First-principles study on transport properties of zigzag graphene nanoribbon with different spin-configurations

The current-voltage(I-V) characteristics and the transmission spectra of zigzag graphene nanoribbon with different spin-configurations are investigated by using first-principles calculations.It is shown that the I-V curves and transmission spectra strongly depend on the spin-configurations of the two sides of the ribbon.For the spin-parallel configuration structure,the curve is linear under lower bias voltage;for the spin-antiparallel configuration structure,there is a strong spin-polarization-dependent transmission which implies that the ribbon can be used as a spin filter;while for other spin-configuration structures,the curve has the characteristics of a semiconductor. It is found that there is a large magneto-resistance(MR) when the bias voltage is small.The impurity in the central scattering region significantly influences the spin-dependent current and the spin filter efficiency,which may lead the large MR to disappear.     

A simplified optical millimeter-wave generation scheme based on frequency-quadrupling

This paper analyzes and demonstrates a simplified frequency quadrupling configuration for optical millimeter-wave(mm-wave)generation,in which the electrical phase shifter and optical filter are omitted.Theoretical analysis is given to reach the optimum operating conditions including direct current(DC)bias voltage,optical transmission point of the dual-parallel Mach-Zehnder modulator(MZM)bias voltage,optical transmission point of the dual-parallel Mach-Zehnder modulator(DP-MZM),amplitude of the radio frequency(RF)driving signal and the impact of the extinction ratio(EF)on the optical sideband suppression ratio(OSSR)and radio frequency spurious suppression ratio(RFSSR).Experiments prove an OSSR of 15 dB and an RFSSR of 26 dB for the new frequency quadrupling scheme at 6 GHz,8 GHz and 10 GHz of RF driving signal without any electrical phase shifter or optical filter.This system exhibits the advantage of low wavelength dependence and large frequency tunable range.     

共振声子THz QCL有源区结构设计

利用Airy函数代换与传输矩阵方法精确计算了有外加偏压下电子在共振声子太赫兹量子级联激光器有源区单个周期内的透射系数与波函数,得到了不同偏压下的电子波函数分布以及准束缚态能级位置与外加偏压的关系曲线.在仿真计算的基础上设计了一种共振声子太赫兹量子级联激光器的有源区结构.计算结果表明,对于设计的结构,当单个周期两端的外加...     

Large magnetoresistance at high bias voltage in double-layer organic spin valves

We report studies of magnetoresistance (MR) in double-layer organic spin valves (DOSV) using tris (8-hydroxyquinolinato) aluminum (Alq₃) spacers. The device exhibits three distinct resistance levels depending on the relative magnetizations of the ferromagnetic electrodes. We observed a much weaker bias voltage dependence of MR in the device compared to that in the conventional organic spin valve (OSV). The MR magnitude reduces by the factor of two at 0.7 V bias voltage in the DOSV compared to 0.02 V in the conventional OSV. Remarkably, the MR magnitude reaches 0.3% at 6 V bias in the DOSVs, the largest MR response ever reported in OSVs at this bias. Our finding may have a significant impact on achieving high efficient bipolar OSVs strictly performed at high voltages.     

The design of bipolar spin filtering junction in zigzag silicene nanoribbons

We performed first-principles simulation on the electronic structure of zigzag silicene nanoribbons (ZSiNRs), and found that semi-hydrogenation can break the extended π-bonding network of silicene, leaving the electrons in the unsaturated Si atoms localized and unpaired, and ferromagnetic semiconducting behavior can be obtained. While the fully hydrogenated ZSiNRs are found to be energetically degenerate and show wide band-gap semiconductor feature. Then, we designed and investigated the spin-dependent electron transport of a heterostructure, consisting of semi-hydrogenation ZSiNRs and ZSiNRs. The results show a perfect dual spin filtering effect at the parallel and antiparallel spin configuration with large bias range. The spin dependent electron transmission spectrum, band structure, transmission pathway, and the molecularly projected self-consistent Hamiltonian state are employed to investigate the physical origin of the spin-polarized effect.     

