Mathematical model of the direct current amplification mode in a channel of a microchannel plate

The boundary-value problem is solved for electric field in a channel of a microchannel plate for a preset value of current at the channel entrance. Analytic equations are determined for the distributions of field, potential, and current along the channel, as well as for the current gain and the current in the circuit of the source of constant voltage as a function of the input current.     

栅漏间表面外延层对4H-SiC功率MESFET击穿 特性的改善机理与结构优化

本文提出了一种带栅漏间表面p型外延层的新型MESFET结构并整合了能精确描述4H-SiC MESFET工作机理的数值模型,模型综合考虑了高场载流子饱和、雪崩碰撞离化以及电场调制等效应. 利用所建模型分析了表面外延层对器件沟道表面电场分布的改善作用,并采用突变结近似法对p型外延层参数与器件输出电流(I_ds)和击穿电压(V_B)的关系进行了研究.结果表明,通过在常规MESFET漏端处引入新的电场峰来降低栅极边缘的强电场峰并在栅漏之间的沟道表面引入p-n结内建电场进一步降低电场峰值,改善了表面电场沿电流方向的分布.通过与常规结构以及场板结构SiC MESFET的特性对比表明,本文提出的结构可以明显改善SiC MESFET的功率特性.此外,针对文中给定的器件结构,获得了优化的设计方案,选择p型外延层厚度为0.12 μupm,掺杂浓度为5× 10¹⁵ cm^-3,可使器件的V_B提高33%而保持I_ds基本不变.     

Optical modulation of the effective channel thickness in GaAs field effect transistors with a Schottky gate (MESFETs)

Using a model relating the change in drain current with modulation of the effective channel thickness upon IR illumination of GaAs field effect transistors with a Schottky gate (MESFETs), it is shown that it is possible to determine the change in channel thickness and the concentration profile for deep centers in an FET channel. Profiles are given for the distribution of deep centers in the channels of GaAs MESFETs with different noise temperatures. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 349–353, May–June, 2006.     

Improved performance of 4H-SiC metal-semiconductor field-effect transistors with step p-buffer layer

An improved 4H-SiC metal-semiconductor field-effect transistors (MESFETs) with step p-buffer layer is proposed, and the static and dynamic electrical performances are analysed in this paper. A step p-buffer layer has been applied not only to increase the channel current, but also to improve the transconductance. This is due to the fact that the variation in p-buffer layer depth leads to the decrease in parasitic series resistance resulting from the change in the active channel thickness and modulation in the electric field distribution inside the channel. Detailed numerical simulations demonstrate that the saturation drain current and the maximum theoretical output power density of the proposed structure are about 30% and 37% larger than those of the conventional structure. The cut-off frequency and the maximum oscillation frequency of the proposed MESFETs are 14.5 and 62 GHz, respectively, which are higher than that of the conventional structure. Therefore, the 4H-SiC MESFETs with step p-buffer layer have superior direct-current and radio-frequency performances compared to the similar devices based on the conventional structure.     

Injection-locking technique for heterodyne optical phase locking of a diode laser

A novel technique is demonstrated for heterodyne optical phase locking of a diode laser to a single-frequency source by injection seeding. By modulation of the drive current of the diode laser at as much as several gigahertz, FM sidebands are imposed upon the output. We demonstrate that it is possible to phase lock either sideband to an injected beam. The carrier of the diode laser output is therefore locked in phase with the injected light but with a frequency difference given by the modulation of the drive current. The phase fluctuations between the lasers are analyzed, and the variance is found to be (4.4( degrees ))(2) , corresponding to 99.4% of the diode carrier light locked to the injected beam.     

