Ferromagnetism in diluted Pb1 ? x ? y Ge x Cr y Te magnetic semiconductors

Magnetic properties of Pb_{1 − x − y} Ge _x Cr _y Te alloys (x = 0.02–0.20, y = 0.01–0.08) were studied. It was detected that the magnetic susceptibility of alloys consists of two contributions: the paramagnetic Curie-Weiss part (the temperature region is T < 50 K) caused, probably, by the Cr³⁺ ion paramagnetism, and the high-temperature ferromagnetic part (T < 300 K). The dependences of the concentration of magnetic centers on the composition of the matrix were obtained from the paramagnetic and ferromagnetic contributions. It was shown that a decrease in the concentration of paramagnetic centers can be, at least qualitatively, explained by the transformation of the electronic structure as the germanium concentration increases. A phenomenological model was suggested, which explains the behavior of magnetic properties as the chromium content increases, and possible mechanisms of ferromagnetic ordering in studied alloys are discussed. Original Russian Text ? E.P. Skipetrov, M.G. Mikheev, F.A. Pakpour, L.A. Skipetrova, N.A. Pichugin, E.I. Slyn’ko, V.E. Slyn’ko, 2009, published in Fizika i Tekhnika Poluprovodnikov, 2009, Vol. 43, No. 3, pp. 316–323.     

N×N optical switch based on cascaded microring resonators

An N×N optical switch based on cascaded microring resonators on chip is proposed. As an example, the 4×4 optical switch is further investigated. It is successfully demonstrated that its insertion loss is relatively low as 2.2 dB, the crosstalk is negligible, and the extinction ratio (ER) is as large as 130 dB. Thermal tuning is employed to make the microrings be in resonance or not, which leads to a response time of several hundred microseconds. Alternatively, doping the desired waveguide regions with p-type or n-type dopants is able to achieve a better response time of several nanoseconds. The proposed design is easily integrated to a large scale with less microring resonators, which ensures the compact size and the low power consumption.     

Surface and Interface Properties of Metal-Organic Chemical Vapor Deposition Grown a -Plane Mg x Zn1– x O (0?≤ x ≤?0.3) Films

The a-plane Mg _x Zn_1−x O (0 ≤ x ≤ 0.3) films were grown on r-plane () sapphire substrates using metal-organic chemical vapor deposition (MOCVD). Growth was done at temperatures from 450°C to 500°C, with a typical growth rate of ∼500 nm/h. Field emission scanning electron microscopy (FESEM) images show that the films are smooth and dense. X-ray diffraction (XRD) scans confirm good crystallinity of the films. The interface of Mg _x Zn_1−x O films with r-sapphire was found to be semicoherent as characterized by high-resolution transmission electron microscopy (HRTEM). The Mg _x Zn_1−x O surfaces were characterized using scanning tunneling microscopy (STM) in ultrahigh vacuum (UHV). Low-energy electron diffraction (LEED) shows well-ordered and single-crystalline surfaces. The films have a characteristic wavelike surface morphology with needle-shaped domains running predominantly along the crystallographic c-direction. Photoluminescence (PL) measurements show a strong near-band-edge emission without observable deep level emission, indicating a low defect concentration. In-plane optical anisotropic transmission was observed by polarized transmission measurements.     

I–V characteristic of p-n structures based on a continuous solid solutions (Si2)1 ? xx(CdS)x

The I–V characteristics of the p-Si-n-(Si₂) _{1 − x} (CdS) _x (0 ≤ x ≤ 0.01) structures are investigated at various temperatures. It is found that the I–V characteristic of such structures has a sublinear portion of the current growth with voltage V ≈ V ₀exp(JaW). The experimental results can be explained on the basis of the theory of the injection depletion effect. It is shown that the mobility of the minority carrier (hole) decreases with an increasing temperature. Original Russian Text ? A.S. Saidov, A.Yu. Leyderman, Sh.N. Usmonov, K.T. Kholikov, 2009, published in Fizika i Tekhnika Poluprovodnikov, 2009, Vol. 43, No. 4, pp. 436–438.     

Continuous analytic I–V model for GS DG MOSFETs including hot-carrier degradation effects

We have studied the influence of hot-carrier degradation effects on the drain current of a gate-stack double-gate (GS DG) MOSFET device. Our analysis is carried out by using an accurate continuous current-voltage (I-V) model, derived based on both Poisson's and continuity equations without the need of charge-sheet approximation. The developed model offers the possibility to describe the entire range of different regions (subthreshold, linear and saturation) through a unique continuous expression. Therefore, the proposed approach can bring considerable enhancement at the level of multi-gate compact modeling including hot-carrier degradation effects.     

