Quantum confinement in the Si-III (BC-8) phase of porous silicon

Porous silicon was recently shown to give rise to the same semimetallic Si-m (BC-8) phase as silicon upon application and release of high pressure. This phase is known to have a direct gap and we examine the effect of quantum confinement on its electronic structure. This is performed by combining empirical tight binding and ab initio local density calculations. The blue shift is found to be similar to what is obtained for nanocrystallites with the diamond structure and the radiative recombination rate is much larger. Comparison with experiment shows that the observed luminescence is not consistent with the quantum confinement hypothesis. (C) 1997 American Institute of Physics.