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  • 1
    Digitale Medien
    Digitale Medien
    Temperature dependence of local vibrational mode optical absorption for carbon acceptors in GaAs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1013-1015 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The local vibrational mode (LVM) absorption band due to CAs in GaAs is reported for three semi-insulating samples at room temperature and for T〈77 K. Data obtained by Fourier transform infrared spectroscopy at resolution values from 1.0 to 0.1 cm−1 indicate that the area of the carbon LVM band increases by ∼60% upon cooling from room temperature, a substantially larger increase than some accounts have suggested. Our recommended value for the calibration factor f in going from LVM band area to carbon concentration is fRT(approximately-equal-to)1.6fLT (approximately-equal-to)(13±3)×1015 cm−1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100783
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  • 2
    Digitale Medien
    Digitale Medien
    Assessment of the ionized EL2 fraction in semi-insulating GaAs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2106-2108 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Both optical and electrical methods were used to provide separate evaluations of the fraction Pi of EL2 defect donors which have lost an electron. The semi-insulating GaAs which permitted these assessments had a large enough fraction of the EL2 compensated (by CAs acceptors) to make this a sensitive test. Room-temperature Hall effect data, analyzed with an ambipolar correction, indicated that Pi (approximately-equal-to)0.34 in material from a vertical-zone grown crystal, while near-infrared optical absorption could be modeled on a superposition of EL2 photoionization and photoneutralization to yield Pi (approximately-equal-to)0.35 in the same crystal. The presence of compensating CAs acceptors was verified by local mode vibrational absorption.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.101163
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  • 3
    Digitale Medien
    Digitale Medien
    An evaluation of horizontal Bridgman-grown, undoped, semi-insulating GaAs (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4413-4417 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An undoped, semi-insulating GaAs crystal grown by the horizontal Bridgman method has been characterized by axial and radial resistivity and mobility measurements. Due to lower thermal gradients, defect densities for wafers from this crystal are less than those observed for liquid-encapsulated Czochralski crystals. Cathodoluminescent images display uniform luminescent intensity around dislocated regions indicating an absence of impurity gettering in these areas. Concentrations of neutral EL2, a native defect and principal deep donor in undoped GaAs, are reported for seed, middle, and tail-end wafers. The distribution of EL2 over the area of each wafer is shown. Wafers were also implanted with 29Si and furnace annealed to form shallow n layers. Capacitance-voltage profiles demonstrate reproducible peak carrier concentrations and penetration depths.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.340185
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  • 4
    Digitale Medien
    Digitale Medien
    The role of crystal-growth properties on silicon implant activation processes for GaAs (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1464-1467 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Crystal properties such as bulk resistivity, mobility, and dislocation density which influence ion-implantation activation are reported for liquid-encapsulated Czochralski, horizontal gradient freeze, and vertical gradient freeze semi-insulating GaAs crystals. The liquid-encapsulated Czochralski crystals used in this study include as-grown, boule-annealed, and indium-alloyed GaAs. Wafer maps displaying the concentration and spatial distribution of neutral EL2 are presented for each crystal. Wafers from the various crystals were implanted with 29Si at a dose of 3×1012 ions/cm2 and an energy of 60 keV. Macroscopic variations in the donor distribution and peak carrier density demonstrate that point defects impact significantly the donor implant activation processes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.341818
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  • 5
    Digitale Medien
    Digitale Medien
    EL2 distributions in vertical gradient freeze GaAs crystals (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 5689-5693 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Spatial distributions of EL2 in undoped, semi-insulating GaAs crystals grown by a novel vertical gradient freeze (VGF) method are reported. As a result of the low-temperature gradients present during growth and post-solidification cooling, these crystals exhibit lower EL2 concentrations and lower dislocation densities than liquid-encapsulated Czochralski crystals. Both the EL2 distribution and dislocation density over the area of a wafer do not display the fourfold symmetric pattern prevalent for LEC-grown GaAs. The radial distributions of EL2 in as-grown VGF crystals have been found to be independent of the dislocation density. Axial and radial Hall-effect measurements are included. Thermal activation energies are also presented and the compensation mechanism for this material is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.340304
