From bare Ge nanowire to Ge/Si core/shell nanowires: A first-principles study

Germanium/Germanium-Silicon core/shell nanowires are expected to play an important role in future electronic devices. We use first-principles plane-wave calculations within density-functional theory in the generalized gradient approximation to investigate the structural and electronic properties of bare and H-passivated Ge nanowires and core/shell Ge/Ge-Si, Ge/Si, and Si/Ge nanowires. The diameters of the nanowires considered are in the range of 0.6--2.9 nm and oriented along [110] and [111] directions. The diameter, the surface passivation, and the substitutional effects on the binding energy, band structure, and effective mass are extensively investigated considering the relative contribution of quantum confinement and surface effects.