| This thesis describes electrical detection of spin transport in Fe/GaAs heterostructures. Spin polarization in GaAs is generated by either spin injection at a reverse-biased Fe/GaAs Schottky tunnel barrier or by spin accumulation at a forward-biased Fe/GaAs Schottky tunnel barrier. An Fe/GaAs Schottky tunnel barrier, which is forward-biased or zero-biased, is used to detect the spin polarization in GaAs.; Using standard semiconductor processing techniques, lateral Fe/GaAs devices are fabricated. The interface between Fe and GaAs is a highly-doped GaAs Schottky tunnel barrier. Tunneling transport at a forward-biased Fe/GaAs drain contact is different for spin-up and spin-down electrons, resulting in spin accumulation. The spin accumulation leads to an additional voltage drop at the drain contact. Ordinary voltage measurements are used to detect this voltage drop. A transverse magnetic field dephases the accumulated spin polarization and suppresses the voltage drop, demonstrating the Hanle effect. The transverse magnetic field dependence of the drain voltage, referred to as the Hanle curve, is modeled using a spin drift-diffusion model incorporating spin relaxation and precession. The temperature, bias, and doping dependences of the Hanle curves are consistent with predictions of the spin drift-diffusion model.; Electrical detection of spin transport is also demonstrated on Fe/GaAs non-local devices, which consist of a series of closely spaced Fe contacts on top of an n-GaAs channel. These Fe contacts are used as spin injectors and detectors. Two reference electrodes are placed at opposite ends of the GaAs channel, allowing for non-local spin detection, in which no charge current flows into the spin detector. The electrochemical potential of the detector is sensitive to the relative magnetization state of the spin injector and detector. In the first type of measurement, an in-plane magnetic field is applied to flip the relative magnetization state from parallel to antiparallel, resulting in a voltage jump which is proportional to spin polarization. In the second type of measurement, spin polarization is dephased by an out-of-plane magnetic field, demonstrating the Hanle effect. Electrical measurement results are confirmed by an optical Kerr experiment and are found to be consistent with the spin drift-diffusion model. |
