Engineering of tunnel junctions for prospective spin injection in germanium

Even though the strong Fermi-level pinning at the metal/germanium (Ge) interface can be alleviated by inserting a thin layer of tunneling oxide, the still sizeable Schottky barriers and the wide depletion regions of the Fe/oxide/$n-Ge$ contacts make the junction resistances strongly dependent of temperature. The resistance-area (RA) products of these junctions are too high for spin injection and cannot be tuned by simply varying oxide thickness or using ferromagnetic metal (FM) with a lower work function. In this work, low energy ion implantation and rapid thermal annealing were utilized to degenerately dope the Ge surface layer to facilitate single-step tunneling transport. The RA products of the junctions with surface doping are significantly reduced and weakly dependent of temperature. This method gives a prospect for spin injection to Ge from FM.