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  • Digitale Medien  (33)
  • 1
    Digitale Medien
    Digitale Medien
    Observation of room temperature surface-emitting stimulated emission from GaN:Ge by optical pumping (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6544-6546 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optically pumped surface-emitting stimulated emission at room temperature was observed from GaN:Ge grown by metalorganic chemical vapor deposition. The sample was optically pumped perpendicularly on the top surface while the stimulated emission was collected from the back colinearly with the pump beam. The cavity was formed by the GaN/air and GaN/sapphire interfaces without any other structure. The stimulated emission was gain guided by the pump beam. The threshold optical pump density for stimulated emission was approximately 2.8 MW/cm2 and the linewidth was 2.5 nm. The emission from GaN:Ge showed a redshift as the pump density increased. The comparison between theoretical calculations and experimental results suggested that many-body interactions can account well for the redshift. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363674
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  • 2
    Digitale Medien
    Digitale Medien
    Thermal stability of GaN thin films grown on (0001) Al2O3, (011¯2) Al2O3 and (0001)Si 6H-SiC substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 236-241 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Single crystals of GaN were grown on (0001), (011¯2) Al2O3 and (0001)Si 6H-SiC substrates using an atmospheric pressure metalorganic chemical-vapor-deposition reactor. The relationship has been studied between the thermal stability of the GaN films and the substrate's surface polarity. It appeared that the N-terminated (0001) GaN surface grown on (0001)Si 6H-SiC has the most stable surface, followed by the nonpolar (112¯0) GaN surface grown on (011¯2) Al2O3, while the Ga-terminated (0001) GaN surface grown on (0001) Al2O3 has the least stable surface. This is explained with the difference in the atomic configuration of each of these surfaces which induces a difference in their thermal decomposition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357133
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  • 3
    Digitale Medien
    Digitale Medien
    Crystallography of epitaxial growth of wurtzite-type thin films on sapphire substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4515-4519 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this article, we present a crystallographic model to describe the epitaxial growth of wurtzite-type thin films such as gallium nitride (GaN) on different orientations of sapphire (Al2O3) substrates. Through this model, we demonstrate the thin films grown on (00⋅1)Al2O3 have a better epilayer-substrate interface quality than those grown on (01⋅2)Al2O3. We also show the epilayer grown on (00⋅1)Al2O3 are gallium-terminated, and both (00⋅1) and (01⋅2) surfaces of sapphire crystals are oxygen-terminated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355943
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  • 4
    Digitale Medien
    Digitale Medien
    A crystallographic model of (00⋅1) aluminum nitride epitaxial thin film growth on (00⋅1) sapphire substrate (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3964-3967 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High-quality thin aluminum nitride films were grown on different orientations of sapphire substrates by metalorganic chemical vapor deposition. (00⋅1) AlN thin film grown on (00⋅1) Al2O3 has better crystallinity than (11⋅0) AlN on (01⋅2) sapphire. Full width at half maximum of a rocking curve is 97.2 arcsec, which is the narrowest value to our knowledge. A crystallographic model between AlN thin films and sapphire substrates was proposed to explain the process of crystal growth. "Extended atomic distance mismatch'' which is the mismatch of atomic distance for a longer period was introduced. It is shown that the mismatch is relaxed by edge-type dislocations. Extended atomic distance mismatch was used to interpret the results that (00⋅1) AlN has better crystallinity than (11⋅0) AlN, but (11⋅0) GaN has better crystallinity than (00⋅1) GaN.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.356017
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  • 5
    Digitale Medien
    Digitale Medien
    Growth of diamond thin films by spiral hollow cathode plasma-assisted chemical vapor deposition (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4676-4684 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A direct current spiral hollow cathode which combines hot-filament, electron-beam, and plasma-assisted chemical vapor deposition mechanisms has been developed to grow diamond crystallites and continuous thin films from CH4/H2 [/Ar] gas mixtures. A comprehensive study of system parameters such as deposition time, gas pressure, susceptor temperature, methane concentration, distance between the cathode and the substrate, substrate material, and surface treatment indicates that diamond deposition in such a reaction is a composite process. By varying the susceptor temperature and gas pressure during deposition, the deposition process can be tailored in favor of the synthesis of structurally uniform diamond thin films. The deposits, obtained at a growth rate of about 1 μm/h, have been characterized using scanning electron microscopy, Raman spectroscopy, Auger spectroscopy, x-ray diffraction, reflection high-energy electron diffraction, infrared absorption spectroscopy, and current-voltage curve plotting.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.343824
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  • 6
    Digitale Medien
    Digitale Medien
