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  • 1
    Digitale Medien
    Digitale Medien
    Lattice constants and thermal expansion of AlxGa1−xAs:Te (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6994-6998 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An influence of Te doping on the lattice parameter and the thermal expansion of AlxGa1−xAs epitaxial layers was examined by high-resolution x-ray diffractometry over a temperature range 77–673 K. For doped AlxGa1−xAs layers the thermal expansion coefficients were found to be larger relative to undoped samples of the same Al content. This phenomenon is attributed to the change of anharmonic part of lattice vibrations by free electrons and/or ionized tellurium atoms. An increase of thermal expansion caused by doping is a factor which should be taken into account in lattice constant measurements at 295 K. We propose an interpretation of the lattice expansion (examined at room temperature by other authors and by us) of GaAs caused by Te doping in terms of three factors: (i) "size'' effect (bigger Te atoms with respect to As), (ii) free electrons via the deformation potential of the conduction-band minimum occupied by these electrons, (iii) increase of the thermal expansion. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.360467
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  • 2
    Digitale Medien
    Digitale Medien
    Thermal expansion of gallium nitride (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4909-4911 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Lattice constants of gallium nitride (wurzite structure) have been measured at temperatures 294–753 K. The measurements were performed by using x-ray diffractometry. Two kinds of samples were used: (1) bulk monocrystal grown at pressure of 15 kbar, (2) epitaxial layer grown on a sapphire substrate. The latter had a smaller lattice constant in a direction parallel to the interface plane by about 0.03%. This difference was induced by a higher thermal expansion of the sapphire with respect to the GaN layer. However, this thermal strain was created mainly at temperatures below 500–600 K. Above these temperatures the lattice mismatch in parallel direction diminished to zero at a temperature of about 800 K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357273
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  • 3
    Digitale Medien
    Digitale Medien
    Mechanism of yellow luminescence in GaN (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2188-2190 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigated the pressure behavior of yellow luminescence in bulk crystals and epitaxial layers of GaN. This photoluminescence band exhibits a blueshift of 30±2 meV/GPa for pressures up to about 20 GPa. For higher pressure we observe the saturation of the position of this luminescence. Both effects are consistent with the mechanism of yellow luminescence caused by electron recombination between the shallow donor (or conduction band) and a deep gap state of donor or acceptor character. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115098
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  • 4
    Digitale Medien
    Digitale Medien
    Optical activation and diffusivity of ion-implanted Zn acceptors in GaN under high-pressure, high-temperature annealing (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 1155-1157 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optical activation of Zn ions implanted to an epitaxial film of GaN was performed by means of sample annealing at N2 overpressure up to 1.6 GPa. By applying pressure we avoided GaN decomposition and could increase the annealing temperature up to 1550 °C versus a limit of 1000–1100 °C at ambient pressure. The Zn-acceptor-related photoluminescence (PL) intensity in implanted samples is maximized by annealing above 1350 °C after which the Zn PL intensity exceeds epitaxially doped GaN:Zn with comparable Zn concentration by factor 15. High-pressure annealing causes a significant diffusion of implanted Zn atoms in GaN films. It is also possible to diffuse Zn from the external source into the implanted/unimplanted layers. High dislocation densities strongly accelarate the Zn diffusion. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368118
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  • 5
    Digitale Medien
    Digitale Medien
    Thermal expansion of GaAs:Te and AlGaAs:Te at low temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4678-4680 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We studied the influence of free electrons on the lattice parameters, thermal expansion, and negative thermal expansion of GaAs:Te and AlGaAs:Te. The samples were examined at temperatures in the range of 10–295 K. Dylatometry and high-resolution x-ray diffraction were used as experimental techniques. Additionally, for the doped layer of Al0.32Ga0.68As, the free-electron concentration was changed in situ by illumination and emptying the metastable DX centers. These results were compared with those for GaAs bulk crystals examined using dylatometry. It was confirmed that n-type doping increases thermal expansion at temperatures higher than about 120 K. At lower temperatures, a phenomenon of the negative thermal expansion becomes much more pronounced for the doped GaAs sample. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.366207
