| This dissertation describes efforts to study and understand magnetic and electrical transport properties of diluted magnetic semiconductors (DMS), particularly the role of manganese (Mn) in II-VI and III-V DMS. It is divided into two chapters; both focused on ferromagnetism, collective alignment of spins, and in the III-V system how this affects transport properties; understanding is vital for semiconductor spintronics applications. All samples discussed were grown by Molecular Beam Epitaxy (MBE). First, magnetization and relevant optical measurements of type-II self-assembled columnar quantum dots, namely (ZnMn)Te dots embedded in a ZnSe matrix are presented. Results for dots containing Mn ions are compared with results for ZnTe dots. The observation of apparent long-range magnetic ordering that is persistent up to high temperatures is discussed, and future research directions are suggested based on these results. Second, epitaxial layers of GaSb doped with Mn, namely Ga1-xMn xSb random alloys, are investigated by detailed magnetization and magneto-transport studies. The Curie temperature in this material system is quite low (< 25 K), but it exhibits very interesting behavior. A unique temperature dependence of the anomalous Hall effect (AHE) is observed and the underlying physics is explained by a simple theoretical model based on the role of impurity bands. Metal-insulator-semiconductor structures have also been studied and gating of the carrier density by this method has shown a change in the sign of the AHE. This result is not fully understood. |
