Inelastic scattering of excitons on Fe^{++} ions in Cd_{1-x}Fe_{x}Se was studied by resonant Raman scattering. Polarization measurements were done using a modulation technique, allowing for the first time to determine the full polarization state of the detected light. The obtained results were compared to a simple calculation in an incoherent model of scattering on Fe^{++} ions.
In this work we present the band gap engineering, epitaxial growth and optical characterization of CdSe/Cd_{0.9}Mg_{0.1}Se and Cd_{0.9}Mg_{0.1}Se/Cd_{0.85}Mg_{0.15}Se quantum wells with a thickness ranging from 1 to 15 nm. These structures exhibit strong near-band-gap photoluminescence from helium up to room temperature. The emission energy is tuned in the range from 1.74 to 2.1 eV at 7 K, depending on the thickness and well composition. The most intense photoluminescence (both at 7 and 300 K) was observed for 10 nm thick CdSe/Cd_{0.9}Mg_{0.1}Se wells. Such a structure gives also a sharp emission line (FWHM = 20 meV) at low temperature. The presented quantum wells are well suited for being embedded in lattice matched ZnTe based microcavities.
We analyze the photoluminescence of excitonic complexes containing p-shell electron in the magnetic field in the Faraday configuration. We demonstrate that despite the p-shell electron is not involved directly in the recombination process, its g-factor influences the emission spectrum. We found that in the case of CdTe/ZnTe quantum dots the p-shell electron is significantly less affected by the magnetic field than s-shell electron in the same dot.
We describe the realization and characterization of a distributed Bragg reflectors and InAs quantum dots grown by molecular beam epitaxy. The distributed Bragg reflectors are based on a stack of eight or twenty pairs of GaAs and AlAs layers with a stopband centered at about E_0=1.24 eV (λ_0=1000 nm). The whole structures exhibit a reflectivity coefficient above 90%. The growth rate was monitored in situ by measurement of the oscillations of the thermal emission intensity. The investigations conducted on the InAs quantum dots grown on GaAs show photoluminescence around E=1.25 eV (λ=990 nm). The combination of these two elements results in the realization of a microcavity containing InAs quantum dots and surrounded by 20 pairs of distributed Bragg reflectors.
We discuss possible mechanisms of quantum dot population control. A set of experiments, including time-resolved photoluminescence, single photon correlations, excitation correlation, and photoluminescence excitation is used to determine the actual mechanism under non-resonant and quasi-resonant regime.
This work contains a selection of our recent experimental results in the field of the spin-related spectroscopy of individual CdTe-based quantum dots. After a short description of the sample growth and experimental methods, optical measurements of the charge state dynamics are presented. Then the influence of in-plane anisotropy of the excitonic states of a quantum dot is discussed, followed by a description of experimental studies of information read-out and writing on quantum dot spin states. In particular, spin memory of a single Mn^{++} ion embedded in a CdTe quantum dot is quantitatively assessed. In an outlook part, perspectives opened by recently developed ZnTe lattice-matched Bragg reflectors are discussed.
In this work we present a statistical study of resonantly excited luminescence of coupled CdTe/ZnTe quantum dots studied by photoluminescence excitation measurements. We investigate the probability of resonance occurrence as a function of resonant energy. We come to the conclusion that the distribution of the inter-dot resonances is uniform, which suggests that the inter-dot excitation transfer is not limited by mean density of states in the emitting quantum dots.
Magnetooptical properties of (Ga,Fe)N layers containing various concentrations of Fe-rich nanocrystals embedded in paramagnetic (Ga,Fe)N layers are reported. Previous studies of such samples demonstrated that magnetization consists of a paramagnetic contribution due to substitutional diluted Fe ions as well as of ferromagnetic and antiferromagnetic components originating from Fe-rich nanocrystals, whose relative abundance can be controlled by the growth conditions. The nanocrystals are found to broaden and to reduce the magnitude of the excitonic features. However, the ferromagnetic contribution, clearly seen in SQUID magnetometry, is not revealed by magnetic circular dichroism. Possible reasons for differences in magnetic response determined by magnetic circular dichroism and SQUID measurements are discussed.
We study polarization resolved correlation between photons emitted in cascaded biexciton-exciton recombination from a single quantum dot formed in type II GaAs/AlAs bilayer. Magnetic field induced transition from anisotropy controlled to the Zeeman controlled emission was demonstrated by a circular polarization correlation between the emitted photons. A simple model describing the effect allowed us to determine the anisotropic exchange splitting of the excitonic state. This method of the anisotropic exchange splitting determination can be useful in the case when other methods are not sensitive enough.
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