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Coherent exciton and biexciton nonlinearities in semiconductor nanostructures: effects of disorder

Langbein, Wolfgang Werner, Borri, Paola and Hvam, J. M. 1998. Coherent exciton and biexciton nonlinearities in semiconductor nanostructures: effects of disorder. Presented at: 10th International Conference on Ultrafast Phenomena in Semiconductors, Vilnius, Lithuania, August-September 1998. Published in: Steponas, Asmontos and Dargys, Adolfas eds. Ultrafast Phenomena in Semiconductors: Proceedings of the 10th International Symposium on Ultrafast Phenomena in Semiconductors (10-UFPS), held in Vilnius, Lithuania, August/September 1998. Materials Science Forum , vol. 297-8. Zurich: Trans Tech Publications, pp. 73-78.

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The coherent response of excitons in semiconductor nanostructures measured in four-wave mixing (FWM) depends strongly on the inhomogeneous broadening of the exciton transition. We investigate GaAs/Al0.3Ga0.7As single quantum wells (SQW) and AlxGa1-xAs mixed crystals. Additional to the usual phase-space filling nonlinearity, excitation-induced dephasing (EID) and biexciton formation (BIF) are important. EID leads to a strong dependence of the signal on the angle between the linear input polarizations. We find that EID persists in inhomogeneous systems, showing that the mutual density-dependent dephasing rate difference between two subsystems within the inhomogeneous distribution is strongly dependent on their energy difference. BIF is strongly affecting the cross-linear polarized FWM response. The signal for positive delay is dominated by the transitions from the one-exciton state X to the two-exciton states. Here, the third-order polarization at X-XX is not at the same resonance as the first-order polarization at 0-X. Consequently, the rephasing of the microscopic third-order polarization to the macroscopic FWM photon echo is blurred by the non-perfect correlation of X and XX energies, leading to a fast and non-exponential signal decay in delay time. For inhomogeneous broadenings larger than the biexciton binding energy, we find an enhanced biexciton binding energy, and a quenching of the oscillator strength of the unbound biexciton.

Item Type: Conference or Workshop Item (Paper)
Date Type: Publication
Status: Published
Schools: Biosciences
Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: nanostructures; semiconductors; quantum wells; non-linear spectroscopy; four-wave mixing; disorder; biexcitons
Publisher: Trans Tech Publications
ISBN: 9780878498246
ISSN: 0255-5476
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Last Modified: 16 May 2019 23:19

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