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  • 1
    Electronic Resource
    Electronic Resource
    Raman analysis of the E1 and A1 quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3535-3539 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article presents a study of the quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN which originate from the interaction of phonons belonging to the A1 and E1 symmetry groups. In order to analyze the allowed quasi as well as pure Raman modes, the modes were observed in a rotating crystallographic coordinate system, and the Raman tensors of the wurtzite crystal structure were calculated as a function of the crystallographic rotation. The frequencies of the quasimodes of wurtzite AlN were also analyzed in terms of the interaction of the polar phonons with the long range electrostatic field model. The experimental values of the Raman frequencies of the quasiphonons concur with these expected from the model, implying that the long range electrostatic field dominates the short range forces for polar phonons in AlN. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369712
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  • 2
    Electronic Resource
    Electronic Resource
    Thermal mismatch stress relaxation via lateral epitaxy in selectively grown GaN structures (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2492-2494 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A reduction in the dislocation density of 104–105 cm−2 has been achieved via lateral epitaxial overgrowth (LEO) of GaN films selectively grown from stripes etched in SiO2 masks deposited on GaN/AlN/6H–SiC(0001) heterostructures. The magnitudes and distribution of stresses generated in the LEO GaN layer and the SiO2, due primarily to differences in the coefficients of thermal expansion, were modeled using finite element (FE) analysis. These calculations showed that localized compressive stress fields of (approximate)3 GPa occurred at the edges of the LEO GaN in the vicinity of the GaN/SiO2 interface. Localized compression along the GaN substrate/SiO2 interface and tension along the 〈0001〉 direction were responsible for the change in shape of the SiO2 stripes from rectangular with flat sides to an airfoil shape with curved sides. The FE calculations also revealed that an increase in the width of the LEO GaN regions over the SiO2 or the reduction in the separation between the GaN stripes (all other dimensions being fixed) resulted in a slight reduction in the compressive stresses along the LEO GaN/SiO2 interface and an increase in the compressive stress along [0001]. An increase in the shear stress, at the corners of the LEO GaN near the LEO GaN/SiO2 interface, with an increase in the width of the LEO GaN region were also indicated. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123017
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  • 3
    Electronic Resource
    Electronic Resource
    Dislocation density reduction via lateral epitaxy in selectively grown GaN structures (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2472-2474 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure and the lateral epitaxy mechanism of formation of homoepitaxially and selectively grown GaN structures within windows in SiO2 masks have been investigated by transmission electron microscopy (TEM) and scanning electron microscopy. The structures were produced by organometallic vapor phase epitaxy for field emission studies. A GaN layer underlying the SiO2 mask provided the crystallographic template for the initial vertical growth of the GaN hexagonal pyramids or striped pattern. The SiO2 film provided an amorphous stage on which lateral growth of the GaN occurred and possibly very limited compliancy in terms of atomic arrangement during the lateral growth and in the accommodation of the mismatch in the coefficients of thermal expansion during cooling. Observations with TEM show a substantial reduction in the dislocation density in the areas of lateral growth of the GaN deposited on the SiO2 mask. In many of these areas no dislocations were observed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120091
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  • 4
    Electronic Resource
    Electronic Resource
    Raman analysis of the configurational disorder in AlxGa1−xN films (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2157-2159 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman analysis of the E2 mode of AlxGa1−xN in the composition range 0≤x≤1 is presented. The line shape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the line shape. The model calculations also indicate the lack of a long-range order in the chemical vapor deposition alloys. These results were confirmed by x-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x≅0.5 indicative of a random disordered alloy system. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119367
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  • 5
    Electronic Resource
    Electronic Resource
    Deposition of highly resistive, undoped, and p-type, magnesium-doped gallium nitride films by modified gas source molecular beam epitaxy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 990-992 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Undoped, highly resistive ((approximately-greater-than)102 Ω cm) and Mg-doped, p-type (0.3 Ω cm) monocrystalline GaN films with a thickness of (4–5)×103 A(ring) have been achieved via modified gas source molecular beam epitaxy on AIN buffer layers without the post-processing procedures of either electron beam irradiation or annealing necessary in chemical vapor deposition (CVD) derived films. The carrier concentrations and mobilities could not be accurately measured in the undoped films; values to 1018 cm−3 and 10 cm2/V s, respectively, have been achieved in the p-type films. These results indirectly support the hypothesis of Mg-H complexes as the cause of the difficulty in achieving highly conducting p-type materials using CVD techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109816
