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  • 1995-1999  (17)
  • 1955-1959
  • 1915-1919
  • 1998  (17)
  • 1
    Electronic Resource
    Electronic Resource
    Comprehensive characterization of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6148-6160 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.367484
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  • 2
    Electronic Resource
    Electronic Resource
    Thin multiplication region InAlAs homojunction avalanche photodiodes (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 783-784 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.122000
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  • 3
    Electronic Resource
    Electronic Resource
    Improved optical response of superlattice graded InAlAs/InGaAs p-i-n photodetectors (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3405-3407 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A number of important optoelectronic device utilize the InAlGaAs/InP material system. The reduction of carrier trapping at the In0.53Ga0.47As/In0.52Al0.48As heterointerface is advantageous towards improving both the quantum efficiency and frequency response of devices utilizing InGaAs active regions. Direct current and transient optical response characteristics were measured for p-i-n double-heterojunction photodiodes utilizing either abrupt or superlattice (SL) graded heterointerfaces. SL graded devices showed improved collection efficiency at electric fields 〈3 kV/cm and faster temporal response at electric field 〈70 kV/cm as compared to identical devices having abrupt interfaces. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122757
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  • 4
    Electronic Resource
    Electronic Resource
    Very high-speed metal-semiconductor-metal ultraviolet photodetectors fabricated on GaN (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2405-2407 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the temporal and the frequency response of metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN. The best devices show a fast 10%–90% rise time of ∼23 ps implying a bandwidth of 〉15 GHz. These time domain data have been corroborated by direct measurement of the power spectral content. From this a cutoff frequency, f3 dB, of ∼16 GHz has been obtained. Analysis in terms of reverse bias and geometric scaling indicates that the photodetectors are transit-time limited. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122448
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  • 5
    Electronic Resource
    Electronic Resource
    Current transport mechanisms in GaN-based metal–semiconductor–metal photodetectors (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 542-544 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the current transport mechanisms dominant at the Schottky interface of metal–semiconductor–metal photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled transport in the 1.5 μm devices using thermionic emission theory, and in the 4.0 μm devices using thermionic field emission theory. We have obtained a good fit to the experimental data. 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. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120752
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  • 6
    Electronic Resource
    Electronic Resource
    The Effects of Oil and Chemical Spillages at Sea (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 12 (1998), S. 0 
    Details
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: At sea around England and Wales, in an average year there can be 10–12 oil and chemical spillage incidents which require action to be taken, and occasionally a major spill may trigger monitoring studies and local controls on fishing activity. This paper discusses the scope of such incidents and their consequences by reference to two particular incidents; the loss of a container of the pesticide lindane from MV Perintis in the English Channel in 1989, and the grounding of the oil tanker Sea Empress in Wales in 1996 and the consequent oilspill. The latter of these incidents is also compared with the loss of the tanker Braer in Shetland in 1993.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1747-6593.1998.tb00179.x
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  • 7
    Electronic Resource
    Electronic Resource
    Local cerebral glucose utilization in the AS/AGU rat: a mutant with movement disorders (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 10 (1998), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The AS/AGU mutant rat is characterized by a wide staggering gait and a movement disorder of the hindlimbs. Local cerebral glucose utilization in the brain was investigated using the [14C]2-deoxyglucose autoradiographic technique to map any functional alterations in the mutant AS/AGU (agu/agu) compared with Albino Swiss controls (+/+). Locomotor tests were also performed to confirm the phenotypic assignment of the animals. Statistically significant reductions in glucose utilization were apparent in 12 of the 44 regions examined in the AS/AGU animals. The regions showing the most significant differences (P 〈 0.01) from the control AS strain were the substantia nigra pars compacta (–23%) and medial geniculate body (–17%). Statistically significant decreases (P 〈 0.05 and P 〈 0.02) in glucose utilization ranging from –15 to –26% were also displayed in the superior colliculus superficial layer, auditory cortex, ventroposterior nucleus of the thalamus, molecular layer of the hippocampus, dentate gyrus, medial amygdaloid nucleus, median raphe nucleus, subthalamic nucleus, medial preoptic area of the hypothalamus and anterior hypothalamus. In no region studied was the mean value of glucose use in the AS/AGU rat greater than in the control animals. The results of this study complement previous behavioural and neurochemical characterization studies of this mutant, confirm that the disorder involves functional disturbances of the basal ganglia, and demonstrate the involvement of the limbic system and some sensory systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.1998.00206.x
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  • 8
    Electronic Resource
    Electronic Resource
    The Practicality of Using a Three-Dimensional Fast Fourier Transform in Auto-Indexing Protein Single-Crystal Oscillation Images (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 407-413 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The feasibility of using a three-dimensional fast Fourier transform as the basis for determining the crystal cell and orientation from a single monochromatic oscillation image of a protein crystal has been investigated. The results of tests, carried out for both simulated and real data-sets, are presented and confirm that a practical method of auto-indexing can be developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897014453
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  • 9
    Electronic Resource
    Electronic Resource
    LAUEGEN version 6.0 and INTLDM (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 496-502 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: LAUEGEN version 6.0 is a significantly developed version of the original LAUEGEN program [Campbell (1995a). J. Appl. Cryst. 28, 228–236]. It is an X-Windows-based program which now carries out the stages of processing Laue diffraction data up to and including the integration of spot intensities. The integration routines have also been incorporated in a stand-alone integration program INTLDM. The programs are distributed as part of the Daresbury Laboratory Laue Software Suite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897016683
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  • 10
    Electronic Resource
    Electronic Resource
    Spatial and temporal distribution of endemic and released entomopathogenic nematode populations in turfgrass (1998)
    Springer
    Entomologia experimentalis et applicata 86 (1998), S. 1-11 
    Details
    ISSN: 1570-7458
    Keywords: Heterorhabditidae ; Steinernematidae ; Heterorhabditis bacteriophora ; Steinernema carpocapsae ; Steinernema feltiae ; entomopathogenic nematodes ; turfgrass ; Japanese beetle ; Popillia japonica ; population dynamics ; spatial distribution ; edaphic factors ; biological control ; colonization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Entomopathogenic nematodes (Rhabdita: Heterorhabditidae and Steinernematidae) have been effective as inundative biological control agents of scarab larvae (Coleoptera: Scarabaeidae) in turfgrass. Entomopathogenic nematodes also occur naturally in turfgrass and endemic or inoculated populations may be able to provide effective long-term control. Variation in Heterorhabditis bacteriophora and Steinernema carpocapsae spatial and temporal distribution along transects placed at different turfgrass sites in central New Jersey, USA, was investigated. H. bacteriophora tended to be recovered from fewer sections in a transect than S. carpocapsae, but the two species, overall, did not differ in patchiness of distribution. In one transect with a H. bacteriophora population S. feltiae was also recovered, but the two populations seldom overlapped spatially. In transects with adequate scarab larvae density for analysis, H. bacteriophora density and Popillia japonica larvae density were inversely correlated. This suggests that endemic H. bacteriophora populations may suppress P. japonica populations. In one transect, an epizootic of H. bacteriophora in an undetermined host may have occurred. Edaphic factors were relatively uniform along transects and were, at most, weakly correlated with nematode recovery. Uniform inoculative releases of H. bacteriophora tended to return to patterns of distribution typical of endemic populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003130111093
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