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  • 6
    Digitale Medien
    Digitale Medien
    Design and performance analysis of deep-etch air/nitride distributed Bragg reflector gratings for AlInGaN laser diodes (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4076-4078 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The key parameters in the fabrication of deep-etch high-order λ/4 Bragg gratings for short-wavelength nitride-based lasers are investigated. Calculations indicate that, for an air-gap thickness of 1.73 μm and single-spot Gaussian beam profile, the reduction in grating reflectivity due to light diffraction in the air gaps is only 17% with respect to a first-order structure with 0.1 μm air gaps. Scanning electron microscopy and microphotoluminescence characterizations confirm the validity of the numerical predictions and show that the 28%–38% reflectivity obtained from prototype focused-ion-beam-etched air/nitride gratings is mainly limited by imperfections and material disorder due to etching. Improving the etching technique would, therefore, allow standard lithographic fabrication of reduced-threshold GaN lasers. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1424061
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  • 7
    Digitale Medien
    Digitale Medien
    Investigation of polarization-pinning mechanism in deep-line-etched vertical-cavity surface-emitting lasers (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 400-402 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recently, it has been shown that the etching of deep trenches in close proximity to GaAs vertical-cavity surface-emitting laser (VCSEL) apertures causes the linearly polarized TE emission to be pinned in a direction parallel to the line etch. In this letter, we show that etching introduces compressive strain or relaxes tensile strain through the creation of free interfaces. An anisotropic variation of strain is the origin of the polarization pinning effect. We report on the enhancement of polarization pinning by postannealing after etching. Photoluminescence and Raman measurements of the VCSEL wafer were taken before and after etching and annealing. The observed shift in the Fabry–Perot mode was used to model the strain, giving 4×108 dyn/cm2, or 0.05%, compressive strain perpendicular to the etch. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125767
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  • 8
    Digitale Medien
    Digitale Medien
    The Alkaloids (1952)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biochemistry 21 (1952), S. 493-520 
    Details
    ISSN: 0066-4154
    Quelle: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Thema: Chemie und Pharmazie , Biologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1146/annurev.bi.21.070152.002425
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  • 9
    Digitale Medien
    Digitale Medien
    Compensation assessment in "undoped'' high-resistivity GaAs (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 256-261 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Attainment of semi-insulating status when an "undoped'' GaAs crystal is grown from the melt requires a delicate balance among concentrations of "unintentional'' donor and acceptor impurities, and defects, notably the EL2 midgap donor. In qualifying and improving material for device uses, defect identification and characterization is important. The compensation balance is analyzed in this paper for various "undoped'' crystals, relying largely on Hall data over the 290–430 K range, coupled with optical absorption measurements of carbon and EL2. The temperature-dependent data, converted into Fermi energy and into EL2 ionized fraction, provide a clearer picture than just room-temperature measurements as to whether EL2 controls the Fermi energy (giving the desired semi-insulating behavior), or whether a shallower defect species is in control.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.343866
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  • 10
    Digitale Medien
    Digitale Medien
    Properties of semi-insulating GaAs grown by a vertical molten zone method (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 852-858 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electrical and optical measurements are reported for samples from two undoped semi-insulating GaAs crystals grown by a vertical molten zone method. The electrical data, taken over the range 290–420 K, included results for samples from both crystals that were so close to intrinsic as to require an ambipolar correction in determining the electron concentration. The compensation balance in this material is controlled by the EL2 midgap defect, of which the fraction ionized depends on trace presence of CAs shallow acceptors, and of shallow donors, probably including SiGa . An increase of the latter towards the tail (top) end of one crystal led to a reduction of the EL2 ionized fraction, and a lowered resistivity—but one still within the conventional semi-insulating range. Carbon was measured from the strength of its local vibrational mode absorption, while near-infrared measurements showed that EL2 was present in a concentration ∼1016 cm−3, with relatively small variation across a wafer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.345742
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