A. V. Koudinov

Exciton spin decay modified by strong electron-hole exchange interaction

We study exciton spin decay in the regime of strong electron-hole exchange interaction, which occurs in a wide variety of semiconductor nanostructures. In this regime the electron spin precession is restricted within a sector formed by the external magnetic field and the effective exchange fields triggered by random spin flips of the hole. Using Hanle effect measurements, we demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te quantum wells. We present calculations that provide a consistent description of the experimental results, which is supported by independent measurements of the parameters entering the model.

Optical orientation of excitons in quantum wells with semimagnetic barriers

Abstract Optical orientation of excitons in quantum wells CdTe CdMnTe has been observed in a steady-state regime. The luminescence polarization arising due to optical orientation of exciton angular momenta under optical pumping has been studied as a function of excitation quantum energy and transverse magnetic field. The magnetic depolarization of exciton radiation has been qualitatively understood by separate decay of electron and hole angular momenta taking into account the magnetic field induced mixing of involved states. The observation of luminescence linear polarization confirms this interpretation.

Linear polarization of the photoluminescence of quantum wells subject to in-plane magnetic fields

The degree and orientation of the magnetic-field induced linear polarization of the photoluminescence from a wide range of heterostructures containing (Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a function of detection photon energy, applied magnetic field strength and orientation in the quantum well plane. A theoretical description of this effect in terms of an in-plane deformation acting on the valence band states is presented and is verified by comparison with the experimental data. We attempted to identify clues to the microscopic origin of the valence band spin anisotropy and to the mechanisms which actually determine the linear polarization of the PL in the quantum wells subject to the in-plane magnetic field. The conclusions of the present paper apply in full measure to non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain anisotropy.

Two-step versus one-step model of the interpolarization conversion and statistics of CdSe/ZnSe quantum dot elongations

The magneto-optical interpolarization conversions by a layer of quantum dots have been investigated. Various types of polarization response of the sample were observed as a function of external magnetic field and of the orientation of the sample. The full set of experimental dependences is analyzed in terms of a one-step and a two-step model of spin evolution. The angular distribution of the quantum dots over the directions of elongation in the plane of the sample is taken into account in terms of the two models, and the model predictions are compared with experimental observations.

Modulation of Quantum Well Optical Properties by Illumination above the Barrier Bandgap

The spin-flip Raman scattering signals associated with the Mn-2+ 3d(5) electrons in a range of CdTe-based dilute magnetic semiconductor quantum well structures is shown to be sensitive to even very weak above-barrier illumination, as are the quantum-well photoluminescence from exciton and trion recombination and acoustic phonon Raman scattering signals excited in resonance with the quantum well. This surprising degree of sensitivity is discussed in terms of the modulation of the carrier densities in the quantum wells, leading to a modulation of the resonant intermediate state for Raman scattering and, therefore, of the scattering cross section. Depending on the majority intrinsic carrier type in the quantum wells, we show that either enhancing or quenching of the Raman signals can result.

Paulo blockade in spin-flip Raman scattering via donor bound excitons

We have investigated spin-flip Raman scattering by manganese ions in (001-CdTe/CdMnTe quantum wells. The intensity of the SFRS obtained in resonance with the donor bound exciton in the Voigt geometry was found to depend strongly on the orientation of the crystal with respect to the magnetic field: Raman intensities for field parallel to [110] and [110] directions differ by about a factor of 8. The observed phenomenon is interpreted in terms of an electron spin blockade in the D0X complex. The role of double resonance is discussed.

A New Opportunity of Probing Lateral Distortions in Quantum Wells

The in-plane distortions of quantum well structures as revealed by polarised luminescence are studied. It is shown that C2v, distortions induce an extreme anisotropy of the in-plane g factor of quantum confined heavy holes. The anisotropy of the linear polarisation of the photoluminescence turns out to be much less pronounced in structures with a special buffer layer introduced to stop spreading misfit dislocations.