A first-principles study of the electronic properties of silicon quantum wires

We describe the results of first-principles pseudopotential calculations for H-terminated Si wires, with thickness up to 16 Å, which yield the band gaps, effective masses and optical matrix elements. The zero-phonon radiative lifetime for recombination of localised excitons in a 16 Å-wide wire is calculated to be 560 μs. This is in reasonable agreement with the value of 130 μs deduced from experiments on samples of porous Si. Comparison with effective-mass theory indicates that the latter is likely to be valid for wires wider than about 33 Å. Our results are consistent with a model in which the luminescent properties of porous Si are due to quantum-confined carriers in wire-like crystalline Si structures.