Showing papers by "Le Si Dang published in 2005"
TL;DR: In this article, the authors observed dramatic changes in the near-field and far-field emission from a semiconductor microcavity excited by a pulsed and nonresonant optical pump with varying power.
Abstract: We observe dramatic changes in the near-field and far-field emission from a semiconductor microcavity excited by a pulsed and nonresonant optical pump with varying power. Above a threshold pumping power, light is emitted by a single quantum state lying at the bottom of the lower exciton-polariton band. Its intensity increases exponentially with the pump power and its linewidth becomes narrower than the cavity mode width. Near-field spectroscopy shows that the stimulated emission comes from several bright spots in the cavity plane, but no diffraction-induced angular broadening of the emission is observed. This is direct evidence for spontaneous formation of a nonequilibrium Bose condensate of coherent exciton polaritons with their wave function sharply peaked at structural imperfections.
139 citations
TL;DR: In this article, the authors investigated the polariton population and first-order coherence of a CdTe-based microcavity under nonresonant pumping and showed that it comes from a narrow ring in k space, exhibiting enhanced spatial and angular coherence at the stimulation onset.
Abstract: We report on evidence for polariton condensation out of a reservoir of incoherent polaritons. Polariton population and first-order coherence are investigated by spectroscopic imaging of the far-field emission of a CdTe-based microcavity under nonresonant pumping. With increasing pumping power, stimulated emission with thresholdlike behavior and spectral narrowing is observed in the strong exciton-photon coupling regime. We show that it comes from a narrow ring in k space, exhibiting enhanced spatial and angular coherence at the stimulation onset.
127 citations
TL;DR: In this paper, a single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots is presented, showing that the phonon sideband contribution in this emission reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission.
Abstract: We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission.
38 citations
TL;DR: In this article, the authors report on time-resolved photoluminescence measurements on a II-VI semiconductor microcavity in the strong coupling regime and observe the buildup of a large population in the polariton states close to the Brillouin-zone center.
Abstract: We report on time-resolved photoluminescence measurements on a II-VI $\mathrm{Cd}\mathrm{Te}∕\mathrm{Cd}\mathrm{Mn}\mathrm{Te}$ semiconductor microcavity in the strong-coupling regime. Under nonresonant excitation, we observe the buildup of a large population in the polariton states close to the Brillouin-zone center with occupation factors larger than 10. A spectacular spectral narrowing is measured, together with a strong acceleration of the polariton relaxation. A simple rate equation model describing the stimulated polariton-polariton scatterings toward the lowest-energy polariton states gives a good overall description of the measured dynamic.
25 citations
TL;DR: In this paper, it was shown that leaky modes and excitons can be strongly coupled and lead to complex multimode polaritons, and the consequences for photoluminescence under nonresonant excitation and potential applications were discussed in terms of polariton state occupancy and photonic weight.
Abstract: Semiconductor microcavities are known to exhibit the so-called leaky modes due to the Bragg structure of the cavity mirrors. In case of microcavities operating in the strong coupling regime, the leaky modes are usually considered as a perturbation for the polariton modes. Using microcavities based on II–VI compounds we observed that leaky modes and excitons can be strongly coupled and lead to complex multimode polaritons. The consequences for photoluminescence under nonresonant excitation and potential applications are discussed in terms of polariton state occupancy and photonic weight.
24 citations
TL;DR: In this paper, the optical and structural properties of wurtzite-phase Tm-doped GaN quantum dots sQDsd embedded in an AlN matrix, grown by plasma-assisted molecular beam epitaxy, were analyzed.
Abstract: We report on optical and structural properties of wurtzite-phase Tm-doped GaN quantum dots sQDsd embedded in an AlN matrix, grown by plasma-assisted molecular beam epitaxy. The influence of Tm on the size and shape of the QDs is analyzed. The optical properties are studied using cathodoluminescence and photoluminescence. Intra-4 f-Tm transitions from the 1 D 2 level show constant temperature behavior from 10 K to room temperature. The internal electric field and strains in the QDs yield a redshift and an additional broadening of the lines. We demonstrate that Tm atoms are partially located in the GaN QDs and partially at the GaN/ AlN interface.
