Top-down fabrication of Ge nanowire arrays by nanoimprint lithography and hole gas accumulation in Ge/Si core–shell nanowires

Germanium (Ge) nanowire arrays are expected to be a promising channel material for high-performance field-effect transistors (FETs) due to their excellent electronic transport properties, silicon (Si) compatibility, and high integration. To produce highly ordered Ge nanowires with low contamination, nanoimprint lithography (NIL) and Bosch etching are used and the size of nanowires is reduced from 220 nm to ∼30 nm by adjusting the H2O2 etching time. Furthermore, Ge/Si core–shell nanowires are prepared by forming p-Si shells on Ge nanowires, and their good crystalline quality and sharp interfaces are confirmed by transmission electron microscope (TEM) observations. This structure is used as a high-mobility channel in HEMT-type devices, and the accumulation of hole gas inside the Ge nanowires, which is the most important, is demonstrated and investigated by Raman scattering.