Effective surface passivation methodologies for high performance germanium metal oxide semiconductor field effect transistors

We demonstrate methodologies to improve the interface characteristics between a germanium (Ge) substrate and high-$k$ gate dielectrics. GeON and $SiOx$ were investigated as passivating layers on a Ge surface. Smaller hysteresis and interface state density $(Dit)$ were obtained using $SiOx$ interface layer and $p$-type metal oxide semiconductor field effect transistors (MOSFETs) fabricated with a gate stack of $Ge/SiOx/HfSiO/WN$ showed about two times higher effective mobility compared to universal $Si/SiO2$ MOSFET. Because the formation of $GeOx$ at the interface resulted in higher hysteresis and equivalent oxide thickness, the effective suppression of growth of unstable $GeOx$ by $SiOx$ interface layer contributed to the good device characteristics of the fabricated devices.