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  • 1995-1999  (16)
  • 1
    Electronic Resource
    Electronic Resource
    Carrier dynamics and photodetection in charge injection transistors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3312-3317 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study picosecond carrier transport dynamics induced by 200 fs 1.55 μm optical pulses in charge injection transistor structures. We propose and demonstrate a new optoelectronic method for exploring the interactions of hot majority carriers and cold minority carriers, as well as the optical control of real space transfer in these devices. The minority holes photogenerated in the channel produce substantial cooling of the hot-electron majority carriers and lead to the reduction of the real space transfer. The new method also provides a direct measure of the minority carrier lifetime in the transistor channel. These effects are demonstrated in InGaAs-channel devices with both InAlAs and InP barriers. The similarities in the device characteristics are explained in terms of the interaction of photogenerated minority holes with majority electrons in the channel leading to a photoconductor-like drain current and to a reduction in the real space transfer collector current. The differences are attributed to the different conduction and valence band energy offsets between the wide band gap barrier and the low band gap collector and channel layers. Furthermore, the InAlAs-barrier device shows a capability of serving as a practical photodetector with the measured, system-limited recovery speed of ∼5 ps. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361231
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  • 2
    Electronic Resource
    Electronic Resource
    Nonstationary 1/f noise in InP/InGaAs heterojunction bipolar transistors (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 198-200 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 1/f noise for most electronic systems is stationary in that repeated measurements of the noise power will give the same result within statistical uncertainty. In contrast, we have observed highly nonstationary 1/f noise in the output current of a series of InP based heterojunction bipolar transistors (HBTs). We have applied higher order statistics to the non-Gaussian fluctuations of these devices to probe the source of the intrinsic 1/f noise. We find signatures of superimposed Lorentzians making up an otherwise featureless 1/f noise spectrum consistent with generation-recombination-type noise in the base-emitter region of the device. The nonstationarity of these devices scales inversely with the device size as would be expected for an intrinsic mechanism. We suggest that these techniques may be utilized to a greater extent in the future as device sizes are reduced. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113133
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  • 3
    Electronic Resource
    Electronic Resource
    On the origin of oval defects in metalorganic molecular beam epitaxy of InP (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2358-2360 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the dependence of oval-shaped defects on growth conditions during metalorganic molecular beam epitaxy of InP. The density of oval defects is independent of growth conditions but strongly dependent on the initial substrate surface preparation. Contaminants existing on the surface prior to growth are indicated as the likely cause of oval defect formation due to local enhancement of metalorganic molecules cracking on the surface and the subsequent formation of group III rich structures. High densities of such defects are shown to degrade the optical properties of InGaAs quantum wells. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113982
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  • 4
    Electronic Resource
    Electronic Resource
    Optical transitions between light hole subbands in InGaAs/InP strained layer multiquantum wells (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2268-2270 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The observation of light hole intersubband absorption in both p-doped and photoexcited undoped strained InxGa1−xAs/InP (x(approximately-equal-to)0.35) quantum-well structures is reported. The absorption is polarized along the growth direction and is in agreement with calculations which show that the strain causes the light hole level to be first occupied upon p-doping or photoexcitation. Both impurity bound and free holes transitions are identified. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113188
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  • 5
    Electronic Resource
    Electronic Resource
    Measurement of the electron ionization coefficient at low electric fields in InGaAs-based heterojunction bipolar transistors (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1095-1097 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of the electron impact-ionization coefficient αn in In0.53Ga0.47As is measured with unprecedented sensitivity down to very low electric fields. The data are derived from measurements of the multiplication coefficient M−1 in suitably designed heterojunction bipolar transistors. Previously available data are extended by two orders of magnitude in the low field domain, down to αn≈1 cm−1. The experimental behavior of αn at fields below 200 kV/cm is in agreement with the theoretical prediction of a weak field dependence of αn at low electric fields. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113583
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  • 6
    Electronic Resource
    Electronic Resource
    Carbon doping of Ga0.47In0.53As using carbontetrabromide by metalorganic molecular beam epitaxy for InP-based heterostructure bipolar transistor devices (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2226-2228 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Metalorganic molecular beam epitaxy of carbon-doped heterostructures and InP/Ga0.47In0.53As heterostructure bipolar transistors using carbontetrabromide (CBr4) as the dopant source is reported. Secondary ion mass spectrometry show H incorporation associated with the carbon doping. Hall data for as-grown and postgrowth annealed samples showed a clear increase in doping only for samples grown at the lowest temperature, 450 °C, and higher doping levels. An increase in the mobility, however, was measured for nearly all samples after annealing, indicating that the neutral C–H complexes most likely contribute to majority carrier scattering. The gain variation for various devices with base thickness, WB, and base doping, p, was found to be nearly proportional to 1/(WB×p)2 consistent with diffusive base transport and Auger dominated recombination in the heavily doped base region. It was also observed that in devices where the C-doped base was grown at temperatures (approximately-greater-than)500 °C, the gain was shifted to much lower values possibly indicating a reduced electron carrier lifetime. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115111
