The binding energy of excitons and <Emphasis Type="Italic">X</Emphasis><Superscript>+</Superscript> and <Emphasis Type="Italic">X</Emphasis><Superscript>−</Superscript> trions in one-dimensional systems

The exciton and trion states in semiconductor quantum wires are treated by the variational method. Simple trial functions provide an adequate precision of the calculation over a wide region of wire radii, with an arbitrary relation between the effective masses of charge carriers. The precision of the results obtained by the variational method is checked by numerical diagonalization of the Hamiltonian of excitons and positively and negatively charged trions. The asymptotic behavior of the binding energies of excitons and trions in narrow quantum wires is established in the analytical form. The structure of the excited X ⁺ trion states is analyzed in the context of the adiabatic approximation.     

Radiation-induced bistable centers with deep levels in silicon <Emphasis Type="Italic">n</Emphasis> <Superscript>+</Superscript>–<Emphasis Type="Italic">p</Emphasis> structures

The method of deep level transient spectroscopy is used to study electrically active defects in p-type silicon crystals irradiated with MeV electrons and α particles. A new radiation-induced defect with the properties of bistable centers is determined and studied. After keeping the irradiated samples at room temperature for a long time or after their short-time annealing at T ～ 370 K, this defect does not display any electrical activity in p-type silicon. However, as a result of the subsequent injection of minority charge carriers, this center transforms into the metastable configuration with deep levels located at E_V + 0.45 and E_V + 0.54 eV. The reverse transition to the main configuration occurs in the temperature range of 50–100°C and is characterized by the activation energy ～1.25 eV and a frequency factor of ～5 × 10¹⁵ s^–1. The determined defect is thermally stable at temperatures as high as T ～ 450 K. It is assumed that this defect can either be a complex of an intrinsic interstitial silicon atom with an interstitial carbon atom or a complex consisting of an intrinsic interstitial silicon atom with an interstitial boron atom.     

New CMOS process using a thermal-oxide mask for making <Emphasis Type="Italic">n</Emphasis><Superscript>−</Superscript>- and <Emphasis Type="Italic">p</Emphasis><Superscript>−</Superscript>-Wells

A new manufacturing process is proposed and evaluated for CMOS memory circuits that is designed to decrease labor input and to increase yield. It essentially uses thermal silicon dioxide instead of silicon nitride as the material of the mask for n ^?- and p ^?-wells, and employs an improved doping procedure for the wells. The new process is shown to decrease considerably the residual stress and defect density in the wafer. Its advantages over the standard process are supported by a two-dimensional computer simulation with Silvaco’s SSUPREM4.     

The <Emphasis Type="Italic">α</Emphasis> − λ − <Emphasis Type="Italic">μ</Emphasis> and <Emphasis Type="Italic">α − η − μ</Emphasis> Small-Scale General Fading Distributions: A Unified Approach

In this paper, a general small-scale fading model for wireless communications, that explores the nonlinearity and at the same time the inhomogeneous nature of the propagation medium, is presented, studied in terms of its first-order statistics of the envelope, and validated by means of field measurements and the Monte Carlo simulation. It is indeed a novel distribution with many advantages such as its generality, its physical interpretation that is directly associated with the propagation channel, and its mathematical tractability due to its simple and closed-form expression. By fitting to measurement data, it has been shown that the proposed distribution outperforms the widely known fading distributions. Namely, the α − λ − μ model, which can be in fact called α − η − μ format 2 model, can also be obtained from the α − η − μ format 1 model by a rotation of the axes. Both formats are combined, in order to result to a unified model in a closed form that may describe the propagation environment in a variety of different fading conditions. Its physical background is hidden behind the names of its parameters. The unified model includes the already known general distributions α − μ′, η − μ, λ − μ (η − μ format 2), and their inclusive ones as special cases.     

Quantum Oscillations of Photoconductivity Relaxation in <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> GaAs/InAs/AlAs Heterodiodes

The photoconductivity and its relaxation characteristics in tunneling p–i–n GaAs/AlAs heterostructures under pulsed illumination is studied. Quantum oscillations in the photoconductivity are detected depending on the bias voltage with the period independent of the light wavelength, as well as an oscillating component of the relaxation curves caused by modulation of the recombination rate at the edge of a triangular quantum well in the undoped i layer, as in the case of photoconductivity oscillations. The common nature of oscillations of the steady-state photoconductivity and relaxation curves under pulsed illumination is directly confirmed by the lack of an oscillating component in both types of dependences of some studied p–i–n heterostructures. Simultaneous suppression of the observed oscillations of dependences of both types as the temperature increases to 80 K also confirms the proposed mechanism of their formation. The dependences of these oscillations on the magnetic field and light flux power are studied. Oscillation-amplitude suppression in a magnetic field of ~2 T perpendicular to the current is caused by the effect of the Lorentz force on the ballistic motion of carriers in the triangular-quantum-well region.     

