Infrared properties of the Double Barrier Structure

The infrared admittance of the Double Barrier Structure (DBS) is investigated by using a time-dependent quantum theory. The analysis is carried out under the small signal condition with no dc bias. The calculated results show conductance oscillations in the infrared frequency region. The oscillations are associated with the quantum well transit time resonances.     

Design and Analysis of InGaN-GaN Modulation Doped Field-Effect Transistors (MODFETs) for Over 60 GHz Operation

A Modulation-Doped Field-Effect Transistor (MODFET) structure realized in InGaN-GaN material system is presented for the first time. An analytical model predicting the transport characteristics of the proposed MODFET structure is given in detail. Electron energy levels inside and outside the quantum well channel of the MODFET are evaluated. The two-dimensional electron gas (2DEG) density in the channel is calculated by self-consistently solving Schrödinger and Poisson's equations simultaneously. Analytical results of the current-voltage and transconductance characteristics are presented. The unity-current gain cutoff frequency (f _T) of the proposed device is computed as a function of the gate voltage V _G . The results are compared well with experimental f _T value of a GaN/AlGaN HFET device. By scaling the gate length down to 0.25 m the proposed InGaN-GaN MODFET can be operated up to about 80GHz. It is shown in this paper that InGaN-GaN system has small degradation in f _T as the operating temperature is increased from 300°K to 400°K.     

Observation of the tensor glueball

In the reactions p-p → π ⁰ π ⁰, ηη, ηη′, in the mass region 1900–2400 MeV there are four relatively narrow resonances f ₂(1920), f ₂(2020), f ₂(2240), and f ₂(2300) and a broad one f ₂(2000). In the framework of quark combinatorics, we carry out an analysis of the decay constants for all five resonances. It is shown that the relations for the decay constants corresponding to the broad resonance f ₂(2000) → π ⁰ π ⁰, ηη, ηη′ are the same as those corresponding to a glueball. An additional argument in favor of the glueball nature of f ₂(2000) is the fact that f ₂(1920), f ₂(2020), f ₂(2240), and f ₂(2300) fit well the q-q trajectories in the (n, M ²) plane (where n is the radial quantum number), while the broad f ₂(2000) resonance turns out to be an unnecessary extra state for these trajectories. The text was submitted by the authors in English.     

Very large blue and red Stark shifts of the excitonic transition in InGaAs-InP-InAsP antisymmetric coupled quantum wells

A new strained InGaAs-InP-InAsP antisymmetric coupled quantum well (CQW) structure with both very large blue and red quantum-confined Stark shifts for the first heavy-hole-to-electron excitonic transition, E _hh1fE _e1, is studied theoretically in this paper. In the antisymmetric coupled quantum well, an antisymmetric-like pair of potential profiles between the shallow-deep conduction band profile and the deepshallow valence band profile are formed. The sub-band eigen-energies, E, and the associated envelope wave functions in the CQW structures with or without an applied electric field are calculated by the transfer-matrix method. The effect of strain on the pseudomorphic layers has been taken into account. Results indicate that the strained InGaAs-InP-InAsP antisymmetric CQW structure exhibits significant enhancement of the blue and red Stark effects in the E _hh1fE _e1 transition. The influences of various antisymmetric CQW structural parameters, such as the total well width, the individual well width, the central barrier thickness and the composition of the strained layer on the quantum-confined Stark shift, as well as the envelope wave function overlap, are studied systematically. These strong Stark effects in the antisymmetric CQW structure may have potential applications in sophisticated new electronic devices, such as optical switching devices.     

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.     

Quantum Computer Algorithm for Parity Determination Based on Quantum Counting

A new quantum computer algorithm is proposed for determining the parity of function f(x) by using quantum counting algorithm. The parity of function f(x) can be determined by counting exactly the number of satisfying f(x)=−1, which is equivalent to determine the number of solutions, M, to an N item search problem. The algorithm can be accomplished in time of order .     