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  • 6
    Digitale Medien
    Digitale Medien
    Influence of redistribution of electrons in the conduction band on the lattice parameters of AlxGa1−xAs (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3366-3368 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Lattice parameters of GaAs layers were measured using the Bond method. For samples heavily doped with S and Se, we observed an increase of lattice parameters with respect to the undoped samples. The results are compared with those observed for AlxGa1−xAs:S (Wagner et al.) and both are explained by the influence of free electrons and their redistribution in the conduction band. For Al0.39Ga0.61As, the following values of deformation potentials of the conduction-band minima were obtained: DΓ=−6.7 eV, DL=1.4 eV, and DX=1 eV. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.117308
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  • 7
    Digitale Medien
    Digitale Medien
    Lattice parameters of gallium nitride (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 73-75 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Lattice parameters of gallium nitride were measured using high-resolution x-ray diffraction. The following samples were examined: (i) single crystals grown at pressure of about 15 kbar, (ii) homoepitaxial layers, (iii) heteroepitaxial layers (wurtzite structure) on silicon carbide, on sapphire, and on gallium arsenide, (iv) cubic gallium nitride layers on gallium arsenide. The differences between the samples are discussed in terms of their concentrations of free electrons and structural defects. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.118123
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  • 8
    Digitale Medien
    Digitale Medien
    Evidence for localized Si-donor state and its metastable properties in AlGaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3833-3835 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Transport studies of AlxGa1−xN (0.5〈x〈0.6) doped with Si have been performed in the pressure range up to 1.4 GPa. For these alloys, the Si dopant forms two donor states. One of them has an effective mass character and the other one represents the localized state strongly coupled to the crystal lattice (metastable state). The localized state of Si forms the corresponding level in the gap for x exceeding 0.5. For the higher x, an increase of the activation energy of this state occurs. Metastable properties of the localized state of Si lead to a persistent photoconductivity effect and to a pressure induced freeze-out of electrons. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124195
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  • 9
    Digitale Medien
    Digitale Medien
    GaN homoepitaxial layers grown by metalorganic chemical vapor deposition (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1276-1278 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: GaN homoepitaxial layers were grown using metalorganic chemical vapor deposition on the highly conductive GaN bulk crystals grown at high hydrostatic pressure. The epitaxial growth process was monitored by reflectivity of red laser light. The oscillations of its intensity served for the precise evaluation of the growth rate. The layers were then investigated using far-infrared reflectivity (FIR), x-ray diffraction, and photoluminescence. The FIR spectrum gave small free-electron concentration in the layers in contrast to the substrates which had about 2.5×1019 cm−3 of free electrons. In x-ray diffraction, the peaks of the substrate and of the layer were separated due to the difference between the lattice parameters of the bulk GaN substrate (expanded by free electrons and point defects) and the layer which had a low free electron concentration. Both peaks had rocking curves with half widths of about 20 arcsec. The photoluminescence spectrum contained narrow peaks of less than 1 meV with the excitonic lines well resolved. The spectrum was dominated by the donor-bound exciton peak. All acceptor-related peaks had small intensities that indicated a very low acceptor concentration in the layers. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124666
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  • 10
    Digitale Medien
    Digitale Medien
    Lattice dilation by free electrons in heavily doped GaAs:Si (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 539-541 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Lattice constants of GaAs layers grown by molecular beam epitaxy were examined by using the high resolution x-ray diffractometer. For highly doped samples (up to 9×1018 cm−3 of free-electron concentration) we observed an increase of the lattice constant with respect to the undoped layers. Since substitutional silicon atoms decrease the lattice constant of GaAs, the results are explained by the influence of free-electrons via the deformation potential of the Γ minimum of the conduction band. The best fit to our diffractometric data was obtained for the band-gap deformation potential equal to −8.5 eV. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115181
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