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  • 1
    Electronic Resource
    Electronic Resource
    Hidden symmetries in the energy levels of excitonic ‘artificial atoms’ (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 405 (2000), S. 923-926 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Quantum dots or ‘artificial atoms’ are of fundamental and technological interest—for example, quantum dots may form the basis of new generations of lasers. The emission in quantum-dot lasers originates from the recombination of excitonic complexes, so it is important ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35016020
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  • 2
    Electronic Resource
    Electronic Resource
    Short-wavelength laser diodes based on AlInAs/AlGaAs self-assembled quantum dots (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 1496-1502 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-assembled quantum dots (QDs) of highly strained InAlAs have been grown by molecular beam epitaxy in separate-confinement p–i–n heterostructures on (001) GaAs substrates. Results from a systematic study of samples with varying amounts of deposited material relates the observed emission peaks with QD levels, wetting layer states, or barrier materials. For samples with high-QD concentration, lasing is observed in the upper-QD shells. A sample with contact layers improving carrier and optical confinement operates up to room temperature and displays lowered threshold current densities. A threshold current density of ∼4 A/cm2 is measured for this structure at T=5 K and continuous-wave operation is obtained up to T∼77 K. A material gain larger than 1.7×104 cm−1 is measured for this single-layer structure. Lasing is observed in the upper-QD shells for small gain media, and progresses towards the QD lower states for longer cavity lengths representing an emission shift of 45 meV. A minor dependence of the threshold on QD density is found for samples having densities between 20 and hundreds of QDs per micron squared. For samples with multiple QD layers displaying vertical self-assembling, an increase in the emission linewidth is observed compared with single-layer samples and multilayer samples with uncorrelated growth. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372040
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  • 3
    Electronic Resource
    Electronic Resource
    Luminescence, level saturation, and optical gain in a single InGaAs/GaAs quantum well (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4854-4857 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photo- and electroluminescence spectra were performed on InxGa1−xAs/GaAs single quantum wells (x=0.13) under varying excitation conditions. Both types of spectra display strong 11H-associated emission, as well as impurity-related features. Saturation effects are observed for both the intrinsic and impurity emission under high excitation conditions. When optically pumped at energies higher than the GaAs band gap, the InGaAs single quantum well gave optical gains in the 10-cm−1 range, saturating at a pumping intensity of 104 W/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343802
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum dot infrared photodetectors (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 79-81 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-assembled strained semiconductor nanostructures have been grown on GaAs substrates to fabricate quantum dot infrared photodetectors. State-filling photoluminescence experiments have been used to probe the zero-dimensional states and revealed four atomic-like shells (s,p,d,f) with an excitonic intersublevel energy spacing which was adjusted to ∼60 meV. The lower electronic shells were populated with carriers by n doping the heterostructure, and transitions from the occupied quantum dot states to the wetting layer or to the continuum states resulted in infrared photodetection. We demonstrate broadband normal-incidence detection with a responsivity of a few hundred mA/W at a detection wavelength of ∼5 μm. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337649
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  • 5
    Electronic Resource
    Electronic Resource
    Near-surface InAs/GaAs quantum dots with sharp electronic shells (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2707-2709 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction between zero-dimensional states and surface states is studied using near-surface quantum dot (QD) ensembles with well-defined electronic shells. The inhomogeneous broadening of self-assembled InAs/GaAs QDs increases from ∼30 to more than ∼46 meV as the distance of the QDs from the surface is changed from 100 to 5.0 nm. Simultaneously, a decrease of the radiative recombination intensity by ∼3 orders of magnitude, and a red-shift of ∼65 meV are observed. For QDs capped with less than ∼10 nm, remarkable charge transfers between the QD and surface states lead to optical memory effects lasting over time-scales of several minutes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126450
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  • 6
    Electronic Resource
    Electronic Resource
