Dresden 2003 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 10: Halbleiterlaser II
HL 10.5: Vortrag
Montag, 24. März 2003, 16:15–16:30, BEY/81
Coherent versus incoherent charge transport in semiconductor quantum cascade structures — •M. Woerner1, F. Eickemeyer1, K. Reimann1, T. Elsaesser1, S. Barbieri2, C. Sirtori2, G. Strasser3, T. Müller3, R. Bratschitsch3, and K. Unterrainer3 — 1Max-Born-Institut, Berlin, Germany — 2Thales-CSF, Orsay, France — 3Technische Universität, Wien, Austria
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 [1]. 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. 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. The experimental data strongly suggest that because of the strong Coulomb interaction between the carriers the electrons in the upper laser subband together with those in the preceding injector form a single plasma, allowing for coherent collective charge density oscillations through the injection barrier.
[1] F. Eickemeyer et al., Phys. Rev. Lett. 89, 047402 (2002).