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Reflectivity and modulated photoreflectivity spectra of ZnO and Zn1 – xMgxO epitaxial layers as well as ZnO/Zn1 – xMgxO quantum wells have been studied at normal and oblique light incidence. Comparison of experimental and calculated spectra allowed refinement of certain parameters of excitons in these structures and the order of energy bands in ZnO.

Polariton photoluminescence from cylindrical microcavities was studied under optical excitation below and above a nonlinear regime threshold. Lines of lateral excitonic polaritons quantization were observed in the spectra. In addition to quantization lines with a small orbital quantum number m, exciton-polariton whispering gallery modes with large m > 10 were observed in the cavities of relatively large diameter. In addition to the spectral distribution of the polariton size quantized modes, it was possible to observe their wavefunctions' spatial distribution.

Reflectance and photoluminescence spectra of the ZnO/Zn0.78Mg0.22O structures with ZnO quantum wells and thick ZnO and Zn0.78Mg0.22O layers have been thoroughly investigated at different temperatures and excitation intensities and wavelengths. All the observed spectral lines have been identified. It has been established that the built-in electric field does not affect the spectrum as strongly as was expected. The built-in field is apparently effectively screened by the carriers that have migrated to the bands from donor and acceptor levels. The parameters determining the exciton properties in zinc oxide have been estimated.

Heterostructures of the CdTe/ZnTe type with ultrathin quantum wells are studied. Lines of light and heavy excitons bound to the CdTe layers are observed in the spectra. It is found that the photoluminescence intensity of the light exciton is comparable to the luminescence intensity of the heavy exciton. The temperature shifts of these lines are different, and the lines are intersected at a temperature of 65 K. The estimates of the energy and wave functions of the exciton states have made it possible to clarify parameters of some bands and excitons in such structures.

—Effects implying violation of the Fresnel light reflection laws in semiconductor structures with quantum wells (QWs) have been investigated. This violation is related to the manifestation of spatial dispersion caused by spin–orbit coupling in structures without inversion centers. The spin–orbit coupling constants characterizing polarization conversion in symmetric and asymmetric structures with QWs have been measured.

The optical activity of crystals leads to the occurrence of ellipticity at the reflection of light which is linearly polarized in the interface plane or normally to it. The effect experimentally discovered in the investigated structures with quantum wells is due to a spin-orbit interaction and birefringence. The qualitative dependence of the effect on the change in the orientation of the linear polarization of the incident light has been revealed. A sharp increase in the degree of the polarization conversion in a narrow range of incidence angles for light polarized in the incidence plane has been detected. The latter is due to the influence of the interference of the reflected wave on the structure thickness.

The dependences of the exciton-polariton photoluminescence spectra on the intensity of optical excitation and external magnetic fields are investigated in cylindrical mesas based on high-quality microcavities. It was found that with an increase of the intensity of optical excitation above a certain threshold at sufficiently large magnetic field or with an increase of magnetic fields at constant optical excitation, the distribution of exciton-polaritons over Zeeman sublevels becomes substantially non-Boltzmannian.

International audience; Bulk inversion asymmetry (BIA) of III-V and II-VI semiconductor quantum wells is demonstrated by reflection experiments in magnetic field oriented in the structure plane. The linear in the magnetic field contribution to the reflection coefficients is measured at oblique incidence of s and p polarized light in vicinity of exciton resonances. We demonstrate that this contribution to the reflection is caused by magnetogyrotropy of quantum wells, i.e. by the terms in the optical response which are linear in both the magnetic field strength and light wavevector. Theory of magnetogyrotropic effects in light reflection is developed with account for linear in momentum BIA induced terms in the electron and hole effective Hamiltonians. Theoretical estimates agree with the experimental findings. We have found the electron BIA splitting constant in both GaAs and CdTe based quantum wells is about three times smaller than that for heavy holes.

The photoluminescence spectra of exciton polaritons in microcavities under conditions of three-dimensional quantization are studied as a factor of the density of the optical excitation and magnetic field. The behavior of the degree of circular polarization of the exciton luminescence in a magnetic field shows that, when the concentration of excitons increases, they condense at the lowest Zeeman sublevel.

