二维Bloch电子在电场和磁场作用下输运的突变现象及非线性理论分析

磁场作用下二维Bloch电子，在非极低温情况下，电子Bloch能带的磁致裂隙对电子运动的影响将不重要，这时在准经典近似下分析霍耳漂移速率．通过数值求解，得到不同磁感应强度下波矢空间的稳定唯一周期解或稳定焦点不动解，并通过大量数值计算找出了参数空间中周期解与不动解的参数划分；进一步给出了霍耳漂移速率随磁感应强度变化过程中的突变现象．数值解的性质与Poincaré-Bendixson定理相一致 关键词：     

太赫兹场和倾斜磁场对超晶格电子动力学特性调控规律研究

微带超晶格在磁场和太赫兹场调控下表现出丰富而复杂的动力学行为, 研究微带电子在外场作用下的输运性质对于太赫兹器件设计与研制具有重要意义. 本文采用准经典的运动方程描述了超晶格微带电子在沿超晶格生长方向(z方向)的THz场和相对于z轴倾斜的磁场共同作用下的非线性动力学特性. 研究表明, 在太赫兹场和倾斜磁场共同作用下, 超晶格微带电子随时间的演化表现出周期和混沌等新奇的运动状态. 采用庞加莱分支图详细研究了微带电子在磁场和太赫兹场调控下的运动规律, 给出了电子运行于周期和混沌运动状态的参数区间. 在电场和磁场作用下, 微带电子将产生布洛赫振荡和回旋振荡, 形成复杂的协同耦合振荡. 太赫兹场与这些协同振荡模式之间的相互作用是导致电子表现出周期态、混沌态以及倍周期分叉等现象的主要原因.     

3C-SiC体特性的Monte Carlo模型

采用Monte Carlo方法模拟了3C-SiC材料中电子的静态输运特性．在细致分析材料的能带结构和主要散射机构，建立了适于统计模拟的物理模型的基础上，采用自洽的SPMC方法进行模拟，得出了电子迁移率随温度、电子平均漂移速度随电场的变化规律，及电子的能量和动量弛豫时间随温度和电场的变化规律．所得结果与实验符合较好． 关键词：     

C-BN电子输运特性的Monte Carlo模拟

根据C-BN的能带结构和极性半导体的具体特征,确立了C-BN的主要散射机构,建立了适于Monte Carlo模拟的物理模型,采用单电子Monte Carlo法对C-BN体材的稳态电子输运特性进行了模拟.得出了电子的平均漂移速度、迁移率和电子能量随电场的变化规律,及电子的能量、动量弛豫时间随电场的变化规律. 关键词：     

6H-SiC高场输运特性的多粒子蒙特卡罗研究

采用非抛物性能带模型,对6H-SiC高场电子输运特性进行了多粒子蒙特卡罗(Ensemble Monte Carlo)研究.研究表明：温度为296 K时,电子横向漂移速度在电场为2.0×104 V/cm处偏离线性区,5.0×105 V/cm处达到饱和.由EMC方法得到的电子横向饱和漂移速度为1.95×107 cm/s,纵向为6.0×106 cm/s,各向异性较为显著.当电场小于1.0×106 V/cm时,碰撞电离效应对高场电子漂移速度影响较小.另一方面,高场下电子平均能量的各向异性非常明显.电场大于2.0×105 V/cm时,极化光学声子散射对电子横向能量驰豫时间影响较大.当电场一定时,c轴方向的电子碰撞电离率随着温度的上升而增大.对非稳态高场输运特性的分析表明：阶跃电场强度为1.0×106 V/cm时,电子横向瞬态速度峰值接近3.0×107 cm/s,反应时间仅为百分之几皮秒量级.     