S波段大间隙速调管放大器输出腔的3维模拟

 利用3维高频软件设计了一种用于S波段大间隙速调管的膜片加载大间隙单重入输出腔,建立了带大耦合孔的输出腔3维全结构模型,采用3维PIC程序对输出腔的提取效果进行了粒子模拟。研究结果表明：膜片加载的大间隙单重入输出腔开大耦合孔后,其所有谐振频点的场分布都不再是TM ₀₁₁模式,因此,在设计此类输出腔时不能以工作频点是否谐振为优化目标。提出了大间隙输出腔设计原则,根据设计原则优化后的输出腔可稳定提取1.07 GW的平均功率,提取效率约35.7%。     

高$lt;i$gt;k$lt;/i$gt;栅介质小尺寸全耗尽绝缘体上锗p型金属氧化物半导体场效应晶体管漏源电流模型

通过求解沟道的二维泊松方程得到沟道表面势和沟道反型层电荷, 建立了高k栅介质小尺寸绝缘体上锗(GeOI) p型金属氧化物半导体场效应晶体管(PMOSFET)的漏源电流解析模型. 模型包括了速度饱和效应、迁移率调制效应和沟长调制效应, 同时考虑了栅氧化层和埋氧层与沟道界面处的界面陷阱电荷、氧化层固定电荷对漏源电流的影响. 在饱和区和非饱和区, 漏源电流模拟结果与实验数据符合得较好, 证实了模型的正确性和实用性. 利用建立的漏源电流模型模拟分析了器件主要结构和物理参数对跨导、漏导、截止频率和电压增益的影响, 对GeOI PMOSFET的设计具有一定的指导作用. 关键词： 绝缘体上锗p型金属氧化物半导体场效应晶体管 漏源电流模型 跨导 截止频率     

High-power SiC MESFET using a dual p-buffer layer for an S-band power amplifier

A silicon carbide (SiC) based metal semiconductor field effect transistor (MESFET) is fabricated by using a standard SiC MESFET structure with the application of a dual p-buffer layer and a multi-recessed gate to the process for an S-band power amplifier. The lower doped upper-buffer layer serves to maintain the channel current, while the higher doped lower-buffer layer is used to provide excellent electron confinement in the channel layer. A 20-mm gate periphery SiC MESFET biased at a drain voltage of 85 V demonstrates a pulsed wave saturated output power of 94 W, a linear gain of 11.7 dB, and a maximum power added efficiency of 24.3% at 3.4 GHz. These results are improved compared with those of the conventional single p-buffer MESFET fabricated in this work using the same process. A radio-frequency power output greater than 4.7 W/mm is achieved, showing the potential as a high-voltage operation device for high-power solid-state amplifier applications.     

Strong electric field modulation of transport in PVDF/MWCNT nanocomposite near the percolation threshold

A nanocomposite comprising of multiwalled carbon nanotubes (MWCNT) embedded in ferroelectric Poly(vinylidene fluoride) PVDF polymer matrix is examined for electric field induced transport modulation. The pulsed laser deposition (PLD) grown thin films of the nanocomposite with different MWCNT content were characterized. When used as a channel layer in a field effect transistor configuration, a strong electric field modulation of the transport was realized just below the percolation threshold. We believe that this nanocomposite non-percolating channel concept can provide several opportunities for FET devices for organic electronics.     

Linewidth of SG-DBR laser and its effect on DPSK transmission

In this paper the linewidth of widely tunable SG-DBR lasers has been investigated theoretically and experimentally. We demonstrate experimentally the importance of obtaining low linewidth operation for the application of SG-DBR laser with advanced modulation format transmission. This is achieved by choosing two sets of tuning currents for an SG-DBR laser that give the same wavelength channel and good SMSR, but different linewidths. When the laser is employed in a DPSK system only the operating point (the set of drive currents used to obtain specific output characteristics) that portrays low linewidth achieves error free transmission. This work shows that although calibration of tunable lasers is normally based on achieving sufficient SMSR and output power, it will be important to consider the linewidth parameter as these lasers begin to be used in more spectrally efficient WDM systems employing advanced modulation formats. The simulation results illustrate that the operating points which achieve narrow linewidth are correlated with those that exhibit low threshold current. This finding may be used for calibration of SG-DBR lasers to achieve minimum linewidth at each operating wavelength.     