Heterostructures with atomically thin double quantum wells based on CdTe/ZnTe are investigated by optical spectroscopy (photoluminescence and reflectivity methods) as a function of temperature and density of excitation. Heavy and light exciton luminescence lines are observed with comparable intensities and different temperature behaviors (they cross each other at about 65° K). All these features agree with a complete calculation that takes into account both a very small chemical band offset for such monolayer CdTe inclusions in the ZnTe matrix (namely, 2%), and, consequently, the importance of Coulombic interaction in these double quantum wells.

International audience; Polarization conversion of light reflected from quantum wells governed by both magnetic field and light propagation direction is observed. We demonstrate that the polarization conversion is caused by the magneto-spatial dispersion in quantum wells which manifests itself in the reflection coefficient contribution bilinear in the in-plane components of the magnetic field and the light wavevector. The magneto-spatial dispersion is shown to arise due to structure inversion asymmetry of the quantum wells. The effect is resonantly enhanced in the vicinity of the heavy-hole exciton. We show that microscopically the magneto-spatial dispersion is caused by the mixing of heavy-and light-hole states in the quantum well due to both orbital effect of the magnetic field and the in-plane hole motion. The degree of the structure inversion asymmetry is determined for GaAs/AlGaAs and CdTe quantum wells.

The reflection and photoluminescence excitation spectra under circular polarization of the incident light are measured in wide quantum wells whose width is much larger than the exciton Bohr radius. It is found that, in the absence of a magnetic field, the relation between the intensities of even and odd absorption peaks is reversed upon reversal of the sign of circular polarization.

A new magnetooptical phenomenon referred to as the parity effect is predicted and observed. This effect takes the form of a redistribution of the exciton oscillator strength between spatially even and odd states of the exciton’s center of mass quantization in a wide quantum well.

In this paper we predicted and observed a new magneto-optical effect – the “effect of parity”. The effect is manifest as a redistribution of the oscillator strengths between spatially even and odd center of mass quantized states of the exciton in the quantum well. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

В данной работе мы предсказали и наблюдали новый магнитооптический эффект – «эффект четности». Этот эффект проявлялся как перераспределение силы осциллятора экситона между пространственно четными и нечетными состояниями квантования движения центра масс экситона в квантовой яме.

The photoluminescence spectra of individual quantum dots incorporated into a quantum wire are studied. From the behavior of the spectra in a magnetic field, it is possible to estimate the exciton binding energy in a quantum dot incorporated into a quantum wire. It is found that the exciton photoluminescence signal emitted from a quantum dot along the direction of the nanowire axis is linearly polarized. At the same time, the photoluminescence signal propagating in the direction orthogonal to the nanowire axis is practically unpolarized. The experimentally observed effect is attributed to the nonaxial arrangement of the dot in the wire under conditions of a huge increase in the exciton binding energy due to the effect of the image potential on the exciton.

International audience

The photoluminescence (PL) spectra of semiconductor structures, namely, Al0.3Ga0.7As-based quasi-one-dimensional cylindrical nanowires (nanowhiskers), are measured. The diameter of a typical nanowire is 20–50 nm, and its length was 0.5–1.0 μm. Samples containing one or several GaAs-based quantum dots at the center of the quantum wire are studied. The dot thickness is 2 nm, and the dot diameter is 15–40 nm. Individual nanowhiskers, several nanowhiskers (3–4), and ensembles consisting of many nanowhiskers are studied. The PL spectra are measured for different optical-excitation intensities and in magnetic fields of up to 11 T.

