University of Stuttgart
Publishes on Semiconductor Quantum Structures and Devices, Semiconductor Lasers and Optical Devices, Spectroscopy and Quantum Chemical Studies. 293 papers and 9.2k citations.
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The fundamental relationship between radiative lifetime and spectral linewidth of free excitons is demonstrated theoretically and experimentally for quasi 2D excitons in GaAs/AlGaAs quantum wells.Received 24 August 1987DOI:https://doi.org/10.1103/PhysRevLett.59.2337©1987 American Physical Society
Ultrafast relaxation processes in poly(p-phenylenevinylene) and its oligomers are investigated using femtosecond luminescence spectroscopy. A quasi-instantaneous luminescence rise and the absence of luminescence near the excitation energy indicate very rapid vibronic relaxation. The subsequent transient redshift of the spectra is attributed to ultrafast energy relaxation of optical excitations within an inhomogeneously broadened density of states.
The origins of line broadening in photoluminescence spectra of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ are analyzed. Thermal broadening, the influence of macroscopic inhomogeneity, and alloy broadening due to random cation distribution are investigated. Quantitative models for the linewidths of the bound exciton and the band-to-acceptor transition are developed, based on compositional fluctuations within the crystal volumes which are characteristic of the two transitions. The linewidths are calculated without any fitting parameter and agree with experimental results. Alloy clustering can be definitely excluded for samples grown (1) in (100) orientation and (2) under optimum conditions. The investigation of alloy broadening in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ leads to a quantitative understanding of low-temperature photoluminescence spectra of ternary and also of quaternary III-V semiconductors.
We present the first study of the dynamics of an extended electronic wave packet in a solid. The wave packet is created in a GaAs/AlGaAs double-quantum-well structure by ultrashort pulse excitation. We observe the oscillatory motion of the wave packet between the two wells by using time-resolved degenerate four-wave-mixing and pump-and-probe spectroscopy.
We present a time-resolved study of the field-induced luminescence quenching in poly(phenylphenylenevinylene) using femtosecond luminescence spectroscopy. The dynamic quenching of the luminescence reveals a delay between the generation of excitons and their breakup into geminate electron-hole pairs. We explain the data by the interplay of the dissociation and the spectral relaxation of the excitons within an inhomogeneously broadened density of states. Our experimental results suggest that the photocarriers in conjugated polymers are not formed directly but result from dissociation of excitons.