    Photovoltaic effects in GaN structures with p-n junctions (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2028-2030 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Large-area GaN photovoltaic structures with p-n junctions have been fabricated using atmospheric pressure metalorganic chemical vapor deposition. The photovoltaic devices typically exhibit selective spectral characteristics with two narrow peaks of opposite polarity. This can be related to p-n junction connected back-to-back with a Schottky barrier. The shape of the spectral characteristic is dependent on the thickness of the n- and p-type regions. The diffusion length of holes in the n-type GaN region, estimated by theoretical modeling of the spectral response shape, was about 0.1 μm. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114776
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  • 7
    Digitale Medien
    Digitale Medien
    Kinetics of photoconductivity in n-type GaN photodetector (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3792-3794 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High-quality ultraviolet photoconductive detectors have been fabricated using GaN layers grown by low-pressure metalorganic chemical vapor deposition on (11⋅0) sapphire substrates. The spectral responsivity remained nearly constant for wavelengths from 200 to 365 nm and dropped sharply by almost three orders of magnitude for wavelengths longer than 365 nm. The kinetics of the photoconductivity have been studied by the measurements of the frequency-dependent photoresponse and photoconductivity decay. Strongly sublinear response and excitation-dependent response time have been observed even at relatively low excitation levels. This can be attributed to redistribution of the charge carriers with increased excitation level. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115385
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  • 8
    Digitale Medien
    Digitale Medien
    A direct current superconducting quantum interference device gradiometer with a digital signal processor controlled flux-locked loop and comparison with a conventional analog feedback scheme (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 222-229 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A double-washer dc superconducting quantum interference device (SQUID) gradiometer with a flux-locked loop (FLL) based on a digital signal processor (DSP) has been developed for biomagnetic applications. All of the analog electronics in the conventional FLL are replaced and implemented by the DSP except for the low-noise field-effect transistor preamplifier at the front end of the signal recovery components. The DSP performs the signal demodulation by synchronously sampling the recovered signals and applying the appropriate full wave rectification. The signals are then integrated, filtered, and applied to the output. At 4.2 K, the white flux noise of the gradiometer measured in a DSP FLL mode is about 4μΦ0/(square root of)Hz and the noise at 1 Hz is 13 μΦ0/(square root of)Hz. The corresponding noise levels in the gradiometer operated by the conventional FLL are 1.8 and 3μΦ0/(square root of)Hz. The poorer system performance in the DSP FLL compared to the analog FLL is mainly caused by the ambient field noise and interference signals picked up through the connecting cables. Additional noise is also added to the overall noise floor by the instruments employed in the DSP system in the present prototype setup. Further improvement in the noise characteristics and the dynamic behavior of the DSP SQUID gradiometer is expected when a better configuration of DSP with the associated I/O devices is implemented. Additional improvements of the DSP programs are expected by incorporating higher-order integration, adaptive control, and noise reduction schemes. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146575
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  • 9
    Digitale Medien
    Digitale Medien
    Spiral hollow cathode plasma-assisted diamond deposition (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2326-2327 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High quality diamond films have been deposited on silicon and sapphire by means of a combined hot filament/electron beam/plasma-assisted chemical vapor deposition technique. A spiral tantalum foil is used as the hot cathode to generate a high-current dc discharge at a low sustaining voltage. Gas mixtures consisting of methane, hydrogen, and argon flowing through the spiral cathode towards the anode are effectively decomposed by the hot cathode and the high-density plasma. Diamond particles and films, grown at a rate between 0.5 and 5 μm/h, have been characterized by scanning electron microscopy, x-ray diffraction, and Raman spectroscopy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100268
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  • 10
    Digitale Medien
    Digitale Medien
    Solar-blind AlGaN photodiodes with very low cutoff wavelength (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 403-405 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the fabrication and characterization of AlxGa1−xN photodiodes (x∼0.70) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The peak responsivity for −5 V bias is 0.11 A/W at 232 nm, corresponding to an internal quantum efficiency greater than 90%. The device response drops four orders of magnitude by 275 nm and remains at low response for the entire near-ultraviolet and visible spectrum. Improvements were made to the device design including a semitransparent Ni/Au contact layer and a GaN:Mg cap layer, which dramatically increased device response by enhancing the carrier collection efficiency. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125768
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