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

To realize high-mobility surface channel pMOSFETs on Ge, a 1.6-nm-thick 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 cm
²
middotV
^-1
middots
^-1
at 0.05 MV/cm-a 2times enhancement over the universal Si/SiO
₂
mobility. The devices show well-behaved output and transfer characteristics, an equivalent oxide thickness of 1.85 nm and an I
_ON
/I
_OFF
ratio of 3times10
³
without detectable fast transient charging. The high hole mobility of these devices is attributed to adequate passivation of the Ge surface