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.     

Chemical Vapor Deposition of <Emphasis Type="Italic">α</Emphasis>-Boron Layers on Silicon for Controlled Nanometer-Deep <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">n</Emphasis> Junction Formation

Nanometer-thick amorphous boron (α-B) layers were formed on (100) Si during exposure to diborane (B₂H₆) in a chemical vapor deposition (CVD) system, either at atmospheric or reduced pressures, at temperatures down to 500°C. The dependence of the growth mechanism on processing parameters was investigated by analytical techniques, such as transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), in conjunction with extensive electrical characterization. In particular, devices fabricated by B deposition effectively demonstrated that p ⁺ doping of the silicon substrate can be achieved within 10 nm from the surface in a manner that is finely controlled by the B₂H₆ exposure conditions. High-quality, extremely ultrashallow, p ⁺ n junctions were fabricated, and their saturation current was tuned from high Schottky-like values to low deep pn junction-like values by the increasing of the deposited B layer thickness. This junction formation exhibited high selectivity, isotropy, spatial homogeneity, and compatibility with standard Si device fabrication.     

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.     

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.     

Modeling of the Structural Properties of Hg<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te

Structural properties of Hg_1–x Cd _x Te are investigated by using first-principles calculations based on density functional theory. An energetically minimized and geometrically optimized model for Hg_1–x Cd _x Te was formulated. A virtual crystal approximation model for Hg_1–x Cd _x Te produced a poor fit to experimental lattice parameters and Vegard’s law. However, the virtual crystal approximation model provides reasonably accurate values for the band gap␣energy. An ordered alloy approximation model produced a good fit to Hg_1–x Cd _x Te lattice parameters and followed Vegard’s law. The ordered alloy approximation also produced a bimodal distribution in Hg-Te and Cd-Te bond lengths in agreement with experimental results.     

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.     

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.     

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.     

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.     

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.     

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.     

Electrical parameters of polycrystalline Sm<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>Eu<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>S rare-earth semiconductors

The electrical parameters of polycrystalline Sm_1–xEu_xS compounds are studied. The conductivity, concentration of free electrons, their mobility, and the conductivity activation energy are measured as functions of the quantity x. The structural parameters of the compounds are determined. A heterostructure is fabricated with x in the range from 0 to 0.3, and the electrical voltage generated by the structure, when heated to a temperature of T = 450 K, due to the thermovoltaic effect is measured. This voltage is found to be 55 mV. A method for measuring the thermally induced voltage is described. The method provides a means for separating the thermovoltaic effect from the Seebeck effect.     

Effect of uniaxial deformation on the current–voltage characteristic of a <Emphasis Type="Italic">p</Emphasis>-Ge/<Emphasis Type="Italic">n</Emphasis>-GaAs heterostructure

The effect of uniaxial deformation under a stress of up to 6 kg/cm² on the current–voltage characteristics of a p-Ge/n-GaAs heterostructure is studied at 300 and 77 K. It is found that both the forward and reverse currents increase with increasing pressure, with the change in the forward current exceeding that in the reverse current by an order of magnitude. Deformation is also examined in relation to different crystallographic directions. It is found that the effect is at a maximum if the compression direction is parallel to <111>. This result can be used in the development of uniaxial-strain sensors.     

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).     

The influence of the magnetic field on the effect of drag of electrons by phonons in <Emphasis Type="Italic">n</Emphasis>-Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

Thermopower in n-Cd_0.2Hg_0.8Te (6–100 K) is studied. A large effect of drag of the charge carriers by phonons α_ph is found. The influence of the magnetic field H on the drag thermopower is considered. It is established that the magnetic field exerts the effect mainly on the electron component of α_ph. The data are interpreted in the context of the theory taking into account the effect of H on thermopower α_ph, in which parameter A(ɛ) proportional to the static force of the drag effect is introduced. By the experimental data α_ph(T, H), T, and H dependences A(ɛ) are determined. It is shown that, as H increases, A(ɛ) sharply decreases. This explains a decrease in α_ph in the magnetic field, power index k in dependence α_ph ∝ T ^−κ, and narrowing the region of manifestation of the drag effect. It is established that at classically high fields, the drag effect in n-Cd_0.2Hg_0.8Te does not vanish.     

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.     

Investigation of MBE-Growth of Mid-Wave Infrared Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se

Undoped mid-wave infrared Hg_1?xCd_xSe epitaxial layers have been grown to a nominal thickness of 8–14 μm on GaSb (211)B substrates by molecular beam epitaxy (MBE) using constant beam equivalent pressure ratios. The effects of growth temperature from 70°C to 120°C on epilayer quality and its electronic parameters has been examined using x-ray diffraction (XRD) rocking curves, atomic force microscopy, Nomarski optical imaging, photoconductive decay measurements, and variable magnetic field Hall effect analysis. For samples grown at 70°C, the measured values of XRD rocking curve full width at half maximum (FWHM) (116 arcsec), root mean square (RMS) surface roughness (2.7 nm), electron mobility (6.6?×?10⁴ cm² V^?1 s^?1 at 130 K), minority carrier lifetime (～?2 μs at 130 K), and background n-type doping (～?3?×?10¹⁶ cm^?3 at 130 K), indicate device-grade material quality that is significantly superior to that previously published in the open literature. All of these parameters were found to degrade monotonically with increasing growth temperature, although a reasonably wide growth window exists from 70°C to 90°C, within which good quality HgCdSe can be grown via MBE.     

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.     

Optical Properties of Epitaxial Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>In<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sb Alloy Layers

Optical studies of unstrained narrow-gap Al _x In_{1 − x} Sb semiconductor alloy layers are carried out. The layers are grown by molecular-beam epitaxy on semi-insulating GaAs substrates with an AlSb buffer. The composition of the alloys is varied within the range of x = 0–0.52 and monitored by electron probe microanalysis. The band gap E _g is determined from the fundamental absorption edge with consideration for the nonparabolicity of the conduction band. The refined bowing parameter in the experimental dependence E _g (x) for the Al _x In_{1 − x} Sb alloys is 0.32 eV. This value is by 0.11 eV smaller than the commonly referred one.