量子阱态光电子谱研究的理论模型

近年来，光电子谱被广泛应用于薄膜中量子阱态的研究。为解释薄膜中分立的量子阱态和薄膜的光电子谱间的关系，发展了一些理论模型。介绍了近自由电子模型、相位积累模型和电子干涉模型等关于薄膜中量子阱态的理论模型，并用它们解释了量子阱态在光电子谱中峰位和线宽．线宽由准粒子寿命的倒数Γ以及电子在表面和界面反射系数的和R决定，电子波矢κ以及电子在表面和界面相位移之和Φ决定了峰的位置。     

单电子器件中电子在耦合能级上的几率分布

两量子点耦合时,根据简并态微扰理论,单量子点的一个能级分裂为系统的两个能级,即对称态和反对称态,当单电子从外部隧穿进入一个量子点时,则电子在两耦合的量子点间振荡,本文讨论了电子在两能级上分布几率随时间的演化规律。     

量子阱态对Pb薄膜局域功函数的调制

理想的厚度均一的薄膜中，由于电子的运动在垂直于膜面方向受到限制，其能级会发生量子化，形成分立的能量本征态，即量子阱态。Pb／Si系统作为典型的量子阱态体系，由于Pb在[111]方向的层间距约为电子费米波长的1／4，所以Pb薄膜的厚度每变化一个单原子层都会引起费米面附近态密度的很大变化，从而导致其物理性质的变化。对此体系的研究表明Pb薄膜的许多物理性质，例如，超导转变温度、热膨胀系数及薄膜稳定性等均受到量子阱态的影响。     

GaAs/AlGaAs量子阱的输运特性

本文研究了低迁移率GaAs/AlGaAs量子阱的散射机制。由电导测量和Shubnikov de-Haas振荡曲线分别得到输运散射时间τ_0和弛豫时间τ_q(量子散射时间)。在GaAs/AlGaAs量子阱中,τ_0≈τ_q;而在调制掺杂的异质结中,τ_0》τ_q。用量子阱、异质结中起支配作用的散射机构不同很好地解释了实验结果。本文还研究了弱磁场下量子阱的负磁阻效应,这是磁场抑制了电子局域态的结果。     

GaN HFET沟道中的电子态转换和沟道右势垒剪裁

在分析AIGaN／GaN沟道阱中电子迁移率、截止频率fT和噪声性能随电子气密度变化的基础上，研究了沟道电子态随电子密度的变化。发现在高电子密度下电子会向量子限制较弱的退局域态转移。同时还经由热电子隧穿而跃迁到表面态。在低电子密度下，沟道阱产生畸变而蜕化为三维态。运用这一电子态转换模型解释了输运噪声特性随电子气密度的变化。最后指出剪裁沟道右势垒可以弱化高、低电子气密度下输运和噪声性能的衰退。     

In0.53Ga0.47As/In0.52Al0.48As量子阱二维电子气中的零场自旋分裂与塞曼分裂

利用变角度磁输运方法研究了高迁移率、高浓度、宽度为20 nm、单边δ掺杂的In0.53Ga0.47As/In0.52Al0.48As量子阱,根据量子阱平面与磁场不同夹角时SdH振荡的拍频节点移动,提取了其自旋分裂能Δ0和有效g因子|g*|,发现Δ0随浓度增加而增大,|g*|随浓度增加而减小.进一步的分析和计算表明,|g*|减小是由量子阱能带结构的非抛物性作用引起的.     

PHEMT器件界面态分析方法综述

介绍了高电子迁移率场效应晶体管(PHEMT)器件的结构,并主要从直流特性、击穿电压和栅延时等方面研究了界面态对PHEMT器件的影响,总结了界面态分析方法.包括:通过沟道峰值电场和碰撞电离率来研究界面态的密度;二维量子模型模拟法的应用;根据跨导随频率变化的规律来测量界面态的密度.     

在外电场作用下有限抛物量子阱中类氢杂质态结合能

采用变分方法研究GaAs/AlxGa1-xAs有限抛物量子阱中类氢杂质态能量和结合能随外电场和阱宽的变化关系.在计算中考虑了电子有效带质量和介电常数随空间坐标(或合金组分)的变化因素.结果表明,外电场对类氢杂质态能量和结合能均有明显的影响,并且这些影响随着阱宽的增大而增大.电子有效带质量和介电常数随空间坐标的变化效应使得类氢杂质态基态能量减小,结合能增大,此效应随着阱宽的增大明显变小.     