Properties and structure of (As2Se3)1 ? z (SnSe2) z ? x (Tl2Se) x and (As2Se3)1 ? z (SnSe) z ? x (Tl2Se) x glasses

Tin is stabilized in the bivalent and tetravalent states in the structure of (As₂Se₃)_{1 − z} (SnSe₂) _{z − x} (Tl₂Se) _x and (As₂Se₃)_{1 − z} (SnSe) _{z − x} (Tl₂Se) _x glasses. The presence of bivalent tin in the structural network of a glass does not give rise to extrinsic conductivity. Dependences of density, microhardness, and the glass-transition temperature on the composition of the glasses are interpreted using a model according to which the structure of the glasses is composed of structural units that correspond to As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. Original Russian Text ? G.A. Bordovsky, A.V. Marchenko, E I. Terukov, P.P. Seregin, T.V. Likhodeeva, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 11, pp. 1353–1356.     

Composition and parameters of domains resulting from spinodal decomposition of quaternary alloys in epitaxial GaInP/Ga x In1 ? x As y P1 ? y /GaInP/GaAs(001) heterostructures

Structural and optical properties of two- and three-layer epitaxial heterostructures containing GaInP/Ga _x In_{1 − x} As _y P_{1 − y} quaternary alloy layers were studied. Domain formation due to spinodal decomposition of the quaternary alloy was detected in three-layer heterostructures. As a result, an additional long-wavelength band appears in the photoluminescence spectra, and an additional doublet of the line appears in X-ray diffraction patterns of the (006) line. The domain composition was determined on the basis of Vegard’s law and the Kouphal equation. Original Russian Text ? E.P. Domashevskaya, N.N. Gordienko, N.A. Rumyantseva, B.L. Agapov, P.V. Seredin, L.A. Bityutskaya, I.N. Arsent’ev, L.S. Vavilova, I.S. Tarasov, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 9, pp. 1086–1093.     

Effect of Atmosphere on n -Type Hg1– x Cd x Te Surface after Different Wet Etching Treatments: An Electrical and Structural Study

The impact on surface recombination velocity (SRV) and minority carrier lifetime of three wet etchants are examined here. The etchants are 60DI +  10HBr + 1H₂O₂ (by volume), 1% bromine–methanol, and 2% bromine–lactic acid. After initial etching, the HgCdTe surfaces were exposed in specific time steps to the atmosphere. At each step in the process, the effect of each etchant and of exposure to atmosphere was determined by photoconductive decay (PCD) measurements as well as by x-ray photoelectron spectroscopy (XPS). The PCD results showed that the 60DI + 10HBr + 1H₂O₂ etchant, after exposure to atmosphere, led to a relatively small change in SRV compared to the changes that occurred for the two bromine-based etchants. In addition, XPS measurements showed that there were no neutral tellurium inclusions in the case of 60DI + 10HBr + 1H₂O₂ and that TeO₂ formed strictly out of tellurium bonded to HgCdTe. Moreover, TeO₂ formed at a much slower rate on surfaces etched with HBr compared with those etched with the bromine-based etchants. A model is proposed in terms of band alignment at HgCdTe-Te⁰ and HgCdTe-TeO₂ interfaces to explain the different surface recombination mechanisms that are due to different etchants and to atmospheric exposure.     

一种新型的Q值与L值可相互独立调谐的低噪声有源电感

提出了一种新型的品质因数(Q)与电感值(L)可相互独立调谐的低噪声有源电感。该电感主要由双回转器、调制支路、可调反馈电阻、跨导增强支路和噪声抑制单元构成。其中,双回转器是由第一回转回路和第二回转回路并联而成,获得了大电感值;调制支路不仅能减小等效并联电阻,提高Q值,还可实现对电感值的大范围调谐;可调反馈电阻不仅能增大Q值,还能实现对Q值的独立调节,也能补偿因调谐L值引起的Q值的变化;跨导增强支路和噪声抑制单元分别降低了第一回转回路和第二回转回路的噪声,从而降低有源电感的整体噪声。最终,通过上述电路模块的紧密配合及所配置的三个外部调控端电压的深度协作,实现了Q值与L值可相互独立调谐以及低噪声的优异特性。仿真结果表明,该有源电感在3.8 GHz频率下,Q峰值可从674调节到5 083,调谐率为153.2%,而L值变化率仅为0.3%;在3.65 GHz下,L值可由6.1 nH调节到15.5 nH,调谐率高达87%,而与之对应的Q值的变化率仅为3.7%;在2~6 GHz范围内,有源电感的最大和最小输入噪声分别为5.29 nV/Hz和1.75 nV/Hz。     

Capacitance–conductance–current–voltage characteristics of atomic layer deposited Au/Ti/Al2O3/n-GaAs MIS structures

