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Polimeni, A.; Patanè, A.; Henini, M.; Eaves, L.; Main, P. C.

doi:10.1103/physrevb.59.5064

Cited by 210 publications

(110 citation statements)

References 29 publications

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“…The first surprising result is that the value of E 0 measured in our InAs/AIGaAs sample is just slightly higher than for the InAs/GaAs case. Values over 1.2 eV have been obtained by luminescence measurements for InAs/AIGaAs QDs with similar Al content in the literature [19,20]. We conclude that, as intended, the inclusion of the quaternary capping layer has red shifted E 0 .…”

Section: Introductionmentioning

confidence: 84%

InAs/AlGaAs quantum dot intermediate band solar cells with enlarged sub-bandgaps

Ramiro

Antolín

Steer

et al. 2012

2012 38th IEEE Photovoltaic Specialists Conference

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-In the last decade several prototypes of intermediate band solar cells (IBSCs) have been manufactured. So far, most of these prototypes have been based on InAs/GaAs quantum dots (QDs) in order to implement the IB material. The key operation principles of the IB theory are two photon subbandgap (SBG) photocurrent, and output voltage preservation, and both have been experimentally demonstrated at low temperature. At room temperature (RT), however, thermal escape/relaxation between the conduction band (CB) and the IB prevents voltage preservation. To improve this situation, we have produced and characterized the first reported InAs/AlGaAs QDbased IBSCs. For an Al content of 25% in the host material, we have measured an activation energy of 361 meV for the thermal carrier escape. This energy is about 250 meV higher than the energies found in the literature for InAs/GaAs QD, and almost 140 meV higher than the activation energy obtained in our previous InAs/GaAs QD-IBSC prototypes including a specifically designed QD capping layer. This high value is responsible for the suppression of the SBG quantum efficiency under monochromatic illumination at around 220 K. We suggest that, if the energy split between the CB and the IB is large enough, activation energies as high as to suppress thermal carrier escape at room temperature (RT) can be achieved. In this respect, the InAs/AlGaAs system offers new possibilities to overcome some of the problems encountered in InAs/GaAs and opens the path for QD-IBSC devices capable of achieving high efficiency at RT.

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Section: Introductionmentioning

confidence: 84%

InAs/AlGaAs quantum dot intermediate band solar cells with enlarged sub-bandgaps

Ramiro

Antolín

Steer

et al. 2012

2012 38th IEEE Photovoltaic Specialists Conference

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“…Increased phonon-assisted non-radiative recombination of charge carriers occurs within the matrix material, causing parasitic losses and additional heating of the gain-chip. For the shallow confining potential of InGaAs-QDs within GaAs matrix material, WL and barrier states were assumed to play an important role for luminescence decrease with increasing temperature [Pol99,Pat99]. For the present device, higher temperatures caused a red shift of active layer emission, which was significantly stronger than the resonance shift.…”

