Accurate control of doping and fabrication of metal contacts
on
n-type germanium nanowires (GeNWs) with low resistance and linear
characteristics remain a major challenge in germanium-based nanoelectronics.
Here, we present a combined approach to fabricate Ohmic contacts on
n-type-doped GeNWs. Phosphorus (P) implantation, followed by millisecond
rear-side flash lamp annealing, was used to produce highly n-type-doped
Ge with an electron concentration in the order of 1019–1020 cm–3. Electron beam lithography, inductively
coupled plasma reactive ion etching, and nickel (Ni) deposition were
used to fabricate GeNW-based devices with a symmetric Hall bar configuration,
which allows detailed electrical characterization of the NWs. Afterward,
rear-side flash lamp annealing was applied to form Ni germanide at
the Ni-GeNW contacts to reduce the Schottky barrier height. The two-probe
current–voltage measurements on n-type-doped GeNWs exhibit
linear Ohmic behavior. Also, the size-dependent electrical measurements
showed that carrier scattering near the NW surfaces and reduction
of the effective NW cross-section dominate the charge transport in
the GeNWs.