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We have investigated the electron spin dynamics on the discrete energy levels of self-organized InAs quantum dots (QDs) covered by the thin InGaAs layer and embedded in the GaAs matrix. The InGaAs layer forms the external quantum well (QW). In particular, we report on the electron mean spin redistribution over the QD and QW energy spectrum resulting in a drastic increase of electron spin polarization of the QD excited levels and the QW ground state. The electron polarization is determined by measuring the degree of circular polarization of the QD and QW emissions after excitation by 1.5 ps circular polarized pulses in the GaAs barrier.

Extremely long electron spin memory times in GaAs are reported. It was established by the optical orientation method that the spin relaxation time of electrons localized at shallow donors in n-type gallium arsenide (N d −N A ≈1014 cm−3) is 290±30 ns at a temperature of 4.2 K. The exchange interaction of quasi-free electrons and electrons at donors suppresses the main spin-loss channel for electrons localized at donors—spin relaxation due to the hyperfine interaction with lattice nuclei.

The magnetic field effect on the spectrum of excitons associated with various minibands in superlattices was studied by resonance Raman spectroscopy. It was found that the intensity of Raman scattering by acoustic phonons with the participation of the ground state of an exciton associated with the second miniband is sharply reduced even in weak magnetic fields if its velocity vector is orthogonal to the external magnetic field. This phenomenon was explained by the ionization of the exciton in the electric filed arising in the system of coordinate associated with the exciton moving perpendicular to the external magnetic field.

Magnetic interaction between spin-polarized nuclei and optically oriented excitons in a self-organized ensemble of size-quantized InP islands in an InGaP matrix has been studied in a magnetic field in Faraday geometry. The effective magnetic fields generated by polarized nuclei at excitons have been measured. The strengths of these fields were found to be different for active and inactive excitons because of the difference between the excitonic g factors. The heavy-hole g factor has been determined. The active and inactive excitonic states were found to be coupled through cross-relaxation.

The energy and momentum relaxation of hot electrons in n-type GaAs/AlAs quantum wells is studied. Hot photoluminescence due to the recombination of hot electrons with holes bound on Si acceptors is observed in structures with a high level of doping with silicon. Using the method of magnetic depolarization of hot photoluminescence, the probability of scattering of hot electrons is found to decrease substantially with increasing temperature in the range 4–80 K. This effect is shown to be due to the ionization of donors. It is established that the probability of inelastic scattering by neutral donors is several times greater than the probability of quasielastic electron-electron scattering.

A study is reported of the anisotropy in magnetic-field-induced linear polarization in (001) CdTe/Cd1−xMnxTe quantum wells. The observed limiting anisotropy is shown to be due to the low C2v symmetry of the quantum well. The relations obtained for the C2v point group are in a good agreement with experiment. Considered on the microscopic scale, the effect is associated with the heavy-hole g-factor anisotropy in the well plane.

A short review is presented of the erbium-ion excitation mechanisms in crystalline and amorphous silicon and of the processes governing thermal quenching of erbium luminescence in these materials, which draws both from the studies carried out by the present authors and from available literature data.

A study of the electroluminescence of erbium-doped, amorphous hydrogenated silicon, a-Si:H 〈Er〉, is reported. It has been found that the electroluminescence intensity at the wavelength λ=1.54 µm corresponding to the 4I13/2→4I15/2 intra-4f shell transition in Er passes through a maximum near room temperature. The unusual temperature and field dependences of the electroluminescence indicate electric-field induced multi-phonon tunneling emission of electrons from deep centers. The electroluminescence of Er3+ ions is due to their becoming excited as conduction-band electrons are captured by neutral dangling bonds (D0 centers), which form when erbium is incorporated into the amorphous matrix. This Auger process transforms the center from its neutral state, D0, to a negatively charged state, D−, and the energy released in the capture is transferred by Coulomb interaction into the erbium-ion 4f shell. The steady-state current through the electroluminescent structure is supported by the reverse process of multi-phonon tunneling-electron emission from the D− center to the conduction band. The proposed theoretical model is in a good agreement with experimental data.

