High-Mobility Ge pMOSFET With 1-nm EOT $\hbox{Al}_{2} \hbox{O}_{3}/\hbox{GeO}_{x}/\hbox{Ge}$ Gate Stack Fabricated by Plasma Post Oxidation

An ultrathin equivalent oxide thickness (EOT) Al
₂
O
₃
/ GeO
_x
/Ge gate stack with a superior GeO
_x
/Ge metal-oxide-semiconductor (MOS) interface and p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) using this gate stack have been fabricated by a plasma post oxidation method. The properties of the GeO
_x
/ Ge MOS interfaces are systemically investigated, and it is revealed that there is a universal relationship between the interface state density (
D
_it
) at the GeO
x
/Ge interface and the GeO
_x
interfacial layer thickness. Ge pMOSFETs on a (100) Ge substrate using the Al
₂
O
₃
/GeO
_x
/Ge gate stack have been demonstrated with an EOT down to 0.98 nm. It is found that the Ge pMOSFETs exhibit the peak hole mobility values of 515, 466, and 401 cm
²
/ V·s at an EOT of 1.18, 1.06, and 0.98 nm, respectively, which has much weaker EOT dependence than the trend of the hole mobility values reported so far, because of low
D
_it
of the present gate stack in the ultrathin EOT region of ~1 nm.