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We report visible single-photon emission from a nitrogen impurity center in AlAs grown on GaAs(001). Sharp emission lines are observed at 2.1-2.2 eV, below the X-conduction bandedge of AlAs from N δ-doped AlAs. The quadratic increase in the photoluminescence intensity with the N concentration reveals that the nitrogen impurity centers consist of NN pairs. Polarization analysis reveals that the peak at 2.191 eV consists of different pair configurations, while the peak at 2.165 eV contains only a single pair configuration along the <110> direction. Photon correlation measurement gives the second-order correlation function g(2)(0) = 0.33, demonstrating single-photon statistics in emissions from an NN pair. [ABSTRACT FROM AUTHOR]

We experimentally and theoretically investigate the photoluminescence broadening of different excitonic complexes in single self-assembled GaAs/AlGaAs quantum dots. We demonstrate that the excitonic fine-structure splitting leads to a sizable line broadening whenever the detection is not resolved in polarization. The residual broadening in polarized measurements is systematically larger for the exciton with respect to both the trion and the biexciton recombination. The experimental data agree with calculations of the quantum confined Stark effect induced by charge defects in the quantum dot (QD) environment, denoting the role of the QD spectator carrier rearrangement in reducing the perturbation of the fluctuating environment. [ABSTRACT FROM AUTHOR]

Photoluminescence from a single InAs/InP quantum dot emitting at a wavelength of 1300 nm is analyzed by the interferography technique. The first-order correlation function was measured for emission signals from an isolated quantum dot with continuous wave photoexcitation. The spectral shape was evaluated by Fourier transform of the correlation function, revealing the contributions of Lorentzian and Gaussian functions. The Lorentzian homogeneous width was determined to be 28(±4) μeV at 8 K. [ABSTRACT FROM AUTHOR]

The authors have demonstrated photopumped laser action of self-assembled ring-shaped GaAs quantum dots (QDs) grown by droplet epitaxy. Morphological control of the QD shape from conelike dots to ringlike ones results in a narrow spectral band of photoluminescence from the QD ensemble, reflecting their small size distribution. Using ring-shaped QDs as an active laser medium, they observed multimodal stimulated emissions from the ground state at temperatures of up to 300 K. [ABSTRACT FROM AUTHOR]

In photoluminescence spectra of symmetric [111] grown GaAs/AlGaAs quantum dots in longitudinal magnetic fields applied along the growth axis, we observe in addition to the expected bright states also nominally dark transitions for both charged and neutral excitons. We uncover a strongly nonmonotonic, sign-changing field dependence of the bright neutral exciton splitting resulting from the interplay between exchange and Zeeman effects. Our theory shows quantitatively that these surprising experimental results are due to magnetic-field-induced ±3/2 heavy-hole mixing, an inherent property of systems with C3v point-group symmetry. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the self-assembly of GaAs/AlGaAs quantum dots (QDs) on GaAs (311)A substrates by droplet epitaxy. High-density Ga droplets were formed on the (311)A surfaces due to the short surface migration distance of Ga atoms. The maximum area density exceeded 1011 /cm2. These Ga droplets were crystallized into dot-shaped nanostructures (QDs) even by the irradiation of low As4 flux intensity. The capped GaAs QDs exhibited efficient, narrow PL emission at 5K, indicating their high quality and uniformity. [Copyright &y& Elsevier]

Abstract: We report on the power dependence of the exciton photoluminescence of single self-assembled GaAs/AlGaAs quantum dots. Interpreting the experimental data with the random population theory we demonstrate that the exciton states occupation probability can be described by Poissonian statistics, allowing to study the state filling condition and evaluate the QDs capture volume. In addition we study the effect of temperature on the QDs capture efficiency. [Copyright &y& Elsevier]

Abstract: We present the results of high resolution photoluminescence spectroscopy of single GaAs/AlGaAs quantum dots grown by droplet epitaxy technique. By measuring the line broadening and the linear polarization of the excitonic photoluminescence we get new insights on the role of extrinsic effects on the quantum dot symmetry. Taking advantage of the lack of strain in the GaAs/AlGaAs system we study the relationship between the geometrical elongation of the confining potential and the exciton fine structure splitting. [Copyright &y& Elsevier]

Abstract: We examine in detail the spontaneous formation process of a cluster of InAs dots on GaAs (100) by droplet epitaxy. A cluster of dots was fabricated by irradiating an As flux for 30s to In droplets. The dots were found to be formed mainly along a ring-like zone stretching in the [011] direction, showing that In atoms migrated from the droplet and reacted with As atoms. This indicates the presence of not only the surface diffusion of In atoms but also the inward diffusion of As atoms. This is supported by the fact that such a ring was not visible when the As irradiation time was shortened (5s). For photoluminescence measurements the dots were capped with a 50-nm-thick GaAs layer. Two peaks at 1.46 and 1.3eV were observed in the sample annealed at 750°C. These peaks were attributed to the wetting layer and the dots, respectively. [Copyright &y& Elsevier]

Abstract: Modified droplet epitaxy GaAs/AlGaAs single quantum dots have been studied by low-temperature magneto-photoluminescence spectroscopy. We observe Zeeman splitting and diamagnetic shift of the neutral exciton line. The Landég factor of different quantum dots has been measured in a wide range of emission energies (i.e. quantum dot size). The measured g factors and diamagnetic shift are compared with conventional quantum dots grown by the Stranski–Krastanov method, as well as GaAs/AlGaAs quantum wells and fluctuation-induced dots. [Copyright &y& Elsevier]

Abstract: Quantized energy levels of nanoscopic concentric double rings are identified by means of micro photoluminescence spectroscopy. High-yield emissions from a single quantum structures are observed. The spectra show several discrete lines reflecting the carrier confinement in the rings. Effective mass calculation is performed to characterize the quantized motion of carriers with rotational and orbital degrees of freedoms. Excellent agreement between the observed spectra and the numerical ones is found. [Copyright &y& Elsevier]