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  • 1
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Biochemistry 15 (1976), S. 65-70 
    ISSN: 1520-4995
    Quelle: ACS Legacy Archives
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3561-3568 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thermal donors (TDs) are generated in Czochralski (CZ)-grown silicon by heat treatments around 450 °C. They form several individual effective-mass-like donors with slightly different ionization energies and act as double donors (TDx0,TDx+). Heat treatments at elevated temperatures (e.g., 〉500 °C) lead to a competition of the formation and the annihilation of TDs. We studied the formation and the annihilation of TDs in the temperature range between 520 and 700 °C. CZ-grown Si samples with an initial total TD concentration of ∼5×1015 cm−3 were employed to study the annihilation of TDs. The number of interstitial oxygen atoms generated per annihilated TD center depends on the temperature and ranges from 4 to 24. For the temperature range investigated the activation energy for thermal annihilation of TDs was determined to be 2.5±0.4 eV. The same CZ-Si material but with an initial TD concentration of ∼2×1013 cm−3 was used to study the formation of TDs. During annealing, the concentrations of individual TDs reach equilibrium concentrations, which depend on the temperature of the final annealing step and the total oxygen concentration. We demonstrate that a model in which the individual TDx centers are represented by oxygen clusters of different sizes consistently explains our experimental data. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3332-3338 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Hall-effect and infrared-absorption measurements are performed on n-type 4H-SiC samples to investigate the energy positions of the ground state and the excited states of the nitrogen donor in the 4H polytype of silicon carbide. Two electrically active levels (Hall effect) and three series of absorption lines (infrared spectra) are assigned to two nitrogen donor species which substitute on the two inequivalent lattice sites (h,k) in 4H-SiC. Valley-orbit splitting of the ground-state level of the nitrogen donors on hexagonal sites (h) is found to be equal to ΔEvo(h)=7.6 meV. It is shown that the energy position of excited states of both nitrogen donors can be calculated by the effective-mass approximation by assuming anisotropic effective masses m⊥=0.18m0 and m(parallel)=0.22m0. The influence of the two inequivalent lattice sites on the values of ionization energy and valley orbit splitting of the nitrogen donor ground-state levels is discussed.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2666-2668 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects of the deliberate hydrogenation of GaN were investigated for heteroepitaxial layers grown by metalorganic chemical vapor deposition. The GaN layers were either Mg-doped, p-type after thermal activation, or Si-doped, n type. Elemental depth profiles from secondary ion mass spectroscopy reveal a striking contrast after a deuteration at 600 °C: the deuterium concentration in Mg-doped GaN is ∼1019 cm−3 while there is no detectable deuterium incorporation in the n-type material. Variable temperature Hall effect measurements provide the most direct evidence to date for Mg–H complex formation with the decrease in the hole concentration upon hydrogenation accompanied by an increase in the hole Hall mobility. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Data are presented on high-power AlGaInN flip-chip light-emitting diodes (FCLEDs). The FCLED is "flipped-over" or inverted compared to conventional AlGaInN light-emitting diodes (LEDs), and light is extracted through the transparent sapphire substrate. This avoids light absorption from the semitransparent metal contact in conventional epitaxial-up designs. The power FCLED has a large emitting area (∼0.70 mm2) and an optimized contacting scheme allowing high current (200–1000 mA, J∼30–143 A/cm2) operation with low forward voltages (∼2.8 V at 200 mA), and therefore higher power conversion ("wall-plug") efficiencies. The improved extraction efficiency of the FCLED provides 1.6 times more light compared to top-emitting power LEDs and ten times more light than conventional small-area (∼0.07 mm2) LEDs. FCLEDs in the blue wavelength regime (∼435 nm peak) exhibit ∼21% external quantum efficiency and ∼20% wall-plug efficiency at 200 mA and with record light output powers of 400 mW at 1.0 A. