Simplified model for ballistic current–voltage characteristic in cylindrical nanowires

The ballistic regime gives the upper limit of an electron device performance. This paper proposes a fast and efficient model for calculating the current–voltage characteristic of a cylindrical nanowire within the framework of the non-equilibrium Green's function. Under certain assumptions, the calculation is simplified to a one-dimensional problem and the modes due to the radial confinement are given by an analytical equation. We further derive an analytical expression for the current–voltage characteristic at temperature approaching 0 K. The relationship between the radius of the nanowire and the electrical current is clearly shown in this expression. The effects of the radius on the current–voltage characteristic curve are also studied. Furthermore, we plot the trend of the saturation current as the radius is increased as predicted by both the numerical result and our analytical model. Our proposed model can be further used to include electron–photon interaction in the calculation of nanoscale optoelectronic devices.     

Direct tunneling at the front contact of amorphous silicon p-i-ndevices

The device physics behind hole direct tunneling currents at the front contact of a-Si:H p-i-n homojunction have been explored. In this paper, the dark I-V, the light I-V, and the QE characteristics of this structure with and without hole direct hole tunneling currents are evaluated and compared. The three differential equation systems of the Poisson's equation, the continuity equation for free electrons, and the continuity equation for free holes have been solved with allowances for direct tunneling currents. Hole direct tunneling currents at the front contact of a-Si:H p-i-n homojunctions give rise to a significant increase in the dark current level at high forward voltages and to an increase in the open-circuit voltage of the light I-V characteristic when the front electron barrier is low. The hole thermionic emission current and the hole direct tunneling current have been carefully compared to the front contact. Hole tunneling currents introduce important modifications to the carrier transport physics not only to the front contact but also in the bulk of the a-Si:H p-i-n homojunction     

掺杂单壁碳纳米管的电流特性

依据Boltzmann方程及单壁碳纳米管(SWNTs)能量色散关系,对单个掺杂SWNTs(金属型和半导体型)所加偏压、掺杂浓度及管口直径影响输运电流的性质进行数值计算.分析表明,掺杂SWNs中的电流随偏压变化呈现跃变结构;管口直径、掺杂后Fermi能级附近的态密度以及各通道输运电子的能力直接决定电流的特性,如电流强度、跃变间隔及跃变幅度;同时电流的特性也与温度有关.     

Self-consistent calculation of tunneling current in w-GaN/AlGaN(0001) two-barrier heterostructures

The specific features of the tunneling current in wurtzite GaN/AlGaN(0001) two-barrier structures are studied by solving the Schrödinger equation and the Poisson equation simultaneously, with regard to spontaneous and piezoelectric polarizations. It is shown that the internal fields manifest themselves in the asymmetry of the tunneling current via the value of the electronic charge in the quantum well. This charge is larger when the internal and external fields in the well compensate each other, resulting in smaller shifts of potential and resonance levels in the active region with voltage, in the higher resistance of the structure, and in the linear current-voltage dependence within a wide range of voltages. When the internal and external fields are the same, the current exhibits a sharp negative-differential-conductivity structure, with the peak-to-valley ratio equal to about four. The structure is similar to one of the branches of the current-voltage characteristic of the GaAs/AlGaAs(001) two-barrier structure, suggesting that nitrides are promising materials for resonance-tunneling devices.     

Noise studies in internal field emission diodes

The breakdown process of a zener diode in reverse direction is governed by internal field emission at low voltage and by impact ionization at higher voltage. For breakdown voltage in the transition range between 3 and 6 V, both physical processes appear in combination. Measuring the I–V characteristic and the noise current fluctuations spectral density it is possible to show the zener current multiplication by the multiplication effect described by Tager. In addition the I–V characteristic can be written empirically I = Vⁿ.     

压电振动能量收集电路的设计与实验研究

压电材料可将机械振动能转换为电能,但其产生的电能较小且具有交流特性,有必要建立储能电路将压电振动产生的电能储存起来并输出稳定的直流电。根据压电构造方程,建立压电振动能量收集系统的耦合场数学模型,对输出电压和最大输出功率进行数值模拟。设计与制作了一种以电容为储能介质的储能电路,通过电压比较器和电压调节器来保证稳定的直流输出。实验结果表明该储能电路能提供稳定的2.24V的直流输出电压,储能效率最高可达66.3%,并分析其能耗及误差产生的原因。     

Coupled coplanar waveguide with anisotropic substrate

Frequency-dependent hybrid-mode values of the characteristic impedances as well as the effective dielectric constants are presented for the coupled coplanar waveguide with uniaxially anisotropic substrate for the first time. The characteristic impedances are calculated by using two different definitions, that is, the voltage/current and power/voltage criteria, and both of them converge to the quasistatic values in lower-frequency ranges.     

