The forward bias current density–voltage–temperature (J–V–T) characteristics of Al–SiO2–pSi (MIS) Schottky diodes

Metal–insulator–semiconductor Schottky diodes were fabricated to investigate the tunnel effect and the dominant carrier transport mechanism by using current density–voltage (J–V) and capacitance–voltage (C–V) measurements in the temperature range of 295–370?K. The slope of the ln?J–V curves was almost constant value over the nearly four decades of current and the forward bias current density J is found to be proportional to J_o (T) exp(AV). The values of N_ss estimated from J–V and C–V measurements decreased with increasing temperature. The temperature dependence of the barrier heights obtained from forward bias J–V was found to be entirely different than that from the reverse bias C–V characteristics. All these behaviours confirmed that the prepared samples have a tunnel effect and the current transport mechanism in the temperature range of 295–370?K was predominated by a trap-assisted multi-step tunnelling, although the Si wafer has low doping concentration and the measurements were made at moderate temperature.     

The temperature dependence of internal optical losses in semiconductor lasers (λ = 900–920 nm)

The temperature dependences of radiative characteristics of semiconductor lasers based on asymmetric heterostructures of the separate confinement with an extended waveguide fabricated by MOCVD epitaxy (the emission wavelength λ = 900–920 nm) are studied. It is established that the threshold concentration in the active region and waveguide layers of the laser heterostructure of the separate confinement increases in the CW lasing mode as the pumping current and temperature of the active region are increased. It is established experimentally that, in the temperature range of 20–140°C, the stimulated quantum yield remains unchanged. It is shown that the temperature delocalization of charge carriers leads to an increase in the carrier concentration in the waveguide layers of the laser heterostructure. The total increase in internal optical losses due to scattering by free charge carriers in the layers of the active region and waveguide layers of the laser heterostructure leads to a decrease in the differential quantum efficiency and to saturation of the watt-ampere characteristic of semiconductor lasers in the continuous lasing mode.     

Ba_xNi_(1–x)La_yFe_(12–y)O_(19)铁氧体的制备与磁性能研究

首先利用溶胶-凝胶法制备了BaxNi1–xFe12O19(x=0.2,0.4,0.6,0.8)样品,通过热重-差示扫描量热仪(TG-DSC)、X射线衍射仪(XRD)和振动试样磁强计(VSM)分析,确定了最佳煅烧温度和最佳Ba-Ni摩尔比。然后利用同样的方法制备了Ba0.6Ni0.4LayFe12–yO19(y=0,0.1,0.3,0.5)样品,利用场发射扫描电镜(FESEM)、XRD和VSM对产物进行表征分析。结果表明Ni2+取代Ba2+,进入其晶格内部,改变了铁氧体的磁性能。La3+的加入改变了铁氧体的矫顽力Hc、饱和磁化强度Ms和剩余磁化强度Mr。当y=0.3时,其Ms和Mr达到最大值,分别为51.0 A.m2/kg和32.3 A·m2/kg。     

Electrosynthesis of organic–inorganic compounds (p–n heterojunction)

An electrochemical deposition procedure by cyclic voltammetry, in an electrolyte solution was adopted for the preparation of thin films of polypyrrole–gallium arsenide composite materials. The properties of the composite layers were studied by cyclic voltammetry, electrochemical impedance spectroscopy and photoelectrochemical measurements. The p- and n-type semiconductor behaviour of the polypyrrole (PPy) and gallium arsenide (GaAs) were studied by photocurrent measurements. It was found that the composite material (PPy–GaAs) had a (p–n) heterojunction behaviour.     

Halogen adsorption at an As-stabilized β2–GaAs (001)–(2 × 4) surface

Halogen (F, Cl, Br, and I) adsorption at an As-stabilized GaAs (001) surface with the β2–(2 × 4) reconstruction is studied using the plane-wave projected-augmented wave method. The effect of halogens on the structural and electronic characteristics of the semiconductor surface is analyzed. The T₂′ site at the missing row edge is shown to be the energetically most favorable for the adsorption of F, Cl, and Br, whereas I prefers the H₃ site between adjacent arsenic dimers in the third layer from the surface. Ga-halogen bond formation suggests that charge is transferred via the depletion of occupied orbitals of the As-dimer surface atoms, which leads to the weakening of Ga–As bonds in the substrate. The weakening of bonds between substrate-surface atoms due to the interaction of halogens with the surface is estimated.     

Nina Aleksandrovna Goryunova (1916–1971)

Personalia

Nina Aleksandrovna Goryunova (1916–1971)     

Room temperature de Haas–van Alphen effect in silicon nanosandwiches

The negative-U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport. The aforesaid also promotes the creation of composite bosons and fermions by the capture of single magnetic flux quanta at the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of quantum kinetic phenomena in weak magnetic fields at high temperatures up to the room temperature. As a certain version noted above, we present the first findings of the high temperature de Haas–van Alphen (300 K) and quantum Hall (77 K) effects in the silicon sandwich structure that represents the ultranarrow, 2 nm, p-type quantum well (Si-QW) confined by the delta barriers heavily doped with boron on the n-type Si (100) surface. These data appear to result from the low density of single holes that are of small effective mass in the edge channels of p-type Si-QW because of the impurity confinement by the stripes consisting of the negative-U dipole boron centers which seems to give rise to the efficiency reduction of the electron–electron interaction.     

