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  • 1990-1994  (15)
  • 1980-1984  (1)
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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Heteroepitaxy, polymorphism, and faulting in GaN thin films on silicon and sapphire substrates (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4430-4437 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of GaN films grown by electron-cyclotron-resonance-assisted molecular beam epitaxy on Si(111), Si(001), basal-plane sapphire, a-plane sapphire, and r-plane sapphire substrates was studied with four-circle x-ray diffractometry. Phase content, domain size, inhomogeneous strain, and in-plane and out-of-plane domain misorientations were measured and compared for films grown on each type of substrate. Wurtzite and zinc blende polymorphs were found to coexist in films grown on Si(111). The two structures grow in the (0002) and (111) orientations, respectively, so that they may transform into each other via stacking faults on close-packed planes. Smaller amounts of zinc blende material were also found in predominately (0002) wurtzitic films on a-plane sapphire and (112¯0) wurtzitic films on r-plane sapphire.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354414
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of the impurity concentration on charge carrier dynamics in GaAs films (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1558-1560 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of the silicon concentration on excess charge carrier kinetics in molecular beam epitaxy grown GaAs films has been studied by transient photoconductivity measurements with a contactless microwave conductivity technique. Several decay channels can be distinguished: an initial, fast second-order decay more active in low impurity films and at high excitation intensities, and a slower decay component characterized by effective decay times ranging from 6 μs for low impurity samples and increasing decay times with increasing Si concentration. The initial, fast second-order decay is attributed to electron-hole recombination and is quenched by hole traps present at higher Si concentrations. In low impurity samples, the slower decay channel is ascribed to a deep electron trapping channel which can be saturated at higher excitation intensities. In high impurity samples, the decay time exceeds 100 μs and may be due to electron-trapped hole transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103152
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of nitrogen on the growth of diamond films (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 403-405 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The incorporation of nitrogen in diamond films and its effect on film growth were investigated. The nitrogen doping efficiency was found to be very low, consistent with a model of film growth involving simultaneous deposition and etching, which predicts a doping efficiency of 10−4. The growth habit was found to change from (111) to (100) with increase of nitrogen in the gas phase from N/C = 0.1% to 10%. The growth rate of the diamond films increases, and the diamond Raman peak sharpens with the amount of nitrogen, a result consistent with the model on defect-induced stabilization of diamond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112315
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  • 10
    Electronic Resource
    Electronic Resource
    Hydrogenation of p-type gallium nitride (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2264-2266 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hole concentrations of up to 1019 cm−3 have been reported for GaN:Mg films grown by molecular beam epitaxy without any post-growth treatment. Comparing results from Hall measurements and secondary ion mass spectrometry, we observe doping efficiencies of up to 10% at room temperatures in such p-type material. By hydrogenating at temperatures above 500 °C, the hole concentration can be reduced by an order of magnitude. A new photoluminescence line at 3.35 eV is observed after this treatment, both in p-type and unintentionally doped n-type material, which suggests the introduction of a hydrogen-related donor level in GaN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111639
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