| In this thesis, we explore the magnetic and transport properties of ferromagnetic semiconductors and their heterostructures.; First, we introduce diluted magnetic semiconductors and their properties. The unique features of diluted magnetic semiconductors are originated from their position in the parameter space. We compare diluted magnetic semiconductors with similar physical systems and discuss the difference between them.; Next, we briefly review the background theories, such as k · p methods, density functional methods, and envelope function methods. These methods serve as the background on which our theory is based.; Third, we develop a mean-field theory in the framework of the self-consistent field method. Our approach improves the RKKY model, allowing spatial inhomogeneity of the system, free-carrier spin polarization, finite temperatures, and free-carrier exchange and correlation to be accounted for self-consistently. As an example, we calculate the electronic structure of a MnxGa 1−xAs/GaAs superlattice with alternating ferromagnetic and paramagnetic layers and demonstrate the possibility of semiconductor magnetoresistance systems with designed properties.; Fourth, we present a mean-field theory of ferromagnetism in diluted magnetic semiconductor quantum wells. Ignoring subband mixing due to exchange interactions between quantum well free carriers and magnetic impurities, we obtain an analytic result for the dependence of the critical temperature and the spontaneous magnetization on the distribution of magnetic impurities and on the quantum well width.; Fifth, we predict that a novel bias-voltage assisted magnetization reversal process will occur in Mn doped II-VI semiconductor quantum wells or heterojunctions with carrier induced ferromagnetism. We analyze the interplay between kinetic exchange coupling and quantum confinement effects, and show that magnetization reversal is due to strong exchange-coupling induced subband mixing.; Finally, we apply the mean-field theory of ferromagnetism to the case of delta-doped Mn layers. We show that the properties of these two-dimensional ferromagnets depend critically on realistic features of the valence band captured by the phenomeno-logical Kohn-Luttinger Hamiltonian. (Abstract shortened by UMI.)... |
