A Low-Leakage Epitaxial High-κ Gate Oxide for Germanium Metal-Oxide-Semiconductor Devices

Germanium (Ge)-based metal-oxide-semiconductor field-effect transistors are a promising candidate for high performance, low power electronics at the 7 nm technology node and beyond. However, the availability of high quality gate oxide/Ge interfaces that provide low leakage current density and equivalent oxide thickness (EOT), robust scalability, and acceptable interface state density (D-it,) has emerged as one of the most challenging hurdles in the development of such devices. Here we demonstrate and present detailed electrical characterization of a high-kappa epitaxial oxide gate stack based on crystalline SrHfO3 grown on Ge (001) by atomic layer deposition. Metal-oxide-Ge capacitor structures show extremely low gate leakage, small and scalable EOT, and good and reducible D-it. Detailed growth strategies and postgrowth annealing schemes are demonstrated to reduce D-it. The physical mechanisms behind these phenomena are studied and suggest approaches for further reduction of D-it.