Al sub(2)O sub(3) tunnel barrier as a good candidate for spin injection into silicon

We report electrical characterisation of NiFe/SiO sub(2)/Si and NiFe/Al sub(2)O sub(3)/Si tunnel diodes that are of potential interest for spin injection into silicon. The effect of the nature of the insulator on the electrical properties of the diode has been studied. Impedance measurements have shown a small difference in charge trap densities between SiO sub(2)/Si and Al sub(2)O sub(3)/Si interfaces. Analyses of the Current-Voltage characteristics of NiFe/SiO sub(2)/Si sample have evidenced assisted tunnelling through defects in the oxide bulk, in contrast to Fowler-Nordheim tunnelling in the NiFe/Al sub(2)O sub(3)/Si structures. This result shows that Al sub(2)O sub(3) is a more efficient barrier against diffusion of magnetic atoms towards the silicon substrate; which is promising for spin injection into silicon.