Tight-binding calculations of Ge-nanowire bandstructures

The subband structure of square Ge 〈100〉-oriented nanowires using a sp3 tight-binding model is studied. Starting from the bulk Ge structure, we describe the bands obtained in nanowires before showing the dependence of the band-gap energy and the effective masses as a function of the wire thickness. For this orientation, the Ge nanowire properties are found to be very sensitive to transverse confinement. In particular the band-gap goes very close to the one of the silicon nanowire, reducing then the impact of the band-to-band tunneling and making it more suitable for nanoelectrics applications.