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Ultrafast Processes in Semiconductor Structures

100%
Viña L.
Acta Physica Polonica A
|
1999
|
vol. 96
|
issue 5
573-592
EN
We review the dynamics of some of the more relevant optical processes in semiconductor quantum wells. We concentrate on the linear regime and study the time evolution of the light emission, using time-resolved photoluminescence spectroscopy. In intrinsic materials, excitonic effects determine their optical properties. Here we describe the formation and recombination of excitons, and the dependence of these processes on lattice temperature, exciton density, and energy of the excitation light pulses. We also describe the dynamics of the exciton's spin by optical orientation experiments. We discuss the principal mechanisms responsible for the spin flip of the excitons and clarify the role of the exciton localization. Finally, we will show that exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors. In doped quantum wells, we show that the two spin components of an optically created two-dimensional electron gas are well described by the Fermi-Dirac distributions with a common temperature but different chemical potentials. The rate of the spin depolarization of the electron gas is found to be independent of the mean electron kinetic energy but accelerated by thermal spreading of the carriers.
2
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Time-Resolved Emission from Semiconductor Microcavities

45%
Kłopotowski Ł., Viña L., Kavokin A., Dang L., André R.
Acta Physica Polonica A
|
2004
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vol. 106
|
issue 3
435-442
EN
We present a time-resolved study of the light emission of a CdTe-based microcavity. In the nonlinear regime, under high excitation conditions, in the strong coupling regime, we observe pronounced beats of the intensity of the photoluminescence arising from the bottleneck region of the exciton-polariton band. These beats are very sensitive to the excitation density and vanish under weak pumping conditions. We attribute the beats to a new nonlinear coupling mechanism of optically active and dark crystal states, related to polariton-polariton scattering, which leads to mixing between bright and dark states.
3
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Dynamics of Polariton Emission in the Linear Regime

39%
Kłopotowski Ł., Santos R., Amo A., Martín M., Viña L., André R.
Acta Physica Polonica A
|
2004
|
vol. 106
|
issue 3
443-450
EN
We studied the dependence of polariton emission dynamics on polariton wave-vector and exciton-photon energy detuning. To reproduce the experimental data, we applied a model that obtains the photonic and the excitonic emission rates of the polariton.
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