Pristine semiconducting [110] silicon nanowires

We report results of ab initio calculations on silicon nanowires oriented along the [110] direction and show for the first time that these pristine silicon nanowires are indirect band gap semiconductors. The nanowires have bulk Si core and are bounded by two (100) and two (110) planes in lateral directions. The (100) planes are atomically reconstructed with dimerization in a manner similar to the (100) surface of bulk Si but the dimer arrays are perpendicular to each other on the two (100) planes. An interesting consequence of surface reconstruction is the possibility of polytypism in thicker nanowires. We discuss its effects on the electronic structure. These findings could have important implications for the use of silicon nanowires in nanoscale devices as experimentally [110] nanowires have been found to grow preferentially in the small diameter range.