InP基HEMT器件中二维电子气浓度及分布与沟道层厚度关系的理论分析

利用数值计算的方法研究了InP基高电子迁移率晶体管(HEMT)中沟道厚度对沟道中二维电子气(2DEG)性质的影响，并对产生这种影响的原因进行了深入探讨.计算结果表明，当沟道层厚度从10nm增加到40nm时，沟道中2DEG的密度几乎没有变化，但激发态和基态上的电子密度之比(R)先增加后减小.当沟道层厚度在20—25nm之间时，R达到最大.此结果可作为优化器件结构设计的依据. 关键词： HEMT 异质结 二维电子气 自洽计算     

Ⅲ族氮化物异质结构二维电子气研究进展

本文总结了近年来Ⅲ族氮化物半导体异质结构二维电子气的研究进展。从Ⅲ族氮化物材料晶格结构和特有的极化性质出发,重点讨论了AlGaN/GaN异质结构中二维电子气的性质,总结分析了异质结构中Al组分、势垒层厚度、应变弛豫度、掺杂等对二维电子气浓度和迁移率的影响,同时还涉及AlGaN/GaN/AlGaN,AlGaN/AlN/GaN和AlGaN/InGaN/GaN等异质结构二维电子气性质。     

Ⅲ族氮化物异质结构二维电子气研究进展

本文总结了近年来Ⅲ族氮化物半导体异质结构二维电子气的研究进展。从Ⅲ族氮化物材料晶格结构和特有的极化性质出发,重点讨论了AlGaN/GaN异质结构中二维电子气的性质,总结分析了异质结构中Al组分、势垒层厚度、应变弛豫度、掺杂等对二维电子气浓度和迁移率的影响,同时还涉及AlGaN/GaN/AlGaN,AlGaN/AlN/GaN和AlGaN/InGaN/GaN等异质结构二维电子气性质。     

一种新的磷化铟复合沟道高电子迁移率晶体管小信号物理模型

针对磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的特点，对常规单沟道HEMT的小信号物理模型进行了修正，提出了一种新的用于复合沟道HEMT的小信号物理模型，用商用器件模拟软件ISE(integrated systems engineering)对其进行了仿真验证，对比了实测和仿真的I-V特性及转移特性曲线，重点研究了在InGaAs/InP双层沟道中考虑量子效应后的电场和电流密度随着不同栅电压的变化趋势，研究结果表明，由于在沟道中存在量子效应，在栅下靠源端低电场区域，电流主要分布在InGaAs沟道 关键词： 高电子迁移率晶体管 复合沟道 物理模型 磷化铟     

AlN隔离层生长时间对AlGaN/AlN/GaN HEMT材料电学性能的影响

利用金属有机化学气相沉积（MOCVD）设备,在蓝宝石（0001）面上外延不同生长时间AlN隔离层的Al_xGa_1-xN/AlN/GaN结构的高电子迁移率的晶体管（HEMT）,研究了AlN隔离层厚度对HEMT材料电学性能的影响。研究发现采用脉冲法外延（PALE）技术生长AlN隔离层的时间为12 s（1 nm左右）时,HEMT材料的方块电阻最小,电子迁移率为1 500 cm²·V^-1·s^-1,二维电子气（2DEG）浓度为1.16×10¹³ cm^-2。AFM测试结果表明,一定厚度范围内的AlN隔离层并不会对材料的表面形貌产生重大的影响。HRXRD测试结果表明,AlGaN/AlN/GaN具有好的异质结界面。     

N极性GaN/AlGaN异质结二维电子气模拟

通过自洽求解薛定谔方程和泊松方程,较系统地研究了GaN沟道层、AlGaN背势垒层、Si掺杂和AlN插入层对N极性GaN/AlGaN异质结中二维电子气(2DEG)的影响,分析表明,GaN沟道层厚度、AlGaN背势垒层厚度及Al组分变大都能一定程度上提高二维电子气面密度,AlGaN背势垒层的厚度和Al组分变大也可提高二维电子气限阈性,且不同的Si掺杂形式对二维电子气的影响也有差异,而AlN插入层在提高器件二维电子气面密度、限阈性等方面表现都较为突出,在模拟中GaN沟道层厚度小于5nm时无法形成二维电子气,超过20nm后二维电子气面密度趋于饱和,而AlGaN背势垒厚度超过40nm后二维电子气也有饱和趋势,对均匀掺杂和delta掺杂而言AlGaN背势垒层Si掺杂浓度超过5×10~(19)cm~(-3)后2DEG面密度开始饱和,而厚度为2nmAlN插入层的引入会使2DEG面密度从无AlN插入层时的0.93×10~(13)cm~(-2)提高到1.17×10~(13)cm~(-2)。     

