6H-SiC电子输运的Monte Carlo模拟

从实际测量和单粒子Monte Carlo模拟两个方面研究了6H-SiC的电子输运规律,在模拟中考 虑了6H-SiC主要的散射机理,模拟的结果体现了6H-SiC具有良好的高温和高场特性以及迁移 率的各向异性,其横向迁移率和纵向迁移率相差近5倍.模拟结果和实验数据的对比说明了对 6H-SiC输运特性的模拟是正确的. 关键词： 6H-SiC Monte Carlo模拟 迁移率 散射机理     

光学极化度测量仪的研制及弱光Stokes参数的测量

极化电子束在物理学及其相关领域应用十分广泛,要深入研究这些应用必须对电子束的极化度进行精确测量,通常测量电子束极化度的仪器有两种：Mott极化度测量仪和光学极化度测量仪。因光学极化度测量仪与Mott极化度测量仪相比有许多优点而倍受关注。文章首先阐述了光学极化度测量仪的理论基础和实验原理,然后介绍了所研制光学极化度测量仪的设计方案和物理结构,最后给出了用该光学极化度测量仪测量弱光的Stokes参数的结果。     

晶格匹配InAlN/GaN和InAlN/AlN/GaN材料二维电子气输运特性研究

文章研究了InAlN/GaN和引入AlN界面插入层形成的InAlN/AlN/GaN材料的输运性质. 样品均在蓝宝石上以脉冲金属有机物化学气相淀积法生长,霍尔迁移率变温特性具有典型的二维电子气(2DEG)特征. 综合各种散射机理包括声学形变势散射、压电散射、极性光学声子散射、位错散射、合金无序散射和界面粗糙度散射,理论分析了温度对迁移率的影响,发现室温下两种材料中2DEG支配性的散射机理都是极性光学波散射和界面粗糙度散射;AlN插入层对InAlN/GaN材料迁移率的改善作用一方面是免除2DEG的合金无序散射,另外还显著改善异质界面,抑制了界面粗糙度散射. 考虑到2DEG密度也是影响其迁移率的重要因素,结合实验数据给出了晶格匹配InAlN/GaN和InAlN/AlN/GaN材料的2DEG迁移率随电子密度变化的理论上限. 关键词： InAlN/GaN 二维电子气 迁移率     

Anisotropic electron mobility in fluorene-PPV and fluorene-MEH-PPV

Polyfluorene copolymers are attractive semiconductor materials, in particular for applications in the organic electronics field. They are versatile to be chemically modified and allow a tuning of the emission to cover the entire visible spectrum. A better understanding of the fundamental aspects of the nature of electronic structure and charge transport properties contribute to the improvement of optoelectronic properties of polymeric materials. Here, we provide a structure–property relationship for models of fluorene-PPV and fluorene-MEH-PPV copolymers, using molecular quantum mechanics modelling. The anisotropy is discussed revisiting Mulliken's transition moment theory. Accordingly, our results show that electron mobility occurs preferentially intrachain for both copolymers. Moreover, the interchain electron mobility has the most propensity to occur via π-stacking interactions.     

不同量子阱宽度的InP基In0.53GaAs/In0.52AlAs高电子迁移率晶体管材料二维电子气的性能研究

用Shubnikov-de Haas(SdH)振荡效应，研究了在1.4 K下不同量子阱宽度(10—35 nm)的InP基高电子迁移率晶体管材料的二维电子气特性.通过对纵向电阻SdH振荡的快速傅里叶变换分析，得到不同阱宽时量子阱中二维电子气各子带电子浓度和量子迁移率.研究发现，在Si掺杂浓度一定时，阱宽的改变对于量子阱中总的载流子浓度改变不大，但是随着阱宽的增加，阱中的电子从占据一个子带到占据两个子带，且第二子带上的载流子迁移率远大于第一子带迁移率.当量子阱宽度为20 nm时，处在第二子能级上的电子数与处在 关键词： 量子阱宽 二维电子气 Shubnikov-de Haas振荡 高电子迁移率晶体管     