Voltage divisions between nonlinear resistances with positive temperature coefficients

The voltage distribution across nominally identical positive-temperature-coefficient thermistors connected in series is distinctly nonuniform. For a nonlinear resistance with this voltage/current characteristic, such a distribution corresponds to stable operation.     

Hyperabrupt junctions in Au-Si Schottky diodes by ion implantation

The application of ion implantation to the fabrication of Au-Si Schottky diodes with highly nonlinear capacitance/voltage characteristics is described. The capacitance/voltage characteristic and the derived impurity profile are given for a typical diode. The forward current/voltage characteristics are described, and an estimate of Au-Si barrier height is made.     

Theory of switching phenomena in metal/semi-insulator/n-p silicon devices

The theory of switching is presented for a structure consisting of a p⁺-n junction and a metal electrode separated from the N-section of the p⁺-n junction by a semi-insulating (leaky) layer.

When a negative bias is applied to the electrode, the section of the n-layer under the electrode goes into deep depletion. In this mode, the current through the device is limited by generation in the deeply depleted region. This is the high-impedance or OFF state of the device.

At a sufficiently high voltage, the switching voltage, V_s, the p⁺-n junction is turned on by either avalanching in the n-layer or by the deep-depletion region extending through to the p⁺-n region (punch-through). When the junction turns on, the n-section goes from deep-depletion towards inversion. Thus, the voltage across the device decreaseswith a concomitant increase in the current through the device. This is the switching mode. The switching voltage may be tailored by varying the doping and/or width of the n-section.

Following switching, the device comes into the steady-state when the current through the insulating layer is equal to the current flowing across the p⁺-n junction. The I-V characteristic of this highly conducting (ON state) mode is determined principally by the I-V characteristic of the semi-insulating film. By suitable choice of material this portion of the characteristic can approach zero dynamic impedance, i.e. a near-vertical characteristic, characterized by a low holding voltage. Capacitance and switching characteristics of the device are also discussed.     

微波功率AlGaN/GaN HFET的二维能带和异质结构设计

在综述微波功率AlGaN/GaN HFET技术发展趋势基础上,提出了二维异质结能带优化设计的新课题.从自洽求解薛定谔方程和泊松方程出发研究了利用异质界面上的极化电荷来剪裁异质结能带.用极化电荷设计近矩形前势垒能增大高能热电子的隧穿势垒宽度,抑制电流崩塌.背势垒中的极化电荷强化了沟道阱的量子限制,减弱了沟道中的强场峰,能提高击穿电压和抑制电流崩塌.薄势垒层中的极化电荷强化了沟道阱的结构,降低势垒高度后能产生高密度的电子气.优化设计二维异质结构能抑制沟道中的强场峰和电流崩塌,提高击穿电压和大漏压下的输出功率.     

宽温区MOSFET反型层载流子迁移率的模型和测定方法

首先介绍了宽温区 (2 7～ 30 0°C) MOSFET的阈值电压、泄漏电流和漏源电流的特点以及载流子迁移率的高温模型 ;进而给出了室温下 MOSFET反型层载流子迁移率的测定方法 ,最后提出了利用线性区 I- V特性方程测定宽温区 MOSFET反型层载流子迁移率的方法 ,并给出了测试结果     

Observation of negative differential resistance inAl0.2Ga0.8As/Al0.4Ga0.6As/GaAs double barrier resonant tunnelling structure

Negative differential resistance has been observed in the current/voltage characteristics of a double barrier resonant tunnelling structure with Al_0.2Ga_0.8As emitters, Al_0.4 Ga_0.6As barriers and GaAs quantum well for the first time. The NDR becomes clear at low temperatures below 77 K, and the current/voltage characteristic is asymmetric. Results demonstrate that high-quality abrupt GaAs-Al_xGa_1-xAs-Al_yGa_1-yAs heterojunctions can be of use in resonant tunnelling structures     

Breakdowns in Si JFET's

A two-dimensional numerical analysis to clarify the breakdown phenomena in Si n-type JFET is described. In this analysis, the continuity equation for minority carriers is introduced to consider the effect of avalanche multiplication. The heat conduction equation is also taken into account to include the thermal effect on the breakdown voltage. The results obtained are: 1) the mechanisms of excess gate current (EGC), current-mode second breakdown (CSB), and thermal-mode second breakdown (TSB). 2) The effects of how channel impurity concentration Nc, drain current ID, and applied drain voltage VDGaffect EGC, CSB, and TSB are also reported.     

