First-principles analysis of electronic states in silicon nanoscale quantum wires

The atomic structure of small-cross-section (≊10 Å), hydrogen-terminated silicon quantum wires is fully relaxed within the local-density approach showing bulklike coordination of the Si atoms. The electronic states near the fundamental gap (substantially blueshifted from that of bulk Si) show a direct gap between bulk-Si-derived states. The new dipole matrix elements and the detailed level orderings depend on the size, symmetry, and surface structure of the wire. The optical response is presented with the implications of the valley orbit splitting for radiative dynamics in light-emitting porous silicon.