A 1ST-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 thicknesses up to 16 angstrom, which yield the band gaps, effective masses and optical matrix elements. The zero-phonon radiative lifetime for recombination of localised excitons in a 16 angstrom-wide wire is calculated to be 560 mus. This is in reasonable agreement with the value of 130 mus 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 angstrom. 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.