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  • 1
    Digitale Medien
    Digitale Medien
    Thermal donor formation and annihilation at temperatures above 500 °C in Czochralski-grown Si (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3561-3568 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.368586
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  • 2
    Digitale Medien
    Digitale Medien
    Hydrogen passivation of Mg acceptors in GaN grown by metalorganic chemical vapor deposition (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2666-2668 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.114330
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  • 3
    Digitale Medien
    Digitale Medien
    A donorlike deep level defect in Al0.12Ga0.88N characterized by capacitance transient spectroscopies (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2379-2381 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.117643
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  • 4
    Digitale Medien
    Digitale Medien
    Homoepitaxy of GaN on polished bulk single crystals by metalorganic chemical vapor deposition (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 917-919 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.116230
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  • 5
    Digitale Medien
    Digitale Medien
    Activation of acceptors in Mg-doped GaN grown by metalorganic chemical vapor deposition (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 667-669 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.116503
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  • 6
    Digitale Medien
    Digitale Medien
    Local vibrational modes of the Mg–H acceptor complex in GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3725-3727 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.117202
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  • 7
    Digitale Medien
    Digitale Medien
    Electronic and structural properties of GaN grown by hydride vapor phase epitaxy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 242-244 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.117937
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  • 8
    Digitale Medien
    Digitale Medien
    Activation energies of Si donors in GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3144-3146 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electronic properties of Si donors in heteroepitaxial layers of GaN were investigated. The n-type GaN layers were grown by metalorganic chemical vapor deposition and either intentionally doped with Si or unintentionally doped. The samples were evaluated by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy. For both types of samples the n-type conductivity was found to be dominated by a donor with an activation energy between 12 and 17 meV. This donor is attributed to Si atoms substituting for Ga in the GaN lattice (SiGa). The range of activation energies is due to different levels of donor concentrations and acceptor compensation in our samples. The assignment of a PL signature to a donor–acceptor pair recombination involving the Si donor level as the initial state of the radiative transition yields the position of the optical Si donor level in the GaN bandgap at ∼Ec–(22±4) meV. A deeper donor level is also present in our GaN material with an activation energy of ∼34 meV which is tentatively assigned to oxygen donors substituting for nitrogen (ON). © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115805
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  • 9
    Digitale Medien
    Digitale Medien
    Deep level defects in Mg-doped, p-type GaN grown by metalorganic chemical vapor deposition (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3470-3472 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Deep level defects in Mg-doped, p-type GaN were characterized by deep level transient spectroscopy (DLTS) and photoemission capacitance transient spectroscopy (ODLTS). The measurements were conducted on n+-p junction diodes grown by metalorganic chemical vapor deposition. DLTS revealed discrete deep levels in the lower half of the band gap with activation energies for hole emission of 0.21, 0.39, and 0.41 eV. While DLTS is able to detect deep levels only in the proximity of the valance band edge in p-type, wide band-gap semiconductors, ODLTS enables detection of deep levels throughout the band gap of GaN. The ODLTS spectrum of Mg-doped, p-type GaN is dominated by a deep level with an optical threshold energy for photoionization of ∼1.8 eV. This deep level, which appears to be energetically located near midgap is present in the highest concentration (∼2.4×1015 cm−3) among the deep levels detected in our GaN material. None of the detected deep levels is present in sufficient concentration to significantly compensate the shallow acceptor dopant in our Mg-doped, p-type GaN. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116075
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  • 10
    Digitale Medien
    Digitale Medien
    Spatial distribution of the luminescence in GaN thin films (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 57-59 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The spatial dependence of the luminescence intensities at the band edge (364 nm) and at the "yellow'' defect-band (centered at 560 nm) regions for epitaxial GaN films have been studied using cathodoluminescence microscopy at room temperature. The films were grown by metalorganic chemical vapor deposition on (0001) sapphire substrates and were not intentionally doped. Significant nonuniformities in the band-to-band and in the yellow band emissions were observed. Yellow luminescence in small crystallites appears to originate from extended defects inside the grains and at low-angle grain boundaries. The size of band-to-band emission sites correlates with low-angle grain sizes observed by transmission electron microscopy. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116756
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