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  • Articles: DFG German National Licenses  (43)
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  • Articles: DFG German National Licenses  (43)
Material
Years
  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Cathodoluminescence imaging of defects and impurities in diamond films grown by chemical vapor deposition (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3212-3218 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defects and impurities in diamond films grown by chemical vapor deposition (CVD) were analyzed by high-resolution cathodoluminescence (CL) spectroscopy and imaging in transmission electron microscopy (TEM). The combination of CL and TEM makes it possible to correlate the film microstructure with the electronic structure due to defects. Broad CL bands observed at 428±1 nm (2.90±0.01 eV) and 551±1 nm (2.250±0.004 eV) are attributed to closely spaced and widely separated donor-acceptor (D-A) pairs, respectively. A narrow peak at 738.7±0.5 nm (1.679±0.001 eV) is attributed to interstitial silicon atom impurities. An additional wide band at 365±1 nm (3.40±0.01 eV) was not identified. The material was found to be type IIb (semiconducting) and varied in quality with the growth conditions. Impurities are evidently distributed nonuniformly on a submicrometer scale, and both highly faulted and defect-free grains were found to emit no visible CL. For the first time in CVD-grown diamond, band-A CL due to closely spaced D-A pairs was found to be directly correlated with dislocations. Widely spaced D-A pairs were more uniformly distributed throughout the film. The distribution of interstitial silicon impurities varied greatly from grain to grain, but was not correlated with any microstructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348539
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  • 3
    Electronic Resource
    Electronic Resource
    Epitaxial growth and characterization of zinc-blende gallium nitride on (001) silicon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4933-4943 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave-plasma-assisted molecular-beam epitaxy, using a two-step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is grown at higher temperatures. This method of film growth was shown to lead to good single-crystalline β-GaN and to promote lateral growth resulting in smooth surface morphology. The full width at half-maximum of the x-ray rocking curve in the best case was found to be 60 min. Optical-absorption measurements indicate that the band gap of β-GaN is 3.2 eV and the index of the refraction below the absorption edge is 2.5. Conductivity measurements indicate that the films may have a carrier concentration below 1017 cm−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350642
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Photoconductive detectors based on partially ordered AlxGa1−xN alloys grown by molecular beam epitaxy (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2203-2205 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoconductive detectors based on partially ordered AlxGa1−xN alloys with AlN mole fractions up to 45% were fabricated and evaluated. The degree of ordering in these alloys was found to increase with the AlN mole fraction and it has a maximum value at about 50%. The resistivity of the AlxGa1−xN films was found to increase from 10 to 108 Ω cm by increasing the Al content in the films. Correspondingly, the mobility-lifetime (μτ) product, which was determined by measuring the photoconductive gain, was found to decrease from 10−2 to 10−5 cm2/V. These high values of the μτ product at the high AlN mole fraction are attributed to spatial separation and indirect recombination of the photogenerated electron hole pairs, due to band-gap misalignment of the ordered and disordered domains in these films. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123801
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Application of near-edge x-ray absorption fine structure for the identification of hexagonal and cubic polytypes in epitaxial GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 4206-4208 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cubic and hexagonal GaN thin films are studied using the angular dependence of the near-edge x-ray absorption fine structure (NEXAFS) spectra recorded at the N–K edge. It is shown that the energy positions of the NEXAFS resonances are characteristic of the cubic and hexagonal structures and, thus, the NEXAFS spectra can be used as a fingerprint of the symmetry of the examined crystal. Deviations from the zinc-blende or wurtzite phases are clearly detectable since they lead to a systematic energy shift in the NEXAFS resonances. Finally, a method is proposed for the quantitative estimation of the percentages of the cubic and wurtzite phases present in a mixed crystal. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116987
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