Germanium nanowires: from synthesis, surface chemistry, and assembly to devices

A low temperature synthesis of single crystalline Ge nanowires via chemical vapor deposition is enabled by balancing the feedstock and its diffusion in growth seeds. Understanding and optimizing the synthetic chemistry leads to deterministic nanowire growth at well-defined locations and bulk quantity production of homogeneous nanowires, both of which greatly facilitate the assembly toward parallel nanowire arrays. Surface chemistry studies reveal that p- and n-type Ge nanowires undergo different oxidation routes and the surface oxide induced states cause opposite band bending for nanowires with different doping. Furthermore, long chain alkanethiols form a dense and uniform protection layer on Ge nanowire surfaces and therefore afford excellent oxidation resistance. Finally, high performance field effect transistors are constructed on Ge nanowires with both thermally grown SiO₂ and atomic layer deposited HfO₂ as gate dielectrics.