Phonon-Limited Electron Mobility in Rectangular Cross-Sectional Ge Nanowires

The phonon-limited electron mobility in rectangular cross-sectional germanium (Ge) nanowires (NWs) with various orientations was theoretically investigated. The electronic states were calculated by a tight-binding model and the phononic states were calculated by a valence force field model. Then, transition probability was calculated by Fermi´s golden rule, and Boltzmann´s transport equation was solved for calculating low-field mobility. The electron mobility of Ge NWs strongly depends on the wire orientations and cross-sectional shapes, and this dependence can be explained by the conduction band structure of Ge NWs. Among several geometries investigated in this paper, [110]-oriented NWs with wider width along [001] showed the highest electron mobility at low carrier concentration, and [112] NWs with wider width along [11̅0] showed the highest electron mobility at high carrier concentration. This result indicates that these kinds of Ge NWs are suitable as n-channel material.