Section: Nm Stranski-krastanow Qd-vecselmentioning

confidence: 79%

Design and Realization of Novel GaAs Based Laser Concepts

Germann

2012

Springer Theses

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ZusammenfassungHalbleiterlaser stellen die Grundlage für eine zunehmende Vielzahl von Anwendungen dar, die von der Informationsspeicherung und digitalen Kommunikation bis hin zur Materialbearbeitung reichen. Neuartige Konzepte überwinden bisherige Limitierungen und erschließen neue Anwendungsgebiete. Viele dieser Anwendungsgebiete verlangen nach kostengünstigen Bauelementen, die maximale Brillanz und hohe Ausgangsleistungen oder höchste Geschwindigkeiten erreichen.Diese Arbeit stellt dar, wie essentielle Leistungsmerkmale von Halbleiterlasern durch das Design von Nanostrukturen und epitaktischen Wachstumsprozessen maßgeschneidert werden können. Hierbei wird auf alle Schritte der Laserherstellung eingegangen, vom Design über das Wachstum der Nanostrukturen mittels metallorganischer Gasphasenepitaxie (MOVPE), bis hin zur Herstellung und Charakterisierung kompletter Bauelemente. AbstractSemiconductor lasers represent the backbone for an increasing variety of applications ranging from information storage and communication, to material treatment. Novel concepts are pushing the limits and are enabling new application areas. Many of these areas demand low-cost laser devices with high-brilliance and high-power light output or high-speed performance.This thesis demonstrates how key performance characteristics of semiconductor lasers can be tailored using nanostructure design and epitaxial growth. All aspects of laser fabrication are discussed, from design to growth of nanostructures using metal-organic vapor-phase epitaxy (MOVPE), to fabrication and characterization of complete devices. By employing industrial tools, all developed processes are compatible with mass production.Pulsed high power laser operation up to 8 W and a ultra-low lasing threshold of 66 A/cm 2 is achieved with electrically pumped quantum dots (QD)-based edge emitters at 1.25 µm due to an improved understanding of the QD growth process. This novel process enables 1.3 µm edge emitters for telecom applications in the established InGaAs/GaAs system. At the heart of these achievements is the careful investigation and optimization of nearly all layers of the laser device structure. Designs are altered and precisely tuned by employing AlGaAs or InGaP claddings and varied doping schemes in order to develop new waveguides to meet different requirements.High-power vertical external-cavity surface-emitting lasers (VECSELs) promise continuous-wave (CW) lasing with perfect circular beam quality, plus direct access to the cavity. While the concept is ideal for a multitude of applications, conventional quantumwell based systems exhibit problematic temperature sensitivity during operation. Here, for the first time, VECSELs with sub-monolayer structures and QDs as active layers are realized by MOVPE. These optically pumped devices cover a wide spectral range from 950 nm to 1210 nm, and achieve excellent temperature-stable CW lasing due to the use of QDs and CW output powers of up to 1.4 W.In order to overcome the physical limitations of directly modulated vertical-c...

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“…In fact the thermal stability of the dot emission is strongly dependent on the composition of the matrix incorporating the dots. We found that the dots embedded in a (AlGa)As barrier and/or in a GaAs/(AlGa)As QW exhibit the highest thermal stability [32]. This can be attributed to the low level of thermal escape of carriers from the dots towards the high energy levels of the AlGaAs barrier or the GaAs/(AlGa)As QW, which therefore act to prevent carrier depopulation of the dot levels.…”

Section: Effects Of Growth Interruptionmentioning

confidence: 86%

“…In contrast, with decreasing d and/or increasing N, the PL red-shifts from 1.1 lm (sample A: y = 0, d = 20 nm, N = 3) to~1.3 lm, (sample C: y = 0, d = 1.7 nm, N = 10), evidence for electronic coupling between vertically stacked QDs. Therefore by engineering the carrier potential profile of the dots it is possible to cover a broad energy range for the room temperature light emission of QDs [32]. This is of particular interest for extending the optical emission range of QDs to 1.3 lm, the window for signal transmission through silica fibers.…”

Section: Effects Of Growth Interruptionmentioning

confidence: 99%

Properties and applications of quantum dot heterostructures grown by molecular beam epitaxy

Henini

2006

Nanoscale Res Lett

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One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two: quantum wires and quantum dots, in order to realize novel devices that make use of low-dimensional confinement effects. One of the promising fabrication methods is to use selforganized three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. This article is intended to convey the flavour of the subject by focussing on the structural, optical and electronic properties and device applications of self-assembled quantum dots and to give an elementary introduction to some of the essential characteristics.

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Temperature dependence of the optical properties ofInAs/Aly

Cited by 210 publications

References 29 publications

InAs/AlGaAs quantum dot intermediate band solar cells with enlarged sub-bandgaps

InAs/AlGaAs quantum dot intermediate band solar cells with enlarged sub-bandgaps

Design and Realization of Novel GaAs Based Laser Concepts

Properties and applications of quantum dot heterostructures grown by molecular beam epitaxy

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