Structure and electronic properties of silicon nanowires grown along the [110] direction: role of surface reconstruction

Silicon single-crystal nanowires (SiNWs) are attracting great interest for future nanoscale devises in recent years. So far, the [110] grown SiNWs with diameters below 4 nm have been successfully fabricated by various methods\footnote{Ma {\it et al.}, Science {\bf 299}, 1874(2003); Wu {\it et al.}, Nano Lett. {\bf 4}, 433(2004).}. Although the size dependence in electronic and optical properties for the [110] grown SiNWs terminated by H-atoms have been intensively studied\footnote{Zhao {\it et al.}, Phys. Rev. Lett. {\bf 92}, 236805(2004).}, effects of surface reconstructions on the electronic structure have been rarely examined. Here, we investigate the atomic and electronic structures of SiNWs along the [110] direction with \{001\} and \{111\} facets using first-principles pseudopotential method. The calculations for SiNWs whose diameters are $\sim$4 nm demonstrate that the reconstructions on these facets are strongly dependent on H-chemical potential $\mu_{\rm H}$: The SiNW consisting of monohydride \{001\} and H-terminated \{111\} facets is stabilized for high $\mu_{\rm H}$($\geq$-0.75 eV) while the pristine SiNW stabilized for low $\mu_{\rm H}$($\leq$-0.82 eV). The reconstructions with partially hydrogenated facets appear for -0.82$<$$\mu_{\rm H}$$<$-0.75 eV. Peculiar features in the electronic structure are also found in partially hydrogenated SiNWs.