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  • 1
    Digitale Medien
    Digitale Medien
    Carbon incorporation in GaAs and AlxGa1−xAs layers grown by molecular-beam epitaxy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 77-81 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: GaAs:C and AlxGa1−xAs:C films, grown by solid-source molecular-beam epitaxy with doping levels beyond 1019 cm−3, have been studied by high-resolution double-crystal x-ray diffraction, Hall-effect measurements, and secondary-ion-mass spectroscopy (SIMS). Comparison between x-ray diffraction and Hall-effect data indicate that carbon is preferentially incorporated as acceptor on As lattice sites both in the GaAs:C and in the AlxGa1−xAs:C films. It was found that the higher the AlAs mole fraction the higher is the concentration of carbon incorporated on As sites (CAs). Moreover, SIMS results showed that the total amount of carbon in the host lattices largely exceeds CAs. Our findings are explained by supposing that carbon atoms are incorporated on As sites and on interstitial sites. Furthermore, it is shown that the carbon interstitial concentration can be reduced growing at higher arsenic flux and higher substrate temperature in GaAs:C as well as in AlxGa1−xAs:C layers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355200
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  • 2
    Digitale Medien
    Digitale Medien
    Magnetic structure of epitaxially grown MnAs on GaAs(001) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2766-2770 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigate in detail the occurrence of magnetic domains in epitaxially grown MnAs films on GaAs(001) by magnetic force microscopy (MFM). MnAs layers exhibit in their demagnetized state a very complex magnetic domain structure. High resolution MFM images reveal detailed information on the domain wall. Additionally, we imaged magnetic domains in the dependence on the applied magnetic field. This detailed investigation gives new insight into the correlation between film topography and magnetic domain structures. Systematic magnetization measurements in-plane and out-of-plane have shown high anisotropy in our films. The out-of-plane magnetization determined as a function of the applied field reveals that the direction of the magnetic moments in the domain walls are out-of-plane, thus the domain walls are determined as 180° Bloch type. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1287607
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  • 3
    Digitale Medien
    Digitale Medien
    Influence of heteroepitaxy on the width and frequency of the E2 (high)-phonon line in GaN studied by Raman spectroscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3634-3641 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Wurtzite GaN layers are commonly grown heteroepitaxially on 6H–SiC or Al2O3 substrates, because of the lack of lattice-matched substrates. We study the influence of these substrates mainly on the E2(high)-phonon Raman line by temperature dependent Raman spectroscopy. We find that the line broadening with sample heating is predominantly caused by intrinsic phonon–phonon scattering in GaN. The small three-phonon contribution as well as the small intrinsic linewidth at low temperature are due to the rather low two-phonon density of states at the E2(high)-phonon energy. Substrates with large lattice mismatch cause inhomogeneous strain and defects in the layers, which lead to a large, temperature independent, line broadening. We show that the temperature shift of the E2(high)-phonon frequency is dominated by the GaN lattice expansion. The lattice of epilayers is strongly modified by the thermal in-plane expansion of the substrate. The degree of relaxation at the growth temperature is reflected by deviation of the E2(high)-line from the intrinsic phonon frequency. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1347406
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  • 4
    Digitale Medien
    Digitale Medien
    Fundamental relationship of excitonic photoluminescence intensity with excitation density in semiconductor quantum well structures (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4075-4078 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The fundamental relationship between excitonic photoluminescence (PL) intensity and excitation intensity in semiconductor quantum well structures is developed. This relationship is further simplified in the regime of low excitation, and used for a fit function of the Arrhenius plot of time-integrated PL intensity. The proposed four fit parameters are definitely correlated to the distinct characteristic quantities of the sample material, which are the binding energy of excitons, the activation energy, the scattering time, and the background concentration in the well. The validity of the model has been confirmed using our experiments. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1290708
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  • 5
    Digitale Medien
    Digitale Medien
    Deformations in (Al,Ga)As epitaxial layers wafer bonded on dissimilar substrates (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2173-2178 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Deformations in heteroepitaxial layer stacks of AlGaAs/GaAs grown on GaAs are measured by triple crystal diffractometry before epitaxial liftoff and after subsequent wafer bonding on various substrates (GaAs, glass, Si, and LiNbO3). The tetragonal deformation present in the as-grown layer stack partially relaxes during epitaxial liftoff. The roughness of the as-grown layer stack gives rise to a bending of the atomic planes after wafer bonding. The widths of the x-ray diffraction peaks are used to estimate the misorientation of the lattice planes and compared with the atomic force microscopy measurements of the surface roughness. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1342804
