Contact barrier height and resistivity reduction using low work-function metal (Yb)-interfacial layer-semiconductor contacts on n-type Si and Ge

We demonstrate the benefit of using a low work-function metal (Yb) to lower the barrier height and hence, the contact resistivity (ρ
c
) in unpinned metal-interfacial layer-semiconductor (MIS) contacts on n-type Ge and Si. Metal/doped TiO
2−x
/n-Ge and n-Si MIS diodes fabricated with varying TiO
2−x
thickness (1–5 nm) exhibit higher (upto 100X) current densities and lower contact barrier heights (upto 30%) for Yb versus Ti metallization. A combination of low work-function Yb, doped TiO
2−x
with low conduction band offsets w.r.t Si and Ge, and high substrate doping( n
⁺
-Si:2×10
²⁰
cm
⁻³
and n
⁺
-Ge:2.5×10
¹⁹
cm
⁻³
) is shown to result in ultra-low ρ
c
values of 2.1×10
⁻⁸
Ω.cm
²
(Si) and 1.4×10
⁻⁸
Ω.cm
²
(Ge) for Yb/TiO
2−x
contacts, significantly lower than Ti/TiO
2−x
control devices, and the best reported contact resistivity on n-Ge till date.