IN-SITU INFRARED SPECTROSCOPIC STUDY OF LUMINESCENT POROUS SILICON

Porous silicon has been studied using in situ infrared spectroscopy co mbined with photoluminescence, electroluminescence, photomodulated and electromodulated infrared absorption, when the porous layer is either chemically etched in HF or anodically oxidized. Infrared vibrational spectra indicate that the luminescence is not very sensitive to the ch emical state of the surface (hydrogenated or oxidized). A more importa nt point seems to be wetting of the surface. The well-known intense or ange-red luminescence is only observed on dry surfaces. Wet surfaces e xhibit instead a weak yellow-green luminescence. The photomodulated an d electromodulated infrared absorption spectra show that the red lumin escence on dry surfaces is associated with a localization of the photo carriers, suggesting that the localization process may be related to t he dielectric constant of the embedding medium.