Electric characteristics of contact junctions between NbTimultifilamentary wires

Anomalous current-voltage characteristics have been found for a mechanical contact junction between NbTi superconducting multifilamentary wires. The pressure contact junctions between superconductors were created by either parallel-conductor contact or crossed-conductor contact. The junctions are superconductive over a limited current range. The current-voltage characteristics show switching phenomena, that are both large and very fast, at transitions between zero voltage and resistive states. The switching time is about 2 μs. A zero-voltage current of about 60 A was obtained for a 75-mm-long junction at zero applied magnetic field. The current-voltage curve of the junction shows hysteresis that varies with the contact junction's structure. It has been confirmed that mechanical pressure contact junctions can be used as persistent switches without heaters. Additionally, contact junctions may provide uniform current distribution for multistrand cables     

Utilization of the Antiferromagnetic IrMn Electrode in Spin Thermoelectric Devices and Their Beneficial Hybrid for Thermopiles

The thermoelectric effect in various magnetic systems, in which electric voltage is generated by a spin current, has attracted much interest owing to its potential applications in energy harvesting, but its power generation capability has to be improved further for actual applications. In this study, the first instance of the formation of a spin thermopile via a simplified and straightforward method which utilizes two distinct characteristics of antiferromagnetic IrMn is reported: the inverse spin Hall effect and the exchange bias. The former allows the IrMn efficiently to convert the thermally induced spin current into a measurable voltage, and the latter can be used to control the spin direction of adjacent ferromagnetic materials. It is observed that a thermoelectric signal is successfully amplified in spin thermopiles with exchange‐biased IrMn/CoFeB structures, where an alternating magnetic alignment is formed using the IrMn thickness dependence of the exchange bias. The scalable signal on a number of thermopiles allowing a large‐area application paves the way toward the development of practical spin thermoelectric devices. A detailed model analysis is also provided for a quantitative understanding of the thermoelectric voltages, which consist of the spin Seebeck and anomalous Nernst contributions.     

Modulation of the magnetic properties in zigzag-edge graphene nanoribbons by connection sites

Based on the first-principles method, the magnetic properties for zigzag–edge graphene nanoribbon (ZGNR) junctions are investigated. The results show the system had the ferromagnetic or antiferromagnetic ground state depending on the connection sites between ZGNR electrodes and the central ZGNR. The junction displays a metallic behavior when the central ZGNR is connected at the middle site of electrodes with a ferromagnetic state, but shows obvious spin semiconductor feature when the connection site is shifted to the edge of the ZGNR. For the antiferromagnetic states, all models show a semiconductor behavior, which originates from the spin-degenerate edge states. While for the antiparallel spin configuration, the spin density of the central ribbon is affected by connection sites, and it shows weaker little by little with the central ribbon moving from bottom to the middle site, which is different obviously from ferromagnetic or antiferromagnetic state. When one edge state of the central ZGNR is broken, bipolar spin semiconductor features can be obtained with different band gaps at suitable connection sites.     

A transistor-only low-pass filter with adjustable bias and smallphase shift at high frequencies

A third-order, low-pass, transistor-only filter with a small phase shift at high frequency and an adjustable cutoff frequency is presented. This low-pass filter overcomes the structure limit of the filter previously reported and achieves the same frequency response. It has an adjustable bias voltage which makes it possible to change its cutoff frequency     

元素V掺杂对ZnO压敏效应的影响机理研究

研究了掺杂不同V_2O_5对ZnO陶瓷压敏特性的影响.实验表明,ZnO压敏电压随V元素掺杂量增加而随之升高,非线性系数随元素V掺杂量增加而先增大后减小,漏电流先减小后增大.分析认为,V元素掺杂对ZnO压敏材料电性能的影响不仅与电子的能级有关,与其自旋特性也紧密相关.ZnO陶瓷中掺杂的V元素在晶界偏析,其V元素都会产生局域磁矩,会对与其取向不同的自旋电子产生强的散射,这样可增大ZnO压敏陶瓷电阻率,使晶界产生非线性特性.     

