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Photoluminescence controls as-grown porous silicon-air interaction

We have studied the stability of the visible photoluminescence (PL) in the stain etched porous silicon (PS) prepared with the help of laser irradiation. The observation of PL evolution from this PS under exposure to ambient air is reported. We find the displacement of the PL intensity peak of the steady-state spectrum from 'green' to 'red' spectral range, (lambda) - integral PL intensity increasing by 50 - 80% during 15 - 30 min. under air exposure. With increase of exposure time during several weeks to air the average relaxation time of the slow component of PL decay increases and the spectra dependence of this time remains exponential. Possible explanation for the observed PL evolution includes processes related to water evaporation, to replacing the unstable H-passivated surface with the more stable O-passivated surface, to decrease the number of the Si dangling bonds, and to increase the oxide barrier which greatly reduces the carrier tunneling from light emitting nanocrystallites. The results can account for the import role of the inner surface chemistry in recombination within the framework of quantum size model of the PL. The change in PL is inferred to be associated with the interaction between as-grown PS and ambient air, so PL controls as-grown PS-air interaction.