Schottky barriers of rare-earth transition-metal intermetallics on silicon

Abstract

The ferromagnetic transition metals Fe, Co and Ni have high work functions (4.5 – 5.0 eV) and they invariably form Schottky barriers on Si, often detrimental to efficient spin injection and detection at the interfaces. The rare earths have lower work functions (2.5 – 3.2 eV) but they order magnetically below room temperature. We therefore investigate a series of 12 rare earth metals and alloys of Gd, Ce or Y with Fe or Co, which are evaporated onto (001) Si wafers. The lowest thermionic emission barrier height is found for CeCo5 (48 meV), much less than those found for the 3d ferromagnets or their silicides (~ 500 meV). Y is found to form an ohmic contact after a diffusion anneal at 1300 K. Further alloy additions are needed to lower the barrier height below 25 meV; a target for room temperature operation with significantly increased reverse bias current.