磷化铟复合沟道高电子迁移率晶体管击穿特性研究

用密度梯度量子模型定量研究了磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的击穿特性，考虑了复合沟道内碰撞电离以及沟道量子效应，重点研究了器件击穿电压随In_0.7Ga_0.3As沟道厚度的变化关系，提出了提高击穿电压的方法，采用商用器件模拟软件Sentaurus模拟了器件的开态击穿电压，对比了实验和模拟的结果. 研究表明：适当减小In_0.7Ga_0.3As沟道层的厚度可以在保持器件饱和电流基本不变的前提下大幅度提高开态击穿电压，这对于提高InP基HEMT的功率性能具有重要意义. 关键词： 磷化铟 高电子迁移率晶体管 密度梯度模型 击穿     

InAs量子点引入应力对调制掺杂结构中二维电子气输运特性的影响

系统研究了在调制掺杂AlGaAs/GaAs异质结中嵌入InAs量子点后对二维电子气输运特性的影响。使用分子束外延设备生长了量子点层与二维电子气沟道距离（T_ch）不同的3个样品,霍尔测试结果表明,二维电子气的电子迁移率和载流子浓度都随T_ch的减小而降低。基于几何相位分析算法对部分样品的高分辨透射电镜图像进行了处理,得到了其应变分布图。结果表明,应变主要分布在量子点的周围,并延伸到了量子点的上方。该不均匀的应力场可能是除库伦散射外影响电子迁移率降低的另一个重要因素。     

赝配InGaAs/InAlAs调制掺杂异质结构的Shubnikov-de Haas振荡

赝配InGaAs/InAlAs调制掺杂异质结构可以获得很高的电子气面密度和电子迁移率，从而可以制成具有优越高频和低噪声特性的高电子迁移率晶体管(HEMT).文中报道InGaAs/InAlAs调制掺杂异质结构低温下纵向和横向磁阻随磁场强度变化的Shubnikov-de Haas(SdH)振荡和量子Hall效应.对SdH振荡曲线作了快速傅里叶变换，获得了二维电子气的能带结构和各能带上的电子气面密度.分析比较了顶层InGaAs不同掺杂情况对SdH振荡的影响，结果发现顶层InGaAs重掺杂，会对表面态起屏蔽作用， 关键词：     

使用AlN/GaN超晶格势垒层生长高Al组分AlGaN/GaN HEMT结构

在蓝宝石衬底上生长了以AlN/GaN超晶格准AlGaN合金作为势垒的HEMT结构材料,并与传统AlGaN合金势垒样品进行了对比.在高Al组分(≥40%)情况下,超晶格势垒样品的表面形貌明显改进,电学性能特别是2DEG面电子浓度也有所改进.对超晶格势垒生长参数进行了初步优化,使得HEMT结构薄层电阻进一步降低,最后获得了251 Ω/□的薄层电阻. 关键词： AlGaN/GaN 结构 AlN/GaN超晶格 二维电子气 高电子迁移率晶体管     

低能电子显微术及其应用

低能电子显微术是新发展起来的一种显微探测技术。它的特点是利用低能（１－３０ｅＶ）电子的弹性背散射使表面实空间实时成像，具有高的横向（１５ｎｍ）和纵向（原子级）分辩率，且易与低能电子衍射及其他电子显微术相结合。近年来它已有效地应用于金属和半导体表面的形貌观测、表面相变、吸附、反应及生长过程的研究。     

On the interpretation of the electron anomalous magnetic moment

Guided by a Compton-sized model, we demonstrate that: (a) the magnetic self-energy of the electron, as estimated initially by Rasetti and Fermi, can be directly related to both the sign and the magnitude of the electron anomalous magnetic moment; and (b) the classical expression for the magnetic self-energy of the electron exhibits the same characteristic logarithmic divergence that occurs in QED. This electron model quantitatively reproduces the spin, magnetic moment, and gyromagnetic ratio of the electron, correct to first order in = e² /c. It also relates the quantum-mechanical spin projection angle to the vanishing of the electric quadrupole moment, and it is capable of reproducing point-like scattering behavior.     