金属/掺杂聚合物/金属结构中载流子的注入与输运

基于紧束缚的Su-Schrieffer-Heeger模型,利用非绝热的动力学方法,研究了金属/聚合物/金属三明治结构中载流子注入与输运的动力学过程,其中,聚合物中含有一个掺杂离子. 电子波函数随时间的演化满足含时Schrdinger方程,晶格运动满足经典的牛顿运动方程. 研究发现,掺杂离子对注入到聚合物中的载流子的作用类似一个控制阀门,阀门的状态与电场的强度和偏压的大小密切相关. 关键词： 载流子输运 波包 非绝热动力学     

金属/掺杂聚合物/金属结构中载流子的注入与输运

基于紧束缚的Su-Schrieffer-Heeger模型，利用非绝热的动力学方法，研究了金属/聚合物/金属三明治结构中载流子注入与输运的动力学过程，其中，聚合物中含有一个掺杂离子. 电子波函数随时间的演化满足含时Schrdinger方程，晶格运动满足经典的牛顿运动方程. 研究发现，掺杂离子对注入到聚合物中的载流子的作用类似一个控制阀门，阀门的状态与电场的强度和偏压的大小密切相关.     

纤锌矿相GaN空穴输运特性的Monte Carlo模拟研究

用全带多粒子Monte Carlo方法模拟纤锌矿相(Wurtzite)GaN空穴输运特性的结果. 用经验赝势法计算得到能带结构数据. 模拟包含了声学声子散射，光学声子散射，极性光学声子散射，压电散射，电离杂质散射及带间散射等散射机理. 计算得到了空穴沿3个主要对称方向上的空穴平均漂移速度和平均能量与电场强度的关系曲线，室温下漂移速度呈现饱和特性. 在所研究的电场范围内，最大平均漂移速度约为6×10⁶cm s^-1，最大空穴平均能量约为0.12eV, 这些值均比电子的相应参数低很多. 还给出了空穴的扩散迁移率与杂质浓度关系的模拟结果. 关键词： 蒙特卡罗 氮化镓 输运特性 能带结构     

自旋玻璃系统的量子输运方程

通过引入电子的弹性散射和非弹性散射的自能和相应的物理格林函数，将磁场中的Ｍａｈａｎ－Ｈ?ｎｓｃｈ量子输运方程推广到自旋玻璃系统中，在电子的近弹性散射近似下，求解了ｓ－ｄ交换相互作用导致的自旋玻璃态霍耳电导；获得了电阻率与自旋玻璃Ｅｄｗａｒｄｓ－Ａｎｄｅｒｓｏｎ（ＥＡ）序参数和局域磁化率之间的关系；讨论了自旋玻璃热电势和特征温度。 关键词：     

有限引导磁场下相对论环形电子注色散特性的研究

采用等效媒质处理方法来研究有限引导磁场下沿纵向运动的相对论环形电子注.首先建立运动坐标系以电子注纵向速度匀速运动,在运动坐标系中电子注可以被考虑成静止的磁化等离子体,再通过四维空间的洛伦兹变换得到电子注在静止的实验室坐标系下可以被等效为双各向异性媒质,其不仅具有张量形式的电导率和磁导率,还具有手征特性.在此基础上同时考虑了由于电子注表面波动所引起的表面电流密度.采用该方法研究了有限引导磁场下圆柱波导中沿纵向运动的相对论环形电子注,推导出该模型的色散方程,并进行了数值计算.计算结果表明该研究方法能够得到更准 关键词： 相对论环形电子注 磁化等离子体 色散特性     

Selectively dopedn-AlxGa1−xAs/GaAs heterostructures with high-mobility two-dimensional electron gas for field effect transistors

The transport properties of warm and hot electrons in selectively dopedn-Al _x Ga_1–x As/GaAs heterostructures created by electric fields up to 500 V/cm were studied by Hall effect, conductivity, and Shubnikov-de Haas measurements at lattice temperatures from 4.2 to 300 K. Hall measurements revealed a substantial decrease of electron mobility and also of sheet electron concentration at 77 K with enhanced electric field. The accelerated 2D electrons are partly scattered into the low-mobility first excited (E ₁) subband, and they are partly trapped in immobile states located in the Al_xGa_1–xAs near the interface. Consequently, two differentv(E) characteristics were obtained at 77 K. The 2D electrons populating only the lowest (E ₀) subband exhibit a velocity of v-2×10⁷ cm/s at 500 V/cm, while the averaged velocity due to all electrons reaches a value of v-1.5×10⁷cm/s at 500 V/cm. The analysis of the Shubnikov-de Haas oscillations and Fast Fourier transformation of the data manifested that the 2D electrons are very rapidly accelerated at 4.2 K and achieve electron temperatures much higher than the lattice temperature at electric fields as low as 1 V/cm. The major cooling process for these electrons is scattering into the low-mobilityE ₁ subband.     

