of the conductivity of the sample to p type. For n-Cd_xHg_1?xTe, the ionization energy of the donor level was found from the temperature dependences of resistivity ρ(T): E _d =24–32 meV. For the same samples, after their thermal conversion to p type, the ionization energies of acceptors, which are related to doubly charged vacancies V _Hg ⁺⁺ , were determined: E _a =32 and 48 meV. In addition, a deep level E _t , related to an unknown amphoteric impurity, was found (E _t ?E _v ≈0.7E _g ).     

The following the perturbed leader algorithm and its application for constructing game strategies

A modification of Hannan’s Following the Perturbed Leaded (FPL) algorithm for the case of unlimited gains and losses is considered. Estimates of the prediction error are obtained in terms of the volume v _t and game fluctuation fluc(t) = Δv _t /v _t , where Δv _t = v _t –v _t–1. We prove the asymptotic consistency on the average of this variant of the algorithm for fluc(t) = o(t). Applications of this algorithm for constructing game strategies are considered. Game strategies employing the difference between the “micro” and “macro” volatility of the discrete time series (prices of the financial instrument) are determined for obtaining arbitrage. Mixing these expert strategies is performed on the basis of the variant of Hannan’s algorithm developed in this work.     

Excition states in semiconductor quantum dots in the modified effective mass approximation

A new modified effective mass approximation is suggested to describe the excitonic energy spectrum of quantum dots of radii a comparable to the exciton Bohr radius a _ex ⁰ . It is shown that, for quantum dots simulated by infinitely deep potential wells, the effective mass approximation is appropriate for describing excitons in quantum dots of radii a ≈ a _ex ⁰ , if the reduced effective mass of the excitons, μ, is considered as a function of the radius of the quantum dot a, μ = μ(a).     

Effect of the magnetic phase transition on the charge transport in layered semiconductor ferromagnets TlCrS<Subscript>2</Subscript> and TlCrSe<Subscript>2</Subscript>

TlCrS₂ and TlCrSe₂ crystals were synthesized by solid-state reaction. X-ray diffraction analysis showed that TlCrS₂ and TlCrSe₂ compounds crystallize in the hexagonal crystal system with lattice parameters a = 3.538 Å, c = 21.962 Å, c/a ≈ 6.207, z = 3; a = 3.6999 Å, c = 22.6901 Å, c/a ≈ 6.133, z = 3; and X-ray densities ρ _x = 6.705 and 6.209 g/cm³, respectively. Magnetic and electric studies in a temperature range of 77–400 K showed that TlCrS₂ and TlCrSe₂ are semiconductor ferromagnets. Rather large deviations of the experimental effective magnetic moment of TlCrS₂ (3.26 μ_B) and TlCrSe₂ (3.05 μ_B) from the theoretical one (3.85 μ_B) are attributed to two-dimensional magnetic ordering in the paramagnetic region of strongly layered ferromagnets TlCrS₂ and TlCrSe₂. The effect of the magnetic phase’s transition on the charge transport in TlCrS₂ and TlCrSe₂ is detected.     

Integer quantum Hall effect and correlated disorder

The effect of the form of the random potential of impurities and defects on the longitudinal σ _xx and Hall σ _xy components of conductivity in the mode of the integer quantum Hall effect is theoretically investigated. It is shown that the width of the Hall conductivity plateau as well as the peak values of the longitudinal conductivity heavily depend on the ratio λ/a _H between the random potential correlation length and the magnetic length. For the first time, it is established that in the case of the short-wavelength potential λ ? a _H, the peak values of σ _xx ^(N) are directly proportional to the Landau level number N ≥ 1, σ _xx = 0.5Ne ²/h, whereas the peak values of σ _xx ^(N) are independent of the Landau level number in the case of the long-wavelength potential λ ? a _H, and their magnitude is much lower than 0.5e ²/h. The obtained results are in good agreement with the available experimental data.     

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p⁺–p⁰–i–n⁰ homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p⁰ and n⁰ layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E _t ), capture cross sections (σ _p ), and concentrations (N _t ) are calculated from the Arrhenius dependences to be E _t = 845 meV, σ _p = 1.33 × 10^–12 cm², N _t = 3.80 × 10¹⁴ cm^–3 for InGaAs/GaAs and E _t = 848 meV, σ _p = 2.73 × 10^–12 cm², N _t = 2.40 × 10¹⁴ cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.     

High-power nano- and picosecond optoelectronic switches based on high-voltage silicon structures with <Emphasis Type="Italic">p–n</Emphasis> junctions: II. Energy efficiency

The energy efficiency of optoelectronic switches based on high-voltage silicon photodiodes, phototransistors, and photothyristors controlled by picosecond laser pulses during the formation of voltage pulses on resistive load R _L is studied for the first time. It is shown that at the given values of the resistive load R _L , pulse amplitude U _R and duration t _R , there exist optimum device areas, energies, and absorbances of control radiation providing a maximum total switch efficiency of ~0.92. All three switch types feature almost the same efficiency at short t _R ; at longer t _R , photothyristors have a noticeable advantage.     

