Many‐Exciton Theory for Multiple Quantum‐Well Structures

The many-exciton theory of highly excited semiconductors is reformulated in order to apply it to the case of a quasi two-dimensional confinement of electrons and holes in a multiple quantum-well structure. Using simple variational ansatzes for the exciton wave function in the low excitation limit density dependent exciton parameters are calculated for a GaAs-GaAlAs multiple quantum-well system. In contrast to bulk material but in agreement with experimental findings a blue shift of the excitonic resonance with increasing excitation intensity is obtained. The results are used to demonstrate nonlinear optical behaviour, especially bistabilities, for such systems. Die Vielexzitonen-Theorie hochangeregter Halbleiter wird fur den Fall der quasizweidimensionalen Begrenzung von Elektronen und Lochern in Vielquantentopfstrukturen umformuliert. Unter Benutzung eines einfachen Variationsansatzes fur die Exzitonwellenfunktion im Grenzfall niedriger Anregungsdichte werden fur ein GaAsGaAlAsVielquantentopf-System dichteabhangige Exziton-Parameter berechnet. In Ubereinstimmung mit experimentellen Ergebnissen und im Gegensatz zum Volumenmaterial wird eine Blauverschiebung der Exzitonenresonanz mit wach-sender Anregungsintensitat erhalten. Die Ergebnisse werden zur Demonstration nichtlinearen optischen Verhaltens solcher Systeme – insbesondere von Bistabilitaten — benutzt.

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