Yu. P. Efimov

Nontrivial relaxation dynamics of excitons in high-quality InGaAs/GaAs quantum wells

Photoluminescence and reflectivity spectra of a high-quality InGaAs/GaAs quantum well structure reveal a series of ultranarrow peaks attributed to the quantum confined exciton states. The intensity of these peaks decreases as a function of temperature, while the linewidths demonstrate a complex and peculiar behavior. At low pumping the widths of all peaks remain quite narrow

Radiative decay rate of excitons in square quantum wells: Microscopic modeling and experiment

(l0.1\phantom{\rule{0.28em}{0ex}}\mathrm{meV})

Interference of polariton waves in structures with wide GaAs/AlGaAs quantum wells

in the whole temperature range studied, 4\char21{}30 K. At the stronger pumping, the linewidth first increases and then drops down with the temperature rise. Pump-probe experiments show two characteristic time scales in the exciton decay,

Increasing of AlGaAs/GaAs quantum well robustness to resonant excitation by lowering Al concentration in barriers

l10\phantom{\rule{0.28em}{0ex}}\mathrm{ps}

Enhancement of the longitudinal magnetic moment of the exciton due to its motion

and 15\char21{}45 ns, respectively. We interpret all these data by an interplay between the exciton recombination within the light cone, the exciton relaxation from a nonradiative reservoir to the light cone, and the thermal dissociation of the nonradiative excitons. The broadening of the low energy exciton lines is governed by the radiative recombination and scattering with reservoir excitons, while for the higher energy states the linewidths are also dependent on the acoustic phonon relaxation processes.

Ion-beam-assisted spatial modulation of inhomogeneous broadening of a quantum well resonance: excitonic diffraction grating.

The binding energy and the corresponding wave function of excitons in GaAs-based finite square quantum wells (QWs) are calculated by the direct numerical solution of the three-dimensional Schrodinger equation. The precise results for the lowest exciton state are obtained by the Hamiltonian discretization using the high-order finite-difference scheme. The microscopic calculations are compared with the results obtained by the standard variational approach. The exciton binding energies found by two methods coincide within 0.1 meV for the wide range of QW widths. The radiative decay rate is calculated for QWs of various widths using the exciton wave functions obtained by direct and variational methods. The radiative decay rates are confronted with the experimental data measured for high-quality GaAs/AlGaAs and InGaAs/GaAs QW heterostructures grown by molecular beam epitaxy. The calculated and measured values are in good agreement, though slight differences with earlier calculations of the radiative decay rate...

Multiple-frequency quantum beats of quantum confined exciton states

The optical reflection spectra of semiconductor GaAs/AlGaAs structures with wide quantum wells are studied experimentally. A theoretical analysis of the spectra is performed in terms of the exciton-polariton model in the approximation of quantum confinement of the exciton center of mass with regard to the contributions of both heavy and light excitons to the crystal polarization. The applicability range of the theory of the center-of-mass confinement for GaAs/AlGaAs heterostructures is estimated. It is established that, for quantum wells more than 180 nm wide, the interference effects observed in the reflection spectra of polariton waves are reproduced, to a good accuracy, by theoretical calculations based on the quantum confinement of the exciton center of mass. For quantum-well widths less than 150 nm, the experimental results are described better by the model of quantum confinement of electrons and holes.

Experimental determination of dead layer thickness for excitons in a wide GaAs/AlGaAs quantum well

The robustness of AlGaAs/GaAs quantum well to strong resonant excitation is studied. It was found that lowering Al concentration in barriers to 3% does not influence the measured radiative linewidth of exciton resonance in the sample at low intensities. At the same time parasitic broadening of the resonance by an additional resonant illumination is strongly suppressed as compared to the quantum well with 30% of Al in barriers.

Investigation of the mechanisms of exciton coherence relaxation in single GaAs/AlGaAs quantum wells by the methods of excitonic induction

A new physical phenomenon has been found, namely a giant enhancement of the exciton magnetic moment due to its motion. This phenomenon was observed in GaAs, CdTe and ZnSe based quantum wells with QW widths much larger than the exciton Bohr radius. Consequently, it is relevant to any crystal with zinc blende structure.

Temperature-induced delocalization of excitations in GaAs/AlAs type-II superlattices

We propose a method of spatial modulation of inhomogeneous broadening of a quantum-well excitonic resonance based on local generation of defects produced by a focused ion beam. The method is applied to fabrication of excitonic diffraction grating in a single quantum-well InGaAs/GaAs structure by irradiating the sample with a beam of 35-keV He+ ions of exposure doses <1012  cm-2. The spectrum of resonant diffraction on such a structure is narrower than that of reflectivity and decreases much faster with increasing temperature. A proposed model of formation of the diffractive response based on the single scattering approximation well describes the results of the spectral and temperature measurements.