Photoluminescence (PL) and reflectivity spectra of a high-quality InGaAs/GaAs quantum well structure reveal a series of ultra-narrow 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 (< 0.1 meV) in the whole temperature range studied, 4 -30 K. At the stronger pumping, the linewidth first increases and than drops down with the temperature rise. Pump-probe experiments show two characteristic time scales in the exciton decay, < 10 ps and 15 -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.

Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [110] and [001] crystallographic directions are extracted demonstrating anisotropy of D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well structures. It is shown that the Rashba spin-orbit splitting is about four times stronger than the Dresselhaus splitting in the studied structure.PACS numbers: 73.21. Fg, 73.63.Hs, 72.25.Rb, 76.60.Jx Spintronics is at present time one of the most important areas of the semiconductor physics for both fundamental research and possible device applications [1]. The main problem of spintronics is creation, registration and lifetime control of carrier spin, especially in lowdimensional systems. Therefore investigation of spin relaxation processes is now an actual problem of the physics of semiconductor heterostructures.The main mechanism of spin relaxation in GaAs based quantum wells (QWs) is the D'yakonov-Perel' kinetic mechanism [2]. It is caused by lack of inversion centrum i) in the bulk semiconductor of which the system is made (bulk inversion asymmetry, or BIA), ii) in the heterostructure (structure inversion asymmetry, or SIA) and iii) in the chemical bonds at heterointerfaces (interface inversion asymmetry, or IIA) [2,3,4]. SIA can be caused by an external electric field or by deformation, BIA and IIA depend strongly on a size of carrier confinement. Therefore spin relaxation times can be controlled by gate voltage or by special heterostructure design.In Ref.[5], anisotropy of spin relaxation has been predicted for heterostructures grown along the axis [001]. It has been theoretically shown that lifetimes of spin oriented along the axes [110], [110] and [001] are different. In particular, changing relation between SIA and BIA one can achieve total suppression of relaxation for spin oriented along one of 110 axes. (IIA in (001)-grown structures is equivalent to BIA, therefore we will use a generalized term 'BIA' for both of them.) Detailed calculations [6,7,8] confirmed that spin relaxation anisotropy exists in real semiconductor heterostructures. Realization of such idea to control spin relaxation times gives new opportunities for spintronics [9]. However experimental discovery of this effect is missed so far.In this Letter, spin relaxation anisotropy in the plane of the QW is observed. In order to demonstrate this effect, the structure has been grown so that SIA and BIA are comparable in efficiency. Note that systems where both SIA and BIA take place have been studied in Refs. [10,11,12,13] but spin relaxation times have not been investigated in such structures.The D'yakonov-Perel' spin relaxation mechanism consists in electron spin precession around an effective magnetic field which is caused by lack of inversion centrum in the system. The corresponding Hamiltonia...

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 Schrödinger 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 are observed.

We report a remarkable enhancement of the magnetic moments of excitons as a result of their motion. This surprising result, which we have observed in magneto-optical studies of three distinct zinc-blende semiconductors, GaAs, CdTe, and ZnSe, becomes significant as the kinetic energy of the exciton becomes comparable with its Rydberg energy and is attributed to motionally induced changes in the internal structure of the exciton. The enhancement of the magnetic moment as a function of the exciton translational wave vector can be represented by a universal equation.