Ionospheric effect of the magnetospheric substorms at middle latitudes

Summary A study is made of theF2-layer effect of magnetospheric substorms over the Mediterranean area using data from several ionospheric stations for selected events in the current sunspot cycle 21. The night-time enhancements in the critical frequency of theF2-layer (f ₀ F2) and the total electron content (TEC) have been found with both premidnight and postmidnightf ₀ F2 peaks and a subsequent decrease in the minimum virtual height of theF region (h′F). It is found that the enhancements occur through the nights under steady geomagnetic conditions and that the time at which it is seen at Rome and Grocka ionospheric stations is progressively earlier as geomagnetic activity increases. It has been further shown that this type of thef ₀ F2 night-time increases is not always accompanied by an increase in TEC, although the reverse holds true during the nights of increased substorm activity. The fact that the considerable variability inf ₀ F2, TEC andh′F at the onset of the substorm expansion are preceded by the ionospheric dynamics associated with these observations can be very useful in the identification of precursor indicative of short-term variations of ionospheric propagation conditions.     

Frequency-domain performance of a femtosecond laser with carrier-envelope phase stabilized by the direct locking method

We analyzed frequency-domain characteristics of a femtosecond laser whose carrier-envelope phase (CEP) was stabilized by the direct locking method (DLM). To evaluate the CEP-stabilized laser with zero carrier-envelope-offset frequency (f _ceo), as imposed by DLM, a self-referencing f-to-2f interferometer with a shifted frequency comb by an acousto-optic modulator was employed in an out-of-loop. The measurement of the square root of triangle variance confirmed that DLM is a phase-locking method. The tight locking was verified from a narrow bandwidth of f _ceo, measured using the out-of-loop interferometer, and from a small frequency jitter measured with a frequency counter referenced to a Rb-clock. The femtosecond laser with CEP stabilized by DLM is, thus, well suited for applications in the frequency domain as well as in the time domain.     

Composite-meson model and meson exchange currents

We study the meson exchange currents (MEC) mechanism for the pion double-charge exchange (DCX) reaction in a composite-meson model. The model assumes that the mesons are two-quark systems and can interact with each other only through quark loops. The contributions of the ρ, σ, and f₀ mesons, the four-quark box diagram as well as a contact diagram has been taken into account. It is shown that the contribution of the ρ, σ, and f₀ mesons increases the forward scattering cross-section in an average by 25% and decreases with energy.     

Modeling of Nonvolatile Quantum Dot Gate Structures Operating at Millimeter Wave Frequencies for Memory Applications

This paper models electrical characteristics of quantum dot nonvolatile memory cells during READ and WRITE operations. Capacitance-voltage characteristics are calculated by self-consistently solving the Schrodinger and Poisson equations. The memory access time for a 32 kb NOR array is 73 ps, which reduces to 13 ps in lightly-doped sheath (LDS) structures. The results show that a change in the quantum dot charge has a strong effect on drain to source current. The calculated cutoff frequency f _T is 135 GHz for a 0.1 m channel length Si field-effect memory structures. The application of a quantum dot memory cell as a programmable resistor in RF circuits is presented. By changing the quantum dot charge, the resistor values can be changed by 25%.     

Properties of ground state and anomalous quantum fluctuations in one-dimensional polaron-soliton systems—the effects of electron-two-phonon interaction and non-adiabatic quantum correlations

