掺杂超晶格量子阱的沟道效应与沟道辐射

分析了超晶格量子阱的沟道效应和沟道辐射,利用正弦平方势描述了掺杂超晶格量子阱沟道粒子的运动行为,并在经典力学框架内,把粒子的运动方程化为摆方程。用Jacobian椭圆函数和椭圆积分解析地给出了系统的解和粒子运动周期,导出了量子阱沟道辐射的辐射强度和辐射能量。结果表明,对于能量为100 MeV左右的电子,辐射能量可达keV量级（X能区）。指出了用量子阱沟道辐射作为X激光或γ激光的可能性。     

Photogalvanic current in a double quantum well

A double quantum well affected by external alternating electric field with in- and out-of-plane components is studied. This field causes transitions between near-degenerate states located in different wells. The phototransitions are accompanied by the in-plane momentum nonconservation caused by the impurity scattering. We study the in-plane stationary current due to the lack of the in-plane symmetry of these indirect phototransitions. It is shown that the value and direction of the current are determined by the polarization of light. The linear and circular photogalvanic coefficients are found. When the photon energy approaches the distance between subbands these coefficients have their symmetric and antisymmetric resonance behaviors, respectively.     

Electron resonance dynamics in a double quantum well

We consider the two-level electron dynamics in a double quantum well in a periodic, anharmonic external electric field. We propose a method for solving the Schrödinger equation, which is based on the generalization of conventional resonance approximation for a system with an arbitrary number of resonances. The method is used for the case of both weak and strong fields. We obtain expressions for the quasi-energy wave functions and the electron dipole moment. It is shown that the dependence of the dipole moment on the constant component of external field is quasi-periodic, and the dipole moment changes sign at different half-periods.     

Organic quantum well and superlattice characteristics in quasi-one-dimensional multiblock copolymers

A tight-binding calculation was presented to describe multiblock copolymers, such as [...-(PA)x-(PPP)y-...] composed of PA (polyacetylene) and PPP (poly(p-phenylene). It is found that a copolymer has a quantum well and superlattice characteristics, and evident is the effect of the composite lengths, the interfacial couplings and the electron-phonon interactions on the electronic properties of a copolymer. The quantum tunneling, the Franz-Keldysh effect and the quantum confinement can be generated under an applied electric field. These results were compared to those of traditional inorganic quantum well and superlattice systems.     

Entanglement of two interacting electrons in a double quantum dot

We study the dynamics of two interacting electrons confined in a double quantum dot in the presence of radiation pulses. We show that the strong transition between two localized states is induced at the avoided crossing between the corresponding energy levels, leading to the maximally entangled Bell states. The frequency and duration of selective light pulses for producing maximally entangled states are identified by both analytic and exact numerical solution of the quantum dynamical equations.     

Parallel transport of electrons in double quantum wells

Calculations have been performed on the mobility of electrons in a double quantum well structure in which the barrier separating the two parts of the channel is sufficiently thin to allow tunnelling. The subband structure is completely taken into account in a self-consistent calculation and all significant scattering mechanisms (scattering on remote impurities, on selectively introduced channel impurities, on acoustic and optical phonons) are included in order to obtain quantitatively realistic results from low to room temperature. We discuss how the thickness of the barrier influences the conductivity of the channel vs density and show that it is possible to design structures having negative transconductance with a peak-to-valley ratio of 6 at T = 77 K.     

Magnetotunneling relaxation of electrons in double quantum wells

Electron tunneling relaxation in double quantum wells subject to a transverse magnetic field is studied. The resonant peaks in the tunneling relaxation rate appear when the energy splitting Δ of the tunnel-coupled pair of the left- and right- well electron states is a multiple of the cyclotron energy ℏω_c and two series of the Landau levels coincide. The shape of such resonant oscillations of the relaxation rate is determined by the Landau levels' broadening (which is associated with the intrawell scattering in the case of small tunnel coupling), but it is not expressed through the electron density of states directly. The dependence of the tunneling relaxation rate on ℏω_c and Δ is calculated taking into account elastic scattering of the electrons by the inhomogeneities of the structure in the limit when the scattering potential is slowly changing on the magnetic length scale.     

Exciton binding energy in a double quantum well: effect of the barrier shift

We have calculated the exciton binding energy in an Al _xGa_1 − x As  / GaAs double quantum well by a variational envelope function procedure using a simple two-band model. The influence of the shift of the AlAs separating barrier, introducing an asymmetry into the system, on the value of the exciton binding energy has been analysed. It has been observed that this shift induces significant changes of the exciton binding energy—even several meVs in the case of very thin barriers.     