Dynamic polarization of 31P nuclei is observed in a self-organized system of InP islands grown by metalorganic-hydride epitaxy in an InGaP matrix. The polarized nuclei produce an effective magnetic field which acts on the polarization of the excitonic radiation. Optical detection of the magnetic resonance signal from 31P nuclei in the crystal lattice of nanosize InP islands is successfully carried out.

Spin splitting of optically active and inactive excitons in nanosized n-InP/InGaP islands has been revealed. Optically inactive states become manifest in polarized-luminescence spectra as a result of excitons being bound to neutral donors (or of the formation of the trion, a negatively charged exciton) in InP islands. The exchange-splitting energies of the optically active and inactive states have been determined.

Optical orientation and alignment of excitons in InAlAs quantum dots in the AlGaAs matrix have been studied both theoretically and experimentally. Experiments performed in a longitudinal magnetic field (Faraday geometry) reveal transformation of optical orientation to alignment and alignment to orientation, which is caused by exchange splitting of the dipole-active exciton doublet and allowed by the quantum-dot low symmetry. A comparison of theory with experiment made with inclusion of the anisotropy of exciton generation and recombination along the \([1\bar 10]\) and [110] axes permits one to determine the character of dipole distribution in direction for resonant optical transitions in the self-organized quantum-dot ensemble studied.

We report the development of a method for recording the low-temperature (T=6 K) near-IR inelastic light scattering spectra and the observation of electronic scattering on the transitions 1s 3/2(Γ8) → 2s 3/2(Γ8) between the ground and excited states of different shallow acceptor centers in a n-type semi-insulating crystal si-GaAs (n=1.0 × 108 cm−3) and in a doped p-InP crystal (p=3.6×1017 cm−3). Moreover, a new line, associated with the transition 1s 3/2(Γ 8) → 2p 3/2(Γ8) and due to a dielectric local mode, recorded for the first time in the spectra of narrow-gap semiconductors, was found in the residual-frequency band in the p-InP spectrum between TO(Γ) and LO (Γ) phonons.

We report on an investigation of the exchange-interaction-induced fine structure of localized excitons in single quantum wells (SQW) CdTe CdMgTe by means of polarized luminescence. The polarization anomalies due to crossing of the Zeeman-split sublevels of optically active and inactive states have been detected. Magnitude of the splittings of localized excitons due to the isotropic exchange has been determined. When studying the optical orientation of excitons in QWs we have observed an increase of the circular-polarization degree in a longitudinal magnetic field. The mechanism responsible for this behavior is suggested to involve lowering of the ideal D2d symmetry of QW leading to the splitting of optically active states.

Er-doped GaAs/AlGaAs structures were grown by the molecular beam epitaxy technique with concentrations of Er in the range 1017–2×1019 cm−3. Photoluminescence (PL) of Er3+ ions and Er-induced defects was studied at liquid helium and higher temperatures. A strong diffusion of erbium and interdiffusion of gallium and aluminum ions are observed [at the boundary of GaAs/AlGaAs quantum wells (QWs)] which leads at high erbium concentrations to degradation of the QW’s and macroscopic (average) leveling of erbium and aluminum concentrations over the whole semiconductor structure. From high-resolution PL spectra the existence of three types of Er centers is deduced, which differ by positions of fine structure lines, PL lifetimes, and temperature dependence. The results indicate that these centers are accompanied by the appearance of three types of carrier traps with binding energies of 20, 50, and about 400 meV, respectively. The experiments show evidence that carriers captured into these traps control the Auger ex...

The experimental results of a study of the fine structure of the levels of excitons localized in InAlAs quantum dots in an AlGaAs matrix are reported. Transformations from optical orientation to alignment and from alignment to orientation, which occur due to the exchange splitting of a dipole-active excitonic doublet and are allowed by the low symmetry of a quantum dot, are observed in a longitudinal magnetic field (Faraday geometry). A comparison of theory with experiment for a self-organized ensemble of quantum dots enables a determination of the character of the distribution over the dipole orientations for resonance optical transitions.

