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HL: Halbleiterphysik

HL 4: Ultrakurzzeitph
änomene

HL 4.7: Vortrag

Montag, 8. März 2004, 11:45–12:00, H13

Stimulated bosonic scattering in the exciton-biexciton system of a ZnSe single quantum well — •Stefan Pfalz, Daniel Hägele, and Michael Oestreich — Universität Hannover, Institut für Festkörperphysik, Abteilung Nanostrukturen, Appelstraße 2, 30167 Hannover

Although it has been long known that semiconductor excitons and biexcitons are quasiparticles of bosonic nature, all experiments claiming bosonic effects are discussed controversially. Here, we give direct experimental evidence that the decay of a spin-zero biexciton into an exciton and a photon with opposite spins (± 1) is subject to bosonic enhancement caused by the presence of other excitons. In an optically created spin polarized gas of excitons, biexcitons decay preferentially into that final state whose resulting exciton has the same spin orientation as the majority of excitons. We measure in a 10 nm ZnSe quantum well a photoluminescence polarization degree of up to 8 % at the biexciton emission line due to stimulated bosonic scattering. The biexcitonic PL polarization is opposite to that of the excitons which exhibit a polarization degree of −50 %. While the polarization of the exciton line can be fully understood by the usual optical spin selection rules, the biexcitonic polarization can only be explained by the bosonic nature of excitons.