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) Al₂O₃/ 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 GeOx/Ge interface and the GeO_x interfacial layer thickness. Ge pMOSFETs on a (100) Ge substrate using the Al₂O₃/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 cm²/ 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.