基于PSpice的半导体激光高频调制系统设计

为了实现高频率的调制激光输出,设计了一种驱动系统由信号放大、电流调制、过流保护和具有慢启动功能的直流偏置电路高度集成的半导体激光高频调制系统。此系统采用了结构简单的直接调制方式,运用线性调频的高频信号去控制半导体激光器发射激光的强度,从而实现高频调制。在运用OrCAD/PSpice对高频调制驱动系统进行模拟仿真的基础上,最终研制出的半导体激光高频调制系统实现了频率为40.02 MHz、直流偏置为493.326 mA、正弦波调制电流峰峰值为850 mA的高频调制输出,调制激光平均功率为300 mW。     

Amplifying discharge instabilities in the emission channel of a plasma electron emitter

We consider the amplification of oscillations of the plasma parameters in the emission channel of an electron source with a plasma emitter. The relationship between the modulation level of the emission current and the oscillations of the concentration and potential of the emitting plasma is determined. The amplification of the discharge instabilities is seen to be a function of the ratio of the size of the boundary layer in the channel to the channel radius. The amplification factor is calculated as a function of the emission current and the accelerating voltage. The change in the plasma parameters at the emission boundary for a plasma shift in the channel is taken into account.Tomsk Academy of Control Systems and Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–76, Feburary, 1994.     

Theory of positive corona in SF6 due to a voltageimpulse

A theoretical examination is made of the mechanism of corona formation for a positive point-plane gap in SF₆ at 100 kPa. The impulse voltage applied has a rise time of 15 ns and peak value of 200 kV. Seed electrons are released 1 ns after the start of the voltage rise. For a 0.5-cm diameter positive sphere located 6.5 cm from a negative plane, the calculated circuit current initially consists of subnanosecond corona onset pulses, and then the current steadily rises to a maximum, as the voltage reaches a maximum, followed by a rapid fall in current. During the current rise a streamer moves out into the gap along a 100-μm channel, with the electric field in the streamer trail E>E*, where E* is the critical field where ionization equals attachment. The light output during the discharge is predicted to be a maximum at the anode with only a minor pulse of light at the streamer head, making it hard to detect. After the current maximum, recombination rapidly reduces the numbers of positive ions, negative ions, and electrons, but the net charge density remains constant and thus so does the electric field. The electric field is E~E* in the streamer trail, but has a sharp maximum, E≫E* at the head of the streamer trail. The origin of mid-gap precursors, observed when the streamer channel reilluminates after some 100 ns, is attributed to this field maximum in the remnant electric field. The evolution of positive ions, negative ions, and electrons is described by one-dimensional continuity equations, with the space-charge electric fields determined by the disk method. The effects of ionization, attachment, recombination, electron diffusion, and photoionization are all included. New numerical methods allow resolution of the streamer head and the anode fall region to be obtained with a 1-μm mesh, while following the streamer propagation for ~2 cm     

电子束收集极对大间隙速调管输出腔效率的影响

 利用高频电磁软件对带电子束收集极的S波段大间隙输出腔进行了高频特性分析,采用3维PIC程序模拟了电子束收集极对大间隙速调管输出效率的影响。研究结果表明：收集极的存在会改变输出腔的本征谐振频率和电子束路径上的特性阻抗等高频特性,但收集极可以短路间隙附近的径向电场,减小电子束的空间电荷压力,同时对群聚电子进行再加速,从而提高大间隙速调管的输出效率;在束电压700 kV,直流电流6 kA时,优化后的带收集极的大间隙输出腔可稳定提取大于1.68 GW的微波功率,提取效率约40.1%,比无收集极时提高约5%。     

Development of a Two-Dimensional Bar-Code Detection System Using Multi Laser Diodes with Time-Sharing Light Emission Operation

A new high-speed two-dimensional bar-code detection system using multi laser diodes with time-sharing light emission operation has been developed. A bias current allowing the laser diode to improve the light output rise time was optimized to slightly below the threshold of the diode, so that channel cross-talk among three-line bar-code signals caused by the bias light can be kept small and a high-speed pulse modulation operation can be achieved. The prototype system for a three-line bar code with spatially overlapping laser-diode heads has achieved an effective scanning speed two and nine tenths times that of conventional scanners. It is estimated that the number of time-sharing light emission laser diodes can be increased to at least four when the current photodetection amplifier with a bandwidth of 6.4 MHz is used. This number can be improved to six by using photodetection amplifiers with double the bandwidth of the present ones.     

