Identity of the light-emitting states in porous silicon wires

We present empirical pseudopotential calculations of the electronic structure of [001] silicon quantum wires, aiming at identification of the states that couple radiatively to the valence-band maximum. We find that the near-gap wave functions differ qualitatively from effective-mass depictions. Instead, they can be described as off-Γ bulk states. The effects of H chemisorption on the wire energies and wave functions are studied. We find that the Si skeleton dominates the emission. The resulting lifetimes versus energy relation agrees with the experimental measurements only if one assumes coexistence of quantum wires with quantum dots.