Based on the Holstein model Hamiltonian of one-dimensional molecular crystals, by making use of the expansion approach of the correlated squeezed-coherent states of phonon instead of the two-phonon coherent state expansion scheme, the properties of the ground state and the anomalous quantum fluctuations are investigated in a strongly coupled electron-phonon system with special consideration of the electron-two-phonon interaction. The effective renormalization (αi) of the displacement of the squeezed phonons with the effect of the squeezed-coherent states of phonon and both the electron-displaced phonon and the polaron-squeezed phonon correlations have been combined to obtain the anomalous quantum fluctuations for the corrections of the coherent state. Due to these non-adiabatic correlations, the effective displacement parameter αi is larger than the ordinary parameter α (0) i . In comparison with the electron-one-phonon interaction (g) corrected as αig, we have found the electron-two-phonon interaction (g1) corrected as αi2 g1 is enhanced significantly. For this reason, the ground state energy (E(2) 0 ) contributed by the electron-two-phonon interaction is more negative than the single-phonon case (E(1) 0 ) and the soliton solution is more stable. At the same time, the effects of the electron-two-phonon interaction greatly increase the polaron energy and the quantum fluctuations. Furthermore, in a deeper level, we have considered the effect of the polaron-squeezed phonon correlation (f-correlation). Since this correlation parameter f > 1, this effect will strengthen the electron-one and two-phonon interactions by fαig and f2αi2 g1, respectively. The final results show that the ground state energy and the polaron energy will appear more negative further and the quantum fluctuations will gain further improvement.     

导纳谱研究两类Si基量子阱基态子能级的性质

用导纳谱技术研究了两类Si基量子阱样品基态子能级的性质.基于量子阱中载流子的热激发模型，从导纳谱中得到的激发能值被认为是阱中重空穴基态位置到阱顶的距离.对于SiGe合金和Si形成的组分量子阱，主要研究了退火对重空穴基态子能级的影响.发现样品的退火温度为800℃时，随退火时间延长，激发能增加.对此现象的解释是，由于Si,Ge互扩散，导致界面展宽，量子限制效应降低，重空穴基态位置下降，从而激发能增加.900℃下退火，由于扩散系数增大和应变弛豫加强，激发能值单调下降，量子限制效应引起的变化被掩盖.对于B高浓度超 关键词：     

Existence of Solutions of a Kinetic Equation Modeling Cometary Flows

A global existence theorem is presented for a kinetic problem of the form _t f+v· _x f=Q(f), f(t=0)=f ₀, where Q(f) is a simplified model wave–particle collision operator extracted from quasilinear plasma physics. Evaluation of Q(f) requires the computation of the mean velocity of the distribution f. Therefore, the assumptions on the data are such that vacuum regions, where the mean velocity is not well defined, are excluded. Also the initial data are assumed to have bounded total energy. As additional results conservation laws for mass, momentum, and energy are derived, as well as an entropy dissipation law and the propagation of higher order moments.     

A geometric generalization of classical mechanics and quantization

A geometrization of classical mechanics is presented which may be considered as a realization of the Hertz picture of mechanics. The trajectories in thef-dimensional configuration spaceV _f of a classical mechanical system are obtained as the projections onV _f of the geodesics in an (f + 1) dimensional Riemannian spaceV _{f + 1}, with an appropriate metric, if the additional (f + 1)th coordinate, taken to be an angle, is assumed to be “cyclic”. When the additional (angular) coordinate is not cyclic we obtain what may be regarded as a generalization of classical mechanics in a geometrized form. This defines new motions in the neighbourhood of the classical motions. It has been shown that, when the angular coordinate is “quasi-cyclic”, these new motions can be used to describe events in the quantum domain with appropriate periodicity conditions on the geodesics inV _{f + 1}.     

基于粒子群算法的有机半导体NPB传输特性辨识

为了研究有机半导体材料的载流子传输特性,制备了单层器件ITO/NPB/Ag,建立了该器件的理论导纳模型.利用正弦小信号频域测试法得到该器件在不同直流偏压下的频率特性样本.定义了同时包含有机半导体阻抗实部和虚部的模型参数辨识问题的目标函数,采用粒子群算法对包括载流子迁移时间τdc,色散度参数M和α在内的模型参数进行辨识.为了验证提出方法的有效性,建立了器件的等效电路模型,并用最小二乘算法辨识出等效电路的时间常数τc.实验上对1000 nm和1200 nm的单层器件进行频域测试,经计算发现τdc和τc之间具有相同的比例关系,通过对计算出的空穴迁移率μdc进行指数拟合发现,两种厚度的NPB器件的空穴迁移率与电场强度呈指数增加,且满足著名的Poole-Frenkel公式.     