A survey of CW and pulsed Gunn oscillators by computer simulation

A computer simulation survey has been carried out on X-band CW and pulsed Gunn oscillators with a variety of contact conditions. It is shown that devices with a large cathode doping notch will have a nearly constant bias voltage-frequency product for optimum RF power generation. Such a relationship is not clear for devices with a smaller notch that is large enough to cause optimum injection of dipolar space charge. For both types of device there is an optimum ratio of transit frequency and cavity controlled frequency for optimum RF power generation. Several other detailed features of operation that cannot be explained by instantaneous-domain-formation models are dealt with, including the frequency dependence of the device conductance and capacity under conditions of optimum efficiency, and the bias current-voltage characteristics.     

On the transmission channels and current-voltage characteristics of a double-barrier nanostructure driven by dc electric and electromagnetic fields of arbitrary strength

A theory of the transmission channels and current-voltage characteristics of a double-barrier resonant tunneling structure driven by dc electric and high-frequency electromagnetic fields of arbitrary strength is proposed based on an obtained exact solution to the complete one-dimensional Schrödinger equation. It is shown for the first time that an increase in the electromagnetic-field strength leads (as a result of the formation of nonresonant transmission channels in the nanostructure) to a change in its current-voltage characteristic from a single-humped to double-humped curve not only in the vicinities of the electron-resonance energies but also in the energy ranges corresponding to the superpositions of pairs of field satellite states.     

Steady-state characteristics of three terminal inversion-controlled switches

The direct current-voltage (I–V) characteristics of three terminal inversion controlled switches are described. These devices are layered sequences of metal/conducting “insulator”/semiconductor junction with electrical terminals at the metal and both sides of the junction. If a bias is applied between the metal and the far side of the junction, in the sense which tends to deplete the surface and forward bias the junction, the device shows bistable impedance states similar to the current-voltage characteristics of a silicon-controlled rectifier. The intermediate terminal which contacts the semiconductor region between the insulator and the junction, can be used, in proper circuit and biasing arrangements, to switch the device both into and out of its low impedance state without varying the voltage supplied to the outer terminals of the device and a series-connected resistor. The I–V characteristics of these three terminal devices support the inversion-controlled conduction model of device behavior which permits high conductivity of the device only when inversion of the semi-conductor surface occurs. The high and low impedance states and the pulses required to induce transistions between states are contained entirely within the “active” bias configuration for these devices, which is defined by analogy with the active bias region of conventional bipolar transistors.     

自旋场效应晶体管的电学特性研究(英文)

用非平衡格林函数方法研究一种自旋场效应晶体管的电子输运特性。结果表明,不考虑自旋散射的作用,当漏极电压比较小时该器件能达到很高的磁阻比率。对该器件在考虑自旋散射和不考虑自旋散射下的输出电流进行对比,发现在铁磁平行(反平行)的条件下,考虑自旋散射时的输出电流要比不考虑自旋散射时的输出电流小(大)。研究结果揭示了该器件的物理机制,为该器件的优化设计提供了理论指导。     

InGaAs探测器片上集成滤光膜的微结构与性能

为了适应未来红外焦平面探测器系统小型化、集成化和高精度的发展要求,采用了热蒸发方法分别在InP衬底和InGaAs探测器上实现了中心波长为1.38μm滤光膜的片上集成。利用偏光显微镜、原子力显微镜(AFM)和扫描电子显微镜(SEM)以及红外傅里叶光谱(FTIR)等实验手段研究了滤光膜的表面界面形貌和光学性能,结果显示,滤光膜为法布里-珀罗三谐振腔结构,与膜系设计一致;滤光膜中心波长为1.38μm,透射率在60%左右。对集成滤光膜InGaAs器件的电学和光学性能测试分析表明,滤光膜制备工艺对器件的电流电压特性和噪声基本没有影响;而集成滤光膜器件的响应要优于滤光膜分离器件的性能。     

