Relaxação de spin em nanoestruturas semicondutoras 0 e 2D
Abstract
This thesis contains a compilation of the work developed and is divided into
three main parts. The first part describes the homogeneous and inhomogeneous
decoherence mechanisms of excitons in GaAs/AlGaAs quantum wells. It was
demonstrated that, for low temperatures, the main decoherence mechanisms are
associated to the acoustic phonon scattering and short-range interactions. Fur-
thermore, the results of magneto-photoluminescence with the luminescence re-
solved with circular polarization, a modulation for one of the spin components
of the exciton was presented as a result of a competition between short-range in-
teractions and spin-flip scattering. In the second part of this thesis, the influence
of substrate orientation on spin relaxation mechanism is detailed. Firtsly, it was
shown that the oscillations in the integrated intensity of the luminescence in the
high magnetic field regime are due to the relaxation process through the Landau
levels of the electron and hole subbands, whereby the substrate orientation has
no influence on these oscillations. Furthermore, it has been shown in the present
study that spin inversion occurs only for the orientation of the GaAs (311)A sur-
face, which is observed both with temperature and power dependence. Finally,
a theoretical framework was created in order to explain the spin inversion, with-
out the need of a conjecture as previously proposed. In the third and final part,
the results of the magnetic control of carrier transfer are presented for the hybrid
samples composed of InAs/GaAs quantum dot - InGaAs/GaAs quantum well
separeted by different GaAs spacer layer. For the thicker spacer, the photolumi-
nescence emission has the same behavior as the reference ones. In comparison,
for the thinner hybrid sample, an increase in the integrated QW intensity was ob-
served with an increasing in magnetic field, which was attributed to a change in
the coupling between QD and QW as well as a change in the carrier dynamics.
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