Two-Dimensional Static Numerical Modeling and Simulation of AlGaN/GaN HEMT

考虑AlGaN/GaN材料的自发、压电极化效应和量子效应,通过泊松方程、薛定谔方程和流体力学方程组的数值自洽求解方法,对AlGaN/GaN HEMT的二维静态模型与模拟问题进行了研究,得到了器件区域的导带图、二维电子气分布、电子温度特性、直流输出和转移特性,并对模拟结果进行了分析与讨论.     

AlGaN/GaN材料HEMT器件优化分析与I-V特性

在考虑AlGaN/GaN异质结中的压电极化和自发极化效应的基础上,自洽求解了垂直于沟道方向的薛定谔方程和泊松方程.通过模拟计算,研究了AlGaN/GaN HEMT器件掺杂层Al的组分、厚度、施主掺杂浓度以及栅偏压对二维电子气特性的影响.用准二维物理模型计算了AlGaN/GaN HEMT器件的输出特性,给出了相应的饱和电压和阈值电压,并对计算结果和AlGaN/GaN HEMT器件的结构优化进行了分析.     

AlGaN/GaN一维模型自洽求解和二维电子气特性研究

实现了一维Poisson-Schrodinger方程的自洽求解,在此基础上求出了AlGaN/GaN异质结导带结构和二维电子气分布。计算结果表明极化效应是形成高浓度电子面密度的主要因素。研究了AlGaN/GaN系统中隔离层厚度对二维电子气浓度的影响,并对计算结果进行了分析。     

AlGaN／GaN二维电子气的特性研究

应用AlGaN/GaN异质结中的压电极化和自发极化边界条件自洽求解了薛定谔方程和泊松方程,求出异质结能带和二维电子气分布。研究了势垒层组分化、势垒层宽度、沟道层掺杂和栅电压变化对二维电子气特性的影响。着重研究了栅电压对二维电子气维性的控制作用,提出了使用薄势垒和重掺杂沟道的新HFET结构。     

AlGaN/GaN界面特性研究进展

GaN是一种宽禁带半导体材料,由于具有优越的热稳定性和化学稳定性,使这种材料和与其相关的器件可以工作在高温和恶劣的环境中,并可用于大功率微波器件。本文主要介绍AlGaN/GaN有关界面特性,该特性反映了纵向纳米尺度下的能带特性;从AlGaN/GaNHEMT设计出发,给出了材料性质和结构参数对AlGaN/GaN异质结二维电子气特性影响的研究结果;讨论了AlGaN/GaN界面2DEG载流子的输运性质;分析了材料缺陷对AlGaN/GaN界面2DEG性质的影响;指出了有待研究的问题和方向。     

AlN阻挡层对AlGaN/GaNHEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.     

AlN阻挡层对AlGaN/GaN HEMT器件的影响

利用低压MOCVD技术在蓝宝石衬底上生长了AlGaN/GaN异质结和AlGaN/AlN/GaN异质结二维电子气材料,采用相同器件工艺制造出了AlGaN/GaN HEMT器件和AlGaN/AlN/GaN HEMT器件.通过对两种不同器件的比较和讨论,研究了AlN阻挡层的增加对AlGaN/GaN HEMT器件性能的影响.     

氧等离子体处理对薄势垒增强型AlGaN/GaN HEMT的影响

提出了一种利用薄势垒结构制造增强型AlGaN/GaN HEMT的方法。研究了SiN钝化对薄势垒AlGaN/GaN异质结的影响,并利用其控制沟道中的二维电子气密度。具有10nm SiN介质插入层欧姆接触在800℃下退火可以得到较好的接触性能。栅极区域中的SiN被刻蚀,以耗尽下面的二维电子气,从而使薄势垒AlGaN/GaN HEMT实现增强特性,其阈值电压为50 mV。对介质刻蚀后暴露的AlGaN表面进行氧等离子体处理,与未经处理的器件作对比,发现阈值电压提升到0.5V,栅漏电降低了一个数量级,击穿特性得到改善,但是最大饱和电流密度降低了。     

偏栅Al_xGa_(1-x)N/GaN HEMT的二维模拟与特性分析

采用泊松方程-薛定谔方程-流体力学方程组自洽求解的方法,对偏栅AlGaN/GaN HEMT器件的电学特性进行了二维模拟。通过与传统正栅器件的模拟结果对比分析,可以看出,偏栅结构除了可以提高器件的击穿电压外,还可以提高直流输出电流和跨导,对输出特性和转移特性均有一定的提高。     