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  • 7
    Electronic Resource
    Electronic Resource
    The cellular environment in computer simulations of radiation-induced damage to DNA (1998)
    Springer
    Radiation and environmental biophysics 37 (1998), S. 167-172 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Radiation-induced DNA single- and double-strand breaks were modeled for 660 keV photon radiation and scavenger capacity mimicking the cellular environment. Atomistic representation of DNA in B form with a first hydration shell was utilized to model direct and indirect damage. Monte Carlo generated electron tracks were used to model energy deposition in matter and to derive initial spatial distributions of species which appear in the medium following radiolysis. Diffusion of species was followed with time, and their reactions with DNA and each other were modeled in an encounter-controlled manner. Three methods to account for hydroxyl radical diffusion in a cellular environment were tested: assumed exponential survival, time-limited modeling and modeling of reactions between hydroxyl radicals and scavengers in an encounter-controlled manner. Although the method based on modeling scavenging in an encounter-controlled manner is more precise, it requires substantially more computer resources than either the exponential or time-limiting method. Scavenger concentrations of 0.5 and 0.15 M were considered using exponential and encounter-controlled methods with reaction rate set at 3×109 dm3 mol–1 s–1. Diffusion length and strand break yields, predicted by these two methods for the same scavenger molarity, were different by 20%–30%. The method based on limiting time of chemistry follow-up to 10–9 s leads to DNA damage and radical diffusion estimates similar to 0.5 M scavenger concentration in the other two methods. The difference observed in predictions made by the methods considered could be tolerated in computer simulations of DNA damage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050112
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  • 8
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of diffusion and reaction in water radiolysis – a study of reactant `jump through' and jump distances (1998)
    Springer
    Radiation and environmental biophysics 36 (1998), S. 229-234 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract In Monte Carlo simulations of water radiolysis, the diffusion of reactants can be approximated by “jumping” all species randomly, to represent the passage of a short period of time, and then checking their separations. If, at the end of a jump, two reactant species are within a distance equal to the reaction radius for the pair, they are allowed to react in the model. In principle, the possibility exists that two reactants could “jump through” one another and end up with a separation larger than the reaction radius with no reaction being scored. Ignoring this possibility would thus reduce the rate of reaction below that intended by such a model. By making the jump times and jump distances shorter, any error introduced by `jump through' is made smaller. This paper reports numerical results of a systematic study of `jump through' in Monte Carlo simulations of water radiolysis. With a nominal jump time of 3 ps, it is found that more than 40% of the reactions of the hydrated electron with itself and of the H atom with itself occur when reactions during `jump through' are allowed. For all other reactions, for which the effect is smaller, the contributions of `jump through' lie in the range l%–16% of the total. Corrections to computed rate constants for two reactions are evaluated for jump times between 0.1 and 30 ps. It is concluded that jump-through corrections are desirable in such models for jump times that exceed about 1 ps or even less. In a separate study, we find that giving all species of a given type the same size jump in a random direction yields results that are indistinguishable from those when the jump sizes are selected from a Gaussian distribution. In this comparison, the constant jump size is taken to be the root-mean-square jump size from the Gaussian distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050076
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  • 9
    Electronic Resource
    Electronic Resource
    Investigation of a Monte Carlo model for chemical reactions (1998)
    Springer
    Radiation and environmental biophysics 37 (1998), S. 151-156 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Monte Carlo computer simulations are in use at a number of laboratories for calculating time-dependent yields, which can be compared with experiments in the radiolysis of water. We report here on calculations to investigate the validity and consistency of the procedures used for simulating chemical reactions in our code, RADLYS. Model calculations were performed of the rate constants themselves. The rates thus determined showed an expected rapid decline over the first few hundred ps and a very gradual decline thereafter out to the termination of the calculations at 4.5 ns. Results are reported for different initial concentrations and numbers of reactive species. Generally, the calculated rate constants are smallest when the initial concentrations of the reactants are largest. It is found that inhomogeneities that quickly develop in the initial random spatial distribution of reactants persist in time as a result of subsequent chemical reactions, and thus conditions may poorly approximate those assumed from diffusion theory. We also investigated the reaction of a single species of one type placed among a large number of randomly distributed species of another type with which it could react. The distribution of survival times of the single species was calculated by using three different combinations of the diffusion constants for the two species, as is sometimes discussed in diffusion theory. The three methods gave virtually identical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050110
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  • 10
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    Carbon doping of Ga0.47In0.53As using carbontetrabromide by metalorganic molecular beam epitaxy for InP‐based heterostructure bipolar transistor devices (1995)
    American Institute of Physics
    Details
    Publication Date: 1995-10-09
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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