Shrinking limits of silicon MOSFETs: numerical study of 10 nm scale devices

We have performed numerical modeling of dual-gate ballistic n-MOSFETs with channel length of the order of 10 nm, including the effects of quantum tunneling along the channel and through the gate oxide. Our analysis includes a self-consistent solution of the full (two-dimensional) electrostatic problem, with account of electric field penetration into the heavily doped electrodes. The results show that transistors with channel length as small as 8 nm can exhibit either a transconductance up to 4000 mS mm ^− 1or gate modulation of current by more than 8 orders of magnitude, depending on the gate oxide thickness. These characteristics make the devices satisfactory for logic and memory applications, respectively, although their gate threshold voltage is rather sensitive to nanometer-scale variations in the channel length.     

电光调制对外部光注入垂直腔表面发射激光器的偏振转换及其非线性动力学行为的操控性研究

针对主和副垂直腔表面发射激光器构成的外部注入激光器系统的偏振转换及其非线性动力学行为, 利用周期性极化铌酸锂晶体中准相位匹配线性电光调制, 本文提出了一种新的操控方案并且探索了其控制规律. 研究结果发现, 受到平行光注入或正交光注入的副激光器输出偏振度随外加电场成周期性振荡变化, 其振荡波峰轨迹包络曲线为正弦曲线, 而振荡波谷轨迹包络曲线为余弦曲线; 选取一定的主激光器偏置电流, 通过对来自主激光器的光进行电光调制, 受到两种方式注入的副激光器可以输出任意偏振模, 并且其非线性动力行为经历不同的演变. 另外, 副激光器的偏振度仅依赖于外加电场, 与副激光器的偏置电流无关.     

X波段相对论大功率速调管放大器的高频结构模拟研究

采用MAGIC 2.5D模拟软件,建立了X波段11.424GHz相对论大功率速调管放大器的高频结构模型。该模型由5个简单药盒型谐振腔组成,包括1个输入腔、3个中间腔和1个输出腔。研究了该模型的高频特性,初步设计漂移管及各谐振腔结构参数,再结合热腔模拟,研究了输入腔的吸收匹配问题,依据各腔体对基波电流逐级调制情况,优化配合各腔体的间隙等结构参数,从而获得电子束的最佳调制状态,最后通过调节外加均匀磁场大小获得百MW功率输出,结果表明:在加速电压520kV、束电流460A、外加磁场0.4T的条件下,当注入信号功率为1kW时,基波电流调制深度达162%,最终输出功率105MW,效率43.5%,增益50dB。     

水声通信中后验符号概率密度分布及概率成形容量分析

考虑到实际水声信道复杂特性对水声通信的影响,对系统的通信容量进行计算分析,并研究了一种适用于水声信道的容量评估算法.文中通过对不同条件下的均衡器输出的后验符号特性进行统计分析,提出了一种基于后验高斯分布的符号方差分段转移函数模型.在此基础上,采用Maxwell-Boltzmann分布来改变均衡器输出符号的成形分布,即引...     

Pulse properties of an electronic emitter with a plasma limited by a boundary ionic layer

Results of the investigation of the pulse control of an electronic emitter with a plasma limited to a boundary ionic layer are presented. The control of the emitter current was realized by modulating the plasma area by means of varying the extent of the ionic layer in the emission channel. It is shown that the time for the formation of the front and trailing edge of the current pulse depends on the time for establishing a stationary distribution of ions in the boundary layer. For an electronic emitter, based on a reflective discharge with a field cathode, this time is of about 10^–8 sec. The experimental setup is described, and the results obtained in the pulse control of an emitter current through modulation of the emission area are presented.Institute of Automated Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 28–33, May, 1992.