AlGaN/GaN HEMT电容及充电时间的研究

通过计算AlGaN/GaN HEMT二维电子气中的电势、载流子以及调制掺杂载流子寿命,得到AlGaN/GaN HEMT电容和充电时间,研究了AlGaN掺杂层浓度和厚度对器件的时间响应分析了AlGaN/GaN HEMT器件的高频特性。结果表明,栅电容随着AlGaN掺杂层浓度和厚度的增加逐渐减小。随着AlGaN层掺杂浓度的增大,电容充电时间先减后增,当掺杂浓度达到 时,电容充电时间达到极小值,在AlGaN掺杂层厚度等于7nm时电容充电时间最短。     

5英寸半球形微通道板光电倍增管的设计与研制

简述了5英寸半球形微通道板光电倍增管(简称:5”半球形MCP-PMT)的电子光学系统设计和优化试验;整管结构设计、工艺路径设计和光电参数设计.介绍了研制过程中,为确保MCP的增益特性和增益的稳定性,针对暗发射、真空性能等所采取的技术措施和相关工艺;分析产生暗电流(Id)和Id稳定性差(跳动)的各种因素,进行多次试验验证,解决了降低Id并使之趋于稳定的关键技术,优化了相关结构,在正常工作条件下,可达到Id≤30nA.为使器件更适用于进行单光子探测,本文还提出了研制量子效率更高、时间特性更好的全球形MCP-PMT的发展方向.     

Design of active inductor-based current-controlled oscillators using gm/Id methodology

This paper presents a novel design procedure based on gm/Id methodology to achieve a trade-off between tuning range, phase noise and output swing of active-inductor-based current-controlled oscillators (CCOs). It is shown that equations for the phase noise and corner frequency of the selected CCO configuration are related to the gm/Id parameters. In accordance with the above relations, the designed CCO is simulated using 0.18 µm TSMC CMOS technology parameters. The simulation exhibits a tuning range of 432 MHz to 3.54 GHz, a phase noise in the range of −84 dBc/Hz to −104.6 dBc/Hz at 1 MHz offset from carrier and a figure of merit of 178.4 dB in 1.453 GHz.     

Evaluating electron induced degradation of triple-junction solar cell by numerical simulation

In this paper, the degradation related parameters of GaInP/GaAs/Ge triple-junction solar cell induced by electron irradiation are carried out by numerical simulation. The degradation results of short-circuit current, open-circuit voltage, maximum power have been investigated, and the degradation mechanism is analyzed. Combining the degradation results, the degradation of normalized parameters versus displacement damage dose is obtained. The results show that the degradation increases with the increase of the electron fluence and electron irradiation energy. The degradation normalized related parameters versus displacement damage dose can be characterized by a special curve that is not affected by the type of irradiated particles. By calculating the annual displacement damage dose and the on-orbit operation time of special space orbit, the degradation of normalized parameters can be obtained with the fitting curve in the simulation. The study will provide an approach to estimate the radiation damage of triple-junction solar cell induced by space particle irradiation.     

Influence of electron mobility modeling on DC I-V characteristicsof WZ-GaN MESFET

We report on the drift-diffusion based simulation of a wurtzite (WZ) GaN MESFET. The main emphasis is put on the influence of electron mobility modeling on DC current-voltage (I-V) characteristics of the WZ-GaN MESFET. Two different analytical expressions are used for the electron mobility as a function of electric field. The first model is based on a simple saturation of the steady-state drift velocity with electric field (conventional three-parameter model). The other model is more realistic since it well reproduces the drift velocity-field characteristics obtained by Monte Carlo (MC) calculations, revealing the peak drift velocity with subsequent saturation at higher electric fields. Thus, it should be implemented in the drift-diffusion model for a following device simulation. However, the MC electron transport data for WZ-GaN are influenced by the specific choice of the material and band structure parameters, resulting in a variation of drift velocity-field characteristics. In addition, it should be noted that the MC simulation also neglects crystal defects in GaN, which, for example, might lead to uncontrolled electron compensation and additional electron scattering. In the present study we show that the DC I-V characteristics of the WZ-GaN MESFET are strongly affected by the MC-like electron mobility model, in particular by the peak steady-state velocity and the shape of the velocity-field characteristics even for the same drift velocity saturation level     

