Observation of persistent photoluminescence in porous silicon: Evidence of surface emission

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Abstract
We report on the observation of persistent photoluminescence (PPL) in oxidized porous silicon. The PPL decay can be well described by a stretched-exponential function, and its decay rate is not sensitive to the change of temperature. We point out that the PPL behavior can be interpreted in terms of the picture that the emission arises from the excited surface complexes, which is produced by capture of photocarriers tunneling from the nearest shallow trap in the nanocrystalline silicon. To explore the microscopic origin of the surface compounds, we performed infrared absorption, and found that the PPL intensity correlates well with Si–OH vibration mode. Further evidence is provided by the recent theoretical calculation showing that the Si–OH complex can emit the photon energy in the range observed here. We thus provide concrete evidence to support the fact that the PL signal of porous silicon does contain surface emission.