Reversible and irreversible changes in the photoluminescence spectra of porous silicon held in water

The change induced in the photoluminescence spectra and photoluminescence excitation spectra by holding porous silicon in water is investigated. It is found that submerging a sample in water gives rise simultaneously to reversible and irreversible changes in the intensity and position of the photoluminescence maximum. It is shown that the irreversible changes are due to the same processes that occur in air: oxidation and desorption of substances which participate in the photoluminescence and which give rise to the visible-range band of the excitation spectrum, from the surface of the porous layer. It is established that the rate of these processes in water is much higher than in air. It is shown that the reversible changes are due to the vanishing of the visible-range photoluminescence excitation band in water. It is inferred that this band is attributable to water clusters that contain components of the etchant. (C) 1999 American Institute of Physics. [S1063-7826(99)02011-6].