Electron Beam Optics System PIC Simulation for MMW TWTs

The basic feature and design method of MMW TWTs electron optics are analyzed in this paper. With the increasing area convergence ratio of the electron gun in TWTs, the initial thermal velocity of electrons at cathode and the non-magnetic shielded effect can no longer be neglected. It brings new challenge for the design and simulation of MMW TWTs electron optics. A method of investigation the beam DC characteristics is described using particle-in-cell (PIC) simulation and incorporate electron beam optics model integrated electron gun with periodic permanent magnetic focusing system. It is valuable for achieving the goal of “first-pass design success” and the electron optics engineering design and optimization.     

Performance of 30 nm Gate Length InAlAs-InGaAs MODFETs: Comparison of Conventional and Asymmetric Coupled-Well Transport Channel Configurations

This paper presents simulation results highlighting the effects of variations in the transverse potential profile of the transport channel, on the electrical characteristics of Modulation Doped Field-Effect Transistors (MODFETs). In particular, the I-V and f_T-V_g characteristics of 30 nm gate length InAlAs-InGaAs MODFETs, having conventional quantum well channels, are in good agreement with our simulations. The simulation further predicts improvement in performance when asymmeteric coupled quantum wells are used as the electron transport channels. Energy bands, 2-D electron distributions, and various I-V characteristics are compared for conventional quantum well and asymmeteric coupled quantum well channels. Both quantum well and quantum wire configurations are enhanced by the incorporation of asymmetric coupled quantum well channel.     

X射线辐照下材料电子发射特性的模拟

稳态 X 射线管是一种重要的 X 射线辐照模拟装置,在辐照效应等研究领域有重要应用。采用蒙特卡罗模拟方法计算了 50 kV,150 kV 和 225 kV 管电压下的 X 射线能谱,并对 X 射线辐照下电子发射进行了模拟;研究了准直孔直径分别为 2 mm,4 mm 和 6 mm 条件下 X 射线的焦斑分布和电子发射弥散情况,以及不同能谱的 X 射线轰击到聚乙烯、聚酰亚胺、Si、SiO₂、Cu、Ta 和 W等样品上产生的电子发射能谱和电流强度等特性,为 X 射线辐照下材料电子发射特性的实验研究和设计提供一定的理论基础和指导。     

Analysis of sit I–V characteristics by two-dimensional simulation

The I–V characteristics of Static Induction Transistor operating in the transition region are studied using a two-dimensional simulation. This simulation takes both electron and hole continuity into account, including temperature dependence. From the result of this simulation, the transition region is physically interpreted by introducing two new concepts; effective channel width and saddle potential pinning. In the transition region, the effective channel width changes distinctively and electron concentration at the saddle point is saturated by the saddle potential pinning, resulting in the gradual change in the drain current. By extrapolating these concepts into the exponential region, the I–V characteristics are comprehensively interpreted. Furthermore, the temperature coefficient of the drain current which is inverted two times is interpreted consistently by these concepts.     

慢性白血病Id4甲基化研究

目的探讨Id4基因在慢性白血病患者中的甲基化情况。方法采用甲基化特异性聚合酶链反应（MS—PCR）,对初发9例慢淋白血病（CLL）和18例慢粒白血病（CML）患者的骨髓进行Id4基因甲基化检测,以正常骨髓作为对照。结果Id4基因在正常骨髓中呈完全性非甲基化状态,在9例CLL患者中全部检测到Id4基因甲基化,而在18例CML患者中,检测到12例Id4基因甲基化。结论慢性白血病患者骨髓Id4基因发生了不同程度的甲基化改变,CLL和CML患者的甲基化发生比例不同。     

An analytic model for HEMT's using new velocity-field dependence

An analytic model is developed for the output current-voltage characteristics and microwave-signal parameters of high electron mobility transistors (HEMT's). In this model, the GSW equation is used to approach the behavior of electron drift velocity versus electric field. The resulting I-V curves are in excellent agreement with experimental data. In order to predict the microwave performance of these devices, this model is then used to derive the small-signal parameters, transconductance, channel conductance, and gate capacitance.