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  • 1
    Electronic Resource
    Electronic Resource
    Surface potential measurements on GaN and AlGaN/GaN heterostructures by scanning Kelvin probe microscopy (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 337-344 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Surface potentials on GaN epilayers and Al0.35Ga0.65N/GaN heterostructures have been studied by scanning Kelvin probe microscopy (SKPM) in conjunction with noncontact atomic force microscopy. The dependence of the surface potential on doping in GaN films, as well as the variation of surface potential with Al0.35Ga0.65N barrier layer thickness has been investigated. The bare surface barrier height (BSBH), as measured by SKPM, is observed to decrease from ∼1. 40±0.1 eV to ∼0.60±0.1 eV with increasing doping in the GaN epilayers. Schottky barrier height calculated from the measurements of BSBH on n-GaN agrees very well with results from previous studies. We have also estimated the surface state density for GaN based on the measured values of BSBH. The semiconductor "work function" at the Al0.35Ga0.65N surface (in heterostructure samples) is observed to decrease by ∼0.60 eV with increase in barrier layer thickness from ∼50 to ∼440 Å. A simple model considering the presence of a uniform density of charged acceptors in the Al0.35Ga0.65N layer is proposed to explain the observed decreasing trend in work function. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371941
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  • 2
    Electronic Resource
    Electronic Resource
    Reduction of Be diffusion in GaAs by migration-enhanced epitaxy (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 59-61 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Be-doped GaAs layers were grown by the migration-enhanced epitaxy (MEE) method at 300 °C. The MEE layers showed practically no electrical activation. Rapid thermal annealing on the MEE layers resulted in mobility and hole concentration comparable to those of conventional molecular beam epitaxy (MBE) layers grown at 600 °C. Secondary-ion mass spectroscopy showed that the Be diffusion in annealed MEE layers was much smaller than that in conventional MBE layers, especially for highly doped layers. Raman spectroscopy and 4 K photoluminescence were also performed. The MEE method can replace the conventional MBE method for device applications which require high hole concentration with small diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101753
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  • 3
    Electronic Resource
    Electronic Resource
    Electron tunneling spectroscopy and defects in GaAs/AlGaAs/GaAs heterostructures (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5333-5336 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron tunneling spectroscopy has been used to study the phonon modes of the GaAs electrode and the AlGaAs barrier of single barrier GaAs/AlGaAs/GaAs heterostructures. The barriers were spiked doped with Si or Be to determine whether defects or impurities in the barrier have an effect on the measured line shapes. The phonon line shapes and intensities have been observed to change after shining light on the devices to photoionize defects in the barrier. The results demonstrate that the charge state of defects in a heterostructure barrier can affect the interaction between a tunneling electron and the phonon modes of a tunnel barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351968
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  • 4
    Electronic Resource
    Electronic Resource
    Deep donor state of vanadium in cubic silicon carbide (3C-SiC) (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1811-1813 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron spin resonance (ESR) of silicon-substitutional vanadium in its neutral V4+Si (3d1) state has been observed in cubic bulk 3C-SiC single crystals. By photo-ESR the position of the (0/+) deep donor level of vanadium could be located at EV+1.7 eV. Using this level as common reference in 3C-SiC and 6H-SiC, the valence-band discontinuity in the 3C-SiC/6H-SiC interface is predicted as ΔEV=0.1 eV, with the valence band of 3C-SiC lying lower in energy. We also offer an explanation for the absence of intra-3d-shell infrared luminescence of V4+ (3d1) in 3C-SiC. © 1994 American Institue of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112851
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  • 5
    Electronic Resource
    Electronic Resource
    Defect assisted tunneling in GaAs/AlGaAs/GaAs heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 368-372 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A zero-bias conductance peak has been observed in conductivity versus voltage G(V) measurements at 4 K on GaAs/AlGaAs/GaAs tunnel junctions. The peak was found in junctions prepared from several different molecular-beam-epitaxial growths. The central portions of the barriers were spike doped with Si or Be. The peak fits the functional form G(V)=M ln(AV+B) which is expected for electron tunneling via paramagnetic impurities in the barrier, or for Coulomb correlation effects at defects. Shining white light on the junctions reduced the amplitude of the peak, and the new G(V) was found to persist for at least 15 h. Following exposure to light, the conductivity peak was recovered by warming the sample to room temperature. The G(V) curves measured before and after exposure to light were independent of temperature between 1.3 and 30 K. The reduction in amplitude of the peak in G(V) results in a negative photo conductivity at zero bias. At high enough biases, the conductivity after the exposure to light is larger than before as is expected when the light removes electrons from the barrier by photo ionizing defects or impurities. The photo effect indicates that the peak is associated with transport via defects. The defects may be associated with either the Si or Be which were used to spike dope the central portion of the barriers, or with stoichiometric defects produced by the growth. Tunneling assisted by interactions with paramagnetic defects or Coulomb correlation effects are possible explanations for the origin and photo behavior of the peak in G(V).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355860
