In recent years, transistor technology has scaled down to sub-20 nm channel length with many
performance-boosting techniques at the material and device levels in order to meet the increasing
demand for higher performance electronics. The nanowire (NW) device architecture has proven itself
as a viable candidate for the sub-20 nm generation transistors. Compared to Si NWs, the Ge/Si
core/shell NW alternative can supply larger on-current due to the increased confined hole mobility
and ohmic behavior at the Ni-alloyed drain/source contacts. It is thus important to understand
transport mechanisms in this core/shell structure, and develop pathway to realize ultra-short channel
core/shell NW field effect transistors (FETs).
In this paper, we report the growth of Ge/Si concentric NWs with precise control of Si shell
thickness. Performance of FETs fabricated from core/shell NWs exhibited a clear dependence on
NWs’ diameters, with steeper sub-threshold slopes for smaller NWs. An 18 nm diameter Ge/Si
heterostructure FET exhibited sub-threshold swing of 102 mV/decade, with a maximum
transconductance of 3.4 μS at VDS =-100 mV. Finally, transmission electron microscopy was utilized
to monitor and control the solid state reaction between Ni contacts and Ge/Si NWs, resulting in ultrascaled
channel lengths, as short as 5 nm.