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  • 6
    Electronic Resource
    Electronic Resource
    Aluminum nitride/silicon carbide multilayer heterostructure produced by plasma-assisted, gas-source molecular beam epitaxy (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3333-3335 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pseudomorphic structures containing β(3C)-SiC and 2H-AlN have been grown on vicinal α(6H)-SiC(0001) at 1050 °C by plasma-assisted, gas-source molecular beam epitaxy. Reflection-high energy electron diffraction and cross-sectional high-resolution transmission electron microscopy showed all layers to be monocrystalline. The AlN layers were uniform in thickness. Defects in these layers initiated at steps on the 6H-SiC film. The 3C-SiC layers contained a high density of stacking faults and microtwins caused primarily by the interfacial stresses generated by the mismatch in lattice parameters between AlN and β-SiC coupled with the very low stacking fault energy of SiC. This is the first report of the deposition of single crystal SiC/AlN/SiC thin film heterostructures on any substrate as well as the first report of the epitaxial growth of single crystal layers of binary materials with three different crystal structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109062
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of self-implantation on structure and oxidation behavior of single crystal β-SiC (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 423-425 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystal β-SiC was self-implanted with high-dose Si and C at 773 K. In situ lattice recovery occurred and SiC remained single crystalline during implantation. Notable structural damage resulted in the implanted region. The residual damage significantly accelerated the oxidation rate of SiC at 1373 K but caused no appreciable rate increase at 1573 K. The diminishing of the effect of the damages on oxidation can be attributed to enhanced damage annealing with temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108922
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  • 8
    Electronic Resource
    Electronic Resource
    Initial stage of aluminum nitride film growth on 6H-silicon carbide by plasma-assisted, gas-source molecular beam epitaxy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 37-39 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The initial stage of AlN film growth on 6H-SiC(0001) substrates by plasma-assisted, gas source molecular beam epitaxy (PAGSMBE) has been investigated in terms of growth mode and interface defects. Cross-sectional high resolution transmission electron microscopy (HRTEM) was used to observe the microstructure of the deposited films and the AlN/SiC interfaces. Surface morphologies and interface atomic structures were compared between films grown on vicinal and on-axis surfaces. Essentially atomically flat AlN surfaces were obtained using on-axis substrates. This is indicative of two-dimensional growth to a thickness of ∼15 A(ring). Islandlike features were observed on the vicinal surface. The coalescence of these features at steps gave rise to double positioning boundaries (DPBs) as a result of the misalignment of the Si/C bilayer steps with the Al/N bilayers in the growing film. The quality of thicker AlN films is strongly influenced by the concentration of DPBs formed at the outset of growth. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114173
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of gas flow ratio on silicon carbide thin film growth mode and polytype formation during gas-source molecular beam epitaxy (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2851-2853 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon carbide thin films have been grown on vicinal 6H-SiC(0001) substrates by gas-source molecular beam epitaxy at 1050 °C. The effect of gas flow ratios (C2H4Si2H6=1,2,10) on the growth mode was examined via cross-sectional high resolution transmission electron microscopy and in situ reflection high energy electron diffraction. Step flow, step bunching, and the deposition of 6H-SiC occurred at the outset of the exposure of the (1×1) surface to the reactants using any flow ratio. Subsequent deposition resulted in step flow and continued growth of 6H films or formation and coalescence of 3C-SiC islands using the gas flow ratio of one of the ethylene-rich ratios, respectively. The (3×3) surface reconstruction observed using the former ratio is believed to enhance the diffusion lengths of the adatoms which, in turn, promotes step flow growth. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112513
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  • 10
    Electronic Resource
    Electronic Resource
    GaN thin films deposited via organometallic vapor phase epitaxy on α(6H)–SiC(0001) using high-temperature monocrystalline AlN buffer layers (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 401-403 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Monocrystalline GaN(0001) thin films, void of oriented domain structures and associated low-angle grain boundaries, have been grown via organometallic vapor phase epitaxy (OMVPE) on high-temperature monocrystalline AlN(0001) buffer layers predeposited on vicinal α(6H)–SiC(0001) wafers using TEG, TEA, and ammonia in a cold wall, vertical, pancake-style reactor. The surface morphology was smooth, and the PL spectrum showed strong near-band-edge emission with a full width at half-maximum (FWHM) value of 4 meV. The dislocation density within the first 0.5 μm was ≈1×109 cm−2; it decreased substantially with increasing film thickness. Controlled n-type Si doping of GaN has been achieved for net carrier concentrations ranging from ∼1×1017 to 1×1020 cm−3. Double-crystal XRC measurements indicated a FWHM value of 66 arcsec for the GaN(0004) reflection. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114642
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