We have studied the admittance and current–voltage characteristics of the Au/Ti/Al₂O₃/n-GaAs structure. The Al₂O₃ layer of about 5 nm was formed on the n-GaAs by atomic layer deposition. The barrier height (BH) and ideality factor values of 1.18 eV and 2.45 were obtained from the forward-bias ln I vs V plot at 300 K. The BH value of 1.18 eV is larger than the values reported for conventional Ti/n-GaAs or Au/Ti/n-GaAs diodes. The barrier modification is very important in metal semiconductor devices. The use of an increased barrier diode as the gate can provide an adequate barrier height for FET operation while the decreased barrier diodes also show promise as small signal zero-bias rectifiers and microwave. The experimental capacitance and conductance characteristics were corrected by taking into account the device series resistance R_s. It has been seen that the non-correction characteristics cause a serious error in the extraction of the interfacial properties. Furthermore, the device behaved more capacitive at the reverse bias voltage range rather than the forward bias voltage range because the phase angle in the reverse bias has remained unchanged as 90° independent of the measurement frequency.     

Nanoplasmonic Enhanced ZnO/Si Heterojunction Metal–Semiconductor–Metal Photodetectors

This paper presents a nanoplasmonic enhanced ZnO/Si heterojunction metal–semiconductor–metal (MSM) photodetector (PD). By depositing different thicknesses of Ag thin film and annealing at a moderate temperature, well-defined silver (Ag) nanoparticles (NPs) with different diameters, densities, and size distributions were produced on the surface of ZnO/Si MSM photodetector devices. By tuning the characteristics of these NPs, a higher-performance ZnO/Si MSM photodetector has been realized. The photocurrent of the detector with NPs was increased by 160% to 680%, depending on the applied voltage. The spectral photocurrent enhancement by a factor of 7 to 18 was broadband from 350 nm to 850 nm.     

Optical properties of quaternary GaNxAsyP1 ? x ? y semiconductor alloys

The optical properties of quaternary GaN _x As _y P_{1 − x − y} semiconductor alloys grown on a GaP (100) substrate surface are studied by photoluminescence spectroscopy in the temperature range 20–300 K and by photoluminescence excitation spectroscopy at liquid-nitrogen temperature. The measurements are carried out for the GaN _x As _y P_{1 − x − y} alloys, for which the nitrogen and arsenic molar fractions x and y range from 0.006 to 0.012 and from 0.00 to 0.18, respectively. A comparative analysis of the data is conducted, and the dependences of the energy position of the photoluminescence peak on the composition of the quaternary alloy are established. From the studies of photoluminescence in the range 20–300 K, it is found that the temperature dependence of the position of the photoluminescence peak substantially differs from the behavior described by Varshni’s expression.     

Study on low-Ag content Sn–Ag–Zn/Cu solder joints

The eutectic Sn–Ag–Cu solder is the most popular lead free solder. But reliability and cost issues limit its application. On the other hand, Sn–Ag–Zn system has many advantages comparing with Sn–Ag–Cu. In this paper, interfaces of Sn–xAg–1Zn/Cu and Sn–2Ag–xZn/Cu (x = 1, 2, 3), Sn–2Ag–2.5Zn/Cu and Sn–1.5Ag–2Zn/Cu solders joints were studied to understand effects of Ag and Zn contents. Results show that shearing strength of as-reflowed Sn–2Ag–2Zn/Cu and Sn–1.5Ag–2Zn/Cu joints is higher than other joints. Because of the strong Cu–Sn reaction and the formation of Ag₃Sn, the Sn–Ag–Zn series solder joints are not suitable for use above 150 °C temperature. After 250 °C soldering for 4 h, while the Zn content increased from 1 wt% to 2 wt%, the interfacial IMC of Sn–Ag–Zn/Cu altered from Cu₆Sn₅ to Cu₅Zn₈. The Cu₅Zn₈ interface has higher shearing strength than Cu₆Sn₅ interface. Relationships among microstructure, strength and aging condition are discussed.     

Optical properties of quantum-confined heterostructures based on GaPxNyAs1 ? x ? y alloys

The results of calculations of the band gap in GaP _x N _y As_{1 − x − y} alloys and the estimated parameter of hybridization of the conduction band in GaP and the localized level of nitrogen are reported. The optical properties of quantum-confined heterostructures based on GaP _x N _y As_{1 − x − y} alloys synthesized on the GaP (100) substrate surface are studied by photoluminescence measurements in the temperature range of 15–300 K. The heterostructures consist of GaP_0.814N_0.006As_0.18 quantum wells separated by GaP barrier layers. The well width and the barrier thickness are 5 nm. Heterostructures with different numbers of periods are considered. On optical excitation of the structures, an intense photoluminescence line is observed in the spectral range 620–650 nm. The photoluminescence spectra of the GaP_0.814N_0.006As_0.18/GaP quantum wells are profoundly broadened because of the inhomogeneity of the quaternary alloy in composition. It is established that the increase in the number of quantum well layers from 10 to 25 does not results in degradation of the photoluminescence properties of the heterostructures. The results of the study support the view that it is possible to produce efficient optoelectronic devices on the basis of GaP _x N _y As_{1 − x − y} alloys.     