On Measurements of the Electrons and Holes Impact-Ionization Coefficients in 4<Emphasis Type="Italic">H</Emphasis>–SiC

All published results of measurements (at 300 K) of the impact ionization coefficients for electrons α_n and holes α_p in 4H–SiC are analyzed. It is shown that the most plausible approximations of dependences of α_{n, p} on electric-field strength E have the usual form α_{n, p} = a_{n, p} exp(–E_{n, p}/E) at fitting-parameter values of a_n = 38.6 × 106 cm^–1, E_n = 25.6 MV/cm, a_p = 5.31 × 106 cm^–1, and E_p = 13.1 MV/cm. These dependences α_{n, p}(E) are used to calculate the highest field strength E_b and thickness w_b of the space-charge region at the breakdown voltage U_b. A number of new formulas for calculating α_{n, p}(E) are obtained from the results of measuring the avalanche-multiplication coefficients and the excess-noise factors under the single-sided illumination of photodiodes with stepped doping.     

Formation of silicon nanocrystals in multilayer nanoperiodic <Emphasis Type="Italic">a</Emphasis>-SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/insulator structures from the results of synchrotron investigations

The problem of the efficiency of the controllable formation of arrays of silicon nanoparticles is studied on the basis of detailed investigations of the electronic structure of multilayer nanoperiodic a-SiO _x /SiO₂, a-SiO _x /Аl₂О₃, and a-SiO _x /ZrO₂ compounds. Using synchrotron radiation and the X-ray absorption near edge structure (XANES) spectroscopy technique, a modification is revealed for the investigated structures under the effect of high-temperature annealing at the highest temperature of 1100°C; this modification is attributed to the formation of silicon nanocrystals in the layers of photoluminescent multilayer structures.     

HVE-mobicast: a hierarchical-variant-egg-based mobicast routing protocol for wireless sensornets

In this paper, we propose a new mobicast routing protocol, called the HVE-mobicast (hierarchical-variant-egg-based mobicast) routing protocol, in wireless sensor networks (WSNs). Existing protocols for a spatiotemporal variant of the multicast protocol called a “mobicast” were designed to support a forwarding zone that moves at a constant velocity, \(\stackrel{\rightarrow}{v}\), through sensornets. The spatiotemporal characteristic of a mobicast is to forward a mobicast message to all sensor nodes that are present at time t in some geographic zone (called the forwarding zone) Z, where both the location and shape of the forwarding zone are a function of time over some interval (t _start ,t _end ). Mobicast routing protocol aims to provide reliable and just-in-time message delivery for a mobile sink node. To consider the mobile entity with the different moving speed, a new mobicast routing protocol is investigated in this work by utilizing the cluster-based approach. The message delivery of nodes in the forwarding zone of the HVE-mobicast routing protocol is transmitted by two phases; cluster-to-cluster and cluster-to-node phases. In the cluster-to-cluster phase, the cluster-head and relay nodes are distributively notified to wake them up. In the cluster-to-node phase, all member nodes are then notified to wake up by cluster-head nodes according to the estimated arrival time of the delivery zone. The key contribution of the HVE-mobicast routing protocol is that it is more power efficient than existing mobicast routing protocols, especially by considering different moving speeds and directions. Finally, simulation results illustrate performance enhancements in message overhead, power consumption, needlessly woken-up nodes, and successful woken-up ratio, compared to existing mobicast routing protocols.     

Increase in the rate and discretization of the kinetics of isothermal surface generation of minority charge carriers in metal-insulator-semiconductor structures with a planar-inhomogeneous insulator

Surface generation of minority charge carriers in silicon metal-oxide-semiconductor (MOS) structures is efficient only at the initial recombinationless stage. Quasi-equilibrium between surface generation centers and the minority-carrier band is established in a time t ～ 10^?5 s. In the absence of other carrier generation channels, an equilibrium inversion state at 300 K would need t = t_∞ > 10³ years to become established. In fact, the time t ∞ is much shorter, due to excess-carrier generation via centers located at the SiO₂/Si interface over the gate periphery. This edge-related generation can easily be simulated in an MOS structure with a single gate insulated from Si by oxide layers of various thicknesses. At gate depleting voltages V _g , the role of the periphery is played by a shallow potential well under a thicker oxide, and the current-generation kinetics becomes unconventional: two discrete steps are observed in the dependences I(t), and the duration and height of these steps depend on V _g . An analysis of the I(t) curves allows determination of the electric characteristics of the Si surface in the states of initial depletion (t = 0) and equilibrium inversion (t = t_∞), as well as the parameters of surface lag centers, including their energy and spatial distributions. The functionally specialized planar inhomogeneity of a gate insulator is a promising basis for dynamic sensors with integrating and threshold properties.     