The electronic structure of the perturbed superlattice: the case of Bragg-confined double quantum well resonant structures

The electronic structure of a perturbed superlattice of the Bragg-confined resonant structure type is discussed within the effective mass approximation. Expressions for bound-state energies and wavefunctions in these structures are derived in general form, valid for any symmetric form of the potential and effective mass modulation. The special case of rectangular superlattices with a perturbation layer is considered in more detail. The influence of the structure parameters on properties of Bragg-confined states is analysed, and positions of bound states lying in minigaps of the structure with the resonant double-well pertubation layer are determined. The possibilities of finding optimal structure parameters in respect to the maximal localization of the bound-state wavefunctions, in a broad range of above-the-barrier energies, are also discussed.     

Hanle effect in an asymmetric CdTe/CdMnTe double quantum well

The observation of optical orientation of excitons and the Hanle effect in an asymmetric CdTe/CdMnTe double quantum well is reported. The characteristics of the magnetic depolarization of radiation from CdTe/CdMnTe quantum wells are discussed. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 241–245 (25 February 1996)     

Energy relaxation and thermalization of hot electrons in quantum wires

We develop a theory of energy relaxation and thermalization of hot carriers in clean quantum wires. Our theory is based on a controlled perturbative approach for large excitation energies and emphasizes the important roles of the electron spin and finite temperature. Unlike in higher dimensions, relaxation in one-dimensional electron liquids requires three-body collisions and is much faster for particles than holes which relax at nonzero temperatures only. Moreover, comoving carriers thermalize more rapidly than counterpropagating carriers. Our results are quantitatively consistent with a recent experiment.     

A double quantum well in a driving laser field

The dynamic effect of electrons in a double quantum well under the influence of a monochromatic driving laser field is investigated. Closed-form solutions for the quasienergy and Floquet states are obtained with the help ofSU (2) symmetry. For the case of weak interlevel coupling, explicit expressions of the quasienergy are presented by the use of perturbation theory, from which it is found that as long as the photon energy is not close to the tunnel splitting, the electron will be confined in an initially occupied eigenstate of the undriven system during the whole evolution process. Otherwise, it will transit between the lowest two levels in an oscillatory behavior.     

Monte Carlo study of hot electrons in quantum wells

We have performed an ensemble Monte Carlo calculation of the high field response at 77 K of two different two-dimensional systems, one a modulation doped (MD) single square well of GaAs/AlGaAs and the other a δ-doping layer formed by a sheet of donor impurities embedded in bulk GaAs. Results of this calculation show a reduced low field mobility and a decrease in the transient overshoot velocity in the δ-doping versus MD system due to the effect of impurity scattering. At high fields, however, the steady state saturated drift velocities appear to be similar in the two systems. Because of the higher carrier density, the performance of short-channel devices based on the δ-layer will be advantageous where high output currents are necessary.     

Integer quantum Hall effect in a PbTe quantum well

Transport measurements have been carried out on a 10 nm n-type PbTe/Pb_0.9Eu_0.1Te quantum well at millikelvin temperatures. The Hall and longitudinal resistances are measured in a Van der Pauw geometry under high magnetic fields up to 23 T. A robust signature of the integer quantum Hall effect is observed without any sign of parasitic parallel conduction. The unconventional sequence of filling factors associated with the integer quantum Hall effect is discussed in terms of the occupancy of multiple valleys.     

Intense laser field effect on impurity states in a semiconductor quantum well: transition from the single to double quantum well potential

In this work are studied the intense laser effects on the impurity states in GaAs-Ga_{1− x} Al _x As quantum wells under applied electric and magnetic fields. The electric field is taken oriented along the growth direction of the quantum well whereas the magnetic field is considered to be in-plane. The calculations are made within the effective mass and parabolic band approximations. The intense laser effects have been included through the Floquet method by modifying the confinement potential associated to the heterostructure. The results are presented for several configurations of the dimensions of the quantum well, the position of the impurity atom, the applied electric and magnetic fields, and the incident intense laser radiation. The results suggest that for fixed geometry setups in the system, the binding energy is a decreasing function of the electric field intensity while a dual monotonic behavior is detected when it varies with the magnitude of an applied magnetic field, according to the intensity of the laser field radiation.     

Plasmons in asymmetric double quantum well structures

We investigate the effects of spatial asymmetry, tunneling coupling, and exchange-correlation correction on the plasmon modes in asymmetric double quantum well (DQW) structures in a time-dependent local-density approximation. Special attention is paid to the properties of the ω _- mode which is always damped in symmetric DQW systems. In addition, the results on the spectral weight of the excitations are also presented. In general, all the modes carry finite spectral weights and should be observable in resonant inelastic light scattering experiments for the specified values of the parameters. Received 2 July 2002 Published online 19 December 2002 RID="a" ID="a"e-mail: c412-1@aphy.iphy.ac.cn