Ferromagnet/Semiconductor interfaces: Spin injection and Anisotropic polar magneto-optic Kerr effect

In this thesis basic research in the field of semiconductor spintronics is performed. Electron spin injection from ferromagnetic contacts into GaAs-based heterostructure systems is investigated by employing scanning Kerr microscopy at the cleaved edge of the samples. The experiments suggest that spin diffusion and charge diffusion in bulk n-GaAs samples have comparable strengths. In contrast, in two-dimensional systems the spin diffusivity is found to be orders of magnitude smaller than the charge diffusivity, suggesting that electron-electron interactions play an important role in those systems. Finally, it is investigated, whether a spin imbalance in n-GaAs can be created via thermal spin injection. However, the measurements suggest that the Seebeck spin tunneling coeffcient for Fe/GaAs is orders of magnitude smaller than the reported values for Si and Ge-based systems with oxide tunnel barriers. The second part of the thesis is dedicated to the optical properties of ultrathin layers of epitaxial Fe/GaAs(001) at room temperature. It is demonstrated that spin-orbit coupling at the Fe/GaAs(001) interface not only affects the transport properties of the heterostructure, as was shown before, but also gives rise to magneto-optical anisotropies. A clear twofold anisotropy of the Kerr rotation angle depending on the orientation of the linear polarization of the probing laser beam with respect to the crystallographic directions of the sample is detected. The observed twofold symmetry of the Kerr angle is fully reproduced by a phenomenological model based on the interference of interfacial Bychkov-Rashba and Dresselhaus spin-orbit coupling fields