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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 5516-5521 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Conductivity modulated devices, similar to photoconductors in operation, for use as radiation detectors were fabricated from polycrystalline chemical vapor deposited diamond films. These detectors were designed to operate under extremely high radiation fields with a large dynamic range in both response and speed. Two types of detectors were studied: a parallel-plate device and a surface device (SDT). The radiation used to excite these detectors was minimum ionizing electrons with an energy of 16 MeV and a nominal pulse width of less than 25 ps. The response time of all detectors was less than 45 ps. The sensitivity of the detectors was in the range 10−5–10−6 A/W. Over the operating range of the detectors, signal saturation was not observed because to the signal size was small in comparison to the applied bias voltage. The detectors appeared to be linear with dose and dose rate over two orders of magnitude, and for dose rates up to 1013 rad/s. Long-lived signal decay tails contributed to much less than 1% of the signal. The response of a SDT detector appeared to be independent of the orientation of the detector to the incident beam direction when the excitation source is minimum ionizing. It appears that the dose-rate linearity may be extended to a range greater than 1013 rad/s. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7425-7433 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-purity GaAs layers which are nearly or fully depleted of carriers at low temperatures, due to surface and interface depletion effects, can be characterized electrically by utilizing the phenomenon of persistent photoconductivity. To facilitate electrical measurements of such layers, at 4.2 K the sample is momentarily illuminated by above band-gap light, which causes a reduction in the surface and interface depletion region. After illumination the effects of the photoinduced charge neutral region persist until at some higher temperature, the charge distribution in the sample relaxes back to its original equilibrium state. Results of variable temperature Hall-effect measurements performed under these conditions show that the sheet carrier concentration is increased as compared to measurements obtained in the dark but that the mobility is unchanged. The increase in the sheet carrier concentration after illumination results from the decrease of the surface and interface depletion widths. Such measurements can provide a method for judging the quality of layers that are fully depleted of carriers. The mobility of a high-purity GaAs layer which becomes fully depleted of carriers at low temperatures in the dark, measures 180 000 cm2/V s at 77 K by this method. Photocapacitance-voltage profiling measurements clearly show the change in the depletion widths. A model is presented which accurately depicts the temperature dependence of the band-bending potentials at the surface and interface after illumination with above band-gap light.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 741-754 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a study of a defect responsible for the "g'' bound exciton line at 1.5112 eV that is frequently detected in photoluminescence spectra of GaAs grown by molecular beam epitaxy (MBE). A direct correlation has been observed between this line and a transition at 1.4946 eV, which is shown to result from a conduction band-to-acceptor recombination involving a shallow, unidentified acceptorlike defect that is labeled "A.'' The activation energy of the defect is 24.8±0.2 meV, about 1.7 meV lower than that of CAs acceptor. Upon hydrogenation the defect is passivated more extensively than any known shallow acceptor species in GaAs. This result is analyzed in terms of a passivation model, from which it can be inferred that the A defect is not due to a simple substitutional Group II impurity on a Ga site. Incorporation of the A defect strongly affects the luminescence properties of the material. An almost complete quenching of the donor-bound exciton lines, profound changes in the line shape and relative intensity of the free exciton recombination, and appearance of a sharp transition of unknown origin at 1.5138 eV were observed with increasing defect concentration. Apparently "donorless'' low temperature exciton recombination spectra are reported for defect-rich p-type MBE GaAs layers with donor concentrations as high as 7×1014 cm−3 and compensation ratios of ∼0.3. The dependence of the defect incorporation on MBE growth parameters is discussed. The feasibility of MBE growth of high purity, nearly shallow defect-free p-type GaAs layers at marginally As-stabilized surface conditions over an about 1–5 μm/h range of deposition rates is demonstrated.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 1077-1079 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep levels in high-purity n-type molecular beam epitaxy (MBE) GaAs and in undoped n-type metalorganic chemical vapor deposition (MOCVD) GaAs samples annealed with various As overpressures were investigated using constant capacitance deep level transient spectroscopy on evaporated Au Schottky barrier diodes. Anomalous hole traps, which could be measured because of a surface effect, were observed in all annealed samples. EL2 traps were created in the MBE material by the annealing, while the concentration of EL2 in the annealed MOCVD material was about the same as that before annealing. The effect of annealing on the other electron traps in these samples is also studied and reported.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1094-1096 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phosphorus-doped polycrystalline and homoepitaxial diamond films were grown using both microwave and dc plasma assisted chemical vapor deposition. P incorporation was quantified using secondary ion mass spectrometry, and was approximately ten times greater for polycrystalline films deposited using dc plasmas compared to microwave plasmas. For microwave-assisted growth, P incorporation was approximately ten times greater in polycrystalline than homoepitaxial films. These effects appear to be due to preferential incorporation at grain boundaries, since higher levels of P are measured in samples with smaller grains. The films were highly electrically resistive, with conductivities of 10−10–10−9/Ω cm at room temperature.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical characteristics of chemically vapor deposited (CVD) diamond films were measured as a function of film thickness. The samples studied were polycrystalline with the average grain size increasing from approximately 1 μm on the substrate side to approximately 30 μm on the growth surface for the thickest sample. Using time-resolved transient photoconductivity and charged-particle induced conductivity, the collection distance (d) that a free carrier drifts under the influence of an applied electric field was measured. Our data indicate that there is a gradient in the collection distance through the material. This gradient in electrical properties has implications for electronic uses of CVD diamond.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 1870-1871 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-paramagnetic-resonance (EPR) studies demonstrate the presence of nitrogen point defects in microwave-assisted chemical vapor deposition (CVD) diamond thin films. Polycrystalline powder pattern EPR spectra are interpreted with g=2.0023, A(parallel)=114.0 MHz, and A⊥=81.3 MHz. These spin parameters are identical to those of nitrogen in single crystal natural diamonds. Quantitative EPR and secondary ion-mass spectrometry (SIMS) results of CVD diamond thin films suggest that nitrogen point defect formation is favored over aggregate nitrogen formation.
    Type of Medium: Electronic Resource
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