  Germanium nanowires with p- and n-dopants were synthesized by chemical vapor
deposition and used to construct complementary field effect transistors .
Electrical transport and x-ray photoelectron spectroscopy data are correlated
to glean the effects of Ge surface chemistry to the electrical characteristics
of GeNWs. Large hysteresis due to water molecules strongly bound to GeO2 on
GeNWs is revealed. Different oxidation behavior and hysteresis characteristics
and opposite band bending due to Fermi level pinning by interface states
between Ge and surface oxides are observed for p- and n-type GeNWs. Vacuum
annealing above 400C is used to remove surface oxides and eliminate hysteresis
in GeNW FETs. High-k dielectric HfO2 films grown on clean GeNW surfaces by
atomic layer deposition (ALD) using an alkylamide precursor is effective
serving as the first layer of surface passivation. Lastly, the depletion length
along the radial direction of nanowires is evaluated. The result suggests that
surface effects could be dominant over the bulk properties of small diameter
wires.