The observation of optical orientation of excitons and the Hanle effect in an asymmetric CdTe/CdMnTe double quantum well is reported. The characteristics of the magnetic depolarization of radiation from CdTe/CdMnTe quantum wells are discussed.

Polarized photoluminescence of Cd1−xMnxTe crystals in a weak magnetic field has been studied in Faraday and Voigt geometries. A simple method is proposed to determine the exciton mobility edge and excitonic magnetic-polaron energy. “Forbidden” polarization components of the recombination radiation have been experimentally detected. It has been established that the moments of magnetic polarons are oriented predominantly along the {111} axes.

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.

We report a large and unexpected suppression of the free electron spin relaxation in lightly-doped n-GaAs bulk crystals. The spin relaxation rate shows weak mobility dependence and saturates at a level 30 times less then that predicted by the Dyakonov-Perel theory. The dynamics of the spin-orbit field differs substantially from the usual scheme: although all the experimental data can be self-consistently interpreted as a precessional spin relaxation induced by a random spin-orbit field, the correlation time of this random field, surprisingly, is much shorter than, and is independent of, the momentum relaxation time determined from transport measurements. Understanding of this phenomenon could lead to high temperature engineering of the electron spin memory.

We report on the optical orientation of negatively charged excitons (trions) in [001] ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum wells (QW's). The spin orientation of equilibrium electrons reveals itself in the polarized luminescence of both excitons and trions. The Hanle effect of the trions differs substantially from that of the neutral excitons. It is found experimentally that the electron-spin-relaxation time in a 14-nm QW exceeds 10 ns at $T=4.2\mathrm{K}.$

Low-temperature electron-spin relaxation is studied by the optical orientation method in bulk n-GaAs with donor concentrations from ${10}^{14}{\mathrm{cm}}^{\ensuremath{-}3}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{17}{\mathrm{cm}}^{\ensuremath{-}3}.$ A peculiarity related to the metal-to-insulator transition is observed in the dependence of the spin lifetime on doping near ${n}_{D}=2\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{cm}}^{\ensuremath{-}3}.$ In the metallic phase, spin relaxation is governed by the Dyakonov-Perel mechanism, while in the insulator phase it is due to anisotropic exchange interaction and hyperfine interaction

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.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the optical manipulation of the electron spin relaxation time in a GaAs based heterostructure. Experimental and theoretical study shows that the average electron spin relaxes through hyperfine interaction with the lattice nuclei, and that the rate can be controlled by the electron-electron interactions. This time has been changed from 300 ns down to 5 ns by variation of the laser frequency. This modification originates in the optically induced depletion of n-GaAs layer.

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.

Erbium was introduce into GaAs/AlGaAs quantum well structures in the process of growth by MBE in an attempt to enhance semiconductor-Er transfer by means of a resonance between quantum well and Er ion transitions. Instead the quantum well was washed out by efficient interdiffusion of Ga and Al and diffusion of Er. We have demonstrated also that erbium interacts with aluminum in arsenides; this interaction leads to the formation of Er-containing Al- enriched clusters.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electroluminescence (EL) of photodiodes fabricated from erbium-implanted silicon is studied at direct bias of p-n junction. A correlation between the intensities of EL of free excitons and erbium ions is found in dependence on pumping current. A model of f-shell excitation of optically active erbium ions is proposed basing on the assumption that the excitation of erbium ions occurs via capture of free excitons on neutral donor formed by erbium-oxygen complex with a subsequent auger-excitation of f-shell of erbium ion during recombination of a bound exciton. The model proposed permits us to described the experimental results.

Photoluminescence of erbium-doped hydrogenated amorphous silicon was observed and compared with that of crystalline erbium-doped silicon. It is shown that a-Si:H:Er exhibits efficient room-temperature photoluminescence at 1.537 micrometer which is as strong as the emission from optimized c-Si:Er at 2 K. Practically no temperature quenching of the emission intensity in the range 2 - 300 K is observed. Saturation of erbium luminescence on increase of excitation level occurs at higher intensities of pumping beam than in c-Si:Er indicating shorter radiation lifetime of erbium ions.