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.     

(Sr_(0.5)Ba_(0.5))_(1.9)Ca_(0.1)NaNb_(5–x)TaxO_(15)陶瓷的介电性能

通过Ta掺杂改性钨青铜陶瓷(Sr0.5Ba0.5)1.9Ca0.1NaNb5–xTaxO15(x=0～0.30),分析了Ta掺杂量对其烧结性能、微观结构及介电性能的影响。陶瓷的烧结温度随x的增大略有提高。当x<0.10时,陶瓷的tC和弛豫性变化不大;当x≥0.10时,tm(1kHz)明显降低,从270℃(x=0)降低至231℃(x=0.30)。且tm随频率增加向高温移动,弛豫性明显增强。认为Ta掺杂引起其性能变化是由于Ta—O键与Nb—O键键能的差异,导致陶瓷氧八面体中心离子位移量以及A位离子有序程度的变化所致。     

High temperature Hall effect measurements of semi-insulating 4H–SiC substrates

High temperature Hall effect and resistivity measurements have been made on semi-insulating 4H–SiC samples. Both vanadium doped and undoped materials have been studied. Resistivity measurements before and after annealing up to 1800 °C are also reported. The thermal activation energy of the resistivity in vanadium doped samples has one of two values, 1.5 and 1.1 eV, due, respectively, to the vanadium donor level and an as yet unidentified defect. The activation energies for high purity semi-insulating material (HPSI) varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI and 1.1 eV V-doped samples. In all cases the material was found to be n-type. Mixed conduction analysis of the data suggests that the hole concentration is negligible in all samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap. The resistivity of V-doped samples were unaffected by anneals up to 1800 °C. The annealing results for HPSI samples were mixed.     

Co含量对Ni_(0.9–0.5x)Co_(0.3+1.5x)Mn_(1.8–x)O_4热敏电阻性能的影响

采用传统的固相反应法制备了Ni0.9–0.5xCo0.3+1.5xMn1.8–xO4(Mn和Ni的摩尔比为2:1,x=0~0.7)陶瓷。并且采用XRD和SEM等手段,系统地分析了Co含量对该热敏陶瓷的相结构及显微形貌的影响。结果表明,所研究的陶瓷均为立方晶相,当x≥0.6时出现第二相CoO岩盐相。在–40~125℃的测试范围内,该陶瓷材料表现出明显的NTC特性。随着Co含量的增加,陶瓷的室温电阻率(2 275~914?·cm)及β值(3 718~3 544 K)均逐渐减小,并且出现两个拐点。其导电机理与小极化子的跳跃电导模型相吻合,并且受CoO岩盐相的影响。     

Three-step concept (TSC) in modeling microelectronics reliability (MR): Boltzmann–Arrhenius–Zhurkov (BAZ) probabilistic physics-of-failure equation sandwiched between two statistical models

When encountering a particular reliability problem at the design, fabrication, testing, or an operation stage of a product’s life, and considering the use of predictive modeling to assess the seriousness and the likely consequences of the a detected failure, one has to choose whether a statistical, or a physics-of-failure-based, or a suitable combination of these two major modeling tools should be employed to address the problem of interest and to decide on how to proceed. A three-step concept (TSC) is suggested as a possible way to go in such a situation. The classical statistical Bayes’ formula can be used at the first step in this concept as a technical diagnostics tool. Its objective is to identify, on the probabilistic basis, the faulty (malfunctioning) device(s) from the obtained signals (“symptoms of faults”). The recently suggested physics-of-failure-based Boltzmann–Arrhenius–Zhurkov’s (BAZ) model and particularly the multi-parametric BAZ model can be employed at the second step to assess the remaining useful life (RUL) of the faulty device(s). If the RUL is still long enough, no action might be needed; if it is not, corrective restoration action becomes necessary. In any event, after the first two steps are carried out, the device is put back into operation (testing), provided that the assessed probability of its continuing failure-free operation is found to be satisfactory. If the operational failure nonetheless occurs, the third, technical diagnostics step should be undertaken to update reliability. Statistical beta-distribution, in which the probability of failure is treated as a random variable, is suggested to be used at this step. While various statistical methods and approaches, including Bayes’ formula and beta-distribution, are well known and widely used in numerous applications for many decades, the BAZ model was introduced in the microelectronics reliability (MR) area only several years ago. Its attributes are addressed and discussed therefore in some detail. The suggested concept is illustrated by a numerical example geared to the use of the prognostics-and-health-monitoring (PHM) effort in actual operation, such as, e.g., en-route flight mission.     