Theory of nonlinear transport for electron-impurity systems in a strong electric field

A force-balance equation is obtained for high electric field transport in electron impurity systems by separating the center of mass motion from the relative motion of electrons, in which the drift velocity and the electron-electron interaction enter dynamically. From this equation the current density as a function of electric field can be determined self-consistently.     

Chirped Bloch oscillations in strain-balanced InGaAs/InGaAs superlattices

Bloch oscillations excited in a strain-balanced In_xGa_1 − xAs/In_yGa_1 − yAs superlattice by fs optical pulses at 1.55 μ m are investigated in time-resolved transmission spectroscopy. The transition from the coherent oscillatory motion to an incoherent drift transport of the electrons is observed via a transient frequency shift of the Bloch oscillations due to the associated screening of the applied electric field. These electric field changes are analyzed quantitatively as a function of the initial field strengths and excitation densities. The incoherent transport can be described by a drift-diffusion model. As a result, the carrier mobility in the superlattice is obtained on a picosecond timescale.     

DC column plasma kinetics in a longitudinal magnetic field

The cylindrical column plasma of a neon dc glow discharge under the influence of a weak longitudinal magnetic field is studied. An extended, fully self-consistent model of the column plasma has been used to determine the kinetic quantities of electrons, ions and excited atoms, the radial space charge field, and the axial electric field for given discharge conditions. The model includes a nonlocal kinetic treatment of the electrons by solving their spatially inhomogeneous kinetic equation, taking into account the radial space charge field and the axial magnetic field. The treatment is based on the two-term expansion of the velocity distribution and comprises the determination of its isotropic and anisotropic components in the axial, radial, and azimuthal direction. A transition from a distinctly nonlocal kinetic behavior of the electrons in the magnetic-field-free case to an almost local kinetic behavior has been found by increasing the magnetic field. The establishment of the electron cyclotron motion around the column axis increasingly restricts the radial electron energy transport and reduces the radial ambipolar current. The complex interaction of these transport phenomena with the alterations in the charge carrier production leads finally to a specific variation of the electric field components. The axial field increases by applying weak magnetic fields, however, decreases with increasingly higher magnetic fields. At higher magnetic fields, the radial space-charge field is considerably reduced     

Simple theoretical analysis of the Fowler-Nordheim field emission from microstructures and quantum wires of optoelectronic materials

We present a simplified theoretical formulation of the Fowler-Nordheim field emission (FNFE) under magnetic quantization and also in quantum wires of optoelectronic materials on the basis of a newly formulated electron dispersion law in the presence of strong electric field within the framework of k.p formalism taking InAs, InSb, GaAs, Hg_1−xCd_xTe and In_1−xGa_x As_yP_1−y lattice matched to InP as examples. The FNFE exhibits oscillations with inverse quantizing magnetic field and electron concentration due to SdH effect and increases with increasing electric field. For quantum wires the FNFE increases with increasing film thickness due to the existence van-Hove singularity and the magnitude of the quantum jumps are not of same height indicating the signature of the band structure of the material concerned. The appearance of the humps of the respective curves is due to the redistribution of the electrons among the quantized energy levels when the quantum numbers corresponding to the highest occupied level changes from one fixed value to the others. Although the field current varies in various manners with all the variables in all the limiting cases as evident from all the curves, the rates of variations are totally band-structure dependent. Under certain limiting conditions, all the results as derived in this paper get transformed in to well known Fowler-Nordheim formula.     