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  • 6
    Digitale Medien
    Digitale Medien
    Structural characterization of lattice matched AlxIn1−xAs/InP and GayIn1−yAs/InP heterostructures by transmission electron microscopy and high-resolution x-ray diffraction (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2403-2410 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this work we report on transmission electron microscopy and high-resolution x-ray diffractometry studies of lattice matched AlxIn1−xAs/InP and GayIn1−yAs/InP epilayers grown by molecular beam epitaxy on InP(100) substrates. High-resolution and diffraction contrast electron microscopy measurements show the presence of different contrast zones in the epilayers. The analysis of high-resolution x-ray diffraction measurements and computer simulations ascribe these zones to the presence of a compositional gradient in the epilayers. A comparison among investigated samples grown under slightly different growth conditions combined with an analysis of the crystal defects is presented. Growth-induced small variations in the chemical composition of the epilayer can produce differences in the structural quality of the epitaxial layer. Finally, a few monolayers thick and highly strained film of InAsP, is observed in all investigated samples at the substrate/epilayer interface. The formation of this interface layer is explained by the exchange of As and P during exposure of the InP surface to As4 before the growth. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.360162
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  • 7
    Digitale Medien
    Digitale Medien
    SnTe-doping of GaAs grown by atomic layer molecular beam epitaxy (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4339-4342 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using x-ray diffraction and ellipsometry we have studied the incorporation process of SnTe in GaAs for n-type doping. Combining these two techniques allows us to decide whether SnTe is incorporated pairwise, as has been proposed in the literature. We found SnTe doping to change the E1 and E1+Δ1 critical point parameters in a way similar to that previously reported for n-type Si-doped GaAs. X-ray diffraction and Hall measurements show that the free carrier concentration is more than 1/2 of the [Sn]+[Te] concentration. We thus conclude that a large proportion of SnTe is incorporated as independent Sn and Te dopant atoms. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359458
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  • 8
    Digitale Medien
    Digitale Medien
    Asymmetrical source-drain characteristics in in-plane-gated transistors written by focused ion beam (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6710-6714 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We observe electrically asymmetrical source-drain characteristics in in-plane-gated transistors with shaped channels, and investigate them for different geometries. We give a qualitative explanation of the asymmetry, which is supported by voltage contrast scanning electron micrographs and the measured interaction between two neighboring channels. These shaped channels show a much higher dc voltage gain than conventional in-plane-gated transistors. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359085
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  • 9
    Digitale Medien
    Digitale Medien
    A Raman spectroscopic study of the Si, Be, and C incorporation in InxGa1−xAs relaxed layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4690-4695 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The incorporation of high concentrations ((approximately-greater-than)1019 cm−3) of Si, Be, and C in InxGa1−xAs relaxed layers has been studied as a function of In content (x≤0.16) by Raman spectroscopy of local vibrational modes (LVM). The frequencies of the Raman peaks resulting from the convolution of several split modes shift to lower values as the In content is increased, the carbon acceptor (CAs) local mode frequency showing the strongest dependency on x. Features attributed exclusively to the influence of In on second-neighbor sites are identified only in the Si-doped samples. The transverse and longitudinal modes expected from the splitting of a LVM of CAs with one In first neighbor are not observed in layers with x up to 0.085. A new calibration for the BeGa, CAs, and Si-related LVM leads to the conclusion that In increases the total electrical activation of Si and favors its incorporation on group-III sublattice sites. In contrast, no influence of In on the Be or C doping activation has been detected. The analysis of the CAs LVM spectra supports the view that in InxGa1−xAs CAs is preferably surrounded by Ga instead of In atoms for x≤0.085. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359816
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  • 10
    Digitale Medien
    Digitale Medien
    Thermal strain effects on the excitonic states in GaAs/AlxGa1−xAs multiple quantum wells (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4750-4752 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Temperature-dependent absorption experiments have been performed to investigate the effect of thermal strain in GaAs/AlxGa1−xAs multiple quantum wells clad by thick AlGaAs layers. A temperature-dependent splitting of the heavy-hole and light-hole excitons is observed between 10 and 300 K. This is ascribed to the different thermal expansion coefficient of GaAs and AlxGa1−xAs, causing the constituent GaAs layers to be under weak tensile strain during the optical measurements at different temperatures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355933
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