Kinetic parameters,collision rates,energy exchanges and transport coefficients of non-thermal electrons in premixed flames at sub-breakdown electric field strengths

The effects of an electric field on the collision rates, energy exchanges and transport properties of electrons in premixed flames are investigated via solutions to the Boltzmann kinetic equation. The case of high electric field strength, which results in high-energy, non-thermal electrons, is analysed in detail at sub-breakdown conditions. The rates of inelastic collisions and the energy exchange between electrons and neutrals in the reaction zone of the flame are characterised quantitatively. The analysis includes attachment, ionisation, impact dissociation, and vibrational and electronic excitation processes. Our results suggest that Townsend breakdown occurs for E/N = 140 Td. Vibrational excitation is the dominant process up to breakdown, despite important rates of electronic excitation of CO, CO₂ and N₂ as well as impact dissociation of O₂ being apparent from 50 Td onwards. Ohmic heating in the reaction zone is found to be negligible (less than 2% of peak heat release rate) up to breakdown field strengths for realistic electron densities equal to 10¹⁰ cm^?3. The observed trends are largely independent of equivalence ratio. In the non-thermal regime, electron transport coefficients are insensitive to mixture composition and approximately constant across the flame, but are highly dependent on the electric field strength. In the thermal limit, kinetic parameters and transport coefficients vary substantially across the flame due to the spatially inhomogeneous concentration of water vapour. A practical approach for identifying the plasma regime (thermal versus non-thermal) in studies of electric field effects on flames is proposed.     

Interface modulated electron mobility enhancement in core-shell nanowires

The transport properties of core-shell nanowires (CSNWs) under interface modulation and confinement are investigated based on the atomic-bond-relaxation (ABR) correlation mechanism and Fermi's golden rule. An analytical expression for the relationship between carrier mobility and interface mismatch strain is derived and the influence of size, shell thickness and alloyed layer on effective mass, band structures, and deformation potential constant are studied. It is found that interface modulation can not only reduce the lattice mismatch to optimize the band alignment, but also participate in the carrier transport for enhancing mobility. Moreover, the underlying mechanism regarding the interface shape dependence of transport properties in CSNWs is clarified. The great enhancement of electron mobility suggests that the interface modulation may become a potential pathway to improving the performance of nanoelectronic devices.     

AlGaAs/InGaAs/GaAs赝配高电子迁移晶体管的kink效应研究

利用二维器件模拟软件MEDICI对AlGaAs/InGaAs/GaAs赝配高电子迁移晶体管器(PHEMT)件进行了仿真，研究了PHEMT器件的掺杂浓度与电子浓度分布，PHEMT器件内部的电流走向及传输特性，重点研究了不同温度和不同势垒层浓度情况下PHEMT器件的kink效应.研究结果表明：kink效应主要与处于高层深能级中的陷阱俘获/反俘获过程有关，而不是只与碰撞电离有关. 关键词： 高电子迁移率晶体管 kink效应 二维电子气     

Mobility of carbon ions and C+(4P) in helium computed from quantum-mechanical transport cross sections

On the light of a previous work and its recommendations by Matoba et al. [J. Phys. B 41, 145205 (2008)], this paper proposes to look at the mobility of ground and metastable-excited states of C⁺ ions moving into a helium buffer gas. The calculations, based on the three-temperature theory for solving the Boltzmann kinetic equation, are accomplished with quantum-mechanical transport cross sections at the low temperatures 4.3 and 77?K. The obtained mobility results are contrasted with the available theoretical data and experimental measurements, which show acceptable agreements.     

AlGaN/GaN高电子迁移率晶体管温度传感器特性

本文制作了基于无栅AlGaN/GaN高电子迁移率晶体管结构的温度传感器,并对其温度相关的电学特性进行了表征.实验测试了器件从50℃到400℃的变温电流-电压特性,研究了器件灵敏度随着器件沟道长宽比的变化,并研究了在300—500℃高温的空气和氮气中经过1 h恒温加热后器件的电学特性变化.理论与实验研究结果表明,随着器件沟道长宽比的增大,器件的灵敏度会随之上升;在固定电流0.01 A下,器件电压随温度变化的平均灵敏度为44.5 mV/℃.同时,稳定性实验显示器件具有较好的高温保持稳定性.     