We report on the observation of optical activity of quantum wells resulting in the conversion of the light polarization state controlled by the light propagation direction. The polarization conversion is detected in reflection measurements. We show that a pure $s$-polarized light incident on a quantum well is reflected as an elliptically polarized wave. The signal is drastically enhanced in the vicinity of the light-hole exciton resonance. We show that the polarization conversion is caused by the spin-orbit splitting of the light hole states and the birefringence of the studied structure. The bulk inversion asymmetry constant $\beta_{h} \approx 0.14$ eV\AA, is determined for the ground light hole subband in a 10 nm ZnSe/ZnMgSSe quantum well., Comment: 5 pages, 3 figures and Online Supplemental Material (4 pages, 4 figures)

The results of a study into the photoluminescence spectra of a set of quantum dots based on GaAs enclosed in AlGaAs nanowires are presented. The steady state and time resolved spectra of photoluminescence under optical excitation both from an array of quantum wires/dots and a single quantum wire/dot have been measured. In the photoluminescence spectra of single quantum dots, emission lines of excitons, biexcitons and tritons have been found. The binding energy of the biexciton in the studied structures was deduced to be 8 meV.

Technology for the fabrication of a homogeneous array of pores in an A3B5 semiconductor matrix has been developed. Characterization with Scanning Electron Microscope and optical characterization of these samples have been carried out. Refractive indexes for the light polarized along and perpendicular to the pores have been measured. We have found that the measured values of the refractive indexes are essentially different from the average values that can be predicted in the simple model of an effective dielectric medium. Filling pores with dielectric liquid induces a dramatic modification of the optical properties of the structures.

In this paper we demonstrate that the magnetic moment of the exciton increases due to its motion along the magnetic field, and the diamagnetic shift decreases. These effects were observed for a set of quantum well structures with different well widths and based on a variety of semiconductor compounds. The reason for these effects is mixing of the exciton’s center of mass motion and the internal motion of the electron and hole in the exciton. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of charge-density fluctuations on trion states and spin-density fluctuation on the exciton states in quantum well are considered in the limit of low doping by electrons. In both cases the quasi-two dimensionality of the systems is taken into account. The trion-chargedensity interaction is considered in the random phase approximation. The influence of the exchange electron-electron interaction on the excitons is considered using a simplified approach. It is shown that the broadening of the trion absorption band profile with free carrier concentration increase is essentially weaker than the broadening of the exciton absorption band. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with well width exceeding by far the exciton Bohr radius) measured in Voigt geometry in a magnetic field. In a magnetic field, forbidden exciton lines were observed to appear for each exciton quantization level. The exciton diamagnetic shift constant has been observed to decrease noticeably with increasing number of the quantum confined level. A comparison of calculated with experimental spectra reveals a growth of the exciton translational mass with increasing magnetic field. It has been shown that both the growth of mass and the decrease of the diamagnetic shift can be traced to mixing of exciton internal with translational motion states.

Photoluminescence spectra taken from modulationdoped CdTe/(Cd0.7Mg0.3)Te quantum well structures with a two-dimensional electron gas of moderate to high density (from ne ∼ 1010 up to ne ∼ 1012 cm–2) in magnetic fields from 0 T to 45 T were studied. The observed spectra were analyzed in terms of combined excitonelectron processes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper we demonstrate that the magnetic moment of the exciton increases by an order of magnitude due to its motion along the magnetic field. The effect was observed for a set of quantum well structures with different well widths and based on various semiconductor compounds. The reason for this effect is mixing of the exciton's center of mass motion and the internal motion of electron and hole in the exciton. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have observed remarkable changes in the magnetic properties of excitons as they acquire kinetic energy. In particular, the Zeeman splittings and diamagnetic shifts of excitonic transitions when magnetic fields are applied along the growth direction of (001) wide quantum wells of CdTe, ZnSe, ZnTe and GaAs are found to to have a strong dependence on the translational wavevector Kz. The behaviour of the Zee-man splittings corresponds to enhancement of the magnetic moments of the excitons. This enhancement is particularly marked when their translational kinetic energy becomes comparable with the exciton Rydberg and can be described by what appears to be a universal function of Kz. A model for the behaviour is outlined which involves motionally-induced mixing between the 1S hydrogenic exciton ground state and excited nP states. The observations imply that there are significant changes in the structure of the exciton as its translational kinetic energy increases. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Modulation-doped CdTe/Cd0.7Mg0.3Te quantum well structures with a two dimensional electron gas of low and moderate density (from ne = 3 × 1010 cm–2 up to ne ≈ 1012 cm–2) have been studied. Photoluminescence spectra taken from the quantum well in magnetic fields from 0 T to 45 T at different electron densities were studied. The observed spectra were analyzed in terms of combined exciton-electron processes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoluminescence spectra of strained structures Zn1 − xMnxTe/Zn1 − yMgyTe with magnetic quantum wells and nonmagnetic barriers are studied. The Zeeman splitting of the heavy exciton is found to follow an unusual behavior: both spin components shift down in energy. The heavy-exciton photoluminescence Zeeman components are observed to be inversely distributed in intensity, with the higher energy component being stronger than the lower energy component. The Zeeman splitting of the exciton in a magnetic field is calculated. The data obtained permit refinement of some parameters of the energy spectrum and magnetic properties of these structures.

