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Sökning: WFRF:(Lu W) > (2000-2004) > Tidskriftsartikel > (2003)

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1.
  • Fu, Y, et al. (författare)
  • Electron mobilities, Hall factors, and scattering processes of n-type GaN epilayers studied by infrared reflection and Hall measurements
  • 2003
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 67:11
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the drift and Hall mobilities of electrons in metal-organic chemical-vapor-deposited wurtzite GaN thin films on sapphire substrate by infrared (IR) reflection and Hall measurements. By analyzing the Hall factor (the ratio between the drift mobility obtained from IR reflection spectra and the Hall mobility from the Hall measurements), it has been concluded that the electron mobility in GaN epilayer is determined by the ionized impurity when the electron concentration is low. At a high carrier concentration of 3.2x10(18) cm(-3), electronic states of more than 70 meV become populated taking into account the thermal excitation, so that the optical-phonon-scattering process becomes activated (the optical-phonon energy is 69.43 meV obtained from IR reflection measurements). Thus, in highly doped wurtzite GaN epilayers, ionized-impurity- and optical-phonon-scattering processes jointly determine the carrier transport properties.
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2.
  • Fu, Y, et al. (författare)
  • Photocurrents of 14 mu m quantum-well infrared photodetectors
  • 2003
  • Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 93:12, s. 9432-9436
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the factors that determine photogenerated carriers and response wavelengths of photocurrents of long wavelength (similar to14 mum) quantum well (QW) infrared photodetectors (QWIPs). The material structures of QWIPs are first characterized by the photoluminescence measurements (PL). By calculating the density of photogenerated carriers in the continuum above the energy barriers using the PL calibrated QWIP structures, we have demonstrated that due to the sample quality, the photocarriers can be either in miniband states (Bloch states in the multiple quantum wells), or they transport from one quantum well to the next in the form of running waves. By including possible scattering processes at the QWIP working temperature to link the theoretically calculated photocarrier density with the experimentally measured photocurrent, it is shown that the width of the photocurrent peaks of 14 mum GaAs/AlGaAs QWIPs under investigation is determined by the optical phonon emissions of photocarriers. We have further calculated the densities of photocarriers in the QWIPs reported in the literature. It is shown that the Bloch wave boundary conditions are appropriate for QWIPs with narrow QWs, whereas running wave boundary conditions are appropriate for wide QWs.
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3.
  • Li, Z-F, et al. (författare)
  • Determination of carrier-transfer length from side-wall quantum well to quantum wire by micro-photoluminescence scanning
  • 2003
  • Ingår i: Journal of Electronic Materials. - : Springer Science Business Media. - 0361-5235 .- 1543-186X. ; 32:8, s. 913-916
  • Tidskriftsartikel (refereegranskat)abstract
    • Micro-photoluminescence (mu-PL) line scanning across a single V-groove, GaAs/AlGaAs quantum wire (QWR) has been performed at room temperature, revealing a clear spatial-dependence of the PL. After fitting each PL spectrum by multi-Gaussian line shapes, intensity profiles of each PL component from confined structures have been obtained as functions of the scanning position. The PL quenching of a side-wall quantum well (SQWL) has been recognized in a certain area in the vicinity of the QWR and is interpreted by carrier transfer into the QWR within effective transfer length. By simulating the carrier-transfer process from SQWL to QWR as a convolution of a step function for carrier distribution and a Gaussian function for exciting laser irradiance, the effective transfer length of about 1.8+/-0.3 mum has, therefore, been concluded.
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4.
  • Lu, W, et al. (författare)
  • Enhancement of room-temperature photoluminescence in InAs quantum dots
  • 2003
  • Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 83:21, s. 4300-4302
  • Tidskriftsartikel (refereegranskat)abstract
    • We report pronounced enhancement of room-temperature photoluminescence up to 80-fold induced by proton implantation and the rapid thermal annealing process in a multilayer InAs/GaAs quantum-dot structure. This effect is studied by a combination of material methods and resulted from both proton passivation and carrier capture enhancement effects. The maximum photoluminescence peak shift is about 23 meV, resulting from the intermixing of quantum dots. Linear dependence behavior as observed for both the nonradiative recombination time and carrier relaxation time on the ion-implantation dose. Maximum enhancement of the photoluminescence is observed for a proton implantation dose of 1.0x10(14) cm(-2) followed by rapid thermal annealing at 700 degreesC. These effects will be useful for quantum dot optoelectronic devices.
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5.
  • Scherer, SW, et al. (författare)
  • Human chromosome 7: DNA sequence and biology
  • 2003
  • Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 300:5620, s. 767-772
  • Tidskriftsartikel (refereegranskat)abstract
    • DNA sequence and annotation of the entire human chromosome 7, encompassing nearly 158 million nucleotides of DNA and 1917 gene structures, are presented. To generate a higher order description, additional structural features such as imprinted genes, fragile sites, and segmental duplications were integrated at the level of the DNA sequence with medical genetic data, including 440 chromosome rearrangement breakpoints associated with disease. This approach enabled the discovery of candidate genes for developmental diseases including autism.
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  • Resultat 1-5 av 5

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