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  • 1
    Electronic Resource
    Electronic Resource
    Reduction mechanisms for defect densities in GaN using one- or two-step epitaxial lateral overgrowth methods (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4175-4181 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A transmission electron microscopy study of the reduction mechanisms for defect densities in epitaxial lateral overgrown (ELO) GaN films is presented. In the standard one step ELO, the propagation of defects under the mask is blocked, whereas the defects in the window regions thread up to the surface. We propose an alternative two step ELO method. In a first step, dislocations close to the edge of the (0001) top facet bend at 90°, thereby producing a drastic reduction in the density of defects above the window. After the coalescence, induced by lateral growth in a second step, dislocations are mainly observed in the coalescence boundaries. The density of defects is decreased to 2×10−7 cm−2 over the entire surface and areas nearly 5 μm wide with 5×106 cm−2 dislocations between the center of the windows and the coalescence boundaries are obtained. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373048
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  • 2
    Electronic Resource
    Electronic Resource
    Metalorganic vapor-phase epitaxy-grown AlGaN materials for visible-blind ultraviolet photodetector applications (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5286-5292 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-pressure metalorganic vapor-phase epitaxy growth conditions of AlxGa1−xN epilayers on c-oriented sapphire have been optimized for aluminum mole fractions x lying in the 0–0.35 range both on GaN and AlN nucleation layers, with a view to application in visible blind UV photodetectors. Good structural, electrical, and optical properties were obtained for undoped and n-type doped AlGaN alloys on (0001)-oriented sapphire substrates. A typical full width at half maximum of 670–800 arc s is measured for the (0002) x-ray double-diffraction peak in the ω mode of 1-μm-thick AlGaN epilayers grown on a GaN nucleation layer. Room-temperature electron mobilities up to 90 cm2/V s are measured on n-type (1018 cm−3) AlGaN epilayers. The low-temperature photoluminescence (T=9 K) performed on nonintentionally doped AlGaN epilayers with low-Al content (10% and 14%) exhibits reproducibly a sharp exciton-related peak, associated with two phonon replica and does not exhibit any low-photon energy transitions. Optical transmission as well as absorption coefficient measurements using photothermal deflection spectroscopy have been used to study the variation of the T=300 K energy gap of AlGaN with the aluminum concentration. Visible-blind AlGaN(Si)-based photoconductors and Schottky barrier photodiodes with good operating characteristics have been fabricated with these materials. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371512
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  • 3
    Electronic Resource
    Electronic Resource
    Buffer free direct growth of GaN on 6H–SiC by metalorganic vapor phase epitaxy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 577-583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of GaN on 6H–SiC is three dimensional (3D) and results in the formation of large islands presenting hexagonal truncated shape with {1–101} lateral facets and a top {0001} facet. In this work, we present a three steps growth process that enables us to grow high quality mirrorlike GaN layers without using AlN buffer layers. During a first step, a thin 3D GaN layer is deposited at high temperature. This layer is smoothed under ammonia flow for several minutes when the growth is interrupted. The subsequent growth of GaN is two dimensional. 600 nm thick GaN films were grown. They were analyzed by high resolution x-ray diffraction, reflectivity, and photoluminescence. All the layers are under strong tensile biaxial strain. The correlation between residual tensile strain in GaN layers and their optical properties is reported for biaxial deformations cursive-epsilonxx ranging up to 0.37%. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371902
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  • 4
    Electronic Resource
    Electronic Resource
    TORE SUPRA fast reciprocating radio frequency probea) (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1210-1215 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fast reciprocating ion cyclotron range of frequencies (ICRF) probe was installed and operated on TORE SUPRA during 1992/1993. The body of the probe was originally used on the ATF experiment at Oak Ridge National Laboratory. The probe was adapted for use on TORE SUPRA, and mounted on one of the two fast reciprocating probe mounts. The probe consists of two orthogonal single-turn wire loops, mounted so that one loop senses toroidal rf magnetic fields and the other senses poloidal rf magnetic fields. The probe began operation in June, 1993. The probe active area is approximately 5 cm long by 2 cm, and the reciprocating mount has a slow stroke (5 cm/s) of 30 cm and a fast stroke (1.5 m/s) of about 10 cm. The probe was operated at distances from the plasma edge ranging from 30 to −5 cm (i.e., inside the last closed flux surface). The probe design, electronics, calibration, data acquisition, and data processing are discussed. First data from the probe are presented as a function of ICRF power, distance from the plasma, loop orientation, and other plasma parameters. Initial data show parametric instabilities do not play an important role for ICRF in the TORE SUPRA edge and scrape-off-layer (SOL) plasmas. Additionally it is observed that the probe signal has little or no dependence on position in the SOL/plasma edge. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146008
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  • 5
    Electronic Resource
    Electronic Resource
