Low resistivity contact on n-type Ge using low work-function Yb with a thin TiO2 interfacial layer

This work demonstrates the benefit of a lower contact barrier height, and hence reduced contact resistivity (rho(c)), using a low work-function metal (Yb) in unpinned metal-interfacial layer-semiconductor (MIS) contacts on n-type Ge. Fermi-level unpinning in MIS contacts on n-Ge is first established by introducing a 2 nm TiO2-x interfacial layer between various contact metals (Yb, Ti, Ni, Pt) and n-Ge. Further, Yb/TiO2,/n-Ge MIS contact diodes exhibit higher current densities (up to 100s<) and lower effective contact harrier height (up to 30%) versus Ti/TiO2, control devices over a wide range of TiO2-x thickness (1-5 nm). Finally, low work-function Yb combined with doped TiO2-x having a low conduction band offset with Ge and high substrate doping (n 2.5 x 10(19) cm(-3)) is shown to result in an ultra-low P. value of 1.4 x 10(-8) cm(2), cm(2), 10 x lower than Ti/TiO2-x control devices. (C) 2016 AIP Publishing LLC,