Single-crystalline Ni2Ge/Ge/Ni2Ge nanowire heterostructure transistors

In this study, we report on the formation of a single-crystalline Ni2Ge/Ge/Ni2Ge nanowire heterostructure and its field effect characteristics by controlled reaction between a supercritical fluid-liquid-solid (SFLS) synthesized Ge nanowire and Ni metal contacts. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies reveal a wide temperature range to convert the Ge nanowire to single-crystalline Ni2Ge by a thermal diffusion process. The maximum current density of the fully germanide Ni2Ge nanowires exceeds 3.5 x 107 A cm-2, and the resistivity is about 88 μΩ cm. The in situ reaction examined by TEM shows atomically sharp interfaces for the Ni2Ge/Ge/Ni2Ge heterostructure. The interface epitaxial relationships are determined to be Ge[01 1-bar ]||Ni2Ge[0 1-bar 1] and Ge(1 1-bar 1-bar )||Ni2Ge(100). Back-gate field effect transistors (FETs) were also fabricated using this low resistivity Ni2Ge as source/drain contacts. Electrical measurements show a good p-type FET behavior with an on/off ratio over 103 and a one order of magnitude improvement in hole mobility from that of SFLS-synthesized Ge nanowire.