Surface and Electronic Properties of Hydrogen Terminated Si [001] Nanowires

Abstract

The calculated band gaps reported previously for silicon nanowires (SiNW) have disagreed with the experimental values both in magnitude and in the behavior with radius. We resolve this discrepancy here. We report ab initio quantum mechanical calculations of hydrogen terminated Si (001) nanowires (HSiNWs) asafunctionofdiameter(d) andhydrogencoverage using theB3LYP density functional. For smaller diameters (d e 1.9 nm) we find that the most stable surface is fully saturated with hydrogen leading to directbandgaps.Forlargerdiameters, thesurfacedanglingbonds are notsaturated,leading tosurface LUMO and HOMO states thatlower the gap andlead toan indirectband gap.Thistransition from direct to indirect gap resolves the previous disagreement in the scaling of band gap with diameter. We conclude that the electronic properties of Si NW depend sensitively on controlling the diameter and surface hydrogen coverage.