TEM Study on Diffusion Process of NiFe Schottky and MgO/NiFe Tunneling Diodes for Spin Injection in Silicon

Analytical electron microscopy is employed to study the structural properties of NiFe Schottky diodes and NiFe/MgO tunneling diodes after annealing up to 400° C. Electrical characterization revealed a drop of the barrier height for the Schottky diodes, while the tunneling diodes are thermally stable. From the cross-sectional TEM images of the Schottky diodes, metal diffusion into Si substrate was found. Investigations of the diffusion using energy dispersive spectroscopy and energy filtered transmission electron microscopy revealed that Ni diffused into the Si substrate to form nickel silicide. Moreover, in some cases, the gold capping layer also diffused into the substrate even deeper than Ni. In the case of the tunneling diodes, metal diffusion was inhibited by the presence of MgO.