Ferromagnetic Germanide in Ge Nanowire Transistors for Spintronics Application

Abstract

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 Mn₅Ge₃/Ge/Mn₅Ge₃ 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 Mn₅Ge₃ and Ge with a relatively small lattice mismatch of 10.6% indicates that Mn₅Ge₃ is a high-quality ferromagnetic contact to Ge. Temperature-dependent <i>I</i>–<i>V</i> measurements on the Mn₅Ge₃/Ge/Mn₅Ge₃ nanowire heterostructure reveal a Schottky barrier height of 0.25 eV for the Mn₅Ge₃ contact to <i>p</i>-type Ge. The Ge nanowire field-effect transistors built on the Mn₅Ge₃/Ge/Mn₅Ge₃ heterostructure exhibit a high-performance <i>p</i>-type behavior with a current on/off ratio close to 10⁵, and a hole mobility of 150–200 cm²/(V s). Temperature-dependent resistance of a fully germanided Mn₅Ge₃ nanowire shows a clear transition behavior near the Curie temperature of Mn₅Ge₃ at about 300 K. Our findings of the high-quality room-temperature ferromagnetic Mn₅Ge₃ 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