The temperature-induced variations in the photoluminescence spectra measured in a magnetic field of trions and excitons in CdTe/CdMgTe quantum wells with modulated doping are studied. It is found that the temperature-induced redistribution of the intensity between the exciton and trion emission lines in a magnetic field is opposite to that expected from the simple Boltzmann distribution model. Coupled rate equations for the trion-exciton system are solved to construct the temperature dependences of the exciton and trion emission line intensities. The relations thus calculated are in good agreement with experiment.

The paper is an overview of recent studies of the optical anisotropy of heterostructures with quantum wells, quantum wires, and quantum dots based on cubic semiconductors. This subject area is essentially an extension of the research conducted by professor A.A. Kaplyanskii in the optical anisotropy of cubic crystals.

International audience; 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.

Modifications of photoluminescence (PL) spectra taken from modulation doped CdTe/CdMgTe quantum well (QW) structures have been studied in magnetic fields up to 45T as a function of 2D electron concentration.

Photoluminescence (PL) spectra of modulation-doped CdTe/CdMgTe quantum-well structures containing two dimensional electron gases with electron concentrations around 1010 cm–2 have been recorded under a high magnetic field up to 45 T. Radiative recombination lines of dark and bright triplet trion states were found in the spectra at magnetic field strengths larger than 20 T. A model that takes into account the full symmetry of the structure under the magnetic field fits all the experimental results. Recording reflectivity spectra confirms the proposed model and the results from PL experiments. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The observation of a new physical phenomenon, a giant increase in the longitudinal magnetic moment of an exciton in motion, is reported. The effect is observed in the wide GaAs-, CdTe-, and ZnSe-based quantum wells, with a width much larger than the exciton Bohr radius, and hence relates to any crystals with a zinc-blend structure.

Modifications of photoluminescence (PL) and Reflectivity (Ref) spectra taken from modulation doped CdTe/CdMgTe quantum well (QW) structures have been studied in magnetic fields up to 45T as a function of 2D electron concentration.

Reflectivity spectra from GaAs and CdTe based wide quantum wells (widths L = 50–1000 nm) have been studied in magnetic fields in Faraday geometry. The magnitude of the exciton Zeeman splitting has been found to grow with increase of the quantization index N for the exciton energy levels. Since N is related to the magnitude of the exciton wave vector K, the observed effect means that the magnetic moment of the exciton gets larger as the kinetic energy increases. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Modification of photoluminescence spectra taken from modulation doped CdTe/CdMgTe QW structures have been studied in magnetic fields up to 45 T at high concentrations of 2D electrons. The following peculiarities were found in relatively low magnetic fields when filling factors ν was higher than 2: (i) linear energy shift of the photoluminescence (PL) peak with increasing magnetic fields, (ii) periodic variation of PL intensities for σ– and σ+ circular polarizations, (iii) smooth jumps of the PL peak position at integer filing factors. In high magnetic fields the behavior of the PL in the heavily doped structure coincided with the behavior of the lightly doped one. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

