Intrinsic origin of visible light emission from silicon quantum wires: Electronic structure and geometrically restricted exciton

We theoretically investigate excitonic effects on the optical properties of silicon quantum wires, based on ab initio electronic structure calculations. The Si wires have a direct, allowed band gap in the visible energy range and exhibit a strong optical anisotropy. Taking into account the electron-hole Coulomb interaction, the geometrical restriction of excitons dramatically enhances the oscillator strength of the optical transitions. Comparisons with recent experimental results are also made.