23 citations
TL;DR: In this paper, a new method, using amorphous selenium, was proposed for inducing a well-controlled 2D-3D transition of a strained CdSe/ZnSe layer.
Abstract: We present a new method, using amorphous selenium, for inducing a well-controlled 2D–3D transition of a strained CdSe/ZnSe layer, i.e. for initiating self-organization of CdSe quantum dots that does not occur spontaneously during epitaxial growth. X-ray diffraction results evidence the very good crystal quality of the samples obtained using this technique. Optical characterizations by photoluminescence and time-resolved photoluminescence show the interest of this process in the growth of CdSe/ZnSe quantum dots.
17 citations
TL;DR: It is shown that stimulated emission with thresholdlike behavior and spectral narrowing is observed in the strong exciton-photon coupling regime, exhibiting enhanced spatial and angular coherence at the stimulation onset.
Abstract: We report on the non linear laser-like regime occuring in CdTe microcavities under strong non-resonant excitation. We find that the sharp peak responsible for the nonlinearities is dispersionless. This feature is discussed in terms of coherent polariton-polariton scattering. A phase transition on the coherence of the emission is demonstrated experimentally : firstly, images of the luminescence in the Fourier plane exhibits a contrasted speckle patterning that doesn't exist under weak excitation. Secondly, a direct measurement of the transverse coherence is realized. It shows that the coherence is strongly enhanced at the transition toward the nonlinear regime. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
16 citations
TL;DR: In this article, the growth conditions for growing high-quality CdSe/ZnSe quantum dots with photoluminescence emission measurable up to room temperature were presented.
Abstract: We present new growth conditions for growing high-quality CdSe/ZnSe quantum dots with photoluminescence emission measurable up to room temperature. The surface morphology is characterized in situ by Reflective High Energy Electron Diffraction (RHEED). The key point is the introduction of a new step in the growth process using amorphous selenium to induce a 2D–3D transition of a CdSe strained layer on ZnSe to form the dots. Optical characterizations by photoluminescence of CdSe/ZnSe quantum dots obtained that way, as well as X-ray diffraction results are also discussed here.
15 citations
TL;DR: In this paper, the MBE growth of GaN and InGaN quantum dots (QDs) doped with rare earth ions, namely Eu, Tm and Tb exhibiting red, blue and green luminescence, respectively, was reported.
Abstract: We report on the MBE growth of GaN and InGaN quantum dots (QDs) doped with rare earth ions, namely Eu, Tm and Tb exhibiting red, blue and green luminescence, respectively. Intense photoluminescence/cathodoluminescence is observed, resulting from the spatial localization of rare earth ions in dots combined with the confinement properties of the carriers. White light emission has been produced by combining the three rare earths in a multilayer sample of stacked GaN QD planes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
7 citations
TL;DR: In this article, two approaches for placing II-VI quantum dots in resonance with a pillar microcavity are presented. But neither of them is suitable for the measurement of the Purcell effect.
Abstract: We present results on two approaches for placing II-VI quantum dots in resonance with a pillar microcavity. The first approach consists in growing a fully epitaxial structure: a ZnTe 3λ/2 cavity containing CdTe quantum dots sandwiched between two CdMgTe/CdZnMgTe distributed Bragg reflectors. We observed a strong enhancement of the emission intensity for a dot well located into a 0.9 µm diameter pillars. More striking results were obtained using CdSe QDs in a λ/2 ZnSe cavity sandwiched between SiO2/TiO2 Bragg reflectors. We probed the Purcell effect by time-resolved photoluminescence and intensity saturation measurements performed on single quantum dots located in a 1.1 µm diameter hybrid pillar. A four-fold enhancement of quantum dot spontaneous emission rate is observed for quantum dots in resonance with excited degenerated modes of the pillar. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the polariton coherent dynamics in II-VI semiconductor microcavities in the parametric scattering regime is studied. But the authors focus on the phase matching conditions for parametric dephasing.