Low temperature electron mobility in a coupled quantum well system

We study low temperature electron mobility μ_nin a GaAs/Al_x Ga _1 − xAs coupled double quantum well structure. Both the extreme barriers are δ -doped with Si so that the electrons diffuse into the adjacent wells forming two sheets of two-dimensional electron gas (2DEG) separated by a thin central barrier. The subband electron wavefunctions and energy levels are numerically obtained as a function of the well width, barrier width and doping concentration. The screening of ionized impurity potential by the 2D-electrons is obtained in terms of the static dielectric response function within the random phase approximation (RPA). μ_nis calculated by solving the coupled Boltzmann equation in the relaxation time approximation. The coupling of wavefunctions through the barrier, screening of ionized impurities and intersubband scattering effects on μ_nare investigated.     

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.     

Photoluminescence of n-doped double quantum well—electron subbands under influence of in-plane magnetic fields

We report on photoluminescence (PL) measurements of a GaAs/AlGaAs double quantum well (DQW) in high magnetic fields. Measurements were carried out on a selectively contacted symmetric p-δn-DQW-δn-p structure, which allows a variation of the electron density in DQW by a p–n bias and simultaneously a tilting of DQW, when a p–p bias is applied. Attention was paid to phenomena in in-plane magnetic fields, theoretically studied by Huang and Lyo (HL), [Phys. Rev. B 59, (1999) 7600]. In this paper, we compare our results for both symmetric and asymmetric DQWs with the theoretical model made by HL. Whereas the spectra from a symmetric DQW fully confirmed the theoretical predictions, the results gained from DQW with an electric-field-induced asymmetry did not allow a proper study of anticipated effects. The reasons for that are discussed.     

Intersubband transitions and refractive index changes in coupled double quantum well with different well shapes

In this study, both the linear intersubband transitions and the refractive index changes in coupled double quantum well (DQW) with different well shapes for different electric fields are theoretically calculated within framework of the effective mass approximation. Results obtained show that intersubband transitions and the energy levels in coupled DQW can importantly be modified and controlled by the electric field strength and direction. By considering the variation of the energy differences, it should point out that by varying electric field we can obtain a blue or red shift in the intersubband optical transitions. The modulation of the absorption coefficients and the refractive index changes which can be suitable for good performance optical modulators and various infrared optical device applications can be easy obtained by tuning applied electric field strength and direction.     

Magnetic anticrossing of 1D subbands in ballistic double quantum wires

We study the low-temperature in-plane magnetoconductance of vertically coupled double quantum wires. Using a novel flip-chip technique, the wires are defined by two pairs of mutually aligned split gates on opposite sides of a  ≤ 1 micron thick AlGaAs/GaAs double quantum well heterostructure. We observe quantized conductance steps due to each quantum well and demonstrate independent control of each 1D wire. A broad dip in the magnetoconductance at  ∼ 6 T is observed when a magnetic field is applied perpendicular to both the current and growth directions. This conductance dip is observed only when 1D subbands are populated in both the top and bottom constrictions. This data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.     

Ring interferometer on the basis of 2D electron gas in a double quantum well

Magnetotransport properties of submicron rings fabricated on the basis of 2D electron gas in a GaAs double quantum well are studied. It is shown that, in such interferometers, the Aharonov-Bohm effect is caused by coherent processes in two weakly coupled rings, which have different widths of electron channels. In these interferometers, a phase inversion of h/e oscillations is observed under the action of the parallel component of a tilted magnetic field. This phenomenon is qualitatively explained by a redistribution of charge carriers in the two rings.     

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.     

Dynamics of electron in a surface quantum well

This paper studies the quantum dynamics of electrons in a surface quantum well in the time domain with autocorrelation of wave packet. The evolution of the wave packet for different manifold eigenstates with finite and infinite lifetimes is investigated analytically. It is found that the quantum coherence and evolution of the surface electronic wave packet can be controlled by the laser central energy and electric field. The results show that the finite lifetime of excited states expedites the dephasing of the coherent electronic wave packet significantly. The correspondence between classical and quantum mechanics is shown explicitly in the system.     

Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated,and expressions for the electronic states are presented.The system is modeled by considering T = 0 K and also with a single parabolic conduction band,which is split into a subband system due to the confinement.The gain and differential cross-section for an electron Raman scattering process are obtained.In addition,the emission spectra for several scattering configurations are discussed,and interpretations of the singularities found in the spectra are given.The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.     

Transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure

The transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure is reported. The transient process of the system, which is induced by the external coherent coupling field, shows the property of no inverse gain. We find that the transient behavior of the probe field can be tuned by the change of tunneling barrier. Both the amplitude of the transient gain and the frequency of the oscillation can be affected by the lifetime broadening.     

Ac response of a coupled double quantum dot

The effect of phase-breaking process on the ac response of a coupled double quantum dot is studied in this paper based on the nonequilibrium Green function formalism. A general expression is derived for the ac current in the presence of electron--phonon interaction. The ac conductance is numerically computed and the results are compared with those in [Anatram M P and Datta S 1995 Phys. Rev. B 51 7632]. Our results reveal that the inter-dot electron tunnelling interplays with that between dots and electron reservoirs, and contributes prominently to the ac current when inter-dot tunnelling coupling is much larger than the tunnelling coupling between dots and electron reservoirs. In addition, the phase-breaking process is found to have a significant effect on the ac transport through the coupled double dot.     

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.     

Tilted magnetic field effect on the subbands of a GaAlAs diode with a GaAs quantum well

We have calculated the subbands in the GaAs quantum well at the n-side of the junction in a Ga_1−xAl_xAs diode. We show that the density of carriers confined in the quantum well increases by the increasing magnetic field strength but also decreases depending on the magnetic length. We have observed oscillatory behavior of the density of carriers due to the in-plane magnetic field.     

Controllable electron dynamics in a finite-size quantum well lattice

The nonstationary electron dynamics in a quantum well lattice is considered. We investigate the influence of quasi-constant electric field applied to the system in addition to variable electric field periodic in time. It is shown that various types of controllable motion of an electron density in the lattice can be realized.     

Electric field induced non-linear multisubband electron mobility in V-shaped asymmetric double quantum well structure

ABSTRACT

We study the effect of the external electric field F_ext on the low-temperature electron mobility μ in an asymmetrically doped Al_xGa_1-xAs based V-shaped double quantum well (VDQW) structure. We show that nonlinearity of µ occurs under double subband occupancy on account of intersubband effects. The field F_ext alters the VDQW potential leading to transfer of subband wave functions between the wells, which affects the scattering potentials and hence μ. In the VDQW structure, due to the alloy channel layer, the alloy disorder (Al-) scattering happens to be significant along with the ionised impurity (Imp-) scattering. The non-linear behaviour of μ is because of μ^Imp, while the overall magnitude of μ is mostly due to μ^Al. The increase of difference in the doping concentrations of the outer barriers increases the nonlinearity of μ. The oscillatory character of μ is amended by varying the width of the well and barrier and also the height of the VDQW. Our results can be used to study VDQW based nanoscale field effect transistor structures.     

周期耦合量子阱中的输运问题

采用Gurvitz等人直接求解薛定谔方程的方法并结合数值计算,分析了驱动频率对周期耦合量子阱体系的电流的影响.结果表明：当驱动频率小于耦合量子阱间的能级差时,随着驱动频率的增大,系统平衡时的电流增加,当驱动频率大于耦合量子阱间能级差时,随着驱动频率的增大,平衡时的电流减小.这样,通过控制外场驱动频率来达到控制电流的目的. 关键词： 量子阱 驱动频率 电流