Intersegment resistance in silicon <Emphasis Type="Italic">p</Emphasis>—<Emphasis Type="Italic">n</Emphasis>-Junction position-sensitive detectors

Intersegment insulation in p—n-junction arrays based on high-resistivity silicon, which controls the interaction of neighboring elements of position-sensitive detectors, was studied. It was shown that current-voltage characteristics of the intersegment gap of the p—n junction deeply depleted due to an applied reverse voltage contain a portion of a step change in the current, which controls the intersegment insulation resistance. This feature is caused by the effect of switching of a small fraction of the bulk current between neighboring segments. In this case, the effect of the ohmic conductance between segments on the intersegment insulation resistance is ten times weaker than the effect of bulk current switching.     

Cathodoluminescence from dilute GaN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> solutions (<Emphasis Type="Italic">x</Emphasis> ≤ 0.03)

Cathodoluminescence from GaN _x As_1?x layers (0 ≤ x ≤ 0.03) was measured at photon energies ranging from the intrinsic absorption edge to 3 eV at room temperature. An additional emission band was visible in the visible range of the cathodoluminescence spectra. The intensity of this band is two orders of magnitude lower than the edge-emission intensity. The photon energy corresponding to the peak of this band and its FWHM are virtually independent of x and equal to ～2.1 and 0.6–0.7 eV, respectively. This emission is related to indirect optical transitions of electrons from the L _6c and Δ conduction-band minimums to the Γ₁₅ valence-band maximum.     

Low-temperature microwave magnetoresistance of lightly doped <Emphasis Type="Italic">p</Emphasis>-Ge and <Emphasis Type="Italic">p</Emphasis>-Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>

The magnetoresistance of a lightly doped p-Ge_1?xSi_x alloy is studied in the range of compositions x = 1–2 at %. The results are compared with the available data for lightly doped p-Ge. The studies have been carried out using ESR measurements at a frequency of 10 GHz in the temperature range 10–120 K. It is established that micrononuniformity in the distribution of Si in the Ge lattice (Si clusters) suppresses the interference part of the anomalous magnetoresistance and, in addition, results in an averaging of the effects of light and heavy holes. This observation suggests a sharp decrease in the inelastic scattering time in the case of a Ge_1?xSi_x solid solution as compared to that of Ge.     

Mechanisms of formation of <Emphasis Type="Italic">N–S</Emphasis> transition in nonisothermal <Emphasis Type="Italic">I–V</Emphasis> characteristics of a <Emphasis Type="Italic">p–i–n</Emphasis> diode

On the basis of the self-consistent model of transport processes in the semiconductor p–i–n diode during its self-heating under conditions of limited heat sink, the mechanisms of unusual effect—the formations of N–S transition in nonisothermal I–V characteristics of the device were numerically analyzed. It is established that such an effect is caused by a pronounced temperature reduction of the mobility of carriers in the high-resistivity base and the injection-level saturation at the current densities J > 300–500 A/cm². The saturation is attained due to the Auger recombination or the leakage of carriers from plasma into heavily doped emitter layers, the integrated current of which, as a rule, exceeds the recombination integrated current in the base under these conditions. The Auger recombination in the anode emitter also starts to play an appreciable role in the injection-level restriction in the base if the impurity concentration becomes higher than 10¹⁸ cm⁻³ in there.     

Performance of Dual Branch SSC Receiver in Correlated <Emphasis Type="Italic">α</Emphasis>-<Emphasis Type="Italic">μ</Emphasis> Fading Channels

In this paper, the performance analysis of dual branch switch and stay combining (SSC) receivers operating over correlated and identically distributed (i.d.) α-μ fading channels is presented. Assuming this diversity technique, infinite series expressions with fast converging properties are derived for the probability density function (pdf), cumulative distribution function (cdf) and the moments of the output envelope. The proposed analysis is used for evaluating the important performance criteria, such as the outage probability, the mean square output envelope, the amount of fading and the average bit error probability (ABEP). The effects of fading severity, branch correlation and optimum choice of switching threshold are considered and numerically presented. Monte Carlo simulations confirm the validity and accuracy of the derived analytical expressions.     

