Ferromagnetic germanide in Ge nanowire transistors for spintronics application

To explore spintronics applications for Ge nanowire heterostructures formed by thermal annealing, it is critical to develop a ferromagnetic germanide with high Curie temperature and take advantage of the high-quality interface between Ge and the formed ferromagnetic germanide. In this work, we report, for the first time, the formation and characterization of Mn ₅Ge ₃/Ge/Mn ₅Ge ₃ nanowire transistors, in which the room-temperature ferromagnetic germanide was found through the solid-state reaction between a single-crystalline Ge nanowire and Mn contact pads upon thermal annealing. The atomically clean interface between Mn ₅Ge ₃ and Ge with a relatively small lattice mismatch of 10.6% indicates that Mn ₅Ge ₃ is a high-quality ferromagnetic contact to Ge. Temperature-dependent I-V measurements on the Mn ₅Ge ₃/Ge/Mn ₅Ge ₃ nanowire heterostructure reveal a Schottky barrier height of 0.25 eV for the Mn ₅Ge ₃ contact to p-type Ge. The Ge nanowire field-effect transistors built on the Mn ₅Ge ₃/Ge/Mn ₅Ge ₃ heterostructure exhibit a high-performance p-type behavior with a current on/off ratio close to 10 ⁵, and a hole mobility of 150-200 cm ²/(V s). Temperature-dependent resistance of a fully germanided Mn ₅Ge ₃ nanowire shows a clear transition behavior near the Curie temperature of Mn ₅Ge ₃ at about 300 K. Our findings of the high-quality room-temperature ferromagnetic Mn ₅Ge ₃ contact represent a promising step toward electrical spin injection into Ge nanowires and thus the realization of high-efficiency spintronic devices for room-temperature applications.