Role of SiO 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 PL.