Electroluminescence of InAs/InAs(Sb)/InAsSbP LED heterostructures in the temperature range 4.2–300 K

The electroluminescence of InAs/InAsSbP and InAsSb/InAsSbP LED heterostructures grown on InAs substrates is studied in the temperature range T = 4.2–300 K. At low temperatures (T = 4.2–100 K), stimulated emission is observed for the InAs/InAsSbP and InAsSb/InAsSbP heterostructures with an optical cavity formed normal to the growth plane at wavelengths of, respectively, 3.03 and 3.55 μm. The emission becomes spontaneous at T > 70 K due to the resonant “switch-on” of the CHHS Auger recombination process in which the energy of a recombining electron–hole pair is transferred to a hole, with hole transition to the spin–orbit-split band. It remains spontaneous up to room temperature because of the influence exerted by other Auger processes. The results obtained show that InAs/InAs(Sb)/InAsSbP structures are promising for the fabrication of vertically emitting mid-IR lasers.     

高介电(1–x)Ca_(0.7)Nd_(0.2)TiO_(3-x)Ba_(0.4)Sr_(0.6)TiO_3陶瓷微波介电特性

采用固相反应法制备了具有钙钛矿结构的(1–x)Ca_(0.7)Nd_(0.2)TiO_(3-x)Ba_(0.4)Sr_(0.6)TiO_3(0.05≤x≤0.5)陶瓷,并对其烧结行为、相组成、显微结构及微波介电性能进行了研究。结果表明:随着(Ba0.4Sr0.6)2+含量的增加,(1–x)Ca_(0.7)Nd_(0.2)TiO_(3-x)Ba_(0.4)Sr_(0.6)TiO_3(0.05≤x≤0.5)陶瓷的品质因数(Q·f)及谐振频率温度系数(τf)单调递减,而相对介电常数(εr)先升后小幅降低。当x=0.2,且烧结温度为1 450℃时,该介质陶瓷的微波介电性能为:εr=151.3,Q·f=5 900 GHz,τf=399.4×10–6/℃。与CaTiO_3(εr=160,Q·f=6 800 GHz,τf=850×10–6/℃)相比,Q·f和εr略微降低,τf有较大程度的减少,故此陶瓷体系有望替代CaTiO_3成为新一类高介电性微波陶瓷。     

Sn addition on the tensile properties of high temperature Zn–4Al–3Mg solder alloys

The Zn–4Al–3Mg based solder alloy is a promising candidate to replace the conventional Pb–5Sn alloy in high-temperature electronic packaging. In this study, the tensile properties of Zn–4Al–3Mg–xSn alloys (x = 0, 6.8 and 13.2 wt.%) at high temperatures (e.g., 100 °C, and 200 °C) were investigated. It was found that the uniaxial tensile strength (UTS) of Zn–4Al–3Mg–xSn solder alloys all decrease monotonously with the increment of temperature. The elongation ratio at 100 °C is superior to that at room temperature whereas follows a significant drop at 200 °C. The microstructure observations show that a typical brittle fracture of Zn–4Al–3Mg alloy occurs at room temperature and 200 °C under normal tension, whereas a ductile fracture is found at 100 °C. The 6.8 wt.% Sn addition in Zn–4Al–3Mg alloy causes a dramatic decrease of yield strength, and a slight deterioration of the ductility.     

Effect of temperature on the electrophysical properties of Si–polymer composite varistors

A low voltage Si–polymer composite varistor was prepared at a temperature of 130 °C and a pressure of 60 MPa and its current–voltage characteristic was studied. Also, temperature dependence of current–voltage characteristic was investigated in the temperature range of 25–100 °C. It was found that any increase in ambient temperature lowers breakdown voltage as well as nonlinearity coefficient. Each sample has hysteresis which decreases through increase in temperature. Annealing effect on leakage current, breakdown voltage and nonlinear coefficient was both investigated and analyzed using SEM micrographs and XRD patterns.     

Optical anisotropy in thin films of poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulfonate)

Anisotropic optical constants spectrum of spin-coated thin films of poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulfonate) (PEDOT–PSS) from 200 to 1700 nm were determined using variable-angle spectroscopic ellipsometry and polarized intensity transmission data together with absorption spectroscopy. PEDOT–PSS was found to be very anisotropic, uniaxial with the optic axis parallel to the surface normal. The result is in good agreement with results obtained of chemically polymerized PEDOT layers doped with toluenesulfonate. By adding sorbitol to the PEDOT–PSS dispersion before spin-coating, layers with a higher conductivity were obtained. A detailed study was made of the optical response of these layers in comparison to the PEDOT–PSS prepared from dispersions without sorbitol. The optical anisotropy is important to consider when using PEDOT–PSS in optoelectronic devices, such as polymer light-emitting diodes and photovoltaic devices.