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  • Articles  (71)
  • 2000-2004  (34)
  • 1985-1989  (37)
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  • 1
    Electronic Resource
    Electronic Resource
    The effect of level broadening on the tunneling of electrons through semiconductor double-barrier quantum-well structures (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3089-3097 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scattering and well-width nonuniformities in double-barrier structures introduce level broadening, particularly in the quantum-well region, and the effect of this level broadening on coherent and sequential transmission of electrons through these structures has been examined. First, it is shown that resonant energies are eigenenergies of the overall system, so that it is the same energy level which is involved in both tunneling mechanisms. This explains why the negative differential resistance (NDR) peak occurs at the same voltage for coherent and sequential tunneling. Expressions for the transmission coefficients and, consequently, for the current density are derived, and it is shown that the effect of broadening is to reduce the peak current and the peak-to-valley ratio for both tunneling processes, this reduction being quite remarkable for the case of coherent tunneling through the structures with thick barriers. Based on this, ways are suggested to distinguish between the two tunneling phenomena. This broadening-induced reduction in peak current and peak-to-valley ratio leads to a reduction in the NDR-related maximum operating frequency in these structures. On the other hand, the effect of broadening on coherent tunneling itself is to reduce the resonant tunneling time, thus allowing higher-frequency operation in optical devices. Above a critical amount of broadening the assumption of coherent tunneling breaks down, and sequential tunneling takes over. Critical broadenings for a number of cases are estimated. It is emphasized that the form of the NDR and hence the frequency response is dependent on whether the emitter density of states is two- or three-dimensional-like.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341548
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  • 2
    Electronic Resource
    Electronic Resource
    Coupled surface and channel transport in semiconductor heterostructures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6135-6139 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron transport in a channel separated from the surface by a thin insulating barrier layer is shown to be profoundly affected by electrical conditions on the surface. Nonuniformities in the coupled surface and channel systems lead to depletion and accumulation regions in the channel and the depletion regions can cause the current to saturate at unusually low voltages. Even when there are no nonuniformities it is shown that the coupled system exhibits a density instability that leads to similar phenomena. These effects are described in terms of an analytical model that takes into account diffusion and hot-electron transport applied to the AlGaN/GaN system. It is noted that the effect of any extension of the channel under the cathode (source) can produce depletion and current saturation that can be mistaken for the result of a nonohmic contact resistance. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1412569
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  • 3
    Electronic Resource
    Electronic Resource
    Polarization-induced electron populations (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 990-992 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron populations induced by spontaneous and piezoelectric polarization in semiconductor heterostructures can be estimated simply by using elementary electrostatic theory. The method is illustrated for the AlGaN/GaN system in which the AlGaN barrier is either undoped, or doped n type, and the effect of a GaN overlayer is described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288817
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  • 4
    Electronic Resource
    Electronic Resource
    Comparative analysis of zinc-blende and wurtzite GaN for full-band polar optical phonon scattering and negative differential conductivity (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2707-2709 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For high-power electronics applications, GaN is a promising semiconductor. Under high electric fields, electrons can reach very high energies where polar optical phonon (POP) emission is the dominant scattering mechanism. So, we undertake a full-band analysis of POP scattering of conduction-band electrons based on an empirical pseudopotential band structure. To uncover the directional variations, we compute POP emission rates along high-symmetry directions for the zinc-blende (ZB) crystal phase of GaN. We also compare the results with those of the wurtzite phase. In general, the POP scattering rates in the zinc-blende phase are lower than the wurtzite phase. Our analysis also reveals appreciable directional dependence, with the Γ–L direction of ZB GaN being least vulnerable to POP scattering, characterized by a scattering time of 11 fs. For both crystal phases, we consider the negative differential conductivity possibilities driven by the negative effective mass part of the band structure. According to our estimation, for the ZB phase the onset of this effect requires fields above ∼1 MV/cm. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1320020
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  • 5
    Electronic Resource
    Electronic Resource
    Biased organelle transmission in somatic hybrids ofLycopersicon esculentum andSolanum lycopersicoides (1988)
    Springer
    Current genetics 14 (1988), S. 177-182 
    Details
    ISSN: 1432-0983
    Keywords: RFLP ; Tomato ; Plastid ; Mitochondria ; Protoplasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Restriction fragment length polymorphisms (RFLPs) were used to determine the transmission of organelle genomes in somatic hybrid plants of tomato and its wild relativeSolanum lycopersicoides. Biased frequencies of organelle combinations were observed in a population of 70 somatic hybrid plants each derived from a separate callus. The plastids in 68 of 70 hybrids examined were fromL. esculentum. One of the remaining hybrids, plant 240, hadS. lycopersicoides plastids and the other, plant 63, had a mixture of parental plastids. Forty-six of the same 70 plants were analyzed for mtDNA and all had that ofS. lycopersicoides including plant 240. One of these hybrids had novel mtDNA fragments which mayhave resulted from recombination or rearrangement. The biased transmission may have resulted from an initial unequal input of organelles, differential replication of organelles, or nucleo-organelle incompatibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00569342
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship between peroxyacetyl nitrate and nitrogen oxides in the clean troposphere (1985)
    [s.l.] : Nature Publishing Group
    Nature 318 (1985), S. 347-349 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The measurements were made at the C-l research site of the Mountain Research Station of the University of Colorado (402' N lat, 10532' W long., 3.05-km elevation above sea level). Prevailing winds at this site are from the west and are relatively free of anthropogenic pollution. However, there are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/318347a0
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of the photodissociation coefficient of NO2 in the atmosphere: II, stratospheric measurements (1985)
    Springer
    Journal of atmospheric chemistry 3 (1985), S. 233-245 
    Details
    ISSN: 1573-0662
    Keywords: J NO 2 ; NO2 photolysis ; atmospheric photochemistry ; J NO 2 measurement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The photodissociation coefficient of NO2, J NO 2, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J NO 2 measured were 10.5±0.3 and 10.3±0.3×10-3 s-1 at 24 and 32 km respectively. The decrease in J NO 2 at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J NO 2 using a simplified isotropic multiple scattering computer routine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210498
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  • 8
    Electronic Resource
    Electronic Resource
    Is the Arctic Surface Layer a Source and Sink of NOx in Winter/Spring? (2000)
    Springer
    Journal of atmospheric chemistry 36 (2000), S. 1-22 
    Details
    ISSN: 1573-0662
    Keywords: active nitrogen ; ozone ; radicals ; snow chemistry ; Arctic ; surface layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of ≤10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be ∼1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006301029874
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  • 9
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    Comparative analysis of zinc-blende and wurtzite GaN for full-band polar optical phonon scattering and negative differential conductivity (2000)
    American Institute of Physics
    Details
    Publication Date: 2000-10-23
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Polarization-induced electron populations (2000)
    American Institute of Physics
    Details
    Publication Date: 2000-01-01
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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