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Sökning: swepub > Larsson Anders > Tidskriftsartikel > Sadeghi Mahdad 1964

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  • Fu, Ying, et al. (författare)
  • Energy band structure and spectral gain characteristics of dilute-nitride zinc blende InGaNAs quantum wells embedded in GaAs and GaNAs barriers
  • 2006
  • Ingår i: Journal of Applied Physics. - 00218979. ; 100:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The spectral gain characteristics of dilute-nitride zinc blende InxGa1-xNyAs1-y quantum wells embedded in GaNy1As1-y1 barriers have been investigated experimentally and theoretically. Two samples, both with the gain peak at 1300 nm, were studied for comparison. One has a high nitrogen concentration in the quantum well with the surrounding barriers being pure GaAs. The other has a lower and uniform nitrogen concentration in the quantum well and the barriers (GaNAs barriers). Measurements show the redshift of the gain peak induced by the incorporation of nitrogen and difference in the spectral gain characteristics. The energy band structures and spectral gain characteristics are analyzed theoretically using the standard eight-band k center dot p theory. It is shown that the introduction of nitrogen atoms in the GaAs barriers reduces the barrier height for the central quantum well so that the energy sublevels in the conduction band becomes condensed. The condensation of the conduction-band energy sublevels reduces the peak gain and makes the gain spectrum narrower, in agreement with measurements.
  • Zhao, Huan, 1982-, et al. (författare)
  • Comparison of Optical and Structural Quality of GaIn(N)As Analog and Digital Quantum Wells Grown by Molecular Beam Epitaxy
  • 2008
  • Ingår i: Semiconductor Science and Technology. - 0268-1242. ; 23:12
  • Tidskriftsartikel (refereegranskat)abstract
    • A set of Ga0.625In0.375(N) As single quantum well (QW) samples with the identical total amounts of Ga and In and QW thicknesses was designed and grown by both the analog and the digital methods using molecular beam epitaxy. The N exposure time in the GaInNAs samples was kept the same. The inter-band gap recombination in the analog and the digital InGaAs QWs appears in a similar transition energy range as a result of In segregation. Temperature-dependent photoluminescence (PL) measurements were performed on the GaInNAs samples. An S-shaped dependence of the transition energy on temperature was observed in the digital GaInNAs QWs but not in the analog GaInNAs QW. Post-growth rapid thermal annealing had remarkably different effects on the PL intensity: an increase for the analog InGaAs QW and for the analog and digital GaInNAs QWs, but a decrease for the digital InGaAs QW with increasing annealing temperature. The GaIn(N) As samples grown by the digital method showed weaker PL intensities and smaller wavelength blue-shifts than the similar samples grown by the analog method. Possible strain relaxation mechanisms are discussed.
  • Zhao, Huan, 1982-, et al. (författare)
  • Very Low Threshold Current Density 1.292 µm GaInNAs Triple Quantum Well Lasers
  • 2008
  • Ingår i: Electronics Letters. - 0013-5194. ; 44:7, s. 475-477
  • Tidskriftsartikel (refereegranskat)abstract
    • Very-low-threshold Ga0.62In0.38N 0.007As0.993/GaN0.011As0.989/GaAs triple quantum well (QW) lasers emitting at 1.29m are demonstrated. The laser structure was grown by molecular beam epitaxy after extensive optimisations of growth and in situ annealing conditions. As-cleaved broad-area lasers with a cavity length of 1mm under pulsed operation showed a record low-threshold current density of 400A/cm2 (∼130A/cm2/QW), a high differential efficiency of 0.32W/A/facet and a characteristic temperature of 94K in the temperature range 10 to 110°C. © The Institution of Engineering and Technology 2008.
  • Zhao, Qingxiang, 1962-, et al. (författare)
  • Nitrogen Incorporation in GaNAs Layers Grown by Molecular Beam Epitaxy
  • 2006
  • Ingår i: Applied Physics Letters. - 0003-6951. ; 89
  • Tidskriftsartikel (refereegranskat)abstract
    •    GaNAs/GaAs quantum wells with high N concentrations, grown by molecular beam epitaxy, have been investigated by secondary-ion mass spectrometry (SIMS), high resolution x-ray diffraction (XRD), and photoluminescence (PL) measurements. The substitutional N concentration in an 18 nm thick strained GaNAs layer varies from 1.4% to 5.9% when the growth rate is reduced from 1 to 0.2 μm/h. By further reducing the growth rate, more N can be incorporated but relaxation occurs. Both the total N concentration, deduced from SIMS measurements, and the substitutional N concentration, deduced from XRD measurements, increase with reduced growth rate. By comparing the SIMS and XRD results, we found that a large amount of N was not in substitutional position when the substitutional N concentration is high (≫4%). The experimental results also show that there is no detectable change of total and substitutional N concentrations, within the instrument resolutions, after rapid thermal annealing at 700 °C for 30 s. However, PL measurements show a strong blueshift of the emission wavelength after annealing and the PL intensity increases by more than one order of magnitude.
