2,042 research outputs found

    Cathodoluminescence spectroscopy of ambipolar diffusion in (Al,Ga)As barriers and capture of nonequilibrium carriers in GaAs quantum well

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    Ambipolar vertical diffusion of carriers generated in an Al0.3Ga0.7As barrier is investigated by cathodoluminescence CL spectroscopy in a system containing a sequence of GaAs-based quantum wells QWs . The intensity distribution of the CL line scan exhibits a single exponential decay for the first QW of the sequence, reflecting a pure diffusion-limited transport. However, the CL line scans of the second, third, and fourth QWs are governed by diffusion only for large separations between the electron beam and the corresponding QW. For smaller distances, the CL intensity distribution is significantly influenced by the carrier capture into the intervening QWs

    In‐plane photocurrent spectroscopy in GaAs-AlAs superlattices

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    The in‐plane photoconductivity of GaAs‐AlAs superlattices on GaAs substrates is experimentally studied as a function of the incident photon energy at different temperatures and light intensities. Superlattice and substrate are electrically isolated by a thick  Al0.3Ga0.7As barrier but connected through penetrating contacts. Depending on the transport properties of the two subsystems pseudo‐negative photoconductivity can be observed, i.e., at the absorption maximum of the superlattice the photocurrent exhibits a minimum

    A Layer Correlation Technique for ATLAS Calorimetry Calibration at the 2004 ATLAS Combined Beam Test

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    A method for calibrating the response of a segmented calorimeter to hadrons is developed. The ansatz is that information on longitudinal shower fluctuations gained from a principal component analysis of the layer energy depositions can improve energy resolution by correcting for hadronic invisible energy and dead material losses: projections along the eigenvectors of the correlation matrix are used as input for the calibration. The technique is used to reconstruct the energy of pions impinging on the ATLAS calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. Simulated Monte Carlo events are used to derive corrections for invisible energy lost in nuclear reactions and in dead material in front and in between the calorimeters. For pion beams with energies between 20 and 180 GeV, the particle energy is reconstructed within 3% and the resolution is improved by about 20%

    Electrically tunable GHz oscillations in doped GaAs-AlAs superlattices

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    Tunable oscillatory modes of electric-field domains in doped semiconductor superlattices are reported. The experimental investigations demonstrate the realization of tunable, GHz frequencies in GaAs-AlAs superlattices covering the temperature region from 5 to 300 K. The orgin of the tunable oscillatory modes is determined using an analytical and a numerical modeling of the dynamics of domain formation. Three different oscillatory modes are found. Their presence depends on the actual shape of the drift velocity curve, the doping density, the boundary condition, and the length of the superlattice. For most bias regions, the self-sustained oscillations are due to the formation, motion, and recycling of the domain boundary inside the superlattice. For some biases, the strengths of the low and high field domain change periodically in time with the domain boundary being pinned within a few quantum wells. The dependency of the frequency on the coupling leads to the prediction of a new type of tunable GHz oscillator based on semiconductor superlattices.Comment: Tex file (20 pages) and 16 postscript figure
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