一维线性非共轭石墨烯基(CH2)n分子链的电子输运

一维非共轭烷烃链虽不具富电子或少电子特征,但常存在于单分子器件或多肽、蛋白质等生物分子中,对电子传输产生重要影响.为理解这类物质的电子输运特征,本研究设计了一维线性非共轭(CH2)n分子结模型,并利用密度泛函理论结合非平衡态格林函数的方法,对(CH2)n(n=1—12)线性分子链与两个石墨烯电极耦合而成的分子结进行了第...     

非典型耦合下二价原子能级的精细结构

在典型耦合理论基础上,给出了在非典型耦合下计算二价原子精细结构能级的理论公式,并将理论应用到若干具体问题,结果与实验数据相符,且直观地显示出典型耦合只是非典型耦合的特例。     

Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors （HEMTs）

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 10¹⁴cm^-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 10¹⁶cm^-3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current--voltage (I--V) characteristic, but has no effect on the transconductance in the saturation area.     

ZnqCl2及其衍生物的电子光谱性质的含时密度泛函理论研究

采用从头算法(abinitio)和密度泛函理论(DFTB3LYP)方法,对二氯取代的八羟基喹啉锌(ZnqCl2)及其2种衍生物的基态结构进行优化,同时用abinitioHF单激发组态相互作用(CIS)法在6-31G(d)基组上优化其最低激发单重态几何结构,用含时密度泛函理论(TD-DFT/B3LYP)及6-31G(d)基组计算吸收和发射光谱。计算表明,该类物质电子在基态与激发态间的跃迁,主要是在配体8-羟基喹啉(q)环内的电荷转移,电子从含O的苯酚环转移至含N的吡啶环上,发射光谱的计算值与实验值基本符合。该类化合物的电子亲和能较大,都是优良的电子传输材料,改变中心金属原子对配合物光谱性质影响不大。     

电子引起的钛和锰的K壳层电离截面测量

报道了电子引起的钛,锰原子的Ｋ壳层电离截面实验值。实验中,采用了薄靶厚衬底技术,并将衬底中反射的电子对测量值的影响进行了修正。实验结果与其他文献报道的测量结果相吻合。最后,还将实验结果与Ｃａｓｎａｔｉ等人的经验公式进行了比较。     

SiC电子霍耳迁移率的计算

基于对自身能带结构的分析以及各向同性弛豫时间近似法,采用三椭球等能面、抛物线性简化,建立了适于模拟n型6H-SiC电子霍耳迁移率和霍耳散射因子的解析模型,精确描述了不同散射机制对于6H-SiC低场电子输运特性的影响.计算结果与实测值有很好的一致性.     

Measurement of Titanium and Manganese K -shell Ionization Cross Sections by Electron Impact

报道了电子引起的钛、锰原子的Ｋ壳层电离截面实验值。实验中,采用了薄靶厚衬底技术,并将衬底中反射的电子对测量值的影响进行了修正。实验结果与其他文献报道的测量结果相吻合。最后,还将实验结果与Ｃａｓｎａｔｉ等人的经验公式进行了比较。     

The integral approach to the sputtering

Summary The emission-oriented integral form of Boltzmann transport equation is applied to the sputtering phenomenon. It is shown that the central quantity in the formulation, namely the characteristic mean free path of the phenomenon, can be the low-energy transport mean free path. The same mean free path gives a measure of the mean escape depth as derived in experiments and computer simulation studies. Finally, the sputtering yields, calculated by using the same mean free path, when compared with the experimental results, show an evident improvement with respect to the Sigmund theory.     

量子点红外探测器的噪声表征

为了表征噪声对量子点红外探测器性能的影响, 本文推导了噪声的理论模型. 该模型通过考虑纳米尺度电子传输和微米尺度电子传输对激发能的共同影响, 并结合噪声增益, 实现了对噪声的估算. 得到的结果与实验的数据相比, 显示了很好的一致性, 从而验证了这个模型的正确性. 关键词： 电子传输 暗电流 增益 噪声