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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 13 (1997), S. 0 
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Use of either three or six occasions to spread similar total amounts of slurry was investigated over the late winter/early spring period in two years, on plots with underdrainage. Slurry was spread on four 7 m by 25 m plots which were instrumented to allow collection of drainflow and runoff. The ‘mobile water’ pore space allowed transport of a small proportion of applied slurry through the 0.75 m soil profile. Evidence of a polluted ‘mobile water’ pulse occurred after periods of up to 48 hours following spreading, suggesting subsurface rather than overland flow. Timing of the pulse depended on whether subsequent rainfall accelerated the flow The contaminated flow persisted for 6–12 hours. The worst contamination of 39 mg/l NH4+ -N occurred under ‘bypass flow’ conditions, when 52 mm of rain fell during the 48 hours after a 5.2 mm application. Two contributory factors appeared important. The first was the long duration of the high intensity storm and the second was an extended period of severe frost believed to have created fissures associated with frost heave. Making several applications of slurry in amounts less than 35 m3/ha is preferable to fewer larger applications during spring, for cereals on medium to heavy soils. This recognises the likelihood of there being underdrainage on arable land and the optimal use of well-drained, partially frozen ground to avoid compaction by slurry tankers.
    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 77 (1995), S. 3641-3644 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results from an investigation of the effects of variations in layer thicknesses during the growth of semiconductor Bragg mirrors on their reflectivity spectra. Different types of variations are investigated and an effort is made to point out the sources of such errors in a typical growth process. It is expected that this study will shed light on the critical control parameters for very highly reflecting mirrors and help the interpretation of the measured spectra from a finished growth run and the identification of the possible sources of deviations from the ideal structure. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 161-163 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Previously it has been shown that resonant-cavity, separate absorption and multiplication (SAM) avalanche photodiodes (APDs) exhibit high peak external quantum efficiency (∼75%), low dark current, low bias voltage (〈15 V), and low multiplication noise (0.2〈k〈0.3). We describe the frequency response of resonant-cavity AlGaAs/GaAs/InGaAs SAM APDs. A unity-gain bandwidth of 23 GHz and a high gain-bandwidth product of 130 GHz have been achieved. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1992-1994 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a very low dark current (∼57 pA at 10 V reverse bias) metal–semiconductor–metal photodetectors fabricated on GaN epitaxial layers grown by low-pressure metalorganic chemical vapor deposition. The photodetectors exhibit the typical sharp band-edge cutoff, with good responsivity. There is indication of a photoconductive gain mechanism. We also performed a Medici simulation to establish an effective area for current density calculations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3734-3736 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This letter presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite "size effect'' for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3123-3124 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate a photodetector with a narrow spectral linewidth (approximately 2 A(ring)) and a useful electrical-tuning range of 35 A(ring). The photodetector features a horizontal resonant cavity in which feedback is achieved using distributed feedback reflectors. The optical and electrical paths in this photodetector are orthogonal. Consequently, this normal incidence horizontal resonant cavity photodetector is completely integrable into wavelength division demultiplexing and other optoelectronic integrated circuits with a potential for high speed operation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6148-6160 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the material, electrical, and optical properties of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled current transport in the 1.5 μm devices using thermionic field emission theory, and in the 4.0 μm devices using thermionic emission theory. We have obtained a good fit to the experimental data. Upon repeated field stressing of the 1.5 μm devices, there is a degradation in the current–voltage (I–V) characteristics that is trap related. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented based on experimental results. For devices fabricated on wafers with very low background free electron concentrations, there is a characteristic "punch-through" voltage, which we attribute to the interaction of the depletion region with the underlying low-temperature buffer layer. We also report GaN metal–semiconductor–metal photodetectors with high quantum efficiencies (∼50%) in the absence of internal gain. These photodetectors have a flat responsivity above the band gap (measured at ∼0.15 A/W) with a sharp, visible-blind cutoff at the band edge. There is no discernible responsivity for photons below the band-gap energy. We also obtained record low dark current of ∼800 fA at −10 V reverse bias. The dark current and ultraviolet photoresponse I–V curves are very flat out to VR〉−25 V, and do not show evidence of trap-related degradation, or punch-through effects. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1104-1106 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The room-temperature photoinduced switching of an InGaAs/AlAs resonant-tunneling diode is demonstrated. When illuminated at an irradiance of greater than 20 W cm−2 using 1.3 μm radiation, the resonant-tunneling diode switches from a high-conductance to a low-conductance electrical state and exhibits a voltage swing of 600 mV. The switching characteristics are reversible and, in the absence of light, the detector returns to its original high conductance operating state. Small-signal optical measurements performed with the device biased prior to resonance demonstrate a 3 dB bandwidth of ∼1.5 GHz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 535-537 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new dual-wavelength, resonant-cavity photodiode is described. It has previously been shown that the resonant-cavity structure can achieve high quantum efficiencies in a relatively narrow spectral region with thin absorbing regions. In this letter, a dual wavelength mirror is incorporated into the cavity to achieve operation in two wavelength regions. Peak external quantum efficiencies greater than 50% were demonstrated at 730 and 910 nm. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 783-784 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low excess noise in avalanche photodetectors (APDs) is desired for improved sensitivity and high-frequency performance. Gain and noise characteristics are measured for InAlAs p-i-n homojunction APDs that were grown with varying i-region widths on InP by molecular beam epitaxy. The effective ionization ratio k (β/α) determined by noise measurements shows a dependence on multiplication region width, reducing from 0.31 to 0.18 for multiplication region thicknesses of 1600–200 nm. This trend follows previously shown results in AlGaAs-based APDs, which exhibit reduced excess noise due to nonlocal multiplication effects. These results show that this effect is a characteristic of thin avalanche regions and is not a material-specific phenomenon. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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