Investigation of Strain Effects on the Band-Structure of Si Nanowires using TB and DFT Methods

Using density functional theory and semi-empirical sp³d⁵s* tight binding calculations, we find that a 1% axial strain can change the bandgap of Hydrogenated Silicon nanowires by up to 100 meV. Further, compressive strain causes a direct-to-indirect bandgap transition. As the nanowire diameter increases, this transition occurs at smaller compressive strains, which makes it easier to experimentally observe. We also find that the rate of change of bandgap with strain is relatively independent of diameter for small diameter nanowires and only the geometry of the bonds (growth direction) determines its value. These robust effects also manifest as a large effective-mass change with strain, which could prove useful in SiNW-based sensors.