Investigation of the Role of Compensation and Origin of Ferromagnetism in Ga_1-xMn_xAs Using Magnetic Circular Dichroism Studies

III-Mn-V dilute magnetic semiconductors have emerged as promising candidatematerials for future spintronic devices that could use the spin property of the carriers(in addition to their electrical charge) to manipulate information. During the pastdecade the most extensively studied semiconductor in this family is GaMnAs.It is widely accepted that the long-range ferromagnetic ordering of Mn moments inthis material is induced by holes contributed by the Mn ions. These acceptors caneither be neutral or in the form of compensated negatively charged centers. Theprecise role which these two centers play in determining the magnetic propertiesof GaMnAs is still not fully understood. Moreover, the role of Mn acceptors indetermining the Zeeman splitting of band edges of GaMnAs needs to be investigatedin depth. Magnetic circular dichroism (MCD) is a powerful tool for investigatingmagneto-optical properties in thin magnetic layers, and in this study we apply thismethod to address the problem of Mn acceptor compensation in GaMnAs and itsimplication in determining the Zeeman splitting of band edges of GaMnAs, with theaim of shedding additional light on the co-relation of hole concentration and Curietemperature of these samples with Zeeman splitting of band edges.

The focus of this thesis is the analysis of magnetic circular dichroism data takenon thin GaMnAs films with low Mn concentration. Our measurements revealed thatexchange-induced spin splitting of the band edges occurs only in samples that showferromagnetic order, and is not observed in paramagnetic samples. These resultslead to the conclusion that Mn ions in the A⁰ configuration (d⁵ + hole) providethe only mechanism for exchange interaction between Mn spins and band carriers.We also show that there is a linear relation between the observed exchange-inducedsplitting of the band edges and the Curie temperature, pointing to a common originof the band edge splitting and ferromagnetism in GaMnAs.