First principles simulations of the structural and electronic properties of silicon nanowires

We report the results of first principles studies of the structural and electronic properties of hydrogen-passivated silicon nanowires with [001], [011], and [111] growth directions and diameters ranging from 1 to 3 nm. We show that the growth direction, diameter, and surface structure all have a significant effect on the structural stability, electronic band gap, band structure, and band-edge effective masses of the nanowires. The band gap is found to decrease with increasing diameter and to be further reduced by surface reconstruction. While the electron and hole effective masses are found to depend on NW size for [001] and [111] NWs, they are almost independent of size for [011] NWs. Our results suggest the possibility of engineering the properties of nanowires by manipulating their diameter, growth direction, and surface structure. Finally, we use FEFF calculations to predict the extended x-ray absorption fine structure spectra produced by the relaxed atomic structure of the NWs and show that these spectra can serve as a tool for detecting surface reconstructions on NWs.