Dresden 2009 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 50: Ultra fast phenomena
HL 50.3: Vortrag
Freitag, 27. März 2009, 10:45–11:00, BEY 118
All-optically induced ultrafast currents in GaAs quantum wells: Excitonic effects and dependence on quantum well width — •Shekhar Priyadarshi1, Ana Maria Racu1, Klaus Pierz1, Uwe Siegner1, Mark Bieler1, and Philip Dawson2 — 1Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany — 2School of Physics and Astronomy, University of Manchester, Manchester, M60 1QD, England
We have studied the influence of excitonic effects on ultrafast current transients that are induced in unbiased GaAs quantum wells by all-optical excitation. The ultrafast current transients result from second-order nonlinear optical effects and were detected by measuring the simultaneously emitted THz radiation. Experiments were performed on (110)-oriented GaAs/AlGaAs quantum well samples with different well widths and with 150 fs excitation laser pulses at room temperature. By studying the dependence of the current amplitude and phase on excitation photon energy in the different samples, we find that Coulomb effects and the quantum well width substantially affect the properties of these ultrafast currents. This becomes most prominently visible when exciting light-hole exciton transitions. The phase data shows that for excitation of light-hole-type transitions a current reversal occurs as compared to excitation of heavy-hole-type transitions. The amplitude dependence of the current transients on excitation photon energy is influenced by the reversed current contribution from heavy- and light-hole-type transitions, the complex bandstructure, and non-instantaneous effects contributing to the current dynamics.