Polariton quantization modes and whispering gallery modes in a cylindrical microcavity

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Exciton resonance reflectivity study of quantum well wires

We report on the first observation of the exciton resonant reflection from a directly grown array of isolated quantum-well-wires. Structures contaned 30 GaAs/AlAs double layers were grown on (311) GaAs substrate by conventional elemental source MBE. GaAs wire-like clasters with an orientation along [233] and size of 32/10.2 Å were introduced inside one of the central AlAs layers. The expected distance between nearest clusters is about 160 Å. In spite of much smaller effective volume occupied by excitons in these clusters, as compared to that in a single quantum well, the quantum-well-wire structures demonstrate much lager resonance amplitude of the reflection spectra. We extracted excitonic parameters from these spectra and found that the exciton oscillator strength in the quantum-well-wires is more than 10 time higer than that in the enviroment superlattice. A 30% anisotropy of the exciton oscillator strength in the quantum-well-wire have been observed. The theory of non-local dielectric responce is extended to calculate reflection spectra from the structures with a grating of quantum-well-wires. A functional relationship between the reflection coefficient and the envelope wave function of an exciton in the structure has been established

Combined exciton-cyclotron resonance in quantum well structures

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Plasmon mechanism of the trion emission band broadening in quantum wells

International audienceThe effects of charge-density fluctuations on negative trion states in a quantum well are considered for the case of intermediate doping by electrons at zero magnetic field. The quasi-two-dimensionality of the system and the trion-plasmon interaction are taken into account in the framework of the random-phase approximation. It is shown that the trion luminescence band has a complex structure consisting of a zero-plasmon line and a trion-plasmon wing. The structure is interpreted as a result of spatial inhomogeneity of the quantum wells

Observation of interface carrier states in no-common-atom heterostructures ZnSe/BeTe

International audienceThe existence of intrinsic carrier interface states in heterostructures with no common atom at the interface (such as ZnSe/BeTe) is shown experimentally by ellipsometry and photoluminescence spectroscopy. These states are located on interfaces and lie inside the effective bandgap of the structure; they are characterized by a high density and a long lifetime. A tight binding model confirms theoretically the existence of these states in ZnSe/BeTe heterostructures for a ZnTe-type interface, in contrast to the case of the BeSe-type interface for which they do not exist

Wave-vector dependence of magnetic properties of excitons in ZnTe

International audienceThe magnetic properties of heavy-hole excitons in wide quantum wells of ZnTe with Znx Mg1−x Te barriers have been studied with photoluminescence and reflectivity measurements. The exciton magnetic moments (as characterized by the g values) and the diamagnetic shifts of the exciton transitions are found to depend strongly on the wave-vector component Kz associated with translational motion of the exciton normal to the plane of the quantum well. The case of ZnTe differs from examples of this behavior previously reported for GaS, CdTe, and ZnSe since the ZnTe is under tensile biaxial strain, so that the heavy-hole exciton states lie higher in energy than the corresponding states of the light-hole excitons. The dependence of the magnetic properties on Kz is nevertheless still in excellent agreement with the predictions of a model proposed by Smith et al. [Phys. Rev. B 78, 085204 (2008)], in which mixing of the heavy-hole 1S exciton state with light-hole nP states is found to be responsible for motion-induced changes in the internal structure of the exciton

Spin properties of trions in a dense quasi-2D electron gas

International audienceThe reflection and photoluminescence spectra of modulation-doped CdTe/CdMgTe quantum-well structures have been studied. It was found that the magnitude and sign of the Zeeman splitting of the trion reflection line depend on the electron concentration in the quantum well, whereas the magnitude and sign of the splitting of the exciton line are absolutely the same for all the electron concentrations under study. In the photoluminescence spectra, the magnitude and sign of the Zeeman splittings for the exciton and trion were the same. This "renormalization" of the trion g factor is explained in terms of the model of combined exciton-electron processes

Combined exciton-electron excitation in quantum wells with a two-dimensional electron gas of low density

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Excitonic polaritons in transverse magnetic fields

International audienceExciton-polariton reflectivity of wide CdTe/CdZnTe quantum-wells (with well widths exceeding by far the exciton Bohr radius) was measured in the 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 was observed to decrease noticeably with increasing quantum number of the 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 between exciton internal and translational motion states. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Bound and unbound exciton-electron states in II-VI quantum well structures with a 2DEG

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