1.3μm无致冷AlGaInAs/InP应变补偿量子阱激光器设计与制作

基于半导体量子阱激光器的基本理论,设计了合理的1.3μm无致冷AlGaInAs/InP应变补偿量子阱激光器结构,通过低压金属有机化学气相外延(LP-MOVPE)工艺在国内首次生长出了高质量的AlGaInAs/InP应变补偿量子阱结构材料,用此材料制作的器件指标为激射波长:1280nm≤λ≤1320nm,阈值电流:I_th(25℃)≤15mA,I_th(85℃)≤30mA,量子效率变化:Δη_ex(25℃～85℃)≤1.0dB,线性功率:P₀≥10mW     

Liouville and Fokker–Planck dynamics for classical plasmas and radiation

We consider a nonequilibrium statistical system formed by many classical non‐relativistic particles of opposite electric charges (plasma) and by the classical dynamical electromagnetic (EM) field. The charges interact with one another directly through instantaneous Coulomb potentials and with the dynamical degrees of freedom of the transverse EM field. The system may also be subject to external influences of: i) either static, but spatially inhomogeneous, electric and magnetic fields (case 1)), or ii) weak distributions of electric charges and currents (case 2)). The particles and the dynamical EM field are described, for any time t > 0, by the classical phase‐space probability distribution functional (CPSPDF) f and, at the initial time (t = 0), by the initial CPSPDF f_in. The CPSPDF f and f_in, multiplied by suitable Hermite polynomials (for particles and field) and integrated over all canonical momenta, yield new moments. The Liouville equation and f_in imply a new nonequilibrium linear infinite hierarchy for the moments. In case 1), f_in describes local equilibrium but global nonequilibrium, and we propose a long‐time approximation in the hierarchy, which introduces irreversibility and relaxation towards global thermal equilibrium. In case 2), the statistical system, having been at global thermal equilibrium, without external influences, for t ≤ 0, is subject to weak external charge‐current distributions: then, new hierarchies for moments and their long‐time behaviours are discussed in outline. As examples, approximate mean‐field (Vlasov) approximations are treated for both cases 1) and 2).     

Oscillator strength measurements of the 4s5s 3S1 → 4snp 3Po2 Rydberg transitions of zinc

In the present experimental work, oscillator strengths of the 4s5s ³S₁ → 4snp ³P^o₂ (18?≤?n?≤?53) Rydberg transitions of zinc are reported. The stepwise laser excitation from the ground state 4s^{2 1}S₀ was achieved using three dye laser beams simultaneously pumped by the second (532?nm) and third (355?nm) harmonics of a Q-switched Nd: YAG (Neodymium-doped yttrium aluminum garnet) laser. The vapor containment and detection system was a single wire thermionic diode ion detector operating in space charge limited mode. A trend of the above-mentioned f-values from n?=?18 to 53 versus the principle quantum number n has been presented. Furthermore, continuity has been verified between the discrete f-values and the oscillator strength density at the threshold.     

A Fixed-Tuned W-Band Waveguide SIS Mixer with 4.0-7.5 GHz IF

The design and performance of a fixed-tuned W-band SIS mixer with a wide band IF of 4.0-7.5 GHz is presented. Waveguide-to-stripline transition of the SIS mixer is designed using the lumped-gap-source port provided by HFSS^TM. Measured receiver noise temperature is less than 25 K in the frequency range of 95-120 GHz, with a minimum value of around 19 K achieved. Mixer noise temperature is determined to be about 8.5 K, which is around twice the quantum limit (i.e., 2hw/k). In spite of the high IF frequencies (f ₀ = 6 GHz), the performance of the SIS receiver is comparable or even superior to those of the best mechanically-tunable waveguide SIS receivers at low IF frequencies (f ₀ = 1.5 GHz). This result suggests that it is easy to design waveguide-to-stripline transitions without scale-model measurements.