Real-time photoluminescence and Raman spectral study of porous Si during F 2 and H 2O exposure

Abstract

Photoluminescence (PL) and Raman spectral changes of porous silicon (PS) during exposure to F 2 and H 2O in succession have been investigated. An exposure to F 2 under Ar + laser (488 nm) irradiation at 373 K leads to significant changes in PL intensity and its peak position. PS samples before exposure to F 2 exhibit a PL band at typically 750 nm. Upon exposure to F 2 this band decreases in intensity and a PL band emerges at 600 nm. With increasing exposure, the 600 nm band increases to a maximum in intensity and then decreases to a minimum with a blue shift to 580 nm. A subsequent exposure to H 2O vapor gives rise to a PL band at 740 nm whose intensity is much more intense than the PL band of the PS before F 2 exposure. In spite of these PL spectral changes, the phonon band of the PS remains almost unchanged throughout these exposures, indicating that the average size of Si particles in the sample is almost constant. These results demonstrate that the PL is dominated by the surface chemical structure of the PS.