Electronic properties of a Weyl semimetal in crossed magnetic and electric fields

The study of Weyl semimetals is one of the most challenging problems of condensed matter physics. These materials exhibit interesting properties in a magnetic field. In this work, we investigate the Landau bands and the density of states (DOS) oscillations in a Weyl semimetal in crossed magnetic and electric fields. An expression is obtained for the energy spectrum of the system using the following three different methods: an algebraic approach, a Lorentz shift-based approach, and a quasi-classical approach. It is interesting that the energy spectrum calculated in terms of the quasi-classical approach coincides with the spectrum obtained using the microscopic approaches. An electric field is shown to change the Landau bands radically. In addition, the classical motion of a three-dimensional Dirac fermion in crossed fields is studied. In the case of a Dirac spectrum, the longitudinal (with respect to magnetic field) component of momentum (p _z ∥ H) is shown to be an oscillating function of the magnetic field. When the electric field is v⊥H/c, the Landau levels collapse and the motion becomes fully linear in an unusual manner. In this case, the wavefunction of bulk states vanishes and only states with p _z = 0 are retained. An electric field affects the character of DOS oscillations. An analytical expression is obtained for the quantum capacitance in crossed fields in the cases of strong and weak electric fields. Thus, an electric field is an additional parameter for adjusting the diamagnetic properties of Weyl semimetals.     

Die Rotation des Elektronenspins beim ebenen Tunnelprozeß mit überlagertem homogenem Magnetfeld

Measurements of the spin polarization of field emitted electrons from various ferromagnetic (Gd, Ni, Fe) and nonferromagnetic metals (W) show a steady increase of the angle? _s between momentum and electron spin with increasing external magnetic field (spin rotation). This effect is refered to the coupling between the magnetic moment of the electron and the strong electric field in the potential barrier at the emitter surface during the tunneling process. A formal application of the equation of spin motion derived by Bargmann, Michel and Telegdi for an electron moving in homogeneous electromagnetic fields delivers a quantitative agreement with the experimental results.     

Allgemeine Berechnung der Elektronenverteilungsfunktion von schwach ionisierten Plasmen in beliebig zeitabhängigen elektromagnetischen Feldern

The behaviour of a weakly ionized plasma in external, arbitrarily time-dependent, electromagnetic fields is treated within the framework of kinetic theory. The Boltzmann kinetic equation is solved using the Lorentz ansatz, taking into account elastic collisions between electrons and neutral particles and assuming that the collision frequency is independent of the electron velocity. The drift velocity of electrons enters into the isotropic part f₀ and into the direction-dependent part f₁ of the electron distribution function. A method is given for the calculation of the drift velocity, which is calculated explicitly for the important but difficult case of a sinusoidal electric field in the presence of a magnetic switching field. f₀ and f₁ are calculated; f₀ is investigated generally. f₀ consists of an expansion in generalized Laguerre polynomials. The influence of the electromagnetic fields on the distribution function and its time variation is discussed and the relaxation behaviour is shown. The following two special cases are calculated explicitly: a linear rising electric field and a sinusoidal electric field, both in the presence of a constant magnetic field.     

Quasi-two-dimensional electron gas in a non-quantizing magnetic field and strong non-quantizing electric field

A calculation is performed to determine the transverse electric field E_y formed in quasi-two-dimensional superlattices in a strong drift field E_x and a weak magnetic field that is perpendicular to the plane of the superlattice (H‖OZ). When the electronic energy spectrum is nonadditive, the field E_y includes both the Hall factor and a spontaneous transverse electric field that exists whetherH is present or not. The situation when the specimen is in a closed circuit with a resistor on the OY axis is examined. As the function E_x, the field E_y is multivalued (multistable) and variable. The stability of the branches of the function E_y(E_x) is determined using a specially introduced (kinetic) “potential” whose minimum corresponds to the steady state of a nonequilibrium electron gas. Volgograd State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 46–51, July, 1996.     

磁约束环境下气体激光介质中电子能量分布与电子输运系数的理论研究

引进磁作用的Ｂｏｌｔｚｍａｎｎ输运方程应用于一类特殊激励的激光器─—工作在横向磁场下的直流放电气体激光器中的工作介质．以二氧化碳激光器为研究对象，通过数值求解Ｂｏｌｔｚｍａｎｎ方程，研究了磁场对电子能量分布及电子输运系数的影响．通过分析，提出了以磁约束作用提高一般气体激光器效率的设想． 关键词：