### Abstract

The coherent response of excitons in semiconductor nanostructures
measured in four-wave mixing (FWM) depends strongly on the
inhomogenous broadening of the exciton transition. We investigate
InAs/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 inhomogenous
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.

Original language | English |
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Journal | Materials Science Forum |

Volume | 297-298 |

Pages (from-to) | 73-78 |

ISSN | 0255-5476 |

Publication status | Published - 1999 |

## Cite this

Langbein, W., Borri, P., & Hvam, J. M. (1999). Coherent Exciton and Biexciton Nonlinearities in Semiconductor
Nanostructures: Effects of Disorder.

*Materials Science Forum*,*297-298*, 73-78.