A. Hernández-Cabrera

Coherent response of a biased double-well superlattice subjected to an ultrashort interband excitation

The temporal evolution of electrons in a biased double-well superlattice, subjected to an ultrashort interband excitation, is theoretically examined. Both the temporal oscillations of the induced current and the evolution of the photoexcited electron concentration are considered for different parameters of the structure subjected to a δ-pulse excitation. Due to the mixing of the Wannier–Stark-ladder branches, the induced response depends on the applied bias voltage in a complicated way. In particular, long-time beats appear in the vicinities of intra- and inter-cell anti-crossings of the energy spectrum. These dependencies are examined within the framework of the Kane model, invoking the parabolic approximation for electron and heavy hole states. Numerical calculations of the carrier coherent dynamics are performed for the case of a δ-pulse excitation and with a phenomenologically introduced damping factor.

VALENCE-BAND MIXING EFFECTS ON EXCITON DIPOLE TERAHERTZ EMISSION FROM ASYMMETRIC TRIPLE QUANTUM WELLS

We analyze the influence of band mixing on the dynamics of hole tunneling in asymmetric GaAs–Ga1−xAlxAs triple quantum wells. A combination of the time‐dependent Schrodinger equation and the Luttinger Hamiltonian is used to calculate the terahertz radiation from excitons. When the electric field required for resonance of electrons between the central and right well coincides with the field needed for hole resonance between the central and left well the radiation is strongly increased. If this field coincides with the hole mixing field at k∥≠0, a new modulation of the dipole emission appears, being drastically affected in frequency and amplitude. The calculated effect is greater than previous results for asymmetric double quantum wells.

Quantum tunnelling of electrons through a GaAs-Ga1-xAlxAs superlattice in a transverse magnetic field: an analytical calculation of the transmission coefficient

The transmission coefficient for tunnelling through double barriers and superlattices of GaAs-Ga1-xAlxAs, under transverse-magnetic-field action, has been calculated using a transfer matrix model. In this work, the one-dimensional effective-mass equation has been first solved analytically by means of the confluent hypergeometric functions as envelope functions

Resonant tunnelling of electrons through parabolic quantum wells: an analytical calculation of the transmission coefficient

The transmission coefficient for tunnelling through a GaAs/GaAlAs parabolic quantum well has been calculated using a transfer matrix model. In this work the one-dimensional effective-mass equation has been first solved analytically by means of confluent hypergeometric functions and airy functions as envelope functions. It is found that barrier width affects significantly the quantum tunnelling current through a parabolic quantum well.

Ultrafast photoexcitation and coherent dynamics of electrons in triple tunnel‐coupled quantum wells

Coherent dynamics of electrons in the triple tunnel‐coupled quantum wells after an ultrafast optical excitation is studied. In a collisionless approximation, we consider temporal evolution of the electron distribution for different parameters of structure and pulse duration. Due to mixing of the tunneling frequencies under the three‐level tunneling resonance condition, transient evolution of the dipole moment demonstrates different kinds of behavior: harmonic oscillations, beats, and nonperiodic oscillations.

Stark effect and excitonic tunneling escape process in semiconductor quantum wells

In this work, we have numerically integrated in space and time the effective mass Schrodinger equation for an exciton in a semiconductor quantum‐well structure. Considering a Coulomb interaction between the electron‐hole pair and an external electric field, we have studied the excitonic tunneling escape process from semiconductor quantum wells. Our method of calculation has been applied to types‐I, ‐II, and ‐III quantum‐well superlattices. In addition, we present the calculated excitonic lifetimes for the GaAs/GaAlAs, InAs/GaSb, and HgTe/HgCdTe systems under an external electric field. In the HgTe/CdTe system, the possibility of having similar electron and hole lifetime values is also found if the applied electric field is large enough.

Electron energy spectrum and density of states for nonsymmetric semiconductor heterostructures in an in-plane magnetic field

Modifications of spin-splitting dispersion relations and density of states for electrons in nonsymmetric heterostructures under in-plane magnetic field are studied within the envelope function formalism. Spin-orbit interactions, caused by both a slow potential and the heterojunction potentials (which are described by the boundary conditions) are taken into account. The interplay between these contributions and the magnetic field contribution to the spin-splitting term in the Hamiltonian is essential when energy amount resulting from the Zeeman and spin-orbit coupling are of the same order. Such modifications of the energy spectra allow us to separate the spin-orbit splitting contributions due to a slow potential and due to the heterojunctions. Numerical estimates for selectively-doped heterojunction and quantum well with narrow-gap region of electron localization are performed. PACS numbers: 72.25.-b, 73.21.-b

Carrier density effects on the exciton binding energy in double quantum well systems

Carrier density effects on the dynamics of an electrically pumped exciton, created by hole-assisted, electron resonant tunneling in an asymmetric coupled quantum well system, has been studied self-consistently. Calculations show that, first, the binding energy and the oscillation period decrease with increasing carrier concentration, the charge oscillation being nonperiodic for sheet densities greater than 5×1010 cm−2 (for the proposed sample). Second, a transition from excitonic to electron–hole plasma states occurs at densities ranging from 5×108 to 2.5×1010 cm−2. As a consequence, the present work shows that many-body effects are necessary to obtain accurate results in calculating tunneling electromagnetic radiation.

Asymmetric doping effects on electronic properties of coupled quantum wells in an in-plane magnetic field

The purpose of this work is to study the influence of asymmetric doping positions on the electronic properties of tunnel-coupled double quantum wells (DQWs) in an in-plane magnetic field. The doping asymmetry introduces peculiarities in the gap due to the anticrossing of the two branches of the electronic dispersion relations. The built-in potential caused by the doping dramatically affects the self-consistent Fermi energy renormalization and strongly opposes an applied bias. As a result, the magnetization shows an abrupt jump when the transition from vertical to horizontal anticrossing occurs. The absolute value of the magnetoinduced voltage of two dimensional electrons in DQWs increases if the Fermi level is localized near such peculiarities and shows additional features in comparison with the symmetric-doping case. We suggest that the transverse voltage induced by a magnetic field and the magnetization are powerful tools for the experimental study of doping characteristics and equilibrium magnetic prop...

Electron‐phonon interaction and tunneling escape process in GaAs/AlAs quantum wells

In this work, we have numerically integrated in space and time the effective mass Schrodinger equation for an electron in a GaAs/AlAs quantum well. Considering the electron–phonon interaction and an external electric field, we have studied the electronic tunneling escape process from semiconductor quantum wells. In this way, electronic lifetimes have been obtained at different well widths and applied electric fields.