Cross-sectional shape effects on the electronic properties of Silicon nanowires

The electronic properties of Silicon nanowires are studied using empirical tight binding sp³d⁵s* model for three different cross-sectional shapes - square, circular and triangular. For two different growth directions <100> and <110>, it is observed that the electron effective masses at the Gamma point is lowest for triangular wire. The conduction band valley splitting at the Gamma point for <100> wire is higher for triangular wire compared to the other two shapes. The valence bands are more degenerate for circular wire than the other two and their splitting is highest for square wire. Hole effective mass at the valence band maxima for <100> wire is significantly lower for triangular wire than that of the other two shapes which show large increase in hole effective mass as a result of quantum confinement. These electronic properties are compared against same cross-section area which is varied from 0-30 nm². The energy band gap shows no variation due to wire shape. It only depends on cross-section area. Variations in the electronic properties due to shape diminish gradually as cross-sectional area is increased.