Lateral spin injection and detection via electrodeposited Fe/GaAs contacts

Experimental studies of lateral spin injection and detection through electrodeposited Fe/GaAs tunnel contacts are reported in this thesis. An enhanced spin valve voltage is demonstrated via non-local lateral spin transport measurements compared to their vacuum-deposited counterparts. We have proposed a simple theoretical model to explain this result. Combined with experimental evidence for interfacial oxygen from atom probe tomography, we speculate that the enhancements occur due to a magnetic iron oxide layer forming at the Fe/GaAs interface during the electrodeposition. This layer acts as a tunnel barrier with a spin-dependent height. This discovery of greatly enhanced spin injection into GaAs via electrodeposited contacts introduces a promising new direction for the development of practical semiconductor spintronic devices. This thesis addresses three major challenges: i) The electrodeposition of Fe onto an epitaxial n-GaAs layer on a semi-insulating substrate to fabricate the tunnel contacts and lower-doped channel required for lateral spin injection. ii) Demonstration of spin accumulation and transport using patterned contacts in lateral configurations. iii) Understanding magnetic in-homogeneities and defects in the thin Fe film and correlating these to the observed enhanced spin injection. Continuous Fe film coverage was achieved over a desired area of the epitaxial GaAs by creating a uniform potential at the back of the sample. Nucleation and growth of Fe was observed within a range of applied current densities from 0.05 to 0.20 mA/mm^2, with the best Fe epitaxy occurring at 0.15 mA/mm^2. Modelling via a micromagnetic simulator showed that magnetic hysteresis curves from the electrodeposited Fe did not follow the standard behavior of a thin Fe film (single or polycrystalline). Instead, these Fe films demonstrated inhomogeneous magnetization controlled by strong local uniaxial anisotropies along both the <100> and <110> crystallographic directions. The presence of defects and coalescence boundaries responsible for these in-homogeneities were detected by transmission electron microscopy. Spin valve and Hanle measurements showed evidence of a local magnetostatic field, possibly originating from magnetic impurities at the electrodeposited Fe/epitaxial GaAs interface. We suggest that these magnetic impurities enhanced the tunneling probability and the spin accumulation within the GaAs channel while reducing the spin lifetime