The effects of the compressive stress on the binding energy and the density of shallow-donor impurity states in symmetrical GaAs/Al x Ga 1Ϫx As double quantum wells are calculated using a variational procedure within the effective-mass approximation. Results are for different well and barrier widths, shallow-donor impurity position, and compressive stress along the growth direction of the structure. We have found that independently of the well and barrier widths, for stress values up to 13.5 kbar ͑in the direct-gap regime͒ the binding energy increases linearly with the stress. For stress values greater than 13.5 kbar ͑indirect gap regime͒ and for impurities at the center of the wells, the binding energy increases up to a maximum and then decreases. For all impurity positions the binding energy shows a nonlinear behavior in the indirect gap regime due to the ⌫-X crossing effect. The density of impurity states is calculated for a homogeneous distribution of donor impurities within the barriers and the wells of the low-dimensional heterostructures. We have found that there are three special structures in the density of impurity states: one associated with on-center-barrier-, the second one associated with on-center-well-, and the third one corresponding to on-external-edge-well-impurity positions. The three structures in the density of impurity states must be observed in valence-to-donor-related absorption and conduction-to-donor-related photoluminescence spectra, and consequently these peaks can be tuned at specific energies and convert the system in a stress detector.

The effects of hydrostatic pressure and aluminum concentration on the conduction-electron effective Landé g factor in semiconductor GaAs-Ga 1−x Al x As quantum wells under in-plane magnetic fields are presented. Numerical calculations of the conduction-electron Landé g factor are performed by taking into account the nonparabolicity and anisotropy of the conduction band via the Ogg-McCombe Hamiltonian as well as the effects of aluminum concentration and applied hydrostatic pressure. Theoretical results are given as functions of the aluminum concentration in the Ga 1−x Al x As barrier, orbit-center position, applied in-plane magnetic field, hydrostatic pressure, and quantum-well width, and found in good agreement with experimental measurements in GaAs-Ga 1−x Al x As quantum wells for various values of the aluminum concentration x in the absence of hydrostatic pressure.

We study the properties of plasmon polaritons in one-dimensional photonic metamaterial superlattices resulting from the periodic repetition of a Fibonacci structure. We assume the system made up of positive refraction and metamaterial layers. A Drude-type dispersive response for both the dielectric permittivity and magnetic permeability of the left-handed material is considered. Maxwell's equations are solved for oblique incidence by using the transfer-matrix formalism. Our results show that the plasmon-polariton modes are considerably affected by the increasing of the Fibonacci-sequence order of the elementary cell. The loss of the long-range spatial coherence of the electromagnetic field along the growth direction, which is due to the quasiperiodicity of the elementary cell, leads to the splitting of the plasmon-polariton frequencies, resulting in a Cantor-type frequency spectra. Moreover, the calculated photonic dispersion indicates that if the plasma frequency is chosen within the photonic ͗n͑͒͘ = 0 gap then the plasmon-polariton modes behave essentially as pure plasmon modes.

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Absorption effects on plasmon-polariton excitations in quasiperiodic (Fibonacci and Thue-Morse) one-dimensional stacks composed of layers of right- and left-handed materials are theoretically investigated. A Drude-type dispersive response for both the dielectric permittivity and magnetic permeability of the left-handed layer is considered. Maxwell's equations are solved for oblique incidence by using the transfer matrix formalism, and the reflection coefficient as a function of the frequency and incidence angle is obtained. The Fibonacci (or Thue-Morse) quasiperiodic structure leads to a Cantor-like photonic spectra for the plasmon-polariton modes. Moreover, results for the photonic band structure, density of states and reflection coefficient indicate that plasmon-polariton modes are robust in the presence of low and moderate levels of absorption.

The effects of hydrostatic pressure on the correlated e h -transition energies in single GaAs -Ga 1 x -Al x As quantum wells are calculated via a variational procedure, in the framework of the effective-mass and nondegenerate parabolic-band approximations. The valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. Both heavy-and light-hole exciton energies are obtained, and correlated e h -transition energies are found in good agreement with available experimental measurements.

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Direct and indirect excitons in GaAs-Ga 1−x Al x As coupled double quantum wells, under growth-direction applied electric and magnetic fields, have been theoretically investigated within a variational procedure in the effective-mass and parabolic-band approximations. The exciton hydrogenic 1s-like envelope wave function is obtained through a variational procedure and an appropriate expansion in trigonometric functions of the electron and hole wave functions. The applied electric field produces a polarization of the exciton by pushing the electron and hole away from each other, whereas the magnetic field contracts the exciton by pushing the electron and hole closer to each other. Intersubband mixing produced by the Coulomb interaction of electronhole pairs is taken into account and a detailed analysis of the properties of direct-and indirect-exciton states in GaAs-Ga 1−x Al x As coupled double quantum wells is presented, with theoretical results in good agreement with available experimental measurements.Coupled double GaAs-Ga 1−x Al x As quantum well ͑CDQW͒ structures under applied electric, magnetic, and stress fields have attracted much attention recently. Some examples of phenomena studied on these systems are the excitonic Bose-Einstein condensation, two dimensional ͑2D͒ electron gas properties, optical absorption, reflection and photoluminescence ͑PL͒ of direct and indirect excitons, donors and acceptors, properties of charged excitons, transition between exciton and 2D electron gas or magnetoexciton regimes, exciton trapping, quantum Stark effect, magnetoexciton dispersion relations, electron-phonon interaction, electron transport, etc. The wide range of applications also attracts a great interest in spintronics, data storage, electronic and optoelectronic devices, lasers, and terahertz detectors. [1][2][3] When an electric field is applied along the growth direction of a symmetrical thin-barrier GaAs-Ga 1−x Al x As doubled quantum well ͑DQW͒, the exciton energy decreases as the field increases and the ground-state exciton may be formed with the electron and hole in different wells, i.e., the exciton ground state may change from a direct-exciton to an indirectexciton state. On the other hand, if a magnetic field is applied along the growth direction of a GaAs-Ga 1−x Al x As quantum well ͑QW͒, an increase in exciton binding energy is found as the magnitude of the magnetic field increases, due to the shrinking of the exciton wave function. The anticrossing between the ground and first-excited exciton states in GaAs-Ga 1−x Al x As CDQWs has been thoroughly studied experimentally. [1][2][3][4] The simultaneous application of an electric field in the growth direction and a magnetic field parallel to the interfaces of the CDQW produces strong changes in the PL spectra and kinetics of the indirect ͑interwell͒ excitons due to the magnetic field induced displacement of the indirect exciton dispersion in momentum space 3,4 which may be used to increase the exciton lifetime. In a recent theoretical work, de Dios-Leyva ...