Estudo experimental de efeitos de spin em heteroestruturas semicondutoras
Resumen
In this thesis, we have investigated optical and spin properties of semiconductor
nanostructures. Photoluminescence and magneto-photoluminescence measurements
were performed in high magnetic field (B ≤ 15T), in GaBiAs nanostructures and GaAs
/AlGaAs semiconductor devices. Particularly, we have studied: (i) GaBiAs layers, (ii)
GaBiAs/GaAs quantum wells (QW) (iii) standard GaAs / AlGaAs resonant tunneling
diodes (RTDs) and (iv) GaAs / AlGaAs RTDs containing quantum rings of InAs in the
QW.
We have investigated the effect of carrier localization by defects on the optical
and spin properties of GaBiAs layers and nanostructures. Our results evidence
important effects of carrier location by defects which was associate by small values of
magnetic shifts. This effect is probably due to the formation of clusters and by the Bi
composition variation on this type of alloy. It was also observed that the thermal
annealing treatment improves the optical quality of these systems and increases the
polarization degree which was associated to the reduction of spin relaxation times.
We have also investigated the optical properties, magneto-optical and of
transport in double barrier semiconductor heterostructures. Particularly, we have
investigated the optical and spin properties of two dimensional electron and hole gases
and the quantum well (QW). It was observe optical emission in the QW associate to the
criation of uncharged exciton and negative charge exciton. The two dimensional gases
acts as a spin polarize carriers injection in the QW, increasing thus the spin polarization
in this region. The experimental results indicated that this process is more efficient in
low voltage region. For high voltages region other processes, such as formation of tríons
and spin polarization loss during tunneling should result in a significant contribution to
the spin and polarization.
Furthermore, it was investigated the spin properties of double barrier diodes
containing InAs quantum rings in the center of the QW. It was observe that the degree
of circular polarization of the emission of the QRs strongly sensitive to the applied
voltage shows oscillation and besides one possible polarization oscillations tendency
with the increase of the magnetic field.