High-Mobility Ge p- and n-MOSFETs With 0.7-nm EOT Using HfO2/Al2O3/GeOx/Ge Gate Stacks Fabricated by Plasma Postoxidation

An ultrathin equivalent oxide thickness (EOT) HfO2/Al2O3/Ge gate stack has been fabricated by combining the plasma postoxidation method with a 0.2-nm-thick Al2O3 layer between HfO2 and Ge for suppressing HfO2-GeOx intermixing, resulting in a low-interface-state-density (D-it) GeOx/Ge metal-oxide-semiconductor (MOS) interface. The EOT of these gate stacks has been scaled down to 0.7-0.8 nm with maintaining the D-it in 10(11) cm(-2) . eV(-1) level. The p- and n-channel MOS field-effect transistors (MOSFETs) (p- and n-MOSFETs) using this gate stack have been fabricated on (100) Ge substrates and exhibit high hole and electron mobilities. It is found that the Ge p- and n-MOSFETs exhibit peak holemobilities of 596 and 546 cm(2)/V.s and peak electron mobilities of 754 and 689 cm(2)/V.s at EOTs of 0.82 and 0.76 nm, respectively, which are the record-high reports so far for Ge MOSFETs in subnanometer EOT range because of the sufficiently passivated GeMOS interfaces in present HfO2/Al2O3/GeOx/Ge gate stacks.