PACS 73.40.Qv, 76.30.Mi, 78.30.Ly, 78.55.Mb An explanation of the mechanism of porous silicon (PS) photodegradation in an oxygen-containing ambient has been proposed. The specific oxidation of luminescent Si nanocrystallites in a porous layer occurs via an intermediate specie, namely ozone produced in oxygen under illumination over a wide range of photon energies. It is shown by photoluminescence (PL), electron spin resonance (ESR) and capacitancevoltage methods that ozone-induced oxidation is accompanied by defect generation at the Si crystallite/oxide interface. Some of these centers act as a nonradiative drain for electron -hole pairs under PL excitation. As revealed by capacitance spectroscopy in an MOS structure with a porous sublayer, these defects constitute an interface states spectrum broadly spread through the silicon band gap. The abovementioned defects appear in ESR spectra as Pb-like centers originated from incomplete passivation of silicon bonds with oxygen at the crystallite surface.
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