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:2×10²⁰ cm^-3 and n⁺-Ge:2.5×10¹⁹ cm^-3) is shown to result in ultra-low ρ_c values of 2.1×10^-8 Ω.cm² (Si) and 1.4×10^-8 Ω.cm² (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.