    TORE SUPRA fast reciprocating radio frequency probe (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 816-816 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fast reciprocating ion cyclotron range of frequencies (ICRF) probe was installed and operated on TORE SUPRA during 1992/1993. The body of the probe was originally used on the ATF experiment at Oak Ridge National Laboratory. The probe was adapted for use on TORE SUPRA, and mounted on one of the two fast reciprocating probe mounts. The probe consists of two orthogonal single-turn wire loops, mounted so that one loop senses toroidal rf magnetic fields and the other senses poloidal rf magnetic fields. The probe began operation in June, 1993. The probe active area is approximately 5 cm long by 2 cm, and the reciprocating mount has a slow stroke (5 cm/s) of 30 cm and a fast stroke (1.5 m/s) of about 10 cm. The probe was operated at distances from the plasma edge ranging from 30 to −5 cm (i.e., inside the last closed flux surface). The probe design, electronics, calibration, data acquisition, and data processing are discussed. First data from the probe are presented as a function of ICRF power, distance from the plasma, loop orientation, and other plasma parameters. Initial data show parametric instabilities do not play an important role for ICRF in the TORE SUPRA edge and scrape-off-layer (SOL) plasmas. Additionally it is observed that the probe signal has little or no dependence on position in the SOL/plasma edge. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146231
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  • 6
    Electronic Resource
    Electronic Resource
    Magnesium induced changes in the selective growth of GaN by metalorganic vapor phase epitaxy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 921-923 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Atmospheric pressure metalorganic vapor phase epitaxy is used to perform selective regrowth of GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. The basic pattern is constituted by a 15 μm period hexagonal array of hexagonal openings in the mask, these openings being circumscribed into 10 μm diam circles. We investigate the effect of Mg incorporation on the growth anisotropy of the localized GaN islands by varying the ratio [Mg]/[Ga] of bis-methylcyclopentadienyl-magnesium and trimethylgallium partial pressures. Both undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R (1 1¯01) facets, are achieved with a good selectivity. It is found that the GaN growth rates VR and VC, measured in the R〈11¯01〉 and C 〈0001〉 directions respectively, are drastically affected by the Mg incorporation. By adjusting the Mg partial pressure in the growth chamber, the VR/VC ratio can be increased so that the delimiting top C facet does not vanish as usually observed in undoped GaN localized growth, but by contrast expands. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120874
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature quenching of photoluminescence intensities in undoped and doped GaN (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3721-3728 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work discusses the temperature behavior of the various photoluminescence (PL) transitions observed in undoped, n- and p-doped GaN in the 9–300 K range. Samples grown using different techniques have been assessed. When possible, simple rate equations are used to describe the quenching of the transitions observed, in order to get a better insight on the mechanism involved. In undoped GaN, the temperature dependence of band edge excitonic lines is well described by assuming that the A exciton population is the leading term in the 50–300 K range. The activation energy for free exciton luminescence quenching is of the order of the A rydberg, suggesting that free hole release leads to nonradiative recombination. In slightly p-doped samples, the luminescence is dominated by acceptor related transitions, whose intensity is shown to be governed by free hole release. For high Mg doping, the luminescence at room temperature is dominated by blue PL in the 2.8–2.9 eV range, whose quenching activation energy is in the 60–80 meV range. We also discuss the temperature dependence of PL transitions near 3.4 eV, related to extended structural defects. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371242
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of the Si/N treatment of a nitridated sapphire surface on the growth mode of GaN in low-pressure metalorganic vapor phase epitaxy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1278-1280 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter, we studied the effect of the high-temperature Si/N treatment of the nitridated sapphire surface followed by the deposition of a low-temperature GaN nucleation layer on the growth mode of GaN in low-pressure metalorganic vapor phase epitaxy. It was shown that the nucleation layer, initially flat and continuous, converts to wide isolated truncated hexagonal islands having {1–101} facet planes and a top (0001) plane, after heating up to 1150 °C. The coalescence of these GaN islands yields a reduction of the total number of extended defects from the 1010–1011 cm−2 range usually obtained down to the low 109 cm−2 range for the best samples. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122148
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  • 9
    Electronic Resource
    Electronic Resource
    Study of open-core dislocations in GaN films on (0001) sapphire (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2434-2436 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article deals with a plan view and cross section transmission electron microscopy study of columnar defects in GaN films epitaxially grown on sapphire (0001). They are identified as open-core (0001) Burgers vector dislocations. Their behavior along the film thickness is described: it alternates from open core sections (nanopipes) to closed core sections. This alternating behavior is observed in the first 0.5 μm close to the interface with sapphire. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118894
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  • 10
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy study of the nitridation of the (0001) sapphire surface (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 4115-4117 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The purpose of this letter is to study, using transmission electron microscopy, the nitridation of the (0001) sapphire surface which is a key step for the fabrication of high-quality GaN materials. A nitridation conducted at 1080 °C during 7 min at atmospheric pressure with a 2 slm NH3 flow, results in the formation of a fully crystalline 10-atomic-planes-thick AlN film by the chemical transformation of the Al2O3 surface. From measurements of interplanar distances in high-resolution images, we show that this chemical transformation is incomplete, i.e., that a few Al vacancies and/or O atoms remain in the AlN structure. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125554
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