Single-electron effect in PtSi/porous Si Schottky junctions

PtSi/porous Si schottky junctions exhibit a breakdown type current-voltage (I-V) curve in reverse bias mode. Below breakdown their current density is much less than regular PtSi/Si junctions. The breakdown voltage decreases with application of infrared radiation for both n and p-type junctions. N-type junctions are sensitive to IR wavelengths of up to 7 /spl mu/m even at room temperature. The small reverse bias current, the change of breakdown voltage with radiation, and IR sensitivity at room temperature can all be explained by single-electron effect. Numerical results show that representative porous schottky junctions exhibit depletion capacitances in 10/sup -19/ f range which is enough to observe single-electron effect at room temperature. Single-electron effect and avalanche multiplication can explain existing experimental data.     

新型BST薄膜可调带阻滤波器

提出了一种基于共面传输线结构的新型带阻滤波器,利用该结构在沉积有钛酸锶钡(BST—0.5)薄膜的氧化镁基片上设计并制作了一个可调带阻滤波器。测试结果表明,在30V的外加偏压下,带阻滤波器的传输特性曲线向高频方向整体移动了190MHz,其形状基本保持不变。     

N-shaped negative differential resistance in a transistor structurewith a resistive gate

Voltage-controlled negative differential resistance (NDR) characteristics in a N-AlGaAs/p⁺-GaAs/n-GaAs transistor structure are proposed and demonstrated. The gate, made using self-aligned p-type diffusion, is placed in the n-GaAs collector layer instead of the p⁺-GaAs base layer, resulting in a so-called resistive gate. For a fixed gate voltage, the device current is modulated by the applied anode voltage. Under appropriate gate voltage with respect to the anode, the device shows good voltage-controllable NDR characteristics, including large peak-to-valley current ratios (PTV's) and a voltage extension in the N-shaped curve which is equivalent to the common-emitter breakdown voltage in a transistor. A numerical model based on the transistor model for the carrier transport in this device, taking account of the influence of the applied anode voltage on the gate, is proposed. The experimental results show large room temperature PTV's (e.g., 140 at a gate bias of 1.5 V) and large voltage extension in N-shaped curves (about 9 V). Reasonable agreement between theoretical and experimental results is observed     

The electrical properties of ion-implanted amorphous siliconprogrammable element in the unprogrammed state

An amorphous silicon layer, confined between metal and single-crystalline silicon, is created by the implantation of ions at high dose into silicon wafers followed by deposition of a metal film. The initial resistance of this structure is very high and drops several orders of magnitude after an external bias that is higher than a specific threshold voltage is applied. The current-voltage characteristics of the device at its initial off state are studied as a function of: (1) doping type and concentration; (2) amorphization ion energy, dose, and type; and (3) alloying conditions. Current measurements are reported as a function of temperature for fixed-bias conditions. The current-voltage characteristics of most of the data are functionally consistent with a Poole-Frenkel trap-to-trap field-induced charge-conduction model. However, there are some deviations from the Poole-Frenkel model that are probably due to the influence of the amorphous-layer boundaries with the metal and the substrate     

Log-domain all pass filter based on integrators

A new all-pass (AP) Log-domain filter is presented. The circuit is based on integrator loop and the current sources. The filter circuit has a very simple structure since it uses only bipolar junction transistors (BJT’s) and a grounded capacitor. The configuration offers large dynamic range at low power supply and higher frequency operation. The filter has a large bandwidth due to its inherent current-mode (CM) nature and Log-domain properties. Phase angle can be electronically tuned through the bias current. The circuit can be implemented in integrated form. PSPICE simulations are given to confirm the theoretical analysis.