Diamond-Shaped Ge Nanowire FETs: Silicon and germanium have crystalline atomic
structures which, like other crystals, have different facets. The materials’ electrical properties can
vary according to which facet is used to build devices, and some facets are more favorable than
others. A team led by Taiwan’s National Nano Device Laboratories will describe how they built
gate-all-around (GAA) nanowire MOSFETs with diamond-shaped Ge and GeSi nanowire
channels. The purpose of the work was to find a way to more effectively use germanium (Ge) as
the channel material in multi-gate device configurations, because high-mobility Ge is seen as
potentially necessary for scaling beyond the 10-nm technology node. Using common dry etching
and blanket epitaxy techniques, the researchers sculpted Ge and GeSi nanowires into diamond
cross-sectional shapes, with four favorable facets (the so-called {111} orientation) exposed.
They used these nanowires as suspended channels in a GAA MOSFET configuration. Both nFET
and pFET transistors with excellent performance were demonstrated, including pFETs with an
Ion/Ioff ratio exceeding 108, the highest ever reported for Ge-based pFETs.
The photos above are transmission electron microscope photos of cross-sections of (a) the
diamond-shaped nanowire FET and (b) a FinFET.
(Paper 15.1, Diamond-shaped Ge and Ge0.9Si0.1 Gate-All-Around Nanowire FETs with Four {111} Facets by Dry
Etch Technology; Yao-Jen Lee et al, National Nano Device Laboratories/National Chiao Tung University/National
Chi Nan University)