The influence of Fermi level pinning/depinning on the Schottky barrier height and contact resistance in Ge/CoFeB and Ge/MgO/CoFeB structures

We demonstrated that an ultrathin MgO layer between CoFeB and Ge modulated the Schottky barrier heights and contact resistances of spin diodes. We confirmed that, surprisingly, an insulating MgO layer significantly decreased the Schottky barrier heights and contact resistances of spin diodes on N+Ge, opposite to the increase observed for P+Ge. A 0.5 nm thick MgO layer on N+Ge decreases the Schottky barrier height from 0.47 to 0.05 eV and lowers the minimum contact resistance 100-fold to 1.5x10(-6) m(2). These results open a pathway for high efficient spin injection from ferromagnetic materials and semiconductors.