Improved Ge Surface Passivation With Ultrathin $ hbox{SiO}_{X}$ Enabling High-Mobility Surface Channel pMOSFETs Featuring a HfSiO/WN Gate Stack

摘要

To realize high-mobility surface channel pMOSFETs on Ge, a 1.6-nm-thick $ hbox{SiO}_{X}$ passivation layer between the bulk Ge substrate and HfSiO gate dielectric was introduced. This approach provides a simple alternative to epitaxial Si deposition followed by selective oxidation and leads to one of the highest peak hole mobilities reported for unstrained surface channel pMOSFETs on Ge: 332 $hbox{cm}^{2}cdot hbox{V}^{-1}cdot hbox{s}^{-1}$ at 0.05 MV/cm—a 2$times$ enhancement over the universal $hbox{Si/SiO}_{2}$ mobility. The devices show well-behaved output and transfer characteristics, an equivalent oxide thickness of 1.85 nm and an $I_{scriptstyle{rm ON}}/I_{scriptstyle{rm OFF}}$ ratio of $hbox{3} times hbox{10}^{3}$ without detectable fast transient charging. The high hole mobility of these devices is attributed to adequate passivation of the Ge surface.