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.