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  • 6
    Electronic Resource
    Electronic Resource
    Growth of GaAs-Al-GaAs by migration-enhanced epitaxy (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2664-2665 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The GaAs-Al-GaAs structure is grown using migration-enhanced epitaxy (MEE) method at low temperature on a molecular beam epitaxy machine. With MEE the interdiffusion between Al and GaAs is reduced by a large amount, and the morphology is improved by a large degree. Still, Raman spectrum indicates poor crystallinity for the GaAs of the top layer. The effect of different annealing temperatures on the interdiffusion is also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100188
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  • 7
    Electronic Resource
    Electronic Resource
    Increase of electrical activation and mobility of Si-doped GaAs, grown at low substrate temperatures, by the migration-enhanced epitaxy method (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 589-591 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si-doped GaAs layers were grown by the migration-enhanced epitaxy (MEE) method and by the conventional molecular-beam epitaxy (MBE) method, for the substrate temperatures between 220 and 670 °C. For the layers grown below 400 °C, the Si activation and mobility of the MEE layers are significantly higher than those of the MBE layers. For substrate temperatures above 400 °C, the MEE and MBE layers have roughly similar Si activation and mobility. The Raman and 4-K photoluminescence spectra of the layers are consistent with the measured electron concentrations. This work suggests that for Si doping in GaAs at low substrate temperatures (below 400 °C), the MEE method is a very desirable alternative to the conventional MBE method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345202
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  • 8
    Electronic Resource
    Electronic Resource
    Metastable defects in Be-doped AlxGa1−xAs (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4828-4831 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep-level transient spectroscopy has been used to study metastable defects in Be-doped Alx Ga1−x As grown by molecular-beam epitaxy. The metastability manifests itself by the appearance of different spectra depending upon whether the sample is cooled from a high temperature with zero bias or a reverse bias applied to it. The defects are found in concentrations of 1015 cm−3 in a sample doped with 1018 Be cm−3 and in much lower concentrations in a 1017 Be cm−3 sample. Isochronal annealing experiments indicate that the defect is multistable and that it is best modeled as a mobile interstitial which can reside at several sites near an acceptor. The activation energies for these defects are between 0.2 and 0.5 eV above the valence band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343216
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  • 9
    Electronic Resource
    Electronic Resource
    Scanning Kelvin probe microscopy characterization of dislocations in III-nitrides grown by metalorganic chemical vapor deposition (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2873-2875 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning Kelvin probe microscopy has been used in conjunction with noncontact atomic force microscopy for characterizing dislocations in n-GaN and Al0.35Ga0.65N/GaN heterostructures. The surface potential variations around the dislocations present in the Al0.35Ga0.65N/GaN heterostructure have been observed to be 0.1–0.2 V with full width at half maximums (FWHMs) of 100–200 nm. On the other hand, n-GaN shows potential variations of 0.3–0.5 V having FWHMs of 20–50 nm. The dislocations (present in densities of ∼109 cm−2) have been found to be negatively charged for both n-GaN and Al0.35Ga0.65N/GaN heterostructure samples. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1369390
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  • 10
    Electronic Resource
    Electronic Resource
    Cantilever effects on the measurement of electrostatic potentials by scanning Kelvin probe microscopy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 545-547 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning Kelvin probe microscopy (SKPM) is a unique way to measure electrostatic potentials for small geometries. It has numerous applications including characterization of integrated circuits and nanoscale devices. SKPM is attractive because of the quantitative nature of the measurements. In this work, we have examined one of the principal sources of measurement error, the cantilever (which holds the probe tip). The accuracy of measurements of electrostatic potentials on closely spaced regions biased differently is reduced due to a large capacitance gradient associated with the cantilever. However, it is observed that the accuracy of measurements increases as the tip–sample distance is decreased because the capacitance gradient of the tip becomes proportionally larger relative to that of the cantilever. It is further observed that longer tips with smaller cantilever areas measure the electrostatic potentials more accurately as the capacitance gradient of the cantilever is reduced. Scanning probe tips are parametrized by a factor R, which indicates their suitability for SKPM measurements. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1384004
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