Improved Ge surface passivation with ultrathin SiOx 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 SiOx 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) center dot V-1 - s(-1) at 0.05 MV/cm-a 2 x enhancement over the universal Si/SiO2 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 3 x 10(3) without detectable fast transient charging. The high hole mobility of these devices is attributed to adequate passivation of the Ge surface.