Role of Si=O in the photoluminescence of porous silicon

It has been proposed recently that localized excitations and recombinations in the silanone Si=O bond is the source for the red photoluminescence (PL) observed for oxygen-exposed porous silicon (PS). One concern with this proposal is the expected low chemical stability of the Si=O bond. By using quantum chemistry calculations and molecular clusters to simulate the PS surface, we show that the hydrated silanone bond is less stable than the hydroxylated Si(OH)(2) surface species. However, we also determine there is a low barrier for the conversion of the hydroxylated Si to a hydrated silanone surface species. Our calculations suggest that the origin of the red PL for oxygen-exposed PS first involves the conversion of hydroxylated Si species, presumably by energy provided by the incident photon source, to a surface with a larger concentration of silanone groups. These metastable ground-state silanone groups would then be excited by additional photons to produce the observed FL.