    Evolution of the energy levels in quantum dot ensembles with different densities (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1866-1868 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ensembles of self-assembled InAs/GaAs quantum dots (QDs) have been obtained with different densities by molecular beam epitaxy. The evolution of the structural and optical properties with coverage shows that lateral interactions are present for QD spacings of hundreds of nanometers (coverage〉∼109 QDs/cm2). Clear evidence for transfer of InAs from the wetting layer to the QDs is observed at the onset of the Stranski–Krastanow's island formation for 1.83 monolayers (MLs). QDs with sharp electronic shell structures are observed by state-filling spectroscopy for the low density ensembles (1.83–1.91 ML). A decrease in the photoluminescence intensity is observed for more than 1.96 ML and is associated with the coalescence of the islands. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124854
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  • 7
    Electronic Resource
    Electronic Resource
    Inhomogeneous broadening in quantum dots with ternary aluminum alloys (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2701-2703 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study how the optical properties of InAs self-assembled quantum dots (QDs) grown on GaAs substrate are affected when using AlGaAs barriers to increase the carrier confinement. The inhomogeneous broadening of the QD ensemble is found to increase when ternary aluminum alloys are used next to or within the QDs. By growing thin GaAs spacers to separate the QDs from the AlGaAs barriers, we obtain QD ensembles which exhibit little photoluminescence quenching and well-defined excited states up to room temperature. Postgrowth rapid thermal annealing is then used to intermix these InAs/GaAs/AlGaAs QDs and diffuse the Al towards the QDs. In contrast with QDs having thick binary GaAs barriers, the inhomogeneous broadening of QDs with nearby AlGaAs barriers is not decreased with intermixing, leading to unresolved excited state peaks when the interdiffusion length becomes comparable to the GaAs spacer thickness. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410333
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  • 8
    Electronic Resource
    Electronic Resource
    Laser-induced InAs/GaAs quantum dot intermixing (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3583-3585 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser annealing of InAs/GaAs quantum-dot (QD) microstructures has been investigated for selective area tuning of their electronic shell structure. Extensive blueshifts of the QD excited states were observed following 20–40 s laser irradiation. In the most extreme case, we were able to shift the position of the ground state transition by 298 meV, i.e., to the spectral region where the photoluminescence signal originates from the as-grown InAs wetting layer. A reduction from ∼50 to 8 meV of the full width at half maximum of the PL peak corresponding to this transition indicates a drastic change in the structural characteristics of the investigated QD ensemble. The attractive feature of the laser-QD-intermixing technique is that it offers the possibility of obtaining targeted blueshifts and inter-sublevel energy spacing on the lateral scale required in the fabrication of QD-based integrated optoelectronic devices and, possibly, photonic band gap crystals. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323997
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  • 9
    Electronic Resource
    Electronic Resource
    Lasing in quantum-dot ensembles with sharp adjustable electronic shells (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 986-988 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantum-dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular-beam epitaxy. Shape-engineered stacks of self-aligned QDs with improved uniformity are used to increase the gain in the active region. Lasing is observed in the upper QD shells for small-gain media, and progresses towards the QD ground states for longer cavity lengths. We obtained at 77 K thresholds of Jth=15 A/cm2 for a 2 mm cavity lasing in the first excited state (p shell), and Jth=125 A/cm2 for a 1 mm cavity lasing in n=3 (d shell). At 300 K for a 1 mm cavity, Jth is 490 A/cm2 with lasing in n=4 (f shell). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124253
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  • 10
    Electronic Resource
    Electronic Resource
    Coupled InAs/GaAs quantum dots with well-defined electronic shells (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2268-2270 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Artificial molecules are studied using coupled quantum-dot (QD) ensembles with well-defined electronic shells. The coupling strength between the zero-dimensional states is varied by changing the distance between two layers of stacked self-assembled InAs/GaAs QDs. For strongly coupled QDs grown with a 4 nm spacer, state-filling spectroscopy reveals a shift of the QD symmetric state to lower energies by ∼23 meV. The wetting layer states are also strongly coupled because of the shallow confinement, resulting in a redshift of its symmetric state by ∼26 meV. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126317
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