在外电场作用下有限抛物量子阱中类氢杂质态结合能

采用变分方法研究GaAs/AlxGa1-xAs有限抛物量子阱中类氢杂质态能量和结合能随外电场和阱宽的变化关系.在计算中考虑了电子有效带质量和介电常数随空间坐标(或合金组分)的变化因素.结果表明,外电场对类氢杂质态能量和结合能均有明显的影响,并且这些影响随着阱宽的增大而增大.电子有效带质量和介电常数随空间坐标的变化效应使得类氢杂质态基态能量减小,结合能增大,此效应随着阱宽的增大明显变小.     

GaNxAs1-x非局域态的动力学特征

通过时间分辨光谱研究了GaNxAs1-x的量子阱以及体材料中非局域态和局域态的动力学特征。实验结果通过比较非局域态与局域态的差别充分展示了GaNxAs1-x材料中非局域态的动力学特征。     

Pulse-time modulation of mutually coupled arrays of oscillators

This paper specifies the coupling parameters for multioscillator arrays (2" in number) such that nondegenerate symmetric and antisymmetric states may be sequentially accessed by electronic control of the coupling parameters. A requirement of this coupling configuration is that, when mutually locked, the oscillator amplitudes are identical to one another. Thus, when the oscillator signals are combined with a series of magic-T's, the output power is the sum of the oscillator powers in the array minus some small loss in the coupling circuit for the symmetric state and zero for the antisymmetric state. Switching from one state to the other is accomplished by control of the feedback phase delay between oscillators. Ideal oscillator cases are analyzed for two, four, and higher numbers of oscillators by induction. By this electronic-mode control of mutually locked oscillators, we have been able to generate pulse-time modulation (PTM) signals which are useful for communication systems. We describe some results of an X-band PTM signal generator     

Theory of directional couplers including transition region phaseshifts

An analysis is made of the operation of the parallel waveguide directional coupler by incorporating eigenmode phase shifts in the input and output transition regions. The set of modes used in the analysis consists of the orthogonal symmetric and antisymmetric modes of the unperturbed parallel waveguide. It is demonstrated how the switching diagram changes as the transitional phase shifts increase. There is no indication that these built-in phase shifts degrade coupler crosstalk performance for the states normally used. Conditions for symmetric switching are derived     

Symmetric solutions and eigenvalue problems of Toeplitz systems

Algorithms and properties of symmetric solutions of a Toeplitz system are studied. It is shown that the numbers of positive and negative eigenvalues associated with symmetric (antisymmetric) eigenvectors are the same as the numbers of positive and negative predictor errors of symmetric (antisymmetric) filters. Based on the odd symmetric solutions and the property that all roots of symmetric and antisymmetric filters are on the unite circle, a method for Pisarenko's decomposition is introduced. Compared with some other methods, it reduces the number of iterations and the computational cost in each iteration considerably     

囚禁离子多体纠缠态的简单制备方案

提出了三种制备冷离子多体纠缠态的简单方案。第一个方案是关于GHZ态的制备,其只需要利用激光对所有离子进行一次集体驱动。第二个方案是制备对称的W态,W态的产生需要两步操作才能完成。第三个方案是研究簇态的制备,并讨论了利用两个小簇态合成一个大簇态的方法和过程,这种合成法可以增加大簇态的产生速度,从而可以减低实验中因退相干而产生的失真。以上三个方案都是利用振动态处于基态的多个离子与激光场的大失谐相互作用来实现的。与以前的方案相比,这些方案有以下四个优点：不需要离子的振动模来存储和传递信息;不需要单个地驱动这些离子;不受激光场的相位涨落的影响;需要相对少的操作步骤。     

Magnetic polarization of a Mn-doped semiconductor nanostructure controlled by an external bias

The interplay between the electric and magnetic properties in a double quantum well heterostructure doped by magnetic ions is theoretically investigated. In this material, the magnetism is mediated by the hole gas. The total magnetic polarization of the system is controllable by an external applied bias. The device has two equilibrium states (symmetric and antisymmetric configurations). In the stable configuration (anti-ferromagnetic type), the particle spin distribution is reversed in the adjacent wells. The stability of the system is investigated by simulating the interaction of the hole gas with the light. By using an ab initio method, we estimate the switching time of the device.     