A model for the drain voltage and gate voltage dependence of the current fluctuation spectrum of unsaturated JFET's

From the standpoint of the number fluctuation model of the generation-recombination noise and 1/fnoise, a model for the drain and gate voltage dependences of the current fluctuation spectrum of an unsaturated JFET ot MESFET can be established. The derived formula can explain the various experimental results, especially the square-law dependence of the drain voltage throughout almost all of the unsaturated region, and the increasing characteristic of the current fluctuation spectrum with increasing reverse gate voltage. It can also explain the dependence of drain current fluctuation on the device geometric parameters, and finally, it points out that Hooge's expression for the spectral intensity of the current fluctuation can be valid only in the linear region of the device.     

Digital control of three-phase PWM inverter with LC filter

A digital control algorithm for the three-phase sinusoidal voltage inverter with an output LC filter has been developed. To take the transient of the LC filter during the discretization time into consideration, a fourth-order matrix state equation of the current and the voltage on the d-q frame is discretized. Precise discrete equations for the inverter are introduced. Using these equations, a deadbeat controller consisting of a d-g current minor loop and a d-q voltage major loop, with precise decoupling of the d-q components, was developed. The voltage major loop controller assures the sinusoidal output voltage and stabilizes the system. A deadbeat controller is used because both the current minor loop and the voltage major loop can used one sampling response. The validity of these techniques is confirmed by simulation studies. This method is expected to be useful for direct digital control of large-capacity sinusoidal voltage inverters using low-switching-frequency devices     

平行板波导CTS 天线的设计与分析

采用传输线理论的方法分析设计了平行板波导CTS 天线。建立平行板波导天线的等效电路模型,利用传输线方 程计算天线上的电压分布、电流分布以及辐射阻抗,进而分析远场的辐射特性。最后用Ansoft HFSS 软件仿真验证了该 方法的正确性。     

InGaAs/InAlAs RTD I-V特性的量子力学隧穿模拟

本文通过数值求解含时Schrodinger方程得到了InGaAs/InAlAs共振隧穿二极管 (RTD)的电流 偏压曲线 ,我们发现数值模拟的结果与实验符合得很好。     

Integration of resonant-tunneling transistors and hot-electrontransistors

We have integrated a tunneling hot-electron transfer amplifier (THETA) and a novel resonant-tunneling hot-electron transfer amplifier (RTHETA) within a single epitaxial growth. At room temperature, the THETA exhibits a common-emitter current gain of greater than six and a voltage swing of 800 mV when measured in an inverter configuration. The RTHETA exhibits similar common-emitter current gain and a four-state voltage transfer characteristic with an output voltage swing of 1 V. In contrast to the resonant-tunneling hot-electron transistor (RHET), the RTHETA exhibits current gain both before and after the resonant peak voltage. From on-wafer S-parameter measurements, the current-gain cut-off frequency (f_T) and the maximum frequency of oscillation f_max) for both transistors are approximately 20 GHz and 9 GHz, respectively     

TFT characteristics with distributed traps in the semiconductor

The development and solutions for the current-voltage drain characteristics of a TFT with exponentially distributed trapping centers in the semiconductor are presented. The development involves rederiving the current-voltage characteristic equation considering the dependence of carrier mobility upon trapping centers. The solutions provide insight regarding the drain current characteristics. The drain current with traps is found to be more dependent on the gate voltage than the trapless case and this dependence is a function of the steepness in the trap concentration. It is observed that a significant change in the shape of the drain characteristics near the knee region is caused by traps. Also the magnitude of the drain current is very dependent on the concentration and steepness of traps. Finally, the general expression for drain current dependence on temperature is found to be in good agreement with CdS experimental data.