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  • Artikel  (35)
  • Oxford University Press  (16)
  • American Institute of Physics (AIP)  (15)
  • International Union of Crystallography  (4)
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  • Artikel  (35)
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  • 1
    Digitale Medien
    Digitale Medien
    Diffusion-induced defects in GaAs by zinc and the effects of post-diffusion anneal (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3494-3502 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The crystallographic defects generated during the diffusion of zinc into GaAs have been studied using transmission electron microscopy and chemical etching techniques. By observing the effects of arsenic pressure on the defect density and the zinc penetration, the annihilation of the diffusion-induced defects in relation to the surface stoichiometry was investigated. It was found that the dissolution of the defects within the crystal is mainly caused by the out-diffusion of the diffusion-induced Ga interstitials to the surface. This is also supported by results obtained from post-diffusion annealing of the samples under different arsenic pressures. In addition, the possible inclusion of arsenic atoms in the interstitial dislocation loops found in GaAs is also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348490
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  • 2
    Digitale Medien
    Digitale Medien
    Role of point defects in the silicon diffusion in GaAs and Al0.3Ga0.7As and in the related superlattice disordering (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2225-2237 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The mechanism of silicon diffusion in GaAs, Al0.3Ga0.7As, and the silicon diffusion-induced layer disordering of multiquantum wells have been studied by photoluminescence, secondary-ion-mass spectroscopy, and transmission electron microscopy across a corner of a wedge-shaped sample. The diffusion source was a grown in highly Si-doped layer. The main photoluminescence properties of point defects in GaAs and Al0.3Ga0.7As are reviewed to interpret the experimental data. The depth profile of the photoluminescence allows the spatial correlation between the luminescence spectra and the Si concentration profile obtained from secondary-ion-mass-spectroscopy measurements. On the basis of the photoluminescence results, the physical processes occurring during the Si diffusion are discussed. Frenkel defects (pairs of element-III vacancies and interstitials) are generated in the highly Si-doped region. The element-III interstitials rapidly diffuse towards the surface where they react with the element-III vacancies generated at the surface when annealing is performed in an external As pressure. This induces a supersaturation of element-III vacancies in the Si-doped region which drives the Si diffusion. Annealing in vacuum reduces the oversaturation of element-III vacancies and, hence, reduces the Si diffusion. A domination of the Si donor–element-III vacancy complex emission band was found in the spectra taken in the Si-diffused region. This gives evidence for the vacancy-assisted mechanism in the Si diffusion and in the impurity-induced disordering.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351120
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  • 3
    Digitale Medien
    Digitale Medien
    Photoreaction dynamics of CO oxidation on Pt(111) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6307-6310 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The dynamics of the surface aligned photoreaction between submonolayers of O2 and CO coadsorbed on a Pt(111) surface at 25 K and laser irradiated at 308 nm are explored by measurement of angle-resolved translational energy distributions for the CO2 photoproduct.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462621
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  • 4
    Digitale Medien
    Digitale Medien
    Photoinduced dissociative electron attachment of CH3Br on Pt(111): The role of the local work function (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9114-9121 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The photoinduced dissociative electron attachment of CH3Br on Pt(111) has been examined by measuring CH3 photofragment translational energy distributions from CH3Br adsorbed on Xe multilayers deposited upon CH3Br covered Pt(111). Subvacuum level, photoexcited substrate electrons produced by 308 nm laser irradiation were found to propagate through the Xe layer where attachment to CH3Br led to fragmentation. A simple model for surface dissociative electron attachment, DEA, was found to quantitatively predict the observed fragmentation dynamics for the CH3Br/Xe/CH3Br/Pt(111) system. The role of the local work function in surface DEA processes was explored by examining the dependence of the photofragment yield upon the thickness of the intermediate Xe layer and the fractional coverage of the Pt(111) bound first layer of CH3Br. Three dimensional variation of the local work function above the substrate was required to account for the observed DEA dynamics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462220
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  • 5
    Digitale Medien
    Digitale Medien
    Photochemistry of adsorbed molecules. IV. Photodissociation, photoreaction, photoejection, and photodesorption of H2S on LiF(001) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1498-1523 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The UV surface-aligned photochemistry (SAP) of submonolayers of H2S physisorbed on LiF(001) has been examined. Translational energy and angular distributions for photodissociation products and for H2S molecules leaving the surface after pulsed laser irradiation at 193 and 222 nm were measured by angularly resolved TOF to a quadrupole mass spectrometer. Single photon surface-aligned photodissociation (PDIS) of adsorbed H2S produced H with structured translational energy distributions P(ET) indicative of vibrational excitation within the complementary SH fragments. The SH vibrational distribution was bimodal and varied markedly with H2S coverage. Photoreaction (PRXN) within the adsorbate layer occurred as the H2S coverage increased beyond ∼0.1 monolayer. Molecular hydrogen was produced by PRXN of H with adjacent H2S(ad) molecules. The product H2 translational energy distribution showed evidence of both direct and indirect PRXN dynamics. At coverages greater than one monolayer, photoejection (PEJ) of H2S molecules with translational energies up to several eV was observed; PEJ was thought to be due to interadsorbate quenching of electronically excited H2S. At all the coverages examined, absorption of UV by the LiF substrate was found to photodesorb (PDES) H2S molecules with low translational energies (0–0.5 eV). The PDES was ascribed to an acoustic wave produced by laser excitation of color centers in the LiF, which were seen to fluoresce.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455716