Putting Queens in Carry Chains,N<Superscript><Emphasis Type="Italic">o</Emphasis>̱</Superscript>27

The N-Queens Puzzle is a fascinating combinatorial problem. Up to now, the number of distinct valid placements of N non-attacking queens on a generalized N × N chessboard cannot be computed by a formula. The computation of these numbers is instead based on an exhaustive search whose complexity grows dramatically with the problem size N. Solutions counts are currently known for all N up to 26. The parallelization of the search for solutions is embarrassingly simple. It is achieved by pre-placing the queens within a certain board region. These pre-placements partition the search space. The chosen extent of the pre-placement allows for a wide range of the partitioning granularity. This ease of partitioning makes the N-Queens Puzzle a great show-off case for tremendously parallel computation approaches and a flexible benchmark for parallel compute resources. This article presents the Q27 Project, an open-source effort targeting the computation of the solution count of the 27-Queens Puzzle. It is the first undertaking pushing the frontier of the N-Queens Puzzle that exploits the complete symmetry group D ₄ of the square. This reduces the overall computational complexity already to an eighth in comparison to a naive exploration of the whole search space. This article details the coronal pre-placement that enables the partitioning of the overall search under this approach. With respect to the physical implementation of the computation, it describes the hardware structure that explores the resulting subproblems efficiently by exploiting bit-level operations and their mapping to FPGA devices as well as the infrastructure that organizes the contributing devices in a distributed computation. The performance of several FPGA platforms is evaluated using the Q27 computation as a benchmark, and some intriguing observations obtained from the available partial solutions are presented. Finally, an estimate on the remaining run time and on the expected magnitude of the final result is dared.     

Analysis of Carrier Transport in <Emphasis Type="Italic">n</Emphasis>-Type Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te with Ultra-Low Doping Concentration

Mercury cadmium telluride (HgCdTe, or MCT) with low n-type indium doping concentration offers a means for obtaining high performance infrared detectors. Characterizing carrier transport in materials with ultra low doping (N_D?=?10¹⁴ cm^?3 and lower), and multi-layer material structures designed for infrared detector devices, is particularly challenging using traditional methods. In this work, Hall effect measurements with a swept B-field were used in conjunction with a multi-carrier fitting procedure and Fourier-domain mobility spectrum analysis to analyze multi-layered MCT samples. Low temperature measurements (77 K) were able to identify multiple carrier species, including an epitaxial layer (x?=?0.2195) with n-type carrier concentration of n?=?1?×?10¹⁴ cm^?3 and electron mobility of μ?=?280000 cm²/Vs. The extracted electron mobility matches or exceeds prior empirical models for MCT, illustrating the outstanding material quality achievable using current epitaxial growth methods, and motivating further study to revisit previously published material parameters for MCT carrier transport. The high material quality is further demonstrated via observation of the quantum Hall effect at low temperature (5 K and below).     

Electrodeposition of Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Thermoelectric Films from DMSO Solution

The electrochemical behavior of nonaqueous dimethyl sulfoxide solutions of Bi^III, Te^IV, and Sb^III was investigated using cyclic voltammetry. On this basis, Bi _x Sb_2−x Te _y thermoelectric films were prepared by the potentiodynamic electrodeposition technique in nonaqueous dimethyl sulfoxide solution, and the composition, structure, morphology, and thermoelectric properties of the films were analyzed. Bi _x Sb_2−x Te _y thermoelectric films prepared under different potential ranges all possessed a smooth morphology. After annealing treatment at 200°C under N₂ protection for 4 h, all deposited films showed p-type semiconductor properties, and their resistances all decreased to 0.04 Ω to 0.05 Ω. The Bi_0.49Sb_1.53Te_2.98 thermoelectric film, which most closely approaches the stoichiometry of Bi_0.5Sb_1.5Te₃, possessed the highest Seebeck coefficient (85 μV/K) and can be obtained under potentials of −200 mV to −400 mV.     

Photosensitive thin-film In/<Emphasis Type="Italic">p</Emphasis>-Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S Schottky barriers: Fabrication and properties

Thin Pb _x Sn_{1 − x} S films are obtained by the “hot-wall” method at substrate temperatures of 210–330°C. The microstructure, composition, morphology, and electrical characteristics of films are investigated. On the basis of the obtained films, photosensitive In/p-Pb _x Sn_{1 − x} S Schottky barriers are fabricated for the first time. The photosensivity spectra of these structures are investigated, and the character of interband transitions and the band-gap values are determined from them. The conclusion is drawn that Pb _x Sn_{1 − x} S thin polycrystalline films may be used in solar-energy converters.     

