16 June 2004 Coherent vs. incoherent charge transport in semiconductor quantum cascade structures
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Abstract
We present an experimental study of electron transport in electrically driven quantum cascade laser structures. Ultrafast quantum transport from the injector into the upper laser subband is investigated by mid-infrared pump-probe experiments directly monitoring the femtosecond saturation and subsequent recovery of electrically induced optical gain. For low current densities, low lattice temperatures, and low pump pulse intensities the charge transport is dominantly coherent, i.e., we observe pronounced gain oscillations upon excitation giving evidence for a coherent electron motion between the injector and the upper laser subband. Increasing either the current density, the lattice temperature, or the pump pulse intensity the gain recovery shows an additional slow incoherent component which essentially follows the pump-initiated heating and subsequent cooling of the carrier gas in the injector.
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Michael Woerner, Felix Eickemeyer, Klaus Reimann, Thomas Elsaesser, Stefano Barbieri, Carlo Sirtori, T. Mueller, Rudolf Bratschitsch, Karl Unterrainer, G. Strasser, "Coherent vs. incoherent charge transport in semiconductor quantum cascade structures", Proc. SPIE 5352, Ultrafast Phenomena in Semiconductors and Nanostructure Materials VIII, (16 June 2004); doi: 10.1117/12.527512; https://doi.org/10.1117/12.527512
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