Propriedades estáticas e dinâmicas de portadores em heteroestruturas semicondutoras.
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Date
2002-10-30Author
Bittencourt, Antonio Carlos Rodrigues
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We have studied the dynamic and the stationary properties of carriers in semiconductor
heterostructures submitted to electric fields AC and DC and to magnetic fields
within the effective-mass approximation based on model multiband k · p. The method
used to calculate the electronic structure uses the combination of techniques of finite differences
and the inverse power method. As example to test the efficiency of the method,
we have studied optical properties in multiple quantum wells of GaAs/AlGaAs containing
a delta-doping nipi structure. We have calculated the single pair electron-hole energy
recombination and we estimated critical temperatures where the interband optical transitions
changes its character from indirect to direct. We have also calculated the electronic
structure of holes in quantum wells of GaAs/Ga1−xAlxAs in the presence of longitudinal
magnetic and electric parallel fields as initial part of the study of the magnetotunneling
in double barrier. The resonant tunneling of the carriers in double barrier is investigated
using the formalisms based on the scatterring-matrix and on the finite difference
technique. The implicit method to simulate the time dependent transport properties
is obtained in terms of Magnus expansion for the evolution operator by using a factorization
based on the approach of Padé (M/M). This method has shown quite stable,
besides allowing high order of precision. We have calculate the quasi-energy, medium displacement,
transmission probability, AC Stark effect and tunneling time of the carriers
in a quantum well GaAs/Ga0,7Al0,3As submitted to an AC potential, both with k = 0
and k 6= 0. Our results have revealed that carriers present dynamics completely different
from each other depending strongly on the ratio between applied AC frequency ω and the
carrier localization frequency ωl = (E
~ ). The AC Stark effect has adiabatic type that is
inserted into the initial conditions. The quasi-energy of all carriers, except the ligth-hole
LH1 at k = 0, present a similar quasi-parabolic dependence with the intensity of the
field β = (eF0Lz
}ω ), as is observed in static cases. The degree of localization of the carriers
is investigated through the calculation of tunneling times. In general, states show time
localization induced by laser frequencies larger that ωl for many states with k = 0. For
k > 0 the inherent mixture among the states of the valence band produces an increase in
the transmission probability. The field tilted barrier of potential leads to quasi-energies
near to the border of the QW, favoring the escape of carriers from quantum well region
if compared to their time localization regimes.