A. Schülzgen

Carrier dynamics in CdSe quantum dots embedded in glass

Abstract The relaxation and recombination of carriers excited by ultrashort optical pulses are studied on specially prepared II–VI quantum dots in a silicate-type host. Photoluminescence with ps resolution allows to observe the emission from the confined, intrinsic energy levels of the dots under non- and size-selective excitation, respectively. A comparison with data of transient non-linear absorption reveals that the relaxation pathway of electron and holes may be substantially different and depends strongly on the dot size.

Exciton dynamics and high density effects in ZnSe/ZnMnSe quantum structures grown by molecular beam epitaxy

ZnSe well exciton features in ZnSe/ZnMnSe quantum structures grown by molecular beam epitaxy (MBE) are investigated using various spectroscopic techniques. Steady-state photoluminescence and excitation spectroscopy demonstrate an enhanced effective band offset due to tensile strain and a confinement induced shift of the excitonic resonances up to 100 meV. Progressive localization of excitons on the 10 ps time scale followed by rapid recombination within 100 ps is observed in time-resolved luminescence. Transient pump-probe measurements show clear nonlinear excitonic absorption under 2 μJ/cm 2 excitation with a recovery on the same time scale as the radiative recombination

Coherent exciton-exciton interaction in wide-gap II–VI quantum wells. The role of alloy disorder

Abstract This paper studies coherent exciton-exciton interaction in ternary ZnCdSe ZnSe quantum wells by femtosecond degenerate four-wave mixing. Distinct two-exciton features are observed the appearance of which depends on the polarization of the excitation pulses. A signal for negative pulse delays disappears for larger Cd concentration.

Dynamics of Exciton Recombination in II-VI Semiconductor Quantum Wells

We have studied the temporal evolution of the inhomogeneously broadend exciton emission band to obtain information about the process of exciton localization in ZnCdSe/ZnSe and ZnSe/ZnMnSe quantum well structures. The observed behavior can be described with quantitative agreement by theoretical calculations taking into account the exciton center-of-mass motion in a disordered potential being Gauss distributed and correlated over distances of the exciton Bohr radius. As predicted by the theory a nearly linear increase of the exciton life-time is observed between 5 K and 40 K for the ZnCdSe/ZnSe structure.

Strain, confinement, carrier dynamics and high density effects in ZnSe/ZnMnSe-quantum structures

Abstract MBE grown ZnSe/ZnMnSe quantum structures are investigated using various spectroscopic techniques. Conventional photoluminescence and excitation spectroscopy demonstrate an enhanced effective band offset due to tensile strain and a confinement induced shift of the excitonic resonances up to 100 meV. Time-resolved luminescence reveals progressive localization of excitons on the 10 ps-time scale followed by rapid recombination within 100 ps. Optical gain on the order of 100 cm−1 is observed under 400 kW/cm2 excitation.

Time-resolved luminescence from II–VI quantum dots

Abstract The transient luminescence after short pulse excitation is studied on specially prepared II–VI quantum dots in glass. A fast ‘band-gap’ resonant component superimposed to a slow background emission from defect states is observed. The lifetime of the fast component is strongly dependent on the dot size. This is related to a transition from dominant non-radiative to radiative recombination with increasing dot size.

Nonlinear absorption sensitization of a photorefractive polymer composite for operation at 1.55 microns

Photorefractivity at 1.55 µm in a polymer composite is demonstrated using twophoton absorption. We show large diffraction efficiency and perform holographic reconstruction of distorted images utilizing thin-film devices made of this polymer.