The effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs -(Ga,Al)As quantum well are investigated. The shallow-donor binding energy for different well widths and different values of the hydrostatic stress has been calculated. It has been found that for wider well widths the binding energy increases slowly with hydrostatic stress contrary to the behavior of the binding energy for wells with smaller widths. In particular, it has been found that the binding energy does not change appreciably with the impurity position when the width of the well is small and for large values of hydrostatic stress. Two structures in both the density of states and the optical absorption spectra, associated with impurities located close to the center and to the edges of the structure, are obtained. Also, it has been observed that the density of states and the optical absorption spectra depend strongly on the applied hydrostatic stress.

Abstract.The interplay between collective pinning on intrinsic structural defects and artificial pinning at a patterned hole is studied in magnetic multilayers with perpendicular anisotropy. The pinning strength of a patterned hole is measured through its efficiency to stop domain wall propagation into a consecutive unpatterned nanowire section (using antisymmetric magnetoresistance to detect the direction of domain wall propagation) whereas collective pinning is characterized by the field dependence of domain wall velocity. Close to room temperature, collective pinning becomes weaker than artificial pinning so that pinning at the hole compensates nucleation-pad geometry, blocking domain wall propagation across the nanowire.

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The electronic and transport properties of double barrier structures are studied using the Kubo formula for the electrical conductivity and a tight-binding respresentation for the Hamiltonian. The theory is able to reproduce the experimental I -U characteristic curves. A self-consistent Hartree treatment permits to study the charge distribution and its influence on the position of the resonant energy levels and on the tunneling properties as a function of the doping of the sample.Les propri6tCs Clectroniques et de transporte des structures de barriere double sont CtudiCes en employant la formule de Kubo pour la conductivite Clectronique et la representation ((tight-binding)). I1 est possible de reproduire avec la thCorie des courbes caracteristiques experimentaux I-U. Un traitement de Hartree auto-consistant nous permets detudier la distribution de charge et son influence sur la position des niveaux CnergCtiques resonantes et sur les propriCtCs de tunnelement dkpendantes du dopage de Iechantillon.

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