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2379-2381 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Si-doped, n-type heteroepitaxial layers of Al0.12Ga0.88N grown by metalorganic chemical vapor deposition on SiC substrates were characterized by capacitance transient spectroscopies. Conventional deep level transient spectroscopy (DLTS) reveals the presence of a dominant deep level with an activation energy for electron emission to the conduction band of (0.61±0.02) eV. The activation energy of this deep level displays a pronounced field dependence as determined from double-correlation DLTS (DDLTS), which is indicative of a deep donor level in n-type semiconductors. A deep level is observed by optical-DLTS (O-DLTS) with a threshold energy for electron photoemission to the conduction band of 0.77 eV, which appears to be of identical origin as the dominant deep level detected by DLTS. Two additional deep levels are detected with O-DLTS in the upper half of the band gap of our Al0.12Ga0.88N sample with threshold energies of 0.83 and 1.01 eV. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 917-919 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Bulk single crystals of GaN were used for epitaxial growth of GaN by metalorganic chemical vapor deposition. Photoluminescence (at 2 K) from polished substrates yields a broad near-band-edge emission band centered at 3.32 eV and the commonly observed yellow luminescence band. In contrast, the epitaxial layer displays a strong, sharp bound exciton line at 3.458 eV and a weak yellow band. Transmission electron microscopy reveals a sharp, planar interface between substrate and epilayer: The substrate contains small Ga inclusions, and the epilayer consists of less than 108 dislocations per cm2, mostly in the form of dislocation loops, which originate at the interface. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 667-669 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The activation kinetics of acceptors was investigated for heteroepitaxial layers of GaN, doped with Mg. After growth, the samples were exposed to isochronal rapid thermal anneals in the temperature range from 500 to 775 °C. The samples were studied by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy in the as-grown condition and after each temperature step. The thermal treatment reduced the resistivity by six orders of magnitude and the p-type conductivity was found to be dominated by an acceptor with an activation energy of ∼170 meV. This acceptor is attributed to Mg atoms substituting for Ga in the GaN lattice and the activation process is consistent with dissociation of electrically inactive Mg–H complexes. It is shown that the appearance of a blue emission band in the PL spectrum of Mg-doped GaN does not directly correlate with the increase in p-type conductivity. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3725-3727 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Local vibrational modes (LVMs) are reported for Mg-doped GaN grown by metalorganic chemical vapor deposition. Hetero-epitaxial layers of GaN:Mg, either as-grown, thermally activated, or deuterated, were investigated with low-temperature, Fourier-transform infrared absorption spectroscopy. The as-grown material, which was semi-insulating, exhibits a LVM at 3125 cm−1. Thermal annealing increases the p-type conductivity, as established with Hall effect measurements, and proportionally reduces the intensity of this LVM. Deuteration of the activated material creates a LVM at 2321 cm−1. The isotopic shift establishes the presence of hydrogen in the vibrating complex. The new LVMs are assigned to the stretch modes of the Mg–H and Mg–D complexes in GaN, with the vibrational frequencies indicative of a strong N–H bond as recently proposed from total-energy calculations. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 242-244 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electronic and structural properties of GaN were investigated for heteroepitaxial layers grown by hydride vapor phase epitaxy. Uniform film nucleation on the sapphire substrates was facilitated by a GaCl pretreatment. The films were all unintentionally doped n type. Variable temperature Hall effect measurements reveal electron concentrations as low as 2×1017 cm−3 and electron mobilities as high as 460 cm2/V s at 300 K. The films exhibit bound exciton photoluminescence lines with a full width at half-maximum (FWHM) of 2.42 meV at 2 K. Transmission electron microscopy studies of the GaN/sapphire interface reveal a ∼200 nm thick, highly defective GaN layer consisting predominantly of stacking faults. The excellent quality of these GaN films is attributed to this "auto-buffer'' layer which enables growth of GaN cells with a dislocation density of ∼3×108 cm−2 after ∼12 μm of film growth. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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