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

A theory for the two-stream free-electron laser(TSFEL) with a helical wiggler and an axial guide magnetic field is developed.In the analysis,the effects of self-fields are taken into account.An analysis of the two-stream steady-state electron trajectories is given by solving the equation of motion.Numerical calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of self-fields.The stability of the trajectories is studied numerically.     

Relaxation between electrons and surface phonons of a homogeneously photoexcited metal film

The energy relaxation between the hot degenerate electrons of a homogeneously photoexcited metal film and the surface phonons (phonon wave vectors in two dimensions) is considered under Debye approximation. The state of electrons and phonons is described by equilibrium Fermi and Bose functions with different temperatures. Two cases for electron scattering by the metal surface, namely specular and diffuse scattering, are considered.     

Investigation of the effect of electron cyclotron heating on runaway generation in the KSTAR tokamak

Wave enhanced runaway generation is expected to play an important role in the conversion of plasma current into runaway current during major disruptions. The fast electrons created by electron cyclotron heating (ECH) were used to study this issue in KSTAR. It is found that the fast electrons driven by ECH can enhance runaway production in the flat top phase with high loop voltage. The runaway current in disruptions was not enhanced by the ECH produced fast electron population due to the strong magnetic fluctuations which inhibited the generation of runaway electrons. It is found that a complete loss of existing REs during thermal quench has occurred in KSTAR limiter configuration discharges.     

Near threshold photodetachment cross section of negative atomic oxygen ions

A 40-target state close-coupling calculation for the photodetachment cross section of negative atomic oxygen near threshold is carried out with core－valence electron correlation by using the R-matrix method. It was shown that after considering the excitations of two electrons from the 2s shell, the electron affinity of O^- (2s^22p^5{}^2P°) agrees with the experimental result much better than that just considering the excitations of electrons only from the 2p shell as well as only one electron from the 2s shell. Total cross section as well as the main contribution of the ionization channels to the partial cross section are illustrated to show the structure near threshold clearly.     

北京自由电子激光器电子束截面监测系统

报告了北京自由电子激光器(BFEL)从30MeV直线加速器出口到摇摆磁铁出口束流输运段的束流截面监测系统。该系统由四台遥控气动可伸缩荧光屏探头、光学放大系统、闭路电视摄象系统及视频图象处理系统组成。利用该系统进行模拟实验,其系统空间分辨率约100μm,达到BFEL总体要求。利用该系统可以测量摇摆磁铁入口处及内部电子束和准直激光的截面、位置和畸变,进行束流准直、聚焦和发射度测量。     

Holes drilling in gold and silver decahedral nanoparticles by the convergent beam electron diffraction electron beam

The 200?kV focused electron beam in the convergent beam electron diffraction patterns mode in a transmission electron microscope (TEM) with field emission gun is able to drill holes in gold and silver decahedral nanoparticles. However, although they are done under the same circumstances, the holes are shapeless in the silver and faceted in gold nanoparticles. In addition to this, the holes are closed during their high-resolution TEM observation in both materials. To comment their differences, displacement energy considerations are taken into account as function of the sputtering energy in order to modify the displacement cross-section of the processes.     

Commissioning of electron cooling in CSRe

The 400 MeV/u 12C6＋ ion beam was successfully cooled by the intensive electron beam near 1 A in CSRe.The momentum cooling time was estimated near 15 s.The cooling force was measured in the cases of difierent electron beam profiles,and the difierent angles between the ion beam and electron beam.The lifetime of the ion beam in CSRe was over 80 h.The dispersion in the cooling section was confirmed as positive close to zero.The beam sizes before cooling and after cooling were measured by the moving screen.The beam diameter after cooling was about 1 mm.The bunch length was measured with the help of the signals from the beam position monitor.The difiusion was studied in the absence of the electron beam.