Width-dependent hole mobility in top-down fabricated Si-core/Ge-shell nanowire metal-oxide-semiconductor-field-effect-transistors

Si-core/Ge-shell nanowire p-channel metal-oxide-semiconductor-field-effect-transistors with high-permittivity-dielectric/metal-gate have been demonstrated by selective epitaxial growth of Ge thin-films on the Si-nanowires fabricated by a top-down scheme. Cross-sectional transmission-electron-microscopy reveals that the epitaxial Ge shell exhibits hexagonal {111} facets, and that the Ge is defected, particularly near the Si corners. The hole mobility increases by 40% as the Si-core size is decreased from 70 to 20 nm. Finite-element simulations of the stress profile induced in the Ge channel by the gate stack suggest that a transformation in the transverse stress component from compression to tension plays a role in the mobility enhancement.