Nonlinear TE waves in a dielectric slab waveguide with two optically nonlinear layers

Properties of TE waves in a slab waveguide composed of five layers, including two Kerr-like nonlinear layers, are analyzed and examined. We find in particular the occurrence of an asymmetric mode, in addition to the expected symmetric and antisymmetric modes, though the waveguide geometry is symmetric. For the TE0symmetric mode, TE1antisymmetric and asymmetric modes, the dispersion curves, the relations between the effective index and the optical power density, and the variations of the transverse electric field patterns are illustrated and discussed in detail. As a result of this analysis, the regions in which the respective modes mainly reside are elucidated. We find that the effective index value of the symmetric mode at which the guide power vanishes is larger than that of the antisymmetric mode. For the case in which the effective indexes of the asymmetric and antisymmetric modes are identical, the power in the former mode is found to be larger than that in the latter.     

Detailed investigation of n-channel enhancement 6H-SiC MOSFETs

Basic MOSFET parameters like inversion layer mobility, threshold voltage, intrinsic mobility reduction factor and interface state density extracted from the subthreshold slope were examined in detail for 6H-SiC enhancement-mode n-channel MOSFETs. The inversion layer mobility and the threshold voltage were determined as a function of substrate doping concentration as well as device temperature. The interface state density was studied for different substrate doping concentrations. The inversion layer mobility was found to decrease strongly with increasing substrate doping. In contrast to earlier reports the inversion layer mobility decreases also with temperature. Furthermore, the threshold voltage depends more pronounced on substrate doping and temperature than theoretically expected. The interface state density extracted from the subthreshold slope increases significantly with substrate doping concentration. All these phenomena are consistently interpreted by the classical MOSFET behavior which is extended by acceptor like interface states. These states are located close to the conduction band and exhibit a density increasing drastically toward the band edge     

Theory and lattice structure of complex paraunitary filterbankswith filters of (Hermitian-)symmetry/antisymmetry properties

The theory of the real-coefficient linear-phase filterbank (LPFB) is extended to the complex case in two ways, leading to two generalized classes of M-channel filterbanks. One is the symmetric/antisymmetric filterbank (SAFB), where all filters are symmetric or antisymmetric. The other is the complex linear phase filterbank (CLPFB), where all filters are Hermitian symmetric or Hermitian antisymmetric and, hence, have the linear-phase property. Necessary conditions on the filter symmetry polarity and lengths for the existence of permissible solutions are investigated. Complete and minimal lattice structures are developed for the paraunitary SAFB and paraunitary CLPFB, where the channel number M is arbitrary (even or odd), and the subband filters could have different lengths. With the elementary unitary matrices in the structure of the paraunitary SAFB constrained to be real and orthogonal, the structure covers the most general real-coefficient paraunitary LPFBs. Compared with the existing results, the number of parameters is reduced significantly     

基于陷落电荷效应的非晶硅TFT的开态电流模型

对非晶硅薄膜晶体管,提出基于陷落电荷和自由电荷分析的新方法。考虑到带隙中指数分布的深能态和带尾态,给出了基于阈值电压的开启区电流模型。定义阈值电压为栅氧/半导体界面处陷落于深能级陷阱态的电荷与陷落于带尾态的电荷相等时所对应的栅压。电流模型中,引入一陷落电荷参数β,此参数建立了电子的带迁移率与有效迁移率之间的关系。最后,将电流模型同时与Pao-Sah模型和实验数据进行比较和验证,结果表现出很好的一致性。     

Analysis of grating surface emitting lasers

An approach to the analysis of grating-coupled semiconductor lasers is presented. It is shown that there are only two resonant solutions when the grating has infinite extent. The solutions are either symmetric or antisymmetric about the center of the longitudinal coordinate system where the antisymmetric solution is nonradiating. The field in the grating layer is expressed in terms of grating eigenfunctions and rigorously matched to the boundary conditions at the waveguide interface. Solutions to the finite-length grating problem are expressed as linear combinations of the infinite-length solutions. It is shown that the two diffraction parameters in the coupled-wave equations are composed of sums and differences of the eigenvalues from the infinite-length problem