Type II broken-gap GaSb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As<Emphasis Type="Italic">x</Emphasis>/InAs heterojunction (<Emphasis Type="Italic">x</Emphasis> < 0.15): Evolution of the band diagram for the ternary solid solution

Layers of the GaSb_{1 ? x} As _x alloy with arsenic content in the range x = 0.06–0.15 have been grown for the first time on InAs (100) substrates by metal-organic vapor-phase epitaxy. A new approach to the calculation of the band diagram of the GaSbAs alloy is suggested. It is demonstrated on the basis of magnetotransport measurements in p-GaSbAs/p-InAs heterostructures and with the method suggested by the authors for the calculation of band diagrams for alloys in the GaSbAs system that, in the composition range under study, the GaSbAs/InAs heterojunction is a type II broken-gap heterojunction.     

Electrical and Optical Characterization of AlGaN/GaN HEMTs with <Emphasis Type="Italic">In Situ</Emphasis> and <Emphasis Type="Italic">Ex Situ</Emphasis> Deposited SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Layers

A comparative study of AlGaN/GaN high-electron-mobility transistor (HEMT) surface passivation using ex situ and in situ deposited SiN _x is presented. Performing ex situ SiN _x passivation increased the reverse gate leakage and off-state channel leakage by about three orders of magnitude. The in situ SiN _x layer was characterized using transmission electron microscopy (TEM) and capacitance–voltage (CV) measurements. Photoluminescence (PL) spectra indicated a reduction of nonradiative recombination centers in in situ SiN _x -passivated samples, indicating improved crystal quality. CV measurements indicated a reduction of surface state density as well, and thus better overall passivation using in situ SiN _x . Electroluminescence (EL) images of the channel regions in AlGaN/GaN HEMT devices operating in forward blocking mode with up to 400 V drain bias demonstrated reduced channel emission profiles of in situ-passivated devices. Compared with a nonpassivated reference sample, the reduced EL emission profiles correlated with a reduced channel temperature on ex situ SiN _x -passivated devices.     

Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te Alloys: Application Considerations

The search for alternative energy sources is at the forefront of applied research. In this context, thermoelectricity, i.e., direct conversion of thermal into electrical energy, plays an important role, particularly for exploitation of waste heat. Materials for such applications should exhibit thermoelectric potential and mechanical stability. PbTe-based compounds include well-known n-type and p-type compounds for thermoelectric applications in the 50°C to 600°C temperature range. This paper is concerned with the mechanical and transport properties of p-type Pb_0.5Sn_0.5Te:Te and PbTe<Na> samples, both of which have a hole concentration of ∼1 × 10²⁰ cm⁻³. The ZT values of PbTe<Na> were found to be higher than those of Pb_0.5Sn_0.5Te:Te, and they exhibited a maximal value of 0.8 compared with 0.5 for Pb_0.5Sn_0.5Te:Te at 450°C. However, the microhardness value of 49 H_V found for Pb_0.5Sn_0.5Te:Te was closer to that of the mechanically stable n-type PbTe (30 H_V) than to that of PbTe<Na> (71 H_V). Thus, although lower ZT values were obtained, from a mechanical point of view Pb_0.5Sn_0.5Te:Te is preferable over PbTe<Na> for practical applications.     

Anomalous Peak in the Forward-Bias <Emphasis Type="Italic">C</Emphasis>–<Emphasis Type="Italic">V</Emphasis> Plot and Temperature-Dependent Behavior of Au/PVA (Ni,Zn-doped)/<Emphasis Type="Italic">n</Emphasis>-Si(111) Structures

In this study, the temperature-dependent mean density of interface states (N_SS)(N_{\rm SS}) and series resistance (R_S)(R_{\rm S}) profiles of Au/PVA (Ni,Zn-doped)/n-Si(111) structures are determined using current–voltage (I−V) and admittance spectroscopy [capacitance–voltage (C–V) and conductance–voltage G/ω–V] methods. The other main electronic parameters such as zero-bias barrier height (F_B0)(\Phi_{{\rm B}0}), ideality factor (n), and doping concentration (N _D) are also obtained as a function of temperature. Experimental results show that the values of F_B0\Phi_{\rm{B}0}, n, R _S, and N _SS are strongly temperature dependent. The values of F_B0\Phi_{\rm{B}0} and R _S increase with increasing temperature, while those of n and N _SS decrease. The C–V plots of Au/PVA (Ni,Zn-doped)/n-Si(111) structures exhibit anomalous peaks in forward bias (depletion region) at each temperature, and peak positions shift towards negative bias with increasing temperature. The peak value of C has been found to be strongly dependent on N _SS, R _S, and temperature. The experimental data confirm that the values of N _SS, R _S, temperature, and the thickness and composition of the interfacial polymer layer are important factors that influence the main electrical parameters of the device.     

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.