| The ferromagnetic semiconductor (Ga,Mn)As has been a focus of much research prompted by its potential applications in semiconductor spintronics. In this thesis, studies of the defect configuration and spin dynamics in this material are reported.; The technique of resonant Raman scattering was used to study the defect configuration. Insulating nano-islands consisting of substitutional Mn Ga acceptors and interstitial MnI donors were observed in ferromagnetic (Ga,Mn)As from resonant Raman spectra. As indicated by a sharp Raman transition from the 1S3/2-2 S3/2 hole levels at 703 cm-1, holes bound to MnGa acceptors inside the islands are partially isolated from the outside ferromagnetic environment. The MnGa ions inside the islands can interact with the ferromagnetic environment through bound excitons, as suggested by the presence of magnon-related side peaks. The radius of the nano-islands is inferred to be 5-10 nm. The islands disappear after annealing due to the removal of the MnI ions.; Furthermore, the technique of pump-probe magneto-optical Kerr spectroscopy was used to study the spin dynamics in (Ga,Mn)As. Coherent oscillations associated with magnetization precessions were observed. Using a comprehensive theoretical description of the processes by which light couples to the magnetization, the anisotropy and spin stiffness constants were gained from the experimental data. Results reveal a relatively large negative contribution to the energy due to surface anisotropy leading to excitations that are a mixture of bulk waves and surface modes. The dependence of the spin wave oscillations on magnetic field direction and temperature is also discussed.; Finally, the pump-probe technique was used to study interlayer coupling in (Ga,Mn)As-based superlattices. A coupled spin precession mode was observed in two layers of (Ga,Mn)As seperated by two-monolayers of AlAs. The spin wave spectra on superlattices with GaAs as spacer layers imply that Mn ions diffuse from (Ga,Mn)As to GaAs layers. |
