F. T. Vasko

Intersubband gain in a biased superlattice

Intersubband transitions in a superlattice under homogeneous electric field is studied within the tight-binding approximation. Since the levels are equi-populated, the non-zero response appears beyond the Born approximation. Calculations are performed in the resonant approximation with scattering processes exactly taken into account. The absorption coefficient is equal zero for the resonant excitation while a negative absorption (gain without inversion) takes place below the resonance. A detectable gain in the THz spectral region is obtained for the low-doped

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

GaAs

Temporal stimulated intersubband emission of photoexcited electrons

-based superlattice and spectral dependencies are analyzed taking into account the interplay between homogeneous and inhomogeneous mechanisms of broadening.

Spin-dependent Rabi oscillations in single quantum dots

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

Negative lateral conductivity of hot electrons in a biased superlattice

We have studied the transient evolution of electrons distributed over two levels in a wide quantum well, with the two levels below the optical phonon energy, after an ultrafast interband excitation and cascade emission of optical phonons. If electrons are distributed near the top of the passive region, a temporal negative absorption appears to be dominant in the intersubband response. This is due to the effective broadening of the upper level state under the optical phonon emission. We have then considered the amplification of the ground mode in a THz waveguide with a multiquantum well placed at the center of the cavity. A huge increase of the probe signal is obtained, which permits the temporal stimulated emission regime of the photoexcited electrons in the THz spectral region.

Transient quantum evolution of two-dimensional electrons under photoexcitation of a deep center

Ultrafast optical pump of exciton resonance in single quantum dot by an elliptically polarized laser pulse is described by the non-Markov balance equations. Population and spin dynamics are investigated and spin-dependent Rabi oscillations are considered for the case of a flat quantum dot, with the lateral size greater than the height. The following peculiarities of temporal evolution have been found: a) a beating of Rabi oscillations under an elliptically polarized pump and b) quenching of spin orientation due to a spin-orbit splitting effect.

Inhomogeneous broadening of the intersubband transitions in nonideal quantum wells

Nonequilibrium electron distribution in a superlattice subjected to a homogeneous electric field (biased superlattice with equipopulated levels) is studied within the tight-binding approximation, taking into account the scattering by optical and acoustic phonons and by lateral disorder. It is found that the distribution versus the in-plane kinetic energy depends essentially on the ratio between the Bloch energy,

Level anticrossing effect on electron properties of coupled quantum wells under an in-plane magnetic field

{\ensuremath{\epsilon}}_{B}

Modulation of intersubband infrared absorption under intense terahertz irradiation

, and the optical phonon energy,

RESONANT TERAHERTZ EXCITATION OF TUNNEL-COUPLED QUANTUM WELLS : NONLINEAR ABSORPTION AND PHOTOVOLTAGE

\ensuremath{\hbar}{\ensuremath{\omega}}_{0}