  • Zhao, Qingxiang, 1962-, et al. (författare)
  • Radiative recombination of localized excitons and mobility edge excitons in GaInNAs/GaAs quantum wells with strong carrier localization
  • 2005
  • Ingår i: Physics Letters A. - 0375-9601. ; 341
  • Tidskriftsartikel (refereegranskat)abstract
    • The radiative recombination in InxGa1-xN0.01As0.99/GaAs quantum well structures exhibiting strong carrier localization was investigated by optical spectroscopy. For In-concentration from 0 to 30%, the results indicate that the degree of carrier localization decreases with increasing In-concentration. At temperatures below 100 K, the mobility edge excitons as well as localized excitons are identified and their transitions energies strongly depend on the excitation intensity. At elevated temperatures the localized excitons become quenched. The temperature dependence of the photoluminescence emission energy shows different behaviors at different excitation intensities.
  • Adolfsson, Göran, 1981-, et al. (författare)
  • Direct observation of lateral carrier diffusion in ridge waveguide InGaNAs lasers
  • 2009
  • Ingår i: IEEE Photonics Technology Letters. - 1041-1135. ; 21:134, s. 134-136
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results from measurements of the subthreshold lateral spontaneous emission profile in 1.3-mu m wavelength ridge waveguide InGaNAs quantum-well lasers using a scanning near-field optical microscopy technique. The measurements reveal the presence of significant lateral carrier diffusion which has a profound effect on the temperature dependence of the threshold current. This effect is frequently omitted when the characteristic temperature of the threshold current is considered.
  • Adolfsson, Göran, 1981-, et al. (författare)
  • Effects of Lateral Diffusion on the Temperature Sensitivity of the Threshold Current for 1.3 um Double Quantum-Well GaInNAs/GaAs Lasers
  • 2008
  • Ingår i: IEEE Journal of Quantum Electronics. ; 44:7, s. 607-616
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an experimental and theoretical investigation of the temperature dependence of the threshold current for double quantum well GaInNAs–GaAs lasers in the temperature range 10 C–110 C. Pulsed measurements of the threshold current have been performed on broad and narrow ridge wave guide (RWG) lasers. The narrow RWG lasers exhibit high characteristic temperatures (T0)of 200 K up to a critical temperature (Tc), above which T0 is reduced by approximately a factor of 2. The T0-values for broad RWG lasers are significantly lower than those for the narrow RWG lasers, with characteristic temperatures on the order of 100 (60) K below (above). Numerical simulations, using a model that accounts for lateral diffusion effects, show good agreement with experimental data and reveal that a weakly temperature dependent lateral diffusion current dominates the threshold current for narrow RWG lasers.
  • Ferdos, Fariba, 1966-, et al. (författare)
  • Influence of a thin GaAs cap layer on structural and optical properties of InAs quantum dots
  • 2002
  • Ingår i: Applied Physics Letters. - 0003-6951. ; 81:7, s. 1195-7
  • Tidskriftsartikel (refereegranskat)abstract
    • In this letter we investigate the changes in the surface morphology and emission wavelength of InAs quantum dots (QDs) during initial GaAs encapsulation by atomic force microscopy and photoluminescence. The density (2.9×1010 cm-2) and height (7.9±0.4 nm) of the uncapped QDs decrease and saturate at 0.6×1010 cm-2 and 4 nm, respectively, after the deposition of 4 monolayers (MLs) of GaAs. A model for the evolution of surface morphology is proposed. Photoluminescence spectra of the surface dots show a wavelength shift from 1.58 to 1.22 ?m when the GaAs capping layer thickness increases from 0 to 8 MLs.
  • Ferdos, Fariba, 1966-, et al. (författare)
  • Influence of initial GaAs and AlAs cap layers on InAs quantum dots grown by molecular beam epitaxy
  • 2003
  • Ingår i: Journal of Crystal Growth. - 0022-0248. ; 251:1-4, s. 145-9
  • Tidskriftsartikel (refereegranskat)abstract
    • Capping of InAs quantum dots (QDs) with AlAs or GaAs causes a significant change in the structural properties of the QDs. However, there is a basic difference between these two capping materials. The GaAs capping causes a dramatic reduction of the dot density and height. AlAs capping, on the other hand, results in a partly suppressed height reduction and a higher dot density.
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