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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 183-185 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the incorporation of carbon in GaAs at doping levels beyond 1019 cm−3 grown by conventional solid-source molecular-beam epitaxy. The correlation of Hall effect measurements at 77 and 300 K and of double crystal x-ray diffractometry allows us to determine the fraction of carbon incorporated on As sites acting as acceptors. These experiments reveal the onset of compensation at the highest doping levels of 5×1019 cm−3.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural characterization of ZnS epilayers grown by hydrogen transport vapor-phase epitaxy on (100)-oriented GaAs substrates is reported. X-ray-diffraction measurements in both double-axis (DA) and single-axis modes were performed to determine the residual strain tensor and the strain temperature dependence of the epilayer in the range between 25 and 650 °C. From the analysis of the data obtained by DA measurements of several symmetric Bragg reflections at different azimuth angles and several asymmetric reflections recorded in different geometries, an orthorhombic distortion of the ZnS lattice was found. The crystallographic symmetry could be explained by an asymmetric distribution of the misfit dislocation density in the interface plane along the [011] and [01¯1] directions. The temperature dependence measurements of the strain tensor components between room temperature and the growth temperature (650 °C) allowed determination of the thermal misfit between ZnS and GaAs and the linear thermal-expansion coefficient of ZnS. Finally, triple-crystal diffractometry and secondary-ion-mass spectrometry were used to investigate the chemical nature of the ZnS-GaAs interface. The results indicate the presence of an interdiffused ZnS-GaAs interface region, whose occurrence turns out to be associated with the initial defect structure of the substrate surface before the growth. © 1995 American Institute of Physics.
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed strain analysis of high resolution x-ray diffraction patterns taken from GaxIn1−xAs and AlyIn1−yAs layers grown lattice matched on (001) InP substrates shows the existence of distinct interface regions. Our dynamical diffraction model allows us to detect buried interface layers with submonolayer resolution and differences in composition of less than 1% from the rest of the epilayer. Comparison between experimental and theoretical rocking curves reveals that the interface region between epilayer and substrate comprises 2 monolayers InAs plus GaxIn1−xAs (or AlyIn1−yAs) interlayer with different group III element ratios.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strained multiple quantum wells of InxGa1−xAs/GaAs were grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) and characterized by secondary ion mass spectrometry, x-ray diffraction, and optical spectroscopy. The structural analysis demonstrates the excellent control of the interface morphology and composition achieved by MOCVD growth. Temperature dependent optical absorption, photoluminescence, and magnetotransmission were used to evaluate the well-width dependence of the major excitonic properties. The samples show sharp excitonic resonances with distinct excited states evolving into Landau-type excited states in high magnetic field. The well-width dependence of the excitonic eigenstates and of the exciton binding energy as well reproduced by envelope function and variational calculations, also in the presence of external electric field. Finally, nonlinear electro-optic modulation induced by the quantum confined Stark effect is demonstrated in a Schottky diode with extremely low switching threshold. © 1996 American Institute of Physics.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a structural study of Si/Ge multilayers grown by molecular-beam epitaxy on (100)-Si substrates. The analyses have been performed by using transmission electron microscopy, high-resolution x-ray diffraction, and secondary-ion-mass spectrometry. The investigated specimens differ in number of periods, period thickness, and in the Si/Ge periods thickness ratio. In particular, we investigate the interdiffusion of the Ge atoms in each superlattice period of the epilayer and in the epilayer as whole. The interdiffusion causes a broadening of the nominal thickness of the Ge layer producing a SixGe1−x alloy. Furthermore, the Ge content in the multilayer periods increases as a function of the growth time, i.e., the superlattice periods close to the sample surface contain more Ge atoms if compared to the periods close to the substrate/superlattice interface. We find two steps in the strain relaxation: (i) In each period the strain energy density is partially reduced by the formation of coherent islands; (ii) at a certain value of the strain energy density the shape of the islands changes and the structures relax partially or completely the accumulated strain energy by nucleation of extended defects. © 1996 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural properties of β-FeSi2 films grown on Si(111) are studied by means of several techniques. The films were grown in ultrahigh vacuum by solid phase epitaxy. The as-deposited Fe films were studied in situ by low energy electron diffraction (LEED) and Auger spectroscopy. Fe thicknesses were calibrated by Rutherford backscattering. The behavior of the FeMVV/SiLVV Auger peaks ratio intensity as a function of Fe thickness indicates a Stranski–Krastanov mode of growth. Annealing of the Fe layers at temperatures between 400 and 600 °C led to the β-FeSi2 formation. Sharp LEED patterns typical of the β-FeSi2 orthorhombic structure were obtained. X-ray double-crystal diffraction was carried out on a film about 200 A(ring) thick in order to determine the lattice mismatch between the β-FeSi2 and the Si(111) planes accurately. The measured value of (2.1±0.1)×10−2 unambiguously indicates that (101) epitaxy takes place only on Si(111). No elastic strain of the overlayer was evident. The full width at half maximum of the overlayer diffraction peak indicates a good crystalline quality. An upper limit for mosaic spread was determined to be about 0.05°.
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