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  • 6
    Digitale Medien
    Digitale Medien
    Photofragmentation dynamics of submonolayers of CH3Br adsorbed on Pt(111) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3957-3965 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Angle-resolved, photofragment translational energy distributions, Pcursive-theta(ET)s, arising from 308 nm laser irradiation of CH3Br adsorbed on Pt(111) are presented. Methyl photofragments were observed with translational energies extending to 2 eV and with Pcursive-theta(ET)s which varied sharply with angle of exit from the surface. The fragmentation dynamics were consistent with a mechanism of dissociative electron attachment of subvacuum level, photoexcited substrate electrons to adsorbed CH3Br. The CH3 Pcursive-theta(ET)s and the angular variation of the CH3 yield gave evidence that submonolayers of CH3Br form islands on Pt(111).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461898
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  • 7
    Digitale Medien
    Digitale Medien
    Photochemistry of adsorbed molecules. III. Photodissociation and photodesorption of CH3Br adsorbed on LiF(001) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1475-1497 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Submonolayers of CH3Br physisorbed on a LiF(001) surface were irradiated by pulsed ultraviolet (UV) in ultrahigh vacuum in a study of surface aligned photochemistry (SAP). Translational energy and angular distributions were obtained for both photofragments and photodesorbed molecules by angularly resolved time of flight to a mass spectrometer. Single-photon adsorbate photolysis (PDIS) led to photofragment distributions, CH3 and Br, which differed from gas-phase photolysis. Photodesorption (PDES) of CH3Br was nonthermal and arose from UV absorption by the LiF crystal. The dynamics for these photoprocesses were found to vary in an informative way with the coverage and the phase of the adsorbed layer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455148
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  • 8
    Digitale Medien
    Digitale Medien
    Improved refractive index formulas for the AlxGa1−xN and InyGa1−yN alloys (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1108-1115 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A detailed understanding of the nitride refractive indices is essential for the modeling and design of III–N laser structures. In this article, we report on the assessment of the refractive index data available for the nitride alloys and present formulas for evaluating the refractive indices for variations in both composition and photon energy. For AlxGa1−xN, an expression is given which fits well to experimental data below x〈0.38, sufficient for the molefractions found in the cladding layers of III–N lasers. Due to the almost complete lack of experimental refractive index data for InyGa1−yN, we propose an expression to give a first-order approximation for the refractive index. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1320007
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  • 9
    Digitale Medien
    Digitale Medien
    Photochemical hydrogenation of methyl radicals on Pt(111) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5971-5973 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Submonolayers of methyl bromide and hydrogen were coadsorbed on a 25 K Pt(111) surface and laser irradiated at 308 nm. Photoinduced dissociative electron attachment of methyl bromide produced energetic methyl radicals that reacted with hydrogen to form methane. The photoreaction dynamics is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464856
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  • 10
    Digitale Medien
    Digitale Medien
    Optical and photoelectric study of mirror facets in degraded high power AlGaAs 808 nm laser diodes (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3227-3233 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Mirror facets of broad area AlGaAs SQW 808 nm lasers with fast degradation of the output power have been investigated by photoluminescence microscopy (PLM), electroluminescence microscopy, and micro-photocurrent spectroscopy techniques. Over 2000 images of the photoluminescent light emitted from the facets of approximately 20 degraded laser bars have been made. Repeating patterns associated with the degradation have been noted and classified. Degraded lasers have dark lines on the mirror facet surface which are inclined from the epitaxial plane by 55°. Pairs of such lines often form V-shaped patterns. The orientation of the observed features suggest they are planar or line defects lying the the {111} crystallographic planes. The defects demonstrate a reduction in the lifetime of nonequilibrium electron–hole pairs and increased density of states in the forbidden gap of the active region of the laser structure, and are directly related to laser failure. Observations of the evolution in size and contrast of PLM patterns with ageing suggest the defects were initially created in the active region side of the laser structures during crystal growth or during the mounting procedure, and later propagate in the {111} planes, stimulated by the lasing action. We interpret the V formation to be a way to relax a compressive strain in the epitaxial plane. A dislocation on the {111} planes could actually translate the portion of the crystal bounded by the V upwards (away from the mounting of the crystal), in response to compressive strain. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372328
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