Space–Time/Space–Frequency/Space–Time–Frequency Block Coded MIMO-OFDM System with Equalizers in Quasi Static Mobile Radio Channels Using Higher Tap Order

In 4G broadband wireless communications, multiple transmit and receive antennas are used to form multiple input multiple output (MIMO) channels to increase the capacity (by a factor of the minimum number of transmit and receive antennas) and data rate. In this paper, the combination of MIMO technology and orthogonal frequency division multiplexing (OFDM) systems is analyzed for wideband transmission which mitigates the intersymbol interference and hence enhances system capacity. In MIMO-OFDM systems, the coding is done over space, time, and frequency domains to provide reliable and robust transmission in harsh wireless environment. Also, the performance of space time frequency (STF) coded MIMO-OFDM is analyzed with space time and space frequency coding as special cases. The maximum achievable diversity of STF coded MIMO-OFDM is analyzed and bit error rate performance improvement is verified by simulation results. Simulations are carried out in harsh wireless environment, whose effect is mitigated by using higher tap order channels. The complexity is resolved by employing sphere decoder at the receiver.     

Synthesis,Structure and Electrical Properties of(SnO2)x(In2O3)1?x(x=0.5–1) Nanocomposites

The experimental results of synthesizing thin films (<1 μm thick) of (SnO₂) _x (In₂O₃)_{1 − x} (x = 0.5–1 wt) nanocomposites fabricated by high-frequency magnetron sputtering of metal-oxide targets in a controlled Ar + O₂ atmosphere are presented. The films, deposited on hot substrates (400°C), are studied by the X-ray diffraction analysis, atomic-force microscopy, and optical and electrical methods. The effect of the synthesis conditions and film composition on the size of crystalline grains, band gap, and the concentration and mobility of free charge carriers was determined. It is shown that films of the composition (SnO₂) _x (In₂O₃)_{1 − x} with x = 0.9 are the most promising for applications in gas sensorics.     

Chemical–Mechanical Polishing of CdTe and ZnxCd1?xTe Single Crystals by H2O2(HNO3)–HBr–Organic Solvent Etchant Compositions

Chemical–mechanical polishing of CdTe and Zn _x Cd_1−x Te single-crystal surfaces by bromine-evolving compositions based on aqueous solutions of H₂O₂(HNO₃)–HBr–solvent has been investigated. The dependences of the chemical–mechanical polishing rate on the dilution of the base polishing etchant for various organic components have been determined. The surface condition after such polishing has been investigated using profilometry. The polishing etchant compositions for CdTe and Zn _x Cd_1−x Te single-crystal surfaces and the chemical polishing conditions have been optimized.     

基于螺旋弹簧的引信用低g值MEMS惯性开关

微机电系统(MEMS)惯性开关在引信领域有广阔的应用前景,但可用于引信工作环境的低g值型MEMS惯性开关较少。对此,为低发射过载的弹药引信提出一种低闭合阈值的MEMS惯性开关设计方案,满足引信识别低g值冲击信号的功能需求,实现稳定接通引信电源的功能,同时具备抵抗引信工作环境中高过载的能力,提高引信可靠性。依据触发信号特征和引信工作环境提出设计要求,对惯性开关的振荡模型进行理论分析,阐明惯性开关结构尺寸对开关性能的影响规律,给出开关整体设计方案,并应用ANSYS有限元软件对设计结果进行仿真验证。仿真结果表明,所设计的惯性开关能够监测幅值为20g、脉宽为1 ms的冲击信号,开关响应时间小于1 ms,电极接触时间长于30 μs,抗过载性能达到12 000g,满足性能指标要求。     

Nonvolatile Metal–Oxide–Semiconductor Capacitors with Ru-RuOx Composite Nanodots Embedded in Atomic-Layer-Deposited Al2O3 Films

Growth of Ru-RuO _x composite nanodots (RONs) on atomic-layer-deposited Al₂O₃ films has been investigated using magnetic sputtering of a Ru target followed by postdeposition annealing. RONs with a density as high as ~2 × 10¹² cm⁻² were obtained together with good uniformity. Subsequently, metal–oxide–semiconductor capacitors with RONs embedded in Al₂O₃ films have been electrically characterized for different configurations of tunneling layers (T)/blocking layers (B), and the underlying mechanisms of charge storage are discussed. For a 6-nm T/22-nm B device, a memory window of 3.7 V is achieved for a ±7 V programing/erasing voltage for 0.1 ms, and superior charge retention of more than 80% is achieved after 10 years.