High-Mobility Ge p- and n-MOSFETs With 0.7-nm EOT Using $\hbox {HfO}_{2}/\hbox {Al}_{2}\hbox {O}_{3}/\hbox {GeO}_{x}/\hbox {Ge}$ Gate Stacks Fabricated by Plasma Postoxid

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 10¹¹ 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 hole mobilities of 596 and 546 cm²/V·s and peak electron mobilities of 754 and 689 cm²/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 Ge MOS interfaces in present HfO₂/Al₂O₃/GeOx/Ge gate stacks.