Energy relaxation of hot electrons by electron-phonon interaction in 2D structures has received much attention in recent years. Not only the confinement of electrons but also the modification of the phonon spectrum, the appearance of the confined and the interface phonons is of great importance in these structures.

In earlier work we have observed the optical alignment of 2D-electrons in quantum-well structures, which results in the polarization of hot photoluminescence (HPL) [1]. It was emphasized that the peculiarity of the 2D-motion of electrons manifested itself in the strong dependence of the degree of HPL polarization ρ on the energy of the 2D-motion (such a dependence did not exist in the 3D case). Taking into account the quantum confinement of electrons (but not holes) and ignoring the valence band warping, we have obtained an approximate equation which describes the energy dependence of ρ: $$ \rho = \frac{{{{({{{{E_o}}} \left/ {{{E_1}}} \right.})}^2}}}{{8(1 + {{{{E_o}}} \left/ {{{E_1}}} \right.}) + 2{{({{{{E_o}}} \left/ {{{E_1}}} \right.})}^2}}} $$ (1) where Eo is the kinetic energy of the 2D-motion (x,y) of electrons at the point of photocreation and E1 is the confinement energy. In deriving Eq. (1) the z-component of the momentum was put equal to pz = (2mE1)1/2.

The circularly polarized recombination radiation produced by optically oriented electrons in GaAs and viewed in the direction of and opposite to the pump light propagation was found to have opposite signs of polarization. The excitation was effected by photons of energy E h ν ∪ E g + Δ through a transparent AlGaAs win- dow. The opposite signs of circular polarization and its complex dependence on the luminescence wavelength are accounted for by the influence of the space charge field created by the depleted layer near the interface. © 2005 Pleiades Publishing, Inc.

A linear polarization of the recombination luminescence of photoexcited hot electrons in a multiple quantum well structure has been observed. The peculiarity of electron 2D-motion manifests itself in an observed increase of the polarization with 2D-motion energy. The time of optical-phonon emission by a 2D electron is determined by measuring a magnetic depolarization of the luminescence.

Experimental and theoretical research on the recombination photoluminescence of free hot electrons in semiconductors (primarily GaAs) is reviewed. The polarization characteristics are discussed. These characteristics reflect, in particular, a momentum alignment of the electrons by linearly polarized light and an effect of a ripple in the constant-energy surfaces in the valence band. The dependence of the linear polarization on the spectrum is discussed in connection with various mechanisms for the energy relaxation of the hot electrons. The depolarization of the hot-electron photoluminescence in a magnetic field is discussed. A procedure is discussed for determining the energy relaxation times and the scale times for intervalley transitions through an analysis of depolarization curves. The energy distribution of the hot electrons is found from the hot-electron photoluminescence spectrum. The recombination luminescence of hot holes is discussed. These holes appear when the semiconductor is illuminated in the spin-split-off subband.

An investigation was made of the optical properties of vanadium oxide films which might be used for repeated recording of optical data. The dependences of the diffraction efficiency on the degree of oxidation and thickness of a vanadium film were determined. The nature of holograms recorded in vanadium oxide films was analyzed and optimization of the characteristics of these films was found to be possible. A diffraction efficiency of 1.4% was obtained at lambda=0.63 ..mu... By way of illustration, vanadium oxide films were used in holographic interferometry in the infrared range.

We have studied electron spin dynamics in self-organized InAs/GaAs quantum dots (QD's) by time-resolved photoluminescence (PL). The electron polarization of the QD discrete energy levels is determined from the circular polarization of the QD emission. When the GaAs barrier is optically pumped, a transient increase of the QD excited-state PL polarization is observed. This effect results from the spin dependence of electron energy relaxation as a consequence of the Pauli exclusion principle. A theoretical model qualitatively describing the experimental results is developed.