G. Karczewski Institute of Physics, Polish Academy of Sciences al. Lotnikow 32/46, 02-668 Warsaw, Poland and P. Tronc Laboratoire d’Optique, Ecole Superieure de Physique et Chimie Industrielles 10 rue Vauquelin, 75005 Paris, France Photoluminescence spectra of modulation-doped CdTe/CdMgTe quantum well structures containing two-dimensional electron gases of low, moderate and high electron concentrations were studied in high magnetic fields up to 45 T. The recombination line of triplet trion state was found in the spectra. A model calculation of photoluminescence spectra in magnetic fields, which takes into account singlet and triplet trion states, was carried out. It was shown that the dark triplet becomes observable in photoluminescence spectra because it becomes the only recombination channel when the formation of the singlet trion state is suppressed by magnetic fields.

The in-plane anisotropy of the refractive index and absorption coefficient in the blue-green spectral region in ZnSe/BeTe type-II heterostructures with no common atoms at the interface has been studied by ellipsometry in reflection. It was established that the relative difference (anisotropy) in the refractive index and absorption coefficient remains nonzero throughout the range covered and reaches 0.6% for the refractive index and 85% for the absorption coefficient. It was found that, in contrast to excitonic transitions involving a heavy hole, the anisotropy in absorption for the light-hole exciton is larger in magnitude and is of the opposite sign.

Time-resolved photoluminescence (PL) spectra of self-assembled CdSe/ZnSe quantum dots (QDs) are measured with a view to identifying the QD-size dependence of carrier capture and recombination in a single QD. The PL is excited by optical absorption in the ZnSe barrier layers under weak and strong irradiation with femto-and nanosecond laser pulses, respectively. In the case of weak excitation, the PL dynamics observed in a QD and the barrier layers are attributed to (i) fast carrier diffusion in the barrier layers, (ii) intense capture of carriers by the QD, (iii) fast carrier relaxation to the QD ground state, and (iv) dependence of the carrier capture and recombination times on the QD size. In the case of strong excitation, PL spectra are measured for different levels of excitation intensity and PL intensity is examined as a function of excitation intensity. It is established that (i) an increase in excitation intensity has a stronger effect on a high-frequency part of the spectrum and (ii) the intensity characteristic is essentially nonlinear. These findings are explained by state filling and/or decrease in carrier capture rate as the QD becomes increasingly full.

Time-resolved and time-integrated circularly-polarized photoluminescence of excitons and trions have been studied in external magnetic fields up to 10 T. ZnSe-based quantum well structures of n-type with carrier densities varied from 5×109 to 1011 cm -2 were used in this study. Absence of the chemical equilibrium in the exciton–trion system has been demonstrated at low temperatures (

Combined exciton–electron processes were found and studied in reflectivity and photoluminescence spectra taken from modulation-doped quantum well structures with different 2DEG densities. At low magnetic fields a Stokes shift between reflectivity and PL exciton and trion peaks due to the renormalization of the exciton and trion self-energy have been found. This shift disappears at high magnetic fields.

We present a detailed study of combined exciton-electron processes in modulation doped quantum well structures contain a 2DEG of low density. We observed resonance exciton-electron processes in magnetic fields reveal in a separate narrow spectral lines, as well as nonresonant processes reveal in the exciton line broadening. Combine processes with participate of the excitons have been observed as well as with participate of trions (negatively charged exciton-electron complexes).

The polarization properties of indirect photoluminescence (PL) in ZnSe/BeTe quantum well structures with a type-II band alignment were studied experimentally and analyzed theoretically. The linear polarization degree appears with increasing density of photoexcitation. It is caused by an electric field along the structure growth axis induced by a spatial separation of photocarriers. The PL circular polarization degree was induced by magnetic fields applied along the structure growth axis. Its maximum value was limited by the in-plane optical anisotropy of the optical matrix elements at the type-II heterointerface. In-plane oriented magnetic fields induce a linear polarization degree that is determined by a non-zero in-plane component of the heavy-hole g-factor in the BeTe layers.