Impact of deployment size on the asymptotic capacity for wireless ad hoc networks under Gaussian channel model

We study the throughput capacity and transport capacity for both random and arbitrary wireless networks under Gaussian Channel model when all wireless nodes have the same constant transmission power P and the transmission rate is determined by Signal to Interference plus Noise Ratio (SINR). We consider networks with n wireless nodes \(\{v_1,v_2,\ldots,v_n\}\) (randomly or arbitrarily) distributed in a square region B _a with a side-length a. We randomly choose n _s node as the source nodes of n _s multicast sessions. For each source node v _i , we randomly select k points and the closest k nodes to these points as destination nodes of this multicast session. We derive achievable lower bounds and some upper bounds on both throughput capacity and transport capacity for both unicast sessions and multicast sessions. We found that the asymptotic capacity depends on the size a of the deployment region, and it often has three regimes.     

Determination of the minority-carrier lifetime in silicon ingots by photoconductivity relaxation measured at microwave frequencies

A new method for determining the bulk lifetime of minority carriers in single-crystal silicon ingots is proposed. A photoconductivity signal measured at a microwave frequency and normalized to its initial value is compared with the results of calculating the total number of excess charge carriers N(t)/N_st, where N_st corresponds to the quasi-steady-state photoconductance. The location of the point of intersection of the photoconductivity-relaxation curve and the dependence N(t=τ)/N_st determines the bulk lifetime τ=τ_v. The measurements were performed on silicon ingots with different resistivities grown by crucibleless zone melting and the Czochralski method. The experimental data obtained agree well with the results of calculation.     

Anderson–Darling statistic and its “inverse”

For more than 60 years, the Anderson–Darling test is most frequently used among all Cramér–von Mises (omega-square) tests. This statistic modifies a classical empirical process defined within the [0, 1] interval by multiplying it by weighting function ψ(t) = (t(1–t))^–1/2. The weighting function redistributes the test sensitivity to deviations of the distribution function of the observed stochastic quantity from a hypothetical distribution function in different its segments. However, the tests with other weighting functions may also be of interest in practice. New formulas for the eigenvalues of the Anderson–Darling statistic are proposed. The statistic “inverse” to the Anderson–Darling statistic with weighting function ψ(t) = (t(1–t))^1/2 is considered. Tests with other weighting functions may also be of interest when weighted Cramér–von Mises statistics are used. The table of quantiles of statistics with weighting functions ψ(t) = t^α(1–t)^β, α >–1, β >–1 is presented. The quantiles are given for 36 different combinations of parameters α >–1 and β >–1. The table was calculated using accurate numerical methods and without application of modeling techniques.     

Determination of the absolute value of the semiconductor surface potential by the quasi-static capacitance-voltage characteristics of an MIS structure

A simultaneous analysis of the derivatives C_V′V_g of the experimental and ideal quasi-static capacitance-voltage characteristics (plotted as a function of the normalized differential capacitance of a metal-insulator-semiconductor (MIS) structure) allows identification of regions within the semiconductor band gap E_g, in which interface states are virtually aTSent and the relation between the surface potential ψ_S of the real semiconductor and the voltage V_g applied to the MIS structure may be readily ascertained. This allows an accurate enough determination of the additive constants ψ_S0(V_g0) necessary to calculate the dependence ψ_S(V_g) in the entire range of V_g by numerical integration of the experimental quasi-static C-V characteristic. The comparison of this dependence with the ideal one characterizes in detail the integral electronic properties of the semiconductor-insulator heterojunction: the E_g-averaged density of interface states, the qualitative pattern of their distribution over the band gap, and the flat-band voltage V_FB and its components caused by a charge fixed in the undergate insulator and a charge localized at boundary states. A high accuracy of the V_FB measurements allows detection of even a weak physical response of MIS structures to external factors or to variations in the heterojunction technology. Results of such an analysis for a typical SiO₂/Si interface of an n-Si-MOS (metal-oxide-semiconductor) structure are considered. The application of C_V′-C_V diagrams for analyzing the high-frequency C-V characteristics is considered.     

Growth,structure, and properties of GaAs-based (GaAs)1–x–y (Ge2) x (ZnSe) y epitaxial films

The possibility of growing the (GaAs)_1–x–y (Ge₂) _x (ZnSe) _y alloy on GaAs substrates by the method of liquid-phase epitaxy from a tin solution–melt is shown. X-ray diffraction shows that the grown film is single-crystal with the (100) orientation and has the sphalerite structure. The crystal-lattice parameter of the film is a _f = 0.56697 nm. The features of the spectral dependence of the photosensitivity are caused by the formation of various complexes of charged components. It is established that the I–V characteristic of such structures is described by the exponential dependence I = I ₀exp(qV/ckT) at low voltages (no higher than 0.4 V) and by the power dependence J ~ V ^α, where the exponent α varies with increasing voltage at high voltages (V > 0.5 V). The results are treated within the framework of the theory of the drift mechanism of current transfer taking into account the possibility of the exchange of free carriers within the recombination complex.