Shape-tunable electronic properties of monohydride and trihydride [112]-oriented Si nanowires

Using first-principles calculations within density-functional theory, we demonstrated shape-dependent electronic properties of [112]-oriented Si nanowires (SiNWs) with monohydride (mh-SiNW) and trihydride (th-SiNW) passivation. We show for both mh-SiNWs and th-SiNWs, an indirect-to-direct band-gap transition can be induced solely by varying the cross-sectional aspect ratio of the {111} and {110} facets enclosing the nanowires, which is explained by the different confinement effects on the conduction-band state at Gamma point by the two facets. For both mh-SiNWs and th-SiNWs, the hole (electron) effective mass converges to a value independent of cross-sectional area (aspect ratio). By analyzing the formation energy, we show that direct band-gap [112] SiNWs are possible to form at experimentally relevant passivation conditions.