| Engineering metal/GaAs interfaces to control magnetic and electrical properties were studied in this thesis. The electrical properties, reaction kinetics, and interface properties during Ni/GaAs reactions were studied by combining molecular beam epitaxy (MBE) growth and in situ reactions together with in situ patterning and electrical characterization. Ni reacts with GaAs to form metastable NixGaAs at reaction temperatures <200°C, resulting in the metal/GaAs interface penetrating into the GaAs. Subsequent exposure to an As4 flux resulted in NiAs formation and GaAs regrowth epitaxially on the unreacted GaAs surface, moving the metal/GaAs interface back towards the surface. Rutherford Backscattering (RBS), X-Ray Diffraction (XRD) and transmission electron microscopy confirmed the reaction-induced interface movement. The regrown-GaAs thickness and electrical properties were determined electrically by in-situ capacitance-voltage (C-V) and current-voltage (I-V) measurements. An interlayer model was applied to explain the Schottky barrier height discrepancy between C-V and IV measurements for metal/regrown-GaAs contacts. The model predicts that the regrown GaAs interlayer is p-type with ∼3 x 1015 holes/cm 3 doping and a dielectric constant of ∼20.5, Ferromagnetic bcc-FeXCo1--X(100) films were grown on GaAs(100) and SC0.3Er0.7Aa(100) by MBE. XRD combined with reflection high energy electron diffraction and low energy electron diffraction revealed the cube-on-cube epitaxial orientation. RBS channeling minimum yields, chi min∼3%, suggest epitaxial films of high crystalline quality. Vibrating sample magnetometry measurements showed in-plane uniaxial anisotropy and 4-fold anisotropy for bcc-FeXCo1--X grown on GaAs(100) and Sc0.3Er0.7As(100) surfaces, respectively. The difference in magnetic anisotropy is interpreted as arising from the Sc 0.3Er0.7As interlayer altering the surface symmetry from 2-fold symmetry for GaAs(100) to 4-fold symmetry. Vicinal GaAs(100) substrates were used to create additional 2-fold surface symmetry, inducing an additional uniaxial anisotropy. In the case of bcc-FeXCo 1--X/Sc0.3Er0.7As/GaAs(100), the combination of bonding-induced 4-fold anisotropy and step-induced uniaxial anisotropy results in an uniaxial anisotropy with easy axis perpendicular to the step edge. For bcc-FeXCo1--X /GaAs(100), the combination of bonding-induced uniaxial anisotropy and step-induced uniaxial anisotropy can enhance or compensate the bonding-induced uniaxial anisotropy, depending on the misorientation direction. |
