Lev S. The electron spin polarization by the double barrier systems and the exciton spectrum in double quantum wells in semimagnetic semiconductors

The optical properties of the exciton in double quantum wells and the electron spin polarization by the double barrier heterostructure, based on semimagnetic semiconductors, are investigated in the present thesis. The oscillator strength of the optical transitions and the exciton lifetime change due to the charge redistribution was theoretically studied as the function of the applied external magnetic field. In the case of double quantum well system based on the CdTe, the system parameters were found, at which at some values of magnetic field, the localization of the exciton in a ground state can be changed. In the situation of the magnetic field growth, transitions of the exciton, either from one well to another, or from spatially direct (electron and a hole in same well) exciton to spatially indirect (electron and a hole in different wells) exciton, which is a the ground state switch, was studied as a function of the type of impurities (magnetic or non-magnetic) and its localization. The double wellsemimagnetic semiconductor system, based on ZnSe with Mn impurities in one of the wells and with Be and Mg impurities in barriers, was studied. The wave functions and overlap integrals behaviors were analyzed as a function of the system parameters - concentrations of impurities, and the widths of wells and barriers. The range of values of well widths, in which the long-lived indirect exciton become the ground state, was determined. It was shown that the exciton lifetime grows by a couple of orders when a transition from direct to indirect exciton takes place or when the width of the barrier between wells grows. The spin polarization of carriers in the double barrier systems, constructed by the heterojunctions of the semimagnetic semiconductor alloy, was studied as a function of external electric and magnetic fields, barrier parameters, magnetic and non-magnetic impurities concentrations, carrier concentrations, temperature, etc. The dependence of the level of spin polarization on the distance from the heterostructure was calculated at the different system parameters - spin relaxation time, carrier mobility and so on.