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  • 1
    Electronic Resource
    Electronic Resource
    Determination of argon in sputtered silicon films by energy-dispersive x-ray fluorescence spectrometry (1981)
    s.l. : American Chemical Society
    Analytical chemistry 53 (1981), S. 1792-1795 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac00235a017
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  • 2
    Electronic Resource
    Electronic Resource
    Structure of tungsten carbide-cobalt multilayers (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4256-4259 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multilayers composed of ceramic and metallic materials, such as tungsten carbide and cobalt, have been synthesized for the first time. The structure of these multilayers was investigated by low-angle x-ray diffraction and transmission electron microscopy lattice imaging and microdiffraction. The data show that the low-temperature process of forming these two-dimensional composites leads to unique crystal structures and morphology in the nanometer scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343309
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  • 3
    Electronic Resource
    Electronic Resource
    Growth of gallium nitride thin films by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 448-455 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on optimization studies for the growth of GaN films by the electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (ECR-MBE) method on the R plane of sapphire. The films were grown by the reaction of Ga vapor with ECR-activated molecular nitrogen and their growth kinetics were found to depend strongly on the distance between the ECR condition and the substrate. Single crystalline films with their α plane (112¯0) parallel to the R plane of sapphire (101¯2) were grown with the substrate held at 400–700 °C. All films were found to be n type with carrier concentrations varying between 1017 and 1019 cm−3. Films grown at 600 °C were found to have the smallest amount of strain and the highest electron mobility, suggesting that strain might be one of the sources of compensating defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353870
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray characterization of GaN/AlGaN multiple quantum wells for ultraviolet laser diodes (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1004-1006 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN/Al0.20Ga0.80N (50 Å/50 Å) multiple quantum wells (MQW) with 15 periods were grown on (0001) sapphire substrates by molecular beam epitaxy and evaluated by x-ray diffraction. To simulate an ultraviolet laser diode structure, the substrate was coated first with n-GaN as the bottom contact layer and n-Al0.25Ga0.75N as the corresponding cladding layer. The crystal structure of this system was investigated by studying the reciprocal lattice map of off-axis diffraction peaks as well as the θ–2θ pattern around the (0002) reflection. The MQW was found to be coherent and has the a-lattice parameter of the underlying Al0.25Ga0.75N. The good agreement between experimental and theoretical data in the relative intensity of up to third-order satellite peaks supports that the interfaces of the MQW are abrupt, and thus, interdiffusion of Ga and Al atoms at the growth temperature was negligible. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120976
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  • 5
    Electronic Resource
    Electronic Resource
    Intensity dependence of photoluminescence in GaN thin films (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 336-338 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the intensity dependence of band-gap and midgap photoluminescence in GaN films grown by electron cyclotron resonance (ECR) microwave plasma-assisted molecular beam epitaxy. We find that the band-gap luminescence depends linearly while the midgap luminescence has a nonlinear dependence on the incident light intensity. These data were compared with a simple recombination model which assumes a density of recombination centers 2.2 eV below the conduction band edge. The concentration of these centers is higher in films grown at higher microwave power in the ECR plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111968
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  • 6
    Electronic Resource
    Electronic Resource
    The role of dislocation scattering in n-type GaN films (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 821-823 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The lateral transport in GaN films produced by electron cyclotron resonance plasma-assisted molecular beam epitaxy doped n type with Si to the levels of 1015–1020 cm−3 was investigated. The room temperature electron mobility versus carrier concentration was found to follow a family of bell-shaped curves consistent with a recently proposed model of scattering by charged dislocations. The mechanism of this scattering was investigated by studying the temperature dependence of the carrier concentration and electron mobility. It was found that in the low carrier concentration region (〈1017 cm−3), the electron mobility is thermally activated with an activation energy half of that of carrier concentration. This is in agreement with the prediction of the dislocation model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122012
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  • 7
    Electronic Resource
    Electronic Resource
    Characteristics of light-emitting diodes based on GaN p-n junctions grown by plasma-assisted molecular beam epitaxy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2779-2783 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the fabrication and physics of mesa-etched light-emitting diodes (LEDs) made from GaN p-n junctions grown by molecular beam epitaxy. Rapid thermal annealing was found to improve the electrical properties of these LEDs. Annealed LEDs turn on at 4 V, exhibit an on-series resistance of approximately 14 Ω, and have only 36 μA of leakage current for reverse bias levels as high as 10 V. Electroluminescence (EL) spectra obtained from devices driven to 15 mA are dominated by a peak at 400 nm, which is attributed to recombination between shallow donors and Mg luminescent centers on the p side of the junction. The full width at half maximum of this peak is only 30 nm, which, to the best of our knowledge, is the narrowest EL peak measured from a GaN p-n junction LED. In other devices, recombination was found to proceed through defect states in the middle of the band gap. The broad emission from these LEDs can be shifted from the orange to the violet spectral region by adjusting the drive current. In addition, these LEDs withstand dc current densities in excess of 700 A/cm2 at room temperature. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361109
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  • 8
    Electronic Resource
    Electronic Resource
    Temperature dependence of the energy gap in GaN bulk single crystals and epitaxial layer (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2429-2434 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We performed optical-absorption studies of the energy gap in various GaN samples in the temperature range from 10 up to 600 K. We investigated both bulk single crystals of GaN and an epitaxial layer grown on a sapphire substrate. The observed positions of the absorption edge vary for different samples of GaN (from 3.45 to 3.6 eV at T=20 K). We attribute this effect to different free-electron concentrations (Burstein–Moss effect) characterizing the employed samples. For the sample for which the Burstein shift is zero (low free-electron concentration) we could deduce the value of the energy gap as equal to 3.427 eV at 20 K. Samples with a different free-electron concentration exhibit differences in the temperature dependence of the absorption edge. We explain the origin of these differences by the temperature dependence of the Burstein–Moss effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357592
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  • 9
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357273
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  • 10
    Electronic Resource
    Electronic Resource
    Growth of gallium nitride by electron-cyclotron resonance plasma-assisted molecular-beam epitaxy: The role of charged species (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4587-4595 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of ionic and nonionic excited species of nitrogen in the growth of GaN thin films by electron-cyclotron resonance (ECR) plasma-assisted molecular-beam epitaxy has been investigated. It was found that the kinetics of film growth is significantly affected by the microwave power in the ECR discharge. Specifically, a transition from the island to a layer-by-layer and, finally, to a three-dimensional growth has been observed as a function of power. These morphological changes are accompanied by degradation of the electrical and luminescence properties, a result attributable to increased native defects and impurities. Secondary-ion-mass spectroscopic (SIMS) analysis indicates that impurity levels in the films increase with the plasma power levels used during the growth. To study the relative role of ion-induced native defects in these films, strategies for charged species extraction were developed by using an off-axis solenoid to modify the magnetic environment during growth. Films grown under a reduced ionic/excited neutral ratio environment show marked improvement in the electrical and luminescence properties. These data, together with SIMS analysis, indicate that observed improvements in these films are due to a reduction of native defects and not impurities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357293
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